Combined RF and thermal heating system and methods of operation thereof

An embodiment of a heating system includes a cavity configured to contain a load, a thermal heating system (e.g., a convection, radiant, and/or gas heating system) in fluid communication with the cavity and configured to heat air, and an RF heating system. The RF heating system includes an RF signal source configured to generate an RF signal, first and second electrodes positioned across the cavity and capacitively coupled, a transmission path electrically coupled between the RF signal source and one or more of the first and second electrodes, and a variable impedance matching network electrically coupled along the transmission path between the RF signal source and the one or more electrodes. At least one of the first and second electrodes receives the RF signal and converts the RF signal into electromagnetic energy that is radiated into the cavity.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally to apparatus and methods of heating a load within a cavity using multiple heating sources.

BACKGROUND

Conventional food heating systems come in several forms, with a primary differentiator being the heating source used to heat food within a system cavity. The most common food heating systems include a conventional oven, a convection oven, and a microwave oven. A conventional oven includes an oven cavity in which one or more radiant heating elements are disposed. Electric current is passed through the heating element(s), and the element resistance causes each element and ambient air around the element to heat up. A convection oven includes an oven cavity, a heating element, and/or a fan assembly, where the heating element may be included in the fan assembly or may be located within the oven cavity. Essentially, the fan assembly is used to circulate air warmed by the heating element throughout the oven cavity, resulting in a more even temperature distribution throughout the cavity, and thus faster and more even cooking than a conventional oven. Finally, a microwave oven includes an oven cavity, a cavity magnetron, and a waveguide. The cavity magnetron produces electromagnetic energy that is directed into the oven cavity through the waveguide. The electromagnetic energy (or microwave radiation) impinges on the food load to heat the outer layer of the food. For example, at a typical microwave oven frequency of 2.54 gigahertz, about the outer 30 millimeters of a homogenous, high water food mass may be evenly heated using microwave heating.

Each of the above-described, conventional food heating systems has advantages and disadvantages when it comes to heating and/or cooking food. For example, conventional ovens are simple in construction, reliable, and relatively inexpensive. In addition, they are very good at producing a Maillard reaction in the outer surface of food, which is essential for browning and crisping. However, conventional ovens are relatively slow at cooking food. Convection ovens may have similar cooking performance as a conventional oven, but with faster cooking times. However, the convection oven fan assembly renders the oven more expensive to manufacture and repair. Finally, a microwave oven is capable of cooking food much faster than conventional and convection ovens. However, microwave energy does not tend to produce the desired Maillard reactions in food, and accordingly microwave ovens are not good at browning and crisping. Given the above-listed characteristics of conventional food heating systems, appliance manufacturers strive to develop improved systems that have the advantages of the various systems while overcoming their deficiencies.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the words “exemplary” and “example” mean “serving as an example, instance, or illustration.” Any implementation described herein as exemplary or an example is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description.

Embodiments of the subject matter described herein relate to heating appliances, apparatus, and/or systems that include multiple heating systems that can operate simultaneously in order to heat a load (e.g., a food load) within a system cavity. The multiple heating systems include a radio frequency (RF) heating system and a “thermal” heating system. The RF heating system includes a solid-state RF signal source, a variable impedance matching network, and two electrodes, where the two electrodes are separated by the system cavity. More specifically, the RF heating system is a “capacitive” heating system, in that the two electrodes function as electrodes (or plates) of a capacitor, and the capacitor dielectric essentially includes the portion of the system cavity between the two electrodes and any load contained therein. The thermal heating system can include any one or more systems that heat the air within the cavity, such as one or more resistive heating elements, a convection blower, a convection fan plus a resistive heating element, a gas heating system, among others. The RF heating system produces an electromagnetic field within the cavity and between the electrodes to capacitively heat the load. The thermal heating system heats the air within the cavity. The combined RF and thermal heating system may more rapidly heat the load than could a thermal heating system alone. In addition, the RF energy radiated in the cavity may provide more even heating of the center of the load and, thus, shorter cooking times. The electromagnetic fields generated using embodiments of the inventive subject matter have been found to penetrate more deeply into food loads than is possible using conventional microwave energy fields and conventional thermal heating systems alone. In addition, the combined RF and thermal heating system can achieve browning and crisping of the load that is not easily achievable using a conventional microwave oven system alone.

Embodiments of thermal heating systems include, at the least, a heating element and a cavity temperature control system. Thermal heating systems may include, for example, convection heating systems, radiant heating systems, and gas heating systems. A convection heating system includes a fan that is configured to circulate air within a system cavity. In some embodiments, the convection heating system also includes a heating element that heats the air (e.g., the convection heating system may include a convection blower with an integrated heating element). In other embodiments, a distinct heating element may be used to heat the air within the system cavity, and the convection system may simply circulate the heated air. A radiant heating system may include one or more heating elements (e.g., heating coils) disposed within the system cavity and configured to heat the air within the cavity. Finally, a gas heating system includes a gas nozzle subsystem and a pilot lighting subsystem configured to ignite natural gas that is released through the nozzle subsystem. The burning natural gas results in heating of the air within the cavity. Each of these thermal heating systems also include a cavity temperature control system, which is configured to sense the temperature of the air within the system cavity, and to activate, deactivate, or adjust the functioning of the thermal heating system's heating element to maintain the air temperature within the cavity within a relatively small temperature range that encompasses a defined processing temperature (e.g., a cavity temperature setpoint specified by a user through the user interface).

Embodiments of the RF heating system, which is included in the heating appliance along with the thermal heating system, differ from a conventional microwave oven system in several respects. For example, embodiments of the RF heating system include a solid-state RF signal source, as opposed to a magnetron that is utilized in a conventional microwave oven system. Utilization of a solid-state RF signal source may be advantageous over a magnetron, in that a solid-state RF signal source may be significantly lighter and smaller, and may be less likely to exhibit performance degradation (e.g., power output loss) over time. In addition, embodiments of the RF heating system generate electromagnetic energy in the system cavity at frequencies that are significantly lower than the 2.54 gigahertz (GHz) frequency that is typically used in conventional microwave oven systems. In some embodiments, for example, embodiments of the RF heating system generate electromagnetic energy in the system cavity at frequencies within the VHF (very high frequency) range (e.g., from 30 megahertz (MHz) to 300 MHz). The significantly lower frequencies utilized in the various embodiments may result in deeper energy penetration into the load, and thus potentially faster and more even heating. Further still, embodiments of the RF heating system include a single-ended or double-ended variable impedance matching network, which is dynamically controlled based on the magnitude of reflected RF power. This dynamic control enables the system to provide a good match between the RF signal generator and the system cavity (plus load) throughout a heating process, which may result in increased system efficiency and reduced heating time.

Generally, the term “heating” means to elevate the temperature of a load (e.g., a food load or other type of load). The term “defrosting”, which also may be considered a “heating” operation, means to elevate the temperature of a frozen load (e.g., a frozen food load or other type of load) to a temperature at which the load is no longer frozen (e.g., a temperature at or near 0 degrees Celsius). As used herein, the term “heating” more broadly means a process by which the thermal energy or temperature of a load (e.g., a food load or other type of load) is increased through provision of thermal radiation of air particles and/or RF electromagnetic energy to the load. Accordingly, in various embodiments, a “heating operation” may be performed on a load with any initial temperature (e.g., any initial temperature above or below 0 degrees Celsius), and the heating operation may be ceased at any final temperature that is higher than the initial temperature (e.g., including final temperatures that are above or below 0 degrees Celsius). That said, the “heating operations” and “heating systems” described herein alternatively may be referred to as “thermal increase operations” and “thermal increase systems.”

FIG. 1is a perspective view of a heating system100(or appliance), in accordance with an example embodiment. Heating system100includes a heating cavity110(e.g., cavity960,1260,FIGS. 9, 12), a control panel120, an RF heating system150(e.g., RF heating system910,1210,FIGS. 9, 12), and a convection heating system160(e.g., an embodiment of thermal heating system950,1250,FIGS. 9, 12), all of which are secured within a system housing102. The heating cavity110is defined by interior surfaces of top, bottom, side, and back cavity walls111,112,113,114,115and an interior surface of door116. As shown inFIG. 1, door116may include a latching mechanism118, which engages with a corresponding securing structure119of the system housing102to hold door116closed. With door116closed, the heating cavity110defines an enclosed air cavity. As used herein, the terms “air cavity” or “oven cavity” may mean an enclosed area that contains air or other gasses (e.g., heating cavity110).

In some embodiments, one or more shelf support structures130,132are accessible within the heating cavity110, and the shelf support structures130,132are configured to hold a removable and repositionable shelf134(shown with dashed lines inFIG. 1, as the shelf is not inserted) at some height above the bottom cavity wall112. For example, as shown inFIG. 1, first shelf support structures130include a first set of rails attached to opposed cavity walls113,114at a first height above the bottom cavity wall112, and second shelf support structures132include a second set of rails attached to opposed cavity walls113,114at a second height above the bottom cavity wall112. The rails protrude into the cavity110from the primary plane of each of the opposed cavity walls113,114. A user may insert a shelf134into the cavity110by sliding the shelf134into the cavity110, and resting the left and right bottom edges of the shelf134on top of the rails of either of the shelf support structures130,132. In an alternate embodiment, the shelf support structures130,132may alternatively be configured as sets of protrusions (e.g., two protrusions on each of the opposed cavity walls113,114) that extend a short distance into the cavity110. In another alternate embodiment, the shelf support structures130,132may alternatively be configured as sets of grooves that are recessed below the primary plane of each of the opposed cavity walls113,114, and into which the shelf134may be slid. However the shelf support structures130,132are configured (e.g., as rails, protrusions, grooves, or otherwise), the shelf support structures130,132are positioned to hold the shelf134parallel with but elevated above the bottom cavity wall112. In some embodiments, the shelf support structures130,132are configured to provide an electrical connection between the shelf134(e.g., an electrode embodied in the shelf) and other portions of the RF heating system or a ground reference. In other embodiments, the shelf support structures130,132may be configured to electrically isolate the shelf134from the cavity walls and/or from other portions of the system.

In some embodiments, the shelf134may simply be configured to hold a load (e.g., a food load) at a desired height above the bottom cavity wall112. In other embodiments, the shelf134may consist of or include an electrode associated with the RF heating system (e.g., electrode942,1450,FIGS. 9, 12). Accordingly, the shelf support structures130,132alternatively may be considered to be electrode support structures, which are configured to hold a removable and repositionable electrode at some height above the bottom cavity wall112. In such embodiments, the shelf134and/or its integrated electrode may be electrically connected to other portions of the RF heating system or to a ground reference through conductive features (not shown) of the shelf support structures130,132, as indicated above. Alternatively, the shelf134and/or its integrated electrode may be electrically connected to other portions of the RF heating system or to a ground reference through a conductive connector136,138in one of the cavity sidewalls (e.g., one of walls113-115, such as the back cavity wall115as shown inFIG. 1). Further, in some embodiments, an electrode-containing shelf134may replace the below-described bottom (or second) electrode172. In other words, an electrode integrated within an electrode-containing shelf134may be connected within the system and perform the functions of the below-described bottom electrode172.

FIG. 2is a top view of a planar structure200, which may be used as a shelf and/or an electrode in system100(and/or in systems600,800,FIGS. 6, 8), in accordance with an example embodiment. Structure200has planar top and bottom surfaces202,204. A thickness between the surfaces202,204may be in a range of 1 to 3 centimeters, in an embodiment, although the thickness may be smaller or larger, as well. Structure200has a width206that may be approximately equal to (or slightly smaller or larger than, in various embodiments) the width of the cavity (e.g., cavity110,FIG. 1) into which the structure200will be inserted. Further, structure200has a depth208that may be approximately equal to (or slightly smaller than) the depth of the cavity (e.g., the distance between the closed door116and back wall115of cavity110,FIG. 1).

When configured simply as a shelf (e.g., shelf134,FIG. 1) that does not function as or include an electrode, structure200desirably is formed from one or more materials (e.g., plastic or other dielectric materials) that do not significantly affect the electromagnetic field produced in the cavity during operation. Alternatively, as indicated previously, structure200may be configured as an electrode, in which case structure200may be formed from one or more planar, electrically conductive materials (e.g., copper, aluminum, and so on), which may (or may not) be coated with or embedded within a protective dielectric material (e.g., plastic or other dielectric materials). In still other embodiments, an electrode272(indicated with dashed lines inFIG. 2) may be included within structure200, where the electrode is formed from one or more planar, electrically conductive materials (e.g., copper, aluminum, and so on). In such an embodiment, the electrode272may be embedded within protective dielectric material that supports the electrode272and forms the remaining planar portions of the structure200.

In the embodiments in which the entire structure200is configured as an electrode, or an electrode272is included as a part of the structure200, the structure200is configured to be electrically connected with other portions of the RF heating system or to a ground reference. For example, as indicated previously, the structure200could include conductive features on bottom edges of the structure, which contact corresponding conductive features of the shelf support structures (e.g., shelf support structures130,132,FIG. 1).

Alternatively, structure200may include a conductive connector230, which is configured to engage with a corresponding connector (e.g., either of conductive connectors136,138,FIG. 1) in a cavity sidewall (e.g., one of walls113-115, such as the back cavity wall115as shown inFIG. 1). When the entire structure200is configured as an electrode, the connector230may simply be an integrally-formed, protruding portion of the structure200. Alternatively, when the structure200includes a distinct electrode272, the connector230may be an integrally-formed, protruding portion of the electrode272, or the connector230may otherwise be electrically connected to the electrode272. Either way, when the structure200is slid into or otherwise inserted into the cavity, the connector230engages with the corresponding connector (e.g., either of conductive connectors136,138,FIG. 1) in a cavity sidewall to electrically connect the structure200or the electrode272to other portions of the RF heating system or to a ground reference.

In some embodiments, structure200may include additional openings220or other features that facilitate securing the structure200to one or more walls of the cavity (e.g., cavity110,FIG. 1) into which structure200is inserted. For example, openings220may be configured to receive screws or other attachment means therethrough, and the screws or other attachment means may be connectable to other features within the cavity. In some cases, electrical connection of the structure200or an electrode272within the structure200may be electrically grounded through the screws or other attachment means.

The structure200ofFIG. 2is a planar structure, and accordingly is not adapted to enable a significant amount of air flow or electromagnetic energy to pass through structure200. In some embodiments, it may be desirable to allow significant amounts of air flow or electromagnetic energy to pass through a shelf or support structure. Accordingly, in some embodiments, a shelf (e.g., shelf134,FIG. 1) or electrode may have openings between the top and bottom surfaces of the shelf or electrode. Such openings could be elongated channels, circular openings, rectangular openings, or any of a number of differently-configured openings. By way of example, but not of limitation, a grid-type structure will be described below. Those of skill in the art would understand, based on the description herein, that “perforated” structures having other types of openings alternatively could be used.

FIG. 3is a top view of a grid-type structure300, which may be used as a shelf or electrode in system100(and/or in systems600,800,FIGS. 6, 8), in accordance with an example embodiment. Structure300has planar top and bottom surfaces302,304, and a plurality of openings310extending between the top and bottom surfaces302,304to provide fluid communication between areas below and above the structure300. In the embodiment ofFIG. 3, structure300has a grid-type configuration in which the openings310are rectangular in shape and arranged in a two-dimensional array. In other embodiments, the openings may be elongated and/or may have different shapes and arrangements.

A thickness between the surfaces302,304may be in a range of 1 to 3 centimeters, in an embodiment, although the thickness may be smaller or larger, as well. Structure300has a width306that may be approximately equal to (or slightly smaller or larger than, in various embodiments) the width of the cavity (e.g., cavity110,FIG. 1) into which the structure300will be inserted. Further, structure300has a depth308that may be approximately equal to (or slightly smaller than) the depth of the cavity (e.g., the distance between the closed door116and back wall115of cavity110,FIG. 1).

When configured simply as a shelf (e.g., shelf134,FIG. 1) that does not function as or include an electrode, structure300desirably is formed from one or more materials (e.g., plastic or other dielectric materials) that do not significantly affect the electromagnetic field produced in the cavity during operation. Alternatively, as indicated previously, structure300may be configured as an electrode, in which case structure300may be formed from one or more perforated, electrically conductive materials (e.g., copper, aluminum, and so on), which may (or may not) be coated with or embedded within a protective dielectric material (e.g., plastic or other dielectric materials). In still other embodiments, an electrode372(indicated with dashed lines inFIG. 3) may be included within structure300, where the electrode is formed from one or more perforated, electrically conductive materials (e.g., copper, aluminum, and so on). In such an embodiment, the electrode372may be embedded within protective dielectric material that supports the electrode372and forms the remaining planar portions of the structure300.

In the embodiments in which the entire structure300is configured as an electrode, or an electrode372is included as a part of the structure300, the structure300is configured to be electrically connected with other portions of the RF heating system or to a ground reference. For example, as indicated previously, the structure300could include conductive features on bottom edges of the structure, which contact corresponding conductive features of the shelf support structures (e.g., shelf support structures130,132,FIG. 1).

Alternatively, structure300may include a conductive connector330, which is configured to engage with a corresponding connector (e.g., either of conductive connectors136,138,FIG. 1) in a cavity sidewall (e.g., one of walls113-115, such as the back cavity wall115as shown inFIG. 1). When the entire structure300is configured as an electrode, the connector330may simply be an integrally-formed, protruding portion of the structure300. Alternatively, when the structure300includes a distinct electrode372, the connector330may be an integrally-formed, protruding portion of the electrode372, or the connector330may otherwise be electrically connected to the electrode372. Either way, when the structure300is slid into or otherwise inserted into the cavity, the connector330engages with the corresponding connector (e.g., either of conductive connectors136,138,FIG. 1) in a cavity sidewall to electrically connect the structure300or the electrode372to other portions of the RF heating system or to a ground reference.

In some embodiments, structure300may include additional openings320or other features that facilitate securing the structure300to one or more walls of the cavity (e.g., cavity110,FIG. 1) into which structure300is inserted. For example, openings320may be configured to receive screws or other attachment means therethrough, and the screws or other attachment means may be connectable to other features within the cavity. In some cases, electrical connection of the structure300or an electrode372within the structure300may be electrically grounded through the screws or other attachment means.

Referring again toFIG. 1, and as mentioned above, heating system100includes both an RF heating system150(e.g., RF heating system910,1210,FIGS. 9, 12), and a convection heating system160(e.g., convection heating system950,1250,FIGS. 9, 12). As will be described in greater detail below, the RF heating system150includes one or more radio frequency (RF) signal sources (e.g., RF signal source920,1420,FIGS. 9, 12), a power supply (e.g., power supply926,1426,FIGS. 9, 12), a first electrode170(e.g., electrode940,1240,FIGS. 9, 12), a second electrode172(e.g., electrode942,1242,FIGS. 9, 12), impedance matching circuitry (e.g., circuits934,970,1000,1100,1234,1272,1300,1400,FIGS. 9-14), power detection circuitry (e.g., power detection circuitry930,1430,FIGS. 9, 12), and an RF heating system controller (e.g., system controller912,1212,FIGS. 9, 12).

The first electrode170is arranged proximate to a cavity wall (e.g., top wall111), and the second electrode172is arranged proximate to an opposite, second cavity wall (e.g., bottom wall112). Alternatively, as indicated above in conjunction with the description of shelf134, the second electrode172may be replaced by a shelf structure (e.g., shelf200,300,FIGS. 2, 3) or an electrode (e.g., electrode272,372,FIGS. 2, 3) within such a shelf structure. Either way, the first and second electrodes170,172(and/or shelf200,300, or electrode272,372,FIGS. 2, 3) are electrically isolated from the remaining cavity walls (e.g., walls113-115and door116), and the cavity walls are grounded. In either configuration, the system may be simplistically modeled as a capacitor, where the first electrode170functions as one conductive plate (or electrode), the second electrode172(or structure200,300or electrode272,372,FIGS. 2, 3) functions as a second conductive plate (or electrode), and the air cavity between the electrodes (including any load contained therein) functions as a dielectric medium between the first and second conductive plates. Although not shown inFIG. 1, a non-electrically conductive barrier (e.g., barrier962,1462,FIGS. 9, 12) also may be included in the system100, and the non-conductive barrier may function to electrically and physically isolate the load from the second electrode172and/or the bottom cavity wall112.

The RF heating system150may be an “unbalanced” RF heating system or a “balanced” RF heating system, in various embodiments. As will be described in more detail later in conjunction withFIG. 9, when configured as an “unbalanced” RF heating system, the system150includes a single-ended amplifier arrangement (e.g., amplifier arrangement920,FIG. 9), and a single-ended impedance matching network (e.g., including networks934,970,FIG. 9) coupled between an output of the amplifier arrangement and the first electrode170, and the second electrode172(or structure200,300or electrode272,372,FIGS. 2, 3) is grounded. Although alternatively the first electrode170could be grounded, and the second electrode172could be coupled to the amplifier arrangement. In contrast, and as will be described in more detail later in conjunction withFIG. 12, when configured as a “balanced” RF heating system, the system150includes a single-ended or double-ended amplifier arrangement (e.g., amplifier arrangement1220or1220′,FIG. 12), and a double-ended impedance matching network (e.g., including networks1234,1272,FIG. 12) coupled between an output of the amplifier arrangement and the first and second electrodes170,172. In either the balanced or unbalanced embodiments, the impedance matching network includes a variable impedance matching network that can be adjusted during the heating operation to improve matching between the amplifier arrangement and the cavity (plus load). Further, a measurement and control system can detect certain conditions related to the heating operation (e.g., an empty system cavity, a poor impedance match, and/or completion of a heating operation).

The convection system160includes a thermal system controller (e.g., thermal system controller952,1452,FIGS. 9, 12), a power supply, a heating element, a fan, and a thermostat, in an embodiment. The heating element may be, for example, a resistive heating element, which is configured to heat air surrounding the heating element when current from the power supply is passed through the heating element. The thermostat (or oven sensor) senses the temperature of the air within the system cavity, and based on the sensed cavity temperature, controls the power supply to provide current to the heating element. More specifically, the thermostat operates to maintain the cavity air temperature at or near the temperature setpoint. In addition, the thermal system controller may selectively activate and deactivate the convection fan to circulate air warmed by the heating element within the system cavity110. In the system100illustrated inFIG. 1, the fan is located in a fan compartment outside of the system cavity110, and fluid (air) communication between the fan and the system cavity110is provided through one or more openings in one or more cavity walls. For example,FIG. 1illustrates an opening162corresponding to an air outlet in cavity wall115between a fan compartment and the system cavity110.

In some embodiments, the heating element and the fan form portions of a complete convection unit (referred to as a “convection blower”) that is configured both to heat air and circulate the heated air. For example,FIG. 4is a perspective view of a convection blower400with a fan and an integrated heating element that could be used in the appliance ofFIG. 1, in accordance with an example embodiment. The components of convection blower400are contained within a housing402, which has features that enable the blower400to be securely mounted within a fan compartment of a heating system (e.g., system100,FIG. 1). Blower400includes a fan motor410configured to operate an internal fan (hidden inFIG. 4) in response to a power input (from a power supply, not shown). In addition, an internal heating element (also hidden inFIG. 4) is used to heat air within an internal compartment. While operating, the fan causes air (e.g., from a system cavity110,FIG. 1) to be drawn into the internal compartment through an air intake420, and causes heated air within the internal compartment to be forced out of the blower400(e.g., back into the system cavity110,FIG. 1) through an air outlet430. When installed in a system (e.g., system100,FIG. 1), the air outlet430is coupled to an opening in the cavity wall(s) to provide fluid communication between the blower400and the system cavity.

In other embodiments, such as the systems600,800ofFIGS. 6 and 8, air circulated by the convection system may be heated by a heating source that is not internal to the convection system, such as a distinct heating element within the cavity (e.g., heating element682,684, FIG.6) or an activated burner (e.g., gas burner882,884,FIG. 8). In such embodiments, the convection system may include a simple fan contained within a fan compartment of the heating system (e.g., systems600,800,FIGS. 6, 8), which is in fluid communication with the system cavity (e.g., cavity610,810,FIGS. 6, 8) through an air intake and an air outlet. For example,FIG. 5is a perspective view of a convection fan500that could be used in a heating system when the system includes an external heating source, such as in the appliances600,800ofFIGS. 6 and 8, in accordance with other example embodiments. Convection fan500simply includes a fan motor510coupled to a fan512, and the fan motor510is configured to operate the fan512in response to a power input (from a power supply, not shown). While operating, the fan causes heated air (e.g., air heated by a heating source within a system cavity610,810,FIGS. 6, 8) to be drawn into the fan compartment through an air intake between the system cavity and the fan compartment, and causes the heated air to be forced back out of the fan compartment into the system cavity through an air outlet between the fan compartment and the system cavity (e.g., opening662,862,FIGS. 6, 8).

Referring again toFIG. 1, and according to an embodiment, during operation of the heating system100, a user (not illustrated) may first place one or more loads (e.g., food and/or liquids) into the heating cavity110, and close the door116. As indicated previously, the user may place the load(s) on the bottom cavity wall112, on an insulating layer over the bottom cavity wall, or on a rotating plate (not illustrated). Alternatively, as indicated previously, the user may place the load(s) on a shelf134that is inserted into the cavity110at any supported position. When utilizing the RF heating system during a cooking operation, and when the shelf134(or an electrode272,372,FIGS. 2, 3within the shelf) functions as a bottom electrode (e.g., replacing electrode172), it may be desirable to insert the shelf134at a position that results in a minimum distance between the top of the load and the first electrode170(or the top cavity wall111). This may enable the capacitive cooking provided by the RF heating system to operate more efficiently than when the top of the load is farther from the first electrode170(or the top cavity wall111).

As will be described in more detail later in conjunction withFIG. 16, to initiate a cooking process, the user may specify a type of cooking (or cooking mode) that the user would like the system100to implement. The user may specify the cooking mode through the control panel120(e.g., by pressing a button or making a cooking mode menu selection). According to an embodiment, the system100is capable of implementing at least the following distinct cooking modes: 1) convection-only cooking; 2) RF-only cooking; and 3) combined convection and RF cooking. For the convection-only cooking mode (mode 1, above), the convection system160is activated during the cooking process, and the RF heating system150is idle or deactivated. For the RF-only cooking mode (mode 2, above, including RF-only defrosting), the RF heating system150is activated during the cooking process, and the convection system160is idle or deactivated. Finally, for combined convection and RF cooking mode (mode 3, above), both the convection system160and the RF heating system150are activated during the cooking process. In this mode, both the convection system160and the RF heating system150may be activated simultaneously and continuously, or either system may be deactivated during portions of the process.

When implementing the convection-only cooking mode (mode 1, above) or the combined convection and RF cooking mode (mode 3, above), the system100may enable the user to provide inputs via the control panel120that specify a cavity temperature setpoint (or target oven temperature) for the cooking process (e.g., in a range of about 65-260 degrees Celsius (or 150-500 degrees Fahrenheit)). Alternatively, the cavity temperature setpoint may otherwise be obtained or determined by the system100. In some embodiments, the cavity temperature setpoint may be varied throughout the process (e.g., the system100may run a software program that varies the oven temperature throughout the cooking process). In addition to specifying the cavity temperature setpoint, the system100also may enable the user to provide inputs via the control panel120that specify a cooking start time, stop time, and/or duration. In such an embodiment, the system100may monitor a system clock to determine when to activate and deactivate the RF and convection heating systems150,160.

The RF-only cooking mode may be particularly useful when gentle warming of the load is desired, such as for a defrosting operation. When implementing the RF-only cooking mode, the system100may enable the user to provide inputs via the control panel120that specify a type of operation to be performed (e.g., a defrost operation, or another RF-only warming operation). For a defrost operation, the system100may be configured to monitor feedback from the RF system that may indicate when the load has reached a desired temperature (e.g., −2 degrees Celsius, or some other temperature), and the system100may terminate operation when the desired load temperature is reached.

In some embodiments, the system also may enable the user optionally to provide inputs via the control panel120that specify characteristics of the load(s). For example, the specified characteristics may include an approximate weight of the load. In addition, the specified load characteristics may indicate the material(s) from which the load is formed (e.g., meat, bread, liquid). In alternate embodiments, the load characteristics may be obtained in some other way, such as by scanning a barcode on the load packaging or receiving a radio frequency identification (RFID) signal from an RFID tag on or embedded within the load. Either way, as will be described in more detail later, information regarding such load characteristics enables the RF heating system controller (e.g., RF heating system controller912,1212,FIGS. 9, 12) to establish an initial state for the impedance matching network of the system at the beginning of the heating operation, where the initial state may be relatively close to an optimal state that enables maximum RF power transfer into the load. Alternatively, load characteristics may not be entered or received prior to commencement of a heating operation, and the RF heating system controller may establish a default initial state for the impedance matching network.

To begin the heating operation, the user may provide a “start” input via the control panel120(e.g., the user may depress a “start” button). In response, a host system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12) sends appropriate control signals to the convection system150and/or the RF heating system160throughout the cooking process, depending on which cooking mode is being implemented. The particulars of system operation will be described in more detail later in conjunction withFIGS. 16-18.

Essentially, when performing convection-only cooking or combined convection and RF cooking, the system100selectively activates, deactivates, and otherwise controls the convention heating system160to pre-heat the system cavity110to the cavity temperature setpoint, and to maintain the temperature within the system cavity110at or near the cavity temperature setpoint. The system100may establish and maintain the temperature within the cavity110based on thermostat signals and/or based on feedback from the convection heating system160.

When performing RF-only cooking or combined convection and RF cooking, the system selectively activates and controls the RF heating system150in a manner in which maximum RF power transfer may be absorbed by the load throughout the cooking process. During the heating operation, the impedance of the load (and thus the total input impedance of the cavity110plus load) changes as the thermal energy of the load increases. The impedance changes alter the absorption of RF energy into the load, and thus alter the magnitude of reflected power. According to an embodiment, power detection circuitry (e.g., power detection circuitry930,1430,FIGS. 9, 12) continuously or periodically measures the reflected power along a transmission path between the RF signal source and the system electrode(s)170and/or172(or shelf134or electrodes272,372within shelf134). Based on these measurements, an RF heating system controller (e.g., RF heating system controller912,1212,FIGS. 9, 12) may alter the state of the variable impedance matching network (e.g., networks970,1272,FIGS. 9, 12) during the heating operation to increase the absorption of RF power by the load. In addition, in some embodiments, the RF system controller may detect completion of the heating operation (e.g., when the load temperature has reached a target temperature) based on feedback from the power detection circuitry.

Heating system100is described as a combination of an RF heating system150and a thermal heating system in the form of a convection heating system160. In other embodiments, an RF heating system also or alternatively may be combined with a radiant heating system or a gas heating system, both of which also may be characterized as “thermal heating systems”. For example,FIG. 6is a perspective view of a heating appliance600with an RF heating system650and a radiant heating system680, in accordance with another example embodiment. Heating system600is similar to heating system100(FIG. 1), in that the components of heating system600are secured within a system housing602, and heating system600includes a heating cavity610(e.g., cavity960,1260,FIGS. 9, 12), a control panel620, and an RF heating system650(e.g., RF heating system910,1210,FIGS. 9, 12). In addition, in an embodiment, heating system600also may include a convection heating system660, although the convection heating system660is optional. In contrast with heating system100(FIG. 1), however, system600includes a radiant heating system680(e.g., one embodiment of thermal heating system950,1250,FIGS. 9, 12) with heating elements682,684disposed in the heating cavity610.

The heating cavity610is defined by interior surfaces of top, bottom, side, and back cavity walls611,612,613,614,615and an interior surface of door616. As shown inFIG. 6, door616may include a latching mechanism618, which engages with a corresponding securing structure619of the system housing602to hold door616closed. In some embodiments, one or more shelf support structures630,632are accessible within the heating cavity610, and the shelf support structures630,632are configured to hold a removable and repositionable shelf634(shown with dashed lines inFIG. 6, as the shelf is not inserted) at various heights above the bottom cavity wall612. As discussed above in conjunction withFIG. 1, the shelf634may be configured as an electrode or contain an electrode. Further, the shelf634may have a simple planar structure (e.g., similar to structure200,FIG. 2), or the shelf634may have a grid-type structure (e.g., similar to structure300,FIG. 3). In such embodiments, the shelf634(or an electrode integrated within the shelf) may be electrically connected to other portions of the RF heating system or to a ground reference through conductive features (not shown) of the shelf support structures630,632. Alternatively, the shelf634and/or its integrated electrode may be electrically connected to other portions of the RF heating system or to a ground reference through a conductive connector636,638in one of the cavity sidewalls.

The cavity walls611-615, door616, latching mechanism618, securing structure619, control panel620, shelf support structures630,632, and repositionable shelf634may be substantially similar or identical to the cavity walls111-115, door116, latching mechanism118, securing structure119, control panel120, shelf support structures130,132, and repositionable shelf134, respectively, which were discussed above in conjunction withFIG. 1, including all of the various alternate embodiments of those system components. Accordingly, the description associated with cavity walls111-115, door116, latching mechanism118, securing structure119, control panel120, shelf support structures130,132, and repositionable shelf134is intended to apply also to cavity walls611-615, door616, latching mechanism618, securing structure619, control panel620, shelf support structures630,632, and repositionable shelf634, but for purposes of brevity, that description is not repeated here.

As mentioned above, heating system600includes both an RF heating system650(e.g., RF heating system910,1210,FIGS. 9, 12), and a radiant heating system680(e.g., radiant heating system950,1250,FIGS. 9, 12). The radiant heating system680includes a thermal system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12), a power supply, one or more radiant heating elements682,684, and a thermostat (or oven sensor), in an embodiment. As will be described in more detail below, each heating element682,684may be, for example, a resistive heating element, which is configured to heat air surrounding the heating element when current from the power supply is passed through the heating element. The thermostat (or oven sensor) senses the temperature of the air within the system cavity610. Based on the sensed cavity temperature, the thermostat (or the thermal system controller) controls the supply of current provided by the power supply to the heating element(s)682,684. More specifically, the thermostat (or the thermal system controller) operates to maintain the cavity air temperature at or near the temperature setpoint.

According to an embodiment, the heating elements682,684may be positioned at or near the bottom and/or top of the system cavity610, respectively. In other embodiments, one or more heating elements may be located elsewhere (e.g., at or near the sides of the system cavity610, and/or in separate compartments from the system cavity610). Either way, the heating elements682,684are in fluid communication with the system cavity610, meaning that air heated by the heating elements682,684may flow throughout the system cavity610. The heating element682located at the bottom of the system cavity610provides heat to a load within the cavity610from below (e.g., for warming and baking), and the heating element684located at the top of the system cavity610provides heat to a load within the cavity610from above (e.g., for warming, baking, broiling, and/or browning).

Each heating element682,684is configured to heat air surrounding the heating element682,684when electrical current is passed through the element. For example, each heating element682,684may include a sheath heating element that is configured to heat surrounding air through the process of resistive or Joule heating. An example of such a heating element is illustrated inFIG. 7, which is a top view of a heating element700that could be used in the appliance ofFIG. 6(e.g., as either or both of heating elements682,684,FIG. 6), in accordance with an example embodiment. Heating element700includes a tubular heating element710that has an undulating shape within a two-dimensional area (or plane), so that an outer perimeter of the tubular heating element710fits within the perimeter of a given space (e.g., within the perimeter of the top or bottom cavity wall611,612). The tubular heating element710may include an inner conductor comprised of a wire or coil formed from an electrically-conductive and electrically-resistive material (e.g., nichrome (NiCr)), a surrounding metallic tube (e.g., formed from copper or a stainless steel alloy), and an outer insulating coating (e.g., magnesium oxide powder). Ends of the heating element710may be held in place with a bracket720, in some embodiments, so that exposed ends712,714of the inner conductor can be inserted into corresponding pairs of connectors in a radiant heating system (e.g., connector pairs in one or more walls611-615of the system). When current is passed through the wire of the heating element710, the current encounters resistance, resulting in heating of the element710and the surrounding air.

The RF signal source(s), power supply, first electrode670, second electrode672, impedance matching circuitry, power detection circuitry, and RF heating system controller of RF heating system650may be substantially similar or identical to the RF signal source(s), power supply, first electrode170, second electrode172, impedance matching circuitry, power detection circuitry, and RF heating system controller, respectively, which were discussed above in conjunction withFIG. 1, including all of the various alternate embodiments of those system components. Accordingly, the description associated with these components in conjunction withFIG. 1apply also to the analogous components in RF heating system650, but for purposes of brevity, that description is not repeated here.

That said, the first electrode670and/or the second electrode672(and/or shelf634) may be specifically designed so as not to substantially restrict or interfere with the movement of air heated by the heating elements682,684. Further, the heating elements682,684and the first and second electrodes670,672may be oriented with respect to each other so that the heating elements682,684do not substantially alter or interfere with the electromagnetic field produced by either or both electrodes670,672.

According to one embodiment, when both a heating element and an electrode are proximate to a same cavity wall, the heating element is positioned between the electrode and the cavity wall. For example, in the embodiment ofFIG. 6, on the top side of cavity610, electrode670is positioned proximate to cavity wall611, and heating element684is positioned between the electrode670and the cavity wall611. On the bottom side of cavity610, electrode672is positioned proximate to cavity wall612, and heating element682is positioned between the electrode672and the cavity wall612. Posts or other structures may be utilized to hold the electrodes670,672and the heating elements682,684in their desired orientations with respect to each other and the cavity walls611,612. In an embodiment, and as illustrated inFIG. 6, each of electrodes670,672includes a plurality of openings that provide fluid communication between the area proximate to heating element684,682, respectively, and the system cavity610. For example, each of electrodes670,672may have a grid-like structure similar to structure300(FIG. 3), in an embodiment.

In other embodiments, either of heating elements682,684may be excluded from system600. In an embodiment in which heating element682is excluded, electrode672alternatively may be a simple planar electrode (e.g., similar to structure200,FIG. 2). In another embodiment in which heating element684is excluded, electrode670alternatively may be a simple planar electrode (e.g., similar to structure200,FIG. 2). In still other alternate embodiments, either or both of electrodes670,672could be positioned between their corresponding heating elements684,682and the proximate cavity walls611,612, and in such embodiments, the electrode670,672could be a simple planar electrode (e.g., similar to structure200,FIG. 2).

As mentioned above, system600optionally could include a convection system660, as well. When included, convection system660could simply include a power supply and a fan, since heating of the air in the cavity610can be achieved by the heating elements682,684. However, convection system660also could include an integrated heating element and a thermostat, in some embodiments. Either way, the convection system fan may be selectively activated and deactivated by the system controller to circulate within the system cavity610. In the system600illustrated inFIG. 6, the fan is located in a fan compartment outside of the system cavity610, and fluid (air) communication between the fan and the system cavity610is provided through one or more openings in one or more cavity walls (e.g., through opening662in cavity wall615).

During operation of the heating system600, a user (not illustrated) may first place one or more loads (e.g., food and/or liquids) into the heating cavity610, and close the door616. The user may place the load on the bottom electrode672(or the bottom cavity wall612if electrode672and heating element682are excluded), or on an insulating structure over the bottom electrode672, heating element682, and/or cavity wall612. Alternatively, as indicated previously, the user may place the load on a shelf634that is inserted into the cavity610at any supported position.

Again, as will be described in more detail later in conjunction withFIG. 16, to initiate a cooking process, the user may specify a type of cooking (or cooking mode) that the user would like the system600to implement. The user may specify the cooking mode through the control panel620(e.g., by pressing a button or making a cooking mode menu selection). According to an embodiment, the system600is capable of implementing at least the following distinct cooking modes: 1) radiant-only cooking; 2) RF-only cooking; and 3) combined radiant and RF cooking. When the system600also includes a convection heating system660, the system600also may be capable of implementing the following additional cooking modes: 4) combined convection and radiant cooking; and 5) combined convection, radiant, and RF cooking.

When implementing the radiant-only cooking mode (mode 1, above), the combined radiant and RF cooking mode (mode 3, above), the convention and radiant cooking mode (mode 4, above), or the combined convection, radiant, and RF cooking mode (mode 5, above), the system600may enable the user to provide inputs via the control panel620that specify a cavity temperature setpoint for the cooking process (e.g., in a range of about 65-260 degrees Celsius (or 150-500 degrees Fahrenheit)). Alternatively, the cavity temperature setpoint may otherwise be obtained or determined by the system600. In some embodiments, the cavity temperature setpoint may be varied throughout the process (e.g., the system600may run a software program that varies the oven temperature throughout the cooking process). In addition to specifying the cavity temperature setpoint, the system600also may enable the user to provide inputs via the control panel620that specify a cooking start time, stop time, and/or duration. In such an embodiment, the system600may monitor a system clock to determine when to activate and deactivate the RF and radiant heating systems650,680.

For the RF-only cooking mode (mode 2, above, including RF-only defrosting), the RF heating system650is activated during the cooking process, and the radiant heating system680and convection system660are idle or deactivated. Conversely, for combined radiant and RF cooking mode (mode 3, above), and the combined convection, radiant, and RF cooking mode (mode 5, above), of the RF heating system650and the radiant heating system680and/or the convection system660are activated during the cooking process. In these modes, RF heating system650and the radiant heating system680and/or the convection system660may be activated simultaneously and continuously, or either system may be deactivated during portions of the process.

To begin the heating operation, the user may provide a “start” input via the control panel620(e.g., the user may depress a “start” button). In response, a host system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12) sends appropriate control signals to the radiant heating system680, the RF heating system660, and/or the convection system660(when included) throughout the cooking process, depending on which cooking mode is being implemented. The particulars of system operation will be described in more detail later in conjunction withFIGS. 16-18.

Essentially, when performing radiant-only cooking or combined radiant and RF cooking, the system600selectively activates, deactivates, and otherwise controls the radiant heating system680to pre-heat the system cavity610to the cavity temperature setpoint, and to maintain the temperature within the system cavity610at or near the cavity temperature setpoint. The system600may establish and maintain the temperature within the cavity610based on thermostat readings and/or based on feedback from the radiant heating system680. When performing RF-only cooking or combined radiant and RF cooking, the system selectively activates and controls the RF heating system650in a manner in which maximum RF power transfer may be absorbed by the load throughout the cooking process.

In still other embodiments, an RF heating system also or alternatively may be combined with a gas heating system, as mentioned above. For example,FIG. 8is a perspective view of a heating appliance800with an RF heating system850and a gas heating system880, in accordance with another example embodiment. Heating system800is similar to heating systems100,600(FIGS. 1, 6), in that the components of heating system800are secured within a system housing802, and heating system800includes a heating cavity810(e.g., cavity960,1260,FIGS. 9, 12), a control panel820, and an RF heating system850(e.g., RF heating system910,1210,FIGS. 9, 12). In addition, in an embodiment, heating system800also may include a convection heating system860, although the convection heating system860is optional. In contrast with heating systems100,600(FIGS. 1, 6), however, system800includes a gas heating system880(e.g., one embodiment of thermal heating system950,1250,FIGS. 9, 12) with gas burners882,884in fluid (air) communication with the heating cavity810.

The heating cavity810is defined by interior surfaces of top, bottom, side, and back cavity walls811,812,813,814,815and an interior surface of door816. As shown inFIG. 8, door816may include a latching mechanism818, which engages with a corresponding securing structure819of the system housing802to hold door816closed. In some embodiments, one or more shelf support structures830,832are accessible within the heating cavity810, and the shelf support structures830,832are configured to hold a removable and repositionable shelf834(shown with dashed lines inFIG. 8, as the shelf is not inserted) at various heights above the bottom cavity wall812. As discussed above in conjunction withFIG. 1, the shelf834may be configured as an electrode or contain an electrode. Further, the shelf834may have a simple planar structure (e.g., similar to structure200,FIG. 2), or the shelf834may have a grid-type structure (e.g., similar to structure300,FIG. 3). In such embodiments, the shelf834(or an electrode integrated within the shelf) may be electrically connected to other portions of the RF heating system or to a ground reference through conductive features (not shown) of the shelf support structures830,832. Alternatively, the shelf834and/or its integrated electrode may be electrically connected to other portions of the RF heating system or to a ground reference through a conductive connector836,838in one of the cavity sidewalls.

The cavity walls811-815, door816, latching mechanism818, securing structure819, control panel820, shelf support structures830,832, and repositionable shelf834may be substantially similar or identical to the cavity walls111-115, door116, latching mechanism118, securing structure119, control panel120, shelf support structures130,132, and repositionable shelf134, respectively, which were discussed above in conjunction withFIG. 1, including all of the various alternate embodiments of those system components. Accordingly, the description associated with cavity walls111-115, door116, latching mechanism118, securing structure119, control panel120, shelf support structures130,132, and repositionable shelf134is intended to apply also to cavity walls811-815, door816, latching mechanism818, securing structure819, control panel820, shelf support structures830,832, and repositionable shelf834, but for purposes of brevity, that description is not repeated here.

As mentioned above, heating system800includes both an RF heating system850(e.g., RF heating system910,1210,FIGS. 9, 12), and a gas heating system880(e.g., gas heating system950,1250,FIGS. 9, 12). The gas heating system880includes a gas heating system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12), an ignition source (e.g., a hot surface or glow bar ignitor), a gas valve, one or more burners882,884, and a thermostat (or oven sensor), in an embodiment. The thermostat (or oven sensor) senses the temperature of the air within the system cavity810. Based on the sensed cavity temperature, the thermostat (or the gas heating system controller) controls the gas valve to increase or decrease a supply of gas provided by to the burner(s)882,884. More specifically, the thermostat (or the gas heating system controller) operates to maintain the cavity air temperature at or near the temperature setpoint.

According to an embodiment, the burners882,884may be positioned at or near the bottom and/or top of the system cavity810, respectively (e.g., in separate compartments from the system cavity810). The burners882,884are in fluid communication with the system cavity810, meaning that air heated by ignited gas at the burners882,884may flow throughout the system cavity810. The burner882located at the bottom of the system cavity810provides heat to a load within the cavity810from below (e.g., for warming and baking), and the burner884located at the top of the system cavity810provides heat to a load within the cavity810from above (e.g., for warming, baking, broiling, and/or browning).

The RF signal source(s), power supply, first electrode870, second electrode872, impedance matching circuitry, power detection circuitry, and RF heating system controller of RF heating system850may be substantially similar or identical to the RF signal source(s), power supply, first electrode170, second electrode172, impedance matching circuitry, power detection circuitry, and RF heating system controller, respectively, which were discussed above in conjunction withFIG. 1, including all of the various alternate embodiments of those system components. Accordingly, the description associated with these components in conjunction withFIG. 1apply also to the analogous components in RF heating system850, but for purposes of brevity, that description is not repeated here.

That said, the first electrode870and/or the second electrode872(and/or shelf834) may be specifically designed so as not to substantially restrict or interfere with the movement of air heated by the burners882,884. Further, the burners882,884and the first and second electrodes870,872may be oriented with respect to each other so that the burners882,884do not substantially alter or interfere with the electromagnetic field produced by either or both electrodes870,872.

According to one embodiment, when both a burner and an electrode are proximate to a same cavity wall, the electrode is positioned between the burner and the cavity810. For example, in the embodiment ofFIG. 8, on the top side of cavity810, electrode870is positioned proximate to cavity wall811, and burner884is positioned in a separate burner cavity behind (above) the cavity wall811. On the bottom side of cavity810, electrode872is positioned proximate to cavity wall812, and burner882is positioned in a separate burner cavity behind (below) the cavity wall812. Air heated by ignited gas at the burners882,884may enter the system cavity810through slots883,885. In other embodiments, either of burners882,884may be excluded from system800.

As mentioned above, system800optionally could include a convection system860, as well. When included, convection system860could simply include a power supply and a fan, since heating of the air in the cavity810can be achieved by the ignited gas at the burners882,884. However, convection system860also could include an integrated heating element and a thermostat, in some embodiments. Either way, the convection system fan may be selectively activated and deactivated by the system controller to circulate within the system cavity810. In the system800illustrated inFIG. 8, the fan is located in a fan compartment outside of the system cavity810, and fluid (air) communication between the fan and the system cavity810is provided through one or more openings in one or more cavity walls (e.g., through opening862in cavity wall815).

During operation of the heating system800, a user (not illustrated) may first place one or more loads (e.g., food and/or liquids) into the heating cavity810, and close the door816. The user may place the load on the bottom electrode872(or the bottom cavity wall812), or on an insulating structure over the bottom electrode872and/or cavity wall812. Alternatively, as indicated previously, the user may place the load on a shelf834that is inserted into the cavity810at any supported position.

Again, as will be described in more detail later in conjunction withFIG. 16, to initiate a cooking process, the user may specify a type of cooking (or cooking mode) that the user would like the system800to implement. The user may specify the cooking mode through the control panel820(e.g., by pressing a button or making a cooking mode menu selection). According to an embodiment, the system800is capable of implementing at least the following distinct cooking modes: 1) gas-only cooking; 2) RF-only cooking; and 3) combined gas and RF cooking. When the system800also includes a convection heating system860, the system800also may be capable of implementing the following additional cooking modes: 4) combined convection and gas cooking; and 5) combined convection, gas, and RF cooking.

When implementing the gas-only cooking mode (mode 1, above), the combined gas and RF cooking mode (mode 3, above), the convention and gas cooking mode (mode 4, above), or the combined convection, gas, and RF cooking mode (mode 5, above), the system800may enable the user to provide inputs via the control panel820that specify a cavity temperature setpoint for the cooking process (e.g., in a range of about 85-260 degrees Celsius (or 150-500 degrees Fahrenheit)). Alternatively, the cavity temperature setpoint may otherwise be obtained or determined by the system800. In some embodiments, the cavity temperature setpoint may be varied throughout the process (e.g., the system800may run a software program that varies the oven temperature throughout the cooking process). In addition to specifying the cavity temperature setpoint, the system800also may enable the user to provide inputs via the control panel820that specify a cooking start time, stop time, and/or duration. In such an embodiment, the system800may monitor a system clock to determine when to activate and deactivate the RF and gas heating systems850,880.

For the RF-only cooking mode (mode 2, above, including RF-only defrosting), the RF heating system850is activated during the cooking process, and the gas heating system880and convection system860are idle or deactivated. Conversely, for combined gas and RF cooking mode (mode 3, above), and the combined convection, gas, and RF cooking mode (mode 5, above), of the RF heating system850and the gas heating system880and/or the convection system860are activated during the cooking process. In these modes, RF heating system850and the gas heating system880and/or the convection system860may be activated simultaneously and continuously, or either system may be deactivated during portions of the process.

To begin the heating operation, the user may provide a “start” input via the control panel820(e.g., the user may depress a “start” button). In response, a host system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12) sends appropriate control signals to the gas heating system880, the RF heating system860, and/or the convection system860(when included) throughout the cooking process, depending on which cooking mode is being implemented. The particulars of system operation will be described in more detail later in conjunction withFIGS. 16-18.

Essentially, when performing gas-only cooking or combined gas and RF cooking, the system800selectively activates, deactivates, and otherwise controls the gas heating system880to pre-heat the system cavity810to the cavity temperature setpoint, and to maintain the temperature within the system cavity810at or near the cavity temperature setpoint. The system800may establish and maintain the temperature within the cavity810based on thermostat readings and/or based on feedback from the gas heating system880. When performing RF-only cooking or combined gas and RF cooking, the system selectively activates and controls the RF heating system850in a manner in which maximum RF power transfer may be absorbed by the load throughout the cooking process.

The heating systems100,600,800ofFIGS. 1, 6, 8each are embodied as a counter-top type of appliance. Those of skill in the art would understand, based on the description herein, that embodiments of heating systems may be incorporated into systems or appliances having other configurations, as well. Accordingly, the above-described implementations of heating systems in a stand-alone appliance are not meant to limit use of the embodiments only to those types of systems. Instead, various embodiments of heating systems may be incorporated into wall-cavity installed appliances, and systems that include multiple types of appliances incorporated in a common housing.

Further, although heating systems100,600,800are shown with their components in particular relative orientations with respect to one another, it should be understood that the various components may be oriented differently, as well. In addition, the physical configurations of the various components may be different. For example, control panels120,620,820may have more, fewer, or different user interface elements, and/or the user interface elements may be differently arranged. In addition, although a substantially cubic heating cavity110is illustrated inFIGS. 1, 6, and 8, it should be understood that a heating cavity may have a different shape, in other embodiments (e.g., cylindrical, and so on). Further, heating systems100,600,800may include additional components (e.g., a stationary or rotating plate within the cavity, an electrical cord, and so on) that are not specifically depicted inFIGS. 1, 6, and 8.

FIG. 9is a simplified block diagram of an unbalanced heating system900(e.g., heating system100,600,800,FIGS. 1, 6, 8), in accordance with an example embodiment. Heating system900includes host/thermal system controller952, RF heating system910, thermal heating system950, user interface992, and a containment structure966that defines an oven cavity960, in an embodiment. It should be understood thatFIG. 9is a simplified representation of a heating system900for purposes of explanation and ease of description, and that practical embodiments may include other devices and components to provide additional functions and features, and/or the heating system900may be part of a larger electrical system.

The containment structure966may include bottom, top, and side walls, the interior surfaces of which define the cavity960(e.g., cavity110,610,810,FIGS. 1, 6, 8). According to an embodiment, the cavity960may be sealed (e.g., with a door116,616,816,FIGS. 1, 6, 8) to contain the heat and electromagnetic energy that is introduced into the cavity960during a heating operation. The system900may include one or more interlock mechanisms (e.g., latching mechanisms and securing structures118,119,618,619,818,819,FIGS. 1, 6, 8) that ensure that the seal is intact during a heating operation. If one or more of the interlock mechanisms indicates that the seal is breached, the host/thermal system controller952may cease the heating operation.

User interface992may correspond to a control panel (e.g., control panel120,620,820,FIGS. 1, 6, 8), for example, which enables a user to provide inputs to the system regarding parameters for a heating operation (e.g., the cooking mode, characteristics of the load to be heated, and so on), start and cancel buttons, mechanical controls (e.g., a door/drawer open latch), and so on. In addition, the user interface may be configured to provide user-perceptible outputs indicating the status of a heating operation (e.g., a countdown timer, visible indicia indicating progress or completion of the heating operation, and/or audible tones indicating completion of the heating operation) and other information.

As will be described in more detail in conjunction withFIGS. 16 and 18, the host/thermal system controller952may perform functions associated with the overall system900(e.g., “host control functions”), and functions associated more particularly with the thermal heating system950(e.g., “thermal system control functions”). Because, in an embodiment, the host control functions and the thermal system control functions may be performed by one hardware controller, the host/thermal system controller952is shown as a dual-function controller. In alternate embodiments, the host controller and the thermal system controller may be distinct controllers that are communicatively coupled.

The thermal heating system950includes host/thermal system controller952, one or more thermal heating components954, thermostat956, and in some embodiments, a fan958. Host/thermal system controller952may include one or more general purpose or special purpose processors (e.g., a microprocessor, microcontroller, Application Specific Integrated Circuit (ASIC), and so on), volatile and/or non-volatile memory (e.g., Random Access Memory (RAM), Read Only Memory (ROM), flash, various registers, and so on), one or more communication busses, and other components. According to an embodiment, host/thermal system controller952is coupled to user interface992, RF heating system controller912, thermal heating components954, thermostat956, fan958, and sensors994(if included). In some embodiments, host/thermal system controller952and portions of user interface992may be included together in a host module990.

Host/thermal system controller952is configured to receive signals indicating user inputs received via user interface992, and to provide signals to the user interface992that enable the user interface992to produce user-perceptible outputs (e.g., via a display, speaker, and so on) indicating various aspects of the system operation. In addition, host/thermal system controller952sends control signals to other components of the thermal heating system950(e.g., to thermal heating components954and fan958) to selectively activate, deactivate, and otherwise control those other components in accordance with desired system operation. The host/thermal system controller952also may receive signals from the thermal heating system components954, thermostat956, and sensors994(if included), indicating operational parameters of those components, and the host/thermal system controller952may modify operation of the system900accordingly, as will be described later. Further still, host/thermal system controller952receives signals from the RF heating system controller912regarding operation of the RF heating system910. Responsive to the received signals and measurements from the user interface992and from the RF heating system controller912, host/thermal system controller952may provide additional control signals to the RF heating system controller912, which affects operation of the RF heating system910.

The one or more thermal heating components954may include, for example, one or more heating elements (e.g., heating elements682,684,FIG. 6, and/or heating element(s) within a convection system160,660,860,FIGS. 1, 6, 8), one or more gas burners (e.g., gas burners882,884,FIG. 8), and/or other components that are configured to heat air within the oven cavity960. The thermostat956(or an oven sensor) is configured to sense the air temperature within the oven cavity960, and to control operation of the one or more thermal heating components954to maintain the air temperature within the oven cavity at or near a temperature setpoint (e.g., a temperature setpoint established by the user through the user interface992). This temperature control process may be performed by the thermostat956in a closed loop system with the thermal heating components954, or the thermostat956may communicate with the host/thermal system controller952, which also participates in controlling operation of the one or more thermal heating components954. Finally, fan958is included when the system900includes a convection system (e.g., convection system160,660,860,FIGS. 1, 6, 8), and the fan958is selectively activated and deactivated to circulate the air within the oven cavity960.

The RF heating system910includes RF heating system controller912, RF signal source920, power supply and bias circuitry926, first impedance matching circuit934(herein “first matching circuit”), variable impedance matching network970, first and second electrodes940,942, and power detection circuitry930, in an embodiment. RF heating system controller912may include one or more general purpose or special purpose processors (e.g., a microprocessor, microcontroller, ASIC, and so on), volatile and/or non-volatile memory (e.g., RAM, ROM, flash, various registers, and so on), one or more communication busses, and other components. According to an embodiment, RF heating system controller912is coupled to host/thermal system controller952, RF signal source920, variable impedance matching network970, power detection circuitry930, and sensors994(if included). RF heating system controller912is configured to receive control signals from the host/thermal system controller952indicating various operational parameters, and to receive signals indicating RF signal reflected power (and possibly RF signal forward power) from power detection circuitry930. Responsive to the received signals and measurements, and as will be described in more detail later, RF heating system controller912provides control signals to the power supply and bias circuitry926and to the RF signal generator922of the RF signal source920. In addition, RF heating system controller912provides control signals to the variable impedance matching network970, which cause the network970to change its state or configuration.

Oven cavity960includes a capacitive heating arrangement with first and second parallel plate electrodes940,942that are separated by an air cavity960within which a load964to be heated may be placed. For example, a first electrode940may be positioned above the air cavity960, and a second electrode942may be positioned below the air cavity960. In some embodiments, the second electrode942may be implemented in the form of a shelf or contained within a shelf (e.g., shelf134,200,300,634,834,FIGS. 1-3, 6, 8) that is inserted in the cavity960as previously described. In other embodiments, a distinct second electrode942may be excluded, and the functionality of the second electrode may be provided by a portion of the containment structure966(i.e., the containment structure966may be considered to be the second electrode, in such an embodiment).

According to an embodiment, the containment structure966and/or the second electrode942are connected to a ground reference voltage (i.e., containment structure966and second electrode942are grounded). Alternatively, at least the portion of the containment structure966that corresponds to the bottom surface of the cavity960may be formed from conductive material and grounded when the containment structure966(or at least the portion of the containment structure966that is parallel with the first electrode940) functions as a second electrode of the capacitive heating arrangement. To avoid direct contact between the load964and the second electrode942(or the grounded bottom surface of the cavity960), a non-conductive barrier962may be positioned over the second electrode942or the bottom surface of the cavity960.

Again, oven cavity960includes a capacitive heating arrangement with first and second parallel plate electrodes940,942that are separated by an air cavity960within which a load964to be heated may be placed. The first and second electrodes940,942are positioned within containment structure966to define a distance946between the electrodes940,942, where the distance946renders the cavity960a sub-resonant cavity, in an embodiment.

In various embodiments, the distance946is in a range of about 0.10 meters to about 1.0 meter, although the distance may be smaller or larger, as well. According to an embodiment, distance946is less than one wavelength of the RF signal produced by the RF subsystem910. In other words, as mentioned above, the cavity960is a sub-resonant cavity. In some embodiments, the distance946is less than about half of one wavelength of the RF signal. In other embodiments, the distance946is less than about one quarter of one wavelength of the RF signal. In still other embodiments, the distance946is less than about one eighth of one wavelength of the RF signal. In still other embodiments, the distance946is less than about one 50th of one wavelength of the RF signal. In still other embodiments, the distance946is less than about one 100th of one wavelength of the RF signal.

In general, an RF heating system910designed for lower operational frequencies (e.g., frequencies between 10 MHz and 100 MHz) may be designed to have a distance946that is a smaller fraction of one wavelength. For example, when system910is designed to produce an RF signal with an operational frequency of about 10 MHz (corresponding to a wavelength of about 30 meters), and distance946is selected to be about 0.5 meters, the distance946is about one 60th of one wavelength of the RF signal. Conversely, when system910is designed for an operational frequency of about 300 MHz (corresponding to a wavelength of about 1 meter), and distance946is selected to be about 0.5 meters, the distance946is about one half of one wavelength of the RF signal.

With the operational frequency and the distance946between electrodes940,942being selected to define a sub-resonant interior cavity960, the first and second electrodes940,942are capacitively coupled. More specifically, the first electrode940may be analogized to a first plate of a capacitor, the second electrode942may be analogized to a second plate of a capacitor, and the load964, barrier962(if included), and air within the cavity960may be analogized to a capacitor dielectric. Accordingly, the first electrode940alternatively may be referred to herein as an “anode,” and the second electrode942may alternatively be referred to herein as a “cathode.”

Essentially, the voltage across the first electrode940and the second electrode942contributes to heating the load964within the cavity960. According to various embodiments, the RF heating system910is configured to generate the RF signal to produce voltages between the electrodes940,942in a range of about 90 volts to about 3000 volts, in one embodiment, or in a range of about 3000 volts to about 10,000 volts, in another embodiment, although the system910may be configured to produce lower or higher voltages between the electrodes940,942, as well.

The first electrode940is electrically coupled to the RF signal source920through a first matching circuit934, a variable impedance matching network970, and a conductive transmission path, in an embodiment. The first matching circuit934is configured to perform an impedance transformation from an impedance of the RF signal source920(e.g., less than about 10 ohms) to an intermediate impedance (e.g., 50 ohms, 75 ohms, or some other value). According to an embodiment, the conductive transmission path includes a plurality of conductors928-1,928-2, and928-3connected in series, and referred to collectively as transmission path928. According to an embodiment, the conductive transmission path928is an “unbalanced” path, which is configured to carry an unbalanced RF signal (i.e., a single RF signal referenced against ground). In some embodiments, one or more connectors (not shown, but each having male and female connector portions) may be electrically coupled along the transmission path928, and the portion of the transmission path928between the connectors may comprise a coaxial cable or other suitable connector. Such a connection is shown inFIG. 12and described later (e.g., including connectors1236,1238and a conductor1228-3such as a coaxial cable between the connectors1236,1238).

As will be described in more detail later, the variable impedance matching circuit970is configured to perform an impedance transformation from the above-mentioned intermediate impedance to an input impedance of oven cavity960as modified by the load964(e.g., on the order of hundreds or thousands of ohms, such as about 1000 ohms to about 4000 ohms or more). In an embodiment, the variable impedance matching network970includes a network of passive components (e.g., inductors, capacitors, resistors).

According to one more specific embodiment, the variable impedance matching network970includes a plurality of fixed-value lumped inductors (e.g., inductors1012-1015,1154.FIGS. 10, 11) that are positioned within the cavity960and which are electrically coupled to the first electrode940. In addition, in one embodiment, the variable impedance matching network970includes a plurality of variable inductance networks (e.g., networks1010,1011,FIG. 10), which may be located inside or outside of the cavity960. According to another embodiment, the variable impedance matching network970includes a plurality of variable capacitance networks (e.g., networks1142,1146,FIG. 11), which may be located inside or outside of the cavity960. The inductance or capacitance value provided by each of the variable inductance or capacitance networks is established using control signals from the RF heating system controller912, as will be described in more detail later. In any event, by changing the state of the variable impedance matching network970over the course of a heating operation to dynamically match the ever-changing cavity plus load impedance, the amount of RF power that is absorbed by the load964may be maintained at a high level despite variations in the load impedance during the heating operation.

According to an embodiment, RF signal source920includes an RF signal generator922and a power amplifier (e.g., including one or more power amplifier stages924,925). In response to control signals provided by RF heating system controller912over connection914, RF signal generator922is configured to produce an oscillating electrical signal having a frequency in the ISM (industrial, scientific, and medical) band, although the system could be modified to support operations in other frequency bands, as well. The RF signal generator922may be controlled to produce oscillating signals of different power levels and/or different frequencies, in various embodiments. For example, the RF signal generator922may produce a signal that oscillates in the VHF (very high frequency) range (i.e., in a range between about 30.0 megahertz (MHz) and about 300 MHz), and/or in a range of about 10.0 MHz to about 100 MHz, and/or from about 100 MHz to about 3.0 gigahertz (GHz). Some desirable frequencies may be, for example, 13.56 MHz (+/−5 percent), 27.125 MHz (+/−5 percent), 40.68 MHz (+/−5 percent), and 2.45 GHz (+/−5 percent). In one particular embodiment, for example, the RF signal generator922may produce a signal that oscillates in a range of about 40.66 MHz to about 40.70 MHz and at a power level in a range of about 10 decibel-milliwatts (dBm) to about 15 dBm. Alternatively, the frequency of oscillation and/or the power level may be lower or higher.

In the embodiment ofFIG. 9, the power amplifier includes a driver amplifier stage924and a final amplifier stage925. The power amplifier is configured to receive the oscillating signal from the RF signal generator922, and to amplify the signal to produce a significantly higher-power signal at an output of the power amplifier. For example, the output signal may have a power level in a range of about 100 watts to about 400 watts or more. The gain applied by the power amplifier may be controlled using gate bias voltages and/or drain supply voltages provided by the power supply and bias circuitry926to each amplifier stage924,925. More specifically, power supply and bias circuitry926provides bias and supply voltages to each RF amplifier stage924,925in accordance with control signals received from RF heating system controller912.

In an embodiment, each amplifier stage924,925is implemented as a power transistor, such as a field effect transistor (FET), having an input terminal (e.g., a gate or control terminal) and two current carrying terminals (e.g., source and drain terminals). Impedance matching circuits (not illustrated) may be coupled to the input (e.g., gate) of the driver amplifier stage924, between the driver and final amplifier stages925, and/or to the output (e.g., drain terminal) of the final amplifier stage925, in various embodiments. In an embodiment, each transistor of the amplifier stages924,925includes a laterally diffused metal oxide semiconductor FET (LDMOSFET) transistor. However, it should be noted that the transistors are not intended to be limited to any particular semiconductor technology, and in other embodiments, each transistor may be realized as a gallium nitride (GaN) transistor, another type of MOSFET transistor, a bipolar junction transistor (BJT), or a transistor utilizing another semiconductor technology.

InFIG. 9, the power amplifier arrangement is depicted to include two amplifier stages924,925coupled in a particular manner to other circuit components. In other embodiments, the power amplifier arrangement may include other amplifier topologies and/or the amplifier arrangement may include only one amplifier stage (e.g., as shown in the embodiment of amplifier1224,FIG. 12), or more than two amplifier stages. For example, the power amplifier arrangement may include various embodiments of a single-ended amplifier, a Doherty amplifier, a Switch Mode Power Amplifier (SMPA), or another type of amplifier.

Oven cavity960and any load964(e.g., food, liquids, and so on) positioned in the oven cavity960present a cumulative load for the electromagnetic energy (or RF power) that is radiated into the cavity960by the first electrode940. More specifically, the cavity960and the load964present an impedance to the system, referred to herein as a “cavity plus load impedance.” The cavity plus load impedance changes during a heating operation as the temperature of the load964increases. The cavity plus load impedance has a direct effect on the magnitude of reflected signal power along the conductive transmission path928between the RF signal source920and electrode940. In most cases, it is desirable to maximize the magnitude of transferred signal power into the cavity960, and/or to minimize the reflected-to-forward signal power ratio along the conductive transmission path928.

In order to at least partially match the output impedance of the RF signal generator920to the cavity plus load impedance, a first matching circuit934is electrically coupled along the transmission path928, in an embodiment. The first matching circuit934may have any of a variety of configurations. According to an embodiment, the first matching circuit934includes fixed components (i.e., components with non-variable component values), although the first matching circuit934may include one or more variable components, in other embodiments. For example, the first matching circuit934may include any one or more circuits selected from an inductance/capacitance (LC) network, a series inductance network, a shunt inductance network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. Essentially, the fixed matching circuit934is configured to raise the impedance to an intermediate level between the output impedance of the RF signal generator920and the cavity plus load impedance.

According to an embodiment, power detection circuitry930is coupled along the transmission path928between the output of the RF signal source920and the electrode940. In a specific embodiment, the power detection circuitry930forms a portion of the RF subsystem910, and is coupled to the conductor928-2between the output of the first matching circuit934and the input to the variable impedance matching network970, in an embodiment. In alternate embodiments, the power detection circuitry930may be coupled to the portion928-1of the transmission path928between the output of the RF signal source920and the input to the first matching circuit934, or to the portion928-3of the transmission path928between the output of the variable impedance matching network970and the first electrode940.

Wherever it is coupled, power detection circuitry930is configured to monitor, measure, or otherwise detect the power of the reflected signals traveling along the transmission path928between the RF signal source920and electrode940(i.e., reflected RF signals traveling in a direction from electrode940toward RF signal source920). In some embodiments, power detection circuitry930also is configured to detect the power of the forward signals traveling along the transmission path928between the RF signal source920and the electrode940(i.e., forward RF signals traveling in a direction from RF signal source920toward electrode940). Over connection932, power detection circuitry930supplies signals to RF heating system controller912conveying the magnitudes of the reflected signal power (and the forward signal power, in some embodiments). In embodiments in which both the forward and reflected signal power magnitudes are conveyed, RF heating system controller912may calculate a reflected-to-forward signal power ratio, or an S11 parameter, or a voltage standing wave ration (VSWR) value. As will be described in more detail below, when the reflected signal power magnitude exceeds a reflected signal power threshold, or when the reflected-to-forward signal power ratio exceeds an S11 parameter threshold, or when a VSWR value exceeds a VSWR threshold, this indicates that the system900is not adequately matched to the cavity plus load impedance, and that energy absorption by the load964within the cavity960may be sub-optimal. In such a situation, RF heating system controller912orchestrates a process of altering the state of the variable matching network970to drive the reflected signal power or the S11 parameter or the VSWR value toward or below a desired level (e.g., below the reflected signal power threshold, and/or the reflected-to-forward signal power ratio threshold, and/or the S11 parameter threshold, and/or the VSWR threshold), thus re-establishing an acceptable match and facilitating more optimal energy absorption by the load964.

For example, the RF heating system controller912may provide control signals over control path916to the variable matching circuit970, which cause the variable matching circuit970to vary inductive, capacitive, and/or resistive values of one or more components within the circuit, thus adjusting the impedance transformation provided by the circuit970. Adjustment of the configuration of the variable matching circuit970desirably decreases the magnitude of reflected signal power, which corresponds to decreasing the magnitude of the S11 parameter and/or VSWR, and increasing the power absorbed by the load964.

As discussed above, the variable impedance matching network970is used to match the cavity plus load impedance of the oven cavity960plus load964to maximize, to the extent possible, the RF power transfer into the load964. The initial impedance of the oven cavity960and the load964may not be known with accuracy at the beginning of a heating operation. Further, the impedance of the load964changes during a heating operation as the load964warms up. According to an embodiment, the RF heating system controller912may provide control signals to the variable impedance matching network970, which cause modifications to the state of the variable impedance matching network970. This enables the RF heating system controller912to establish an initial state of the variable impedance matching network970at the beginning of the heating operation that has a relatively low reflected to forward power ratio, and thus a relatively high absorption of the RF power by the load964. In addition, this enables the RF heating system controller912to modify the state of the variable impedance matching network970so that an adequate match may be maintained throughout the heating operation, despite changes in the impedance of the load964.

Non-limiting examples of configurations for the variable matching network970are shown inFIGS. 10 and 11. For example, the network970may include any one or more circuits selected from an inductance/capacitance (LC) network, an inductance-only network, a capacitance-only network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. In an embodiment, the variable matching network970includes a single-ended network (e.g., network1000,1100,FIG. 10, 11). The inductance, capacitance, and/or resistance values provided by the variable matching network970, which in turn affect the impedance transformation provided by the network970, are established using control signals from the RF heating system controller912, as will be described in more detail later. In any event, by changing the state of the variable matching network970over the course of a heating operation to dynamically match the ever-changing impedance of the cavity960plus the load964within the cavity960, the system efficiency may be maintained at a high level throughout the heating operation.

The variable matching network970may have any of a wide variety of circuit configurations, and non-limiting examples of such configurations are shown inFIGS. 10 and 11. According to an embodiment, as exemplified inFIG. 10, the variable impedance matching network970may include a single-ended network of passive components, and more specifically a network of fixed-value inductors (e.g., lumped inductive components) and variable inductors (or variable inductance networks). According to another embodiment, as exemplified inFIG. 11, the variable impedance matching network970may include a single-ended network of passive components, and more specifically a network of variable capacitors (or variable capacitance networks). As used herein, the term “inductor” means a discrete inductor or a set of inductive components that are electrically coupled together without intervening components of other types (e.g., resistors or capacitors). Similarly, the term “capacitor” means a discrete capacitor or a set of capacitive components that are electrically coupled together without intervening components of other types (e.g., resistors or inductors).

Referring first to the variable-inductance impedance matching network embodiment,FIG. 10is a schematic diagram of a single-ended variable impedance matching network1000(e.g., variable impedance matching network970,FIG. 9) that may be incorporated into a heating system (e.g., system100,600,800,900,FIGS. 1, 6, 8, 9), in accordance with an example embodiment. As will be explained in more detail below, the variable impedance matching network970essentially has two portions: one portion to match the RF signal source (or the final stage power amplifier), and another portion to match the cavity plus load.

Variable impedance matching network1000includes an input node1002, an output node1004, first and second variable inductance networks1010,1011, and a plurality of fixed-value inductors1012-1015, according to an embodiment. When incorporated into a heating system (e.g., system900,FIG. 9), the input node1002is electrically coupled to an output of the RF signal source (e.g., RF signal source920,FIG. 9), and the output node1004is electrically coupled to an electrode (e.g., first electrode940,FIG. 9) within the heating cavity (e.g., oven cavity960,FIG. 9).

Between the input and output nodes1002,1004, the variable impedance matching network1000includes first and second, series coupled lumped inductors1012,1014, in an embodiment. The first and second lumped inductors1012,1014are relatively large in both size and inductance value, in an embodiment, as they may be designed for relatively low frequency (e.g., about 40.66 MHz to about 40.70 MHz) and high power (e.g., about 50 watts (W) to about 500 W) operation. For example, inductors1012,1014may have values in a range of about 200 nanohenries (nH) to about 600 nH, although their values may be lower and/or higher, in other embodiments.

The first variable inductance network1010is a first shunt inductive network that is coupled between the input node1002and a ground reference terminal (e.g., the grounded containment structure966,FIG. 9). According to an embodiment, the first variable inductance network1010is configurable to match the impedance of the RF signal source (e.g., RF signal source920,FIG. 9) as modified by the first matching circuit (e.g., circuit934,FIG. 9), or more particularly to match the impedance of the final stage power amplifier (e.g., amplifier925,FIG. 9) as modified by the first matching circuit (e.g., circuit934,FIG. 9). Accordingly, the first variable inductance network1010may be referred to as the “RF signal source matching portion” of the variable impedance matching network1000. According to an embodiment, the first variable inductance network1010includes a network of inductive components that may be selectively coupled together to provide inductances in a range of about 10 nH to about 400 nH, although the range may extend to lower or higher inductance values, as well.

In contrast, the “cavity matching portion” of the variable impedance matching network1000is provided by a second shunt inductive network1016that is coupled between a node1022between the first and second lumped inductors1012,1014and the ground reference terminal. According to an embodiment, the second shunt inductive network1016includes a third lumped inductor1013and a second variable inductance network1011coupled in series, with an intermediate node1022between the third lumped inductor1013and the second variable inductance network1011. Because the state of the second variable inductance network1011may be changed to provide multiple inductance values, the second shunt inductive network1016is configurable to optimally match the impedance of the cavity plus load (e.g., cavity960plus load964,FIG. 9). For example, inductor1013may have a value in a range of about 400 nH to about 800 nH, although its value may be lower and/or higher, in other embodiments. According to an embodiment, the second variable inductance network1011includes a network of inductive components that may be selectively coupled together to provide inductances in a range of about 50 nH to about 800 nH, although the range may extend to lower or higher inductance values, as well.

Finally, the variable impedance matching network1000includes a fourth lumped inductor1015coupled between the output node1004and the ground reference terminal. For example, inductor1015may have a value in a range of about 400 nH to about 800 nH, although its value may be lower and/or higher, in other embodiments.

The set1030of lumped inductors1012-1015may form a portion of a module that is at least partially physically located within the cavity (e.g., cavity960,FIG. 9), or at least within the confines of the containment structure (e.g., containment structure966,FIG. 9). This enables the radiation produced by the lumped inductors1012-1015to be safely contained within the system, rather than being radiated out into the surrounding environment. In contrast, the variable inductance networks1010,1011may or may not be contained within the cavity or the containment structure, in various embodiments.

According to an embodiment, the variable impedance matching network1000embodiment ofFIG. 10includes “only inductors” to provide a match for the input impedance of the oven cavity960plus load964. Thus, the network1000may be considered an “inductor-only” matching network. As used herein, the phrases “only inductors” or “inductor-only” when describing the components of the variable impedance matching network means that the network does not include discrete resistors with significant resistance values or discrete capacitors with significant capacitance values. In some cases, conductive transmission lines between components of the matching network may have minimal resistances, and/or minimal parasitic capacitances may be present within the network. Such minimal resistances and/or minimal parasitic capacitances are not to be construed as converting embodiments of the “inductor-only” network into a matching network that also includes resistors and/or capacitors. Those of skill in the art would understand, however, that other embodiments of variable impedance matching networks may include differently configured inductor-only matching networks, and matching networks that include combinations of discrete inductors, discrete capacitors, and/or discrete resistors.

FIG. 11is a schematic diagram of a single-ended variable capacitive matching network1100(e.g., variable impedance matching network970,FIG. 9) that may be incorporated into a heating system (e.g., system100,600,800,900,FIGS. 1, 6, 8, 9), and which may be implemented instead of the variable-inductance impedance matching network1000(FIG. 10), in accordance with an example embodiment. Variable impedance matching network1100includes an input node1102, an output node1104, first and second variable capacitance networks1142,1146, and at least one inductor1154, according to an embodiment. When incorporated into a heating system (e.g., system900,FIG. 9), the input node1102is electrically coupled to an output of the RF signal source (e.g., RF signal source920,FIG. 9), and the output node1104is electrically coupled to an electrode (e.g., first electrode940,FIG. 9) within the heating cavity (e.g., oven cavity960,FIG. 9).

Between the input and output nodes1102,1104, the variable impedance matching network1100includes a first variable capacitance network1142coupled in series with an inductor1154, and a second variable capacitance network1146coupled between an intermediate node1151and a ground reference terminal (e.g., the grounded containment structure966,FIG. 9), in an embodiment. The inductor1154may be designed for relatively low frequency (e.g., about 40.66 MHz to about 40.70 MHz) and high power (e.g., about 50 W to about 500 W) operation, in an embodiment. For example, inductor1154may have a value in a range of about 200 nH to about 600 nH, although its value may be lower and/or higher, in other embodiments. According to an embodiment, inductor1154is a fixed-value, lumped inductor (e.g., a coil). In other embodiments, the inductance value of inductor1154may be variable.

The first variable capacitance network1142is coupled between the input node1102and the intermediate node1111, and the first variable capacitance network1142may be referred to as a “series matching portion” of the variable impedance matching network1100. According to an embodiment, the first variable capacitance network1142includes a first fixed-value capacitor1143coupled in parallel with a first variable capacitor1144. The first fixed-value capacitor1143may have a capacitance value in a range of about 1 picofarad (pF) to about 100 pF, in an embodiment. The first variable capacitor1144may include a network of capacitive components that may be selectively coupled together to provide capacitances in a range of 0 pF to about 100 pF. Accordingly, the total capacitance value provided by the first variable capacitance network1142may be in a range of about 1 pF to about 200 pF, although the range may extend to lower or higher capacitance values, as well.

A “shunt matching portion” of the variable impedance matching network1100is provided by the second variable capacitance network1146, which is coupled between node1151(located between the first variable capacitance network1142and lumped inductor1154) and the ground reference terminal. According to an embodiment, the second variable capacitance network1146includes a second fixed-value capacitor1147coupled in parallel with a second variable capacitor1148. The second fixed-value capacitor1147may have a capacitance value in a range of about 1 pF to about 100 pF, in an embodiment. The second variable capacitor1148may include a network of capacitive components that may be selectively coupled together to provide capacitances in a range of 0 pF to about 100 pF. Accordingly, the total capacitance value provided by the second variable capacitance network1146may be in a range of about 1 pF to about 200 pF, although the range may extend to lower or higher capacitance values, as well. The states of the first and second variable capacitance networks1142,1146may be changed to provide multiple capacitance values, and thus may be configurable to optimally match the impedance of the cavity plus load (e.g., cavity960plus load964,FIG. 9) to the RF signal source (e.g., RF signal source920,FIG. 9).

Referring again toFIG. 9, some embodiments of heating system900may include temperature sensor(s), IR sensor(s), and/or weight sensor(s)994. The temperature sensor(s) and/or IR sensor(s) may be positioned in locations that enable the temperature of the load964to be sensed during the heating operation. When provided to the host/thermal system controller952and/or the RF heating system controller912, for example, the temperature information enables the host/thermal system controller952and/or the RF heating system controller912to alter the power of the thermal energy produced by the thermal heating components954and/or the RF signal supplied by the RF signal source920(e.g., by controlling the bias and/or supply voltages provided by the power supply and bias circuitry926), and/or to determine when the heating operation should be terminated. In addition, the RF heating system controller912may use the temperature information to adjust the state of the variable impedance matching network970. The weight sensor(s) are positioned under the load964, and are configured to provide an estimate of the weight of the load964to the host/thermal system controller952and/or the RF heating system controller912. The host/thermal system controller952and/or RF heating system controller912may use this information, for example, to determine an approximate duration for the heating operation. Further, the RF heating system controller912may use this information to determine a desired power level for the RF signal supplied by the RF signal source920, and/or to determine an initial setting for the variable impedance matching network970.

The description associated withFIGS. 9-11discuss, in detail, an “unbalanced” heating apparatus, in which an RF signal is applied to one electrode (e.g., electrode940,FIG. 9), and the other electrode (e.g., electrode942or the containment structure966,FIG. 9) is grounded. As mentioned above, an alternate embodiment of a heating apparatus comprises a “balanced” heating apparatus. In such an apparatus, balanced RF signals are provided to both electrodes.

For example,FIG. 12is a simplified block diagram of a balanced heating system1200(e.g., heating system100,600,800,FIGS. 1, 6, 8), in accordance with an example embodiment. Heating system1200includes host/thermal system controller1252, RF heating system1210, thermal heating system1250, user interface1292, and a containment structure1266that defines an oven cavity1260, in an embodiment. It should be understood thatFIG. 12is a simplified representation of a heating system1200for purposes of explanation and ease of description, and that practical embodiments may include other devices and components to provide additional functions and features, and/or the heating system1200may be part of a larger electrical system.

The containment structure1266may include bottom, top, and side walls, the interior surfaces of which define the cavity1260(e.g., cavity110,610,810,FIGS. 1, 6, 8). According to an embodiment, the cavity1260may be sealed (e.g., with a door116,616,816,FIGS. 1, 6, 8) to contain the heat and electromagnetic energy that is introduced into the cavity1260during a heating operation. The system1200may include one or more interlock mechanisms (e.g., latching mechanisms and securing structures118,119,618,619,818,819,FIGS. 1, 6, 8) that ensure that the seal is intact during a heating operation. If one or more of the interlock mechanisms indicates that the seal is breached, the host/thermal system controller1252may cease the heating operation.

User interface1292may correspond to a control panel (e.g., control panel120,620,820,FIGS. 1, 6, 8), for example, which enables a user to provide inputs to the system regarding parameters for a heating operation (e.g., the cooking mode, characteristics of the load to be heated, and so on), start and cancel buttons, mechanical controls (e.g., a door/drawer open latch), and so on. In addition, the user interface may be configured to provide user-perceptible outputs indicating the status of a heating operation (e.g., a countdown timer, visible indicia indicating progress or completion of the heating operation, and/or audible tones indicating completion of the heating operation) and other information.

As will be described in more detail in conjunction withFIGS. 16 and 18, the host/thermal system controller1252may perform functions associated with the overall system1200(e.g., “host control functions”), and functions associated more particularly with the thermal heating system1250(e.g., “thermal system control functions”). Because, in an embodiment, the host control functions and the thermal system control functions may be performed by one hardware controller, the host/thermal system controller1252is shown as a dual-function controller. In alternate embodiments, the host controller and the thermal system controller may be distinct controllers that are communicatively coupled.

The thermal heating system1250includes host/thermal system controller1252, one or more thermal heating components1254, thermostat1256, and in some embodiments, a fan1258. Host/thermal system controller1252may include one or more general purpose or special purpose processors (e.g., a microprocessor, microcontroller, ASIC, and so on), volatile and/or non-volatile memory (e.g., RAM, ROM, flash, various registers, and so on), one or more communication busses, and other components. According to an embodiment, host/thermal system controller1252is coupled to user interface1292, RF heating system controller1212, thermal heating components1254, thermostat1256, fan1258, and sensors1294(if included). In some embodiments, host/thermal system controller1252and portions of user interface1292may be included together in a host module1290.

Host/thermal system controller1252is configured to receive signals indicating user inputs received via user interface1292, and to provide signals to the user interface1292that enable the user interface1292to produce user-perceptible outputs (e.g., via a display, speaker, and so on) indicating various aspects of the system operation. In addition, host/thermal system controller1252sends control signals to other components of the thermal heating system1250(e.g., to thermal heating components1254and fan1258) to selectively activate, deactivate, and otherwise control those other components in accordance with desired system operation. The host/thermal system controller1252also may receive signals from the thermal heating system components1254, thermostat1256, and sensors1294(if included), indicating operational parameters of those components, and the host/thermal system controller1252may modify operation of the system1200accordingly, as will be described later. Further still, host/thermal system controller1252receives signals from the RF heating system controller1212regarding operation of the RF heating system1210. Responsive to the received signals and measurements from the user interface1292and from the RF heating system controller1212, host/thermal system controller1252may provide additional control signals to the RF heating system controller1212, which affects operation of the RF heating system1210.

The one or more thermal heating components1254may include, for example, one or more heating elements (e.g., heating elements682,684,FIG. 6, and/or heating element(s) within a convection system160,660,860,FIGS. 1, 6, 8), one or more gas burners (e.g., gas burners882,884,FIG. 8), and/or other components that are configured to heat air within the oven cavity1260. The thermostat1256(or an oven sensor) is configured to sense the air temperature within the oven cavity1260, and to control operation of the one or more thermal heating components1254to maintain the air temperature within the oven cavity at or near a temperature setpoint (e.g., a temperature setpoint established by the user through the user interface1292). This temperature control process may be performed by the thermostat1256in a closed loop system with the thermal heating components1254, or the thermostat1256may communicate with the host/thermal system controller1252, which also participates in controlling operation of the one or more thermal heating components1254. Finally, fan1258is included when the system1200includes a convection system (e.g., convection system160,660,860,FIGS. 1, 6, 8), and the fan1258is selectively activated and deactivated to circulate the air within the oven cavity1260.

The RF subsystem1210includes an RF heating system controller1212, an RF signal source1220, a first impedance matching circuit1234(herein “first matching circuit”), power supply and bias circuitry1226, and power detection circuitry1230, in an embodiment. RF heating system controller1212may include one or more general purpose or special purpose processors (e.g., a microprocessor, microcontroller, ASIC, and so on), volatile and/or non-volatile memory (e.g., RAM, ROM, flash, various registers, and so on), one or more communication busses, and other components. According to an embodiment, RF heating system controller1212is coupled to host/thermal system controller1252, RF signal source1220, variable impedance matching network1270, power detection circuitry1230, and sensors1294(if included). RF heating system controller1212is configured to receive control signals from the host/thermal system controller1252indicating various operational parameters, and to receive signals indicating RF signal reflected power (and possibly RF signal forward power) from power detection circuitry1230. Responsive to the received signals and measurements, and as will be described in more detail later, RF heating system controller1212provides control signals to the power supply and bias circuitry1226and to the RF signal generator1222of the RF signal source1220. In addition, RF heating system controller1212provides control signals to the variable impedance matching network1270, which cause the network1270to change its state or configuration.

Oven cavity1260includes a capacitive heating arrangement with first and second parallel plate electrodes1240,1242that are separated by an air cavity1260within which a load1264to be heated may be placed. For example, a first electrode1240may be positioned above the air cavity1260, and a second electrode1242may be positioned below the air cavity1260. In some embodiments, the second electrode1242may be implemented in the form of a shelf or contained within a shelf (e.g., shelf134,200,300,634,834,FIGS. 1-3, 6, 8) that is inserted in the cavity1260as previously described. To avoid direct contact between the load1264and the second electrode1242(or the grounded bottom surface of the cavity1260), a non-conductive barrier1262may be positioned over the second electrode1242.

Again, oven cavity1260includes a capacitive heating arrangement with first and second parallel plate electrodes1240,1242that are separated by an air cavity1260within which a load1264to be heated may be placed. The first and second electrodes1240,1242are positioned within containment structure1266to define a distance1246between the electrodes1240,1242, where the distance1246renders the cavity1260a sub-resonant cavity, in an embodiment.

In various embodiments, the distance1246is in a range of about 0.10 meters to about 1.0 meter, although the distance may be smaller or larger, as well. According to an embodiment, distance1246is less than one wavelength of the RF signal produced by the RF subsystem1210. In other words, as mentioned above, the cavity1260is a sub-resonant cavity. In some embodiments, the distance1246is less than about half of one wavelength of the RF signal. In other embodiments, the distance1246is less than about one quarter of one wavelength of the RF signal. In still other embodiments, the distance1246is less than about one eighth of one wavelength of the RF signal. In still other embodiments, the distance1246is less than about one 50th of one wavelength of the RF signal. In still other embodiments, the distance1246is less than about one 100th of one wavelength of the RF signal.

In general, an RF heating system1210designed for lower operational frequencies (e.g., frequencies between 10 MHz and 100 MHz) may be designed to have a distance1246that is a smaller fraction of one wavelength. For example, when system1210is designed to produce an RF signal with an operational frequency of about 10 MHz (corresponding to a wavelength of about 30 meters), and distance1246is selected to be about 0.5 meters, the distance1246is about one 60th of one wavelength of the RF signal. Conversely, when system1210is designed for an operational frequency of about 300 MHz (corresponding to a wavelength of about 1 meter), and distance1246is selected to be about 0.5 meters, the distance1246is about one half of one wavelength of the RF signal.

With the operational frequency and the distance1246between electrodes1240,1242being selected to define a sub-resonant interior cavity1260, the first and second electrodes1240,1242are capacitively coupled. More specifically, the first electrode1240may be analogized to a first plate of a capacitor, the second electrode1242may be analogized to a second plate of a capacitor, and the load1264, barrier1262(if included), and air within the cavity1260may be analogized to a capacitor dielectric. Accordingly, the first electrode1240alternatively may be referred to herein as an “anode,” and the second electrode1242may alternatively be referred to herein as a “cathode.”

Essentially, the voltage across the first electrode1240and the second electrode1242contributes to heating the load1264within the cavity1260. According to various embodiments, the RF heating system1210is configured to generate the RF signal to produce voltages between the electrodes1240,1242in a range of about 90 volts to about 3000 volts, in one embodiment, or in a range of about 3000 volts to about 10,000 volts, in another embodiment, although the system1210may be configured to produce lower or higher voltages between the electrodes1240,1242, as well.

An output of the RF subsystem1210, and more particularly an output of RF signal source1220, is electrically coupled to the variable matching subsystem1270through a conductive transmission path, which includes a plurality of conductors1228-1,1228-2,1228-3,1228-4, and1228-5connected in series, and referred to collectively as transmission path1228. According to an embodiment, the conductive transmission path1228includes an “unbalanced” portion and a “balanced” portion, where the “unbalanced” portion is configured to carry an unbalanced RF signal (i.e., a single RF signal referenced against ground), and the “balanced” portion is configured to carry a balanced RF signal (i.e., two signals referenced against each other). The “unbalanced” portion of the transmission path1228may include unbalanced first and second conductors1228-1,1228-2within the RF subsystem1210, one or more connectors1236,1238(each having male and female connector portions), and an unbalanced third conductor1228-3electrically coupled between connectors1236,1238. According to an embodiment, the third conductor1228-3comprises a coaxial cable, although the electrical length may be shorter or longer, as well. In an alternate embodiment, the variable matching subsystem1270may be housed with the RF subsystem1210, and in such an embodiment, the conductive transmission path1228may exclude the connectors1236,1238and the third conductor1228-3. Either way, the “balanced” portion of the conductive transmission path1228includes a balanced fourth conductor1228-4within the variable matching subsystem1270, and a balanced fifth conductor1228-5electrically coupled between the variable matching subsystem1270and electrodes1240,1250, in an embodiment.

As indicated inFIG. 12, the variable matching subsystem1270houses an apparatus configured to receive, at an input of the apparatus, the unbalanced RF signal from the RF signal source1220over the unbalanced portion of the transmission path (i.e., the portion that includes unbalanced conductors1228-1,1228-2, and1228-3), to convert the unbalanced RF signal into two balanced RF signals (e.g., two RF signals having a phase difference between 120 and 340 degrees, such as about 180 degrees), and to produce the two balanced RF signals at two outputs of the apparatus. For example, the conversion apparatus may be a balun1274, in an embodiment. The balanced RF signals are conveyed over balanced conductors1228-4to the variable matching circuit1272and, ultimately, over balanced conductors1228-5to the electrodes1240,1250.

In an alternate embodiment, as indicated in a dashed box in the center ofFIG. 12, and as will be discussed in more detail below, an alternate RF signal generator1220′ may produce balanced RF signals on balanced conductors1228-1′, which may be directly coupled to the variable matching circuit1272(or coupled through various intermediate conductors and connectors). In such an embodiment, the balun1274may be excluded from the system1200. Either way, as will be described in more detail below, a double-ended variable matching circuit1272(e.g., variable matching circuit1300,1400,FIGS. 13, 14) is configured to receive the balanced RF signals (e.g., over connections1228-4or1228-1′), to perform an impedance transformation corresponding to a then-current configuration of the double-ended variable matching circuit1272, and to provide the balanced RF signals to the first and second electrodes1240,1250over connections1228-5.

According to an embodiment, RF signal source1220includes an RF signal generator1222and a power amplifier1224(e.g., including one or more power amplifier stages). In response to control signals provided by RF heating system controller1212over connection1214, RF signal generator1222is configured to produce an oscillating electrical signal having a frequency in an ISM (industrial, scientific, and medical) band, although the system could be modified to support operations in other frequency bands, as well. The RF signal generator1222may be controlled to produce oscillating signals of different power levels and/or different frequencies, in various embodiments. For example, the RF signal generator1222may produce a signal that oscillates in the VHF range (i.e., in a range between about 30.0 MHz and about 300 MHz), and/or in a range of about 10.0 MHz to about 100 MHz and/or in a range of about 100 MHz to about 3.0 GHz. Some desirable frequencies may be, for example, 13.56 MHz (+/−12 percent), 27.125 MHz (+/−12 percent), 40.68 MHz (+/−12 percent), and 2.45 GHz (+/−12 percent). Alternatively, the frequency of oscillation may be lower or higher than the above-given ranges or values.

The power amplifier1224is configured to receive the oscillating signal from the RF signal generator1222, and to amplify the signal to produce a significantly higher-power signal at an output of the power amplifier1224. For example, the output signal may have a power level in a range of about 100 watts to about 400 watts or more, although the power level may be lower or higher, as well. The gain applied by the power amplifier1224may be controlled using gate bias voltages and/or drain bias voltages provided by the power supply and bias circuitry1226to one or more stages of amplifier1224. More specifically, power supply and bias circuitry1226provides bias and supply voltages to the inputs and/or outputs (e.g., gates and/or drains) of each RF amplifier stage in accordance with control signals received from RF heating system controller1212.

The power amplifier may include one or more amplification stages. In an embodiment, each stage of amplifier1224is implemented as a power transistor, such as a FET, having an input terminal (e.g., a gate or control terminal) and two current carrying terminals (e.g., source and drain terminals). Impedance matching circuits (not illustrated) may be coupled to the input (e.g., gate) and/or output (e.g., drain terminal) of some or all of the amplifier stages, in various embodiments. In an embodiment, each transistor of the amplifier stages includes an LDMOS FET. However, it should be noted that the transistors are not intended to be limited to any particular semiconductor technology, and in other embodiments, each transistor may be realized as a GaN transistor, another type of MOS FET transistor, a BJT, or a transistor utilizing another semiconductor technology.

InFIG. 12, the power amplifier arrangement1224is depicted to include one amplifier stage coupled in a particular manner to other circuit components. In other embodiments, the power amplifier arrangement1224may include other amplifier topologies and/or the amplifier arrangement may include two or more amplifier stages (e.g., as shown in the embodiment of amplifier924/925,FIG. 9). For example, the power amplifier arrangement may include various embodiments of a single-ended amplifier, a double-ended (balanced) amplifier, a push-pull amplifier, a Doherty amplifier, an SMPA, or another type of amplifier.

For example, as indicated in the dashed box in the center ofFIG. 12, an alternate RF signal generator1220′ may include a push-pull or balanced amplifier1224′, which is configured to receive, at an input, an unbalanced RF signal from the RF signal generator1222, to amplify the unbalanced RF signal, and to produce two balanced RF signals at two outputs of the amplifier1224′, where the two balanced RF signals are thereafter conveyed over conductors1228-1′ to the electrodes1240,1250. In such an embodiment, the balun1274may be excluded from the system1200, and the conductors1228-1′ may be directly connected to the variable matching circuit1272(or connected through multiple coaxial cables and connectors or other multi-conductor structures).

Heating cavity1260and any load1264(e.g., food, liquids, and so on) positioned in the heating cavity1260present a cumulative load for the electromagnetic energy (or RF power) that is radiated into the interior chamber1262by the electrodes1240,1250. More specifically, and as described previously, the heating cavity1260and the load1264present an impedance to the system, referred to herein as a “cavity plus load impedance.” The cavity plus load impedance changes during a heating operation as the temperature of the load1264increases. The cavity plus load impedance has a direct effect on the magnitude of reflected signal power along the conductive transmission path1228between the RF signal source1220and the electrodes1240,1250. In most cases, it is desirable to maximize the magnitude of transferred signal power into the cavity1260, and/or to minimize the reflected-to-forward signal power ratio along the conductive transmission path1228.

In order to at least partially match the output impedance of the RF signal generator1220to the cavity plus load impedance, a first matching circuit1234is electrically coupled along the transmission path1228, in an embodiment. The first matching circuit1234is configured to perform an impedance transformation from an impedance of the RF signal source1220(e.g., less than about 10 ohms) to an intermediate impedance (e.g., 120 ohms, 75 ohms, or some other value). The first matching circuit1234may have any of a variety of configurations. According to an embodiment, the first matching circuit1234includes fixed components (i.e., components with non-variable component values), although the first matching circuit1234may include one or more variable components, in other embodiments. For example, the first matching circuit1234may include any one or more circuits selected from an inductance/capacitance (LC) network, a series inductance network, a shunt inductance network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. Essentially, the first matching circuit1234is configured to raise the impedance to an intermediate level between the output impedance of the RF signal generator1220and the cavity plus load impedance.

According to an embodiment, and as mentioned above, power detection circuitry1230is coupled along the transmission path1228between the output of the RF signal source1220and the electrodes1240,1250. In a specific embodiment, the power detection circuitry1230forms a portion of the RF subsystem1210, and is coupled to the conductor1228-2between the RF signal source1220and connector1236. In alternate embodiments, the power detection circuitry1230may be coupled to any other portion of the transmission path1228, such as to conductor1228-1, to conductor1228-3, to conductor1228-4between the RF signal source1220(or balun1274) and the variable matching circuit1272(i.e., as indicated with power detection circuitry1230′), or to conductor1228-5between the variable matching circuit1272and the electrode(s)1240,1250(i.e., as indicated with power detection circuitry1230″). For purposes of brevity, the power detection circuitry is referred to herein with reference number1230, although the circuitry may be positioned in other locations, as indicated by reference numbers1230′ and1230″.

Wherever it is coupled, power detection circuitry1230is configured to monitor, measure, or otherwise detect the power of the reflected signals traveling along the transmission path1228between the RF signal source1220and one or both of the electrode(s)1240,1250(i.e., reflected RF signals traveling in a direction from electrode(s)1240,1250toward RF signal source1220). In some embodiments, power detection circuitry1230also is configured to detect the power of the forward signals traveling along the transmission path1228between the RF signal source1220and the electrode(s)1240,1250(i.e., forward RF signals traveling in a direction from RF signal source1220toward electrode(s)1240,1250).

Over connection1232, power detection circuitry1230supplies signals to RF heating system controller1212conveying the measured magnitudes of the reflected signal power, and in some embodiments, also the measured magnitude of the forward signal power. In embodiments in which both the forward and reflected signal power magnitudes are conveyed, RF heating system controller1212may calculate a reflected-to-forward signal power ratio, or the S11 parameter, and/or a VSWR value. As will be described in more detail below, when the reflected signal power magnitude exceeds a reflected signal power threshold, or when the reflected-to-forward signal power ratio exceeds an S11 parameter threshold, or when the VSWR value exceeds a VSWR threshold, this indicates that the system1200is not adequately matched to the cavity plus load impedance, and that energy absorption by the load1264within the cavity1260may be sub-optimal. In such a situation, RF heating system controller1212orchestrates a process of altering the state of the variable matching circuit1272to drive the reflected signal power or the S11 parameter or the VSWR value toward or below a desired level (e.g., below the reflected signal power threshold, and/or the reflected-to-forward signal power ratio threshold, and/or the VSWR threshold), thus re-establishing an acceptable match and facilitating more optimal energy absorption by the load1264.

More specifically, the system controller1212may provide control signals over control path1216to the variable matching circuit1272, which cause the variable matching circuit1272to vary inductive, capacitive, and/or resistive values of one or more components within the circuit, thus adjusting the impedance transformation provided by the circuit1272. Adjustment of the configuration of the variable matching circuit1272desirably decreases the magnitude of reflected signal power, which corresponds to decreasing the magnitude of the S11 parameter and/or the VSWR value, and increasing the power absorbed by the load1264.

As discussed above, the variable matching circuit1272is used to match the input impedance of the heating cavity1260plus load1264to maximize, to the extent possible, the RF power transfer into the load1264. The initial impedance of the heating cavity1260and the load1264may not be known with accuracy at the beginning of a heating operation. Further, the impedance of the load1264changes during a heating operation as the load1264warms up. According to an embodiment, the system controller1212may provide control signals to the variable matching circuit1272, which cause modifications to the state of the variable matching circuit1272. This enables the system controller1212to establish an initial state of the variable matching circuit1272at the beginning of the heating operation that has a relatively low reflected to forward power ratio, and thus a relatively high absorption of the RF power by the load1264. In addition, this enables the system controller1212to modify the state of the variable matching circuit1272so that an adequate match may be maintained throughout the heating operation, despite changes in the impedance of the load1264.

The variable matching circuit1272may have any of a variety of configurations. For example, the circuit1272may include any one or more circuits selected from an inductance/capacitance (LC) network, an inductance-only network, a capacitance-only network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. In an embodiment in which the variable matching circuit1272is implemented in a balanced portion of the transmission path1228, the variable matching circuit1272is a double-ended circuit with two inputs and two outputs. In an alternate embodiment in which the variable matching circuit is implemented in an unbalanced portion of the transmission path1228, the variable matching circuit may be a single-ended circuit with a single input and a single output (e.g., similar to matching circuit1000or1100,FIGS. 10, 11). According to a more specific embodiment, the variable matching circuit1272includes a variable inductance network (e.g., double-ended network1300,FIG. 13). According to another more specific embodiment, the variable matching circuit1272includes a variable capacitance network (e.g., double-ended network1400,FIG. 14). In still other embodiments, the variable matching circuit1272may include both variable inductance and variable capacitance elements. The inductance, capacitance, and/or resistance values provided by the variable matching circuit1272, which in turn affect the impedance transformation provided by the circuit1272, are established through control signals from the RF heating system controller1212, as will be described in more detail later. In any event, by changing the state of the variable matching circuit1272over the course of a heating operation to dynamically match the ever-changing impedance of the cavity1260plus the load1264within the cavity1260, the system efficiency may be maintained at a high level throughout the heating operation.

The variable matching circuit1272may have any of a wide variety of circuit configurations, and non-limiting examples of such configurations are shown inFIGS. 13 and 14. For example,FIG. 13is a schematic diagram of a double-ended variable impedance matching circuit1300(e.g., matching circuit1272,FIG. 12) that may be incorporated into a heating system (e.g., system100,600,800,1200,FIGS. 1, 6, 8, 12), in accordance with an example embodiment. According to an embodiment, the variable matching circuit1300includes a network of fixed-value and variable passive components.

Circuit1300includes a double-ended input1301-1,1301-2(referred to as input1301), a double-ended output1302-1,1302-2(referred to as output1302), and a network of passive components connected in a ladder arrangement between the input1301and output1302. For example, when connected into system1200, the first input1301-1may be connected to a first conductor of balanced conductor1228-4, and the second input1301-2may be connected to a second conductor of balanced conductor1228-4. Similarly, the first output1302-1may be connected to a first conductor of balanced conductor1228-5, and the second output1302-2may be connected to a second conductor of balanced conductor1228-5.

In the specific embodiment illustrated inFIG. 13, circuit1300includes a first variable inductor1311and a first fixed inductor1315connected in series between input1301-1and output1302-1, a second variable inductor1316and a second fixed inductor1320connected in series between input1301-2and output1302-2, a third variable inductor1321connected between inputs1301-1and1301-2, and a third fixed inductor1324connected between nodes1325and1326.

According to an embodiment, the third variable inductor1321corresponds to an “RF signal source matching portion”, which is configurable to match the impedance of the RF signal source (e.g., RF signal source1220,FIG. 12) as modified by the first matching circuit (e.g., circuit1234,FIG. 12), or more particularly to match the impedance of the final stage power amplifier (e.g., amplifier1224,FIG. 12) as modified by the first matching circuit (e.g., circuit1234,FIG. 12). According to an embodiment, the third variable inductor1321includes a network of inductive components that may be selectively coupled together to provide inductances in a range of about 5 nH to about 200 nH, although the range may extend to lower or higher inductance values, as well.

In contrast, the “cavity matching portion” of the variable impedance matching network1300is provided by the first and second variable inductors1311,1316, and fixed inductors1315,1320, and1324. Because the states of the first and second variable inductors1311,1316may be changed to provide multiple inductance values, the first and second variable inductors1311,1316are configurable to optimally match the impedance of the cavity plus load (e.g., cavity1260plus load1264,FIG. 12). For example, inductors1311,1316each may have a value in a range of about 10 nH to about 200 nH, although their values may be lower and/or higher, in other embodiments.

The fixed inductors1315,1320,1324also may have inductance values in a range of about 50 nH to about 800 nH, although the inductance values may be lower or higher, as well. Inductors1311,1315,1316,1320,1321,1324may include discrete inductors, distributed inductors (e.g., printed coils), wirebonds, transmission lines, and/or other inductive components, in various embodiments. In an embodiment, variable inductors1311and1316are operated in a paired manner, meaning that their inductance values during operation are controlled to be equal to each other, at any given time, in order to ensure that the RF signals conveyed to outputs1302-1and1302-2are balanced.

As discussed above, variable matching circuit1300is a double-ended circuit that is configured to be connected along a balanced portion of the transmission path1228(e.g., between connectors1228-4and1228-5), and other embodiments may include a single-ended (i.e., one input and one output) variable matching circuit that is configured to be connected along the unbalanced portion of the transmission path1228.

By varying the inductance values of inductors1311,1316,1321in circuit1300, the system controller1212may increase or decrease the impedance transformation provided by circuit1300. Desirably, the inductance value changes improve the overall impedance match between the RF signal source1220and the cavity plus load impedance, which should result in a reduction of the reflected signal power and/or the reflected-to-forward signal power ratio. In most cases, the system controller1212may strive to configure the circuit1300in a state in which a maximum electromagnetic field intensity is achieved in the cavity1260, and/or a maximum quantity of power is absorbed by the load1264, and/or a minimum quantity of power is reflected by the load1264.

FIG. 14is a schematic diagram of a double-ended variable impedance matching circuit1400(e.g., matching circuit1272,FIG. 12) that may be incorporated into a heating system (e.g., system100,600,800,1200,FIGS. 1, 6, 8, 12), and which may be implemented instead of the variable-inductance impedance matching network1300(FIG. 13), in accordance with another example embodiment. As with the matching circuit600(FIG. 6), according to an embodiment, the variable matching circuit1400includes a network of fixed-value and variable passive components.

Circuit1400includes a double-ended input1401-1,1401-2(referred to as input1401), a double-ended output1402-1,1402-2(referred to as output1402), and a network of passive components connected between the input1401and output1402. For example, when connected into system1200, the first input1401-1may be connected to a first conductor of balanced conductor1228-4, and the second input1401-2may be connected to a second conductor of balanced conductor1228-4. Similarly, the first output1402-1may be connected to a first conductor of balanced conductor1228-5, and the second output1402-2may be connected to a second conductor of balanced conductor1228-5.

In the specific embodiment illustrated inFIG. 14, circuit1400includes a first variable capacitance network1411and a first inductor1415connected in series between input1401-1and output1402-1, a second variable capacitance network1416and a second inductor1420connected in series between input1401-2and output1402-2, and a third variable capacitance network1421connected between nodes1425and1426. The inductors1415,1420are relatively large in both size and inductance value, in an embodiment, as they may be designed for relatively low frequency (e.g., about 40.66 MHz to about 40.70 MHz) and high power (e.g., about 120 W to about 1200 W) operation. For example, inductors1415,1420each may have a value in a range of about 100 nH to about 1000 nH (e.g., in a range of about 200 nH to about 600 nH), although their values may be lower and/or higher, in other embodiments. According to an embodiment, inductors1415,1420are fixed-value, lumped inductors (e.g., coils, discrete inductors, distributed inductors (e.g., printed coils), wirebonds, transmission lines, and/or other inductive components, in various embodiments). In other embodiments, the inductance value of inductors1415,1420may be variable. In any event, the inductance values of inductors1415,1420are substantially the same either permanently (when inductors1415,1420are fixed-value) or at any given time (when inductors1415,1420are variable, they are operated in a paired manner), in an embodiment.

The first and second variable capacitance networks1411,1416correspond to “series matching portions” of the circuit1400. According to an embodiment, the first variable capacitance network1411includes a first fixed-value capacitor1412coupled in parallel with a first variable capacitor1413. The first fixed-value capacitor1412may have a capacitance value in a range of about 1 pF to about 100 pF, in an embodiment. The first variable capacitor1413may include a network of capacitive components that may be selectively coupled together to provide capacitances in a range of 0 pF to about 100 pF. Accordingly, the total capacitance value provided by the first variable capacitance network1411may be in a range of about 1 pF to about 200 pF, although the range may extend to lower or higher capacitance values, as well.

Similarly, the second variable capacitance network1416includes a second fixed-value capacitor1417coupled in parallel with a second variable capacitor1418. The second fixed-value capacitor1417may have a capacitance value in a range of about 1 pF to about 100 pF, in an embodiment. The second variable capacitor1418may include a network of capacitive components that may be selectively coupled together to provide capacitances in a range of 0 pF to about 100 pF. Accordingly, the total capacitance value provided by the second variable capacitance network1416may be in a range of about 1 pF to about 200 pF, although the range may extend to lower or higher capacitance values, as well.

In any event, to ensure the balance of the signals provided to outputs1402-1and1402-2, the capacitance values of the first and second variable capacitance networks1411,1416are controlled to be substantially the same at any given time, in an embodiment. For example, the capacitance values of the first and second variable capacitors1413,1418may be controlled so that the capacitance values of the first and second variable capacitance networks1411,1416are substantially the same at any given time. The first and second variable capacitors1413,1418are operated in a paired manner, meaning that their capacitance values during operation are controlled, at any given time, to ensure that the RF signals conveyed to outputs1402-1and1402-2are balanced. The capacitance values of the first and second fixed-value capacitors1412,1417may be substantially the same, in some embodiments, although they may be different, in others.

The “shunt matching portion” of the variable impedance matching network1400is provided by the third variable capacitance network1421and fixed inductors1415,1420. According to an embodiment, the third variable capacitance network1421includes a third fixed-value capacitor1423coupled in parallel with a third variable capacitor1424. The third fixed-value capacitor1423may have a capacitance value in a range of about 1 pF to about 500 pF, in an embodiment. The third variable capacitor1424may include a network of capacitive components that may be selectively coupled together to provide capacitances in a range of 0 pF to about 200 pF. Accordingly, the total capacitance value provided by the third variable capacitance network1421may be in a range of about 1 pF to about 700 pF, although the range may extend to lower or higher capacitance values, as well.

Because the states of the variable capacitance networks1411,1416,1421may be changed to provide multiple capacitance values, the variable capacitance networks1411,1416,1421are configurable to optimally match the impedance of the cavity plus load (e.g., cavity1260plus load1264,FIG. 12) to the RF signal source (e.g., RF signal source1220,1220′,FIG. 12). By varying the capacitance values of capacitors1413,1418,1424in circuit1400, the RF heating system controller (e.g., RF heating system controller1212,FIG. 12) may increase or decrease the impedance transformation provided by circuit1400. Desirably, the capacitance value changes improve the overall impedance match between the RF signal source1220and the impedance of the cavity plus load, which should result in a reduction of the reflected signal power and/or the reflected-to-forward signal power ratio. In most cases, the RF heating system controller1212may strive to configure the circuit1400in a state in which a maximum electromagnetic field intensity is achieved in the cavity1260, and/or a maximum quantity of power is absorbed by the load1264, and/or a minimum quantity of power is reflected by the load1264.

It should be understood that the variable impedance matching circuits1300,1400illustrated inFIGS. 13 and 14are but two possible circuit configurations that may perform the desired double-ended variable impedance transformations. Other embodiments of double-ended variable impedance matching circuits may include differently arranged inductive or capacitive networks, or may include passive networks that include various combinations of inductors, capacitors, and/or resistors, where some of the passive components may be fixed-value components, and some of the passive components may be variable-value components (e.g., variable inductors, variable capacitors, and/or variable resistors). Further, the double-ended variable impedance matching circuits may include active devices (e.g., transistors) that switch passive components into and out of the network to alter the overall impedance transformation provided by the circuit.

Referring again toFIG. 12, some embodiments of heating system1200may include temperature sensor(s), IR sensor(s), and/or weight sensor(s)1294. The temperature sensor(s) and/or IR sensor(s) may be positioned in locations that enable the temperature of the load1264to be sensed during the heating operation. When provided to the host/thermal system controller1252and/or the RF heating system controller1212, for example, the temperature information enables the host/thermal system controller1252and/or the RF heating system controller1212to alter the power of the thermal energy produced by the thermal heating components1254and/or the RF signal supplied by the RF signal source1220(e.g., by controlling the bias and/or supply voltages provided by the power supply and bias circuitry1226), and/or to determine when the heating operation should be terminated. In addition, the RF heating system controller1212may use the temperature information to adjust the state of the variable impedance matching network1270. The weight sensor(s) are positioned under the load1264, and are configured to provide an estimate of the weight of the load1264to the host/thermal system controller1252and/or the RF heating system controller1212. The host/thermal system controller1252and/or RF heating system controller1212may use this information, for example, to determine an approximate duration for the heating operation. Further, the RF heating system controller1212may use this information to determine a desired power level for the RF signal supplied by the RF signal source1220, and/or to determine an initial setting for the variable impedance matching network1270.

According to various embodiments, the circuitry associated with the single-ended or double-ended variable impedance matching networks (e.g., networks1000,1100,1300,1400,FIGS. 10, 11, 13, 14) discussed herein may be implemented in the form of one or more modules, where a “module” is defined herein as an assembly of electrical components coupled to a common substrate (e.g., a printed circuit board (PCB) or other substrate). In addition, as mentioned previously, the host/thermal system controller (e.g., controller952,1252,FIGS. 9, 12) and portions of the user interface (e.g., user interface992,1292,FIGS. 9, 12) may be implemented in the form of a host module (e.g., host module990,1290,FIGS. 9, 12). Further still, in various embodiments, the circuitry associated with the processing and RF signal generation portions of the RF heating system (e.g., RF heating system910,1210,FIGS. 9, 12) also may be implemented in the form of one or more modules.

For example,FIG. 15is a perspective view of an RF module1500that includes an RF subsystem of the RF heating system (e.g., RF heating system910,1210,FIGS. 9, 12), in accordance with an example embodiment. The RF module1500includes a PCB1502coupled to a ground substrate1504. The ground substrate1504provides structural support for the PCB1502, and also provides an electrical ground reference and heat sink functionality for the various electrical components coupled to the PCB1502.

According to an embodiment, the PCB1502houses system controller circuitry1512(e.g., corresponding to RF heating system controller912,1212,FIGS. 9, 12), RF signal source circuitry1520(e.g., corresponding to RF signal source920,1220,FIGS. 9, 12, including an RF signal generator922,1222and power amplifier924,925,1224), power detection circuitry1530(e.g., corresponding to power detection circuitry930,1230,FIGS. 9, 12), and impedance matching circuitry1534(e.g., corresponding to first matching circuitry934,1234,FIGS. 9, 12).

In the embodiment ofFIG. 15, the system controller circuitry1512includes a processor integrated circuit (IC) and a memory IC, the RF signal source circuitry1520includes a signal generator IC and one or more power amplifier devices, the power detection circuitry1530includes a power coupler device, and the impedance matching circuitry1534includes a plurality of passive components (e.g., inductors1535,1536and capacitors1537) connected together to form an impedance matching network. The circuitry1512,1520,1530,1534and the various sub-components may be electrically coupled together through conductive traces on the PCB1502as discussed previously in reference to the various conductors and connections discussed in conjunction withFIGS. 9 and 12.

RF module1500also includes a plurality of connectors1516,1526,1538,1580, in an embodiment. For example, connector1580may be configured to connect with a host system that includes a host/thermal system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12) and other functionality. Connector1516may be configured to connect with a variable matching circuit (e.g., circuit970,1272,FIGS. 9, 12) to provide control signals to the circuit, as previously described. Connector1526may be configured to connect to a power supply to receive system power. Finally, connector1538(e.g., connector1236,FIG. 12) may be configured to connect to a coaxial cable or other transmission line, which enables the RF module1500to be electrically connected (e.g., through a coaxial cable implementation of conductor928-2,1228-3,FIGS. 9, 12) to a variable matching circuit or subsystem (e.g., circuit or subsystem970,1270,1272,FIGS. 9, 12). In an alternate embodiment, components of the variable matching subsystem (e.g., variable matching network970, balun1274, and/or variable matching circuit1272,FIGS. 9, 12) also may be integrated onto the PCB1502, in which case connector1536may be excluded from the module1500. Other variations in the layout, subsystems, and components of RF module1500may be made, as well.

Embodiments of an RF module (e.g., module1500,FIG. 15), a host module (e.g., module990,1290,FIGS. 9, 12), and a variable impedance matching network module (not illustrated) may be electrically connected together, and connected with other components, to form a combined apparatus or system (e.g., apparatus100,600,800,900,1200,FIGS. 1, 6, 8, 9, 12). For example, an RF signal connection may be made through a connection (e.g., conductor928-2,1228-3,FIGS. 9, 12), such as a coaxial cable, between the RF connector1538(FIG. 15) and a variable impedance matching network module, and control connections may be made through connections (e.g., conductors916,1216,FIGS. 9, 12), such as a multi-conductor cable, between the connector1516(FIG. 15) and the variable impedance matching network module. To further assemble the system, a host system module (e.g., module990,1290,FIGS. 9, 12) may be connected to the RF module1500through connector1580, a power supply may be connected to the RF module1500through connector1526, and electrodes (e.g., electrodes940,942,1240,1242,FIGS. 9, 12) may be connected to outputs of the variable impedance matching network module. Of course, the above-described assembly also would be physically connected to various support structures and other system components so that the electrodes are held in a fixed relationship to each other across a defrosting cavity (e.g., cavity110,610,810,960,1260,FIGS. 1, 6, 8, 9, 12), and the defrosting apparatus may be integrated within a larger system (e.g., systems100,600,800,FIGS. 1, 6, 8).

Now that embodiments of the electrical and physical aspects of heating systems have been described, various embodiments of methods for operating such heating systems will be described in conjunction withFIGS. 16-18. More specifically,FIG. 16is a flowchart of a method of operating a heating system (e.g., system100,600,800,900,1200,FIGS. 1, 6, 8, 9, 12) with an RF heating system (e.g., system150,650,850,910,1210,FIGS. 1, 6, 8, 9, 12) and a thermal heating system (e.g., system160,660,680,860,880,910,1210,FIGS. 1, 6, 8, 9, 12), in accordance with an example embodiment.

The method may begin, in block1602, when the host system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12) receives an indication that a heating operation should start. Such an indication may be received, for example, after a user has place a load (e.g., load964,1264,FIGS. 1, 6, 8, 9, 12) into the system's heating cavity (e.g., cavity110,610,810,960,1260,FIGS. 1, 6, 8, 9, 12), has sealed the cavity (e.g., by closing a door or drawer), and has pressed a start button (e.g., of the control panel120,620,820, or user interface992,1282,FIGS. 1, 6, 8, 9, 12).

As discussed previously, prior to placing the load into the system's heating cavity, the user may install a shelf (e.g., shelf134,200,300,634,834,FIGS. 1, 2, 3, 6, 8) into the heating cavity, where the shelf may embody or include an electrode (e.g., electrode942,1242,FIGS. 9, 12) of the RF heating system. In an embodiment, sealing of the cavity may engage one or more safety interlock mechanisms, which when engaged, indicate that RF power supplied to the cavity will not substantially leak into the environment outside of the cavity. As will be described later, disengagement of a safety interlock mechanism may cause the system controller immediately to pause or terminate the heating operation.

According to various embodiments, the host system controller optionally may receive additional inputs indicating the load type (e.g., meats, liquids, or other materials), the initial load temperature, and/or the load weight. For example, information regarding the load type may be received from the user through interaction with the user interface (e.g., by the user selecting from a list of recognized load types). Alternatively, the system may be configured to scan a barcode visible on the exterior of the load, or to receive an electronic signal from an RFID device on or embedded within the load. Information regarding the initial load temperature may be received, for example, from one or more temperature sensors and/or IR sensors (e.g., sensors994,1294,FIGS. 9, 12) of the system. Information regarding the load weight may be received from the user through interaction with the user interface, or from a weight sensor (e.g., sensor994,1294,FIGS. 9, 12) of the system. As indicated above, receipt of inputs indicating the load type, initial load temperature, and/or load weight is optional, and the system alternatively may not receive some or all of these inputs.

Prior to pressing the start button, the user may select a cooking mode, which indicates which heating systems will be activated during the heating process. For example, the user may specify the cooking mode by pressing a dedicated cooking mode button (e.g., of the control panel120,620,820, or user interface992,1282,FIGS. 1, 6, 8, 9, 12) or by accessing a cooking mode menu through the control panel and making a selection. As described previously, depending on what type of thermal heating system is combined with the RF heating system, a number of different cooking modes are available for selection, where the different cooking modes can be generally classified as a thermal-only cooking mode, an RF-only cooking mode, and a combined thermal and RF cooking mode. For example, a thermal-only mode may include any of the following, previously-discussed modes: 1) a convection-only cooking mode that may utilize the convection system160,660,860, of any of systems100,600,800(FIGS. 1, 6, 8); 2) a radiant-only cooking mode that may utilize the radiant heating system680of system600(FIG. 6); and 3) a gas-only cooking mode that may utilize the gas heating system880of system800(FIG. 8). As further examples, a combined thermal and RF cooling mode may include any of the following, previously-discussed modes: 1) a combined convection and RF cooking mode; 2) a combined radiant and RF cooking mode; 3) a combined convection, radiant, and RF cooking mode; 4) a combined gas and RF cooking mode; and 5) a combined convection, gas, and RF cooking mode. In addition to the above modes, when a convection system is combined with another type of thermal cooking system, the following additional modes also may be available: 1) a combined convection and radiant cooking mode; and 2) a combined convection and gas cooking mode.

When a user selects a cooking mode that utilizes a thermal heating system (e.g., convection system160,660or860, radiant heating system680, or gas heating system880), the user may be prompted or enabled to enter a desired cavity (oven) temperature (or temperature setpoint) through interaction with the control panel or user interface. Alternatively, the cavity temperature setpoint may otherwise be obtained or determined by the system.

After selecting the cooking mode and, if applicable, the temperature setpoint, and receiving the start indication, the remaining process steps that are performed depend on which cooking mode was selected. Starting with a thermal-only cooking mode selection (e.g., convection-only, radiant-only, and gas-only cooking modes), in block1630, the system controller (e.g., host/thermal system controller952,1252,FIGS. 9, 12) activates the thermal heating components (e.g., thermal heating components954,1254,FIGS. 9, 12) of the thermal heating system (e.g., the convection system160, the radiant heating system680, the gas heating system880, the thermal cooking system950,1250,FIGS. 1, 6, 8, 9, 12). Once activated, the thermal heating components begin to heat the air within the oven cavity. When a convection cooking mode is selected, the system controller also activates the fan (e.g., fan958,1258,FIGS. 9, 12) of the convection system. After a period of time, the oven cavity will be pre-heated to the temperature setpoint.

In block1632, the oven temperature is maintained at the temperature setpoint. For example, in an embodiment, a closed-loop or feedback-based system that includes the thermal heating component and a system thermostat (e.g., thermostat956,1256,FIGS. 9, 12), and possibly the host/thermal system controller, may continuously or periodically monitor the air temperature within the oven cavity, and may maintain the thermal heating system in an activated when the air temperature is below the temperature setpoint. Conversely, when the air temperature is above the temperature setpoint, the system temporarily may deactivate the thermal heating component, and may thereafter continue to monitor the air temperature. Once the air temperature has fallen below the temperature setpoint, the thermal heating component may be re-activated to again increase the air temperature. This process may thereafter continue in a hysteresis loop.

As the oven temperature is being maintained, the host/thermal system controller may evaluate whether or not a cessation or exit condition has occurred, in block1634. In actuality, determination of whether a cessation or exit condition has occurred may be an interrupt driven process that may occur at any point during the heating process. However, for the purposes of including it in the flowchart ofFIG. 16, the process is shown to occur after block1632.

In any event, some conditions may warrant temporary cessation of the heating operation, and other conditions may warrant an exit altogether of the heating operation. For example, the system may determine that a temporary cessation condition has occurred when the system door (e.g., door116,616,816,FIGS. 1, 6, 8) has been opened during a heating process. For example,FIG. 17is a flowchart of a method of performing a temporary cessation process associated with the state of a heating system door, in accordance with an example embodiment. The process may be triggered by interrupt, for example, when the host/thermal system controller detects that the system door has been opened in block1702. For example, opening of the door may be detected when a safety interlock is breached (e.g., when a latching mechanism118,618,818is disengaged from a corresponding securing structure119,619,819,FIGS. 1, 6, 8).

When the system detects that the system door has been opened, the host/thermal system controller may temporarily deactivate some of the heating system components, in block1704. For example, if the convection system is active during the selected cooking mode, the host/thermal system controller may send a control signal to the convection fan to deactivate the fan (and possibly an integrated heating element within the convection fan). In addition, if a radiant heating system or a gas heating system is active during the selected cooking mode, the host/thermal system controller may deactivate the corresponding radiant heating element(s) or gas burner(s). Further still, if the RF heating system is active during the selected cooking mode, the host/thermal system controller may send a control signal to the RF system controller, which invokes the RF system controller to discontinue generation and provision of the RF signal to the system electrode(s).

The heating system components that are deactivated in block1704will remain deactivated until the system door is subsequently closed, as determined in block1706. For example, closing of the door may be detected by the host/thermal system controller when the safety interlock is re-engaged (e.g., when the latching mechanism118,618,818is re-engaged with the corresponding securing structure119,619,819,FIGS. 1, 6, 8). Unless a pre-emptory permanent exit condition occurs before the system door is closed, the host/thermal system controller re-activates the heating system components (e.g., the convection fan, radiant heating element(s), gas burner(s)) in block1708after detection that the system door has been closed, and the process returns to block1634(FIG. 16).

Referring again to block1634, the host/thermal system controller alternatively may determine that a permanent cessation (or exit) condition has occurred. For example the host/thermal system controller may make a determination that an exit condition has occurred upon expiration of a timer that was set by the user (e.g., through user interface992,1292,FIGS. 9, 12) or upon expiration of a timer that was established by the host/thermal system controller based on the system controller's estimate of how long the heating operation should be performed. In still another alternate embodiment, the host/thermal system controller may otherwise detect completion of the heating operation (e.g., a determination may be made that the load is cooked or has attained a desired temperature).

If a temporary cessation condition has been resolved or a permanent cessation (exit) condition has not occurred, then the heating operation may continue by iteratively performing block1632and1634. When a permanent cessation (exit) condition has occurred, then in block1636, the host/thermal system controller deactivates (turns off) the thermal heating system. In addition, the host/thermal system controller may send signals to the user interface (e.g., user interface992,1292,FIGS. 9, 12) that cause the user interface to produce a user-perceptible indicia of the exit condition (e.g., by displaying “done” on a display device, or providing an audible tone). The method may then end.

Returning again to block1602, and moving next to the process description when an RF-only cooking mode selection has been made, a determination may first be made, in block1604, whether the oven cavity may be empty. This determination may be made by the RF heating system controller (e.g., controller912,1212,FIGS. 9, 12) to ensure that the RF heating system is not activated when the oven cavity is empty (e.g., if no load has been placed in the oven cavity), because activation of the RF heating system under such a condition may cause damage to the system.

According to an embodiment, the RF heating system controller may determine that an empty cavity condition exists by controlling the RF signal source (e.g., RF signal source920,1220,FIGS. 9, 12) to provide a relatively low-power RF signal to the RF system electrode(s) (e.g., electrodes940,1240,1242,FIGS. 9, 12), and receiving a signal from power detection circuitry (e.g., power detection circuitry930,1230,1230′,1230″,FIGS. 9, 12) that is indicative of an empty cavity condition. For example, an empty cavity condition may be indicated when the power detection circuitry detects a reflected power that exceeds a pre-determined threshold. In addition or alternatively, the RF heating system controller may determine that an empty cavity condition is indicated when particular match conditions exist (e.g., when the variable impedance matching network is set to particular states, during the calibration process, which are associated with an empty cavity condition). When an empty cavity condition has been detected, in block1604, then in block1606, a user-perceptible indication of the empty cavity condition may be output through the user interface (e.g., a message may be displayed), the low-power RF signal may be discontinued, and the RF heating system may be deactivated. The RF heating system may remain in the deactivated state at least until the system door is opened and re-closed, which may be consistent with a user placing a load in the cavity. In such a scenario, once the user has again provided a start indication, block1604may be repeated.

When an empty cavity condition is not detected in block1604(e.g., the reflected power indicates that a load is present within the cavity), then in block1608, a variable matching network calibration process is performed. To avoid cluttering the flowchart ofFIG. 16, an embodiment of a variable network calibration process is shown inFIG. 18.

The variable network calibration process begins, in block1802, when the RF heating system controller provides control signals to the variable matching network (e.g., network970,1000,1100,1272,1300,1400,FIGS. 9-14) to establish an initial configuration or state for the variable matching network. The control signals affect the values of variable inductances and/or capacitances (e.g., inductances1010,1011,1311,1316,1321,FIGS. 10, 13, and capacitances1144,1148,1413,1418,1424,FIGS. 11, 14) within the variable matching network. For example, the control signals may affect the states of bypass switches across the various inductances and capacitances, which are responsive to the control signals from the RF heating system controller, and which are operable to switch sub-inductances and sub-capacitances into and out of the network to increase or decrease the inductance and capacitance values of the variable components. Desirably, the initial configuration of the variable matching network is established to provide an optimum match between the RF signal source and the cavity plus load.

Once the initial variable matching network configuration is established, the system controller may perform a process1810of adjusting, if necessary, the configuration of the variable impedance matching network to find an acceptable or best match based on actual measurements that are indicative of the quality of the match. According to an embodiment, this process includes causing the RF signal source (e.g., RF signal source920,1220,FIGS. 9, 12) to supply a relatively low power RF signal through the variable impedance matching network to the electrode(s) (e.g., first electrode940or both electrodes1240,1242,FIGS. 9, 12), in block1812. The system controller may control the RF signal power level through control signals to the power supply and bias circuitry (e.g., circuitry926,1226,FIGS. 9, 12), where the control signals cause the power supply and bias circuitry to provide supply and bias voltages to the amplifiers (e.g., amplifier stages924,925,1224,FIGS. 9, 12) that are consistent with the desired signal power level. For example, the relatively low power RF signal may be a signal having a power level in a range of about 10 W to about 20 W, although different power levels alternatively may be used. A relatively low power level signal during the match adjustment process1810is desirable to reduce the risk of damaging the cavity or load (e.g., if the initial match causes high reflected power), and to reduce the risk of damaging the switching components of the variable inductance networks (e.g., due to arcing across the switch contacts).

In block1814, power detection circuitry (e.g., power detection circuitry930,1230,1230′,1230″,FIGS. 9, 12) then measures the reflected and (in some embodiments) forward power along the transmission path (e.g., path928,1228,FIGS. 9, 12) between the RF signal source and the electrode(s), and provides those measurements to the RF heating system controller. The RF heating system controller may then determine a ratio between the reflected and forward signal powers, and may determine the S11 parameter and/or VSWR value for the system based on the ratio. The system controller may store the received power measurements (e.g., the received reflected power measurements, the received forward power measurement, or both), and/or the calculated ratios, S11 parameters, and/or VSWR values for future evaluation or comparison, in an embodiment.

In block1816, the system controller may determine, based on the reflected power measurements, and/or the reflected-to-forward signal power ratio, and/or the S11 parameter, and/or the VSWR value, whether or not the match provided by the variable impedance matching network is acceptable (e.g., the reflected power is below a threshold, or the ratio is 10 percent or less, or the measurements or values compare favorably with some other criteria). Alternatively, the system controller may be configured to determine whether the match is the “best” match. A “best” match may be determined, for example, by iteratively measuring the reflected RF power (and in some embodiments the forward reflected RF power) for all possible impedance matching network configurations (or at least for a defined subset of impedance matching network configurations), and determining which configuration results in the lowest reflected RF power and/or the lowest reflected-to-forward power ratio.

When the RF heating system controller determines that the match is not acceptable or is not the best match, the RF heating system controller may adjust the match, in block1818, by reconfiguring the variable impedance matching network. For example, this may be achieved by sending control signals to the variable impedance matching network, which cause the network to increase and/or decrease the variable inductances within the network (e.g., by causing the variable inductance networks1010,1011,1311,1316,1321(FIGS. 10, 13) or variable capacitance networks1142,1146,1411,1416,1421(FIGS. 11, 14) to have different inductance or capacitance states, or by switching inductors or capacitors into or out of the circuit. After reconfiguring the variable inductance network, blocks1814,1816, and1818may be iteratively performed until an acceptable or best match is determined in block1816.

Once an acceptable or best match is determined, the flow returns toFIG. 16, and the RF heating operation may commence. Commencement of the RF heating operation includes increasing the power of the RF signal supplied by the RF signal source (e.g., RF signal source920,1220,FIGS. 9, 12) to a relatively high power RF signal, in block1610. Once again, the RF heating system controller may control the RF signal power level through control signals to the power supply and bias circuitry (e.g., circuitry926,1226,FIGS. 9, 12), where the control signals cause the power supply and bias circuitry to provide supply and bias voltages to the amplifiers (e.g., amplifier stages924,925,1224,FIGS. 9, 12) that are consistent with the desired signal power level. For example, the relatively high power RF signal may be a signal having a power level in a range of about 50 W to about 500 W, although different power levels alternatively may be used.

In block1614, measurement circuitry (e.g., power detection circuitry930,1230,1230′,1230″,FIGS. 9, 12) then periodically measures system parameters such as the one or more currents, one or more voltages, the reflected power and/or the forward power along the transmission path (e.g., path928,1228,FIGS. 9, 12) between the RF signal source and the electrode(s), and provides those measurements to the RF heating system controller. The RF heating system controller again may determine a ratio between the reflected and forward signal powers, and may determine the S11 parameter and/or VSWR value for the system based on the ratio. The RF heating system controller may store the received power measurements, and/or the calculated ratios, and/or S11 parameters, and/or the VSWR values for future evaluation or comparison, in an embodiment. According to an embodiment, the periodic measurements of the forward and reflected power may be taken at a fairly high frequency (e.g., on the order of milliseconds) or at a fairly low frequency (e.g., on the order of seconds). For example, a fairly low frequency for taking the periodic measurements may be a rate of one measurement every 10 seconds to 20 seconds.

In block1616, the RF heating system controller may determine, based on one or more reflected signal power measurements, one or more calculated reflected-to-forward signal power ratios, one or more calculated S11 parameters, and/or one or more VSWR values whether or not the match provided by the variable impedance matching network is acceptable. For example, the RF heating system controller may use a single reflected signal power measurement, a single calculated reflected-to-forward signal power ratio, a single calculated S11 parameter, or a single VSWR value in making this determination, or may take an average (or other calculation) of a number of previously-received reflected signal power measurements, previously-calculated reflected-to-forward power ratios, previously-calculated S11 parameters, or previously-calculated VSWR values in making this determination. To determine whether or not the match is acceptable, the RF heating system controller may compare the received reflected signal power, the calculated ratio, S11 parameter, and/or VSWR value to one or more corresponding thresholds, for example. For example, in one embodiment, the RF heating system controller may compare the received reflected signal power to a threshold of, for example, 5 percent (or some other value) of the forward signal power. A reflected signal power below 5 percent of the forward signal power may indicate that the match remains acceptable, and a ratio above 5 percent may indicate that the match is no longer acceptable. In another embodiment, the RF heating system controller may compare the calculated reflected-to-forward signal power ratio to a threshold of 10 percent (or some other value). A ratio below 10 percent may indicate that the match remains acceptable, and a ratio above 10 percent may indicate that the match is no longer acceptable. When the measured reflected power, the calculated ratio or S11 parameter, or the VSWR value is greater than the corresponding threshold (i.e., the comparison is unfavorable), indicating an unacceptable match, then the RF heating system controller may initiate re-configuration of the variable impedance matching network by again performing process1608(e.g., the process ofFIG. 17).

As discussed previously, the match provided by the variable impedance matching network may degrade over the course of a heating operation due to impedance changes of the load (e.g., load964,1264,FIGS. 9, 12) as the load warms up. It has been observed that, over the course of a heating operation, an optimal cavity match may be maintained by adjusting the cavity match inductance or capacitance and by also adjusting the RF signal source inductance or capacitance.

According to an embodiment, in the iterative process of re-configuring the variable impedance matching network, the RF heating system controller may take into consideration this tendency. More particularly, when adjusting the match by reconfiguring the variable impedance matching network in block1608, the RF heating system controller initially may select states of the variable inductance networks for the cavity and RF signal source matches that correspond to lower inductances (for the cavity match) and higher inductances (for the RF signal source match). Similar processes may be performed in embodiments that utilize variable capacitance networks for the cavity and RF signal source. By selecting impedances that tend to follow the expected optimal match trajectories, the time to perform the variable impedance matching network reconfiguration process1608may be reduced, when compared with a reconfiguration process that does not take these tendencies into account. In an alternate embodiment, the RF heating system controller may instead iteratively test adjacent configurations to attempt to determine an acceptable configuration.

In actuality, there are a variety of different searching methods that the RF heating system controller may employ to re-configure the system to have an acceptable impedance match, including testing all possible variable impedance matching network configurations. Any reasonable method of searching for an acceptable configuration is considered to fall within the scope of the inventive subject matter. In any event, once an acceptable match again is established in block1608, the heating operation is resumed in blocks1610and1614, and the process continues to iterate.

Referring back to block1616, when the RF heating system controller determines, based on one or more reflected power measurements, one or more calculated reflected-to-forward signal power ratios, one or more calculated S11 parameters, and/or one or more VSWR values that the match provided by the variable impedance matching network is still acceptable (e.g., the reflected power measurements, calculated ratio, S11 parameter, or VSWR value is less than a corresponding threshold, or the comparison is favorable), the RF heating system controller and/or the host/thermal system controller may evaluate whether or not a cessation or exit condition has occurred, in block1618. In actuality, determination of whether a cessation or exit condition has occurred may be an interrupt driven process that may occur at any point during the heating process. However, for the purposes of including it in the flowchart ofFIG. 16, the process is shown to occur after block1616. Block1618may be substantially the same as block1636and the associated discussion of a temporary cessation condition in the flowchart ofFIG. 17, which were discussed previously. For purpose of brevity, that discussion will not be repeated here, but is intended to apply equally.

If a temporary cessation condition has been resolved, or a permanent cessation condition has not occurred, then the heating operation may continue by iteratively performing blocks1614and1616(and the matching network reconfiguration process1608, as necessary). When a permanent cessation (exit) condition has occurred, then in block1620, the RF heating system controller causes the supply of the RF signal by the RF signal source to be discontinued. For example, the RF heating system controller may disable the RF signal generator (e.g., RF signal generator922,1222,FIGS. 9, 12) and/or may cause the power supply and bias circuitry (e.g., circuitry926,1226,FIGS. 9, 12) to discontinue provision of the supply current. In addition, the host/thermal system controller may send signals to the user interface (e.g., user interface992,1292,FIGS. 9, 12) that cause the user interface to produce a user-perceptible indicia of the exit condition (e.g., by displaying “done” on a display device, or providing an audible tone). The method may then end.

Returning once again to block1602, when a combined thermal and RF cooking mode has been selected that includes activation of both a thermal heating system and the RF heating system, the previously-discussed thermal cooking process (i.e., including blocks1630,1632,1634) and RF cooking process (i.e., blocks1604,1606,1608,1610,1614,1616,1618) are performed in parallel and simultaneously. More specifically, the host/thermal system controller controls the appropriate thermal heating system to heat the air in the oven cavity at the same time that the RF system controller controls the RF heating system to radiate RF energy into the oven cavity. During some periods of the cooking process, either the thermal heating system or the RF heating system may be temporarily de-activated, while the other system remains activated. Overall control of the activation states of the thermal heating system and the RF heating system may be performed by the host/thermal system controller, in an embodiment.

Implementation of an embodiment of a system that combines RF capacitive cooking by an RF heating system with thermal cooking by a thermal heating system may have significant performance advantages over conventional systems. For example,FIGS. 19 and 20are charts plotting the internal temperature of initially frozen and refrigerated food loads, respectively, during a convection-only cooking process and during a combined convection and RF cooking process.

Referring first toFIG. 19, chart1900plots internal load temperature (in degrees Celsius along the vertical axis) over cooking time (in minutes along the horizontal axis) for an initially frozen mass of chicken. Specifically, trace1910plots internal load temperature over time when the load was heated using a convection-only heating process, and trace1920plots internal load temperature over time when the load was heated using an embodiment of a heating apparatus that includes both an RF heating system and a convection heating system (e.g., system100,FIG. 1). Trace1910shows that the convection-only heating process raised the internal temperature of the load from about −20 degrees Celsius to about 80 degrees Celsius in about 108 minutes. Conversely, trace1920shows that the combined RF and convection heating process raised the internal temperature of the load from about −20 degrees Celsius to about 80 degrees Celsius in about 62 minutes, which represents a significant reduction in the cooking time for the initially frozen load.

Referring next toFIG. 20, chart2000plots internal load temperature (in degrees Celsius along the vertical axis) over cooking time (in minutes along the horizontal axis) for an initially refrigerated mass of chicken. Specifically, trace2010plots internal load temperature over time when the load was heated using a convection-only heating process, and trace2020plots internal load temperature over time when the load was heated using an embodiment of a heating apparatus that includes both an RF heating system and a convection heating system (e.g., system100,FIG. 1). Trace2010shows that the convection-only heating process raised the internal temperature of the load from about 5 degrees Celsius to about 75 degrees Celsius in about 75 minutes. Conversely, trace2020shows that the combined RF and convection heating process raised the internal temperature of the load from about 5 degrees Celsius to about 75 degrees Celsius in about 36 minutes, which again represents a significant reduction in the cooking time.

Accordingly, given the results depicted inFIGS. 19 and 20, it is evident that implementation of embodiments of the inventive subject matter that include combined RF and thermal heating systems may achieve significantly reduced cooking times, when compared with conventional systems.

The foregoing description refers to elements or nodes or features being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element is directly joined to (or directly communicates with) another element, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element is directly or indirectly joined to (or directly or indirectly communicates with) another element, and not necessarily mechanically. Thus, although the schematic shown in the figures depict one exemplary arrangement of elements, additional intervening elements, devices, features, or components may be present in an embodiment of the depicted subject matter.

An embodiment of a heating system includes a cavity configured to contain a load, a thermal heating system in fluid communication with the cavity and configured to heat air, and an RF heating system. The RF heating system includes an RF signal source configured to generate an RF signal, first and second electrodes positioned across the cavity and capacitively coupled, a transmission path electrically coupled between the RF signal source and one or more of the first and second electrodes, and a variable impedance matching network electrically coupled along the transmission path between the RF signal source and the one or more electrodes. At least one of the first and second electrodes receives the RF signal and converts the RF signal into electromagnetic energy that is radiated into the cavity.

An embodiment of a method of operating a heating system that includes a cavity configured to contain a load, includes heating air in the cavity by a thermal heating system in fluid communication with the cavity. The method further includes, simultaneously with heating the air in the cavity, supplying, by an RF signal source, one or more RF signals to a transmission path that is electrically coupled between the RF signal source and first and second electrodes that are positioned across the cavity and capacitively coupled. At least one of the first and second electrodes receives the RF signal and converts the RF signal into electromagnetic energy that is radiated into the cavity. The method further includes detecting, by power detection circuitry, reflected signal power along the transmission path, and modifying, by a controller, one or more component values of one or more components of a variable impedance matching network to reduce the reflected signal power.