Phased array cofire antenna structure and method for operating the same

An antenna structure for an implantable medical device (IMD) is provided that includes an antenna embedded within a structure derived from a plurality of discrete dielectric layers. An array of electrodes are connected to the antenna structure and arranged for applying a bias across selected segments of the dielectric layers for altering the performance characteristics of the antenna. The bias applied by the array of electrodes can be selected to provide desired impedance matching between the antenna and the surrounding environment of the implant location to mitigate energy reflection effects at the transition from the antenna structure to the surrounding environment, to provide beam steering functionality for the antenna, or to alter the gain of the signals received by the antenna. IMD is configured to monitor received signal characteristics (e.g., RSSI, EVM or bit error rate) and alter material properties of the dielectric material through biasing to control antenna performance.

TECHNICAL FIELD

The present invention relates generally to implantable medical devices (IMDs) and, more particularly, the present invention relates to telemetry antennas suitable for deployment in IMDs.

BACKGROUND

Various types of devices have been developed for implantation into the human body to provide various types of health-related therapies, diagnostics and/or monitoring. Examples of such devices, generally known as implantable medical devices (IMDs), include cardiac pacemakers, cardioverter/defibrillators, cardiomyostimulators, cardiac event monitors, various physiological stimulators including nerve, muscle, and deep brain stimulators, various types of physiological monitors and sensors, and drug delivery systems, just to name a few. IMDs typically include functional components contained within a hermetically sealed enclosure or housing, which is sometimes referred to as a “can.” In some IMDs, a connector header or connector block is attached to the housing, and the connector block facilitates interconnection with one or more elongated electrical medical leads. The header block is typically molded from a relatively hard, dielectric, non-conductive polymer. The header block includes a mounting surface that conforms to, and is mechanically affixed against, a mating sidewall surface of the housing.

It has become common to provide a communication link between the hermetically sealed electronic circuitry of the IMD and an external programmer, monitor, or other external medical device (“EMD”) in order to provide for downlink telemetry transmission of commands from the EMD to the IMD and to allow for uplink telemetry transmission of stored information and/or sensed physiological parameters from the IMD to the EMD. Conventionally, the communication link between the IMD and the EMD is realized by encoded radio frequency (“RF”) transmissions between an IMD telemetry antenna and transceiver and an EMD telemetry antenna and transceiver. Generally, the IMD antenna is disposed within the hermetically sealed housing. However, the typically conductive housing can limit the radiation efficiency of the IMD RF telemetry antenna, thereby traditionally limiting the data transfer distance between the programmer head and the IMD RF telemetry antenna to a few inches. This type of system may be referred to as a “near field” telemetry system. In order to provide for “far field” telemetry, or telemetry over distances of a few to many meters from an IMD or even greater distances, attempts have been made to provide antennas outside of the hermetically sealed housing and within the header block. Many of such attempts of positioning an RF telemetry antenna outside of the hermetically sealed housing and in the header block have utilized wire antennas or planar, serpentine antennas, such as the antennas described in U.S. Pat. No. 7,317,946, which is hereby incorporated by reference in its entirety. The volume associated with the antenna and header block conventionally required for the implementation of distance telemetry in implanted therapy and diagnostic devices has been a significant contributor to the size of the IMD.

SUMMARY

In one or more embodiments, an antenna structure for an implantable medical device (IMD) is provided that includes an antenna embedded within a structure derived from a plurality of discrete dielectric layers. A plurality of electrodes are connected to the antenna structure and arranged for applying a bias across at least a portion of at least one of the dielectric layers. The electrodes are connected to a power source in the IMD. A controller is communicatively coupled with the antenna for sending and receiving telemetry signals. In operation, the IMD is configured to measure a performance of the antenna based on certain characteristics of the signals being received by the antenna and cause a bias to be applied between the plurality of electrodes to at least a portion of a dielectric layer to alter the performance of the antenna. In one or more embodiments, an array of the plurality of electrodes may be provided such that selectable segments of dielectric material between corresponding electrodes in the array may be biased. In this manner, a phased array antenna is provided that allows a bias to be applied to alter the operating characteristics of the antenna structure. In some embodiments, the bias can be selected to provide desired impedance matching between the antenna and the surrounding environment of the implant location to mitigate energy reflection effects at the transition from the antenna structure to the surrounding environment. In some embodiments, the bias can be selected in order to provide beam steering functionality to the antenna, such that signals communicated to and from the antenna can be selectably directed in a desired direction. In some embodiments, the bias can be selected in order to provide beam steering functionality to the antenna, such that interfering signals are attenuated (i.e., that might otherwise disrupt desired communication). In some embodiments, the bias can be selected in order to alter the gain of the signals received by the antenna.

In one or more embodiments, the IMD can be configured to select the desired bias to be applied for the phased array antenna by monitoring the characteristics of the signals received by the antenna. For example, the signal strength (e.g., RSSI), error vector magnitude (e.g., EVM), or the bit error rate of the received signals can be measured to assess the performance of the antenna, where the bias selected to be applied to the dielectric material will alter the performance of the antenna (e.g., the signal strength or bit error rate) to a desired level.

In one or more embodiments, the antenna structure may be formed as a cofired monolithic structure derived from the plurality of discrete dielectric layers having an antenna conductor embedded within multiple layers of the plurality of dielectric layers. By forming a monolithic antenna structure derived from the plurality of dielectric layers, the dielectric constants of the plurality of dielectric layers can be selected and further controlled by the bias applied to control the effective dielectric between the antenna and the surrounding environment to suit the needs of the particular IMD and/or the particular implant location. In one or more embodiments, the dielectric layers comprise at least one of a low temperature co-fire ceramic (LTCC) material and/or a high temperature co-fire ceramic (HTCC) material, where the ceramic dielectric layers, the antenna, and the plurality of electrodes can be co-fired together to form a monolithic antenna structure.

DETAILED DESCRIPTION

The following detailed description is merely illustrative and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

The following description refers to components or features being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one component/feature is directly or indirectly connected to another component/feature, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one component/feature is directly or indirectly coupled to another component/feature, and not necessarily mechanically. Thus, although the figures may depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment (assuming that the functionality of the IMDs are not adversely affected).

In one or more embodiments, an IMD having a phased array antenna structure derived from a plurality of discrete dielectric layers is provided. For the sake of brevity, conventional techniques and aspects related to RF antenna design, IMD telemetry, RF data transmission, signaling, IMD operation, connectors for IMD leads, and other functional aspects of the systems (and the individual operating components of the systems) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical embodiment.

An IMD antenna generally has two functions: to convert the electromagnetic power of a downlink telemetry transmission of an EMD telemetry antenna propagated through the atmosphere (and then through body tissues) into a signal (e.g., a UHF signal or the like) that can be processed by the IMD transceiver into commands and data that are intelligible to the IMD electronic operating system; and to convert the uplink telemetry signals (e.g., a UHF signal or the like) of the IMD transceiver electronics into electromagnetic power propagated through the body tissue and the atmosphere so that the EMD telemetry antenna or antennas can receive the signals.

FIG. 1is a perspective view of an IMD10implanted within a human body12in which one or more embodiments of the invention may be implemented. IMD10comprises a hermetically sealed housing14(or “can”) and connector header or block module16for coupling IMD10to electrical leads and other physiological sensors arranged within body12, such as pacing and sensing leads18connected to portions of a heart20for delivery of pacing pulses to a patient's heart20and sensing of heart20conditions in a manner well known in the art. For example, such leads may enter at an end of header block16and be physically and electrically connected to conductive receptacles, terminals, or other conductive features located within header block16. IMD10may be adapted to be implanted subcutaneously in the body of a patient such that it becomes encased within body tissue and fluids, which may include epidermal layers, subcutaneous fat layers, and/or muscle layers. While IMD10is depicted inFIG. 1in an ICD configuration, it is understood that this is for purposes of illustration only and IMD10may comprise any type of medical device requiring a telemetry antenna.

In some embodiments, hermetically sealed housing14is generally circular, elliptical, prismatic, or rectilinear, with substantially planar major sides joined by perimeter sidewalls. Housing14is typically formed from pieces of a thin-walled biocompatible metal such as titanium. Two half sections of housing12may be laser seam welded together using conventional techniques to form a seam extending around the perimeter sidewalls. Housing14and header block16are often manufactured as two separate assemblies that are subsequently physically and electrically coupled together. Housing14may contain a number of functional elements, components, and features, including (without limitation): a battery; a high voltage output capacitor; integrated circuit (“IC”) devices; a processor or controller; memory elements; a therapy module or circuitry; an RF module or circuitry; and an antenna matching circuit. These components may be assembled in spacers and disposed within the interior cavity of housing14prior to seam welding of the housing halves. During the manufacturing process, electrical connections are established between components located within housing14and elements located within header block16. For example, housing14and header block16may be suitably configured with IC connector pads, terminals, feedthrough elements, and other features for establishing electrical connections between the internal therapy module and the therapy lead connectors within header block16and for establishing connections between the internal RF module and a portion of a telemetry antenna located within header block16. Structures and techniques for establishing such electrical (and physical) feedthrough connections are known to those skilled in the art and, therefore, will not be described in detail herein. For example, U.S. Pat. No. 6,414,835 describes a capacitive filtered feedthrough array for an implantable medical device, the contents of which are hereby incorporated by reference.

Header block16is preferably formed from a suitable dielectric material, such as a biocompatible synthetic polymer. In some embodiments, the dielectric material of header block16may be selected to enable the passage of RF energy that is either radiated or received by a telemetry antenna (not shown inFIG. 1) encapsulated within header block16. The specific material for header block16may be chosen in response to the intended application of IMD10, the electrical characteristics of the environment surrounding the implant location, the desired operating frequency range, the desired RF antenna range, and other practical considerations.

FIG. 2is a simplified schematic representation of an IMD10and several functional elements associated therewith. IMD10generally includes hermetically sealed housing14and header block16coupled to housing14, a therapy module22contained within housing14, and an RF module24contained within housing14. In practice, IMD10will also include a number of conventional components and features necessary to support the functionality of IMD10as known in the art, such as a controller, a memory and battery as a power source. Such conventional elements may not be fully described herein.

Therapy module22may include any number of components, including, without limitation: electrical devices, ICs, microprocessors, controllers, memories, power supplies, and the like. Briefly, therapy module22is configured to provide the desired functionality associated with the IMD10, e.g., defibrillation pulses, pacing stimulation, patient monitoring, or the like. In this regard, therapy module22may be coupled to one or more sensing or therapy leads18. In practice, the connection ends of therapy leads18are inserted into header block16, where they establish electrical contact with conductive elements coupled to therapy module22. Therapy leads18may be inserted into suitably configured lead bores formed within header block16. In the example embodiment, IMD10includes a feedthrough element26that bridges the transition between housing14and header block16. Therapy leads18extend from header block16for routing and placement within the patient.

RF module24may be positioned inside or outside of housing14and may include any number of components, including, without limitation: electrical devices, ICs, amplifiers, signal generators, a receiver and a transmitter (or a transceiver), modulators, microprocessors, controllers, memories, power supplies, and the like. RF module24may further include a matching circuit or a matching circuit may be positioned between RF module24and antenna28. Matching circuit may include any number of components, including, without limitation: electrical components such as capacitors, resistors, or inductors; filters; baluns; tuning elements; varactors; limiter diodes; or the like, that are all suitably configured to provide impedance matching between antenna28and RF module24, thus improving the efficiency of antenna28. Briefly, RF module24supports RF telemetry communication for IMD10, including, without limitation: generating RF transmit energy; providing RF transmit signals to antenna28; processing RF telemetry signals received by antenna28, and the like. In practice, RF module24may be designed to leverage the conductive material used for housing14as an RF ground plane (for some applications), and RF module24may be designed in accordance with the intended application of IMD10, the electrical characteristics of the environment surrounding the implant location, the desired operating frequency range, the desired RF antenna range, and other practical considerations.

Antenna28is coupled to RF module24to facilitate RF telemetry between IMD10and an EMD (not shown). Generally, antenna28is suitably configured for RF operation (e.g., UHF or VHF operation, 401 to 406 MHz for the MICS/MEDS bands, 900 MHz/2.4 GHz and other ISM bands, etc.). In the example embodiment shown inFIG. 2, antenna28is located within header block16and outside of housing14. However, the volume associated with the antenna28and the volume within the header block16required for the implementation of distance telemetry in implanted therapy and diagnostic devices can be a significant contributor to the size of the IMD10. Antenna28may have characteristics resembling a monopole antenna, characteristics resembling a dipole antenna, characteristics resembling a coplanar waveguide antenna, characteristics resembling a stripline antenna, characteristics resembling a microstrip antenna, and/or characteristics resembling a transmission line antenna. Antenna28may also have any number of radiating elements, which may be driven by any number of distinct RF signal sources. In this regard, antenna28may have a plurality of radiating elements configured to provide spatial, pattern or polarization diversity

In one or more embodiments, antenna28is coupled to RF module24via an RF feedthrough in feedthrough26, which bridges housing14and header block16. Antenna28may include a connection end that is coupled to RF feedthrough in feedthrough26via a conductive terminal or feature located within header block16. Briefly, a practical feedthrough26includes a ferrule supporting a non-conductive glass or ceramic insulator. The insulator supports and electrically isolates a feedthrough pin from the ferrule. During assembly of housing14, the ferrule is welded to a suitably sized hole or opening formed in housing14. RF module24is then electrically connected to the inner end of the feedthrough pin. The connection to the inner end of the feedthrough pin can be made by welding the inner end to a substrate pad, or by clipping the inner end to a cable or flex wire connector that extends to a substrate pad or connector. The outer end of the feedthrough pin serves as a connection point for antenna28, or as a connection point for an internal connection socket, terminal, or feature that receives the connection end of antenna28. The feedthrough26for antenna28may be located on any desired portion of housing14suitable for a particular design.

Referring now toFIG. 3, a perspective, exploded view of an antenna structure100formed in accordance with one or more embodiments is respectively illustrated. Certain features and aspects of antenna structure100are similar to those described above in connection with antenna28, and shared features and aspects will not be redundantly described in the context of antenna structure100. Antenna structure100includes at least one antenna106formed on a dielectric layer104. One or more additional discrete dielectric layers may be positioned above the antenna106serving as superstrates108and/or below the antenna106serving as substrates112. In one or more embodiments, the antenna structure100includes a biocompatible layer110positioned as the outermost layer over the superstrate dielectric layers108serving as an interface between the antenna structure110and the surrounding environment. In some embodiments, the biocompatible layer110may comprise the outermost of the superstrate dielectric layers108. Different types of biocompatible materials can be selected based on the intended use of antenna structure100and IMD10and the intended surrounding environment. For example, outermost layer110may comprise inorganic materials, such as Alumina (Al2O3), zirconium oxide (ZrO2), mixtures thereof or bone-like systems [hydroxyapatite—Ca5(POH)(PO4)3], organic materials, such as silicone and its derivatives, and other traditionally implantable biocompatible materials.

With further reference toFIG. 4, in one or more embodiments, a plurality of electrodes120are connected to respective portions of antenna structure100and arranged such that a voltage bias can be applied between the electrodes120across at least a portion of one or more of the dielectric layers104,108or112(with electrodes120being illustrated as being connected to dielectric layer108inFIG. 3). Electrodes are connected to a power source in IMD10for providing such voltage bias. A controller, either located in RF module24or otherwise located within IMD10, is communicatively coupled with antenna106for sending and receiving telemetry signals.

In some embodiments, antenna structure100may include an shielding layer114positioned in a layer under the antenna106formed from a metalized material that provides electromagnetic shielding of device circuitry inside of the hermetically sealed housing14to which the antenna structure100is attached through a feedthrough via116. In some embodiments, the shielding layer114is positioned as the innermost layer of the antenna structure100, while it is understood that shielding layer114can also be positioned within another intermediate substrate layer112positioned under the antenna106. In one or more embodiments, a layer of electromagnetic bandgap material115may be positioned under antenna106to function as an electromagnetic bandgap between antenna106and shielding layer114(i.e., ground plane). Typically, when a radiating antenna element is placed above and in parallel with a ground plane, the field radiated by the antenna element and the field reflected by the ground plane are 180° out of phase due to the reflection coefficient presented by the ground plane short circuit. As a result, when the separation distance between the antenna element and the ground plane is reduced, the total antenna radiated fields tend to zero as the field radiated from the antenna element and its ground plane reflection will tend to completely cancel each other. An electromagnetic bandgap layer115prevents this reduction in antenna radiation efficiency by introducing a ground perturbation known as an electromagnetic bandgap, or high impedance surface, between antenna106and ground plane shielding layer114. The electromagnetic bandgap layer115prevents or minimizes a reduction in antenna radiation efficiency from occurring as a result of the close proximity of the antenna conductor106to the ground plane114. In one aspect, the electromagnetic bandgap layer115at resonance appears as an open circuit with a reflection coefficient in phase with the incident field. For instance, the electromagnetic bandgap layer115will cause the field radiated from antenna106and the field radiated by its ground plane image to be co-directed thus maintaining the same orientation and not canceling each other out. The electromagnetic bandgap layer115further provides a high electromagnetic surface impedance that allows the antenna106to lie directly adjacent to the ground plane114without being shorted out. This allows compact antenna designs where radiating elements are confined to limited spaces Thus, the electromagnetic bandgap layer115assists in miniaturization of the device by allowing the distance between antenna106and ground plane shielding layer114to be reduced to a small distance. In one or more embodiments, electromagnetic bandgap layer115may be vacuum deposited on the surface of one of the layers of the device100or adhered via epoxy after ceramic densification (described later) in order to minimize material alterations induced by thermal excursion of the firing process.

In one or more embodiments, dielectric layers104,108and112can be selected to possess respective dielectric constants that match the dielectric constant of the environment (e.g., body tissue) surrounding the antenna structure100to mitigate energy reflection effects at the transition from the antenna structure100to the surrounding environment. This matching of dielectric constants in the various layers of device100can be achieved by incorporating materials that are cofireable, compatible and possess desired dielectric constants.

In one or more embodiments, various biocompatible layers formed for the superstrate dielectric layers108may comprise polymers that are loaded with high dielectric constant powders, such that powders with different dielectric constants can be loaded on the different polymer layers, different concentrations of powder loading can be performed on the different polymer layers, or the dielectric constant of each polymer layer can otherwise have its powder loading adjusted to produce a structure having a desired effective dielectric constant for the superstrate dielectric layers108. In one or more embodiments, the substrate dielectric layers112under conductor106may comprise materials with higher dielectric values than dielectric layer104on which antenna106is formed, such that the higher dielectric values associated with substrate dielectric layers112allow the distance between antenna conductor106and ground plane shielding layer114to be minimized, thereby allowing a reduction in size of antenna structure100to be achieved. The high dielectric constant K of each layer may be achieved by incorporating cofireable materials having high dielectric constants K (e.g., capacitive materials). Depending upon the materials used to form substrate dielectric layers112, dielectric constant values can vary anywhere from k=5-6 for the LTCC layer itself to at least 1-2 orders of magnitude higher with the use of capacitive pastes that are LTCC compatible. In addition, a ceramic loaded printed wiring board (PWB) is another embodiment to the LTCC based structure. LTCC materials offer the ability to embed passive components to spatially and functionally tailor the dielectric constant or capacitance to optimize packaging efficiency and/or performance. Since materials with high dielectric constants are typically not biocompatible, substrate dielectric layers112may be separated and isolated from potential contact with body environment surrounding IMD10by the biocompatible materials used to form outermost biocompatible layer110or other superstrate dielectric layers108. The isolation of substrate layers112from the body environment surrounding IMD10allows the possible selection of materials for superstrate dielectric layers108to be wide ranging. For example, dielectric oxide (e.g., barium titanium oxide (BaTiO3)) based systems with dielectric constants k in the hundreds to thousands are possible.

In one or more embodiments, the various layers used to form antenna structure100may be formed using any material layer deposition technique known in the art, including but not limited to depositing, spraying, screening, dipping, plating, etc. In some embodiments, molecular beam epitaxy (MBE), atomic layer deposition (ALD) or other thin film, vacuum deposited processes may be used to deposit the various layers building them on top of one another, such that ALD allows thin high dielectric materials to be used in forming substrate dielectric layers112and thin lower dielectric materials to be used in forming superstrate dielectric layers108, thereby achieving size reduction and miniaturization of overall antenna structure100while still improving performing of antenna structure100. The metal layers can be stacked to form a stacked plate capacitor structure to increase the dielectric constant of the area surrounding the antenna106.

In one or more embodiments, after the various layers of antenna structure100and formed or otherwise deposited with respect to one another, as illustrated inFIG. 3, the various layers may be co-fired to a monolithic structure102derived from the various layers, as illustrated inFIG. 4, having antenna106embedded within the resulting monolithic structure102. Feedthrough via116extends through monolithic structure102and may be used to connect antenna106to housing14, such as through a feedthrough. By forming a monolithic antenna structure102derived from the plurality of dielectric layers104,108and112, the dielectric constants of the plurality of dielectric layers104,108and112can be selected or controlled to provide matching characteristics and the dimensions of the overall antenna structure can be minimized to provide a miniature antenna structure.

In one or more embodiments, the material properties of at least a portion of at least one of the plurality of dielectric layers104,108and112can further be altered or adjusted by subjecting such portion of dielectric layers104,108and112to an electric field. The electric field122is initiated in the selected portion of dielectric layers104,108and112by applying a voltage bias between corresponding electrodes120. Electrical connections124(e.g., traces of biocompatible conductive material) connect electrodes120to a power source (not shown inFIG. 4) in IMD10. For example, the dielectric constant and/or capacitance of at least a portion of at least one of dielectric layers104,108and112(or the resulting dielectric material in the cofired structure102) can be altered or changed by appropriately applying a desired voltage bias between electrodes120. By altering the material properties of the selected portion of the dielectric material with the applied bias, the overall performance characteristics of antenna106can be selectively controlled.

In one or more embodiments, the biasing of electrodes120can be selected to alter the effective dielectric constant of the dielectric material surrounding antenna106in order to provide a desired impedance matching between antenna106and the surrounding environment of the implant location to mitigate energy reflection effects at the transition from antenna structure102to the surrounding environment. In one or more embodiments, the biasing of electrodes120can be selected to alter the gain of the signals received by antenna106. Depending upon the implant location of IMD10and the particular surrounding environment of the implant location (e.g., tissue or body mass having different dielectric values or depth of implant location, etc.), the operating characteristics of antenna106will be affected by such conditions of the surrounding environments. The biasing of electrodes120allows the operating performance characteristics of antenna106to be adjusted to account for such conditions of the surrounding environments, such as by adjusting the bias to alter the impedance matching between antenna106and the surrounding environment or to alter the gain of antenna106. This allows the operation of telemetry communications to be fine tuned for optimal antenna performance after IMD10has been implanted within a patient12.

In one or more embodiments, the biasing of electrodes120can be selected to beam steering functionality to antenna106, such that signals communicated to and from antenna106can be selectably directed in a desired direction. Referring toFIG. 4, antenna106may have a radiation emission direction126under unbiased conditions, where segments of antenna structure102can be biased to introduce a phase shift (φ) to modify the wave propagation characteristics of communicating signals through application of an electric field122to a segment of antenna structure102. Thus, the introduced phase shift (φ) could alter the radiation emission direction to direction128. In this manner, the biasing of electrodes120can be selected to provide beam steering functionality to antenna106by introducing a introduced phase shift (φ). Such beam steering functionality can be used to improve the quality of telemetry transmissions. Further, when multiple external devices are capable of communicating with IMD10or when multiple IMDs are present at a certain location capable of communicating with one particular external device, such beam steering functionality can be utilized to control the direction of communications to ensure communication only occurs between two intended devices (i.e., Space Division Multiple Access (SDMA)). In some embodiments, the biasing of electrodes120can be selected in order to provide beam steering functionality to antenna106, such that the phase shift (φ) and resultant antenna directivity attenuates undesired (i.e., interfering) signals that might otherwise degrade desired communications.

In operation, referring to the operational flow diagram ofFIG. 5, IMD10is configured to operate an algorithm stored in its memory to control the operating characteristics of antenna structure102. Initially, an antenna structure102as described herein is provided (operation200) having an antenna structure102comprising antenna106embedded within at least one layer of dielectric material. In operation202, a performance of antenna106is measured based on certain monitored characteristics of the signals being received by antenna106, and it is determined in operation204whether the performance of antenna106is acceptable. For example, the signal strength (e.g., RSSI), error vector magnitude (e.g., EVM), or the bit error rate of the received signals can be measured to assess the performance of antenna106. If antenna106is operating as desired, then no adjustments to the operation of the overall antenna structure may be required and IMD10may either do nothing or may continue to monitor the characteristics of the signals being received by antenna106. If antenna106is not operating as desired, then IMD10will cause a bias to be applied in operation206to at least a portion of antenna structure102(i.e., a portion of at least one dielectric layer104,108, or112) between electrodes to alter the material properties of the dielectric material and thus alter the performance of antenna106. In this manner, a bias can be used on a segment of antenna structure102to control the operating characteristics of the antenna structure102. The embodiment described is merely illustrative as the analytical algorithms for generating said bias are well known in the art and any of such analytical algorithms could be utilized, such as those described in the paper, “Applications of Antenna Arrays to Mobile Communications, Part II: Beam-Forming and Direction-of-Arrival Considerations,” by Lal C. Godara, Proceedings of the IEEE, Vol. 85, No. 8, August 1997, the contents of which are hereby incorporated by reference in its entirety.

In one or more embodiments, the plurality of electrodes120are formed as an array of electrodes120that are arranged to impart an electric field122on selected segments of superstrate dielectric layer108, as illustrated inFIG. 6. A voltage bias may be variably selected to be generated between particular combinations of electrodes120to bias particular segments of dielectric layer108in order to alter the operating characteristics of the antenna structure102in different manners. Electrodes120may be formed to be positioned on dielectric layer108, to extend at least partially through dielectric layer108, to be positioned on a side surface of dielectric layer108, or any combination thereof, in order to create different possible segments of dielectric layer108capable of being biased. In this manner, the material properties of selected segments of superstrate dielectric layer108can be adjusted by the selected biasing in the path of the emitted radiation from antenna106.

In one or more embodiments, the array of electrodes120may be formed on the same dielectric layer104as antenna106is formed on, as illustrated inFIG. 7. In one or more embodiments, the array of electrodes120may be formed on a substrate dielectric layer112formed under antenna106, as illustrated inFIG. 8.

In one or more embodiments, after the antenna structure100has been formed as a co-fired monolithic structure102, the edges118or side surfaces of the various layers of the antenna structure100(i.e., dielectric layers104,108and112, electromagnetic bandgap layer115, outermost biocompatible layer110and innermost shielding layer114) may be brazed or otherwise sealed to hermetically seal the edges118of antenna structure100. The brazed side edges118along with the outermost biocompatible layer110of antenna structure100provide a hermetic seal for antenna structure100so that it can be connected directly to housing14without requiring a header to enclose and seal the antenna conductor106, as typically required with conventional far field telemetry antennas for IMDs. As illustrated inFIG. 9, antenna structure100may be coupled to housing14using brazing, glassing, diffusion bonding or other suitable bonding techniques that will provide a hermetic seal, as known to those skilled in the art. The antenna structure100thus reduces the overall volume and physical dimension required for antenna conductor106for adequate radiation. In some embodiments, a header block16having reduced dimensions may still be utilized for connecting external leads to therapy module16.

In one or more embodiments, antenna106is formed from a biocompatible conductive material, such as but not limited to at least one of the following materials: Platinum, Iridium, Platinum-Iridium alloys, Alumina, Silver, Gold, Palladium, Silver-Palladium or mixtures thereof, or Niobium, Molybdenum and/or Moly-manganese or other suitable materials. In one or more embodiments, dielectric layers104,108and112may be comprise at least one of a ceramic material, a semiconductor material, and/or a thin film dielectric material. In some embodiments in which the dielectric layers104include at least one ceramic material, the dielectric layers104,108and112may include at least one of a low temperature co-fired ceramic (LTCC) material or a high temperature co-fired ceramic (HTCC) material or a PWB material that enable the incorporation of materials having desired dielectric constant values. Generally, a LTCC material has a melting point between about 850 C.° and 1150 C.°, while a HTCC material has a melting point between about 1100 C.° and 1700 C.°. The ceramic dielectric layers104,108and112, antenna106, electromagnetic bandgap layer115, outermost biocompatible layer110and innermost shielding layer114, via116, electrodes120, and the conductive pathways serving as electrical connections124can be sintered or co-fired together to form the monolithic antenna structure102including an embedded antenna conductor106, as illustrated inFIG. 4. Methods for co-firing layers of ceramic materials together to form monolithic structures for use in IMDs are described, for example, in U.S. Pat. Nos. 6,414,835 and 7,164,572, the contents of both of which are hereby incorporated by reference in their entireties.

According to one or more embodiments, the use of a co-firing technique to form a monolithic antenna structure102including an embedded antenna106allows for the manufacture of low-cost, miniaturized, hermetically sealed antenna structures100suitable for implantation within tissue and/or in direct or indirect contact with diverse body fluids.

In one or more embodiments, the plurality of different individual discrete layers or sheets of materials (or segments of tape) that comprise the various ceramic dielectric layers104,108and112, antenna106, electrodes120, electrical connections124, electromagnetic bandgap layer115, outermost biocompatible layer110and innermost shielding layer114may be printed with a metalized paste and other circuit patterns, stacked on each other, laminated together and subjected to a predetermined temperature and pressure regimen, and then fired at an elevated temperature(s) during which the majority of binder material(s) (present in the ceramic) and solvent(s) (present in the metalized paste) vaporizes and/or is incinerated while the remaining material fuses or sinters. The number of dielectric layers104,108and112may be variably selected based on the desired antenna characteristics. In some embodiments, the materials suitable for use as cofireable conductors for forming the antenna106are the biocompatible metal materials described herein or other materials suitable for the metalized paste. In one or more embodiments, the stacked laminates are then co-fired together at temperatures between about 850 C.° and 1150 C.° for LTCC materials and between about 1100 C.° and 1700 C.° for HTCC materials.

In one or more embodiments, the dielectric layers104,108and112include a plurality of planar ceramic layers. Each ceramic layer may be shaped in a green state to have a desired layer thickness. In general, the formation of planar ceramic layers starts with a ceramic slurry formed by mixing a ceramic particulate, a thermoplastic polymer and solvents. This slurry is spread into ceramic sheets of predetermined thickness, from which the solvents are volitized, leaving self-supporting flexible green sheets. Holes in certain dielectric layers104and112that will be filled with conductive material to form via116or electrical connections124are made, using any conventional technique, such as drilling, punching, laser cutting, etc., through the green sheets from which the ceramic layers104and112are formed. The materials suitable for use as cofireable ceramics include alumina (Al2O3), aluminum nitride, beryllium oxide, Silica (SiO2), Zirconia (ZrO2), glass-ceramic materials, glass suspended in an organic (polymer) binder, or mixtures thereof.

Many of the algorithms or methods described herein may be implemented by a controller that operates programs or routines stored in memory of IMD10. The controller may comprise any of a wide variety of hardware or software configurations capable of executing algorithms. Example hardware implementations of controller include implementations within an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a programmable logic device, specifically designed hardware components, one or more processors, or any combination thereof. If implemented in software, a computer readable medium, such as a memory in the IMD10, may store computer readable instructions, e.g., program code, that can be executed by the controller to carry out one of more of the techniques described herein. For example, the memory may comprise random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), flash memory, or the like.

While the system and method have been described in terms of what are presently considered to be specific embodiments, the disclosure need not be limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. The present disclosure includes any and all embodiments of the following claims.