Flexible thermal regulation device

A flexible temperature management device that uses powered thermoelectric elements to transfer thermal energy between a user and the environment to thermally regulate the user.

BACKGROUND

Humans are acutely attuned to changes in their surrounding temperature and often seek means to make themselves more thermally comfortable. A person's temperature regulation may be accomplished by modifying the temperature of the surrounding atmosphere, like HVAC systems, or by applying a thermal regulation device, such as an icepack or a heat pad, to the user themselves. The use of personal thermoregulation devices allows a user to try to achieve a desired level of thermal comfort without interfering with other people around them. Additionally, it is economical and desirable to allow a user to adjust their own thermal comfort, as each person's thermal tolerance varies.

One of the most common devices used for thermoregulation of body temperature is a “cool vest.” These are vests that are worn by a user and absorb excess body heat, thereby keeping the user more comfortable. The vests may also serve a vital health role in ensuring a user's core temperature does not climb dangerously high as the user is performing a task in a hot environment. Such vests are often worn by surgeons in operating theaters, racecar drivers during races and other users who wish to maintain a comfortable or safe body temperature in an environment or while performing tasks. The cool vest may utilize either a passive or active cooling system. In the passive cooling form, the vest or inserts, such as gel ice packs, are chilled before being worn by a user.

As the vest is worn, the vest or inserts cools the user and help maintain user comfort and body temperature. The vests in a passive cooling form are limited in duration and ability to remove excess user heat since they lack a means to maintain their cool state. As the vest or inserts absorb a user's heat, they themselves start to warm up thereby lessening the cooling affect the user experiences. If the cooling means are in the form of the inserts, the inserts can be replaced as their efficacy wanes, but the user would be required to have access to pre-chilled inserts when replacement is necessary. Often the passive cooling vests are cheaper than active cooling vests since they are not required to have additional plumbing or wiring. In the active cooling form, the vest often features tubing through which a fluid may be circulated. As the fluid is circulated about the vest it absorbs body heat from the user, thus maintaining the user in a safe and/or comfortable temperature range. The fluid is often chilled and recirculated once it exits the vest. The need to rechill the fluid and provide recirculation means the vest needs to be connected to such equipment. Often this is an insulated vessel that has some sort of heat exchanger submerged in a cold fluid or a refrigeration type unit. The constant circulation of continuously chilled fluid about the vest keeps the user in a cool and comfortable state. The drawbacks of these active cooling vests are that they are typically bulky and may require additional resources, such as power, to function. These drawbacks limit the portability and deployability of such vests due to their required infrastructure.

Another active cooling device are cool gloves. These are small device in which users place their hand, which grips a metal cylinder. A vacuum is pulled in the chamber causing the blood vessels of the user's hand to come to the surface where they contact the cool metal cylinder. The contact between the cylinder and the user's hand cools the user's blood. The metal cylinder is kept cool by pumping chilled water through it. These devices are smaller and more portable than a cool vest but are still somewhat bulky. Additionally, the user is incapable of using their hand while using the device.

Another method of thermoregulation used by many people is the use of gel packs or other contained substances that can be chilled or warmed before applying. These are applied and held or restrained against the user's skin where the user experiences coolness or warmth. As these devices are used, their efficacy wanes as they either warm up or cool down due to the user's own body heat.

There exists a need for a user wearable device that provides the user thermal comfort, either by heating or cooling and does not hinder the user and their movements.

SUMMARY OF THE INVENTION

The invention is a flexible device having active thermoregulation abilities. The device has multiple layers, including an active thermal energy transfer layer, a thermal energy spreading layer and a thermal energy exchange layer. The active thermoregulation is accomplished by utilizing thermoelectric elements in an active thermal energy transfer layer. The thermoelectric elements are embedded in a graded material matrix that allows the overall device to be flexible, while allowing the thermoelectric elements to be rigid elements. The thermoelectric elements can generate heat or extract heat from a user. The extracted heat is then transferred to the thermal energy spreading layer where the thermal energy is then distributed across the layer and transferred to the thermal energy exchange layer. The thermal energy exchange layer transfers the thermal energy extracted from a user into the surrounding environment.

DETAILED DESCRIPTION

The Active Thermal Regulation Device

FIG. 1shows the various layers of an embodiment of the active temperature control device100. The bottom layer, the adhesive layer110, has wicking elements111disposed thereon. The second layer, the thermal energy transfer layer120, has thermoelectric elements126and power circuitry128disposed thereon. The third layer, a circuitry layer130, contains a set of interconnects that electrically connect the thermoelectric elements126of the thermal energy transfer layer120. The fourth layer, a thermal energy spreading layer140, distributes thermal energy from the thermal energy transfer layer120throughout the thermal energy spreading layer140. The fifth layer, a thermal energy exchange layer150, dissipates energy from the thermal energy transfer layer120to the surrounding atmosphere. The sixth and top layer, a protective layer160, encapsulates and protects the layers of the sticker from the surrounding environment. The protective layer can be conformal to the shape, contour, and flexibility of the other device layers and the user.

The device100is placed on a user's skin. The user's body heat is then drawn into the device by the thermal energy transfer layer120. The thermoelectric elements in the thermal energy transfer layer120create a cool sink into which the user's body heat is drawn. The extracted heat is then distributed across the thermal energy spreading layer140. From there, the heat is transferred into the thermal energy exchange layer150where it is dissipated into the surrounding environment.

One or more devices,100, may be placed on a user to help regulate the user's body temperature.

A cross-section of the device100and its layers are shown inFIG. 2A. The thermal energy transfer layer120has sub-layers: an interconnect layer122and a functionally graded material layer124that includes the thermoelectric elements126and the power circuitry128.

In an alternative embodiment as shown inFIG. 2B, the device102layers are similar to the device inFIG. 1. In this embodiment, the thermoelectric elements and functionally graded material are integrated into a single layer125. In this embodiment, the individual thermoelectric elements may have their own power circuitry or may be powered by an external power source. This arrangement of the thermoelectric elements may reduce or eliminate the need for on-device power circuitry as shown in the embodiment ofFIG. 2A.

In another alternative embodiment as shown inFIG. 2C, the device104is similar to the device ofFIG. 1. In this embodiment, the first interconnect layer122, the thermoelectric elements126and the power circuitry128compose the thermal energy transfer layer120. Rather than placing the thermoelectric elements126and power circuitry128in functionally graded material as shown in the previous embodiments ofFIGS. 2A and 2B, the thermoelectric elements126and power circuitry128are discrete elements that are placed in the device. The discrete elements126and128contain functionally graded material about the thermoelectric elements and power circuitry to enable each to flex.

The device100contains thermoelectric elements that actively cool or heat the user. The thermoelectric elements use the Peltier Effect to affect temperature change. The Peltier Effect occurs when current is passed through a junction between two different conductors. The flow of current causes the junction to either gain or lose heat depending on the directions of the current flow. Two conductors, a N-type and a P-type, are in contact with each other, and current is passed through them. As the current flows through the conductor pair, so does the heat, as one side of the conductor pair cools down and the other side heats up.

The thermoelectric element conductors can be composed of thermoelectric material such as Bismuth chalcogenides and others. Multiple conductors can be arranged thermally in parallel and/or electrically connected in series to increase their thermal capabilities. Thermoelectrics do not have any moving parts. Therefore, maintenance is minimal and the working life span of such devices is extended.

Functionally graded material (FGM) is a material that has varying mechanical properties across its dimensions. In the case of the device100, the FGM has varying strain properties, meaning that the stiffness or rigidity of the material is varied. The FGM surrounds the rigid thermoelectric elements (TEs) to form a matrix that is stiffer around the TEs and gradually gets less so away from the TEs. The mechanical properties of the FGM are capable of being modified to desired levels during the manufacturing process.

Thermal Energy Transfer Layer

The thermoelectric elements (TEs) in the functionally graded material (FGM) matrix of the thermal energy transfer layer300are shown inFIGS. 3A and 3B. P-type conductor material304and N-type conductor material306are disposed in the FGM matrix302. The conductor material,304and306, are arranged in parallel rows and spaced in an alternating pattern as shown inFIG. 3B.

The conductor materials304and306, as shown inFIG. 3B, are each rectangularly shaped, but may be alternate shapes such as round or other shapes as desired. Alternatively, the conductor materials may have different shapes. It may be desirable to have alternatively shaped conductor material depending on the desired mechanical properties for the layer.

The TEs,404and406, are shown disposed between the two interconnects,410and412, inFIG. 4A.FIG. 4Bshows the TEs,404and406, ofFIG. 4Ain a top view, showing the details of the interconnects410and412. The first interconnect410connects the bottom portions of the p- and n-type conductor materials404and406of the TEs. The second interconnect412connects the top portion of the TEs. As shown inFIG. 4B, the TEs404and406are connected in a staggered fashion, i.e., the TEs404and406are connected in series. Further, the connections between the elements404and406are staggered vertically between the first and second interconnects. The vertically staggered series connection pathways between the TEs404and406create the hot and cold side of the thermoelectric elements. The direction of current flow through the array of TEs determines whether the top or bottom side is the cold side. With the cold side towards the user's skin, the TEs function as a heat sink, removing thermal energy from the user.

FGM402surrounds the TEs, as shown inFIG. 4A. The FGM allows the layer400to flex without disrupting the interconnects410and412and minimizes the strain, induced by flexing the layer, into the individual TEs. The interconnects410and412are also flexible and ideally are strain matched to the TEs,404and406, and the surrounding FGM402. By strain matching the various components, the layer can flex and bend without dislodging the components and connections.

Power circuitry408is disposed in the layer400and is connected to the interconnects410and412to power the TEs404and406. The power circuitry408is also constructed in manner to maintain the flexibility of the layer400. In this embodiment, a flexible polymer base is constructed with disposed interconnects. It may be preferred to have the interconnect base be strain matched to the TEs disposed thereon, i.e., the base is stiffer where the TEs are located.

Thermal Energy Spreading Layer

An embodiment of the thermal energy spreading layer140is shown inFIGS. 5A and 5B. Flexible thermal energy spreading elements504are disposed in a flexible matrix502. In the embodiment shown, the thermal energy spreading elements504are thermally conductive traces that are printed onto the matrix material502. Alternatively, thermal energy spreading elements504may be thermally conductive structures that are then suspended in the matrix502. The matrix502may be FGM or other strain suitable material. The thermally conductive structures disposed on the layer spread the heat transferred from the thermal energy transfer layer120across the layer140. The spread of thermal energy enlarges the area through which the heat may then be transferred to the thermal energy exchange layer150. The increased thermal transfer capacity through the layer allows for greater efficiency in dissipating the heat from the user.

Alternatively, the heat spreading layer can have a flexible heat pipe structure, not shown. A heat pipe is a sealed device containing a liquid that is readily vaporized into a gas. The gas then expands to fill the device, thereby increasing the surface area of the gas available for thermal energy transfer. In the device100, the heat pipe is a flexible structure, able to bend and flex with the device without damaging the structure. As thermal energy is transferred from the thermal energy transfer layer130into the flexible heat pipe of the thermal energy spreading layer140, the gas within the heat pipe heats. The heated gas then flows evenly throughout the heat pipe, thereby spreading the thermal energy over a large area. The thermal energy of the gas can then be transferred to the next layer, the thermal exchange layer150.

Ideally the strain properties of the layer140should match the strain properties of the other layers in the device. Strain matching assists in maintaining the overall structure of the device100when the device100is flexed.

Thermal Energy Exchange Layer

An embodiment of the thermal energy exchange layer150is shown inFIGS. 6A and 6B. The layer150consists of a conductive polymer base602, which receives thermal energy from the thermal energy spreading layer140. The thermal energy is then transferred into thermal dissipating structures604. The vertical configuration of the structures604increases the surface area through which the heat may be convected away from the thermal energy exchange layer150. In the embodiment shown, the structures604are filled with a thermally conductive polymer. By using thermally conductive materials, the user's heat is more efficiently transferred through the device100and evacuated by the thermal energy exchange layer150. The dissipating structures604can be formed, by a process such as injection molding or other suitable means. Alternatively, the structures may be placed on or created in-situ on the base layer602. Further, the base602and604may be the same thermally conductive material with the structures604later formed thereon using a forming process. Other structure604designs exist and may be utilized as needed. The amount of heat to dissipate and the manufacturing process used may determine the design of the structures604.

Adhesive Layer

The adhesive layer100, shown inFIG. 1, provides the connecting interface between the device100and the user. An embodiment of the adhesive layer is shown inFIGS. 7A and 7B. The layer features thermally conductive material702, adhesive704and wicking elements706. The thermally conductive material702assists in the transfer of thermal energy from the user into the device100. This provides a more efficient pathway through which heat may be directed into the device100. Further, the device100may be designed such that the thermally conductive material702channels the thermal energy to a desired part of the device100, such as the TEs of the thermal energy transfer layer120.

An adhesive portion704of the layer700affixes the device100to the skin of the user. In the embodiment shown inFIGS. 7A and 7B, the adhesive coats the base of the polymer element704. A wicking element706is also disposed in the adhesive portion704. The element706assists in managing and transferring moisture exuded from the user. If the moisture was not managed and transferred away from the user's skin, user comfort and device affixment to the user could be compromised. The wicking element706, as shown in the embodiment ofFIGS. 7A and 7B, draws moisture away from the user's skin into the wicking element706. The adhesive portion704may be constructed of hydrophilic material that helps conduct moisture through the layer. The moisture may then be transferred through the device100, where it may be trapped or evaporated into the surrounding atmosphere. The adhesive used can be a number of potential temporary, skin safe adhesives. In the embodiment shown, the adhesive is a medical-grade adhesive used to affix medical devices and sensors to a user's skin temporarily. Alternatively, the adhesive may be a more permanent type.

Another embodiment of the adhesive layer is shown inFIGS. 8A and 8B. In this embodiment, the wicking elements806are holes. The holes806allow moisture to travel from the user's skin and into the device100. Alternatively, the holes806may extend through the entire device100. The moisture from the user's skin may be drawn through the holes806by capillary action. Alternatively, the moist vapor from the user can be exhausted through the holes806into the surrounding environment.

The adhesive portions804are interspersed with the thermally conductive material802as in the previous embodiment shown inFIGS. 7A and 7B.

Another embodiment of the adhesive layer is shown inFIGS. 9A and 9B. In this embodiment, the thermally conductive material902is concentrated under the TEs of the thermal energy transfer layer130. This configuration channels the heat transferred from a user into the thermal energy transfer layer130thereby increasing user comfort. The adhesive portion904features the wicking elements906. As with the previous embodiment, the wicking elements906are holes. The holes may extend through the adhesive layer or through the device.

FIG. 10shows a cross-section of an alternative embodiment of the thermal regulation device1000. The device is composed of an adhesive layer1010which has wicking pores1012that extend through the entire device1000. The adhesive layer1010interfaces with and affixes the device1000to the user's skin. As with previous embodiments, the layer1010may contain thermally conductive material to assist with the conduction of thermal energy between the device1000and a user. The wicking pores1012assist in the removal of moisture from the user's skin. Trapped moisture may hinder the adhesives ability to affix the device1000to the user's skin and may decrease a user's comfort. The TEs and power circuitry in FGM are contained in the thermal energy transfer layer1040, which is atop a thermal energy spreading layer1030. The thermal energy spreading layer1030distributes the thermal energy from the user across the area of the TEs in the energy transfer layer1040. Insulation1020surrounds the energy transfer layer1040.

FIG. 11illustrates a view of one thermoelectric conductor, showing the graded reinforcement decreasing in density the further away from the conductor. The changes in reinforcement agent, which may be particles made from material similar in composition to the thermoelectric conductor, increase the mechanical modulus of the surrounding material and create the grading to allow the structure to be flexible and stretchable.

FIG. 12further illustrates the interconnection of the TEs1204and1206in the FGM matrix1220. The top interconnect1208alternates with the upper interconnect1210in connecting the alternating TEs1204and1206. The interconnect1212links the rows of the TEs, keeping the elements thermally parallel and electrically connected in series. The FGM1220is graded to be stiffer about the TEs and interconnects.

FIG. 13illustrates a method of powering the device. In the embodiment shown, the device100is powered wirelessly using inductive power circuitry, such as inductive loop charging circuitry. The inductive power circuitry uses radiating power1304emitted from a source1302to power the device100. One or more inductive charging base stations could be strategic placed in an environment in which one or more users are wearing one of the disclosed devices. As the users wearing the device nears one of the inductive charging base stations, the device is activated by the inductive charging loop and can optionally communicate with other base stations.

A user can set user-specific preferences through a user interface at a particular base station, which can command the network of base stations to power the user's device on and off according to the user-specific preferences. The base stations can also be used to collect data about the user(s) wearing the devices and/or the energy and temperature data in the environment in which the users and base stations interact.

Alternatively, the device100may be powered by a power source disposed on the device100. The power source may be wired or wirelessly rechargeable, replaceable or not. In another embodiment, the device may be powered by electricity delivered by a wire or cord from an external source. Varying the supplied power to the device will vary the rate of thermal energy the TEs can transfer across themselves.

The flexible thermal management device is a flexible device that a user affixes to their skin. Once affixed, the unit uses active thermal management to remove thermal energy from a user. The powered thermoelectric elements create a temperature differential across their layer. The orientation of the temperature differential is determined by the flow of current through the thermoelectric elements. By creating the cool side of the thermoelectric elements oriented towards the user, the user's heat is drawn into the device and into the thermoelectric elements. The heat is then transferred to the outer side of the thermoelectric elements where it is dissipated through the thermal energy exchange layer that convects the extracted heat into the environment.

Alternatively, the direction of current flow through the TEs may be revered, which reverses the direction of the thermal differential. The reoriented thermal differential can then add thermal energy to the user, thereby warming the user.