WO2020081469A1

WO2020081469A1 - Thermoelectric systems with thermally conductive materials

Info

Publication number: WO2020081469A1
Application number: PCT/US2019/056157
Authority: WO
Inventors: Douglas W. Tham; Haifan Liang
Original assignee: Tham Douglas W; Haifan Liang
Priority date: 2018-10-16
Filing date: 2019-10-14
Publication date: 2020-04-23

Abstract

The present disclosure provides an electronic device comprising a heat collecting unit, a thermoelectric generator, thermally conductive material, and a heat expelling unit. The present disclosure also provides a method for collecting thermal energy comprising providing an electronic device comprising a heat collecting unit, a thermoelectric generator, thermally conductive material, and a heat expelling unit; and positing the electronic device so that the heat collecting unit is disposed adjacent to a body surface of the user.

Description

THERMOELECTRIC SYSTEMS WITH THERMALLY CONDUCTIVE MATERIALS

CROSS-REFERENCE

[0001] This application claims priority to U.S. Provisional Patent Application No.

62/746,200, filed on October 16, 2018, which is entirely incorporated herein by reference.

BACKGROUND

[0002] Over 15 Terawatts of heat is lost to the environment annually around the world by heat engines that require petroleum as their primary fuel source. This is because these engines only convert about 30 to 40% of petroleum's chemical energy into useful work. Waste heat generation is an unavoidable consequence of the second law of thermodynamics.

[0003] The term“thermoelectric effect” encompasses the Seebeck effect, Peltier effect and Thomson effect. Solid-state cooling and power generation based on thermoelectric effects typically employ the Seebeck effect or Peltier effect for power generation and heat pumping.

The utility of such conventional thermoelectric devices is, however, typically limited by their low coefficient-of-performance (COP) (for refrigeration applications) or low efficiency (for power generation applications).

[0004] Thermoelectric device performance may be captured by a so-called thermoelectric figure-of-merit, Z = S2 s / k, where‘S’ is the Seebeck coefficient,‘o’ is the electrical conductivity, and‘k’ is thermal conductivity. Z is typically employed as the indicator of the COP and the efficiency of thermoelectric devices— that is, COP scales with Z. A dimensionless figure-of-merit, ZT, may be employed to quantify thermoelectric device performance, where‘T’ can be an average temperature of the hot and the cold sides of the device.

[0005] Applications of conventional semiconductor thermoelectric coolers are rather limited, as a result of a low figure-of-merit, despite many advantages that they provide over other refrigeration technologies. In cooling, low efficiency of thermoelectric devices made from conventional thermoelectric materials with small figure-of-merit limits their applications in providing efficient thermoelectric cooling.

SUMMARY

[0006] Provided herein are thermoelectric systems with thermally conductive materials.

Foils or sheets (or other form factors) of highly thermally conductive materials can be used to collect, diffuse and transfer heat between heat collecting units (e.g., skin contact plate) and thermoelectric generators. Foils or sheets of highly thermally conductive material can be used to collect, diffuse and transfer heat between thermoelectric generators and heat expelling units (e.g., watch case). For example, a large foil or sheet can collect heat from a large effective area on the skin, routing and concentrating the heat flow into the smaller area of the thermoelectric generator. A large foil or sheet can also diffuse heat from the small area of the thermoelectric generator into a large area of the wearable device case for expulsion into the environment. In some cases, the foil or sheet can be backed with adhesive on one or both faces for easy attachment and die cut to the correct shape and size for application.

[0007] Because a wearable device may have an electrically and thermally insulating back surface in contact with the body to enable wireless charging of the device, thermal resistance between the body and the thermoelectric generator of the wearable device may be high. The application of the foil or sheet as thermally conductive materials can decrease the high thermal resistance exiting between the body and the thermoelectric generator of a wearable device. The thermally conductive materials may include conductive metals (e.g., copper, aluminum), conductive ceramic (e.g., alumina, boron nitride), and graphite (e.g., the pyrolytic variety). The thermally conductive material may have the particular advantage of being highly thermally conductive yet not particularly electrically conductive to deleteriously impact wireless charging.

[0008] In some cases, the application of the foil or sheet as thermally conductive materials can enable design flexibility, allowing small, inexpensive, and rectangular thermoelectric generator to be placed at any location inside a wearable device while not impacting thermal transfer for successful thermal energy harvesting. In some cases, the application of the foil or sheet as thermally conductive materials can enable the use of insulating watch case materials (e.g., plastic or insulating ceramic) by diffusing heat flow laterally through the thermal foil and utilizing the entire watch case for thermal expulsion.

[0009] In an aspect, an electronic device comprises a heat collecting unit that is configured to be positioned adjacent to a body surface of a user, wherein the heat collecting unit is configured to collect thermal energy from the body surface of the user; a thermoelectric generator comprising a plurality of thermoelectric elements, wherein the thermoelectric generator is in thermal communication with the heat collecting unit; thermally conductive material between the heat collecting unit and the thermoelectric generator, wherein the thermally conductive material has a thermal resistance of at most 10 K/W, wherein the thermally conducive material is in thermal communication with the thermoelectric generator along a first area and the heat collecting unit along a second area, wherein a ratio of the first area to the second area is at most 0.5; and a heat expelling unit in thermal communication with the thermoelectric generator.

[0010] In some embodiments, the ratio of the first area to the second area is at most 0.25. In some embodiments, the ratio of the first area to the second area is at most 0.1. In some embodiments, the thermoelectric generator is disposed in a position offset from the center of the heat collecting unit. In some embodiments, the thermally conductive material is in sheet form. In some embodiments, a thickness of the sheet is at most 2 millimeters. In some embodiments, the thickness of the sheet is at most 1 millimeter.

[0011] In some embodiments, the electronic device further comprises an additional thermally conductive material adjacent to the thermoelectric generator, wherein the additional thermally conductive material has a thermal resistance of at most 10 K/W, wherein the additional thermally conducive material is in thermal communication with the thermoelectric generator along the first area and the heat expelling unit along a third area, wherein a ratio of the first area to the third area is at most 0.5.

[0012] In some embodiments, the additional thermally conductive material is in sheet form. In some embodiments, a thickness of the sheet is at most 2 millimeters. In some embodiments, the thermoelectric generator generates power upon flow of the thermal energy from the heat collecting unit to the thermoelectric generator. In some embodiments, the electronic device further comprises an electronic display with a user interface for displaying information to the user. In some embodiments, the plurality of thermoelectric elements comprises an n-type semiconductor element comprising a periodic array of holes or wires. In some embodiments, the plurality of thermoelectric elements comprises a p-type semiconductor element that is adjacent to the n-type semiconductor element, wherein the p-type semiconductor element comprises a periodic array of holes or wires.

[0013] In another aspect, a method for collecting thermal energy comprises providing an electronic device comprising (i) a heat collecting unit that is configured to collect thermal energy from a body surface of a user; (ii) a thermoelectric generator comprising a plurality of thermoelectric elements, wherein the thermoelectric generator is in thermal communication with the heat collecting unit; (iii) thermally conductive material between the heat collecting unit and the thermoelectric generator, wherein the thermally conductive material has a thermal resistance of at most 10 K/W, wherein the thermally conducive material is in thermal communication with the thermoelectric generator along a first area and the heat collecting unit along a second area, wherein a ratio of the first area to the second area is at most 0.5; and (iv) a heat expelling unit in thermal communication with the thermoelectric generator; and positing the electronic device so that the heat collecting unit is disposed adjacent to a body surface of the user, such that (i) the thermal energy flows from the body surface of the user through the thermally conductive material to the thermoelectric generator, and (ii) at least a portion of the thermal energy is directed through the thermoelectric generator to the heat expelling unit.

[0014] In some embodiments, the thermally conductive material is in sheet form. In some embodiments, a thickness of the sheet is at most 2 millimeters. In some embodiments, the electronic device further comprises an additional thermally conductive material adjacent to the thermoelectric generator, wherein the additional thermally conductive material has a thermal resistance of at most 10 K/W, wherein the additional thermally conducive material is in thermal communication with the thermoelectric generator along the first area and the heat expelling unit along a third area, wherein a ratio of the first area to the third area is at most 0.5. In some embodiments, the additional thermally conductive material is in sheet form. In some

embodiments, a thickness of the sheet is at most 2 millimeters.

[0015] In some embodiments, the thermoelectric generator has a rectangular shape. In some embodiments, the thermally conductive material is a graphite sheet. In some embodiments, the electronic device has an internal volume opposite the thermoelectric generator.

[0016] Another aspect of the present disclosure provides a non-transitory computer readable medium comprising machine executable code that, upon execution by one or more computer processors, implements any of the methods above or elsewhere herein.

[0017] Another aspect of the present disclosure provides a system comprising one or more computer processors and computer memory coupled thereto. The computer memory comprises machine executable code that, upon execution by the one or more computer processors, implements any of the methods above or elsewhere herein.

[0018] Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only illustrative embodiments of the present disclosure are shown and described. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

INCORPORATION BY REFERENCE

[0019] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and/or take precedence over any such contradictory material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings (also“figure” and“FIG.” herein), of which:

[0021] FIG. 1 shows an example of an assembly of an electronic device;

[0022] FIG. 2 shows an example of an assembly of an electronic device with thermally conductive material between a heat collecting unit and a thermoelectric generator;

[0023] FIG. 3 shows an example of an assembly of an electronic device with thermally conductive material between a heat collecting unit and a thermoelectric generator, and with additional thermally conductive material above a thermoelectric generator; and

[0024] FIG. 4 shows a computer system that is programmed or otherwise configured to implement methods provided herein.

DETAILED DESCRIPTION

[0025] While various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.

[0026] The term“nanostructure,” as used herein, generally refers to structures having a first dimension (e.g., width) along a first axis that is less than about 1 micrometer (“micron”) in size. Along a second axis orthogonal to the first axis, such nanostructures can have a second dimension from nanometers or smaller to microns, millimeters or larger. In some cases, the dimension (e.g., width) is less than about 1000 nanometers (“nm”), or 500 nm, or 100 nm, or 50 nm, or smaller. Nanostructures can include holes formed in a substrate material. The holes can form a mesh having an array of holes. In other cases, nanostructure can include rod-like structures, such as wires, cylinders or box-like structure. The rod-like structures can have circular, elliptical, triangular, square, rectangular, pentagonal, hexagonal, heptagonal, octagonal or nonagonal, or other cross-sections.

[0027] The term“nanowire,” as used herein, generally refers to a wire or other elongate structure having a width or diameter that is less than or equal to about 1000 nm, or 500 nm, or 100 nm, or 50 nm, or smaller.

[0028] The term“n-type,” as used herein, generally refers to a material that is chemically doped (“doped”) with an n-type dopant. For instance, silicon can be doped n-type using phosphorous or arsenic. [0029] The term“p-type,” as used herein, generally refers to a material that is doped with a p-type dopant. For instance, silicon can be doped p-type using boron or aluminum.

[0030] The term“metallic,” as used herein, generally refers to a substance exhibiting metallic properties. A metallic material can include one or more elemental metals.

[0031] The term“adjacent” or“adjacent to,” as used herein, includes‘next to’,‘adjoining’, ‘in contact with’, and‘in proximity to’. In some instances, adjacent components are separated from one another by one or more intervening layers. The one or more intervening layers may have a thickness less than about 10 micrometers (“microns”), 1 micron, 500 nanometers (“nm”), 100 nm, 50 nm, 10 nm, 1 nm, 0.5 nm or less. For example, a first layer adjacent to a second layer can be in direct contact with the second layer. As another example, a first layer adjacent to a second layer can be separated from the second layer by at least a third layer.

[0032] Successful thermal transfer for energy harvesting may require heat to pass from the heat collecting unit, through the thermoelectric generator, into the heat expelling unit and out into the environment. At each stage there may be a balance to be struck between thermal series resistance and thermal spreading resistance. Thermal series resistance may be typified by poor thermal contact at interfaces as well as the use of thermally insulating materials to conduct heat. Thermal spreading resistance may be encountered at a situation when the heat current passes from a larger component into a smaller one (e.g., heat transfers between surfaces of different area) and the heat current moves laterally in the larger component near the interface before it can enter the smaller one. The thermal spreading (or crowding) resistance may increase thermal resistance substantially when the size disparity is large, or the large component is thin and has a high thermal resistivity.

Electronic device with thermally conductive material

[0033] In an aspect, an electronic device may comprise a heat collecting unit, a

thermoelectric generator, thermally conductive material between the heat collecting unit and the thermoelectric generator, and a heat expelling unit. The electronic device may be a portable electronic device. The electronic device may be mobile phones, PCs, tablets, printers, consumer electronics, and appliances. The electronic devices may be wearable devices, including but not limited to, Fitbit, Apple watch, Samsung health, Misfit, Xiaomi Mi band, and Microsoft band. The electronic device may be a watch. The watch may be a quartz wrist watch.

[0034] The heat collecting unit may be configured to be positioned adjacent to a heat source. The heat collecting unit may collect heat from the heat source. The heat source may be a body surface of a user. The heat collecting unit may be configured to be positioned adjacent to a body surface of a user. The heat collecting unit may be configured to collect thermal energy from the body surface of the user. The heat collecting unit may provide the heat to adjacent components (e.g., thermoelectric generator). The heat collecting unit may be in any design, shape, and/or size. Examples of possible shapes or designs include but are not limited to: mathematical shapes (e.g., circular, triangular, square, rectangular, pentagonal, or hexagonal), two-dimensional geometric shapes, multi-dimensional geometric shapes, curves, polygons, polyhedral, polytopes, minimal surfaces, ruled surfaces, non-orientable surfaces, quadrics, pseudo spherical surfaces, algebraic surfaces, miscellaneous surfaces, riemann surfaces, box-drawing characters, cuisenaire rods, geometric shapes, shapes with metaphorical names, symbols, Unicode geometric shapes, other geometric shapes, partial shapes or combination of shapes thereof. The heat collecting unit may be part of the electronic device. If the electronic device is a watch, the heat collecting unit of the watch may include the watch back. In this situation, the watch back may be held against the skin of a user by a watch band. The watch back may collect the heat of the user and direct the heat into the thermoelectric generator.

[0035] The heat collecting unit may be formed of a metallic (or metal-containing) material. The metallic material may include one or more elemental metals. For example, the metallic material may include one or more of aluminum, copper, titanium, iron, steel, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium, and their alloys. The heat collecting unit may be formed of a semiconductor- containing material, such as silicon or a silicide. The heat collecting unit may be formed of a polymeric material. The polymeric material may include one or more polymers. For example, the polymeric material may include one or more of polyvinyl chloride, polyvinylidene chloride, polyethylene, polyisobutene, and poly[ethylene-vinylacetate] copolymer. The heat collecting unit may be formed of a composite material. The composite material may include, for example, reinforced plastics, ceramic matrix composites, and metal matrix composites. The heat collecting unit may comprise a stainless-steel plate, an aluminum plate, or a thin glass plate.

[0036] The thermoelectric generator may comprise a plurality of thermoelectric elements. The thermoelectric generator may be in thermal communication with the heat collecting unit.

The plurality of thermoelectric elements may be in thermal communication with the heat collecting unit. The thermoelectric generator may be used with the electronic device. The thermoelectric generator may be used in consumer electronic devices (e.g., smart watches, portable electronic devices, and health / fitness tracking devices). The thermoelectric generator may be used in an industrial setting, such as at a location where there is heat loss. The thermoelectric generator can be used to generate power upon the application of a temperature gradient across the plurality of thermoelectric elements. Such power can be used to provide electrical energy to various types of devices, such as consumer electronic devices. [0037] The thermoelectric generator may be disposed in a position offset from the center of the heat collecting unit. In this situation, the distance between the center point of the heat collecting unit and the center point of the thermoelectric generator may be at least about 1 millimeter (“mm”), 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, or greater. In some cases, the distance between the center point of the heat collecting unit and the center point of the thermoelectric generator may be at most about 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm,

1 mm, or less.

[0038] A given thermoelectric element of the plurality of thermoelectric elements can have various non-limiting advantages and benefits. The given thermoelectric element can have substantially high aspect ratios, uniformity of holes or wires, and figure-of-merit, ZT, which can be suitable for optimum thermoelectric performance. With respect to the figure-of-merit, Z can be an indicator of coefficient-of-performance (COP) and the efficiency of the given

thermoelectric element, and T can be an average temperature of the hot and the cold sides of the given thermoelectric element. The figure-of-merit (ZT) of the given thermoelectric element may be at least about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,

1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 or greater at 25°C. The figure-of-merit may be from about 0.01 to 3, 0.1 to 2.5, 0.5 to 2.0 or 0.5 to 1.5 at 25°C. The figure of merit (ZT) can be a function of temperature. The ZT may increase with temperature.

[0039] The plurality of thermoelectric elements may be disposed between electrodes. The plurality of thermoelectric elements may comprise an array of nanostructures (e.g., holes or wires). The array of nanostructures can include a plurality of holes or elongate structures, such as wires (e.g., nanowires). The holes or wires can be ordered and have uniform sizes and distributions. As an alternative, the holes or wires may not be ordered and may not have a uniform distribution. There may not be long range order with respect to the holes or wires. The holes or wires may intersect each other in random directions.

[0040] The plurality of thermoelectric elements may be flexible or substantially flexible. A flexible material can be a material that can be conformed to a shape, twisted, or bent without experiencing plastic deformation. This can enable the thermoelectric elements to be used in various settings, such as settings in which contact area with a heat source or heat sink may be important. The plurality of thermoelectric elements can include at least one semiconductor element which can be flexible. Individual semiconductor elements may be rigid but

substantially thin (e.g., 500 nm to 1 mm or 1 micrometer to 0.5 mm) such that they provide a flexible thermoelectric element when disposed adjacent one another [0041] The thermally conductive material may be placed between the heat collecting unit and the thermoelectric generator. The thermally conductive material may have a thermal resistance of at most about 10 K/W, 9 K/W, 8 K/W, 7 K/W, 6 K/W, 5 K/W, 4 K/W, 3 K/W, 2 K/W, 1 K/W, or less. In some cases, the thermally conductive material may have a thermal resistance of at least about 1 K/W, 2 K/W, 3 K/W, 4 K/W, 5 K/W, 6 K/W, 7 K/W, 8 K/W, 9 K/W, 10 K/W or greater. The work-life time of the thermally conductive material may be at least about 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 1 day, 2 days, or longer. In some cases, the work-life time of the thermally conductive material may be at most about 2 days, 1 day, 20 hours, 15 hours, 10 hours, 5 hours, 1 hour, or shorter.

[0042] The thermally conducive material may be in thermal communication with the thermoelectric generator along a first area and the heat collecting unit along a second area. The size of the first area may be at least about 0.01 square centimeters (“cm²”), 0.02 cm², 0.03 cm², 0.04 cm², 0.05 cm², 0.06 cm², 0.07 cm², 0.08 cm², 0.09 cm², 0.1 cm², 0.2 cm², 0.3 cm², 0.4 cm², 0.5 cm², 0.6 cm², 0.7 cm², 0.8 cm² or greater. In some cases, the size of the first area may be at most about 0.8 cm², 0.7 cm², 0.6c m², 0.5 cm², 0.4 cm², 0.3 cm², 0.2 cm², 0.1 cm², 0.09 cm²,

0.08 cm², 0.07 cm², 0.06 cm², 0.05 cm², 0.04 cm², 0.03 cm², 0.02 cm², 0.01 cm², or smaller. The size of the second area may be at least about 0.1 cm², 0.2 cm², 0.3 cm², 0.4 cm², 0.5 cm², 0.6 cm², 0.7 cm², 0.8 cm², 0.9 cm², 1 cm², 2 cm², 3 cm², 4 cm², or greater. In some cases, the size of the second area may be at most 4 cm², 3 cm², 2 cm², 1 cm², 0.9 cm², 0.8 cm², 0.7 cm², 0.6 cm², 0.5 cm², 0.4 cm², 0.3 cm², 0.2 cm², 0.1 cm², or smaller. A ratio of the first area to the second area may be at most 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, or less. In some cases, the ratio of the first area to the second area may be at least 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, or greater.

[0043] The thermally conducive material may be formed of conductive material. The conductive material may comprise metallic (or metal-containing) material, conductive ceramics, and graphite. The metallic material may include one or more elemental metals. For example, the metallic material may include one or more of aluminum, titanium, copper, iron, steel, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium, and their alloys. The conductive ceramics may comprise alumina, boron nitride, lead oxide, ruthenium dioxide, bismuth ruthenate, and bismuth iridate. The thermally conducive material may be formed of a semiconductor-containing material, such as silicon or a silicide. The thermally conducive material may be formed of a polymeric material. The polymeric material may include one or more polymers. For example, the polymeric material may include one or more of polyvinyl chloride, polyvinylidene chloride, polyethylene, polyisobutene, and poly[ethylene-vinylacetate] copolymer. The thermally conducive material may be formed of a composite material. The composite material may include, for example, reinforced plastics, ceramic matrix composites, and metal matrix composites. The thermally conductive material may comprise graphite or pyrolytic graphite.

[0044] The thermally conductive material may be in any form, including, but not limited to, sheet form, tile form, wrap form, tape form, or foil form. If the thermally conductive material is in sheet form, a thickness of the sheet may be at most 3 mm, 2 mm, 1 mm, 0.9 mm, 0.8 mm, 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm, or less. In some cases, the thickness of the sheet may be at least 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm or greater.

[0045] The heat expelling unit may be in thermal communication with the thermoelectric generator. The heat expelling unit may be in thermal communication with the plurality of thermoelectric elements. In some cases, the heat expelling unit may be in direct contact with the thermoelectric generator. In other cases, the heat expelling unit may be in contact with the thermoelectric generator through conductive material. The conductive material may be a thermally conductive material. The heat expelling unit may be in any design, shape, and/or size. Examples of possible shapes or designs include but are not limited to: mathematical shapes (e.g., circular, triangular, square, rectangular, pentagonal, or hexagonal), two-dimensional geometric shapes, multi-dimensional geometric shapes, curves, polygons, polyhedral, polytopes, minimal surfaces, ruled surfaces, non-orientable surfaces, quadrics, pseudospherical surfaces, algebraic surfaces, miscellaneous surfaces, riemann surfaces, box-drawing characters, cuisenaire rods, geometric shapes, shapes with metaphorical names, symbols, Unicode geometric shapes, other geometric shapes, partial shapes or combination of shapes thereof.

[0046] The heat expelling unit may be formed of a metallic (or metal-containing) material. The metallic material may include one or more elemental metals. For example, the metallic material may include one or more of aluminum, titanium, iron, steel, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium, and their alloys. The heat expelling unit may be formed of a semiconductor-containing material, such as silicon or a silicide. The heat expelling unit may be formed of a polymeric material. The polymeric material may include one or more polymers. For example, the polymeric material may include one or more of polyvinyl chloride, polyvinylidene chloride, polyethylene, polyisobutene, and poly [ethyl ene-vi nyl acetate] copolymer. The heat expelling unit may be formed of a composite material. The composite material may include, for example, reinforced plastics, ceramic matrix composites, and metal matrix composites. The heat expelling unit may comprise a metallic aluminum, a stainless steel, ceramic zirconium dioxide, plastic, or any polymer blend or co-polymer. The plastic may comprise acrylonitrile butadiene styrene

(“ABS”), polystyrene (“PS”), or polyvinyl chloride (“PVC”).

[0047] The heat expelling unit may expel the thermal energy from the thermoelectric generator. The heat expelling unit may expel the thermal energy from the thermoelectric generator to the environment. The heat expelling unit can be sufficiently thermally conductive to remove heat from the thermoelectric generator and expel it to the environment. If the electronic device is a watch, the heat expelling unit may be a watch case.

[0048] The heat expelling unit may comprise one or more heat sinks. The heat expelling unit may be connected to one or more heat sinks. The heat sink can aid in collecting or dissipating heat. A heat sink can include one or more heat fins which can be sized and arranged to provide increased heat transfer area. A heat sink may be any flexible material, which can be sufficiently thermally conductive to provide low internal thermal resistance and sufficiently thin to bend in a flexible manner. The heat sink can have a thickness from about 0.1 millimeters (mm) to 100 mm, or 1 mm to 10 mm. The heat sink can have a thickness less than 0.1 mm. The heat sink can have a thickness more than 100 mm. The heat sink can be within or in contact with a matrix.

The matrix can be a polymer foil, elastomeric polymer, ceramic foil, semiconductor foil, insulator foil, insulated metal foil or combinations thereof. To increase the surface area presented to the environment for effective thermal transfer, the matrix may be patterned with dimples, corrugations, pins, fins or ribs.

[0049] The heat sinks may be integrated with the electronic device disclosed herein. The electronic device may be a portable electronic device. The electronic devices may be mobile phones, PCs, tablets, printers, consumer electronics, and appliances. The electronic devices may be wearable devices, including but not limited to, Fitbit, Apple watch, Samsung health, Misfit, Xiaomi Mi band, and Microsoft band. The electronic device may be a watch. If the electronic device is a watch, the heat sink may be a watch case or part of the watch case. Heat sinks integrated with electronic device can be used with other objects, such as objects with surfaces that can provide for a temperature gradient. As an alternative, the heat sink may be separated from the electronic device.

[0050] Heat sink may be formed with electrically insulating material, which can be sufficiently thin (e.g., thickness from about 0.01 millimeter to 1 millimeter) to present a low thermal resistance (e.g., thermal resistance of at most 1 K/W). Examples include polymer foil (e.g., polyethylene, polypropylene, polyester, polystyrene, polyimide, etc.); elastomeric polymer foil (e.g., polydimethylsilazane, polyisoprene, natural rubber, etc.); fabric (e.g., conventional cloths, fiberglass mat, etc.); ceramic, semiconductor, or insulator foil (e.g., glass, silicon, silicon carbide, silicon nitride, aluminum oxide, aluminum nitride, boron nitride, etc.); insulated metal foil (e.g., anodized aluminum or titanium, coated copper or steel, etc.); or combinations thereof. The electrically insulating material can be both flexible and stretchable when an elastomeric material is used.

[0051] The electronic device may further comprise an additional thermally conductive material. The additional thermally conductive material may be adjacent to the thermoelectric generator. In some cases, the additional thermally conductive material may replace part of or the whole heat expelling unit. In other cases, the additional thermally conductive material may be placed adjacent to the heat expelling unit. The additional thermally conductive material may have a thermal resistance of at most about 10 K/W, 9 K/W, 8 K/W, 7 K/W, 6 K/W, 5 K/W, 4 K/W, 3 K/W, 2 K/W, 1 K/W, or less. In some cases, the additional thermally conductive material may have a thermal resistance of at least about 1 K/W, 2 K/W, 3 K/W, 4 K/W, 5 K/W, 6 K/W, 7 K/W, 8 K/W, 9 K/W, 10 K/W or greater. The work-life time of the additional thermally conductive material may be at least 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 1 day, 2 days, or longer. In some cases, the work-life time of the additional thermally conductive material may be at most about 2 days, 1 day, 20 hours, 15 hours, 10 hours, 5 hours, 1 hour, or less.

[0052] The additional thermally conducive material may be in thermal communication with the thermoelectric generator along the first area and the heat expelling unit along a third area.

The size of the first area may be at least about 0.01 square centimeters (“cm²”), 0.02 cm², 0.03 cm², 0.04 cm², 0.05 cm², 0.06 cm², 0.07 cm², 0.08 cm², 0.09 cm², 0.1 cm², 0.2 cm², 0.3 cm², 0.4 cm², 0.5 cm², 0.6 cm², 0.7 cm², 0.8 cm² or greater. In some cases, the size of the first area may be at most about 0.8 cm², 0.7 cm², 0.6c m², 0.5 cm², 0.4 cm², 0.3 cm², 0.2 cm², 0.1 cm², 0.09 cm², 0.08 cm², 0.07 cm², 0.06 cm², 0.05 cm², 0.04 cm², 0.03 cm², 0.02 cm², 0.01 cm², or smaller. The size of the third area may be at least about 0.1 cm², 0.2 cm², 0.3 cm², 0.4 cm², 0.5 cm², 0.6 cm², 0.7 cm², 0.8 cm², 0.9 cm², 1 cm², 2 cm², 3 cm², 4 cm², or greater. In some cases, the size of the third area may be at most about 4 cm², 3 cm², 2 cm², 1 cm², 0.9 cm², 0.8 cm², 0.7 cm², 0.6 cm², 0.5 cm², 0.4 cm², 0.3 cm², 0.2 cm², 0.1 cm², or smaller. A ratio of the first area to the third area may be at most about 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, or less. In some cases, the ratio of the first area to the third area may be at least about 0.1, 0.15, 0.2,

0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, or greater.

[0053] The additional thermally conducive material may be formed of conductive material. The conductive material may comprise a metallic (or metal-containing) material, conductive ceramics, and graphite. The metallic material may include one or more elemental metals. For example, the metallic material may include one or more of aluminum, titanium, copper, iron, steel, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium, and their alloys. The conductive ceramics may comprise alumina, boron nitride, lead oxide, ruthenium dioxide, bismuth ruthenate, and bismuth iridate. The additional thermally conducive material may be formed of a semiconductor-containing material, such as silicon or a silicide. The additional thermally conducive material may be formed of a polymeric material. The polymeric material may include one or more polymers. For example, the polymeric material may include one or more of polyvinyl chloride, polyvinylidene chloride, polyethylene, polyisobutene, and poly[ethylene-vinylacetate] copolymer. The additional thermally conducive material may be formed of a composite material. The composite material may include, for example, reinforced plastics, ceramic matrix composites, and metal matrix composites. The composite material may include plastics composite. The plastics composites may have inclusions to increase thermal conductivity, such as boron nitride, aluminum nitride/oxide, or graphite particles.

[0054] The additional thermally conductive material may be in any form, including, but not limited to, sheet form, tile form, wrap form, tape form, or foil form. If the additional thermally conductive material is in sheet form, a thickness of the sheet may be at most about 3 mm, 2 mm, 1 mm, 0.9 mm, 0.8 mm, 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm, or less. In some cases, the thickness of the sheet may be at least about 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, or greater.

[0055] The thermoelectric generator may generate power upon flow of the thermal energy from the heat collecting unit to the thermoelectric generator. The thermoelectric generator may be configured to generate power for transmission to the circuit upon flow of at least the portion of the thermal energy from the heat collecting unit to the heat expelling unit. The power may be generated by the flow of heat from the heat collection unit, through the thermally conductive material, across thermoelectric generator (or the plurality of thermoelectric elements), and to the heat expelling unit. The portion of the thermal energy may be at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or greater of the thermal energy collected by the heat collecting unit. In some cases, the portion of the thermal energy may be at most about 90%,

80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, or less of the thermal energy collected by the heat collecting unit.

[0056] With the thermally conductive material between the heat collecting unit and the thermoelectric generator, the thermal spreading resistance between the heat collecting unit and the thermoelectric generator may be at most about 10 K/W, 9 K/W, 8 K/W, 7 K/W, 6 K/W, 5 K/W, 4 K/W, 3 K/W, 2 K/W, 1 K/W, 0.5 K/W, 0.1 K/W, or less. In some cases, with the thermally conductive material between the heat collecting unit and the thermoelectric generator, the thermal spreading resistance between the heat collecting unit and the thermoelectric generator may be at least about 0.1 K/W, 1 K/W, 2 K/W, 3 K/W, 4 K/W, 5 K/W, 6 K/W, 7 K/W, 8 K/W, 9 K/W, 10 K/W or greater. With the thermally conductive material between the thermoelectric generator and the heat expelling unit, the thermal spreading resistance between the thermoelectric generator and the heat expelling unit may be at most about 10 K/W, 9 K/W, 8 K/W, 7 K/W, 6 K/W, 5 K/W, 4 K/W, 3 K/W, 2 K/W, 1 K/W, 0.5 K/W, 0.1 K/W, or less. In some cases, with the thermally conductive material between the thermoelectric generator and the heat expelling unit, the thermal spreading resistance between the thermoelectric generator and the heat expelling unit may be at least about 0.1 K/W, 1 K/W, 2 K/W, 3 K/W, 4 K/W, 5 K/W, 6 K/W, 7 K/W, 8 K/W, 9 K/W, 10 K/W or greater. When the thermally conductive material is used, the thermal spreading resistance may be at most 50%, 40%, 30%, 20%, 10%, 5%, 1% or less of the thermal spreading resistance when the thermally conductive material is not used. In some cases, when the thermally conductive material is used, the thermal spreading resistance may be at least about 1%, 5%, 10%, 20%, 30%, 40%, 50% or greater of the thermal spreading resistance when the thermally conductive material is not used.

[0057] The generated power may be used to power the electronic device. A portion of the generated power may be stored in the energy storage device. The power stored in the energy storage device may be at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or greater of the generated power. In some cases, the power stored in the energy storage device may be at most about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10% or less of the generated power. A current may be formed upon flow of at least the portion of the thermal energy from the heat collecting unit to the heat expelling unit. The current at a maximum temperature difference may be at most about 10 Amperes (“A”), 9 A, 8 A, 7 A, 6 A, 5 A, 4 A, 3 A, 2 A, 1 A, 0.9 A, 0.8 A, 0.7 A, 0.6 A, 0.5 A, 0.4 A, 0.3 A, 0.2 A, 0.1 A, or less. In some cases, the current at the maximum temperature difference may be at least about 0.1 A, 0.5 A, 1 A, 2 A, 3 A, 4 A, 5 A, 6 A, 7 A, 8 A, 9 A, 10 A, or greater. The maximum temperature difference may be at most about 20°C, l5°C, l0°C, 9°C, 8°C, 7°C, 6°C, 5°C, 4°C, 3°C, 2°C, l°C, or less. In some cases, the maximum temperature difference may be at least about l°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, l0°C, l5°C, 20°C, or more.

[0058] The current can be a direct current (“DC”) or alternating current (“AC”), or a combination of DC and AC. If the current is AC, a AC resistance may be at least about 1 Ohm, 2 Ohms, 3 Ohms, 4 Ohms, 5 Ohms, 6 Ohms, 7 Ohms, 8 Ohms, 9 Ohms, 10 Ohms, 11 Ohms,

12 Ohms, 13 Ohms, 14 Ohms, 15 Ohms, 16 Ohms, 17 Ohms, 18 Ohms, 19 Ohms, 20 Ohms, 21 Ohms, 22 Ohms, 23 Ohms, 24 Ohms, 25 Ohms, 26 Ohms, 27 Ohms, 28 Ohms, 29 Ohms, or greater. In some cases, the AC resistance may be at most about 29 Ohm, 28 Ohms, 27 Ohms, 26 Ohms, 25 Ohms, 24 Ohms, 23 Ohms, 22 Ohms, 21 Ohms, 20 Ohms, 19 Ohms, 18 Ohms, 17 Ohms, 16 Ohms, 15 Ohms, 14 Ohms, 13 Ohms, 12 Ohms, 11 Ohms, 10 Ohms, 9 Ohms, 8 Ohms, 7 Ohms, 6 Ohms, 5 Ohms, 4 Ohms, 3 Ohms, 2 Ohms, 1 Ohm, or less.

[0059] The plurality of thermoelectric elements may comprise an n-type semiconductor element. The n-type semiconductor element may comprise a periodic array of holes or wires. An individual hole or wire of the periodic array may have an aspect ratio of at least about lOO-to-l. The array of holes can have an aspect ratio (e.g., the length of the element divided by width of an individual hole) of at least about 1.5: 1, or 2: 1, or 5: 1, or 10: 1, or 20: 1, or 50: 1, or 100: 1, or 1000: 1, or 5,000: 1, or 10,000: 1, or 100,000: 1, or 1,000,000: 1, or 10,000,000: 1, or

100,000,000: 1, or more. In some cases, the array of holes can have an aspect ratio of at most about 100,000,000: 1, or 10,000,000:1, or 100,000: 1, or 10,000: 1, or 5,000: 1, or 1000: 1, or 100: 1, or 50: 1, or 20: 1, or 10: 1, or 5: 1, or 2: 1, or 1.5: 1, or less.

[0060] The plurality of thermoelectric elements may comprise a p-type semiconductor element that may be adjacent to an n-type semiconductor element. The p-type semiconductor element may comprise a periodic array of holes or wires. An individual hole or wire of the periodic array may have an aspect ratio of at least about lOO-to-l. The array of holes can have an aspect ratio (e.g., the length of the element divided by width of an individual hole) of at least about 1.5: 1, or 2: 1, or 5: 1, or 10: 1, or 20: 1, or 50: 1, or 100: 1, or 1000: 1, or 5,000: 1, or 10,000: 1, or 100,000:1, or 1,000,000: 1, or 10,000,000: 1, or 100,000,000: 1, or more. In some cases, the array of holes can have an aspect ratio of at most about 100,000,000: 1, or 10,000,000: 1, or 100,000:1, or 10,000: 1, or 5,000: 1, or 1000: 1, or 100: 1, or 50: 1, or 20: 1, or 10: 1, or 5: 1, or 2: 1, or 1.5:1, or less.

[0061] The plurality of thermoelectric elements may comprise n-type and p-type

semiconductor elements. The n-type and p-type semiconductor elements may be disposed between the heat collecting unit and the heat expelling unit. The heat colleting unit may be in contact with a first electrode of the electronic device. The heat expelling unit may be in contact with a second electrode of the electronic device. The heat expelling unit and the heat collecting unit may be electrically insulating but thermally conductive. The application of an electrical potential to the first electrode and the second electrode may lead to the flow of current, which generates a temperature gradient (DT) across the electronic device. The temperature gradient (DT) may extend from a first temperature (average), Tl, at the heat collecting unit to a second temperature (average), T2, at the heat expelling unit, where Tl > T2. The temperature gradient can be used for heating and cooling purposes.

[0062] The n-type and p-type semiconductor elements can be formed of structures having dimensions from nanometers to micrometers, such as, e.g., nanostructures. The nanostructures may be holes or inclusions, which can be provided in an array of holes (i.e., mesh). The nanostructures may be rod-like structures, such as nanowires. The rod-like structures may be laterally separated from one another. The n-type and p-type semiconductor elements may be formed of an array of wires or holes oriented along the direction of the temperature gradient.

The wires may extend from the first electrode to the second electrode. The n-type and p-type semiconductor elements may be formed of an array of holes oriented along a direction that is angled between about 0° and 90° in relation to the temperature gradient. The array of holes may be orthogonal to the temperature gradient. The holes or wires may have dimensions on the order of nanometers to micrometers. The holes may define a nanomesh.

[0063] The electronic device may further comprise an electronic display with a user interface for displaying information to the user. The electronic display may be a screen. The screen may be accompanied by one or more speakers. The electronic display may be configured for providing visual and audial instructions to the user. The one or more speakers may work in conjunction with the electronic display to provide information, guidance, and instructions to the user. The screen may be a touchscreen. The touchscreen may be a capacitive touch screen. The touchscreen may be a resistive touch screen. Applying pressure or contact to the electronic display may transfer input from the user to a PCB board of the electronic device to activate the electronic device. The user interface may enable the user to interact with the electronic device. The user interface may be graphical user interface. The user interface may enable the user to access different functionalities of the electronic device. The user interface may be actuated by buttons. The user interface may be actuated through use of the touchscreen. The user interface may be actuated by both buttons and the use of a touch screen.

[0064] The electronic device may further comprise a power management unit operatively coupled to the electronic display. The power management unit may provide at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or greater of a power requirement of the electronic device. In some cases, the power management unit may provide at most about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, or less of the power requirement of the electronic device. The power management unit may comprise an energy storage device in electrical communication with the thermoelectric generator.

[0065] The energy storage device may be configured to collect power from the

thermoelectric generator for storage. At least a portion of the power may be stored in the energy storage device. The portion of the power stored in the energy storage device may be at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the power collected from the

thermoelectric generator. In some cases, the portion of the power stored in the energy storage device may be at most about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, or less of the power collected from the thermoelectric generator. The energy storage device can be a battery. The battery may be a rechargeable battery. The power management unit may further comprise an external power unit for providing external power to charge the energy storage device.

[0066] The electronic device may further comprise a body comprising the heat collecting unit, the thermoelectric generator, the thermally conductive material, and the heat expelling unit. If the electronic device is a watch, the body may comprise a watch case. The watch case may further comprise an electronic display and power management unit. The watch case may be assembled from multiple components. The electronic display may be positioned adjacent to the top of the watch case. The top of the watch case may include a transparent material and the electronic display may be visible through the top of the watch case. The components of the watch may be assembled into the watch case from the top side, the bottom side, or both sides. The watch may be substantially waterproof or water resistant. The watch may be water resistant but not waterproof. The watch may include a user interface. The user interface may enable the user to access different functionalities of the watch. The user interface may be actuated by buttons. The user interface may be actuated through use of a touchscreen. The user interface may be actuated by both buttons and the use of a touch screen. The touchscreen may be a capacitive touch screen. The touch screen may be a resistive touch screen.

[0067] The watch may include one or more power generation units in electrical

communication with the power management unit in addition to the thermoelectric device. The power generation unit may include a solar cell, inductive coupling unit, RF coupling unit, and a kinetic power generation unit. The watch may include one or more solar cells. The solar cells may be integrated in the body of the watch or the band of the watch. The solar cells may generate power during exposure to light. The watch may have at least about 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, or more solar cells integrated into the body and/or band of the watch. The inductive coupling unit may be integrated into the power management unit of the watch. The inductive coupling unit may generate power inductively. The RF coupling unit may be integrated into the power management unit of the watch. The RF coupling unit may generate power from RF waves. The kinetic power generation unit may be integrated into the power management unit of the watch. The kinetic power generation unit may generate power by motion of the user’s body.

[0068] The body may be coupled to a mounting unit configured to secure the electronic device adjacent to the body surface of the user. If the electronic device is a watch, the mounting unit may be a watch band. The watch band may ensure that the user of the wearable device can comfortably tighten the watch strap, such that the case back conductor of the wearable device may be solidly pressed against their body (e.g., wrist). A tight thermal connection between the case back conductor and the user’s body (e.g., wrist) may ensure a sufficient temperature gradient in the case back conductor for electrical power generation by the plurality of thermoelectric elements. The watch band may be made from a flexible material, such as silicone or TPE, with a conventional buckle with discrete adjustment points, to allow comfortable tightening of the watch band.

[0069] The watch band may include one or more of a clasp and one or more straps. The one or more straps may include a top strap and a bottom strap, which may be wrapped around either side of the wearable device user’s body (e.g., wrist) for secure wearing. The top strap may have a clasp at the end. The bottom strap may have a row of several holes. The clasp may be used to secure the one or more straps of the wearable device around the user’s body (e.g., wrist). The clasp may adjust to the size of the user’s body for comfortable and secure wearing.

[0070] The electronic device may comprise at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more thermoelectric generators. Each of the thermoelectric generators may comprise the same number of the plurality of thermoelectric elements. Each of the thermoelectric generators may comprise different numbers of the plurality of thermoelectric elements. The multiple thermoelectric generators may be stacked together in the electronic device.

Methods for collecting thermal energy

[0071] A method for collecting thermal energy may comprise providing an electronic device comprising a heat collecting unit, a thermoelectric generator, thermally conductive material, and a heat expelling unit; and positing the electronic device so that the heat collecting unit is disposed adjacent to a body surface of the user. The electronic device may further comprise an additional thermally conductive material adjacent to the thermoelectric generator. The electronic device may be a portable electronic device. The electronic device may be mobile phones, PCs, tablets, printers, consumer electronics, and appliances. The electronic devices may be wearable devices, including but not limited to, Fitbit, Apple watch, Samsung health, Misfit, Xiaomi Mi band, and Microsoft band. The electronic device may be a watch. The watch may be a quartz wrist watch. The heat collecting unit, the thermoelectric generator, the thermally conductive material, the heat expelling unit, and the additional thermally conductive material are described elsewhere herein.

[0072] By positing the electronic device so that the heat collecting unit is disposed adjacent to a body surface of the user, the thermal energy may flow from the body surface of the user through the thermally conductive material to the thermoelectric generator. The thermoelectric generator may generate power upon flow of the thermal energy from the heat collecting unit to the thermoelectric generator. The thermoelectric generator may be configured to generate power for transmission to the circuit upon flow of at least the portion of the thermal energy from the heat collecting unit to the heat expelling unit. The power may be generated by the flow of heat from the heat collection unit, through the thermally conductive material, and to thermoelectric generator (or the plurality of thermoelectric elements).

[0073] With the thermally conductive material between the heat collecting unit and the thermoelectric generator, the thermal spreading resistance between the heat collecting unit and the thermoelectric generator may be at most about 10 K/W, 9 K/W, 8 K/W, 7 K/W, 6 K/W, 5 K/W, 4 K/W, 3 K/W, 2 K/W, 1 K/W, 0.5 K/W, or less. In some cases, with the thermally conductive material between the heat collecting unit and the thermoelectric generator, the thermal spreading resistance between the heat collecting unit and the thermoelectric generator may be at least about 1 K/W, 2 K/W, 3 K/W, 4 K/W, 5 K/W, 6 K/W, 7 K/W, 8 K/W, 9 K/W, 10 K/W or greater. When the thermally conductive material is used, the thermal spreading resistance may be at most about 50%, 40%, 30%, 20%, 10%, 5%, 1% or less of the thermal spreading resistance when the thermally conductive material is not used. In some cases, when the thermally conductive material is used, the thermal spreading resistance may be at least about 1%, 5%, 10%, 20%, 30%, 40%, 50% or greater of the thermal spreading resistance when the thermally conductive material is not used.

[0074] By positing the electronic device so that the heat collecting unit is disposed adjacent to a body surface of the user, at least a portion of the thermal energy may be directed through the thermoelectric generator to the heat expelling unit, either through or not through an additional thermally conductive material. The portion of the thermal energy may be at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or greater of the thermal energy collected by the heat collecting unit. In some cases, the portion of the thermal energy may be at most about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, or less of the thermal energy collected by the heat collecting unit.

[0075] With the additional thermally conductive material between the heat expelling unit and the thermoelectric generator, the thermal spreading resistance between the heat expelling unit and the thermoelectric generator may be at most about 10 K/W, 9 K/W, 8 K/W, 7 K/W, 6 K/W, 5 K/W, 4 K/W, 3 K/W, 2 K/W, 1 K/W, 0.5 K/W, or less. In some cases, with the additional thermally conductive material between the heat expelling unit and the thermoelectric generator, the thermal spreading resistance between the heat expelling unit and the

thermoelectric generator may be at least about 1 K/W, 2 K/W, 3 K/W, 4 K/W, 5 K/W, 6 K/W, 7 K/W, 8 K/W, 9 K/W, 10 K/W or greater. When the additional thermally conductive material is used, the thermal spreading resistance may be at most about 50%, 40%, 30%, 20%, 10%, 5%,

1% or less of the thermal spreading resistance when the additional thermally conductive material is not used. In some cases, when the additional thermally conductive material is used, the thermal spreading resistance may be at least about 1%, 5%, 10%, 20%, 30%, 40%, 50% or greater of the thermal spreading resistance when the additional thermally conductive material is not used.

[0076] FIG. 1 shows an example of an assembly of an electronic device. In the illustrated example, the electronic device 100 is a watch. The electronic device 100 may comprise a heat collecting unit 102, a thermoelectric generator 104, a heat expelling unit 106, and a watch case 108. The heat colleting unit 102 may be a glass or plastic skin contact plate. The heat collecting unit 102 may be placed below the thermoelectric generator 104. The heat expelling unit 106 may be placed above the thermoelectric generator 104. The heat expelling unit 106 may be integrated with the watch case 108. To minimize thermal spreading resistance, the thermoelectric generator 106 may be in ring shape. The thermal spreading resistance of the electronic device 100 may be about 4 K/W. The thermal spreading resistance of the electronic device may be small in comparison with the thermal resistance between the heat expelling unit and the environment, which may be from 50 K/W to 100 K/W. The ring-shaped thermoelectric generator may be expensive and hard to fabricate. The heat expelling unit 106 and the watch case 108 may be fabricated out of one or more thermally conductive materials. The thermally conductive materials may comprise, but not limited to, metallic material and ceramic material.

[0077] FIG. 2 shows an example of an assembly of an electronic device with thermally conductive material between a heat collecting unit and a thermoelectric generator. In the illustrated example, the electronic device 200 is a watch. The electronic device 200 may comprise a heat collecting unit 202, thermally conductive material 204, a thermoelectric generator 206, a heat expelling unit 208, and a watch case 210. The heat colleting unit 202 may be a glass or plastic skin contact plate. The heat collecting unit 202 may be placed below the thermoelectric generator 206. The thermally conductive material 204 may be placed between the heat collecting unit 202 and the thermoelectric generator 206. The heat expelling unit 208 may be placed above the thermoelectric generator 206. The heat expelling unit 208 may be integrated with the watch case 210. Because of the use of the thermally conductive material 204, a small rectangular thermoelectric generator 206 can be used instead of the ring shape thermoelectric generator 104 of FIG. 1. A large internal volume 212 can be freed up. The heat expelling unit 208 and the watch case 210 may be fabricated out of thermally conductive materials. The thermally conductive materials may comprise, but not limited to, metallic material and ceramic material.

[0078] FIG. 3 shows an example of an assembly of an electronic device with thermally conductive material between a heat collecting unit and a thermoelectric generator, and additional thermally conductive material above a thermoelectric generator. In the illustrated example, the electronic device 300 is a watch. The electronic device 300 may comprise a heat collecting unit 302, thermally conductive material 304, a thermoelectric generator 306, additional thermally conductive material 308, and a watch case 310. The heat colleting unit 302 may be a glass or plastic skin contact plate. The heat collecting unit 302 may be placed below the thermoelectric generator 306. The thermally conductive material 304 may be placed between the heat collecting unit 302 and the thermoelectric generator 306. The heat expelling unit 208 of FIG. 2 can be replaced with the additional thermally conductive material 308. The additional thermally conductive material may be placed above the thermoelectric generator 206 and in contact with the watch case 310. The additional thermally conductive material 308 may be integrated with the watch case 310. In this example, the watch case can be a heat expelling unit. Because of the use of the thermally conductive material 304 and additional thermally conductive material 308, a small rectangular thermoelectric generator 306 can be used instead of the ring shape

thermoelectric generator 104 of FIG. 1. A large internal volume 312 can be freed up. The watch case 310 may be fabricated out of thermally conductive materials. The thermally conductive materials may comprise, but not limited to, metallic material and ceramic material. The watch case 310 can be fabricated with insulating materials because the small thickness of the case may add negligibly to thermal resistance of the entire electronic device. For example, if the insulating material is 1 mm thick with thermal conductivity of 1 W/m-K, the insulating material may exhibit a thermal resistance of 0.001 m²-K/W (each square meter exhibits 0.001 K/W of thermal resistance). For natural convection, the thermal transfer coefficient may be about 10 W/m²-K, so each square meter may have 0.1 K/W of thermal resistance. In this situation, natural convection at the watch case may contribute the largest to thermal resistance and the use of sufficiently thin insulating materials for the watch case may not add large thermal resistance.

Methods for forming thermoelectric devices

[0079] The heat expelling unit or the heat collecting unit may be formed by using one or more manufacturing techniques. The one or more manufacturing techniques may include subtractive manufacturing, injection molding, blow molding, or additive manufacturing processes such as 3D printing. The subtractive manufacturing may be used to create the heat expelling unit or the heat collecting unit by successively cutting material away from a solid block of material. The injection molding may comprise a high-pressure injection of raw materials into one or more molds. The one or more molds may shape the raw material into the desired shape of the heat collecting unit or heat expelling unit. The blow molding may comprise multiple steps. The multiple steps may comprise melting down the raw material, forming the raw material into a parison, placing the parison into a mold, and air blowing through the parison to push the material out to match the mold. The additive manufacturing processes may be used to create the heat expelling unit or heat collecting unit by laying down successive layers of material, each of which can be seen as a thinly sliced horizontal cross-section of the target heat expelling unit or heat collecting unit.

[0080] The heat expelling unit and the heat collecting unit may be manufactured as a single (or unitary) piece, thus no assembly may be required. The heat expelling unit and the heat collecting unit may be manufactured as two pieces, thus at least one assembly step may be required. The two pieces may be manufactured separately. The two pieces may be manufactured simultaneously. The heat expelling unit and the heat collecting unit may be manufactured as three pieces, thus multiple assembly steps may be required. The multiple assembly steps may include at least two, three, four or more steps. The heat expelling unit and the heat collecting unit may be manufactured as more than three pieces.

[0081] A thermoelectric element can be formed using electrochemical etching. The thermoelectric element may be formed by cathodic or anodic etching, in some cases without the use of a catalyst. The thermoelectric element can be formed without use of a metallic catalysis. The thermoelectric element can be formed without providing a metallic coating on a surface of a substrate to be etched. This can also be performed using purely electrochemical anodic etching and suitable etch solutions and electrolytes. As an alternative, a thermoelectric can be formed using metal catalyzed electrochemical etching in suitable etch solutions and electrolytes, as described in, for example, PCT/US2012/047021, filed July 17, 2012, PCT/US2013/021900, filed January 17, 2013, PCT/US2013/055462, filed August 16, 2013, PCT/US2013/067346, filed October 29, 2013, each of which is entirely incorporated herein by reference.

[0082] A thermoelectric element can be formed using one or more sintering processes. The one or more sintering processes comprise spark plasma sintering, electro sinter forging, pressureless sintering, microwave sintering, and liquid phase sintering. For example, the thermoelectric element can be formed using one of the techniques described in

PCT/US2015/022312, filed March 24, 2014, which is entirely incorporated herein by reference. The spark plasma sintering may be conducted by using a spark plasma sintering instrument. The spark plasma sintering instrument may apply external pressure and an electric field

simultaneously to enhance the densification of a precursor of the thermoelectric element. The spark plasma sintering instrument may use a direct current (DC) pulse as the electric current to create spark plasma and spark impact pressure.

[0083] A thermoelectric can alternatively be formed by heating an uncompacted powder in a mold as described in U.S. Patent Publication 2016/0380175, filed on December 29, 2016, which is entirely incorporated herein by reference.

[0084] The heat collecting unit, the plurality of thermoelectric elements, and/or the heat expelling unit may be assembled with surface-mount technology. Surface-mount technology may be used to place the plurality of thermoelectric elements on the heating collecting unit and/or the heat expelling unit.

Computer control systems

[0085] The present disclosure provides computer control systems that are programmed to implement methods of the disclosure. FIG. 4 shows a computer system 401 that is programmed or otherwise configured to control the electronic device of the present disclosure. The computer system 401 can be part of an electronic device of a user. The electronic device can be a mobile electronic device.

[0086] The computer system 401 includes a central processing unit (CPU, also“processor” and“computer processor” herein) 405, which can be a single core or multi core processor, or a plurality of processors for parallel processing. The computer system 401 also includes memory or memory location 410 (e.g., random-access memory, read-only memory, flash memory), electronic storage unit 415 (e.g., hard disk), communication interface 420 (e.g., network adapter) for communicating with one or more other systems, and peripheral devices 425, such as cache, other memory, data storage and/or electronic display adapters. The memory 410, storage unit 415, interface 420 and peripheral devices 425 are in communication with the CPU 405 through a communication bus (solid lines), such as a motherboard. The storage unit 415 can be a data storage unit (or data repository) for storing data. The computer system 401 can be operatively coupled to a computer network (“network”) 430 with the aid of the communication interface 420. The network 430 can be the Internet, an internet and/or extranet, or an intranet and/or extranet that is in communication with the Internet. The network 430 in some cases is a telecommunication and/or data network. The network 430 can include one or more computer servers, which can enable distributed computing, such as cloud computing. The network 430, in some cases with the aid of the computer system 401, can implement a peer-to-peer network, which may enable devices coupled to the computer system 401 to behave as a client or a server.

[0087] The CPU 405 can execute a sequence of machine-readable instructions, which can be embodied in a program or software. The instructions may be stored in a memory location, such as the memory 410. The instructions can be directed to the CPU 405, which can subsequently program or otherwise configure the CPU 405 to implement methods of the present disclosure. Examples of operations performed by the CPU 405 can include fetch, decode, execute, and writeback.

[0088] The CPU 405 can be part of a circuit, such as an integrated circuit. One or more other components of the system 401 can be included in the circuit. In some cases, the circuit is an application specific integrated circuit (ASIC). [0089] The storage unit 415 can store files, such as drivers, libraries and saved programs.

The storage unit 415 can store user data, e.g., user preferences and user programs. The computer system 401 in some cases can include one or more additional data storage units that are external to the computer system 401, such as located on a remote server that is in communication with the computer system 401 through an intranet or the Internet.

[0090] The computer system 401 can communicate with one or more remote computer systems through the network 430. For instance, the computer system 401 can communicate with a remote computer system of a user. Examples of remote computer systems include personal computers (e.g., portable PC), slate or tablet PC’s (e.g., Apple® iPad, Samsung® Galaxy Tab), telephones, Smart phones (e.g., Apple® iPhone, Android-enabled device, Blackberry®), or personal digital assistants. The user can access the computer system 401 via the network 430.

[0091] Methods as described herein can be implemented by way of machine (e.g., computer processor) executable code stored on an electronic storage location of the computer system 401, such as, for example, on the memory 410 or electronic storage unit 415. The machine executable or machine-readable code can be provided in the form of software. During use, the code can be executed by the processor 405. In some cases, the code can be retrieved from the storage unit 415 and stored on the memory 410 for ready access by the processor 405. In some situations, the electronic storage unit 415 can be precluded, and machine-executable instructions are stored on memory 410.

[0092] The code can be pre-compiled and configured for use with a machine having a processer adapted to execute the code, or it can be compiled during runtime. The code can be supplied in a programming language that can be selected to enable the code to execute in a pre- compiled or as-compiled fashion.

[0093] Aspects of the systems and methods provided herein, such as the computer system

401, can be embodied in programming. Various aspects of the technology may be thought of as “products” or“articles of manufacture” typically in the form of machine (or processor) executable code and/or associated data that is carried on or embodied in a type of machine readable medium. Machine-executable code can be stored on an electronic storage unit, such as memory (e.g., read-only memory, random-access memory, flash memory) or a hard disk.

“Storage” type media can include any or all of the tangible memory of the computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives and the like, which may provide non-transitory storage at any time for the software programming. All or portions of the software may at times be communicated through the Internet or various other telecommunication networks. Such communications, for example, may enable loading of the software from one computer or processor into another, for example, from a management server or host computer into the computer platform of an application server. Thus, another type of media that may bear the software elements includes optical, electrical and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links or the like, also may be considered as media bearing the software. As used herein, unless restricted to non-transitory, tangible “storage” media, terms such as computer or machine“readable medium” refer to any medium that participates in providing instructions to a processor for execution.

[0094] Hence, a machine readable medium, such as computer-executable code, may take many forms, including but not limited to, a tangible storage medium, a carrier wave medium or physical transmission medium. Non-volatile storage media include, for example, optical or magnetic disks, such as any of the storage devices in any computer(s) or the like, such as may be used to implement the databases, etc. shown in the drawings. Volatile storage media include dynamic memory, such as main memory of such a computer platform. Tangible transmission media include coaxial cables; copper wire and fiber optics, including the wires that comprise a bus within a computer system. Carrier-wave transmission media may take the form of electric or electromagnetic signals, or acoustic or light waves such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media therefore include for example: a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD or DVD-ROM, any other optical medium, punch cards paper tape, any other physical storage medium with patterns of holes, a RAM, a ROM, a PROM and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave transporting data or instructions, cables or links transporting such a carrier wave, or any other medium from which a computer may read programming code and/or data. Many of these forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution.

[0095] The computer system 401 can include or be in communication with an electronic display 435 that comprises a user interface (EΊ) 440 for providing, for example, information regarding the power generated by the thermoelectric generator. Examples of ET’s include, without limitation, a graphical user interface (GET) and web-based user interface.

[0096] Methods and systems of the present disclosure can be implemented by way of one or more algorithms. An algorithm can be implemented by way of software upon execution by the central processing unit 405.

Example(s)

[0097] The example below is provided for illustrative purposes only. [0098] Example 1. Characteristics of thermally conductive material

[0099] Table 1 shows three different situations: 1). a glass disc with a small rectangle thermoelectric generator; 2) a glass disc with a large ring-shape thermoelectric generator; and 3). a graphite sheet placed between a glass disc and a small rectangle thermoelectric generator. In this example, the glass disc is 36 mm in diameter and 0.5 mm thick, the small rectangle thermoelectric generator is 20 mm in length and 10 mm in width, the large ring-shape thermoelectric generator is with 36 mm outside diameter and 25 mm inside diameter, and the graphite sheet is thermally conductive material. Table 1 shows that if the glass disc is used to collect heat into the small rectangular thermoelectric generator, the thermal spreading resistance is 25 K/W. If the glass disc is used to collect heat into the large ring-shape thermoelectric generator, the thermal spreading resistance is 4 K/W. If the graphite sheet is placed between the glass disc and the small rectangle thermoelectric generator, the thermal spreading resistance is 1 K/W. The results of Table 1 show that by using thermally conductive material (e.g., graphite sheet), even with a smaller size thermoelectric generator, the thermal spreading resistance can be much lower than the thermal spreading resistance when the thermally conductive material is not used.

[00100] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. It is not intended that the invention be limited by the specific examples provided within the specification. While the invention has been described with reference to the aforementioned specification, the descriptions and illustrations of the

embodiments herein are not meant to be construed in a limiting sense. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Furthermore, it shall be understood that all aspects of the invention are not limited to the specific depictions, configurations or relative proportions set forth herein which depend upon a variety of conditions and variables. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is therefore contemplated that the invention shall also cover any such alternatives, modifications, variations or equivalents. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. An electronic device, comprising:

a heat collecting unit that is configured to be positioned adjacent to a body surface of a user, wherein said heat collecting unit is configured to collect thermal energy from said body surface of said user;

a thermoelectric generator comprising a plurality of thermoelectric elements, wherein said thermoelectric generator is in thermal communication with said heat collecting unit;

thermally conductive material between said heat collecting unit and said thermoelectric generator, wherein said thermally conductive material has a thermal resistance of at most 10 Kelvin/Watt (K/W), wherein said thermally conducive material is in thermal communication with said thermoelectric generator along a first area and said heat collecting unit along a second area, wherein a ratio of said first area to said second area is at most 0.5; and

a heat expelling unit in thermal communication with said thermoelectric generator.

2. The electronic device of claim 1, wherein said ratio of said first area to said second area is at most 0.25.

3. The electronic device of claim 2, wherein said ratio of said first area to said second area is at most 0.1.

4. The electronic device of claim 1, wherein said thermoelectric generator is disposed in a position offset from the center of said heat collecting unit.

5. The electronic device of claim 4, wherein said electronic device has an internal volume opposite said thermoelectric generator.

6. The electronic device of claim 1, wherein said thermally conductive material is in sheet form.

7. The electronic device of claim 6, wherein a thickness of said sheet is at most 2 millimeters.

8. The electronic device of claim 7, wherein said thickness of said sheet is at most 1 millimeter.

9. The electronic device of claim 1, further comprising an additional thermally conductive material adjacent to said thermoelectric generator, wherein said additional thermally conductive material has a thermal resistance of at most 10 K/W, wherein said additional thermally conducive material is in thermal communication with said thermoelectric generator along said first area and said heat expelling unit along a third area, wherein a ratio of said first area to said third area is at most 0.5.

10. The electronic device of claim 9, wherein said additional thermally conductive material is in sheet form.

11. The electronic device of claim 10, wherein a thickness of said sheet is at most 2 millimeters.

12. The electronic device of claim 1, wherein said thermoelectric generator generates power upon flow of said thermal energy from said heat collecting unit to said thermoelectric generator.

13. The electronic device of claim 1, further comprising an electronic display with a user interface for displaying information to said user.

14. The electronic device of claim 1, wherein said plurality of thermoelectric elements comprise an n-type semiconductor element comprising a periodic array of holes or wires.

15. The electronic device of claim 14, wherein said plurality of thermoelectric elements comprise a p-type semiconductor element that is adjacent to said n-type semiconductor element, wherein said p-type semiconductor element comprises a periodic array of holes or wires.

16. The electronic device of claim 1, wherein said thermoelectric generator has a rectangular shape.

17. The electronic device of claim 1, wherein said thermally conductive material is a graphite sheet.

18. A method for collecting thermal energy, comprising:

positioning, adjacent to a body surface of a user, an electronic device comprising (i) a heat collecting uni; (ii) a thermoelectric generator comprising a plurality of thermoelectric elements, wherein said thermoelectric generator is in thermal communication with said heat collecting unit; (iii) thermally conductive material between said heat collecting unit and said thermoelectric generator, wherein said thermally conductive material has a thermal resistance of at most 10 Kelvin/Watt (K/W), wherein said thermally conducive material is in thermal communication with said thermoelectric generator along a first area and said heat collecting unit along a second area, wherein a ratio of said first area to said second area is at most 0.5; and (iv) a heat expelling unit in thermal communication with said thermoelectric generator,

wherein with said electronic device disposed adjacent to said body surface of said user,

(i) said heat collecting unit collects thermal energy from said body surface of said user, (ii) at least a portion of said thermal energy is directed from said heat collecting unit to said thermoelectric generator through said thermally conductive material, and (iii) at least a portion of said thermal energy is directed through said thermoelectric generator to said heat expelling unit.

19. The method of claim 18, wherein said thermally conductive material is in sheet form.

20. The method of claim 19, wherein a thickness of said sheet is at most 2 millimeters.

21. The method of claim 18, wherein said electronic device further comprises an additional thermally conductive material adjacent to said thermoelectric generator, wherein said additional thermally conductive material has a thermal resistance of at most 10 K/W, wherein said additional thermally conducive material is in thermal communication with said thermoelectric generator along said first area and said heat expelling unit along a third area, wherein a ratio of said first area to said third area is at most 0.5.

22. The method of claim 21, wherein said additional thermally conductive material is in sheet form.

23. The method of claim 22, wherein a thickness of said sheet is at most 2 millimeters.