U.S. patent application number 13/051941 was filed with the patent office on 2011-09-15 for thermoelectric heterostructure assemblies element.
This patent application is currently assigned to ZT PLUS. Invention is credited to Lon E. Bell.
Application Number | 20110220163 13/051941 |
Document ID | / |
Family ID | 26987549 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110220163 |
Kind Code |
A1 |
Bell; Lon E. |
September 15, 2011 |
THERMOELECTRIC HETEROSTRUCTURE ASSEMBLIES ELEMENT
Abstract
Improved thermoelectric assemblies are disclosed, wherein layers
of heterostructure thermoelectric materials or thin layers of
thermoelectric material form thermoelectric elements. The layers
are bound together with agents that improve structural strengths,
allow electrical current to pass in a preferred direction, and
minimize or reduce adverse affects, such a shear stresses, that
might occur to the thermoelectric properties and materials of the
assembly by their inclusion.
Inventors: |
Bell; Lon E.; (Altadena,
CA) |
Assignee: |
ZT PLUS
Irwindale
CA
|
Family ID: |
26987549 |
Appl. No.: |
13/051941 |
Filed: |
March 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10897292 |
Jul 22, 2004 |
7932460 |
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13051941 |
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09987232 |
Nov 6, 2001 |
6812395 |
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10897292 |
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60331021 |
Oct 24, 2001 |
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Current U.S.
Class: |
136/203 ;
136/201; 136/205 |
Current CPC
Class: |
H01L 35/34 20130101;
H01L 35/08 20130101 |
Class at
Publication: |
136/203 ;
136/205; 136/201 |
International
Class: |
H01L 35/28 20060101
H01L035/28; H01L 35/34 20060101 H01L035/34 |
Claims
1. A thermoelectric element comprising: a first heterostructure
thermoelectric portion and a second heterostructure thermoelectric
portion, the first and second thermoelectric portions of the same
conductivity type and electrically coupled in series to one another
such that current flows from the first heterostructure
thermoelectric portion to the second heterostructure thermoelectric
portion; and an electrically conductive material coupled to the
first and second hetero structure thermoelectric portions.
2. The thermoelectric element of claim 1, wherein the electrically
conductive material comprises at least one electrode.
3. The thermoelectric element of claim 1, wherein the first and
second heterostructure thermoelectric portions form layers.
4. The thermoelectric element of claim 3, wherein the electrically
conductive material is coupled to the layers at least one end of
the layers.
5. The thermoelectric element of claim 3, wherein the electrically
conductive material is coupled to at least the top or bottom of the
layers.
6. The thermoelectric element of claim 1, wherein the first and
second heterostructure thermoelectric portions form wires.
7. The thermoelectric element of claim 6, wherein the electrically
conductive material comprises at least one electrode.
8. The thermoelectric element of claim 7, wherein the electrically
conductive material is coupled to the wires at least one end of the
wires.
9. The thermoelectric element of claim 7, wherein the electrically
conductive material is coupled to at least the top or bottom of the
wires.
10. The thermoelectric element of claim 1, further comprising a
bonding material between the first and second heterostructure
thermoelectric portions.
11. The thermoelectric element of claim 10, wherein the bonding
material is configured to reduce the power density of the
thermoelectric.
12. The thermoelectric element of claim 10, wherein the bonding
material is configured to reduce shear stress in the first and
second heterostructure thermoelectric portions when the
thermoelectric element is operated.
13. The thermoelectric element of claim 1, further comprising an
intermediate material between at least one of the first and second
heterostructure thermoelectric portions and the electrically
conductive material.
14. The thermoelectric element of claim 13, wherein the
intermediate material is configured to reduce shear stress in the
first and second heterostructure thermoelectric portions when the
thermoelectric element is operated.
15. The thermoelectric element of claim 14, wherein the
intermediate material is resilient.
16. The thermoelectric element of claim 1, wherein the first and
second heterostructure thermoelectric portions are of substantially
the same thermoelectric material.
17. The thermoelectric element of claim 1, wherein at least one of
the first and second heterostructure thermoelectric portions
comprises at least two layers of hetero structure thermoelectric
material.
18. A method of producing a thermoelectric device comprising the
steps of: layering first and second heterostructure thermoelectric
segments to be electrically coupled in series to one another such
that current flows from the first heterostructure thermoelectric
segment to the second heterostructure thermoelectric segment; and
connecting at least one electrode to the segments.
19. The method of claim 18, wherein the step of layering comprises
bonding said first and second heterostructure thermoelectric
segments with a bonding material.
20. The method of claim 19, further comprising the step of
providing an intermediate material between at least one of the
heterostructure thermoelectric segments and the at least one
electrode.
Description
REFERENCE TO PRIOR APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/897,292, filed Jul. 22, 2004 and
incorporated in its entirety by reference herein, which is a
continuation of U.S. application Ser. No. 09/987,232, filed Nov. 6,
2001, issued as U.S. Pat. No. 6,812,395, which claims the benefit
of U.S. Provisional Application No. 60/331,021, filed Oct. 24,
2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The following disclosure relates generally to
thermoelectrics configured from heterostructures or thin layers of
thermoelectric material to improve performance or usability of such
thermoelectrics.
[0004] 2. Description of the Related Art
[0005] The bulk properties of thermoelectric (TE) materials can be
altered if the materials are formed from very thin films or
segments of alternating materials. The resultant assemblies formed
of segments of such thin films are usually called heterostructures.
Each film segment is the order of tens to hundreds of angstroms
thick. Since each segment is very thin, multiple segments are
needed to fabricate cooling, heating and power generating devices.
The shape, dimensions and other geometrical characteristics of
conventional heterostructures often make attachment of suitable
thermal heat transfer members and electrodes to the individual
heterostructures assembly difficult. Further complications arise in
the extraction of thermal power from the structures. New
fabrication techniques, material combinations, and forming methods
are required to fabricate TE elements from such materials. New
fabrication techniques are even more critical for systems made from
thousands of segments since materials formed of many segments tend
to be fragile and weakened by (1) internal stresses that result
from fabrication, (2) the very nature of the materials and (3)
internal weakness caused by contamination and process variation.
Further, certain TE materials, such as those based on
Bismuth/Tellurium/Selenium mixtures, are inherently mechanically
weak and hence, fragile in heterostructure form.
[0006] Heterostructure TE materials generally are configured to be
long in one dimension (e.g., wires) or two dimensions (e.g.,
plates). The TE materials are usually anisotropic with varying
thermal, electrical, and mechanical properties along different
axes. Electric current either flows parallel to a long dimension or
perpendicular to the long dimension(s). In TE elements where the
current flows parallel to the long dimension, the length can range
up to thousands of times the thickness or diameter of the material.
To achieve the desired performance, such TE elements can be made of
a multiplicity of heterostructure wires or plates.
SUMMARY OF THE INVENTION
[0007] Various embodiments using heterostructures in forming
thermoelectric elements are disclosed. The heterostructures are
constructed with layers of bonding and/or intermediate materials
that add strength and/or improve manufacturability of completed
thermoelectric elements formed of the heterostructures. In
addition, the bonding and intermediate materials are used in
various manners to facilitate or enhance the operation of
thermoelectric assemblies. The thickness of the intermediate and
bonding materials take into account the desired thermal and
electrical characteristics and attributes for the particular
configuration or application. Both the thermal conductivity and
thermal conductance can be taken into account, in considering the
thickness of each bonding and intermediate material.
[0008] Several configurations for thermoelectrics are described.
One configuration involves a thermoelectric element that has at
least two heterostructure thermoelectric portions of the same
conductivity type (such as N-type or P-type). It should be noted
that the use of the term "same conductivity type" in this
configuration does not mean that these portions need to be of the
same material, nor doping concentration. An electrically conductive
material is coupled to the thermoelectric portions to form at least
one electrode.
[0009] Preferably, the heterostructure thermoelectric portions form
layers in the thermoelectric element, and the electrically
conductive material is coupled to at least one of the layers at
least one end of the layers. Preferably, the conductive material
couples to all or substantially all of the layers, where the
electrode is an end electrode. Alternatively, the electrically
conductive material may be coupled to at least the top or bottom of
the layers.
[0010] In one configuration, the heterostructure thermoelectric
portions form wires or a wire bundle, and the electrically
conductive material forms at least one electrode at the end of the
wire bundle. Preferably, an electrode is provided for each end.
Alternatively, the electrically conductive material is coupled to
at least the top or bottom of the wire bundle, or separate
electrodes are provided for the top and bottom of the wire
bundle.
[0011] In one example, a bonding material is between the at least
two heterostructure thermoelectric portions. The bonding material
is advantageously configured to reduce the power density or the
shear stress in the element, or both.
[0012] An intermediate material may also be provided between the
heterostructure thermoelectric portions and respective electrodes.
Advantageously, the intermediate material is configured to reduce
shear stress in the heterostructure thermoelectric portions when
the thermoelectric element is operated. For example, the
intermediate material may be resilient.
[0013] In one example, the heterostructure thermoelectric portions
are of substantially the same thermoelectric material. The
heterostructure thermoelectric portions may also be constructed of
at least two layers of heterostructure thermoelectric material.
[0014] Another example of a thermoelectric element described has at
least two layers of substantially the same thermoelectric material
of the same conductivity type. At least one electrically conductive
material is coupled to the thermoelectric material to form at least
one electrode. In one form, the electrically conductive material is
coupled to the layers at least one end of the layers. Preferably,
an electrode is provided at least two ends. Alternatively, the
electrically conductive material is coupled to at least the top or
bottom of the layers, forming top and bottom electrodes. The layers
may also form wires, with the electrodes coupled to the wires at
least one end of the wires, or coupled to at least the top or
bottom of the wires.
[0015] In this example, a bonding material may also be provided
between the at least two layers. Advantageously, the layers and the
bonding material are configured to reduce the power density of the
thermoelectric. The layers and the bonding material may be
configured to reduce shear stress as an alternative, or in addition
to, reducing the power density.
[0016] An intermediate material may also be provided between at
least one electrode and at least one layer of the thermoelectric
material. Preferably, the intermediate material is also configured
to reduce shear stress in the layers. In one configuration, the
intermediate material is resilient.
[0017] The at least two layers may also be heterostructures, as
with the previous example. The heterostructures themselves may be
made from at least two layers of heterostructure thermoelectric
material.
[0018] Also disclosed is a method of producing a thermoelectric
device involving the steps of layering at least two heterostructure
thermoelectric segments, and connecting at least one electrode to
the segments to form at least one thermoelectric element.
[0019] The step of layering may comprise bonding the at least two
heterostructure thermoelectric segments with a bonding material. A
further step of providing an intermediate material between at least
one of the at least two heterostructure thermoelectric segments and
at least one electrode may be used.
[0020] Preferably, the layers and/or the bonding and/or
intermediate materials are configured to decrease power density.
One or another, or all, may be configured to reduce shear stress as
well, and/or reducing the power density.
[0021] Another method of producing a thermoelectric device involves
the steps of forming at least two layers of substantially the same
thermoelectric material, and connecting at least one electrode to
at least one of the layers. Preferably, the step of forming
involves bonding the at least two layers with a bonding
material.
[0022] Advantageously, as mentioned above, the bonding material is
configured to decrease power density and/or shear stresses.
Similarly, an intermediate layer may be provided between the layers
and the electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1a and FIG. 1b illustrate a thermoelectric element
constructed of thermoelectric heterostructures.
[0024] FIG. 2a and FIG. 2b illustrate a thermoelectric wire bundle
assembly.
[0025] FIG. 3 illustrates a portion of a thermoelectric
element.
[0026] FIG. 4 illustrates thermoelectric element assembly of
heterostructures.
[0027] FIG. 5 illustrates a thermoelectric element portion of a
heterostructure.
[0028] FIG. 6 illustrates a thermoelectric element portion.
[0029] FIG. 7 illustrates another thermoelectric element.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0030] Several embodiments of thermoelectrics are disclosed where
layers of heterostructure thermoelectric materials or thin layers
of thermoelectric material form a thermoelectric element.
Advantageously, the layers are of the same conductivity type
(N-type or P-type) for each thermoelectric element. In one
embodiment, the layers are of the same, or at least substantially
the same, thermoelectric material. Where the layers are
heterostructures, the heterostructures themselves may be formed of
layers of thermoelectric material. The layers may be bound together
with agents that improve structural strength, allow electrical
current to pass in a preferred direction, and minimize adverse
effects that might occur to the thermoelectric properties of the
assembly by their inclusion. Fabrication of useful TE systems
requires a careful understanding of the TE materials' individual
properties, such as thermal conductivity, electrical conductivity,
coefficient of thermal expansion, properties over the processing
and operating temperature ranges, and long-term stability. Often
properties associated with other materials used in assembly of TE
elements also can affect performance. Often interfacial
diffusivity, work function, bond strength and the like are
characteristics that arise from the use of combinations of
materials and can affect performance.
[0031] In systems where the preferred direction of current flow is
parallel to a long dimension (e.g., along a bundle of wires or
along the long direction of plates), a bonding material for the
heterostructures or thermoelectric layers advantageously has low
thermal and electrical conductivity, high adhesive strength, and
stable general properties that do not change during use.
[0032] For systems where the current flows perpendicular to the
long dimensions, such as through heterostructures or thermoelectric
material layers forming plates, preferred binding agents have high
electrical conductivity so that electric current passes through the
material with little resistive loss. Preferably, this is achieved
by the binding agent wetting the TE materials' surfaces either
directly, or through the use of an intermediate compatible wetting
agent. Advantageous binding agents also do not degrade the
performance of the resultant system either by requiring high
fabrication temperatures that could cause diffusion in the TE
heterostructure or promote degradation with time through diffusion,
ionic exchange, corrosion or other mechanisms. FIG. 1 depicts a TE
100 constructed of TE heterostructure plates 101 terminated at each
end with electrodes 102, 103. The layered plates 101 are assembled
with a bonding material 104. The TE 100 may make up one leg or
element of a TE module, and is either N or P conductivity type TE
material. Generally, many such TE elements are arrayed so that
current 105 flows alternately between N and P type materials, with
electrodes 102 and 103 making part or all of the current flow path
between TE elements 100.
[0033] At a first interface between the electrode 102 and the TE
plates 101, thermal energy, for example, is removed and at the
second interface between other electrode 103 and the TE plates 101
in this example, thermal energy is absorbed. Thus, electrode 102 is
cooled and electrode 103 is heated. In normal heating or cooling
operation, the heated electrode 103 is hotter than the cooled
electrode 102 so that heat flows from electrode 103 to electrode
102. In power generation operation, a temperature gradient applied
across the electrodes causes current to flow. Advantageously, the
properties of the TE plates 101 and bonding material 104, the
current 105 and the overall dimensions are chosen to minimize the
combination of the resultant conductive heat loss and Joule heating
from the current 105 passing through the TE element 100 so as to
maximize cooling or thermoelectric efficiency, or power generation
as is known in the art.
[0034] The bonding material 104 attaches the thin TE plates 101
into a slab that can be further processed (i.e., to connect
electrodes 102 and 103 with greater ease). Note, however, the
bonding material 104 conducts heat and thereby degrades the overall
performance of the TE element 100. Advantageously, therefore the
bonding material 104 should have poor thermal conductivity. It
could be an unfilled epoxy and should be in as low a proportion as
possible to the TE plates 101. Further it should not degrade with
time, and should not reduce in other ways the TE system's thermal
performance. Similarly, the bonding material 104 should not conduct
electrical current to the extent that such conductance measurably
increases Joule heating or causes current to bypass the TE plates
101. However, it is noted that some degree of electrical
conductivity in the bonding material 104 can be of benefit in
assemblies as noted below in connection with the description of
FIG. 7.
[0035] FIG. 2 depicts a TE element 200 in which the end electrodes
203 and TE wires 205 or wire bundle are in contact with an
intermediate conductor 202. The wire assembly 201 has a bonding
material 206 and a sheath 207 around the wire bundle 205.
[0036] The considerations that relate to efficiency and performance
of this configuration are the same as those for the TE element 100
of FIG. 1. Thus, advantageously, the bonding material 206 should
have low thermal conductivity and either be an electrical insulator
or be of low electrical conductivity. Preferably, the sheath 207
should have very low thermal and electrical conductivity.
[0037] The intermediate conductor material 202 serves to assure
uniform, very low electrical and thermal resistance between the TE
wires 205 and the electrodes 203. Advantageously, it makes uniform
electrical and mechanical connections to every wire. In some
configurations, where electrically conductive bonding material 206
is appropriate, the intermediate material 202 makes electrical
contact with the bonding material 206 as well. The intermediate
material 202 can be applied by vapor deposition, sputtering,
plating or any other process that forms a suitable electrical and
mechanical connection. In addition, the intermediate material 202
can be a solder that wets the wire 205 ends, can be conductive
adhesive, can be a flexible or otherwise resilient material that is
maintained under compressive force to provide electrical continuity
or any other suitable electrical connection mechanism. Further, the
intermediate material 202 can itself be made of more than one
material. For example, a first layer could be nickel sputtered onto
the wires at their ends, and a second layer of tin plating for
solderability. A copper electrode 203 could have a copper flash and
gold plating for solderability. Finally these two assemblies could
be bonded together with solder to form the complete terminator of
the assembly 200.
[0038] Similarly, the sheath 207 could be multi-layered. For
example, it could consist of an inner conformal coating covered by
a solid or mesh outer layer. It could serve any of several
mechanical purposes, such as providing the mechanical attachment to
maintain compressive forces on electrodes 202 as described above.
Alternately, the sheath 207 could be omitted altogether as in the
design in FIG. 1.
[0039] The bonding material 206 could be omitted as well, or it
could only partially fill the voids so as to have air or vacuum
spaced within the assembly. It could be a coating applied to the
outer surface of the wires 205 and then sintered or pressed, so as
to electrically connect and/or mechanically hold the wires 205 in
the desired final configuration.
[0040] Finally, the electrodes 203 could be placed on the top
and/or bottom of the wires rather than forming end electrodes.
[0041] FIG. 3 depicts a portion of a TE element 300 that has a
lower electrode 305, an intermediate conductor material 304, a
first diffusion barrier 302 and TE material 301, in plate form. The
TE material 301 is depicted as three layers for convenience; in
actual TE elements it could be of any number of layers and could
have bonding materials (not shown) between the layers as in FIG. 1,
to electrically and uniformly connect them. (Alternatively, a
material constituent of the hetero structure TE material 301 itself
would make the connection if the assembly were suitably processed
(such as with heat and pressure). A second diffusion barrier 302
attaches to another intermediate material 304, which attaches to an
upper electrode 303. In the example, a current 306 passes from the
lower electrode 305 through, the layer and to the upper electrode.
Since current passes through the intermediate material 304 and the
diffusion barriers 302, advantageously, both are of high electrical
and thermal conductivity since the materials are in series with the
TE material 301. Thus, the criterion is the same as for the
intermediate material 202 of FIG. 2, but the opposite of the
bonding material 104 and 206 of FIGS. 1 and 2.
[0042] FIG. 4 depicts a portion of a TE element 400. A first
portion consists of an upper electrode 401, an intermediate
material 402, TE material 403, an intermediate material 404 and a
lower electrode 405. The second TE element consists of an upper
electrode 407, and intermediate material 408, TE material 409, an
intermediate material 410 and a lower electrode 411. Solder 406 or
other conductive material is between the lower electrode 405 and
the upper electrode 407.
[0043] As an example of operation, current 412 passes from the
lower electrode 411 through the TE assembly 400 to the upper
electrode 401. In this embodiment of the invention, two TE portions
both of either N or P conductivity type TE material of the general
type of FIG. 3 are connected in series by an intermediate material
such as solder 406. This can be done for any of three principal
purposes: (1) reduce the power per unit area produced by the
assembly; (2) reduce thermal shear stresses; and (3) make the
assembly thicker and more rugged. The first purpose is important
since costs of fabricating heterostructure TE material increase
substantially as the number of layers increases. Furthermore, added
layers increase fabrication complexity and reduce yields.
[0044] It is important to have the ability to adjust power levels
to meet the demands of particular applications. If all else is
equal, power density is inversely proportional to TE material
thickness. Since heterostructures are most easily made thin, power
densities can be over 700 watts/square centimeter, which is
hundreds of times more than that of typical TE modules fabricated
from bulk materials. The high heat fluxes that can result can be
difficult to transport without substantial losses. As a result, TE
performance can be reduced so as to partially or completely negate
the higher intrinsic TE performance of the heterostructures. By
fabricating devices from multiple heterostructures, the TE material
is thicker and power density can be reduced. TE performance is
reduced by the electrical and thermal resistivity of the
intermediate materials, electrodes, solder and other materials in
electrical series with the TE material, but such losses are
minimized advantageously by careful choice of the materials and how
they are mated together. Thermal shear stresses are reduced by
making the physical distance between the cold electrode and the hot
electrode larger, using multiple layers of the heterostructures,
and by choosing materials throughout the assembly that have low
coefficients of thermal expansion. Also, stresses can be reduced by
utilizing intermediate materials that flex easily, such as
conductive rubbers, or materials that contain fluids, conductive
greases, mercury, other conductive liquids, and any other material
that so that they do not transmit significant shear stresses.
[0045] The third purpose of increased thickness is to make the
assembly more rugged so that it can withstand subsequent
processing, handling, usage and the like. Also, its durability and
stability can be increased by cladding and encapsulating or
otherwise protecting sensitive constituent materials.
[0046] In FIG. 4, the TE materials 403 and 409 may themselves be
layers of heterostructure TE materials as in FIGS. 1, 3, 5, and
6.
[0047] FIG. 5 depicts a TE element portion 500 formed of
heterostructure thermoelectric material or thin film layers of
thermoelectric material with a first electrode 501, bonding
materials 502, 506 and 507, TE plates 503 and 505, and a second
electrode 504. The TE plates 505 have gaps 509 due to defects or
manufacturing tolerances of the TE plates 503 and 505, joints
between the plates, or the assembly of many small TE plates into a
larger array or the like. Advantageously, the TE plates 503 and 505
are heterostructures of TE material and the bonding materials 502,
506, 507 generally cover the surfaces of the TE plates 503 and 505,
fill the gaps 509 and electrically connect the plates in the
direction of current flow 508. The bonding materials 502, 506 and
507 can be made of multiple materials as discussed in the
description of FIGS. 2 and 3. In this embodiment, the bonding
materials 502, 506 and 507 should have moderate to very high
electrical and thermal conductivity. If many gaps 509 exist,
electrical conductivity of the bonding materials at 506 and 507 and
between the stacked plates 503 and 505 should be moderate. In this
case, conductivity should not be so high and bonding material
thickness so great that significant current flow 508 is shunted
through the gaps 509 in the plates 505 rather than through the TE
plates.
[0048] FIG. 6 depicts a TE element portion 600 with electrodes 601,
intermediate materials 602, TE plates 603 and 604, and gap 605 in a
TE plate 604. In addition, bonding materials 608 are depicted
between the TE heterostructure layers 603, 604.
[0049] As in FIGS. 3, 4 and 5, current 606 passes through the TE
element portion 600 generally upward. In this design, two features
are presented. First, the TE plates 603 and 604 are fabricated with
an outer layer, not shown, that when processed by heat and pressure
or other suitable means, causes the plates 603 and 604 to adhere to
one another so as to allow current to pass generally uniformly and
with very low electrical resistance through the entire TE element
600. Alternately, and as shown in FIG. 6, bonding material 608 can
be used to the heterostructure layers 603 and 604. The intermediate
materials 602 make similar low electrical and thermal resistance
connections to the electrodes 601. Second, if the gaps 605 occur
sufficiently infrequently in the TE element 600, no special
provisions need be incorporated to enhance current flow in them.
Similarly, the intermediate material could be omitted if the bond
characteristics between the electrodes 601 and plates 603 are
suitable for the conditions discussed related to FIG. 6.
Advantageously the TE layers 603, 604 are heterostructure
thermoelectric material or thin layers of thermoelectric
material.
[0050] FIG. 7 depicts a TE element 700 with electrodes 701,
heterostructure TE plates 702, 703, and bonding materials 704, 706.
The current 707 flows generally parallel to a long dimension of the
plates 702 and 703. In this configuration, if either a significant
number of gaps 705 (or breaks) in the heterostructure plates 703
are present or the number of plates 702 and 703 in the stack is
small and some gaps 705 or breaks exist, the current 707 will be
diverted by the gaps 705, unless the bonding material 704 and 706
(1) fills the gaps 705, (2) possesses the appropriate degree of
electrical conductivity, (3) makes good electrical contact between
the gaps 705 and the conductive layers that comprise part of the
plates 703, and (4) does not contribute significantly to overall
electrical and thermal losses in the TE element. Advantageously,
distortion of the current flow 708 can be minimized by utilizing a
bonding material 704 with electrical and thermal conductivity
somewhat lower than that of the TE plates 702 and 703 in the
direction of current flow 707. The bonding materials 706 and 704
need to be thin enough or otherwise configured so that they do not
contribute significantly to the TE elements' 601 overall electrical
or thermal conductivity and thereby reduce TE efficiency.
[0051] If the gaps 705 occur sufficiently infrequently, the bonding
material 704 and 706 need not fill the gaps 705, and only need to
provide electrical continuity between adjacent plates 702 and 703
so that the current 708 can be accommodated without significant
distortion from the infrequent gaps 705 or breaks, as was discussed
in the description of FIG. 6.
[0052] The TE plates 702, 703 may also be formed of thin layers of
thermoelectric material. As mentioned above, the bonding material
is also advantageously selected to reduce the shear stresses in the
element. For example, flexible or otherwise resilient bonding
material may be advantageous in some circumstances.
[0053] Table 1 presents a summary of the advantageous
characteristics of sleeve, bonding material and intermediate
materials. Notwithstanding the guidance presented in Table 1, other
considerations or alternative design details may alter the
teachings. Thus, Table 1 does not limit the scope of the present
invention, but serves instead to give general design guidance.
TABLE-US-00001 TABLE 1 DIRECTION OF CURRENT FLOW MATERIAL Parallel
Perpendicular PARAMETER S BM.sub.1 BM.sub.2 IM S BM.sub.1 BM.sub.2
IM Thermal Conductivity L L L H L H M H Electrical Conductivity L L
M H L H M H Thickness L L L OPT L OPT L OPT L = Low; M = Medium; H
= High; OPT = Optional S = Sleeve; BM.sub.1 = Bonding Material
insignificant gaps; BM.sub.2 = Bonding Material significant gaps;
IM = Intermediate Material
[0054] It should be understood that the thickness of the
intermediate and bonding materials is generally indicated to meet
the desired thermal and electrical characteristics of these layers.
As will be understood from the above description, both the thermal
conductance and thermal conductivity of these materials is taken
into account in selecting the thickness and other properties of
these materials.
[0055] Although several examples of thermoelectric compositions
using the heterostructures and binding concepts described herein,
the above-described embodiments are merely illustrative and
variations from these could be made. For example, thin layers of TE
material could be used rather than heterostructures in any
embodiment. Further, features described in any one figure could be
combined with features of any other figure, if appropriate, to
achieve an advantageous combination in a particular device. Such
combinations are also the objects and teachings of the present
invention. Accordingly, the invention is defined by the appended
claims, wherein the terms used are given their ordinary and
accustomed meaning with no particular or special definition
attributed to those terms by the specification.
* * * * *