Description: This invention relates to thermoelectric transducers.

Thermoelectric transducers are useful devices as they can be used to provide power sources for low-powered devices, such as sensors. In the aircraft industry, for example, a thermoelectric generator located next to a sensor may be employed to power wingtip sensors to avoid the need for power lines to extend from the fuselage to the wingtips, which can reduce the weight and/or complexity of the aircraft's wiring. Similar technologies are under development in the automotive industry with the aims of increasing fuel economy and reducing wiring loom complexity, as well as in un-manned, remotely-located installations, such as automated weather stations and the like.

Thermoelectric transducers can also be usefully employed in trace heating or cooling applications, for example, to cool wiring or to heat pipework. Advantageously, because the heating or cooling output of thermoelectric transducers is dependent on temperature differentials, thermoelectric transducers can be self-regulating, which can reduce the amount of control equipment needed to maintain items within desired temperature ranges.

Thermoelectric transducers are devices that exploit the thermoelectric effect, that is to say, a direct conversion of temperature differences into electricity or vice-versa. This invention relates, in particular, to thermoelectric transducers that employ thermocouple junctions to generate voltages in response to temperature differentials (using the Seebeck effect) or to create temperature differentials in response to applied voltages (using the Peltier effect).

A known problem with the use of thermocouple junctions used to generate power is that their thermodynamic efficiency is generally very low such that the conversion of heat to electrical currents, and thus the power output of such devices can be very small, meaning that large numbers of thermocouples are often needed to obtain a useful output. Simply multiplexing a plurality of thermocouples introduces unwanted complexity and additional wiring, so a solution is needed that provides the benefits of having multiple thermocouples, but without large amounts of wiring. In addition, to obtain the maximum power output or cooling effect, it is often necessary to arrange the thermocouples in areas that are maintained at different temperatures to obtain, or create, the requisite temperature differential. Arranging the thermocouples thus can be difficult, time- consuming, expensive and error-prone.

The invention therefore aims to provide a solution to one or more of the above problems and/or to provide an improved and/or alternative thermoelectric transducer.

According to a first aspect of the invention, there is provided a thermoelectric transducer formed from an undulating conductor having positive and negative inflection points arrangeable, in use, such that there is a temperature differential across the distance between the said positive and negative inflection points, the undulating conductor comprising a plurality of alternating conductor portions manufactured from different first and second electrically conductive materials, the alternating conductor portions being electrically interconnected to form a series of thermocouple junctions where they interconnect, and wherein the thermocouple junctions are located at substantially equal distances from their respective nearest inflection points.

The undulating conductor is suitably a bi-material conductor.

By using an undulating conductor incorporating a number of thermocouple junctions, it is possible to address more than one thermocouple simultaneously via electrical connections made at spaced apart points on the conductor. As such, the invention suitably provides a means of addressing a number of thermocouples simultaneously, which reduces the wiring requirements compared to addressing each thermocouple individually.

The conductor of the invention undulates, which may conveniently enable it to be positioned such that some or all of the positive inflection points are maintained at, or substantially at, a first temperature, whilst the negative inflection points are maintained at, or substantially at a second temperature that is different to the first temperature. Suitably, such a configuration enables the undulating conductor to be embedded in, or incorporated into, a support structure or material that places the positive and negative infection points on opposite sides of the support.

The undulating conductor comprises a plurality of alternating conductor portions manufactured from different first and second electrically conductive materials. The selection of the different materials is a matter of choice and design requirements. However, it will be appreciated that to maximise the efficacy of the invention, the first and second materials should meet one or more, but preferably as many as possible, of the following requirements:

1. The difference between the Peltier coefficients of the two materials should be as high as possible to maximise the potential for the generation of electrical power; and/or

2. The two materials should each have the lowest possible electrical resistance to minimise Ohmic and/or resistive losses along the undulating conductor, which could otherwise result in a reduction in electrical power output; and/or

3. The two materials should each have the lowest possible thermal conductance to minimise the transmission and/or conduction of heat across the system, which could otherwise reduce the temperature differential thus reducing the efficacy of the transducer; and/or

4. The relative cross-sections of the two conductors should be selected to balance both Ohmic energy losses and thermal convection.

Suitably, the two different materials could comprise: Constantan (a Cu-Ni alloy commonly used as resistor wire); and a Nichrome (a Ni-Cr alloy), although other material combinations meeting the above requirements could also be used.

The alternating conductor portions are electrically interconnected to form a series of thermocouple junctions, which interconnections could be made by any suitable means, such as spot welding.

The thermocouple junctions are located at substantially equal distances from their respective nearest inflection points, and suitably, the undulating conductor may have substantially equally-spaced positive and negative infection points and the thermocouple junctions may suitable located to align with, or to substantially align with, the inflection points. By aligning the thermocouple junctions with the inflection points, the maximum possible transverse spacing between the thermocouple junctions can be obtained.

The undulating conductor comprises a plurality of alternating conductor portions of different materials. Such a configuration could be formed by laying a pair of conductors manufactured from the said different materials side-by-side and by joining them at intervals to form the said thermocouple junctions. The alternating material nature of the undulating conductor could then be formed by creating a discontinuity in a first one of conductors at a point located between a first and a second one of the junctions, and by creating a discontinuity in a second one of the conductors at a point located between the second and a third one of the junctions, the first, second and third junctions being arranged in sequence along the length of the conductors. This "repeat unit" could be repeated along the length of the conductor to form the undulating conductor.

Conveniently, the undulating conductor could be woven into a support web such that the positive inflection points and/or the first type of thermocouple junctions are arranged at, or substantially at, a first surface of the web, and the such that the negative inflection points and/or the second type of thermocouple junctions are arranged at, or substantially at a second surface of the web opposite the first surface. Such a configuration may conveniently provide a structure incorporating the requisite undulations: the undulations being formed as the conductor (laid in the weft direction) rises and falls over strands in the warp direction of the web.

Suitably, an undulating conductor formed from a pair of conductors that are electrically interconnected at intervals, and broken at staggered intervals (as previously described) could be woven into a web of textile, such as a fabric web, or a composite material web, such as woven glass fibre sheets. Suitably, the weave of the fabric web or textile is a twill weave of a 2/2 (two up-two down) configuration. A second aspect of the invention therefore provides a web comprising a plurality of substantially electrically insulative warp strands and a plurality of substantially electrically insulative weft strands interwoven substantially perpendicularly to the warp strands to form a support web, wherein at least one adjacent pair of warp or weft strands of the support web are substituted by a pair of electrically conductive strands manufactured from different materials, the or each pair of electrically conductive strands being electrically interconnected to form thermocouple junctions at intervals and wherein the conductive strands comprise an electrical discontinuity at staggered and alternating positions interposed between the thermocouple junctions.

Preferably, the web is a twill woven web.

A third aspect of the invention provides a laminated composite material comprising a web as described herein.

A fourth aspect of the invention provides a textile comprising a web as described herein. The textile is suitably a flexible textile material, which may be used, for example, in clothing, upholstery, drapery and the like.

A fifth aspect of the invention provides a loom for manufacturing a web as described herein comprising means for supporting and tensioning a plurality of warp strands, one or more lifters for selectively raising one or more of the warp strands to form a shed for one of a plurality of shuttles to pass through when laying the weft strands, the shuttles carrying the insulative weft strands and the two types of conductive weft strands, characterised by a first electrode arranged to make a first electrical contact with the conductive weft strands and a second electrode arranged to make a second electrical contact with the weft strands and further comprising an electrical power source electrically connected to the first and second electrodes to pass an electrical current through pairs of adjacent conductive weft strands to weld or to break them.

A sixth aspect of the invention provides a loom for manufacturing a web as described herein comprising means for supporting and tensioning a plurality of conductive and non-conductive warp strands, the conductive warp strands being arranged as pairs of adjacent strands separated by one or more non-conductive warp strands, one or more lifters for selectively raising one or more of the warp strands to form a shed for one of a plurality of shuttles to pass through when laying the weft strands, the shuttles carrying the insulative weft strands, characterised by a first electrode arranged to make a first electrical contact with a first one of the conductive warp strands and a second electrode arranged to make a second electrical contact with a second one of the conductive warp strands and further comprising an electrical power source electrically connected to the first and second electrodes to pass an electrical current through pairs of adjacent conductive warp strands to weld or to break them.

Suitably, the first electrode comprises a bar electrode arranged to engage the web from one side to make electrical contact with the electrically conductive weft strands. Suitably, the bar electrode further comprises an insulator for electrically isolating the bar electrode from the second electrode. The second electrode suitably comprises a comb electrode, the teeth of which electrode are locatable, in use, in the spaces between the warp strands.

Additionally or alternatively, the first and second electrodes may comprise pins or protrusions that can be positioned in the gaps between the warp and weft strands, and which can be moved relative to one another to clamp adjacent conductive strands together whilst an electrical current is passed.

Means is preferably provided for pressing the second electrode against a second one of the pair of conductive weft strands of the web.

The loom's power source may be adapted to deliver pulses of electrical energy to the first and/or second electrode and may additionally comprise a switching circuit enabling the pulses of electrical energy to be delivered to each tooth of the comb electrode individually. The power source may optionally further comprise a switching circuit enabling the pulses of electrical energy to be delivered to each tooth of the comb electrode sequentially.

A seventh aspect of the invention provides a method of weaving substantially as described herein. Advantageously, by weaving the electrically conductive strands into a support web, the conductors can be arranged to undulate and support web itself can provide a separating layer interposed between regions of different temperatures on opposite sides of the woven web. Put another way, an aspect of the invention suitably provides a series of interconnected conductors of differing materials that extend through the thickness of the web with spaced apart, and serially-, and electrically-interconnected thermocouple junctions at their extremities thus enabling the series of conductive strands to function as a thermoelectric transducer comprising a plurality of thermocouples. Such a configuration may also enable a large number of thermocouples to be addressed simultaneously by making an electrical connection with the ends of the conductive strands.

Preferably, the twill woven web comprises a plurality of pairs of electrically conductive strands at spaced-apart locations.

The or each pair of electrically conductive strands may be addressed by electrical connections at spaced apart locations. The pairs of electrically conductive strands could be addressed individually, although the support web may additionally comprise one or more spaced- apart electrically conductive warp or weft strands, which may suitably provide an electrical connection between multiple pairs of electrically conductive warp or weft strands.

The support web may be manufactured from any desired, electrically insulative material. It is envisaged, in particular, that the pairs of electrically conductive weft strands could be woven into structural textiles, such as sheets of woven glass fibre so that the thermoelectric transducer can be embedded in a laminated composite lay-up. Additionally or alternatively, the support web may comprise conventional textiles, such as cotton, flax or synthetic fibres, so that the woven web incorporating the thermoelectric transducer can be used in clothing, drapery, upholstery and so on.

Preferred embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic plan view of a twill woven textile incorporating three thermoelectric transducers according to the invention;

Figure 2 is a schematic cross-section of Figure 1 on ll-ll;

Figure 3 is a simplified schematic side view of a loom for manufacturing the twill woven textile of Figures 1 and 2;

Figure 4 is a simplified schematic perspective view of the loom of Figure 3;

Figure 5 is a simplified perspective view of a welding operation for a twill-woven web in which the undulating conductor of the invention is in the warp direction; and

Figure 6 is a simplified view of an arrangement for electrically welding and/or breaking the warp or weft strands

Figure 1 is a schematic plan view of a section of twill woven web 10 in accordance with the invention. The web 10 comprises a plurality of substantially parallel, electrically insulative warp strands 12 interwoven with a substantially perpendicularly aligned set of weft strands in a 2/2 or "two up-two down" configuration to form a twill weave. The weft strands comprise a set of spaced- apart, electrically insulative weft strands 14 that separate pairs 34 of electrically conductive weft strands 16, 18 manufactured from individual wires or braids of two different metals, in the illustrated embodiment, Constantan and Ni-Cr alloy, respectively.

As can be seen most clearly in Figure 2, the conductive strands 16, 18 undulate within the support web 10, rising to the upper surface 20 and falling to the lower surface 22 in a staggered, alternating fashion. The conductive strands 16, 18 are welded to one another by spot welds 24 at points where they meet. In addition, alternate strands 16, 18 are broken 26 at intervals at locations corresponding to intervals where they meet the lower surface 22 of the web, but it will be appreciated that they could be broken instead, where they meet the upper surface 20, provided the arrangement of welds 24 and breaks 26 is consistent. Accordingly, a structure is formed within the support web providing a continuous conductor formed from the pair of conductive strands, with the path of electrical conductance approximately following the line indicated by 28.

In such a structure, it will be noted that an electrical current can pass alternately through a section of the first conductor 16 and then through the second conductor 18. Thereby, a series of thermocouples are formed - each thermocouple comprising a pair of dissimilar conductor sections 30, 32 joined to one another by the spot welds 24.

It will be appreciated, from Figure 2 in particular, that the conductor sections 30 formed from the first conductive strands 16 are aligned in one direction (i.e. upwards from left to right in Figure 2), whereas the conductor sections 32 formed from the second conductive strands 18 are aligned in the opposite direction (i.e. downward from left to right in Figure 2). As such, if the opposite sides 20, 22 of the web are maintained at different temperatures, the thermocouple junctions formed by the welds 24 will cooperate to generate electrical currents flowing in the same direction in the weft direction of the web 10. Accordingly, the structure of Figures 1 and 2 provides a plurality of serially-interconnected thermocouples that cooperate to produce a net voltage output that is greater than the voltage output of any individual thermocouple.

In order to balance the system, each conductor section 30, 32 ideally has the same, or substantially the same, electrical resistance. Given that the two materials 16, 18 will normally have different resistivities, it may be necessary for the cross-sectional areas of the conductor sections 30, 32 to be appropriately sized to meet this criterion.

In Figure 1, it will be noted that the web 10 comprises a number of sets 34 of conductor pairs 16, 18, each producing a net voltage across the weft direction of the web 10. The conductor sets 34 can be addressed individually by connecting, say, fly leads (not shown) to opposite ends of the sets 34, or in parallel, by spaced-apart, electrically conductive weave strands 36.

Although not shown in Figure 1, each conductor section 32 can be separated by an appropriate number of non-conducting sections such that the conductors are aligned in the warp direction, which facilitates making electrical connections using conductive weft strands. In the example of Figure 1, such a configuration could be achieved by providing two insulating weft strands 14 between each pair of conductors 32. Aligning the conductors conveniently allows the web to be cut to various sizes without unbalancing the electrical potentials of the undulating conductors, in use. Such a configuration therefore avoids the need to cut the web in integer multiples of weft strand widths to maintain the utility of the resultant thermoelectric web.

The web of Figures 1 and 2 can be manufactured on a modified loom 50, as shown schematically in Figures 3 and 4. The weaving operation of the loom 50 to form a twill weave is well- known in the weaving art, and does not warrant detailed discussion here. However, it will be appreciated that separate shuttles are required for each of the two types of conductive weft strands 16, 18 and insulating weft strands 14.

The main modifications to the loom 50 subsist in the manner of forming the welds 24 and the breaks 26, which can be accomplished using, for example, electrical resistance welding techniques, laser welding and laser cutting or ablation.

In Figure 3, a loom 100 comprises a set of rollers (not shown) which support and tension the warp strands 12 in a known manner. The loom 100 additionally comprises a lifter (not shown) associated with each warp strand 12 to enable them to be raised individually, or in groups, to form a space 102 for the shuttle (not shown) to pass through when laying the weft strands 14, 16, 18.

Located below, and in contact with the underside of the web 10, there is provided a first bar electrode 104 that makes electrical contact with the conductive weft strands from below, whilst a second comb electrode 106 is placed into the loom 100 such that the teeth of the comb electrode 106 are positioned in the spaces between the warp strands 12.

The comb electrode 106 is then pressed, as indicated by arrow 108, by a suitable drive device, such as a linear motorised actuator 110 to bear against the second one 18 of the pair of conductive weft strands of the web 10. An electrical voltage can then be applied between the comb electrode 106 and the bar electrode 104 to pass a current through the conductive weft strands 16, 18, whereupon a weld 24 and subsequent thermocouple is formed at each point where the two meet.

To avoid short-circuiting the comb 106 and bar 104 electrodes, the bar electrode 104 is provided with an insulative surface 114 which allows the teeth of the comb electrode 106 to safely clamp against the second one of the conductive weft strands, thereby holding it in place during the welding process.

The welding current/voltage is delivered by a power source 116, which is configured to deliver a short pulse of energy to each of the teeth of the comb electrode 106. A switching circuit 120 is provided to enable the pulse of energy to be delivered to each tooth of the comb electrode 106 individually, thereby providing for a more controlled welding operation.

It will be appreciated that the comb electrode 106 will also make contact with the conductive weft strands at points where they do not meet. Because each pulse of energy is substantially the same, where the pulse is delivered to two conductive weft strands 16, 18 where they meet, the energy will be shared, meaning that the energy density will be sufficient to melt, and thus weld, the two strands together. However, when the same pulse of energy is delivered to just one conductive weft strand only, the same energy will not be shared forming a "bad weld", which thus forms the requisite breaks/discontinuities 26 in the structure previously described. This operation also works where a conductive warp strand 12 meets one or two conductive weft strands 16, 18, thus forming the parallel connections between rows of thermoelectric transducers in the web 10. Of course, where the comb electrode 106 encounters non-conductive weft strands only, this will create an open circuit and no, or substantially no, welding or breaking will occur.

Figure 5 shows an alternative version of the web of Figures 1 to 4 in which the warp strands are formed by alternating pairs of conducting strands 16, 18 separated by insulative warp strands (not shown). In such a situation, the weft strands are electrically insulative, except for occasional conductive weft strands that can be used to address the undulating conductor or conductors to obtain the voltage output or input, as desired. By weaving the web in this orientation, the setup of the loom can be greatly facilitates because the shuttles only need to carry one type of strand, that is to say, the insulative strands, which can greatly simplify the weaving process.

As can be seen from Figure 5, the welding/cutting operation can be accomplished by using electrode pairs that are inserted into the gaps between the strands. In this case, however, the electrodes 106 are moved transverse to the warp direction to clamp adjacent pairs of conductors 16, 18 together during a welding/cutting operation.

Other methods of forming welds may be employed without detriment to the invention. In Figure 6, for example, a woven web is pulled between a pair of opposing rollers 150 having a series of radial protrusions 152 that are positioned to protrude into alternate gaps 154 between the weft and weave strands from above and below the web. The protrusions 152 are conical to facilitate insertion into the gaps 154, and when brought into opposition, act as wedges to pinch adjacent strands together thus facilitating the welding/cutting operation. By applying a voltage to the rollers 150, electrical connections can be made between the protrusions 152 via the conductive strands 16, 18 to form the welds or breaks as required. The correct registration and alignment of the rollers and web will, of course, need to be carefully setup, but it will be appreciated that by weaving the web first, and then welding/breaking appropriate conductors using a roller-based electrode system may greatly simply and aid automation of the manufacturing process.

The invention is not restricted to the details of the foregoing embodiments, which are merely exemplary of the invention. For example, the type of weave could be altered; the materials and methods of construction; or the applications for the resulting invention could be changed without departing from the scope of the invention. For example, the conductors need not necessarily be metal or alloy conductors, but could be conductive polymers or composite materials. In particular, the invention may be formed as a three-dimensional structure comprising several layers of support webs with the undulating conductor woven through it. In addition, a thermal ballast layer may be provided on one or both sides of the web to encourage a more uniform temperature and voltage distribution within the plane of the web, and to produce a more even thermal gradient across its thickness.