WO2011157394A1

WO2011157394A1 - Heat therapy apparatus

Info

Publication number: WO2011157394A1
Application number: PCT/EP2011/002912
Authority: WO
Inventors: Andrew Barr
Original assignee: Gentleheat Ltd
Priority date: 2010-06-15
Filing date: 2011-06-14
Publication date: 2011-12-22
Also published as: GB201009958D0

Abstract

A heat therapy apparatus comprising a heat application device having an electrical heating element incorporated into a multi-layer structure. The multi-layer structure includes a heat absorbent layer between the heating element and a heat reflective layer. The heating element comprises concentric rings provided on an electrically insulating substrate layer. The apparatus includes a control unit configured to control the heat generated by the device in accordance with a pulse waveform.

Description

HEAT THERAPY APPARATUS

Field of the Invention The present invention relates to heat therapy apparatus. The invention relates particularly to heat therapy apparatus for wearing by a user.

Background to the Invention For generations people have used the heat from, for example, hot water bottles to soothe and relieve pain in their muscles or joints. The widespread nature of this practice is testimony to the effectiveness of heat as either therapeutic or palliative. However, there are a number of inadequacies in a hot water bottle for this application. The most obvious weakness is that a hot water bottle has no self- heating mechanism. It can only release heat - and as it does so its temperature falls, thereby reducing its ability to go on delivering heat. A corollary to this weakness is that in order to achieve a therapeutic level of average heat delivery over a long enough period, the initial water temperature in the hot water bottle must be so hot that the user is at risk from scalding. Besides these obvious weaknesses, a hot water bottle is not designed to be worn or carried. It can therefore only be used as a therapeutic device while a person is sitting or lying down.

In recent years a number of alternative products have emerged that provide similar benefits as a hot water bottle for pain relief. None of these products address the primary weakness viz. inadequate temperature regulation. Most of these new products offer instant heat by a chemical reaction, others avoid the risk of water leaks by using solid beads to store heat by heating in a microwave oven. It would be desirable to mitigate the problems associated with the known products. Summary of the Invention

Accordingly, a first aspect of the invention provides a heat application device for a heat therapy apparatus, the device comprising at least one electrical heating element, typically incorporated into a multi-layer structure. Advantageously, said multi-layer substrate comprises a flexible, electrically insulating substrate layer, the or each heating element comprising an electrically conductive track carried by said electrically insulating substrate, typically provided on the surface of said substrate.

In preferred embodiments, said at least one electrical heating element comprises one or more heating element segments, each segment comprising a plurality of ring portions arranged substantially concentrically. More preferably, the portions comprise substantially circular rings arranged concentrically and connected together by at least one radial portion. Alternatively, the ring portions may be arranged in the form of a spiral.

It is preferred that the, or each, heating element, substantially fills the surface area of the heat application device. More than one segment may be used in cases where a single segment does not substantially fill the surface area of the heat application device. In one embodiment, the device is elongate (for example for application across a user's back) and includes two or more segments side by side. In this case it is convenient to arrange that the diameter of each segment is approximately the same as the width of the device, and that the length of the device is approximately equal to a multiple of the diameter of the segments

It is preferred that the segments are connected in series to form a continuous heating element. Ideally, any gaps left between segments may be filled by zig-zag portions of the heating element. In order to allow control of the heat generated by the heating element(s), one or more temperature sensors are preferably provided in the heat application device. Conveniently, the or each sensor may be provided on the surface of the heating element. Preferably, a respective temperature sensor is provided for each segment of a multi-segment heating element. Ideally, the respective temperature sensors are provided at the centre of the respective segment. Preferably, the temperature sensors are monitored independently of each other, each for example being included in a separate respective temperature monitoring circuit.

The multi-layer structure has an obverse face for applying heat to the user. The obverse face is preferably provided by a user-engaging layer. The user-engaging layer is preferably thermally insulating. The user-engaging layer is preferably formed from a padding material, especially a moisture absorbent material such as foam.

The or each heating element is preferably provided in or on an electrically insulating substrate to form a layer of the multi-layer structure. Conveniently, the or each heating element comprises an electrically conductive track provided on a surface of an electrically insulating substrate.

In preferred embodiments, the multi-layer structure includes a heat absorbent layer, which may also be referred to as a heat sink, that is preferably located adjacent the layer that includes the heating element(s). The heat absorbent layer acts as a heat sink in that it absorbs and retains heat energy emanating from the heating element(s) during use. The heat absorbent layer is advantageously provided behind the heating element(s) with respect to said obverse face of the multi-layer structure, more preferably adjacent the reverse face of the layer that includes the heating element(s). The heat absorbent layer is typically formed from a material having a relatively high specific heat capacity. The heat absorbent layer may for example be formed from high density foam. Advantageously, the heat absorbent layer is provided between said heating element(s) and a heat reflecting layer. The heat reflecting layer may for example be formed from copper, or other metallic material.

Preferably, a thermally insulating layer is provided behind (directly or indirectly) said heating element(s) with respect to said obverse face. The thermally insulating layer is preferably provided behind said heat absorbent layer, and may be located adjacent the reverse face of said heat absorbent layer, especially when said reflecting layer is not present. In the preferred embodiment, however, said thermally insulating layer is located behind both said heat absorbent layer and said heat reflecting layer, typically adjacent the reverse face of the heat reflecting layer. Alternatively, said thermally insulating layer may be provided between said reflecting layer and said heat absorbing layer. Ideally, said thermally insulating layer is provided against the reverse side of the heat reflecting layer, or against the reverse side of the heat absorbing layer if the heat reflecting layer is not present.

Each layer of the multi-layer structure is advantageously flexible to facilitate application to a user's body. The device is shaped and dimensioned to fit a target area of a user's body, for example the lower back or stomach.

A second aspect of the device provides a control unit for the heat application device of the first aspect of the invention. The control unit typically includes an electrical power source for supplying electrical power to the heating element(s) of the multi-layer structure. The control unit preferably also includes a controller for controlling the supply of power to the heating element(s). The control unit preferably includes a user interface for enabling a user to adjust one or more characteristics of the supplied power in order to control the heat generated by the device during use. The user interface may be operable to allow a range of temperatures (relative or absolute) to be selected. In preferred embodiments, the control unit includes means for allowing the user to select from a plurality of profiles for the heat output from the device. To this end, the user interface may be configured to allow a range of heat profiles to be selected, and controller may be arranged to control the output temperature of the device based on the heat profile selected by the user. For example, the arrangement may be such that the user can select from one of a plurality of pulse waveforms for the applied heat. To this end, the controller may control the temperature of the heat device to be cycled between two limiting values at a variable (or fixed) frequency and variable (or fixed) duty cycle conforming to a selected one of the following waveforms: sinusoidal, triangular, saw-tooth or rectangular. The user may be allowed to select either the frequency and/or the duty cycle of the waveform. A third aspect of the invention provides a heat therapy device comprising the heat application device of the first aspect of the invention and a control unit of the second aspect of the invention.

A fourth aspect of the invention provides a method of generating heat in a heat therapy device, the method comprising causing the heat to be generated in accordance with a pulse waveform. Preferably, the method involves causing the output temperature to be cycled between two limiting values at a variable (or fixed) frequency and variable (or fixed) duty cycle conforming to one of, or a selectable one of, the following waveforms: sinusoidal, triangular, saw-tooth, or rectangular.

Preferred embodiments of the invention provide improved heat regulation, preferably to a substantially constant temperature throughout the treatment period, in a package that is capable of being worn comfortably under normal clothing.

Further advantageous aspects of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of a preferred embodiment and with reference to the accompanying drawings.

Brief Description of the Drawings

An embodiment of the invention is now described by way of example and with reference to the accompanying drawings in which:

Figure 1 is a partially cut-away perspective view of a heat application device being a first part of a heat therapy apparatus embodying the invention;

Figure 2 is a perspective view of a control unit being a second part of said heat therapy apparatus; Figure 3 is a plan view of a first embodiment of an electrical heating element for use in the heat application device of Figure 1 ; and

Figure 4 is a plan view of a second embodiment of an electrical heating element. Detailed Description of the Drawings

Referring now to Figure 1 of the drawings, there is shown, generally indicated as 10, a heat application device that forms part of a heat therapy apparatus embodying the invention. The device 10 is intended to be worn against a user's body in the region that requires heat therapy, e.g. against the user's back or stomach, preferably under or within the user's clothing. To this end, the device 10 may be provided with attachment means for attaching it to a user's body, for example it may have one or more straps, be incorporated into a belt or garment (not shown) or may be provided with adhesive portions to allow direct adherence to the user's body. To facilitate its attachment to the user, and for reasons of comfort and unobtrusiveness, the preferred device 10 is relatively small, thin and lightweight. It is also preferably flexible such that it may conform to the shape of the user's body. Figure 1 shows the device 10 in the preferred form of a pad.

The preferred device 10 comprises a multi-layered structure having an obverse face for application to a user. The device 10 comprises means for generating heat. Advantageously, the heat generating means is electrically powered and comprises a heating device having one or more electrical heating elements 12 (Figure 3). Typically, each heating element 12 comprises a length of electrically conductive material, which may optionally be covered by an electrically insulating material. In preferred embodiments, the or each heating element 12 is provided on an electrically insulating substrate 14. The substrate 14 is preferably flexible and may for example be formed from a polycarbonate material. Advantageously, the or each heating element 12 is formed by pattern etching a layer of electrically conductive material, e.g. copper foil, provided on a face of the substrate 14.

Alternatively, the or each heating element 12 may be formed by screen printing or any other technique for incorporating conductive tracks onto or into an electrically insulating substrate. An electrical connector 16 is provided for electrically connecting the heating element(s) 12 to a power source, as is described in more detail hereinafter. The connector 16 may be a conventional cable connector, especially a multi-way cable connector.

The heating element(s) 12 are preferably provided on the obverse face of the substrate 14 (i.e. the face that faces the user during use), but may alternatively be provided on the reverse face of the substrate 14. Alternatively still, the heating element(s) 12 may be embedded in the substrate 14.

A preferred electrical heating device is shown in Figure 3 and comprises a single heating element 12. In designing a heating element for this application, consideration is given to the creation of a relatively uniform heat distribution across the device 10, as well as achieving a sufficient level of power output to provide a beneficial therapeutic effect. To these ends, it is desirable to provide a heating element 12 with a relatively low electrical resistance and relatively few discontinuities, e.g. sharp bends (which affect localized resistance and can create "hot spots"). For example, the power output of the heating element 12 may be approximately 20 W and its resistance may be approximately 3 ohms. In order to achieve a desired power output for a given size of device, it can also be desirable to maximize the length of the heating element 12 over a given area.

Preferably, the heating element 12 comprises one or more segment 12 A, 12B comprising a plurality of ring portions 13, e.g. substantially circular or non- circular rings, arranged concentrically. In the illustrated embodiment, the portions 13 are arranged as concentric rings connected together by a radial portion 15. Alternatively, the ring portions may be arranged in the form of a spiral.

More than one segment 12 A, 12B may be used in cases where a single segment does not adequately fill the area of the heat application device 10. In Figure 3, the device 10 is elongate (for example for application across a user's back) and is suited to two segments 12 A, 12B side by side. In this case it is convenient to arrange that the diameter of each segment 12 A, 12B is approximately the same as the width of the device 10, and that the length of the device 10 is approximately equal to a multiple of (in this case two times) the diameter of the segments 12 A, 12B. For devices 10 of different shapes and/or sizes, additional segments can be added, which may be the same or a different size to each other. It is preferred that the segments are connected in series to form a continuous heating element 12. Any gaps left between the segments may be filled by zig-zag portions of the element 12, see for example portions 12C and 12D in Figure 3.

In order to allow control of the heat generated by the heating element 12, one or more temperature sensors (not shown), for example one or more thermistor, are provided in the heat application device 10. Conveniently, the or each sensor may be provided on the surface of the heating element 12, or otherwise coupled to the heating element 12 to detect the generated heat. Preferably, a respective temperature sensor is provided for each segment 12 A, 12B of the heating element 12. Ideally, the temperature sensors are provided at the centre of the respective segment 12 A, 12B since this is typically the hottest portion of the heating element 12 during use. It is preferred that the temperature sensors are monitored independently of each other, each for example being included in a separate respective temperature monitoring circuit (not illustrated). Hence, failure of one temperature sensor (or its associated circuit) does not necessarily cause overheating. The temperature sensors are monitored by a control unit 50, described in more detail hereinafter.

Figure 4 illustrates an alternative arrangement of heating elements 12 on a substrate 14, wherein the heating elements 12 comprise substantially concentric circular segments as described above, and are arranged on the substrate in a substantially rectangular two dimensional array. In this example, each heating element 12 is connected in series to common terminals Tl, T2 by which power is supplied to all of the elements 12 collectively. Alternatively, one or more of the heating elements 12 may be connected to a respective circuit by which power may be supplied to the element(s) 12 of the respective circuit independently of the power being supplied to the respective heating element(s) of one or more other similar circuits. A respective temperature sensor (not shown) may be provided for each element 12 or for each circuit of elements 12.

Preferably, a layer 18 of padding is provided on the obverse face of the substrate 14. The padding layer 18 is intended to be placed against the user during use and so improves comfort. The layer 18 is preferably formed from a thermally insulating material. This helps to protect the user from any excessive heat, e.g. a hot spots, that may arise during use. The layer 18 is preferably formed from a foam material. This is particularly advantageous when the device 10 is placed directly against a user's skin, since the foam will absorb perspiration thereby increasing comfort. By way of example, the layer may be formed from a synthetic foam, especially a relatively low density foam. The material from which the layer 18 is formed may also be selected such that it provides electrical insulation. The outer surface of the layer 18 may be provided with adhesive to enable it to be attached directly to the user. The layer 18 may be fixed to the substrate layer 14 by any suitable means, e.g. adhesive. In use, the obverse face 19 of the padded layer 18 is placed in direct or indirect contact with the user's skin in order to apply heat thereto.

A layer 20 of heat absorbent material is provided on the opposite side of the substrate 14 to the layer 18, i.e. the reverse face of the substrate. The layer 20 is heat absorbent to the extent that it is able to store, during use, heat generated by the heating element 12. The layer 20 acts as a heat sink, absorbing and retaining heat energy from heating element 12. It is formed typically from a material having a relatively high specific heat capacity. The layer 20 is not regarded as a heat insulting layer, at least in that it has, in preferred embodiments, poorer heat insulating properties that the layer 18 and the layer 24. By way of example, the layer 20 may be formed from a foam material, for example silicone foam, preferably with a relatively high density. The layer 20 may be fixed to the layer(s) with which it is in contact by any suitable means, e.g. adhesive. During use, the heat absorbent layer 20 helps to create a relatively uniform heat distribution over the surface of the heat device 10. This complements the effect of the preferred heating element shape, which also serves to make heat distribution more uniform than it would otherwise be. Advantageously, a heat reflecting layer 22 is provided on the opposite side of the heat absorbent layer 20 to the substrate 14. The heat reflecting layer may be formed from any suitable heat reflecting material, for example a metallic foil. The heat reflecting layer 22 acts to reduce heat loss from the heating absorbent layer 20 and to reflect heat back into the layer 20. The layer 22 may be fixed to the layer(s) with which it is in contact by any suitable means, e.g. adhesive. Advantageously, a thermal insulating layer 24 is provided on the opposite side of the heat reflecting layer 22 to the heat absorbent layer 20. The insulating layer 24 acts to reduce heat loss from the reflector layer 22. The layer 24 may be formed from any suitable heat insulating material, for example a relatively low density foam. The layer 24 may be fixed to the layers with which it is in contact by any suitable means, e.g. adhesive.

During use, loss of heat from the surface of the device 10 is reduced by the combined action of the reflecting layer 22 and the insulating layer 24. This reduces the amount of electrical power that is required to achieve a target temperature and to hold it for a target duration.

Optionally, an outer layer 26 is provided on top of the insulating layer 24. The layer 26 may be formed from any suitable material, for example a water-proof or water resistant material such as vinyl. The layer 26 may provide a protective function to the layers beneath. The layer 24 may be fixed to the layers beneath by any suitable means, e.g. adhesive.

The layers of the multilayer structure need not be adhered directly to one another. For example, in a preferred embodiment, the device 10 is incorporated into a wearable item (not shown) such as a belt or garment. The wearable item includes one or more respective pocket for receiving one or more respective layers of the multilayer structure. The pocket(s) may be sealed or openable. One or more layers of the multi-layer structure may be fixed to the wearable item by any suitable fixing means, e.g. adhesive or stitching. One or more layers of the multilayer structure may be provided by the wearable item itself, which may be formed at least partly from, or include a panel of, material having the required characteristics of one or more of the layers of the multi-layer structure, e.g.

electrically insulating, thermally insulating, padded, foamed and/or heat absorbent. In the preferred embodiment, the substrate 14 with the heating element(s) 12 is provided in a pocket, preferably an openable pocket from which it can be removed and replaced. The pocket wall that, in use, is located between the obverse face of the substrate 14 and the user's body is preferably formed from a thermally insulating material although any natural or synthetic fabric or rubber, e.g. neoprene, may be used. Said pocket wall may be padded, e.g. foamed. The or each other layer of the multi-layer structure may be provided by the wearable item itself, fixed to the wearable item in the region of the pocket or insertable into the pocket or another pocket as is convenient. The wearable item, or at least part of it such as one or both walls of the pocket, may be formed from a synthetic fibre or synthetic rubber, e.g. lycra or neoprene. The layers of the multilayer structure are held together by the wearable item, and are held in close contact with one another particularly when the item is being worn by a user. Because, the layers, including the substrate 14 layer, are flexible, the multilayer structure can conform closely to the shape of the user's body. It can be seen from the foregoing description that the preferred device 10 comprises a multi-layered pad incorporating an electrical heating device. The preferred pad is thin and flexible and conforms readily to the shape of the user's body. The particular nature and arrangement of the layers described above may vary. For example, the padded layer 18 could be omitted or replaced with an alternative outer layer, such as a heat resistant electrically insulating layer. One or other or both of the reflecting and insulating layers 22, 24 could be omitted. The heat absorbent layer 20 could be omitted. Alternatively, or in addition, one or more further layers could be added to the device between or at the outside of one or more of the other layers. Such additional layers could be provided for, for example, thermal insulation, electrical insulation, heat absorption and/or heat reflection, and may be formed from any suitable material. Advantageously, all of the layers of the device are formed from a respective flexible material, optionally resiliently flexible. The layers may be fixed together by any suitable means, e.g. adhesive, heat sealing and/or mechanical fixing elements, including being incorporated into a belt or garment, or a pocket provided in a belt or garment. The heat therapy apparatus also includes a control unit, an embodiment of which is shown in Figure 2, generally indicated as 50. The control unit 50 includes an electrical power source (typically one or more batteries (not shown)) for supplying electrical power to the heating device 12 of the multi-layer device 10. The control unit 50 also includes a controller (not shown) for controlling the supply of power to the heating device 10. The controller conveniently comprises a suitably programmed microprocessor, microcontroller or other processor. The control unit 50 also includes means (e.g. one or more switches or other user operable controls that may be referred to generally as a user interface 52) for enabling a user to adjust one or more characteristics of the supplied power in order to control the heat generated by the device 10 during use.

In a simple mode of operation, this involves switching the heating device on or off. Preferably, the control unit includes means for allowing the user to select a desired temperature for the output of the heating device 10. To this end, the user operable controls may be configured to allow a range of temperatures (relative or absolute) to be selected, and one or more temperature sensors may be provided in the device 10 co-operable with the heating device. The controller may control the output temperature of the device 10 based on the temperature selected by the user and the feedback provided by the temperature sensor(s). Similarly, means for incrementally increasing or decreasing the temperature based on user input may be provided. The control unit 50 may include a display 54 for indicating the selected temperature. In preferred embodiments, the apparatus includes means for allowing the user to select from a plurality of profiles for the heat output from the device 10. To this end, the user operable controls may be configured to allow a range of heat profiles to be selected, and controller may control the output temperature of the device 10 based on the heat profile selected by the user and the feedback provided by the temperature sensor(s). For example, the arrangement may be such that the user can select from one of a plurality of pulse waveforms for the applied heat. To this end, the controller may control the temperature of the heat device 10 to be cycled between two limiting values at a variable (or fixed) frequency and variable (or fixed) duty cycle conforming to a selected one of the following waveforms:

sinusoidal, triangular, saw-tooth or rectangular. The user may be allowed to select either the frequency and/or the duty cycle of the waveform.

The control unit 10 may include a timer for allowing the user to monitor the length of time for which the device 10 is in use. For example, the arrangement may be such that the heat device 10 can be switched off by the user interface 52 and reactivated at a later time up to a maximum allowed time on the heat device 10. The user interface 52 on the control unit 50 may display, or otherwise indicate, to the user the amount of usage time remaining on the heat device 10. The control unit 50 may include a memory device and be arranged to keep a record of usage of the heat device 10.

The control unit 50 and heat application device 10 are inter-connectable by means of a communication link (not shown) which, in the illustrated embodiment, comprises a cable or other wired link and is arranged to provide electrical power to the device 10 (if required) and/or to carry control signals (e.g. temperature sensor output signals) between the control unit 50 and the device 10. The cable is connectable to the connector 16 on the heat device 10 and a suitable connector 56 is provided on the control unit for this purpose. In alternative embodiments, the power source may be provided at the heat device 10, in which case the

communication link may be wireless.

To prevent unauthorised use of the apparatus, it is preferred to provide on the heat application device 10 means for storing a unique identifier and for enabling a connected control unit 50 to check the unique identifier upon connection to the device 10. The control unit 10 may be arranged to co-operate only with one or more heat application devices 10 having recognised unique identifiers. For example, this may be achieved by providing the heat device 10 with one or more memory device, e.g. an eeprom, on which the unique ID is stored and from which it can be read when connected to a control unit 50.

The invention is not limited to the embodiment described herein, which may be modified or varied without departing from the scope of the invention.

Claims

CLAIMS:

1. A heat therapy apparatus comprising a heat application device, the heat application device comprising an electrically insulating substrate and at least one heating elements wherein said at least one heating element comprises a electrically conductive track provided on a surface of said electrically insulating substrate, and wherein said electrically insulating substrate layer is flexible.

2. An apparatus as claimed in claim 1, further including a control unit configured to control the operation of the heat application device, the apparatus further including an electrical power source for supplying electrical power to the or each heating element, and wherein the control unit includes control means configured to control the supply of power to the heating element(s) from said power source.

3. An apparatus as claimed in any claim 1 or 2, wherein said control unit is arranged to control the output temperature of the heat application device in accordance with a heat profile.

4. An apparatus as claimed in claim 3, wherein said apparatus includes user- operable control means for enabling a user to adjust said heat profile, preferably to select said heat profile from a plurality of selectable heat profiles.

5. An apparatus as claimed in claim 3 or 4, wherein said control unit is configured to control the temperature of the heat application device to vary between first and second temperature values over time.

6. An apparatus as claimed in claim 5, wherein said control unit is configured to control the temperature of the heat application device to cycle between said first and second temperature values according to a pulse waveform associated with said heat profile.

7. An apparatus as claimed in claim 6, wherein said pulse waveform is substantially sinusoidal, substantially triangular, substantially saw-tooth or substantially rectangular.

8. An apparatus as claimed in claim 6 or 7, wherein said control unit includes means, preferably user-controllable means, for adjusting the frequency and/or duty cycle of said pulse waveform.

9. An apparatus as claimed in any one of claims 2 to 8, wherein said control unit includes user-operable means for adjusting the temperature applied in use by said heat application device.

10. An apparatus as claimed in claim 9 when dependent on any one of claims 6 to

8, wherein said user-operable temperature adjusting means is configured to allow said user to select one or both of said first and second temperatures.

1 1. An apparatus as claimed in any one of claims 2 to 10, wherein said control unit is configured to control said generated heat in response to signals received or derived from one or more temperature sensor configured to monitor the temperature of the or each heating element.

12. An apparatus as claimed in claim 11, wherein said control unit is configured to control independently each segment of a multi-segment heating element in response to signals received from a respective temperature sensor.

13. An apparatus as claimed in any preceding claim, wherein said at least one electrical heating element is incorporated into a multi-layer structure having an obverse face for applying heat to the user, the obverse face being provided by a thermally insulating user-engaging layer of said multi-layer structure.

14. An apparatus as claimed in claim 13, wherein the user-engaging layer is formed from a padding material, preferably a moisture absorbent material such as foam.

15. An apparatus as claimed in claim 13 or 14, wherein the multi-layer structure includes a heat absorbent layer located behind the or each heating element with respect to said obverse face.

16. An apparatus as claimed in claim 15, wherein said heat absorbent layer is located adjacent a layer that includes the or each heating element, preferably adjacent the reverse face of the layer that includes the or each heating element.

17. An apparatus as claimed in any one of claims 13 to 16, wherein the multilayer structure includes a heat reflecting layer located behind the or each heating element with respect to said obverse face.

18. An apparatus as claimed in claim 17 when dependent on claim 15 or 16, wherein the heat absorbent layer is provided between the or each heating element and said heat reflecting layer.

19. An apparatus as claimed in any one of claims 13 to 18, wherein said multilayer structure includes a thermally insulating layer behind the or each heating element with respect to said obverse face.

20. An apparatus as claimed in claim 19 when dependent on any one of claims 15 to 18, wherein the thermally insulating layer is located behind said heat absorbent layer with respect to said obverse face, and behind said heat absorbent layer, when present, with respect to said obverse face.

21. An apparatus as claimed in any preceding claim, wherein said heat application device is incorporated into a wearable item, such as a belt or garment.

22. An apparatus as claimed in claim 21 when dependent on any one of claims 13 to 20, wherein said wearable item comprises at least one pocket, at least one of the layers of said multi-layer structure being located, in use, in said at least one pocket.

23. An apparatus as claimed in claim 21 or 22, wherein at least one of said layers of said multi-layer structure is incorporated into the structure of said wearable item by fixing means.

24. An apparatus as claimed in any one of claims 21 to 23, wherein at least one of said layers of said multi-layer structure is provided by said wearable item.

25. An apparatus as claimed in any one of claims 13 to 24, wherein each of said layers of said multi-layer structure is flexible.

26. An apparatus as claimed in any preceding claim, wherein, said at least one electrical heating element comprises one or more heating element segments, each segment comprising a plurality of ring portions arranged substantially

concentrically.

27. An apparatus as claimed in claim 26, wherein said ring portions comprise substantially circular rings arranged concentrically and connected together by at least one radial portion.

28. An apparatus as claimed in claim 26, wherein said ring portions are arranged in the form of a spiral.

29. An apparatus as claimed in any preceding claim, wherein said at least one heating element is shaped and dimensioned to substantially fill the surface area of the heat application device.

30. An apparatus as claimed in any preceding claim, wherein said at least one electrical heating element comprises a plurality of substantially co-planar heating element segments located side-by-side.

31. An apparatus as claimed in any one of claims 26 to 30, wherein the segments are connected in series to form a continuous heating element.

32. An apparatus as claimed in any preceding claim, wherein one or more temperature sensors are provided in the heat application device, the or each temperature sensor being arranged to detect the temperature of the or each heating element.

33. An apparatus as claimed in claim 32 when dependent on any one of claims 26 to 32, wherein a respective temperature sensor is provided for each segment of the or each heating element, preferably located at the centre of the respective segment.

34. A method of generating heat in a heat therapy apparatus as claimed in any preceding claim, the method comprising causing the heat to be generated in accordance with a pulse waveform.