GB2562548B - Wireless power and data transfer via resonant yarn structure - Google Patents

Description

WIRELESS POWER AND DATA TRANSFER VIA RESONANT YARN STRUCTURE

Technical Field

This disclosure relates to the formation of yarns, textiles and membranes with wireless power transmitting capabilities suitable for integration into fabrics and wearables to power useful sensors and equipment.

Background

Mid-range Wireless PowerTransfer (WPT) technologies have gone through a recent technological leap making them worth consideration for integration in future wearable products. This document describes a use for WPT technologies with this application in mind. It is envisaged that the technology described herein is suitable and applicable for powering and monitoring bio-data driven systems to assess a wearer's health and fitness characteristics. WPT technologies are becoming more affordable due to the growing demand for distributed and small embedded sensors in future devices. Today, WPT technologies have still not been combined effectively with wearable technologies due to the size and area requirements of the electronic components and sensors that manufacturers might wish to combine into a garment in order to make a valid assessment of physical or mental health of a wearer.

Digital consumer health monitoring is gaining momentum in the fields of sports, healthcare, military and space exploration; but these are currently powered by cumbersome power sources, such as larger supercapacitors and battery packs which make solutions uncomfortable to wear for any extended period of time. Carrying battery packs and power supplies to monitor the health of an individual means that significant advances in sensor design and low power electronics are reduced to marginal gains due to an overshadowing worry of battery life.

For centuries, near-field wireless power transmission has been constrained to short distances as it was thought that efficient magnetic induction was not possible over larger distances. Far-field power transfer has been possible for some time, but it suffers from poor efficiency and directionality and has historically been limited to data transfer applications. In 2007, mid-range wireless transfer was shown to be possible using a technique referred to as Strongly Coupled Magnetic resonance (SCMR), a concept originally theorised by Nikola Tesla in the early 1890's. Advancements in mid-range power transfer efficiencies have also been made possible using intermittent or 'relay' resonators, any number of which may be placed between the source transmitter and end receiver.

SUMMARY

To fuel the next generation of wearables, there exists a need for a wireless system suitable for safe and efficient integration into fabrics or yarns in order to transfer power effectively to small low-power distributed sensors. A novel resonator structure composed of multiple small-sized resonators (with diameters of lOum-2mm) spaced along a central axis is proposed. This architecture of intermittent resonators, helps to overcome many common problems associated with WPT systems. The proposed embodiment overcomes some of these core problems with existing techniques and state-of-the-art demonstrations of effective wireless power transmission: improved resilience against receiver coil misalignment; a sub wavelength coil resonators and ferromagnetic core suitable for integration into fabric yarns for wearable technologies; a plurality of receiver circuits designed to receive power from an intermittent resonator.

According to an aspect, there is provided a yarn to be incorporated in a fabric or membrane to provide the fabric or membrane with wireless power transfer capabilities. The yarn comprises a ferromagnetic core including a non-conductive central core of a magnetically permeable material. The yarn also comprises a plurality of resonator coils wound around the core.

Disclosed herein is a yarn structure composed of multiple coil resonators which gives this yarn structure inherent wireless transfer capabilities which, when combined and repeated through weaving, knitting or depositing, creates a fabric or membrane that can safely receive and distribute wirelessly transferred power in useful amounts. This inventive technique creates a strong coupling between the individual small-sized coil resonators within the yarns of the fabric to share the received power with its direct neighbours thereby propagating a flow of energy to a multitude of tuned receiver circuits that may drive an electronic load or drain along the energy flow path. This system is capable of evenly distributing power and/or data over a wide surface area from multiple transmitter sources over mid-range distances. Furthermore, this fabric or membrane can in itself act as a large receiver or intermittent 'metamaterial1 capable of enhancing WPT involving a source due to its increased effective surface area. Multiple sources supplying power and/or data may have different or similar signal phases, and be placed at different distances away from the receiver. A wireless power source may be placed along the wall, ceiling or in the corner of a room to power an electronic wearable garment in, say, a hospital ward, fitness studio, scientific or space environment. The textile or garment may capture this wireless energy to power onboard micro-sensors also embedded into the yarns or larger external sensors which are connected to the garment using an appropriate clip, physical connector or wireless link. A wireless source for such a system is expected to make use of impedance matching circuits, control systems, amplifiers and where possible metamaterials or intermittent resonant coils to manipulate the electromagnetic field generated, enhancing energy transfer.

Within a single yarn, this wireless transfer system is achieved using a plurality of closely positioned (lum to 1 cm) coil resonators tuned to the transmission frequency of one or more wireless power sources. These coil resonators are magnetically linked through a ferromagnetic core within the core of the yarn which is shared by many, but not necessarily all coil resonators along the axis. A ferromagnetic core assists this system for a number of reasons: it confines much of the magnetic field received and transmitted within the yarn; and it reduces magnetic field leakage into the surroundings and away from human or animal users. These attributes are seen as safety requirements for medical health, military and space applications where reducing EM radiation is important so as not to affect other electrical equipment or users. The optimum behaviour of this core will ensure the greatest possible coupling and will significantly contribute to the overall efficiency and power capability of the system. This core may be made of a plurality of materials any of which may vary in length, diameter and cross-sectional area along the length of any given yarn. The upper limits for these parameters will be determined by the yarn's own length and diameter.

Coil resonators may receive power directly from the transmitting source or through a plurality of neighbouring resonators to further improve the coupling with the intermittent receiver structure at specific or changing distances from the source.

Receiving circuits, situated anywhere along the yarn structure or fabric could rectify the power flowing through these coil resonators in order to power electronics and/or sensors. The exact position of these drains circuits would be dependent on the needs of the specific application. Along with power capture, these circuits may also perform demodulation to extract any useful data which may have been added to the power signal. It is envisioned that these micro- and/or nano-scale receiver circuits could be embedded within neighbouring yarns or within the core of an existing yarn, or externally connected/attached to the larger textile structure or membrane. These receiver circuits may be physically interconnected in parallel or series to supply useful amounts of current and electrical potential to drive low power sensors and electronics.

The proposed system has been designed with the intention of using a wireless source supplying 1MHz - 5GHz with data transmission capabilities. The yarns would have diameters of 10um-2mm making them suitable for numerous applications in a variety of different textiles and garments for a wide range of different applications in many different markets.

Core benefits of an intermittent resonator yarn structure for wireless power transmission include: A very large surface area made available for the integrated receiver coils, with improved likelihood for power transmission with couple coil misalignment.

Any textile or garment produced with the yarn would support near omni-directional power transmission over the surface of the garment with little to no leakage in the direction of the wearer. This property arises partly due to the high permeability of the ferromagnetic core, which aids to confine any receiver side magnetic field generated, and partly from a high permeability material layer which could be integrated between the wearer and the garment, thus acting as a magnetic shield. This property, as well as the others discussed makes the garment an ideal platform for full body medical analysis where embedded sensors may be interlaced into the fabric of the garment.

BRIEF DESCRIPTION OF FIGURES

Fig. 1 depicts an exemplary WPT system with a source, a tuneable intermediate electromagnetic resonator, and a receiver incorporating a novel intermediate electromagnetic resonator a distance D from the wireless source.

Fig. 2(A) and (B) depicts a circuit diagram representation of the disclosed intermediate resonator yarn with open and closed resonator tank coils respectively. The resonators described may be optimized for coupling with a power source or wireless data source.

Fig. 3(A) depicts an isometric view of a plurality of resonators with a central ferromagnetic core and non-conducting protective encasing. The resonators herein are displayed with different lengths and numbers of turns and different radiuses. Resonant coils may be tuned to different fundamental frequencies to receive and transmit power and/or data. Fig. 3(B) is an embodiment of two intertwined intermediate resonators that may be tuned with different fundamental frequencies and different impedance matching and driving circuits

Fig. 4(A) depicts the cross-section of an intermittent resonator with an exemplary resonator coil. Through the cross section, the various layers and materials are labelled. FIG. 4 (B) examines an extension case of (A) where further insulation layers are included in the embodied resonator yarn.

Fig. 5 depicts the propagation path of power through an intermittent resonator yarn. A strongly coupled resonator is depicted as an initial receiver coil and the propagation of 90° phase changes in the induced current from the coupled electromagnetic field from neighbouring coils. Furthermore, a graph displaying the direction of the propagated power is also depicted.

Fig. 6 depicts a parallel array of intermittent resonator yarns placed in series as if to create a flat plane capable of receiving and transmitting larger amounts of received power from a distant wireless power source.

Fig. 7 combines an arrangement of intermittent resonator yarns with modern fabric weaves in order to have the characteristics of strength, stretch or compression. Interweaving a plurality of resonator yarns at a multitude of angles allows wireless power to be received from multiple resonator orientations at different times.

Fig. 8 depicts an embodiment of a receiver design suitable for integration within a yarn. This design describes a tuned varicap network with a strongly coupled antenna to that of the intermittent resonators embedded into the same or a neighbouring yarn.

Fig. 9 is an alternative receiver circuit suitable for embedding into a yarn. This circuit has two blocks, one for the receiver coil, designed for strong coupling with a nearby intermittent resonator and a processing block to rectify and filter power or data from a wireless source.

Fig. 10 embodies a parallel or series interconnection circuit of a plurality of receiver circuits. The blocks represent either a varicap or tuned receiver circuit suitable for extracting power or data and transmitting the output down an embedded conductor to a local drain or load.

DETAILED DESCRIPTION

As described above, this disclosure relates to a textile or membrane composed of yarns with wireless power harvesting and transfer capabilities for the purposes of providing distributed devices such as sensors and microprocessors with usable amounts of power as well as data transmission capabilities. The system described does not depend or rely necessarily on a dedicated wireless power source, as wireless radio frequency (RF) transmitters are already commonplace in analogue and digital RF transmitters used in everyday communications, such as but not limited to Wi-Fi and Bluetooth from the KHz up to the GHz range. Moreover, the yarn and its described techniques of use are not limited to the embodiment of a wearable garment. The core principles of production and manufacture allow for the yarn structures described herein to be fully or partially integrated into any textile product, including, but not limited to clothing, upholstery, carpeting, curtains, bedding, headwear, shoes and others.

Induction and Strongly Coupled Magnetic Resonance

In a typical non-resonant wireless setup, practical energy transfer between a source coil and a receiver coil could only take place at a very close distance (several millimetres up to a few centimetres) and would likely make use of a ferromagnetic cores. These requirements define the common set-up of a transformer. It is known that if the transmitter and receiver of a traditional transformer were separated by air and given a greater distance of separation, the performance and efficiency of the trancfpr \A/ni iId rlrnn dramatirallv

In 1893, Tesla introduced magnetic resonance and applied it in several experiments. In these experiments resonance in AC circuits was achieved by tuning the self-inductance of a coil with a series capacitor so that they form a resonant coil at a certain operating frequency. This principle however does not guarantee high efficiency or practical levels of transmitted power for mid-range distances in the order of tens of centimetres to several meters.

Strongly Coupled Magnetic Resonators (SCMR), for which resonance is a precondition, has been demonstrated to transmit reliable amounts of power over mid-range distances and can facilitate high power transfer. Prior art has already proven the performance of such systems, such as US8400021B2, which outlines many of the core physical and mathematical principles of designing a system for practical use. For the yarn described herein, a dedicated and strongly coupled wireless power source may be specifically designed for purpose, or the yarn may be strongly coupled or tuned to receive and harvest common propagating radio frequencies electromagnetic waves such as in the lMHz-5Ghz range used in many wireless appliances.

Wearable applications obtaining/harvesting wireless power through a SCMR system receive the benefits of such a system due to the natural behaviour of fabrics and textiles, and a wearer moving through a building or enclosed space. These natural benefits of SCMR in this context include: A WPT system less dependent on changes in relative coil orientation and alignment; reduced interference from non-resonant extraneous objects in the environment such as wood, metals or any other electronics; A very low coupling with the human body, thereby making the system safer for commercial, medical, military and space applications; It has also been shown that this method copes much better in the case of line-of-sight obstructions between and wireless receiver coil and wireless transmitter.

For any optimized WPT system, the transmitting source, and its limitations must be understood before wireless devices or loads can be designed to harness and make use of this wireless power. Fig. 1 depicts a mature or established wireless energy source 8 with an AC or DC power supply 1, this is may be attached to a larger electronic control circuit 2 for further refinement of the power signal. These control circuits can comprise fixed frequency inverters through to more complex closed loop control systems that perform analysis on the produced wireless signal and further optimize the efficiency of the overall system on the device or receiver side.

It is commonplace for the output of a controller to be fed into an impedance matching circuit with and output amplifier. Block 4 will achieve the resonant frequency of the antenna coil to produce the highest possible energy transfer efficiency, defined partly through the quality factor Q. of the coils.

Numerous techniques are already known to identify the correct circuit component values for such circuits.

Ensuring high Q factor (Q>100) on both coils in our source 8 requires that the resonant frequency of both 5 and 7 are achieved simultaneously and that the coils have sufficiently low electrical resistance (R«l), high electrical inductance (L>1 uH) and high operating frequency (100s of KHz to GHz). For an intermittent resonator 7 this may be done with an independent impedance matching circuit 6. Furthermore, block 7 may represent a plurality of sub-wavelength resonant coils, which may be referred to as a 'metamaterial', designed to act as a lens for the electromagnetic coil 5 acting as a power source to the wireless system. It may also be favourable for the intermittent resonators in 7 to act as a focusing or de-focusing lens for the electromagnetic field by purposefully tuning a select number of intermittent resonators either just above or just below the resonant frequency of the source. The amount by which the resonators in a metamaterial are tuned will be a function of the pattern structure, distance from the source, and distance from the receiver, as well as the shape of the source and receiver electromagnetic fields respectively and the material of the metamaterial. Through careful design, a metamaterial may be produced to accurately shape the electromagnetic field generated by the source resonator to be coupled to a receiver such as block 10. For most purposes, a metamaterial may have resonators with a resonant frequency slightly higher (i.e. up to 5%) than the source resonance frequency to focus the outer regions of the electromagnetic field towards a calculated focal point. Intermittent resonators with a resonant frequency slightly below (i.e. up to 5%) that of the source would de-focus the field away from a focal point. Cases where the resonant frequencies are equal for the source and the metamaterial will correct the electromagnetic field lines to make them linear and perpendicular to the place of the metamaterial.

For further control and tuning abilities of the system, an adjustable member of the source is included to automatically adjust the displacement and alignment between coils 5 and 7. Overall, Fig. 1 describes a good state-of-the-art SCMR system to act as a source for wireless applications where the target device 10 may be moving in an environment and line-of sight may be possible to improve output power performance. A yarn with wireless power transmission abilities

On the receiving end of the wireless system, for a textile based receiver 16, which may be a distance D away from the wireless power source, there is a desire to maintain a strong magnetic coupling with a receiving intermittent structure such as 9. This application is concerned primarily with a unique yarn based application of an intermittent resonator architecture that couples strongly with numerous receiver resonators/coils and drives power towards distributed loads or charge circuit to make use for the received power and data.

The intermittent resonator yarn on the receiver side is a strongly coupled array of resonator coils which may be wrapped around a flexible ferromagnetic core. This structure allows the yarn to transmit power bi-axially to other neighbouring resonators until it is received by block 11. Block 11 may be part of a yarn with an embedded receiver coil 11, an embedded integrated circuit 13 to rectify or clean the received signal and drive usable amounts of current along the length of the yarn to power a one or many small embedded sensors, or another device within or electrically attached to a wearable garment 15. Block 15 is representative of the receiver which may include, but not be limited to a sensor such as an Analogue Digital Converter ADC attached to a small thermocouple, flex or capacitive sensor for the measurement of sports related metrics again not limited to temperature, sweat and blood pressure. Block 15 may be a battery, small microprocessor or a peripheral to interface with a remote system. Furthermore 15 may constitute a subsystem of further wireless transmitters or receivers of data generated by the wearable or another system on or off the wireless network. This receiver block 10, may require a small receiver block 11, an impedance matching or signal rectifying block 13 and a load or common drain into the sensor or device in question.

Intermittent resonator textile yarn

The magnetically resonant yarn 9 is based on the known principles of coupled resonators and the effect of "domino resonators". In which resonators within the circuit depicted in Fig. 2(A) will have substantially the same resonant frequency, and exchange energy through the strong coupling of their nearfields and an adjoining ferromagnetic core 17. This ferromagnetic core is made of a nonconductive core to which a conductor was applied to its exterior. Examples of such conductive materials may include, but are not limited to cobalt, iron, manganese, nickel and chromium with a preference to a material that does not suffer from oxidation in humid and warm environments. Furthermore, this ferromagnetic core may magnetically link to a plurality of intermittent resonators, and may not be a single core over the total length of the yarn.

Fig. 2(A) and 2(B) depict two of many possible permutations of differently coupled coil structures for the intermittent resonators. First is selection 20, where the coils 18, 18' and 18" are all open-loop whereby they are characterized only by their self-inductance and parasitic capacitance. Alternatively, a coil configuration 20' is also described which provides a small impedance matching circuit 19", to the coil in order to better control and lower the resonant frequency and confine any electric field components. This is the preferred method of system delivery, but is prone to additional complexity in component manufacture and quality control. It should be noted that the circuit blocks within 19,19' and 19" may be different from one another along the length of any yarn. Blocks 19,19' and 19" may represent circuits such as, but not limited to impedance matching circuits, rectification, transistor TTL logic and op-amp circuits for high gain and feedback control. Those trained in the art of integrated circuit design and modern CPU architectures will be aware that transistors are now manufactural at sizes in the order of ~8nm in area at the time of writing. These incredibly small component sizes available through modern lithography and chemical processes ensure that such systems are feasible within the context of incorporating such technologies within a yarn to receive power/data wirelessly.

Combining strongly coupled coil resonators within a single yarn. A yarn of intermittent resonators may be constructed through a combination of open coil 20 and closed coil 20'. These may have different resonant frequencies in order to perform different tasks or receive power from a different WPT source elsewhere in the surroundings. Based on the natural resonant frequencies of open coil resonators it will be expected that the system will relay power from WPT with a resonant frequency in the order of high MHz into the GHz frequency range. For lower operation, closed coil resonators are preferred, thereby requiring that a WPT source only requires a transmitter with a frequency in the order of low MHz to Low GHz.

Fig. 3 is an isometric view of the same circuit/coil components described in Fig. 2(A) and 2(B). Here scalar and dimension characteristics of the resonators are clearer to recognize. Labelled 18 as before are two resonators of different length. Depicted are two coils in A that have the same coil radius r and conductor cross section (or conductor thickness). These two coils have a different length and number of turns which influences and dictates their fundamental resonant frequency. It may be desired to have two coils with different resonant frequencies. The first to couple strongly with the fundamental power frequency and a second set of coils to couple with any data signal superimposed on the resonant carrier frequency of a source transmitter.

It is understood that intermittent resonators may have specific tasks for separating signals because of their different fundamental frequencies and impedance matched circuits. Throughout the body of this document two types of intermittent resonators embedded within the yarn will be references. Termed 'P-coils' these resonators are coupled with the carrier or power signal from the wireless energy source. Secondly, resonators termed 'D-Coil' which are coupled with the data signal superimposed on the carrier. These two different coils may be placed in series along the same ferromagnetic core within the same magnetically resonant yarn 9. Lastly, a yarn may include a yarn that embodies both 'P-coil' and 'D-coil' to create a 'PD-Coil' yarn. As a naming convention, a yarn consisting of a plurality of P-coils may be called a 'P-yarn' and those with D or PD coils a 'P-yarn' and 'PD-yarn' respectively.

Multiple Coil Design

It is understood, that coils may occupy the same space around the ferromagnetic core. This may be achieved as in Fig. 3(B) where one or more smaller coils 18 is intertwined with a longer coil 18'. Fig. 3(B) depicts a singular case where the coil radius of both 18 and 18' are equal in coil radius, this may not be true for a system designed to receive power at one or more resonant frequencies (P-coils) from one or more transmitters and data to be received by other resonators at another resonant frequency (D-coils). In the case of wearables, the advantage of interwinding a plurality of resonators offers the ability for a single yarn to receive both power and data from a number of known carrier frequencies and data transceivers without the need to make a fabric with function specific yarns or introduce too many fabric layers into a garment. The addition of too many layers may cause the fabric to become too uncomfortable for everyday use or not flexible enough for many intended applications (medical and sports analysis).

Anyone trained in the art of inductor design and strong magnetic coupling will be aware of ensuring that the saturation level of the ferromagnetic level is constrained to within a known and desired amount. If the ferromagnetic core becomes saturated the level of leakage from the coil must be monitored to ensure it is safe for the wearer of the garment. The material properties of the resonators and ferromagnetic coil must be understood in order to achieve desired performance. P-coils and D-coils coils may have other characteristics to improve their performance for power and data extraction. These may include, but are not limited to, changing coil radius, increasing or decreasing spaces between turns - leading to a 'spiral-in' or 'spiral-out', or a combination of the characteristics. Lastly, coils may be made of different materials and cross sections, and require ferromagnetic cores made of different or a plurality of materials.

Yarn cross-section

Fig. 3 and Fig. 4 depict the various layers that form part of the construction of an magnetically resonant yarn. Starting with the outermost surface, a non-conductive shielding 21 made from, but not limited to nylon and polyester, protects the conductive resonators from surface damage, abrasion and oxidization. This material may be applied as winding of a smaller diameter fibre on the outside of the aids in increasing the rigidity and strength of the yarn. It may be deposited on the surface of the yarn through a plastic extrusion or applied as a liquid or powder coating. Should a winding be used, the angle of wind of this non-conductive shielding provides further tuning of characteristics of flexibility. Fig. 4 goes into further detail on the various layers that make up a complete yarn.

Fig. 4(A) depicts the first instance of the embodiment, with a coil resonator 18 (open or closed coil type) wound around a central ferromagnetic core 17. As described earlier the ferromagnetic core is constructed of more than one material. Depicted is a central core that is non-conductive 24, an outer composite coating 23 of highly magnetically permeable material that may be electroplated or chemically applied to the surface of 24. Further layers may include a protective coating to prevent against oxidization and prevent conductive contact with the resonant coil 18 that is wound around it. Those skilled in the art will have identified that it is beneficial that coil 18 is insulated or isolated from the conductive elements of the ferromagnetic core. Fig. 4(B) adds further chemical, potting or epoxy coatings between the elements to further strengthen and isolate the components within the yarn. This material coating 25 may occupy the spaces between the turns on the coils. Marginal free-space 22 has been included in the diagram as it is expected that spaces will exist between elements as a tolerance during manufacture.

Power transfer A yarn capable of wireless power transfer has been described in Fig. 5 which illustrates the natural transmission of power through a series of coupled resonators 20 that run down the length of a yarn. In this illustration, a central resonator 27 is coupled with the source resonator and extends an electromagnetic field through the ferromagnetic core 17 to its neighbours. This coupling then discharges 27 at a rate defined by the operating frequency/resonant frequency of the coils.

The sinusoidal output in graph Fig. 5. Depicts arrows 26 and 26' to specify the directionality and phase of the apparent current wave that traverses the length of the coil yarn. These principles have been demonstrated at much larger scales and have been termed as 'domino resonators' which pass power from one resonator to another. Outside research has primarily investigated this technique with large resonators of the same scale as that possessed by the wireless power source.

In the case of a yarn capable of achieving an effective power transfer, significant constraints are set on the maximum diameter of the resonators. As such there is no literature to suggest that this application was intended for integration in wearable technologies at this scale. P, D and PD Yarns in textile and membrane applications

The creation of a fabric that functions as a holistic intermittent resonator or 'metamaterial' for a wireless power transfer system is best demonstrated with a plurality of magnetically resonant yarns 9 as in Fig. 6. Here the same characteristic transmission of power is demonstrated over a substantially larger area, and with a much larger capacity for transferring power to either ends of the magnetically resonant yarn. Fig. 7 depicts a plurality of coil yarns woven, into a crisscross arrangement to form a traditional textile. The textile produced with a series of coil yarns is not limited to a crisscross arrangement and may be arranged into a more complex weave such as a triaxial-weave which introduces a multitude of diagonal yarns into the textile design.

Fabric Design A fabric or textile may be made of a plurality of magnetically resonant yarns 9, which may contain P-yarns, D-yarns or PD-yarns and any combination or permutation thereof, be woven into a textile or fabric for use in a wirelessly powered garment. Choosing specific fabric weaves for different areas of a garment introduces another set of parameters to optimize the power and data receiving and transmitting abilities of the garment. It will be obvious that this optimization is described as the tuning or optimization of the wireless network. Logically, in the case of wearables safety may and should always be considered. A piece of fabric does not necessarily require magnetically resonant yarns 9 to make up a total of 100% of the material in the fabric, instead an existing fabric manufacturer may include a lower percentage of magnetically resonant yarns 9 into their fabric. Reducing the number of magnetically resonant yarns 9 in a fabric enables fabric manufacturers to retain the characteristics of existing fabrics where these are more desirable. As an example, a certain colour or texture of fabric may be more desirable, similarly a specific combination of different yarns may allow for greater combinations of fabric colour and texture.

The specific weave of a garment that makes use of the described magnetically resonant yarn can have great advantages in particular applications. For military applications, it is more advantageous to supply a wearable system with greater energy harvesting abilities. This ensures that equipment is always transmitting. For medical applications wearables supporting larger numbers of sensors is more important. In this case, more D-coils will be used to transmit and receive data to and from a hospital transmitter, this data may include, but not be limited to heart rate, respiration, hydration level, blood sugar and more. For any garment, there may be a greater need for P-coil yarn or D-coil yarn, this tradeoff may benefit from different types of weave that make use of yarns at different angles in order to maximize the length of a particular yarn. For example, prior art such as US3446251A enables a fabric to have a number of diagonal weaves in order to further maximize the length of any given yarn.

Power will traverse a fabric made of the P-coil and D-coil type yarns mostly linearly through the central ferromagnetic core 17 that runs through the centre of the yarn. Leakage flux may couple to nearby magnetically resonant yarns to create a flow of energy along the place of the textile. Extending the manufacture of a garment may be characterized by the type of garment and the unique power characteristics can be demonstrated by extrapolating the linear traversal of power through a single yarn into a second dimension. In the case of the arrangement in Fig. 7, the coupled power would traverse the textile as a 3-Dimensional Gaussian through the ferromagnetic cores.

Power receiver, drain and driving loads

Further to the depiction of Fig. 1 in which a complete fabric based system is described, this section outlines how a receiver might be constructed to harvest the energy propagating along the magnetically resonant yarns. The simplest method of power extraction is using an adjustable varicap network. This embodiment of the circuit is beneficial for applications within yarns and wearables as it typically requires fewer components and offers the least difficulty in manufacture. Fig. 8 depicts a single variable varicap circuit, with a tuned receiver antenna block 28 and a diode with suitable doping to fulfil the design implementation of a small varicap. The result of this setup is a simple method of extracting the power from the traversing power signals within the radiation caustic of surrounding coils.

Fig. 9 represents an alternative method of receiving power and data from a magnetically resonant yarn. This highly repeatable circuit may include a specifically designed antenna block 28 with very specific characteristics. Block 31 is then a more complex rectifying and signal processing circuit with DSP capabilities. These elements will provide output connections allows for massively series or parallel interconnection with their neighbours throughout the length and inner diameter of the yarn.

With a plurality of receiver block elements 30 in a network such as Fig. 10 a possible first approach to harvesting the energy from surrounding coils is described. This network ensures that all currents produced within the system travel in the same direction and rectify the output between both ends of the yarn. The received power may then be used with more receiver yarns to collect and extract the desired/required amount of power to operate a small sensor integrated into the textile or piece of clothing. This network may have components oriented in either a massively series or massively parallel configuration to drive current or voltage driven loads.

Claims (25)

1. A yarn to be incorporated in a fabric or membrane to provide the fabric or membrane with wireless power transfer capabilities, the yarn comprising: a ferromagnetic core including a non-conductive central core and an outer layer, surrounding the non-conductive central core, of a magnetically permeable material; and a plurality of resonator coils wound around the core.

2. A yarn according to claim 1, wherein at least some of said plurality of coils are spaced from one another along the length of the yarn.

3. A yarn according to claim 1 or claim 2, wherein at least some of said plurality of coils are interwound with one another.

4. A yam according to any one of the preceding claims, further comprising a shield layer that surrounds the core and the resonator coils.

5. A yarn according to claim 4, wherein the shield layer is non-conductive.

6. A yarn according to claim 5, wherein the shield layer is nylon and/or polyester.

7. A yarn according to any one of the preceding claims, further comprising an insulating layer to electrically insulate the resonator coils from the core.

8. A yarn according to any one of the preceding claims, wherein at least some of the resonant coils have different resonant frequencies from one another.

9. A yarn according to any one of the preceding claims, wherein at least some of the resonant coils are tuned to different transmitter frequencies from one another.

10. A yarn according to any one of the preceding claims, wherein a cross-section of the core is non-uniform along the length of the yarn.

11. A yarn according to any one of the preceding claims, wherein at least some of said plurality of resonator coils are of a closed type with a connected capacitor network to reduce resonance of the coil to the MHz range.

12. A yarn according to any one of the preceding claims, wherein some of said plurality of resonant coils are configured for power transmission and others of said plurality of resonant coils are configured for data transmission.

13. A fabric comprising a plurality of yarns according to any one of the preceding claims.

14. A fabric according to claim 13, wherein the fabric is a woven fabric and said yarns are woven into the fabric.

15. A fabric according to claim 13, wherein the fabric is a knitted fabric and said yarns are knitted into the fabric.

16. A membrane comprising a plurality of yarns according to any one of claims 1 to 12.

17. A membrane according to claim 16, wherein said yarns are adhered to a surface of the membrane.

18. A membrane according to claim 16, wherein the membrane has multiple layers and said yarns are help between membrane layers.

19. A fabric or membrane according to any one of claims 13 to 18, further comprising one or more receiver circuits incorporated in the fabric or membrane and coupled with the resonator coils to harvest power from the plurality of coils.

20. A fabric or membrane according to claim 19, wherein at least one of said one or more receiver circuits comprises a demodulation block for demodulating a received signal to extract a data signal.

21. A fabric or membrane according to claim 19 or claim 20, wherein each receiver circuit comprises a receiver antenna by which the receiver circuit is coupled to the resonator coils.

22. A fabric or membrane according to any one of claims 19 to 21, wherein each receiver circuit is encapsulated in a protective coating.

23. A fabric according to claim 22, wherein the protective coating has the form of a yarn and is part of the fabric construction.

24. A fabric or membrane according to any one of claims 19 to 23, wherein the receiver circuits comprise a varicap circuit.

25. A fabric or membrane according to any one of claims 19 to 24, comprising a plurality of said receiver circuits connected to one another in a network.