Abstract:
Wireless power transfer system include: a seat configured to support a human and including a first resonator featuring a conductive coil formed by a plurality of loops that each encircle a common first axis, a layer of magnetic material, and a conductive shield; an article of clothing featuring a second resonator having a conductive coil formed by a plurality of loops that each encircle a common second axis, so that when the article of clothing is worn by the human and the human is seated in the seat, the first and second axes are aligned; and a first electronic apparatus positioned in the seat and coupled to the first resonator, and configured to deliver electrical power to the first resonator so that during operation of the system, power is transferred wirelessly from the first resonator to the second resonator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 13/544,688, filed on Jul. 9, 2012, which claims the benefit of U.S. Provisional Application No. 61/505,593, filed on Jul. 8, 2011. This application also claims the benefit of U.S. Provisional Application No. 61/922,406, filed on Dec. 31, 2013, and U.S. Provisional Application No. 62/043,320, filed on Aug. 28, 2014. The entire contents of each of the foregoing applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to wireless power transfer techniques. 
       BACKGROUND 
       [0003]    Energy or power may be transferred wirelessly using a variety of known radiative, or far-field, and non-radiative, or near-field, techniques as detailed, for example, in commonly owned U.S. patent application Ser. No. 12/613,686 published on May 6, 2010 as U.S. 2010/010909445 and entitled “Wireless Energy Transfer Systems,” U.S. patent application Ser. No. 12/860,375 published on Dec. 9, 2010 as 2010/0308939 and entitled “Integrated Resonator-Shield Structures,” U.S. patent application Ser. No. 13/222,915 published on Mar. 15, 2012 as 2012/0062345 and entitled “Low Resistance Electrical Conductor,” U.S. patent application Ser. No. 13/283,811 published on Oct. 4, 2012 as U.S. 2012/0248981 and entitled “Multi-Resonator Wireless Energy Transfer for Lighting,” and U.S. patent application Ser. No. 13/534,966 published on Jan. 2, 2014 as U.S. 2014/0002012 and entitled “Wireless Energy Transfer for Rechargeable Batteries,” the contents of which are incorporated by reference. 
         [0004]    As advanced mobile communication, computing, and sensing devices become more essential, the burden of carrying, operating, and maintaining multiple batteries, fuel cells, and the like, increases. In both civilian and military scenarios, people are often required to carry and operate multiple electronic devices. One or more devices such as headlamps, portable computers, global positioning system devices (GPS), sensors, cameras, radios, flashlights, and the like may all be carried by a person. Each electronic device may require an energy source such as batteries, fuel cells, and the like to provide energy to each or a group of the devices. Large numbers of devices may mean a large number of batteries that may require management and/or monitoring by the user. 
         [0005]    In systems where each device has its own energy source, i.e. batteries, the stored energy may be underutilized and may lead to significant or unnecessary extra weight that may need to be carried by the user. With each device or a group of devices having a separate energy source, the energy storage of each device may need to be large enough to power the device in the worst or maximum usage scenario, even if the device is typically used infrequently. As a result in many use scenarios, the user will be underutilizing the carried energy and perhaps carrying too much battery or stored energy capacity. 
         [0006]    The underutilization of carried energy may be problematic for weight sensitive devices and applications. Underutilization of energy for a device attached to a helmet, for example, may mean a significant weight penalty that a user has to tolerate on their head. In many applications it is desirable to reduce or eliminate the weight attached to a person&#39;s head area since it may cause user discomfort, fatigue, or neck problems. 
         [0007]    One way to reduce the burden of multiple batteries and improve their utilization is to use wearable battery packs and/or central energy generators that can provide power to various peripheral devices that are attached to or carried by a person. With one or several central batteries the potable energy may be shared and distributed to the devices that need the power. However, such devices may be tethered to the person&#39;s battery pack with cables. For devices such as headlamp, microphones, night vision goggles, and the like, that are carried on a person&#39;s head or helmet, the cables may be uncomfortable, limit movement, pose a safety risk (since cables may get snagged or caught on objects and obstacles), and reduce the reliability of the system. 
         [0008]    Thus what is needed is a better way for energy distribution for person worn peripheral devices. 
       SUMMARY 
       [0009]    Wireless energy transfer can enable such peripheral devices to be powered from a wearable battery pack or portable power generator, without the safety and ergonomic drawbacks of multiple wired connections that tether the mobile electronic devices, such as a head worn device or helmet to the user. 
         [0010]    In one aspect, a system for wireless energy transfer includes a person-worn central energy source. The energy source may be used to provide power to one or more wireless power source resonators that generate an oscillating magnetic field. The oscillating magnetic field may be used to transfer energy wirelessly to wireless power repeaters and/or devices worn by a person or carried by a person. The energy source may be a rechargeable battery. To generate electricity from the oscillating magnetic fields the system may include one or more device resonators that are configured to interact with the oscillating magnetic fields and generate an electric current. The device resonator may be helmet mounted and the source resonator may be mounted on the person&#39;s body. 
         [0011]    In another aspect, the power output or the frequency of the person-worn source resonators may be adjusted depending on the type of tissue that is in proximity or interacts with the magnetic fields of the source resonator. The system may further include field shaping structures comprising magnetic materials and/or conducting materials, to reduce the interaction of the magnetic fields with the person&#39;s tissue and body parts. 
         [0012]    In another aspect, a person-worn wireless energy transfer system may include a rechargeable battery and a source resonator configured to receive electrical energy from the battery and generate an oscillating magnetic field. A device resonator configured and positioned to interact with the oscillating magnetic fields may be positioned or attached to a person&#39;s helmet to transfer energy wirelessly to electronic devices mounted to the helmet or near the helmet from the rechargeable battery which may be worn near or on the torso of the person. The system may include more than one source resonator and a controller that may selectively energized each of the source resonators. The source resonators may be spaced or positioned to enable wireless energy transfer from the body of a person to the device resonator on the helmet even if the person moves, rotates, or tilts their head. The source resonators that provide the best coupling to the device resonator on the helmet may be energized depending on the rotation of the helmet. In another aspect the system may include more than one device resonator, the resonators may be positioned such that at least one resonator has good coupling to the source resonator despite any head rotations of the person wearing the helmet. 
         [0013]    In a further aspect, the disclosure features wireless power transfer systems that include: (a) a seat configured to support a human, where the seat includes a first resonator featuring a conductive coil formed by a plurality of loops that each encircle a common first axis, a layer of magnetic material positioned adjacent the conductive coil and intersecting the first axis, and a conductive shield positioned adjacent the layer of magnetic material, where the layer of magnetic material is sandwiched between the conductive coil and the conductive shield; (b) an article of clothing for the human, the article of clothing featuring a second resonator having a conductive coil formed by a plurality of loops that each encircle a common second axis, where the second resonator is positioned in the article of clothing so that, when the article of clothing is worn by the human and the human is seated in the seat, the first and second axes are aligned; and (c) a first electronic apparatus positioned in the seat and coupled to the first resonator, and configured to deliver electrical power to the first resonator so that during operation of the system, power is transferred wirelessly from the first resonator to the second resonator. 
         [0014]    Embodiments of the systems can include any one or more of the following features. 
         [0015]    Each loop in the plurality of loops of the conductive coil of the first resonator can extend in a common first plane that is orthogonal to the first axis. The plurality of loops of the conductive coil of the first resonator can define a spiral in a first plane orthogonal to the first axis. The first resonator can have a dipole moment aligned along the first axis. 
         [0016]    Each loop in the plurality of loops of the conductive coil of the second resonator can extend in a common second plane that is orthogonal to the first axis. The plurality of loops of the conductive coil of the second resonator can define a spiral in a second plane orthogonal to the first axis. The second resonator can have a dipole moment aligned along the second axis. 
         [0017]    The plurality of loops of the conductive coil of the first resonator can define a first dipole moment oriented along a first dipole axis, the plurality of loops of the conductive coil of the second resonator can define a second dipole moment oriented along a second dipole axis, and the second resonator can be positioned in the article of clothing so that, when the article of clothing is worn by the human and the human is seated in the seat, the first and second dipole axes are parallel to within 20 degrees or less (e.g., within 15 degrees or less, within 10 degrees or less, within 5 degrees or less). 
         [0018]    The article of clothing can be configured to be worn on a torso of the human. 
         [0019]    The magnetic material can include a ferrite material, and the conductive shield can include a metal material. The first electronic apparatus can be configured to deliver electrical power to the first resonator in an oscillating electrical signal having a frequency of between 50 kHz and 500 kHz (e.g., between 150 kHz and 300 kHz, between 200 kHz and 300 kHz, between 240 kHz and 260 kHz, of about 250 kHz, of about 200 kHz). 
         [0020]    The first electronic apparatus can include power and control circuitry featuring one or more switches, and the first electronic apparatus can be configured so that during operation of the system, the first electronic apparatus monitors a power transfer rate between the first and second resonators relative to a lower power transfer rate threshold and an upper power transfer rate threshold, increases a phase angle of the one or more switches if the power transfer rate is above the upper power transfer rate threshold, and decreases the phase angle if the power transfer rate is below the lower power transfer rate threshold, where the one or more switches are part of a switching amplifier in the first electronic apparatus, and where the phase angle is defined between the one or more switches in the switching amplifier. 
         [0021]    The article of clothing can be configured to be worn on an upper torso of the human, and the article of clothing can include a battery coupled to the second resonator, a third resonator coupled to the battery, and a second electronic apparatus coupled to the second and third resonators. The system can include a helmet configured to be worn by the human and featuring a fourth resonator, the second electronic apparatus can be configured so that during operation of the system, the second electronic apparatus stores energy in the battery in response to electrical power wirelessly received by the second resonator, and the third resonator can be configured to transmit electrical power to the fourth resonator by generating an oscillating magnetic field using power from the battery. At least one of the third resonator and the fourth resonator can include a curved magnetic material and a conductive wire wrapped around the curved magnetic material. The curved magnetic material can include grooves into which the conductive wire is wound. The curved magnetic material can include two or more pieces of magnetic material. 
         [0022]    A coil-to-coil efficiency of power transfer between the first resonator and the second resonator can be 20% or greater (e.g., 30% or greater, 40% or greater, 50% or greater). The coil-to-coil efficiency of power transfer between the first resonator and the second resonator can be 99% or less (e.g., 98% or less, 95% or less, 90% or less, 85% or less, 80% or less). A quality factors of each of the first and second resonators can be greater than 100. 
         [0023]    During operation, the system can be configured to sustain a transfer of at least 10 W of power between the first and second resonators when the second resonator is displaced laterally in a direction orthogonal to the first axis by up to 5 cm from an initial position. During operation, the system can be configured to sustain a transfer of at least 12 W of power between the first and second resonators when the second resonator is displaced laterally in a direction orthogonal to the first axis by up to 4 cm from an initial position. 
         [0024]    A thickness of the first resonator, measured in a direction along the first axis, can be 5 cm or less (e.g., 1 cm or less). The conductive shield can include a metallic material attached directly to a surface of the magnetic material. 
         [0025]    Embodiments of the system can also include any of the other features and aspects disclosed herein, including features and aspects disclosed in connection with different embodiments, in any combination as appropriate. 
         [0026]    In another aspect, the disclosure features articles of clothing that include: (a) a first resonator featuring a conductive coil formed by a plurality of loops each extending in a common first plane to define a dipole moment for the first resonator that is aligned orthogonal to the common first plane, where the first resonator is configured to wirelessly receive electrical power from an oscillating magnetic field; (b) a battery; (c) an electrical apparatus coupled to the first resonator and configured to store energy in the battery in response to the electrical power wirelessly received by the first resonator; and (d) a second resonator featuring a conductive coil coupled to the battery, where the second resonator is configured to transmit electrical power by generating an oscillating magnetic field using power from the battery. 
         [0027]    Embodiments of the articles can include any one or more of the following features. 
         [0028]    The second resonator can include a curved magnetic material and a conductive wire wrapped around the curved magnetic material. The curved magnetic material can include two or more pieces of magnetic material. The second resonator can be configured to transmit electrical power to a third resonator disposed in an additional article of clothing. 
         [0029]    A coil-to-coil efficiency of power transfer between the second and third resonators can be 40% or greater (e.g., 50% or greater, 60% or greater). A quality factor of each of the second and third resonators can be greater than 100. 
         [0030]    The third resonator can include a curved magnetic material and a conductive wire wrapped around the curved magnetic material. The second and third resonators can have a substantially similar radius of curvature. 
         [0031]    Embodiments of the articles can also include any of the other features and aspects disclosed herein, including features and aspects disclosed in connection with different embodiments, in any combination as appropriate. 
         [0032]    In a further aspect, the disclosure features methods of controlling wireless power transfer between a source and a receiver, the methods including monitoring a rate of wireless power transfer from the source to the receiver, increasing a phase angle of a switch of the source if the wireless power transfer rate is larger than an upper threshold value, and decreasing the phase angle if the wireless power transfer rate is smaller than a lower threshold value, where the switch is part of a switching amplifier in the source. 
         [0033]    Embodiments of the methods can include any one or more of the following features. 
         [0034]    The lower threshold value can be 12.5 W. The upper threshold value can be 14.5 W. 
         [0035]    Embodiments of the methods can also include any of the other steps and features disclosed herein, including steps and features disclosed in connection with different embodiments, in any combination as appropriate. 
         [0036]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the subject matter herein, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
         [0037]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0038]      FIG. 1  is a schematic diagram of an embodiment of a system for wireless energy transfer to a helmet. 
           [0039]      FIG. 2A  is a schematic diagram showing vertically aligned dipole structures. 
           [0040]      FIG. 2B  is a diagram showing horizontally aligned dipole structures. 
           [0041]      FIG. 3  is a schematic diagram of two resonators comprising a conductor wrapped around a block of magnetic material. 
           [0042]      FIG. 4  is a schematic diagram of an embodiment of a system for wireless energy transfer to a helmet. 
           [0043]      FIG. 5  is a graph showing energy transfer efficiency as a function of azimuth angle for a helmet wireless energy transfer system. 
           [0044]      FIG. 6  is a graph showing energy transfer efficiency as a function of coil separation for a helmet wireless energy transfer system. 
           [0045]      FIG. 7  is a schematic diagram of an embodiment of a system for wireless energy transfer to a helmet using multiple source and device resonators. 
           [0046]      FIG. 8  is a schematic diagram of an embodiment of a system for wireless energy transfer to glasses using a shoulder mounted source resonator. 
           [0047]      FIGS. 9A-9B  are images showing embodiments of a wireless power transfer system for a soldier. 
           [0048]      FIG. 10  is a schematic diagram of an embodiment of a wireless power transfer system. 
           [0049]      FIGS. 11A-11B  are schematic diagrams of embodiments of a wireless power transfer system. 
           [0050]      FIGS. 12A-12B  are schematic diagrams of embodiments of a wireless power transfer system. 
           [0051]      FIGS. 13A-13B  are schematic diagrams of embodiments of a wireless power transfer system. 
           [0052]      FIG. 13C  shows a plot of coupling as a function of azimuthal rotation angle in degrees for each of the embodiments shown in  FIG. 13A  and  FIG. 13B . 
           [0053]      FIG. 14A  is a schematic diagram of an embodiment of a wireless power transfer system. 
           [0054]      FIG. 14B  is a plot showing coupling as a function of gap between the wireless power source and device of  FIG. 14A . 
           [0055]      FIG. 14C  is a plot showing efficiency as a function of gap between the wireless power source and device of  FIG. 14A . 
           [0056]      FIG. 15A-15B  are schematic diagrams of embodiments of a wireless power transfer system. 
           [0057]      FIG. 16A  is an image of an embodiment of wireless power transfer in a seat-vest-helmet system. 
           [0058]      FIG. 16B  is an image of an embodiment of wireless power transfer in a seat-vest-helmet system. 
           [0059]      FIG. 17  is a plot showing coil-to-coil efficiency as a function of offset in the X-direction for an embodiment of a wireless power transfer system. 
           [0060]      FIGS. 18A-18B  are schematic diagrams showing coil-to-coil efficiencies with and without a model of a human body in an embodiment of a wireless power transfer system. 
           [0061]      FIGS. 19A-19D  are schematic diagrams of embodiments of source resonators. 
           [0062]      FIGS. 20A-20E  are schematic diagrams of embodiments of device resonators. 
           [0063]      FIG. 21  is a schematic diagram of an embodiment of a wireless energy transfer system. 
           [0064]      FIG. 22A  is a plot of efficiency as function of offset in the X-direction for an embodiment of a wireless energy transfer system. 
           [0065]      FIG. 22B  is a plot of efficiency as a function of offset in the Y-direction for the embodiment of the wireless energy transfer system of  FIG. 22A . 
           [0066]      FIG. 23A  is a plot of power to a load as function of offset in the X-direction for an embodiment of a wireless energy transfer system. 
           [0067]      FIG. 23B  is a plot of power to a load as function of offset in the Y-direction for the embodiment of the wireless energy transfer system of  FIG. 23A . 
           [0068]      FIGS. 24-25  are images showing an embodiment of a wireless energy transfer system in a seat and a vest. 
           [0069]      FIG. 26A  is an image of an embodiment of a wireless energy transfer system as part of a vest and helmet. 
           [0070]      FIG. 26B  is an image of an embodiment of a wireless energy transfer system as part of a seat, vest, and helmet. 
           [0071]      FIG. 27  is an image of an embodiment of a wireless energy transfer system in a vest and helmet. 
           [0072]      FIG. 28  is a plot of coupling as a function of distance between a helmet coil and vest coil for an embodiment of a wireless energy transfer system. 
           [0073]      FIG. 29  is a plot of power at a load as a function of voltage into a source for the embodiment of the wireless energy transfer system of  FIG. 28 . 
           [0074]      FIG. 30  is a plot of efficiency as a function of azimuth rotation for an embodiment of a wireless energy transfer system. 
           [0075]      FIG. 31A-31B  are schematic diagrams showing coil-to-coil efficiencies with and without a model of a human body for a wireless energy transfer system. 
           [0076]      FIGS. 32-33  are schematic diagrams showing embodiments of a curved resonator. 
           [0077]      FIG. 34  is a schematic diagram of an embodiment of a wireless power transfer source. 
           [0078]      FIG. 35  is a plot of efficiency as function of azimuth angle for an embodiment of a wireless energy transfer system. 
           [0079]      FIG. 36  is plot of power to a load function of azimuth angle for an embodiment of a wireless energy transfer system. 
           [0080]      FIG. 37  is a plot of efficiency as a function of azimuth angle for an embodiment of a wireless energy transfer system. 
           [0081]      FIG. 38  is a plot of power to a load function of azimuth angle for an embodiment of a wireless energy transfer system. 
           [0082]      FIG. 39  is an image of an embodiment of a wireless power transfer system as part of a vest and helmet. 
           [0083]      FIG. 40A  is a schematic diagram of an embodiment of a wireless power transfer system near a model of a human body. 
           [0084]      FIG. 40B  is a plot of power as a function of frequency for the embodiment of  FIG. 40A . 
           [0085]      FIG. 41A  is a schematic diagram of an embodiment of a wireless power transfer system near a model of a human body. 
           [0086]      FIG. 41B  is a plot of power as a function of frequency for the embodiment of  FIG. 41A . 
           [0087]      FIG. 42A  is a schematic diagram of an embodiment of a wireless power transfer system near a model of a human body. 
           [0088]      FIG. 42B  is a plot of power as a function of frequency for the embodiment of  FIG. 42A . 
       
    
    
       [0089]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0090]    A wireless energy transfer system may be used to wirelessly transfer energy from one or more central batteries and/or fuel cells and/or solar panels and/or other types of energy packs worn on a vest, backpack, harness, shirt, pant, belt, coat, or any type of clothing and the like, to a head worn or helmet mounted electric or electronic device. The wireless energy transfer system may use strongly-coupled magnetic resonators. The resonators may have a high quality factor Q&gt;100. The two resonators exchanging energy by have sqrt(Q1Q2)&gt;100. The system comprises at least one wireless energy source resonator, which might be embedded or attached to the user&#39;s equipment, clothing, vest, backpack and the like. The source resonator generates an oscillating magnetic field which may be received by one or more energy capture device resonators which may be integrated with the helmet or device. In embodiments, 5 watts or more of power may be transferred across a gap of 10 cm or 18 cm or more from a source resonator to a device resonator. In embodiments, repeaters may be used in the wireless energy transfer system. 
         [0091]    An example embodiment showing one configuration of the system is shown in  FIG. 1 . In the exemplary embodiment, energy is transferred wirelessly to an energy capture device resonator  102  mounted on the back of a helmet  104  from a source resonator  106  mounted on a vest  112  of a person  110 . The source resonator  106  may be energized by a battery (not shown) carried by the person  110 . The source resonator  106  generates an oscillating magnetic field that induces an electric current in the energy capture device resonator  102 . The electrical energy induced in the device resonator  102  may be used to energize electric or electronic devices  108  mounted or attached to the helmet  104 . Thus energy is transferred wirelessly across a gap  114  to power devices  108  on a person&#39;s head without cables between the device and the main battery carried by the person  110 . 
         [0092]    The wireless energy transfer is based on carefully designed, high quality magnetic resonators, strongly coupled to other magnetic resonators, so that electric power is selectively and efficiently transferred from one resonator to another, via a magnetic field, with very little power lost or dissipated to other near-by off-resonant or non-resonant objects. In the system it may be necessary to ensure energy transfer during changes in resonator positioning or movement due to the movement of a person&#39;s head, changes in the mounting of the resonators and the like. 
         [0093]    In embodiments, the system may use any number of resonators and resonator structures. A large number of suitable resonator structures have been described in U.S. patent application Ser. No. 12/789,611 Published as U.S. Publication Number 2010/0237709A1 on Sep. 23, 2010. For example, the so called planar resonator structures comprising an electrical conductor wrapped around a block of magnetic material or various configurations may be used. Likewise many different forms of capacitively loaded loop resonators with or without shielding may be employed. In embodiments, the types of resonators chosen, their orientation, size and the like may depend on the details of the application and the desired offset tolerance, size limits, power transfer efficiency, target weight specifications and the like. 
         [0094]    In embodiments, various coil configurations with different dipole moments and orientations may be effective for person mounted (e.g. vest) to helmet energy transfer. In embodiments the resonators may be oriented with two different dipole moment orientations and configurations.  FIG. 2A  and  FIG. 2B  show two different dipole orientations of resonators, vertically aligned, and horizontally aligned.  FIG. 2A  shows a configuration with vertically aligned dipole moments.  FIG. 2B  shows a configuration with horizontally aligned dipole moments. The benefit of the parallel or horizontally aligned configuration is that both ends of the magnetic dipole resonator on the vest can couple to the helmet resonator. The parallel configuration may also have an advantage in its size, shape, and weight. In an exemplary environment, a coupling coefficient of k=0.02 was achieved with a helmet-resonator weight of 0.17 kg and a vest-resonator weight of 1.1 kg. Also, the shape of each resonator may be more suitable for integration with both the helmet and the vest than the vertical configuration. 
         [0095]    To ensure adequate energy transfer from a source resonator on the body to a device resonator on the head and/or helmet, over a range of resonator offsets and distances with a constraint on size and weight of the resonators, the resonators may preferably be oriented with horizontally aligned dipole moments. Resonators with horizontally aligned dipole moments may be a variant of the so called planar resonator structures. An embodiment of the system with planar resonator structures is shown in  FIG. 3 . The helmet mounted device resonator coil (Helmet coil) and the vest mounted source resonator coil (vest coil) both comprise a conductor  304 ,  308  wrapped around a block or core of magnetic material  302 ,  306 . In this configuration the two resonators have their dipole moments in the horizontal direction or parallel to one another. 
         [0096]    An example embodiment comprising horizontally aligned resonators was used to demonstrate the feasibility and performance of the system. In the example embodiment, the energy capture device resonator mounted on the helmet comprises 10 turns of 1054/44 AWG Litz wire wound around 160 g of 3F3 ferrite material and has a Q&gt;200. The vest-mounted resonator contains 215 g of ferrite encased in a polymer sleeve that is wound with 10 turns of the same type of Litz wire to form planar type resonators similar to that shown in  FIG. 3  and has a Q&gt;200. 
         [0097]    A lithium ion battery back worn in the vest of the user is used as the power source for the electronics board that houses the power and control circuitry for the source resonator. The helmet-mounted resonator is connected to a small device board with a rectifier and output voltage regulator. The output regulator was set for 5 Vdc and connected to a LED headlamp for demonstration purposes. The ferrite material used for both the helmet and vest resonators consists of small rectangular tiles that were stacked to make resonators in a parallel-piped shape. Shaped resonators may be fabricated that conform to the natural contours of both the helmet and the vest. This could be accomplished either by grinding angled faces on the individual tiles or by sintering magnetic powder in a custom mold. 
         [0098]      FIG. 4  shows the experimental configuration used to measure the efficiency and power as a function of head position. The source resonator  106  was mounted on the vest  112  worn by the person  110 . The device or energy capture resonator  102  was mounted on the back of a helmet  104 . The energy captured by the device resonator was used to power a headlamp  108  on the helmet via a wire. The separation distance  114  as well as the azimuth angle or the head rotation angle  402  was modified while parameters of the wireless energy transfer were measured. 
         [0099]    The efficiency of energy transfer as a function of the azimuth rotation for 12 cm separation distance between the source and device resonators is shown in  FIG. 5 . When the resonators are aligned the efficiency of energy transfer reaches almost 60%. A null in the coupling coefficient occurs when the head swivels approximately 60 degrees in azimuth and is manifested as a drop in efficiency of energy transfer in the figure. The null may be extended or moved to larger angles by enlarging the resonators along their dipole moments. 
         [0100]    The efficiency of energy transfer as a function of the separation distance between the source and device resonators is shown in  FIG. 6 . The graph shows that even though the resonators were tuned for a fixed distance of 12 cm the efficiency of energy transfer remain above 50% for the variation of separation distance of 7.5 cm to 15 cm. 
         [0101]    In embodiments, the captured energy may be used to power any number of devices, sensors, electronics, communication equipment and the like on or around the head or on the helmet. The electrical energy from the device resonator may be used directly as AC current or may be conditioned or rectified to provide DC current. In embodiments the system may include a small energy storage element on the helmet or on the head that is charged from the energy captured by the device resonator. The energy storage may be a rechargeable battery or a super capacitor that may be used to provide energy to the devices in cases when the wireless energy transfer gets interrupted. For example if the user rotates his head to reach the null point in the resonator coupling the wireless energy transfer may be interrupted. During this time power delivery to the electronics may be continued by using energy in the small battery or super capacitor. The energy storage element may be sized according to the expected or maximum time of wireless energy interruption for a specific use scenario. For example, use studies may be conducted to examine the frequency and amount of time that a user may turn his head to an area where the wireless energy transfer is no longer effective. The energy storage element may be sized only to provide energy to the devices during those times and recharge when wireless energy transfer is again possible. The energy storage element may therefore be small or light weight compared to a battery that is expected to power the devices continuously. 
         [0102]    In other embodiments, the source resonators and the device resonators may be configured to reduce or eliminate dead spots within the range of the person&#39;s head mobility. In one exemplary embodiment, multiple source resonators may be used as wireless energy sources. The multiple source resonators may be selectively driven depending on the rotation of the head. The source resonator with the strongest coupling may only be activated or some or all of the source resonators may be driven with oscillating currents with different phase or amplitude to steer the magnetic fields. 
         [0103]    In one exemplary embodiment, multiple device resonators  712 ,  710 ,  708  may be used to capture the energy from one or more source resonators  706 ,  704 ,  702  as depicted in  FIG. 7 . The multiple device resonators may be selectively activated depending on the rotation  402  of the head. Only the device resonator with the strongest coupling to the source may be activated or all three or more device resonators may be activated and their captured electrical energy combined to charge a battery or power an electronic device. The system may include a controller to measure the efficiency of energy transfer and electrical characteristics of the energy transfer between the sources and devices. By measuring the voltage and current on the source resonators and voltage and current on the device resonators the controller may actively choose to energize some or all of the sources depending on the measurements. 
         [0104]    In embodiments, the device or source resonator may be used to charge batteries from an external wireless energy source. The source resonator worn by the person may normally be used to transfer energy to the helmet but may be configurable to also capture energy from an external source allowing the resonator to wirelessly recharge the central person worn battery. The source resonator worn by the person may be configured to become a device resonator. The electronics may be configurable from a source amplifier functionality to rectifier and battery charger functionality. External source resonators may be mounted inside vehicles, on the back of seats, beds, and other structures providing wireless energy to the resonator mounted on the person when the person is sitting in the vehicle, resting in a bed, and the like. 
         [0105]    In embodiments source resonators may be located on the shoulders, back, front, neck, chest, stomach, hips, buttocks, thighs, hands, feet, and arms of the person. Device resonators capable of capturing the energy may be positioned on the sides, back, top and the like of the helmet, head, and head-worn devices. The device resonators may be positioned on the outside of the helmet or may be configured to cover the inside of the helmet protecting it from external abrasions and damage. 
         [0106]    Although the example embodiment demonstrated the use of a wireless energy transfer system from a vest to a helmet, it should be understood that other configurations are within the scope of this design. Energy may be transferred from a person to any number of peripherals that may be carried, or attached to a person. For example energy may be transferred to glasses, heads up displays, portable monitors and the like. An example embodiment for wireless energy transfer to a glasses mounted heads up display is shown in  FIG. 8 . The heads up display may have a device resonator  810  mounted on the side or the temple area  812  of the glasses  802 . The source resonator  808  may be worn on the shoulder area of the person. The source resonator  808  may be energized from a person worn battery that may be carried on the back or side of the person eliminating a heavy battery or energy storage element from the glasses. 
         [0107]    In other embodiments energy may be transferred from a vest to a device carried by the user such as a weapon, computer, tool, and the like. Energy may be transferred from the legs to shoes that may be integrated with sensors for monitoring the persons&#39; foot health, or overall fitness and stability by measuring stride length, pressure, movement and the like. 
         [0108]    Likewise, although the exemplary embodiment was described using a military helmet those skilled in the art will appreciate that the design may be configured for any helmet or any head mounted structure for recreational, industrial, and other uses. For example, wireless energy transfer may be used for motorcycle helmets to power radios, lights, and instruments inside the helmet. In another example wireless energy transfer may be used in bicycle helmets to transfer energy from a backpack to a helmet fitted with lights. In another example, wireless energy transfer may be used for hard hats to power lights, radios, sensors, glasses and the like. 
         [0109]    In embodiments, wireless energy transfer for person worn peripherals, a system may include a separate device resonator for each electronic device. Having an independent resonator for each device may allow simpler power control. Each device may be able to control its resonator and detune the resonator from the resonant frequency of the source if it is off or not requiring power. In some embodiments, the device resonators may be imbedded in the devices requiring power. In other embodiments, a single source resonator may power many device resonators. 
         [0110]    In other embodiments, the device resonators may be separate from the devices. The device resonator may be located separately from the device requiring power. The energy captured by the device resonator may be transferred to the device via conductor wire. A separate wired device resonator may be placed away from the device in a location closer to a source resonator or in a location that is less obtrusive to the user. For example, in the helmet embodiment shown in  FIG. 1 , the device resonator  102  is located at a distance away from the headlamp  108  and energy is transferred to the headlamp from the device resonator via a wire (not shown). In this embodiment the device resonator was positioned to reduce inconvenience and obstruction to the user. 
         [0111]    In some embodiments, a single device resonator may deliver power to more than one electronic device. In embodiments energy transfer may be divided into regions or subsystems. For example, wireless energy transfer may be used to span moving human parts or areas where wires are cumbersome or ineffective and once transferred wirelessly may be distributed in a traditional means using electrical conductors such as wires, printed circuit board (PCB) traces, conductive textiles, and the like. For example, a helmet may be such a subsystem. A single device resonator may wirelessly receive energy and distribute the energy to multiple devices on the helmet or near the helmet using wires. Other such systems may include hands, shoes, feet, arms, and the like. In embodiments a subsystem may include more than one device resonator that may receive wireless energy from more than one source resonator and distribute the energy over one or more devices in the subsystem. 
         [0112]    In embodiments, the device resonators may be embedded in the batteries or the battery packs of the devices. The batteries of devices may be configured for wireless energy transfer allowing the batteries to be recharged when within range of a wireless energy source. For example, sample designs of wireless power enabled batteries are described in U.S. patent application Ser. No. 13/534,966 published on Jan. 2, 2014 as U.S. 2014/0002012 and entitled “Wireless Energy Transfer for Rechargeable Batteries,” the contents of which are incorporated by reference. 
         [0113]    In embodiments, the person worn energy transfer system may include safety precautions. The oscillating magnetic fields may cause localized tissue heating or induced currents in some types of tissues. Depending on the location and orientation of the resonators it may be important to limit the power output of the source resonators or the magnitude of the magnetic fields reaching the body tissue or the nervous system of the user. In the example system shown in  FIG. 4 , five watts was safely transferred to the device resonators while meeting all safety limits despite being close to the spinal cord and nervous system tissue of the user. To meet safety limits it may be preferable to operate the resonators at resonant frequencies at higher frequencies of 150 kHz or more. In some embodiments resonant frequencies and the frequencies of the generated magnetic fields may be 1 MHz or more. 
         [0114]    In embodiments, the system may include shielding material around high power (10 W or more) source of device resonators to limit or reduce the interactions of the magnetic fields used for energy transfer with the person&#39;s body parts. The shielding may comprise a good electrical conductor. The electrical conductor shield may be positioned against a portion of the user&#39;s body such that the magnetic fields of the source are deflected away from that portion of the user&#39;s body. In embodiments the shield may comprise a flexible electrical conductor. The conductor may be a thin sheet of copper or an electrically conductive textile for example. 
         [0115]    Going back to the example embodiment of wireless energy transfer to a helmet as shown in  FIG. 4 , the system may include a shield to reduce the interactions of the fields with the back of the neck, spice, and head. In embodiments that may require higher power transfer, 10 W or 20 W or more the system may include a flexible or rigid flap that covers the neck area  404  of the user. The flap may comprise a conductive material that shields the neck and spinal cord from the magnetic fields. The flap map be part of the helmet or part of the headwear of the user. In embodiments, the shield may be part of the collar of the user&#39;s clothing. 
         [0116]      FIG. 9  shows an embodiment of a wireless power transfer system for a soldier&#39;s outerwear or gear, including helmet  904  and vest  908 , where a resonator  902 ,  906  may be shaped to be more conformal to the human body and/or gear. In exemplary embodiments, each resonator may be curved to better conform to the gear of the soldier. In exemplary embodiments, each resonator may be curved to increase efficiency of wireless power transfer from vest to helmet. In embodiments, the source resonator and device resonator may have substantially the same degree and/or radius of curvatures. For example, the degree of curvatures of the resonators may be within ±5 degrees, ±10 degrees, or more relative to one another. In another example, the radii of curvatures of the resonators may be within 5 mm, 10 mm, or more of one another. 
         [0117]      FIG. 10  shows a high-level view of a wireless power transfer system from the power source to the load. In this embodiment, the wireless power transfer system may comprise an AC/DC and/or DC/DC converter, amplifier, source-side impedance matching network, source resonator, device resonator, device-side impedance matching network, rectifier, load protector, DC/DC converter, and the like. In some embodiments, the wireless power transfer system may comprise one or more controllers along the path. In further embodiments, the wireless power transfer system may comprise a communication facility to support system performance monitoring and control. 
         [0118]      FIG. 11A  shows an embodiment of a wireless power transfer system comprising two resonators, both having substantially straight shapes  1106 ,  1108 .  FIG. 11B  shows an embodiment of a wireless power transfer system comprising two resonators, one having a curved shape  1102  and one having a straight shape  1104 . In some embodiments, the coupling between the resonators in  FIG. 11B  may be worse compared to the coupling between resonators in  FIG. 11A  due to the mismatch of shapes within a resonator set. For example, in the example embodiment shown in  FIG. 11 , coupling k for  FIG. 11A  is 0.0182 while the k value for  FIG. 11B  is 0.0162. This may be remedied by designing both resonators of the system to be of similar shape, as seen in  FIG. 12B . In this embodiment, the coupling between the curved resonators  1202 ,  1204  in  FIG. 12B  matches that of the straight resonators  1206 ,  1208  in  FIG. 12A , when other parameters and conditions are kept equal. 
         [0119]      FIG. 13A  shows an embodiment of a wireless power transfer system comprising two straight-shaped resonators  1306 ,  1308  moving with respect to one another. Similarly,  FIG. 13B  shows an embodiment of a wireless power transfer system comprising two curve-shaped resonators  1302 ,  1304  moving with respect to one another. 
         [0120]      FIG. 13C  shows a comparison of the movement of straight-shaped and curve-shaped resonators and the effects on coupling values. The data shows that as there is greater degree of movement (in azimuthal rotation angle), there is an associated decrease in coupling for both sets of straight-shaped and curve-shaped resonators. However, it can also be seen from the data that coupling between the curved-shaped resonators is typically greater than or equal to that of the straight-shaped resonators. Therefore, in some embodiments, such as when an application may require lateral or rotational movement of resonators with respect to one another, curve-shaped resonators may be advantageous. In the example of a soldier wearing a wireless power transfer system integrated in his or her gear as shown in  FIG. 9A  and  FIG. 9B , greater coupling between a source and device resonator while maintaining a greater degree of movement may be important in efficiently delivering power to critical tools, weapons, and the like. 
         [0121]    In some embodiments, a wireless power resonator may comprise more than one piece of magnetic material. It may be advantageous to use multiple pieces (e.g., 3 or more) of magnetic material in a resonator due to weight, cost, size, shape or positional restrictions. For example, in fitting a curve, multiple pieces of magnetic material may be necessary when it is not possible to create or form the magnetic material to a particular shape. In exemplary embodiments, lengths of magnetic material segments may be greater than 1 cm, greater than 3 cm, greater than 5 cm, and the like. 
         [0122]    In a preferred embodiment, a wireless power resonator may comprise multiple pieces of magnetic material in which the pieces are joined so there is little space in between the pieces. In preferable embodiments, the spaces between the segments of magnetic material may be less than 0.5 mm, less than 1 mm, less than 5 mm, and the like. In addition, ends of magnets may be beveled to further reduce the spaces between the segments of magnetic material. Less space between magnetic material may lead to greater coupling and efficiency.  FIG. 14A  shows an example of a source resonator  1406  and a device resonator  1404  where gaps  1402  have been formed at intervals in the magnetic material in the device resonator  1404 .  FIG. 14B  shows how coupling, k, decreases with increasing gap size between the pieces of magnetic material. 
         [0123]    In embodiments, a wireless power resonator comprising a curved shaped magnetic material may be lighter in weight than the straight piece of magnetic material that may be required to achieve similar coupling efficiencies. Similarly, in embodiments, a resonator comprising multiple pieces of magnetic material to create a curve shape may also be lighter due to the gaps in between segments. For example, such a resonator may be greater than 10% lighter, greater than 25% lighter, greater than 50% lighter than a straight-shaped resonator. 
         [0124]    In another exemplary embodiment, a wireless energy transfer system may comprise different types of resonators. For example,  FIG. 15A  shows a pair of resonators  1502 ,  1504  where the source resonator coil  1510  may be shielded using additional magnetic material or conductive material  1512 . This shield may be used to guide or otherwise control the magnetic field. 
         [0125]      FIG. 15B  shows yet another embodiment of a pair of resonators  1506 ,  1508  where the source and device resonators comprise a different coil shape. This resonator coil  1514  may be on one side of the magnetic material and may have a lower profile and weight compared to the coil shape  1516  shown in  FIG. 15A . Such a resonator coil may be designed such that its span varies along its length, as shown in  FIG. 15A . 
         [0126]    Any of the features described may be used alone or in combination without departing from the scope of this disclosure. A resonator may be referred to as a source resonator or a device resonator and may be designed to be interchangeable. Each shown resonator may comprise one or more conducting loops and/or one or more pieces of magnetic material, as well as capacitors, inductors, resistors, other electronics and the like. 
       Seat to Vest Power Transmission 
       [0127]    Several different types of resonators were modeled and analyzed to predict the energy transfer performance and to ensure the design meets Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) limits for human safety. In exemplary embodiments, the system design was chosen to allow for a wide range of positional flexibility and high efficiency. In further embodiments, the system design was chosen to not increase the weight on the soldier. In yet further embodiment, the system design was chosen to decrease the weight on the soldier. In exemplary embodiments, more than 10 W of power was transmitted wirelessly from a wireless power source in the seat back  1602  to a wireless power device in a vest  1604  over a wide range of movement and positioning at an operating frequency of 250 kHz (see  FIG. 16A ). Using the coordinate convention seen in  FIG. 16B , the range over which more than 10 W of power was transmitted is: ±5 cm in the X-direction, ±5 cm in the Y-direction, and 5 cm in the Z-direction. In exemplary embodiments, more than 12 W of power was transmitted wirelessly from a seat to a vest at an operating frequency of 250 kHz. This amount of power was transmitted over the following range: ±4 cm in the X-direction, ±4 cm in the Y-direction, and 5 cm in the Z-direction. 
         [0128]    As shown in  FIG. 16 , the target application consists of a soldier-worn vest-mounted device and a source resonator designed to be incorporated in a vehicle seat. An electromagnetic study was performed to ensure the viability of the system design. As part of this effort, the modeling and simulation results were evaluated with respect to compliance with applicable human exposure limits for Specific Absorption Rates (SARs), as delineated by ICNIRP, Institute of Electrical and Electronics Engineers (IEEE), and or FCC. While the initial study focused on a 10 W system, the simulations have been performed to determine the practical upper limit of power transfer that could be implemented while complying with applicable FCC human exposure limits. 
       Conformal Seat Resonator Constraints 
       [0129]    In exemplary embodiments, mechanical constraints may be defined for the seatback source and vest device resonators based on the dimensions of the selected seat and the soldier vest. The following are constraints that help determine the parameters for the simulation models. In exemplary embodiments, the source resonator area is within the area of a cushion of the seat. In embodiments, the thickness of the source resonator is within the thickness of a seat cushion, such as less than 5 cm, less than 3 cm, less than 1 cm, or less. In embodiments, the source resonator may be shielded using magnetic material to avoid any lossy materials in the construction of a seat. The shielding may be between the resonator and the seat back, the shielding may be around the resonator, and/or the shielding may cover one or more lossy parts of a seat. 
         [0130]    In exemplary embodiments, the device resonator area may be within a width and length of a soldier&#39;s clothing, vest, or jacket. In embodiments, the device resonator is within 20 cm by 20 cm, 15 cm by 15 cm, 10 cm by 10 cm, or smaller. In embodiments, the device resonator thickness is less than 3 cm, less than 2 cm, less than 1 cm, or thinner. In embodiments, the weight of the device is minimized to be less than the 20 lbs, less than 10 lbs, less than 5 lbs, or less. In embodiments, movement in the lateral (X-direction) is at least ±2 cm, ±5 cm, or more. In embodiments, movement in the vertical (Y-direction) is at least ±2 cm, ±5 cm, or more. In embodiments, movement in the separation (Z-direction) is at least ±2 cm, ±5 cm, ±7 cm, or more. 
       Magnetic Performance 
       [0131]    In order to optimize magnetic performance for a given wireless system, priority or design bounds may be placed on the system. Some of the design trades which were considered include but are not limited to the following: human safety, coil-to-coil efficiency, coil-to-coil distance separation, coil-to-coil offset, weight, size, shape, and movement. 
         [0132]    In  FIG. 17 , the result of the modeled and measured coil-to-coil efficiencies for Z=5 cm are shown. The measured data correlates with the modeled data within the expected tolerances. Coil-to-coil efficiencies were computed using the following measured and/or modeled coupling k and quality factor Q values: k: 3%-19%, Q s : 335, Q d : 508. 
         [0133]    In exemplary embodiments, because the wireless energy system may be positioned near the human body, it may be necessary to determine the impact of the body on the coil-to-coil performance.  FIG. 18  demonstrates that when considering various design trades, the effect of the human body for these types of resonators is small and can be neglected. The block  1802  shown in  FIG. 18A  is a model for the human body, specifically muscle tissue. The decrease in coil-to-coil efficiency is small (from 98.12% to 98.10%) compared to the system  1804  without a human body model present ( FIG. 18B ). This approximation may be useful in speeding up the simulation process to draw general conclusions about design trades. In embodiments, during the design trade optimization process, the following assumptions may be made. In embodiments, metallic or lossy objects may be positioned away from the proximity of the source and device resonators. In embodiments, the operating frequency may range between 250 kHz-6.78 MHz. In embodiments, the operating frequency may be greater than 6.78 MHz. In embodiments, the power delivered to the load may be greater than 5 W, greater than 10 W, or more. In embodiments, the distance between the resonator in soldier&#39;s vest and a soldier&#39;s body is greater than 1 cm, greater than 2 cm, or more. In embodiments, the distance between the source and device resonators may be greater than 2 cm, greater than 4 cm, greater than 6 cm, or more. In the interest of targeting a lighter and potentially smaller resonator coil for the device resonator coil (on the vest), performance was evaluated as a function of the area of the device resonator coil. 
       Source Resonator Embodiments 
       [0134]    In exemplary embodiments, various resonator coil types were investigated for both the seatback and vest sides to achieve efficient options for a wireless power transfer system. The resonator coil types shown in  FIG. 19  have been modeled with the system considerations discussed above in order to evaluate coil-to-coil efficiencies, X and Y offset performances as well as human safety limits. 
         [0135]    For the source resonator coils, the types considered include a metal-backed magnetic material (such as ferrite) shield in order to prevent efficiency degradation due to close proximity with any lossy materials, such as the aluminum framework inside the seat cushion.  FIG. 19  shows embodiments of the resonator coil types that were considered: 
         [0136]      FIG. 19A : Type B: Planar resonator coil  1902  made of solid or Litz wire with magnetic material  1904  and a metal shield  1906 ; 
         [0137]      FIG. 19B : Type D: Solenoidal resonator coil  1908  made of solid or Litz wire with magnetic material  1910  and a metal shield  1912 ; 
         [0138]      FIG. 19C : PCB: Resonator coil with PCB trace  1914  with magnetic material  1916  and a metal shield  1918 ; 
         [0139]      FIG. 19D : Type E: Planar resonator coil with double winding  1920  and a magnetic material  1922  and a metal shield  1924 . 
       Device Resonator Embodiments 
       [0140]      FIG. 20  shows exemplary embodiments of device resonator coils considered. In exemplary embodiments of the device resonator, shields may not be considered there are no metallic or lossy objects present in the close proximity of the resonator coil. In embodiments, shields may be used to decreases losses in the case where there are metallic or lossy objects present. By not requiring a shield, the weight of the device may be reduced significantly and also make the device resonator coil more flexible in shape and placement into gear. The following embodiments were considered for a device resonator: 
         [0141]      FIG. 20A : Type A: Planar resonator coil  2002  made of solid wire or Litz wire without magnetic material or a metal shield; 
         [0142]      FIG. 20B : Type B: Planar resonator coil  2004  made of solid wire or Litz wire with magnetic material  2006 ; 
         [0143]      FIG. 20C : Type C: Solenoidal resonator coil  2010  made of solid wire or Litz wire with magnetic material  2008 ; 
         [0144]      FIG. 20D : PCB: Resonator coil  2012  with PCB trace; 
         [0145]      FIG. 20E : Type E: Planar resonator coil  2014  made of solid wire or Litz wire with double winding with magnetic material  2016 . 
         [0146]    Among these coils, the Type A, Type B, and PCB resonator coils have magnetic dipole moments substantially orthogonal to the plane in which the resonator coil is mounted whereas the magnetic dipole moments for Type C, Type D, and Type E resonator coils are substantially parallel with the plane. For optimal overall performance, source and device resonator coil magnetic dipole moments may need to align. 
         [0147]    In exemplary embodiments, the following combinations were studied for this application: 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Source and device resonator coil combinations. 
               
             
          
           
               
                   
                 Source 
                 Device 
               
               
                   
                   
               
               
                   
                 Type B 
                 Type B (no shield) 
               
               
                   
                 Type B 
                 Type A 
               
               
                   
                 Type D 
                 Type C 
               
               
                   
                 PCB (with ferrite and shield) 
                 PCB (no ferrite, no shield) 
               
               
                   
                 Type E 
                 Type E 
               
               
                   
                   
               
             
          
         
       
     
         [0148]    For all of these combinations, efficiency degradation was analyzed as a function of misalignment and maximum power that can be delivered to the load before reaching FCC and ICNIRP SAR and E-field limits. In an exemplary embodiment, based on the results of the magnetic study, a Type B resonator coil with dimensions of 20×16 cm was chosen for the seatback and a Type A resonator coil with dimensions of 16×16 cm was chosen for the vest-worn resonator coil. The operating frequency was chosen to be 250 kHz. Based on the chosen frequency, resonator coil type, geometry, and proximity to the soldier, it was determined that up to approximately 37.6 W could be transferred before reaching the limit in the ICNIRP guidelines. 
       Highly Resonant Wireless Power Transfer (HRWPT) Seat-Vest System and Performance 
       [0149]      FIG. 16  shows an exemplary embodiment of a highly resonant wireless transfer system including a seat-back source  1602  and a vest-worn device  1604 .  FIG. 16B  shows an embodiment of a model of a system further including the vest-worn source and a helmet-mounted device in addition to the system shown in  FIG. 16A . A typical high level block diagram for a HRWPT system is shown in  FIG. 10 . Each stage of the system has a power efficiency rating caused by losses in the stage. The Greek symbol η represents the efficiency of a given stage. Because quiescent currents do not change drastically as output power is increased, the quiescent efficiency (η quiescent ) will actually increase with power. For example, assuming there is a constant quiescent power draw of around 1 W, the quiescent efficiency for a 10 W power delivery would be about 91% whereas if the power delivery were 20 W, the quiescent efficiency would be about 95%. Note, however, that the quiescent power is required for both source and device electronics. The overall efficiency is calculated by multiplying the efficiency of each stage. Considering the same circumstance above where 1 W each is consumed by the source and device electronics, the total quiescent efficiency would be 83% for a 10 W power delivery and 91% for a 20 W delivery. This results in an 8% difference. 
         [0150]    Due to the multiplicative nature of the stages&#39; efficiencies, it is advantageous to minimize quiescent losses and/or eliminate as many stages as possible.  FIG. 21  shows the high level block diagram for a HRWPT seat-vest system with the unnecessary stages removed and a breakdown of efficiencies based on measurements of electronic losses and overall end-to-end efficiency. In this embodiment, the output power is 12.6 W at a Z-distance of 5 cm and X=Y=0 cm. An end-to-end efficiency of 82% was found for the system and is a product of all the individual efficiencies of each block. Efficiencies are shown at a single operating point and will vary across operation. Efficiencies are approximated using measurements and end-to-end system efficiency calculations. 
         [0151]      FIG. 22  shows plots of end-to-end efficiency and  FIG. 23  shows plots of DC output power.  FIG. 22  shows an approximate 80% end-to-end efficiency at ±5 cm X ( FIG. 22A ) and Y ( FIG. 22B ) offset with 5 cm of separation between resonators.  FIG. 23  shows an approximate output power of 12 W at ±4 cm X ( FIG. 23A ) and Y ( FIG. 23B ) offset with 5 cm of separation between resonator coils. Note that the use of a source power algorithm flattens peak power output, allows increased range of operation, and improves efficiency. In exemplary embodiments, the algorithm includes the monitoring of source power to ensure it is within a window of, for example, 12.5 W (lower threshold) to 14.5 W (upper threshold). In embodiments, the monitoring of the source power can be done by measuring the current and/or voltage into the input of the amplifier of the source. If source power is above the upper threshold, the phase angle of the switches of the switching amplifier of the power and control circuitry may be increased. In exemplary embodiments, the switching amplifier may be a differential class D amplifier. In other embodiments, the switching amplifier may of another class of amplifier, such as class E. This in turn may decrease power to below the upper threshold. If the source power is below the lower threshold, the phase angle of the switches of the power and control circuitry may be decreased. This in turn may increase power to above the lower threshold. Other thresholds may be set for the source power. In embodiments, other elements of the power and control circuitry may be adjusted to regulate source power. 
         [0152]    Note also that for the designed HRWPT seatback system, a DC output load resistance of 10.5 Ω was chosen. Embodiments of the HRWPT seatback system with electronics are shown in  FIGS. 24-25 . 
         [0153]    Modeling and simulation tools were utilized to explore and optimize the wireless efficiency and performance of the HRWPT seatback system for the specified range of operation. The modeling and simulation tools were also used to evaluate compliance with applicable human exposure limits for Specific Absorption Rates (SARs) and internal E-field level, as delineated by ICNIRP, IEEE, and/or FCC. The end-result was a highly efficient 250 kHz system capable of 12 W over a lateral and vertical movement of 0 ±4 cm (8 cm total) and a separation distance of up to 5 cm. An additional 2 cm of movement can be obtained yielding a minimum of 10 W output. 
       Vest to Helmet Power Transmission 
       [0154]      FIG. 26  shows an exemplary embodiment of a system that demonstrates the capability to transfer power wirelessly from a battery pack worn on a vest to a helmet mounted electronic device requiring a minimum of 2.5 W. This demonstration provided a DC-AC transfer efficiency near 60% (45%-48% DC-DC transfer efficiency) at optimal positioning with degrading performance for azimuth head rotation. In embodiments, the source mounted to the vest provides at least 5 W of power over the following range to a device mounted on a helmet: azimuthal angle range from 0°±40° and elevation range from 5 to 13 cm. In embodiments, the operating frequency is approximately 200 kHz. In embodiments, the operating frequency may be chosen to be a frequency other than the operating frequency of the seatback to vest power transmission system to avoid unintentional power provided to the helmet from the seatback source. In embodiments, the operating frequency may be chosen to be the same to simply system electronics, such as those converting power transmitted to the vest to be used for the helmet. 
         [0155]    Electromagnetic studies were performed to target positional performance enhancement and ensure the viability of the system design. As part of this effort, the modeling and simulation results were evaluated with respect to compliance with applicable human exposure limits for Specific Absorption Rates (SARs), as delineated by ICNIRP, IEEE, and or FCC. Although initial studies focused on a 5 W system, the simulations have been performed to determine the practical upper limit of power transfer that could be implemented while complying with applicable FCC human exposure limits. 
         [0156]    In exemplary embodiments, the source and device resonator coils have horizontally aligned dipole moments.  FIG. 27  shows the device and source resonator coils on the mock soldier.  FIG. 28  shows measured and computed values of the magnetic coupling coefficient for the embodiment shown in  FIG. 27 . Diamond symbols correspond to measured points and square symbols to computed points.  FIG. 29  shows AC power delivered to a 35-ohm power resistor (diamond shapes) and DC-AC energy transfer efficiency (square shapes) for the embodiment shown in  FIG. 27 . 
       Magnetic Performance Improvements 
       [0157]    In  FIG. 30 , the results of the modeled and measured optimum coil-to-coil efficiencies are shown. The measured data correlates with the modeled data within the expected tolerances. For a radius of helmet rotation of 15 cm, the coupling k has a range 1%-5%. The Q of the source is 450 and the Q of the device is 390. 
         [0158]    Since the application requires that the resonator coils be near the human body, it may be necessary to determine the impact of the body on the coil-to-coil performance.  FIG. 31  demonstrates that when considering various design trades, the effect of the human body muscle for these types of resonator coils can be neglected.  FIG. 31A  shows that the efficiency using a human model is approximately 88.45%, which is a small decrease in efficiency without a human model (88.75%) as shown in  FIG. 31B . This is useful in speeding up the simulation process to draw general conclusions about the trades. During the design trade optimization process, the one or more of the following assumptions may be made. In embodiments, metallic or lossy objects may be positioned away from the proximity of the source and device resonators. In embodiments, the operating frequency may be 250 kHz. In embodiments, the operating frequency may be greater than 250 kHz. In exemplary embodiment, the power delivered to the load is 5 W or greater. In embodiments, there is a distance of approximately 40 mm between the resonator in the helmet and a human head in the helmet. In embodiments, the source resonator may be positioned 5 mm, 10 mm, or greater from the human body. 
         [0159]    In the interest of targeting a lighter and potentially smaller resonator for the device resonator (on the helmet), performance was evaluated as a function of various sizes and geometries of the device resonator. The evaluation resulted in a curved ferrite design for the helmet and vest.  FIG. 32  shows an exemplary embodiment of a geometry of a resonator. This embodiment comprises a curved piece of magnetic material  3204  and a solenoidal coil  3202  wound around the magnetic material.  FIG. 33  shows the mechanical dimensions of an exemplary embodiment of a curved piece of magnetic material. The curved piece has an arc angle of 83 degrees with a radius of curvature of approximately 155 mm and a thickness of approximately 10 mm (±0.3 mm). 
         [0160]    When power transfer occurs between resonators with curved magnetic materials (e.g., curved ferrite), in some embodiments, the curved magnetic materials can have substantially similar radii of curvature. As used herein, two resonators have a substantially similar radii of curvature if the radii of curvature of their curved magnetic materials differ by less than 10%. 
       Highly Resonant Wireless Power Transfer (HRWPT) Helmet-Vest System and Performance 
       [0161]    An exemplary embodiment of a HRWPT helmet-vest system is shown in  FIG. 14  with its associated measured specifications. A high level block diagram for a HRWPT system is shown in  FIG. 10 . 
         [0162]    Each stage of the system has a power efficiency rating caused by losses in the stage. The Greek symbol η represents the efficiency of a given stage. Because quiescent currents do not change drastically as output power is increased, the quiescent efficiency (η quiescent ) will actually increase with power. For example, assuming there is a constant quiescent power draw of around 1 W, the quiescent efficiency for a 10 W power delivery would be about 91% whereas if the power delivery were 20 W, the quiescent efficiency would be about 95%. Note, however, that the quiescent power is required for both source and device electronics. The overall efficiency is calculated by multiplying the efficiency of each stage. Considering the same circumstance above where 1 W each is consumed by the source and device electronics, the total quiescent efficiency would be 83% for a 10 W power delivery and 91% for a 20 W delivery. This results in an 8% difference. Due to the low power delivery of the HRWPT system, the efficiency may not appear as high as systems delivering more power. 
         [0163]    Due to the multiplicative nature of the stages&#39; efficiencies, it is advantageous to minimize quiescent losses and/or eliminate as many stages as possible.  FIG. 34  shows the high level block diagram for the HRWPT helmet-vest system with the unnecessary stages removed and a breakdown of efficiencies based on measurements of electronic losses and overall end-to-end efficiency. Efficiencies are shown at a single operating point and will vary across operation. Efficiencies are approximated using measurements and end-to-end system efficiency calculations. For elevation of approximately 10 cm, azimuth of approximately 0° and output power of approximately 16.71 W, an approximate end-to-end efficiency of 66% was found for the system. 
         [0164]      FIG. 35  shows a plot of end-to-end efficiency and  FIG. 36  shows a plot of DC output power.  FIG. 35  shows an approximate end-to-end efficiency of 66% with 10 cm of separation between resonators at 0° azimuth angle.  FIG. 36  shows output power of 5 W over the azimuth rotation range of ±40° when elevation is less than or equal to 10 cm. 
         [0165]    During testing of the HRWPT helmet system, it was determined that the type of helmet had a substantial impact on the efficiency of the magnetics. The impact on efficiency and performance was determined to be caused by a carbon fiber composite contained in this particular model of the helmet. The effects of the carbon fiber were characterized and are summarized in the  FIGS. 37-38 . The impacts of the helmet shown may be mitigated if an equivalent helmet without carbon fiber composite were used with the HRWPT helmet system. Note that for the designed HRWPT helmet-vest system, an optimum DC output load resistance of 21Ω was chosen.  FIG. 39  shows pictures of the HRWPT helmet-vest system. 
         [0166]    Modeling and simulation tools were utilized to explore and optimize the wireless efficiency and performance of the HRWPT helmet system for the specified range of operation. The modeling and simulation tools were also used to evaluate compliance with applicable human exposure limits for Specific Absorption Rates (SARs), as delineated by ICNIRP, IEEE, and/or FCC. The HRWPT helmet system was designed and tested. The end result was a highly efficient  200  kHz system capable of a minimum of 5 W over an azimuth angular movement of 0°±40° (80° total) and an elevation movement from 5 to 13 cm of resonator coil separation. Additional power can be obtained when operating at a smaller azimuth angle. The improvements in design also allow for a reduction in footprint of the various components of the system. 
         [0167]    Note that article of clothing, gear, apparel, covering, and the like may be used interchangeably. 
         [0168]    In exemplary embodiments, the power received by the device resonator on the vest from the source resonator on the seat may be used directly by the source resonator on the vest to provide power to the device resonator on the helmet. In embodiments, there may be a power manager that controls the power transferred from device resonator on the vest to the source resonator on the vest. The power transfer may be via a wired or wireless connection and the power manager may monitor, filter, and/or convert the power provided to the source resonator on the vest. In embodiments, the power manager may convert the frequency of power transfer in the seat-vest system to a different frequency in the vest-helmet system. For example, the frequency of power transfer in the seat-vest system may be 250 kHz, while the frequency of power transfer in the vest-helmet system may be 200 kHz. 
         [0169]    In exemplary embodiments, the power received by the device resonator on the vest from the source resonator on the seat may be stored in a battery on the vest. In embodiments, there may be a power manager that monitors and controls the stored energy. This stored energy may be used by electronic devices on the vest or other clothing or it may be provided to the source resonator on the vest to wirelessly transfer power to the device resonator on the helmet. In embodiments, the power manager may monitor and control the power provided to the source resonator on the vest based on the electronic devices on the helmet. For example, night vision goggles may draw a different amount of power than another piece of equipment, such as an ear-piece. In embodiments, the battery may be optionally coupled to the power manager such that it may draw power directly from the device resonator (and associated electronics, such as a rectifier) on the vest or draw from a battery. 
       System Safety 
       [0170]      FIGS. 40A-40B  show safety modeling of an exemplary embodiment of a seat to vest system. For the safety modeling shown in  FIG. 40A , the resonator coil to body separation is 2.5 mm.  FIG. 40B  shows a plot of maximum power the source can transfer while staying under the SAR (black diamond data points) and/or electric field limits (gray square data points). The Specific Absorption Rate (SAR) at a power level of 10 W is 0.0118 W/kg. Note that the limit is 1.6 W/kg. The maximum power that can be transferred at the SAR limit is 1.35 kW. The Internal E-field (E) levels at 10 W is 17.4 V/m. Note that the limit is 33.75 V/m. The maximum power that can be transferred at the E limit is 37.6 W. 
         [0171]      FIG. 41A-40B  shows safety modeling of an exemplary embodiment of a vest to helmet system (at the vest side). For the safety modeling shown in  FIG. 41A , the resonator coil to body separation is 5 mm.  FIG. 41B  shows a plot of maximum power the source can transfer while staying under the SAR (black diamond data points) and/or electric field limits (gray square data points). The Specific Absorption Rate (SAR) at a power level of 5 W is 0.0031 W/kg. Note that the limit is 1.6 W/kg. The maximum power that can be transferred at the SAR limit is 1.8 kW. The Internal E-field (E) levels at 5 W is 11.22 V/m. Note that the limit 33.75 V/m. The maximum power that can be transferred at the E limit is 29 W. 
         [0172]      FIG. 42A-42B  shows safety modeling of an exemplary embodiment of a vest to helmet system (at the helmet side). For the safety modeling shown in  FIG. 42A , the resonator coil to body separation is 40 mm. The Specific Absorption Rate (SAR) at a power level of 5 W is 0.0006 W/kg. Note that the limit is 1.6 W/kg. The maximum power that can be transferred at the SAR limit is 9.6 kW. The Internal E-field (E) levels at 5 W is 3.47 V/m. Note that the limit 33.75 V/m. The maximum power that can be transferred at the E limit is 301 W. 
         [0173]    While the invention has been described in connection with certain preferred embodiments, other embodiments will be understood by one of ordinary skill in the art and are intended to fall within the scope of this disclosure, which is to be interpreted in the broadest sense allowable by law. For example, designs, methods, configurations of components, etc. related to transmitting wireless power have been described above along with various specific applications and examples thereof. Those skilled in the art will appreciate where the designs, components, configurations or components described herein can be used in combination, or interchangeably, and that the above description does not limit such interchangeability or combination of components to only that which is described herein. All documents referenced herein are hereby incorporated by reference.