Abstract:
Method and system for wireless power transmission are disclosed. In one aspect, the system includes a charging base positioned on a desktop component and configured to be positioned on a desktop. The system also includes a transmitter located in the charging base and including a transmit coil wound about a plane, the transmitter being configured to wirelessly transfer power, via a wireless field, from the transmit coil to a first receiver. The system further includes a power relay configured to be positioned on the desktop and configured to relay power received from the transmitter to at least one peripheral device different from the first receiver when the peripheral device is positioned on the desktop.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/427,318 entitled “SHORT RANGE EFFICIENT WIRELESS POWER TRANSFER,” filed Apr. 21, 2009, which claims benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/046,757, filed Apr. 21, 2008, the entire contents of which are herewith incorporated by reference. 
         [0002]    Applicant&#39;s previous applications and provisional applications, including, but not limited to, U.S. patent application Ser. No. 12/018,069, filed Jan. 22, 2008, entitled “Wireless Apparatus and Methods”, the entire contents of the disclosure of which is herewith incorporated by reference, describe wireless transfer of power between a transmitter and receiver. 
     
    
     FIELD 
       [0003]    The described technology generally relates to wireless charging, and more specifically to short range efficient wireless power transfer. 
       BACKGROUND 
       [0004]    The transmit and receiving antennas are preferably resonant antennas, which are substantially resonant, e.g., within 10% of resonance, 15% of resonance, or 20% of resonance. The antenna may be of a small size to allow it to fit into a mobile, handheld device where the available space for the antenna may be limited. An embodiment describes a high efficiency antenna for the specific characteristics and environment for the power being transmitted and received. 
         [0005]    One embodiment uses an efficient power transfer between two antennas by storing energy in the near field of the transmitting antenna, rather than sending the energy into free space in the form of a travelling electromagnetic wave. This embodiment increases the quality factor (Q) of the antennas. This can reduce radiation resistance (R r ) and loss resistance (R l ). 
         [0006]    The inventors noticed that many of the solutions raised by this system include power delivery at a distance, for example power delivery over inches or feet from a power transmitter to a receiver. The techniques disclosed in our co-pending applications allow delivery of power at reasonable efficiencies, for example between 3 and 5 feet, for example, and efficiencies from 5 to 40%. 
       SUMMARY 
       [0007]    However, it was noticed that many users and/or manufacturers would actually prefer higher power-delivery efficiencies, and are willing to accept this power delivery at short distances. For example, many would prefer a power delivery solution which was over 90% efficient, even if that power delivery solution was less convenient to use. The inventors noticed that the resonant which have been used for delivery of power at a distance, could actually be used to produce very high efficiencies when used in a close contact situation. 
         [0008]    An aspect describes a magnetically coupled resonance system, that includes a first pad surface against that accepts devices to be provided with power. The device uses the magnetically coupled resonance to provide power at a first efficiency of power transfer to devices on the pad surface. Power is provided at a second efficiency of power transfer, lower than the first efficiency, to other devices that are not on the first surface, e.g., devices that are remote from the pad by e.g., less than 12 inches or less than 3 feet. 
         [0009]    The devices and pad can each use magnetically resonant circuits with antennas formed of an inductor formed by a coil, and a separate capacitor, tuned to an appropriate frequency. 
         [0010]    The present application discloses use of these techniques to form a wireless desktop. The wireless desktop can be used to charge personal electronic devices such as communications terminals, cellular phones, or computer based peripheral devices these charged devices are either or both of powered or recharged, without wires, using a wireless energy transfer technique. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a wireless desktop with wireless powered items. 
           [0012]      FIG. 2  shows an equivalent circuit. 
           [0013]      FIGS. 3A-3F  show single receivers on pads with and without foldouts. 
           [0014]      FIG. 4  shows efficiencies for the single receivers. 
           [0015]      FIGS. 5A-5D  show pads with multiple receivers. 
           [0016]      FIG. 6  shows transfer efficiencies for the multiple receivers. 
           [0017]      FIG. 7  shows coplanar field coupling using parasitic. 
           [0018]      FIG. 8  shows a desktop parasitic. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    An embodiment uses coupled magnetic resonance using magnetic field antennas. Embodiments may operate at any frequency, but two embodiments may operate either at LF (e.g. 135 kHz) or at HF (e.g. 13.56 MHz), but at short distances. One embodiment uses a loop coil in series with a capacitor as the antenna. In one embodiment, the receiver part (e.g., the portable device) is intended to be placed directly on the pad. In this embodiment, there is a relatively small, fixed distance between the transmitter and receiver. That fixed distance, for example, may be set by the thickness of the material of the pad and the material of the housing. This may be less than a centimeter or less than 10 mm, between the coils forming the transmitter and receiver. The distance will be constant, so the item is always the same distance from the antenna when pressed against the pad. 
         [0020]    That fixed distance is dependent on the geometry of the pad and the geometry of the charged item. In the embodiment, the antenna can be tuned to have a maximum response at that constant distance. This tuning, as well as other tuning operations described in this specification, can be calculated and then optimized by trial and error, for example. 
         [0021]    However, unlike other close-charging systems, this system can also charge items which are located at a distance, e.g., inches or feet from the antenna. The antenna is less efficient when charging at a distance, but will still provides power at that distance. That allows charging of items that are not directly placed on the charging pad—unlike pure inductive systems which provide in essence no charge at all other than at the very specific fixed distance and/or orientation. 
         [0022]    This produces certain advantages, including the ability to use less precision in the placement of the device on the charging pad. Even if the device is placed off the pad, it will still receive charging at a lower level from proximity. The lower level charge can be, for example, between 0.05 watts and 0.25 watts, for example, even when the device is not precisely placed on the pad. 
         [0023]    To utilize desktop space efficiently and to reduce desktop wiring, the antenna of the power transmitter/power base may be incorporated into a host device that normally exists on a desktop. Embodiments describe that host device as including either a PC monitor or a lamp, but can be any other item, such as a printer, scanner, fax machine, telephone, router, or the like. 
         [0024]    The transmitter unit may be powered directly from the 110/230 VAC supply already existing in this host device, thus not requiring an extra power cord or power connection. 
         [0025]    In one embodiment, as shown in  FIG. 1 , the transmit antenna is embedded in the pedestal  104  of a PC monitor screen  100  or in the pedestal  112  of a desk lamp  110 . The pedestals may be disk-shaped, to house a circular wire loop antenna generating a symmetric magnetic field. This field is mostly vertically polarized at any position on the desk, in the plane of the antenna loop. This embodiment favors coplanar orientation of antenna loops integrated in wireless-power-enabled devices; that is, the best power-transfer will be obtained when a loop coil in the receiving device is oriented in a substantially parallel plane to a loop coil in the transmitting device. The surface of the charging base may be substantially parallel with the coil, so that the coplanar relationship can be maintained.  FIG. 7  illustrates how the coplanar operation can extend to all the items on the desktop. 
         [0026]    This coplanar orientation can be used, for example, for wire loop antennas integrated into keyboards, mouse devices, and into many other electronic devices such as mobile phones, MP3 players, PDAs, etc. if placed in the usual manner. This may, however, be used in other applications. 
         [0027]    In another embodiment, there may be more than one power base on a desktop as shown in  FIG. 1 . Power is supplied from the base that is closest to the receiving device or from multiple different sources. 
         [0028]    Each power base may also provide an area to place devices directly on the wire loop antenna, resulting in strongest coupling, thus enabling high power transfer at high efficiency. This close proximity coupling is attained by providing a surface  105 , for example, adjacent the charging coil. In this embodiment, more than one device may be placed on such a charging pad surface  105 . This has the other advantage of allowing a larger coil for the transmitting, which also provides improved efficiency. 
         [0029]    Low power devices with long battery autonomy, such as a keyboard or a computer mouse, may be placed in the proximity or vicinity of a power base to charge by proximity coupling. Available power and transfer efficiency for these devices will be lower than for the fixed distance coupling. However, these devices may be constantly charged, and intermittently used. Hence, these devices do not require continuous charging. In one embodiment, the amount of charging may be reduced when other devices are additionally placed on the charging pad, because the multiple devices may more heavily load the system than a single device. 
         [0030]    Magnetic field strength in the vicinity of a power base will preferably be below safety critical levels. The power base may additionally provide a function to automatically reduce magnetic field strength if a person is approaching. This function may use infrared or microwave person detection  108 . This can be a proximity detector, e.g., one that can be activated by user proximity. 
         [0031]    A first embodiment actuates the proximity detector manually. Persons that feel uncomfortable in presence of magnetic fields can turn on the function. This function will can also cause devices in the vicinity to stop receiving power during the time when persons are in proximity. This may use, for example, an IR detector to detect the presence of persons. 
         [0032]    Another embodiment may always have the proximity detector active and automatically turn off the function when 
         [0033]    Other devices such as cordless phones, digicams, etc. may be placed on a charging station. This allows the wireless power receiver and its antenna to be made an integral part of the recharging station. A charging station may provide more area and/or space to integrate an efficient power receiver other than the portable device itself. For example, this may use electrical contacts, or by using a wireless technique or a wireless parasitic antenna, as described herein. The charging station itself may be configured and used as a power relay or a parasitic antenna that improves coupling between the transmitter and the portable devices which receive the charge. 
         [0034]    In an embodiment, shown in  FIG. 1 , there may be a number of different electrically operated devices on a user&#39;s “desktop”, which may be items used by a user for work every day. One such item is a monitor  100  for a PC. This operates off power provided by a 110 V connection  102  which plugs into the AC outlet. The 110 V connection  100  provides power for both the operation of the monitor, and also provides the power for the wireless surface  104  that is integrated into the base of the monitor. The charging pad may use the techniques that are described in detail herein. 
         [0035]    Wireless proximity charging may be enabled in the area  105 , which forms a flat surface on the base. According to this embodiment, the wireless proximity charging may be specifically tuned for short distance connections, although it may also operate properly over longer distance connections. Surface  105  may be sized such that devices such as cell phones and PDAs such as  107  may be rested on the surface. While charging is optimized for the area  105 , charging is still carried out in other areas. 
         [0036]    In this embodiment, there is also another charging base as part of a desk lamp  110 . This forms a charging base  112  with an area  113  thereon. As in the  104  charging base, the charging is optimized for carrying out up close proximity charging of items such as  114  using magnetically coupled resonance. It may also charge items that are distant from the charging base. 
         [0037]    In addition to charging items such as  114  on the charging base, either or both of the items produces magnetically resonant output power that is coupled to remote devices that are enabled for wireless charging. These remote devices, for example, may include a magnetically resonant antenna therein that is resonant to the same frequency of the transmission. In an embodiment, this may be at 13.56 MHz or at 135 Khz, or at any other frequency. 
         [0038]    The charged devices can include a digital camera  121 , a wireless mouse  122 , and a wireless keyboard  123 . Each of these devices, for example, can include a battery therein, which is charged by the operation of the device. 
         [0039]    An important feature is that an up close charge can be carried out at high efficiency, or a distance charge can be carried out lower efficiency. 
         [0040]      FIG. 2  shows an equivalent circuit of the power transmission system, and illustrates how the efficiency can be calculated. A power source  200  portion includes a power source  205 , for example the AC socket. The power source  205  has an equivalent loss resistance  210 . The loss resistance  210  models the resistance and power conversion losses. Alternatively, the power source can include some parts of the conversion electronics, for example in the case that the power from the power source is changed to some other frequency or some other power value. 
         [0041]    The power source  205  is connected across terminals  215 , to antenna part  220 . Antenna includes an inductor  230  and series capacitance  235 . The LC constant of the inductor and capacitance is tuned to be substantially at the frequency of the source  205 . The antenna also has shows a loss resistance value  235 , which is a parasitic value that represents the transmit antenna losses, including internal losses, external losses, and radiation losses. 
         [0042]    A magnetic field  250  is created in the vicinity of the antenna  230 . This is coupled to the antenna  240  of the receiver. As in the antenna  230 , the antenna  240  includes an inductor  242  capacitor  244 . The inductor and capacitor form a circuit that is resonant with the received frequency that is received. 
         [0043]    Receive antenna losses are shown by the series resistance  246 . The input power P r  is connected via the terminals  248  to a load  260 . The load  260  also includes receive power losses  262  shown as a series resistance, which can be modeled as losses in the system. 
         [0044]    These losses can include the power conversion losses as well as series resistance losses. 
         [0045]    Another system can attempt to obtain maximum efficiency in various different scenarios. For example, in one scenario, the transmit antenna can be tuned by changing the capacitance to obtain resonance at the operating frequency in the presence of an unloaded receiver. In an unloaded receiver scenario, the resistance of the load is infinite. Loaded receivers change this resistance. Receiver measurements can also be carried out, by tuning the receiving antenna to change the capacitance etc. in the presence of an unloaded transmitter or in the case of multiple transmitters. 
         [0046]    The different values can be measured. Capacitance value adjustments can be available, for example, for unloaded, moderately loaded (e.g, a single load) or highly loaded systems. Different capacitance values can be dynamically switched to create the highest efficiency value, and to operate with that value. 
         [0047]      FIGS. 3A-3F  show different scenarios of charging.  FIG. 3A  shows a conventional PDA  300  on a large charging pad  305 . In the embodiment, this may be a low-frequency charging pad which may have a 26 cm diameter. Another embodiment may use a PDA  310  which includes a foldout antenna portion  315 . The foldout antenna portion  315  may include a loop antenna that can be folded away from the body of the device to improve the coupling efficiency. 
         [0048]      FIG. 3C  shows a small pad embodiment, where the pad  320  is substantially the same size as the PDA  300 . In this embodiment, the pad may be 6×9 cm.  FIG. 3B  shows how this pad might be used with a foldout embodiment, where the flap  315  fits directly over the pad  320 . A medium pad is shown in  FIGS. 3E and 3F . In this embodiment, the medium pad  330  includes the PDA  300  thereon, or a foldout PDA  310  with its foldout flat. The medium pad may be 18 cm in diameter in this embodiment. 
         [0049]    The efficiency results for these devices are shown in  FIG. 4 , which shows how the different size devices can be located on the different size pads. Five of the six situations have efficiencies which are greater than 80%. Even the lowest efficiency, created by a large pad with an integrated receiver in the phone, had a transfer efficiency of 50%. 
         [0050]    Another embodiment shown in  FIGS. 5A-5D  may use multiple receivers all on the same pad. Since the pads, especially the large and medium pads, have sizes that are large enough to physically hold multiple different phones, multiple different devices can be placed all on the pad. 
         [0051]      FIGS. 5A-5D  illustrates these different embodiments. In  FIG. 5A , the pad  305  includes three PDA phones/devices thereon, shown as  400 ,  402  and  404 ; however, the pad may include more or fewer devices. 
         [0052]    In the  FIG. 5B  embodiment, the devices have foldout antennas, with the devices  510 ,  512  and  514  each representing a PDA on the pad, along with its foldout flat against the pad and away from the body of the phone. 
         [0053]      FIG. 5C  shows the medium pad  330  with two phones thereon,  400 ,  402 , while  FIG. 5B  shows this same pad with two foldouts thereon  510 ,  512 . 
         [0054]      FIG. 6  shows the measured efficiency of this system, with again most of the efficiencies being greater than 80%. 
         [0055]    The efficiency of the system  la  can be calculated as the input power across the terminals  215  divided by receive power across the terminals  248   
         [0056]    or η a =P r /P t . 
         [0057]    Another embodiment shown in  FIG. 8  forms a power relay as a parasitic antenna that improves coupling between energy source and energy sink. The energy source is formed of a resonant antenna  810 , which may be a resonant capacitor and inductor. A parasitic antenna  800 , which may also be resonant at the same frequency, may be used. This parasitic antenna may be expanded to cover a large portion of the desktop area  820  as shown. Such a parasitic loop may either be mounted beneath the desk, or built into the desktop surface, or put on the desk&#39;s surface e.g. as a flat structure, such as a desk mat. The parasitic device can be excited by a single and small active power base, and can be used to dramatically improve performance and efficiency of wireless desktop powering and charging in that area. 
         [0058]    Inductive excitation from a small power base may however be a convenient solution since it does not require integration of any part. This becomes particularly true when the parasitic antenna is invisibly integrated into the desktop.  FIG. 8  illustrates a large parasitic loop thereby improving the coupling between power base and receiver devices. The parasitic loop can cover an entire desk surface, providing a hot zone throughout that desk surface. The parasitic antenna, in this embodiment, provides passive repeating of power to the entire desktop area. 
         [0059]    The same kind of antenna, in another embodiment, may also be driven directly from a transmitter unit. 
         [0060]    The general structure and techniques, and more specific embodiments which can be used to effect different ways of carrying out the more general goals are described herein. 
         [0061]    Although only a few embodiments have been disclosed in detail above, other embodiments are possible and the inventors intend these to be encompassed within this specification. The specification describes specific examples to accomplish a more general goal that may be accomplished in another way. This disclosure is intended to be exemplary, and the claims are intended to cover any modification or alternative which might be predictable to a person having ordinary skill in the art. 
         [0062]    Also, the inventors intend that only those claims which use the words “means for” are intended to be interpreted under 35 USC 112, sixth paragraph. Moreover, no limitations from the specification are intended to be read into any claims, unless those limitations are expressly included in the claims. 
         [0063]    Where a specific numerical value is mentioned herein, it should be considered that the value may be increased or decreased by 20%, while still staying within the teachings of the present application, unless some different range is specifically mentioned. Where a specified logical sense is used, the opposite logical sense is also intended to be encompassed.