Abstract:
System and method for harvesting radio frequency power from a wireless transmitter includes; an antenna having an output voltage, a matching network coupled to the antenna, a booster circuit coupled to the matching network and having an output voltage, and adapted to amplify the output voltage of the antenna. Matching network is adapted to match a power transfer. A voltage stabilizer circuit is adapted to stabilize the booster circuit output voltage. Method includes, determining at least one operating mode and charging a slave device from a master wireless transmitter located within a predetermined distance from the system. A rechargeable battery in the system is charged from a wireless transmitter, and a slave device is connected to the system. The slave device is charged from the rechargeable battery in the system.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims benefit under 35 USC 119(e) of commonly assigned U.S. provisional application No. 61/364,731, filed Jul. 15, 2010, entitled “Method and System For Harvesting RF Signals and Wirelessly Charging A Device,” and U.S. provisional application No. 61/364,739, filed Jul. 15, 2010, entitled “Wireless Battery Charger,” the contents of all of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to supplying power to portable devices. More specifically, some embodiments of the present invention relate to harvesting radio frequency (RF) signals to power portable devices. 
         [0003]    In the world of nanotechnology and wireless communication and networking, power supply of electrical devices still is a matter of concern. Many scientists and researchers are working on various methods of production, transmission and storing energy. Portable devices powered by rechargeable batteries commonly need chargers or base stations that are connected by wire from a power grid. Such portable devices include cell-phones, personal digital assistants, smart-phones, tablets, and remote controls, among others. Some of these devices rely on radio frequency signals for communication purposes. 
         [0004]    The existing wireless chargers have operation distance limitations which prevents them from being used in locations without access to the wired power grid. This means that the device to be charged has to be in locations where a power outlet exists so that the charger can be connected to a power outlet and then the device to be charged must be placed on it (or kept within a short distance from it). 
         [0005]    RF signals in the air have very limited power. Thus, the output power of an RF signal harvester is in the range of micro and milli-watts. Yet, various low power electronic devices can be empowered with this power. 
       BRIEF SUMMARY 
       [0006]    The present invention relates generally to supplying power to portable devices. More specifically, some embodiments of the present invention relate to harvesting radio frequency (RF) power to power portable devices. 
         [0007]    According to one embodiment of the present invention, a system for harvesting radio frequency power from a wireless transmitter includes; (i) an antenna having an output voltage, (ii) a matching network coupled to the antenna, (iii) a booster circuit coupled to the matching network and having an output voltage, and adapted to amplify the output voltage of the antenna. The matching network is adapted to match a power transfer from the antenna to the booster circuit. The system for harvesting radio frequency power from the wireless transmitter further includes a voltage stabilizer circuit adapted to stabilize the output voltage of the booster circuit. 
         [0008]    According to one specific embodiment, the system further includes a user selectable switch adapted to determine at least one operating mode, and a connector adapted to charge a slave device. At least one operating mode is adapted to charge the slave device from a master wireless transmitter located within a predetermined distance from the system. 
         [0009]    According to another specific embodiment, the system further includes: (i) a user selectable switch adapted to determine at least one operating mode, (ii) a rechargeable battery adapted to be charged by the booster circuit, and (iii) a connector adapted to charge a slave device. The at least one operating mode is adapted to charge the rechargeable battery from a wireless transmitter located within a predetermined distance from the system and the rechargeable battery is adapted to charge the slave device. 
         [0010]    According to another specific embodiment, the antenna is a wideband antenna. According to another specific embodiment, the antenna is a wideband circularly polarized micro-strip patch antenna. 
         [0011]    According to another specific embodiment, the matching network is a resonant circuit tuned at a predetermined frequency. According to another specific embodiment, the booster circuit includes a multi-stage voltage multiplier circuit. 
         [0012]    According to another specific embodiment, the system further includes a software executable on the master wireless transmitter and adapted to provide a user selectable amount of radio frequency power from the master wireless transmitter to the slave device. 
         [0013]    According to another specific embodiment, the master wireless transmitter is adapted to transmit a user selectable file. The duration of the transmission corresponds to the amount of radio frequency power transmitted from the master wireless transmitter to the slave device. 
         [0014]    According to another specific embodiment, the master wireless transmitter is chosen from one of the group of a cell-phone, a laptop, or a personal computer. According to another specific embodiment, the master wireless transmitter is adapted to transmit radio frequency power chosen from of one of the group of a Bluetooth signal, or a Wi-Fi signal. 
         [0015]    According to another specific embodiment, the predetermined distance is about 1 meter. According to another specific embodiment, the predetermined distance is about 500 meters. 
         [0016]    According to another specific embodiment, the wireless transmitter is adapted to transmit radio frequency power for the system. According to another specific embodiment, the wireless transmitter is adapted to transmit radio frequency power for the system in the form of one of the group of a GSM signal, or a Wi-Fi signal. According to another specific embodiment, the system is adapted to receive a signal having a power of at least −25 dBm. 
         [0017]    According to one embodiment of the present invention, a method for harvesting radio frequency power from a wireless transmitter by a system including an antenna having an output voltage, a matching network coupled to the antenna, a booster circuit coupled to the matching network and having an output voltage, and a voltage stabilizer circuit, the method includes, matching a power transfer from the antenna to the booster circuit, amplifying the output voltage of the antenna, and stabilizing the output voltage of the booster circuit. 
         [0018]    According to one specific embodiment, the method further includes determining at least one operating mode. According to another specific embodiment, the method further includes charging a slave device from a master wireless transmitter located within a predetermined distance from the system. 
         [0019]    According to another specific embodiment, the method further includes charging a rechargeable battery in the system from a wireless transmitter located within a predetermined distance from the system, and connecting a slave device to the system. The slave device is charged from the rechargeable battery in the system. 
         [0020]    A better understanding of the nature and advantages of the embodiments of the present invention may be gained with reference to the following detailed description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a simplified block diagram showing a system for harvesting radio frequency power from a wireless transmitter in accordance with an embodiment of the present invention; 
           [0022]      FIG. 2  is a simplified schematic diagram showing a matching circuit in accordance with an embodiment of the present invention; 
           [0023]      FIG. 3  is a simplified schematic diagram showing a booster circuit in accordance with a first embodiment of the present invention; 
           [0024]      FIG. 4  is an example of an output voltage response with respect to input RF power for the embodiment shown in  FIG. 1 ; 
           [0025]      FIG. 5  is a simplified schematic diagram showing a booster circuit in accordance with a second embodiment of the present invention; 
           [0026]      FIG. 6  is a simplified block diagram showing a method for harvesting radio frequency power from a wireless transmitter in accordance with an embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    According to the embodiments of the present invention, a system and method for harvesting radio frequency power from a wireless transmitter are described. The system may include a wireless charger that reuses the wasted power of RF signals in the environment. Although the output power of an RF signal harvester is in the range of micro and milli-watts, various low power electronic devices can be empowered with this low power. Some examples of such low power electronic devices may include: calculators, wireless chargers, low power electric devices (sensors, Remote Telemetry Units (RTUs) and the like), low power home appliances (remote controls, watches and the like), biomedical applications (empowering artificial organs such as implanted hearts), and robotics (robotic cells). In such applications, the RF signal harvester can replace batteries. In some applications, a high power transmitter may be placed in the field to provide the RF signals for the RF signal harvester. Using this system, one can charge up his/her portable device enough for a short operation time. For instance, if a cell-phone is to be charged, using the proposed method, the cell-phone will have enough battery power for a few calls. 
         [0028]    Table 1 shows a comparison between an existing RF signal harvester and an RF signal harvester in accordance with embodiments of the present invention. Both of the harvesters were tested under the same conditions (i.e. normal movement, outdoor, and indoor environments). The approximated price of the prototype may be reduced by mass production. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Output  
                   
                   
               
               
                   
                 Size 
                 Voltage 
                 Cost 
                 Special 
               
               
                 Harvester  
                 (cm) 
                 (mV) 
                 ($) 
                 considerations 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Commercialized 
                 4 × 7.5 
                 0.25-0.4  
                 100  
                 Voltage is based on 
               
               
                 Piezoelectric 
                   
                   
                   
                 tested measurements 
               
               
                 Proposed RF  
                 2 × 3.5 
                 0.15-0.5 
                 11.90  
                 Cost is approximated 
               
               
                 Signal Harvester 
                   
                   
                   
                 based on prototype 
               
               
                 (prototype) 
                   
                   
                   
                 assembly components 
               
               
                   
               
             
          
         
       
     
         [0029]      FIG. 1  is a simplified block diagram showing a system  100  for harvesting radio frequency power from a wireless transmitter in accordance with an embodiment of the present invention. System  100  may include an antenna  110 , a matching circuit  120 , a booster circuit  130  a charging unit  140 , a connector  150 , a switch  160 , and a housing  170 . Matching circuit  120  is coupled between antenna  110  and booster circuit  130 . Booster circuit  130  is coupled to charging unit  140 . The antenna  110 , matching circuit  120 , booster circuit  130 , and charging unit  140  may be contained in housing  170 , which may support connector  150  and switch  160 . Alternatively, antenna  110 , matching circuit  120 , booster circuit  130 , and charging unit  140  may be embedded in a low power wireless device. Connector  150  may include either a custom designed connector for each low power electronic device application or may include a general plug and a set of adaptor connectors to couple each low power electronic device application with the general plug. Switch may be user selectable and adapted to determine at least one operating mode to be described below. In one operating mode system  100  may further include an optional rechargeable battery  180 , which is coupled to charging unit  140  in housing  170 . In each operating mode, the switch either couples charging unit  140  to battery  180  and battery  180  to connector  150 , or couples charging unit  140  directly to connector  150 . 
         [0030]    Antenna  110  may be a wideband circularly polarized micro-strip patch antenna. The polarization is selected to be circular so that the antenna can receive signals of all polarizations. Moreover, the antenna is wideband so that a wider range of signals can be harvested. Antenna  110  has an output voltage coupled to matching circuit  120 . 
         [0031]      FIG. 2  is a simplified schematic diagram showing matching circuit  120  in accordance with an embodiment of the present invention. Matching circuit  120  may be tuned at a predetermined frequency, which, depending on the system of wireless communication, can be a Bluetooth frequency of 2.4 GHz or 5 GHz, or a GSM signal of frequencies from 900 MHz to 2 GHz) so that the mismatch losses are reduced and maximum power is delivered to booster circuit  130 . Matching circuit  120  may include a resonant circuit, which can help reduce noise and interference to other operating wireless systems. This noise and interference reduction is achieved by minimization of the reflected back signals due to mismatch. The matching circuit  120  may include a series RLC circuit  220 ,  230 ,  240  respectively. The design of matching circuit  120  is frequency dependent and may be designed in a way that power transfer losses are minimized. 
         [0032]    Booster circuit  130  may either include diodes and capacitors or MOSFET transistors and capacitors to boost the output voltage of antenna  110  to voltage levels acceptable for charging a low power electronic device or battery  180 .  FIG. 3  is a simplified schematic diagram showing a booster circuit  130   a  in accordance with a first embodiment of the present invention, which includes a multi-stage voltage multiplier circuit such as, for example, a six stage voltage multiplier circuit designed with capacitors  301 - 306  and schottky diodes  311 - 316 . Booster circuit  130   a  is designed in a way that changes in the value of capacitors does not affect the output of the booster significantly. In one example, capacitors  301 - 306  are each 1 pF. 
         [0033]    In booster circuit  130   a , the RF signal wave is rectified at its negative half of the cycle by C 301  and D 311 , and in its positive half by C 303  and D 312 . During the positive half-cycle, the voltage stored in C 301  from the negative half-cycle is transferred to C 303 , which causes the voltage of C 303  to be roughly two times the peak voltage of the RF source and is why this 2-stage portion of booster circuit  130   a  may be called a voltage doubler. The doubled voltage level is minus the turn-on voltage of the diode. Each stage of voltage multiplier contains one diode and one capacitor and operates in the manner described above. The number of stages determines the amount of multiplication (alternatively referred to herein as “amplification”). 
         [0034]      FIG. 4  is an example of an output voltage response with respect to input RF power for the embodiment shown in  FIG. 1 . The power of Bluetooth signals may not exceed 0 dBm so the higher powers are provided for lab measurement purposes. As can be observed from  FIG. 4 , a voltage of 3 volts can be achieved using a Bluetooth signal to charge a battery or a low power device. As long as a potential deference across the battery is maintained, the current will flow through it, resulting in charging. 
         [0035]    The booster circuit, which is a voltage multiplier, is used to amplify the output voltage of the antenna. Yet, the current gets reduced since the electric power follows the law of conservation of energy. Thus, the booster or the voltage amplifier may be designed in such a way that the power loss through the booster circuit is minimized. To achieve this goal, the booster circuit may include MOSFET transistors.  FIG. 5  is a simplified schematic diagram showing a booster circuit  130   b , in accordance with a second embodiment of the present invention, which includes a multi-stage voltage multiplier circuit such as, for example, a six stage voltage multiplier circuit designed with capacitors  501 - 506  and n-channel MOSFET transistors  511 - 516 . In this example, NMOS transistors are used, however, other types of transistors such as PMOS, and different combinations of PMOS and NMOS transistors may also be used. 
         [0036]    Booster circuit  130   b  works on the same basic principles as booster circuit  130   a . Booster circuit  130   b  is similar to, but not exactly the same as, booster circuit  130   a . The difference with booster circuit  130   b  is that the output is more stabilized compared to booster circuit  130   b  since the turn-on voltage of the MOSFETs in booster circuit  130   b  is smaller than the turn-on voltage of the diodes included in booster circuit  130   a . Thus, each multiplier stage in booster circuit  130   b  “pumps” current with less voltage loss resulting in better circuit power efficiency and the device technology may use standard CMOS technology, without requiring schottky diodes as in booster circuit  130   a.    
         [0037]    The output signal of booster circuit  130  is a DC signal, which can be used to charge a battery or empower a circuit. However, this DC signal should be stabilized. Thus, a charger unit may include a voltage stabilizer, usually a voltage regulator circuit, and an input-output port to interface between system  100  and the low power device to be charged. Currently, the size of the prototype is 5 cm by 0.4021 cm, which may be further reduced for production. 
         [0038]    System  100  may include two different modes of operation in accordance with an embodiment of the present invention.  FIG. 6  is a simplified block diagram showing a method  600  for harvesting a radio frequency power  620  from a master wireless transmitter  640  in accordance with an embodiment of the present invention, by using a first mode to charge a slave device  660  with system  100  coupled to slave device  660 . Master wireless transmitter  640  may include a device with wireless communication capabilities such as a cell-phone, laptop, PC, or any other device with wireless communication capability such as a base-station, router, and the like. The packet may be transmitted either via Wi-Fi or Bluetooth. 
         [0039]    A packet is transmitted from master wireless transmitter  640  to system  100 . The packet may either be any file such as a photo, music, or the like type of file, from master wireless transmitter  640  or a specific file from a software designed for system  100 . The software provides a file for transmission at a predefined frequency of either 980 MHz or 2.4 GHz. The transmission duration of the file, which determines the amount of transferred power, can be selected by the user through the software interface. If an existing file is to be transmitted, its size determines the amount of the transmitted power. Slave device  660  may be a low power device with its own slave battery, such as a receiver phone, which charges by harvesting the energy of the transferred power packet received through system  100 . System  100  may or may not have embedded battery  180 . The longer the time of the connection, the higher the amount of the power that can be harvested by the slave device. The transmitting and receiving devices should be within a range of 1 meter from each other. After a certain time, the slave device charge reaches a point where it cannot be charged any further by system  100 . 
         [0040]    In the second mode of operation, the system  100  gathers energy from the electromagnetic signals existing in its surroundings and charges a rechargeable battery  180  embedded in system  100 . After rechargeable battery  180  is charged, system  100 , including battery  180 , is coupled to the slave device, which then can be charged from rechargeable battery  180  in system  100 . By storing the energy obtained from these signals in a small rechargeable battery embedded in the system, enough power will always be available for emergency cases where no master device is readily available. 
         [0041]    The RF signals existing in the environment can be either from a transmitter designed for system  100  or from the existing GSM, Wi-Fi, or the like signals in the air. As long as the existing signals have a minimum power of −35 dBm, they can be harvested by system  100 . This may sometimes give a user the freedom of being as far as 500 (or even more) meters from a GSM base station and still charge rechargeable battery  180  in system  100 . The limitation of this mode is that rechargeable battery  180  may not hold much power and may require frequent recharging, which may take extended time for recharging. 
         [0042]    Embodiments of the present invention provides a system and method for harvesting radio frequency power from a wireless transmitter. The embodiments of the present invention are not limited by the type of transistor, PMOS, NMOS or otherwise, used to boost the radio frequency power. The embodiments of the present invention are not limited by the number of voltage multiplier stages used to boost the radio frequency power. It will be apparent to those with skill in the art that modifications to the above methods and apparatuses may occur without deviating from the scope of the present invention. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims along with their full scope of equivalents.