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Energy harvesting circuits and associated methods are provided that employ multiple antennas to optimize the amount of energy that is harvested while at the same time making efficient use of tag space. In some embodiments, matching networks are chosen in a manner that optimizes the DC energy that is

Energy harvesting circuits and associated methods are provided that employ multiple antennas to optimize the amount of energy that is harvested while at the same time making efficient use of tag space. In some embodiments, matching networks are chosen in a manner that optimizes the DC energy that is created from the harvesting process. In other embodiments, phase shifts are introduced into the received signals to allow the signals to be more efficiently combined after they are rectified.

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What is claimed is: 1. An energy harvesting circuit, comprising: a plurality of antennas, each of said antennas being fixedly tuned to the same particular RF frequency range, each of said antennas being structured to receive an RF signal having said particular RF frequency range and output a respec

What is claimed is: 1. An energy harvesting circuit, comprising: a plurality of antennas, each of said antennas being fixedly tuned to the same particular RF frequency range, each of said antennas being structured to receive an RF signal having said particular RF frequency range and output a respective AC signal; a plurality of matching networks, each of said matching networks being operatively coupled to a respective one of said antennas and being structured to receive the AC signal output by said respective one of said antennas; and a plurality of voltage boosting and rectifying circuits, each of said voltage boosting and rectifying circuits being operatively coupled to a respective one of said matching networks and being structured to receive the AC signal received by the respective one of said matching networks and output a DC voltage signal by converting the received AC signal into the DC voltage signal; wherein the DC voltage signals output by the voltage boosting and rectifying circuits are summed together to create a combined DC voltage signal, and wherein an impedance of each of the matching networks is chosen in manner so as to maximize a voltage level of the DC voltage signal that is output by the associated one of the voltage boosting and rectifying circuits. 2. The energy harvesting circuit according to claim 1, wherein each of said voltage boosting and rectifying circuits is a charge pump. 3. The energy harvesting circuit according to claim 1, wherein each of said matching networks is an LC tank circuit. 4. The energy harvesting circuit according to claim 3, wherein an impedance of each of the matching networks is chosen in manner so as to maximize a voltage level of the DC voltage signal that is output by the associated one of the voltage boosting and rectifying circuits by, for each LC tank circuit of each of the matching networks: (i) trying a plurality of different inductance and capacitance value combinations for the LC tank circuit, (ii) measuring the voltage level of the DC voltage signal that is output by the associated one of the voltage boosting and rectifying circuits for each of the inductance and capacitance value combinations, and (iii) choosing one of the inductance and capacitance value combinations that produces a maximum voltage level of the DC voltage signal that is output by the associated one of the voltage boosting and rectifying circuits. 5. The energy harvesting circuit according to claim 1, wherein each of said antennas is a square spiral antenna having an outermost segment, a middle segment and an innermost segment, wherein a length of each outermost segment of is equal to about a quarter of the wavelength of the particular RF frequency or center frequency of the band of RF frequencies included in said particular RF frequency range, wherein a total length of each square spiral antenna is equal to about one half of said wavelength, and wherein the outermost segment of each of said antennas is operatively coupled to the associated one of said matching networks. 6. The energy harvesting circuit according to claim 5, wherein each square spiral antenna alone occupies a first spatial area, and wherein said antennas are provided in an antenna layout that occupies a second spatial area that is less than two times said first spatial area. 7. An energy harvesting method, comprising: providing a plurality of antennas, each of said antennas being fixedly tuned to the same particular RF frequency range; receiving a plurality of RF signals using said antennas, each of said RF signals having said particular RF frequency range; outputting from said antennas a plurality of AC signals in response to receiving said RF signals; converting each of the AC signals into a respective DC voltage signal after first passing each of the AC signals through a respective matching network having an impedance chosen in manner so as to maximize a voltage level of the respective DC voltage signal; and summing each of the respective DC voltage signals together to create a combined DC voltage signal. 8. An energy harvesting circuit, comprising: a plurality of antennas provided in an antenna plane, each of said antennas being tuned to the same particular RF frequency range, each of said antennas being structured to receive an RF signal having said particular RF frequency range and output a respective AC signal; a plurality of matching networks, each of said matching networks being operatively coupled to a respective one of said antennas and being structured to receive the AC signal output by said respective one of said antennas; and a plurality of voltage boosting and rectifying circuits, each of said voltage boosting and rectifying circuits being operatively coupled to a respective one of said matching networks and being structured to receive the AC signal received by the respective one of said matching networks and output a DC voltage signal by converting the received AC signal into the DC voltage signal; wherein the DC voltage signals output by the voltage boosting and rectifying circuits are summed together to create a combined DC voltage signal, and wherein an impedance of each of the matching networks is chosen so as to cause a voltage level of the combined DC voltage signal to have a minimum deviation as a function of angle of rotation as said antenna plane is rotated about a first axis. 9. The energy harvesting circuit according to claim 8, wherein said first axis is a line taken through a center of a transmitting antenna of a source of said RF signal having said particular RF frequency range. 10. The energy harvesting circuit according to claim 8, wherein each of said voltage boosting and rectifying circuits is a charge pump. 11. The energy harvesting circuit according to claim 8, wherein each of said matching networks is an LC tank circuit. 12. The energy harvesting circuit according to claim 11, wherein an impedance of each of the matching networks is chosen so as to cause a voltage level of the combined DC voltage signal to have a minimum deviation as a function of angle of rotation as said antenna plane is rotated about a first axis by: (i) incrementally rotating said antenna plane through a plurality of angle increments, (ii) trying a plurality of different inductance and capacitance value combinations for each LC tank circuit of each of the matching networks at each of said angle increments, (iii) measuring the combined DC voltage signal for each of the inductance and capacitance value combinations at each of said angle increments, (iv) determining which one of the inductance and capacitance value combinations produces a minimum deviation in said measured combined DC voltage signals as a function of each of said angle increments; (v) choosing for each said LC tank circuit the one of the inductance and capacitance value combinations that produces the minimum deviation. 13. The energy harvesting circuit according to claim 8, wherein each of said antennas is a square spiral antenna having an outermost segment, a middle segment and an innermost segment, wherein a length of each outermost segment of is equal to about a quarter of the wavelength of the particular RF frequency or center frequency of the band of RF frequencies included in said particular RF frequency range, wherein a total length of each square spiral antenna is equal to about one half of said wavelength, and wherein the outermost segment of each of said antennas is operatively coupled to the associated one of said matching networks. 14. The energy harvesting circuit according to claim 13, wherein each square spiral antenna alone occupies a first spatial area, and wherein said antennas are provided in an antenna layout that occupies a second spatial area that is less than two times said first spatial area. 15. An energy harvesting method, comprising: providing a plurality of antennas in an antenna plane, each of said antennas being tuned to the same particular RF frequency range; receiving a plurality of RF signals using said antennas, each of said RF signals having said particular RF frequency range; outputting from said antennas a plurality of AC signals in response to receiving said RF signals; converting each of the AC signals into a respective DC voltage signal; and summing each of the respective DC voltage signals together to create a combined DC voltage signal; wherein said converting step is performed after first passing each of the AC signals through a respective matching network having an impedance chosen so as to cause a voltage level of the combined DC voltage signal to have a minimum deviation as a function of angle of rotation as said antenna plane is rotated about a first axis. 16. The energy harvesting method according to claim 15, wherein said first axis is a line taken through a center of a transmitting antenna of a source of each said RF signal having said particular RF frequency range. 17. An energy harvesting circuit, comprising: a plurality of antennas provided in an antenna plane, each of said antennas being tuned to the same particular RF frequency range, each of said antennas being structured to receive an RF signal having said particular RF frequency range and output a respective AC signal; a plurality of matching networks, each of said matching networks being operatively coupled to a respective one of said antennas and being structured to receive the AC signal output by said respective one of said antennas; and a plurality of voltage boosting and rectifying circuits, each of said voltage boosting and rectifying circuits being operatively coupled to a respective one of said matching networks and being structured to receive the AC signal received by the respective one of said matching networks and output a DC voltage signal by converting the received AC signal into the DC voltage signal; wherein the DC voltage signals output by the voltage boosting and rectifying circuits are summed together to create a combined DC voltage signal, and wherein an impedance of each of the matching networks is chosen so as to cause a voltage level of the combined DC voltage signal to have at least a predetermined minimum value as said antenna plane is rotated about a first axis. 18. The energy harvesting circuit according to claim 17, wherein said first axis is a line taken through a center of a transmitting antenna of a source of said RF signal having said particular RF frequency range. 19. The energy harvesting circuit according to claim 17, wherein each of said voltage boosting and rectifying circuits is a charge pump. 20. The energy harvesting circuit according to claim 17, wherein each of said matching networks is an LC tank circuit. 21. The energy harvesting circuit according to claim 20, wherein an impedance of each of the matching networks is chosen so as to cause a voltage level of the combined DC voltage signal to have at least a predetermined minimum value as said antenna plane is rotated about a first axis by: (i) incrementally rotating said antenna plane through a plurality of angle increments, (ii) trying a plurality of different inductance and capacitance value combinations for each LC tank circuit of each of the matching networks at each of said angle increments, (iii) measuring the combined DC voltage signal for each of the inductance and capacitance value combinations at each of said angle increments, (iv) determining which one of the inductance and capacitance value combinations produces at least said predetermined minimum value at each of said angle increments; (v) choosing for each said LC tank circuit the one of the inductance and capacitance value combinations that produces the at least said predetermined minimum value. 22. The energy harvesting circuit according to claim 17, wherein each of said antennas is a square spiral antenna having an outermost segment, a middle segment and an innermost segment, wherein a length of each outermost segment of is equal to about a quarter of the wavelength of the particular RF frequency or center frequency of the band of RF frequencies included in said particular RF frequency range, wherein a total length of each square spiral antenna is equal to about one half of said wavelength, and wherein the outermost segment of each of said antennas is operatively coupled to the associated one of said matching networks. 23. The energy harvesting circuit according to claim 22, wherein each square spiral antenna alone occupies a first spatial area, and wherein said antennas are provided in an antenna layout that occupies a second spatial area that is less than two times said first spatial area. 24. An energy harvesting method, comprising: providing a plurality of antennas in an antenna plane, each of said antennas being tuned to the same particular RF frequency range; receiving a plurality of RF signals using said antennas, each of said RF signals having said particular RF frequency range; outputting from said antennas a plurality of AC signals in response to receiving said RF signals; converting each of the AC signals into a respective DC voltage signal; and summing each of the respective DC voltage signals together to create a combined DC voltage signal; wherein said converting step is performed after first passing each of the AC signals through a respective matching network having an impedance chosen so as to cause a voltage level of the combined DC voltage signal to have at least a predetermined minimum value as said antenna plane is rotated about a first axis. 25. The energy harvesting method according to claim 24, wherein said first axis is a line taken through a center of a transmitting antenna of a source of each said RF signal having said particular RF frequency range. 26. An energy harvesting circuit, comprising: a plurality of antennas provided in an antenna plane, each of said antennas being tuned to the same particular RF frequency range, each of said antennas being structured to receive an RF signal having said particular RF frequency range and output a respective AC signal; a plurality of matching networks, each of said matching networks being operatively coupled to a respective one of said antennas and being structured to receive the AC signal output by said respective one of said antennas; and a plurality of voltage boosting and rectifying circuits, each of said voltage boosting and rectifying circuits being operatively coupled to a respective one of said matching networks and being structured to receive the AC signal received by the respective one of said matching networks and output a DC voltage signal by converting the received AC signal into the DC voltage signal; wherein the DC voltage signals output by the voltage boosting and rectifying circuits are summed together to create a combined DC voltage signal, and wherein an impedance of each of the matching networks is chosen by: (i) incrementally rotating said antenna plane through a plurality of angle increments about a first axis, (ii) trying a plurality of different inductance and capacitance value combinations for each LC tank circuit of each of the matching networks at each of said angle increments, (iii) measuring the combined DC voltage signal for each of the inductance and capacitance value combinations at each of said angle increments, (iv) determining which one of the inductance and capacitance value combinations produces a maximum voltage level for said measured combined DC voltage signals at any one of said angle increments; (v) choosing for each said LC tank circuit the one of the inductance and capacitance value combinations that produces the maximum voltage level. 27. An energy harvesting circuit, comprising: a plurality of antennas, each of said antennas being tuned to the same particular RF frequency range, each of said antennas being structured to receive an RF signal having said particular RF frequency range and output a respective AC signal; and phase shifting and rectifying circuitry operatively coupled to said antennas, said phase shifting and rectifying circuitry being structured to: (i) receive each said respective AC signal, (ii) create a plurality of out of phase AC signals by causing each said respective AC signal to be out of phase with one another, and (iii) convert each of said out of phase AC signals into a respective DC voltage signal; wherein the DC voltage signals are summed together to create a combined DC voltage signal. 28. The energy harvesting circuit according to claim 27, wherein said phase shifting and rectifying circuitry comprises: (i) a plurality of phase shifting circuits, each of said phase shifting circuits being operatively coupled to a respective one of said antennas and creating a respective one of said out of phase AC signals, and (ii) a plurality of voltage boosting and rectifying circuits, each of said voltage boosting and rectifying circuits being operatively coupled to a respective one of said phase shifting circuits and converting a respective one of said of said out of phase AC signals into the respective DC voltage signal. 29. The energy harvesting circuit according to claim 28, wherein each of said voltage boosting and rectifying circuits is a charge pump. 30. The energy harvesting circuit according to claim 27, wherein a phase shift between each of said out of phase AC signals and each one of said out of phase AC signals that is adjacent in phase thereto is equal to 360 degrees divided by a total number of said antennas. 31. The energy harvesting circuit according to claim 27, wherein said phase shifting and rectifying circuitry includes a Cockroft-Walton multiplier. 32. An energy harvesting method, comprising: providing a plurality of antennas, each of said antennas being tuned to the same particular RF frequency range; receiving a plurality of RF signals using said antennas, each of said RF signals having said particular RF frequency range; outputting from said antennas a plurality of AC signals in response to receiving said RF signals; creating a plurality of out of phase AC signals by causing each of said AC signals to be out of phase with one another; converting each of said out of phase AC signals into a respective DC voltage signal; and summing each of the respective DC voltage signals together to create a combined DC voltage signal.