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2.45 GHz Low Power Rectenna Design for Wireless Sensor & RFID Applications

2.45 GHz Low Power Rectenna Design for Wireless Sensor & RFID Applications. Ph.D. Candidate: Yunlei Li Advisor: Jin Liu 9/10/03. Outline. Introduction Rectifier Antenna System Conclusion. Radio Frequency Spectrum. Electromagnetic Power Transmission.

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2.45 GHz Low Power Rectenna Design for Wireless Sensor & RFID Applications

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  1. 2.45 GHz Low Power Rectenna Design for Wireless Sensor & RFID Applications Ph.D. Candidate: Yunlei Li Advisor: Jin Liu 9/10/03

  2. Outline • Introduction • Rectifier • Antenna • System • Conclusion

  3. Radio Frequency Spectrum

  4. Electromagnetic Power Transmission • RF Power launched through electromagnetic waves by an antenna = c/f • Near field:the area from the antenna to the point where the electromagnetic field forms at a distance of D </2 • Far field: The area after the point at which the electromagnetic wave has fully formed and separated from the antenna at a distance of D </2

  5. RF Power Transmission:near field • Passive RFID tag • Inductive Coupling (transformer effect) • Energy in magnetic field strength • Coil antennae • Reader-> transponder Power & data • Transponder-> reader Data back by load modulation

  6. RF Power Transmission:far field • Friis Transmission Equation Pr=PtGtGr2/(4R)2 Pr: Receiveded power Pt:Transimitted power Gt:Transimitter antenna gain Gr: Receiver antenna gain R: Transmission distance Calculated received power Assuming Gt=20dB, Gr=10dB

  7. Rectenna element= Rectifier+Antenna Frequency reflecting plane Dipole or patch antenna Microwave low pass filter Schottky barrier diode Low pass filter passing DC Load resistor Applications Wireless power transmission between space and earth high power Rectenna array Wireless sensor (GAP4S) & long range RFID Low power Rectenna used to convert RF power to DC to charge a battery or big Cap Performance Goal-high efficiency Overall efficiency o=DC output power/incident RF power >85% (high power & optimized load) Conversion efficiency c=DC output power/(incident RF power-reflected RF power) >90% (high power & optimized load) Rectenna: RF to DC Conversion

  8. Single diode Voltage doubler Rectifier/RF Detector

  9. Equivalent circuit of a Schottky diode Rj=0.026/IT, IT=Is+Ib Is=diode saturation current, a function of barrier height Ib=external applied bias current Cj=diode junction capacitance Lp, Cp=Parasitic inductor & Cap Rs=Parasitic resistance representing losses Voltage sensitivity of a diode in mV/W 2=0.52/(IT(1+2Cj2RsRj)(1+Rj/RL)) N-type Low Rs External bias (High barrier, low Is) High flicker noise P-type High Rs Zero bias (low barrier, high Is Low flicker noise Schottky Diode

  10. Low pass filter for better efficiency

  11. Microstrip Patch Antennas

  12. Radiation performance of single layer patch

  13. Microstrip Patch Array

  14. Hybrid-Ring Coupler • Hybrid ring coupler to split powers from the input to two outputs • Power split ratio • Note: there is an upper limit on line impedance of about 150  for many microstrip transmission lines

  15. Gain of Microstrip Patch Array • The Maximum gain of a microstrip phase 2nx2m array GdB=10log(4A/2)-(D1+D2)/2 A=D1*D2 • D1=effective width of the uniformly spaced array • D2=effective height of the uniformly spaced array • =attenuation in dB per unit length of a 50 ohm transmission line being used in the monolithic feed [A typical value of  is 0.4dB/ft for a 50 ohm microstrip line on 1/32th-in (0.794mm) Teflon fiberglass at 2.2 GHz

  16. System Design • Monolithic Integration of rectenna (antenna array with rectifier) with RF detector • Impedance matching of patch antenna (or antenna array) to the input of the rectifier using corporate feed network • Ring coupler to split power from antenna to rectenna and demodulator separately to maintain 8dB power split ratio • Use single diode rectifier to maximize efficiency of the Rectenna • Use voltage doubler detector to maximize its voltage for better demodulation • Ring coupler isolate the Rectenna & Detector and allow separate impedance matching network design

  17. Conclusion • A 2.4GHz low power Rectenna & detector will be designed and simulated with ADS • The system will be monolithically integrated onto a single circuit board • A high gain patch antenna array boosts the power level at the input of the Rectenna for better power conversion efficiency • A hybrid ring coupler is used to divide the power between Rectenna and detector • The system implements a key RF front end for GAP4S wireless sensor system

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