Research On High-Performance Rectifier And Rectenna With Harmonic Feedback In Wireless Power Transfer

With an advance of wireless power transfer(WPT),a long-term,high-efficiency and stable operation of commercial unmanned aerial vehicle(UAV)and implantable medical device(IMD)can be effectively ensured,which has an increasingly important scientific and engineering value for the battery life improvement and maintenance.In a WPT system,a rectenna(rectifier and antenna)operates as a key circuit to efficiently convert the radio-frequency(RF)incidence into direction current(dc)to meet power consumptions of successive electronics,e.g.,sensors.However,a conventional charge pump rectifier is incapable of achieving a high RF-to-dc power conversion efficiency(PCE)and a high output dc voltage simultaneously when the incident power density is ultralow.In addition,an inherent correlation between the threshold and breakdown voltages of commercial Schottky diodes constrains their widespread in rectifiers with wide dynamic ranges.Meanwhile,a WPT link efficiency between the base station and the terminal is practically susceptible to the antenna maximum radiation direction and polarization misalignments.Thus,it is critical to explore and investigate an effective and harmless feedback to assist the rectenna alignments of maximum radiation direction and polarization for both UAV and IMD applications.This dissertation revolves around the WPT and focuses on two aspects: a)how to design a rectifier with an enhanced PCE and wide dynamic ranges;b)how to align the maximum radiation direction and polarization.Firstly,a differential charge pump rectifier and a scalable non-breakdown rectifying diode are proposed and designed to satisfy the technical requirements of high PCEs and wide dynamic ranges,respectively.Secondly,an uneven-to-even power distribution scheme and harmonic-based rectenna alignment method are proposed and validated,which effectively solves the maximum radiation direction and polarization misalignments between the transmitting(TX)and receiving(RX)antennas in a WPT system.Moreover,to reduce the transmission loss of harmonic feedbacks in the human tissue,an intermodulation-assisted IMD rectenna alignment method is innovatively proposed and validated.Hence,by embedding a nearfield resonant inductive coupling technique into the far-field WPT,harmless power transmission and intermodulation feedback links in the human tissue are established.The main contributions of this dissertation are summarized as below:1.Two key techniques(high PCE and wide dynamic range)of a rectifier in a WPT system are investigated.To accomplish both high PCEs and wide dynamic ranges,a differential charge pump rectifier and a scalable non-breakdown rectifying diode are proposed.Under differential incidences,a modified Greinacher charge pump with a symmetrical circuit structure ensures an RF virtual ground,which can be simplified as the differential charge pump rectifier.Hence,its RF-to-dc PCEs can be significantly enhanced while maintaining sufficiently high outputs for the successive dc-to-dc power converter.Based on the commercial Schottky diode,high electron mobility transistors(HEMTs)are introduced to extend the reverse breakdown voltage,which is suitable for the rectifier design with wide dynamic ranges.2.An uneven-to-even power distribution scheme is explored to solve the antenna polarization misalignment.A hybrid coupler is innovatively employed between a dual linearly-polarized(DLP)antenna and a modified Greinacher charge pump.Therefore,two uneven power distributions from the DLP antenna can be equalized under different polarization misaligned angles,satisfying input power requirements of high-efficiency modified Greinacher charge pump rectifier.3.A second harmonic-based rectenna alignment method is explored to solve both antenna maximum radiation direction and polarization misalignments.Two harmonic generation mechanisms are studied: 1).additional nonlinear product during RF-to-dc rectification;2).frequency doubling product from mismatched reflection.According to the above harmonic generation mechanisms,different couplers(hybrid or ring coupler)and harmonic antennas can be introduced to establish harmonic feedback links for the second harmonic-based rectenna alignment.4.A third harmonic-based rectenna alignment method is explored to solve both antenna maximum radiation direction and polarization misalignments,while reserving second harmonics for recycling to enhance the RF-to-dc PCE.According to different harmonic feedback types,different couplers(hybrid or ring coupler)can be employed to multiplex or isolate the fundamental and third-harmonic antennas for the harmonic feedbacks between the base station and WPT terminal.Therefore,the third harmonicbased rectenna alignment is realized.5.An intermodulation-based IMD rectenna alignment method is investigated to solve both antenna maximum radiation direction and polarization misalignments,while reducing the human tissue safety risk.Two-tone waveform can help to enhance the RFto-dc PCE,and generate the intermodulation.Compared to high-frequency harmonics from a continuous waveform excited rectifier,the intermodulation propagates in the human tissue with superiorly low loss.Through near-field resonant inductive coupling,an intermodulation feedback link between the base station and the IMD terminal can be established.Hence,the intermodulation-based IMD rectenna alignment is enabled.