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1. A New Coupling Insensitive Nonlinear Capacitive Resonant Wireless Power Transfer Circuit

   Ruiying Chai; Amir Mortazawi (January 2021, 2021 IEEE Wireless Power Transfer Conference (WPTC))

   This paper presents a nonlinear capacitive WPT system that automatically compensate for the coupling variation between the transmitter and receiver in a capacitive wireless power transfer (WPT) system with no active circuitry. The system is capable of minimizing the output power variation at a fixed operating frequency of13 MHz as the coupling distance varies. A constant output power is achieved over a wide range of coupling capacitance variation in comparison to the conventional capacitive wireless power transmission circuits. Such an approach is attractive for biomedical implants employing a capacitive WPT system. 

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2. Magnetoelectrics enables large power delivery to mm-sized wireless bioelectronics

   https://doi.org/10.1063/5.0156015  

   Kim, Wonjune; Tuppen, C Anne; Alrashdan, Fatima; Singer, Amanda; Weirnick, Rachel; Robinson, Jacob T (September 2023, Journal of Applied Physics)

   To maximize the capabilities of minimally invasive implantable bioelectronic devices, we must deliver large amounts of power to small implants; however, as devices are made smaller, it becomes more difficult to transfer large amounts of power without a wired connection. Indeed, recent work has explored creative wireless power transfer (WPT) approaches to maximize power density [the amount of power transferred divided by receiver footprint area (length × width)]. Here, we analyzed a model for WPT using magnetoelectric (ME) materials that convert an alternating magnetic field into an alternating voltage. With this model, we identify the parameters that impact WPT efficiency and optimize the power density. We find that improvements in adhesion between the laminated ME layers, clamping, and selection of material thicknesses lead to a power density of 3.1 mW/mm2, which is over four times larger than previously reported for mm-sized wireless bioelectronic implants at a depth of 1 cm or more in tissue. This improved power density allows us to deliver 31 and 56 mW to 10 and 27-mm2 ME receivers, respectively. This total power delivery is over five times larger than similarly sized bioelectronic devices powered by radiofrequency electromagnetic waves, inductive coupling, ultrasound, light, capacitive coupling, or previously reported magnetoelectrics. This increased power density opens the door to more power-intensive bioelectronic applications that have previously been inaccessible using mm-sized battery-free devices. 

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3. Dual-Loop Frequency Synchronization and Load Regulation using a Discrete Time Model for a 7-Level Switched Capacitor WPT Rectifier

   https://doi.org/10.1109/COMPEL49091.2020.9265670  

   Cochran, Spencer; Costinett, Daniel (November 2020, 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL))

   null (Ed.)

   In wireless power transfer (WPT) applications, the multi-level switched capacitor topology achieves significant advantages in terms of efficiency, system loading, THD, and output regulation. The topology requires dual-loop control in order to harness these benefits. First, a small signal discrete time model for the 7-level rectifier WPT system is developed. Then, a control loop is designed that enables the rectifier to regulate DC load voltage by varying its modulation scheme. Next, the WPT carrier frequency is sensed and a phase-locked loop is used in combination with the small signal power stage model to design a closed-loop controller that synchronizes frequency and regulates control phase through adjustments of the switching period. Finally, cross-coupling interactions between the two control loops are modeled, and stable dual-loop operation is shown. 

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4. A Coupling Factor Independent Wireless Power Transfer System Employing Two Nonlinear Circuits

   Ruiying Chai, Amir Mortazawi (June 2020, IEEE MTTS International Microwave Symposium digest)

   null (Ed.)

   Conventional linear resonant wireless power trnnsfer (WPT) systems suffe1· from a significant pe1•formance degrndation as the coupling factor between the translnit and receive coils varies. In this paper, the performance of a new WPT circuit that takes the advantage of nonlinear resonant circuit is investigated. It employs passive nonlinear resonators in both the trnnslnitter and receiver sides to regulate the output power without using any active or control circuitry, frequency tuning or complicated coil configurntions. A 60 W nonlinear WPT prototype circuit working at 1.5 MHz is designed, fab1icated and compared with a silnilal'ly designed linear \VPT circuit. The nonlinem· \VPT circuit is capable of maintaining almost a constant output power while the distance between the coils changes from 6 cm to 15 cm, a significant performance improvement as compared to the linear WPT circuit tested under the same conditions. 

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5. Multilevel Switched-Capacitor AC-DC Step-Down Rectifier for Wireless Charging with Reduced Conduction Loss and Harmonic Content

   https://doi.org/10.1109/TPEL.2022.3141607  

   Cochran, Spencer; Zhao, Chongwen; Costinett, Daniel (January 2022, IEEE Transactions on Power Electronics)

   In this paper, a wireless charging architecture employing a multilevel switched-capacitor (MSC) AC-DC rectifier is investigated. The proposed MSC rectifier features a multilevel design which is scalable to accommodate different power ratings and load ranges. The topology showcases advantages for wireless power transfer (WPT) systems in terms of compactness, efficiency, impedance tunability, and harmonic attenuation. The single-stage active topology is capable of varying its low-distortion staircase input voltage to tune the wireless power transfer system for high system-wide efficiency. A 7-level, 20 W prototype is used to verify the WPT loading and loss analysis. The prototype operates at 150 kHz with up to 3:1 step-down conversion ratio to an output voltage of 5.0 V. The experimental peak DC-to-DC efficiency is 93.8% and the rectifier peak efficiency is 98.3%. The rectifier demonstrates low waveform distortion and high efficiency across many WPT loading conditions, solidifying its place as a strong candidate for wireless power applications. 

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