This letter proposes a midfield wireless power transfer system using a bipolar spiral-shape transmitter (BPSP-Tx) for cardiac implants application. Optimal current distribution is built on BPSP-Tx surface following spiral structure to generate a focused field inside human tissue and adapt the implantable receiver (Rx) misalignments. Source performance has been verified by implantable hooked-shape Rx (HKSD-Rx) that separated at a distance of 45 mm from Tx. Measurements are conducted in minced pork for validation. Experimental results show that the transmission coefficient can achieve -20.48 dB at a distance of 45 mm and -22.15 at 60 mm. Furthermore, the Rx misalignment is verified by output power level, which shows that the proposed system can maintain high performance on a rotation range of Rx from -90 ^° to 90 ^° . Finally, the human safety regulations are verified to present a low specific absorption rate, which demonstrates the potential for cardiac implants.

This letter presents a dual-band transmitter (DB-Tx) for wireless power transfer (WPT) to biomedical implants. The DB-Tx operates at $\rm{1.7}~GHz$ (LF-band) and $\rm{2.1}~GHz$ (HF-band) to power implantable devices in deep and shallow implantation, respectively. A bipolar concentric loop (BCL) radiating plane is employed to obtain field-focusing characteristics at dual frequencies, and hence enhance the power transfer efficiency (PTE). Furthermore, a wide-band implantable receiver (Rx) is implemented to verify DB-Tx's performance. Experimental results show that, by utilizing the DB-Tx, the transmission range can be extended three times in HF-band and 30% in LF-band, compared to the Tx operating at a single frequency band. The Rx can receive power with the PTE of $-14.7~dB$ and $-23~dB$ at $\rm{10}~mm$ and $\rm{40}~mm$ implantation depth, respectively.

This letter proposes a compact transmitter (Tx) for radiative nearfield wireless power transfer (WPT) to deep-implanted biomedical applications. A multiple-loop radiating plane and slotted-ring excitation ring structure are analyzed to generate a strong focused field inside the human tissue without using any controllable circuit. Meanwhile, an impedance matching network (IMN) is implemented on the Tx side to obtain the antenna operation and enhance the PTE at 1.9 GHz. Furthermore, a miniaturized receiver (Rx) is employed to verify the proposed Tx's performance. Experimental results show that our proposed WPT can supply power in a distance of up to $0.127\lambda _{0}$ with a PTE of -20.12 dB. Finally, our proposed WPT system is compared to other works in nearfield WPT to show our high PTE and compact antenna's dimensions.

In recent years, the requirement for a compact wireless power transfer (WPT) system that can supply power to multiple devices in various practical usage scenarios has been attracted many researchers. The receiver (Rx) misalignment problem is contributory to the power transfer efficiency (PTE) degradation. Moreover, in a multiple-output WPT system, the overall system efficiency is also affected by cross-coupling between receivers. This paper proposes a dual-band free-positioning transmitting coil (FPDB-Tx) for multiple-receiver WPT. A three-dimensional Tx structure is modeled by investigating the current direction on each coil loop to adapt the Rx angular and axial misalignment. The Tx configuration is designed following a wireless charging box concept, where multiple Rx devices can receive energy freely without a null efficiency point. The mutual inductance is examined by a mathematical method in various Rx orientations to verify the free-positioning characteristic. Furthermore, an equivalent circuit model of the WPT system is theoretically analyzed to obtain dual operating frequency bands and then maximized the PTE. The experimental results show that the proposed WPT system achieves a stable PTE in various Rx positions. Especially, the WPT system has a maximum PTE of 97.27% and 91% at 6.78 MHz and 13.56MHz, respectively.

This paper presents an anti-symmetric wing transmitter (ASW-Tx) for angular misalignment insensitive WPT to biomedical implants. Symmetrical field distribution on two orthogonal planes of Oxz and Oyz are analyzed theoretically to obtain stable power transfer efficiency (PTE) by rotating Rx around the Oz axis. Moreover, toroidal magnetic fluxes are generated by ASW to adapt with different Rx’s tilted angles on Ox and Oy axes. An impedance matching network (IMN) is proposed and implemented to match ASW-Tx’s impedance to source impedance. An implantable Rx is employed to verify the ASW-Tx’s performance. Experimental measurements are carried out with selected Rx’s tilted angles (vary from 0° to 90° around Ox , Oy , and Oz axis) to validate the effectiveness of proposed ASW-Tx’s. Verification results show that a stable efficiency variation was achieved with a maximum fluctuation of 4 dB by rotating Rx tilted angles. Moreover, the ASW-Tx can supply power effectively with a transmission efficiency of up to -18.4 dB to an implantation depth of 15 mm .

In this letter, a wide dynamic-range rectifier is proposed to match with three individual antennas for wireless power transfer at 433 MHz. Based on arbitrary impedance matching techniques in radio frequency identification (RFID), this rectifier is designed to match with impedance of three receiving antennas (Rx). As a result, different input power ranges are obtained when cyan the proposed rectifier is integrated at each receiver. Furthermore, size of each design is reduced as a cause of elimination of standard impedance at both antenna and rectifier. The fabricated rectifier and the compact rectenna size are 7.5 x 7.2 mm² and 18.9 x 16.4 mm², respectively. Our proposed rectifier has the measured RF-to-dc conversion efficiency above 50% when the input power spans from -8 dBm (0.158 mW) up to 14 dBm (25.12 mW), and the peak of measured rectifier efficiency is 71.6% at 5 dBm (3.16 mW).