Circuit-Level Modeling and Simulation of Wireless Sensing and Energy Harvesting With Hybrid Magnetoelectric Antennas for Implantable Neural Devices

A Miniaturized, Low-Frequency Magnetoelectric Wireless Power Transfer System for Powering Biomedical Implants

This work experimentally demonstrates the operation of a miniaturized magnetoelectric (ME) wireless power transfer (WPT) system by incorporating a ME transducer and a suitable interface power management circuit (PMC) for potentially powering implantable medical devices (IMD) wirelessly. A ME heterostructure is micromachined to obtain desired device dimensions of 3.5 × 5 mm 2 and to restrict the operating frequency at a clinically approved frequency of 50 kHz. The proposed work also aims to address the trade-off between the device miniaturization, power attenuation and limiting the specific absorption rate (SAR) in the human tissue. By limiting the operating frequency to 50 kHz, the SAR is reduced to less than 1 μW/kg. The fabricated device is characterized with low-intensity AC magnetic field up to 40 μT without using any DC bias, resulting in 0.4 V output voltage and 6.6 μW power across 8 k Ω load. Alignment misorientation between the Tx and Rx is studied for in-plane and out-of-plane angular rotations to confirm the device's reliability against angular misalignment. By eliminating the bulky biasing magnets, the proposed device achieves a significant size reduction compared to the previously reported works. In addition, a self-powered interface PMC is incorporated with the ME system. The PMC generates 3.5 V regulated DC voltage from the input AC voltage range 0.7 V to 3.3 V. The PMC is fabricated on a 2-layered PCB and the over all ME WPT system consumes 12 × 12 mm 2 area. The overall PMC has intrinsic current consumption less than 550 nA with peak power conversion efficiency higher than 85 %. The in vitro cytotoxicity analysis in the human hepatic cell line WRL-68 confirmed the biocompatibility of the Parylene-C encapsulated ME device for up to 7 days, suggesting its potential use in implantable electronic devices for biomedical and clinical applications.

Array Study of VLF Thin-Film Magnetoelectric Antenna with a Microbridge Structure

Recently, magnetoelectric (ME) antennas have become a hot topic in the field of antenna miniaturization in the very-low-frequency (VLF) band because their size can be reduced to one-ten-thousandth of the size of conventional electric antennas. However, they still suffer from narrow transmission/reception bandwidth and weak radiation intensity. To address these issues, VLF thin-film ME antennas with a microbridge structure are designed, and the method of array connection is used. Test results show that the detection limit of the ME antenna unit is 636 pT/√Hz at 23 kHz and the radiant magnetic field intensity at 0.12 m is 0.87 nT (input power of 10 mW). By series-connecting three ME antenna units with the same resonance frequency, the output response has been increased to 1.72 times and the EM wave radiation intensity is increased to 1.9 times compared to a single unit. By parallel-connecting two ME antenna units with different resonance frequencies, the output response bandwidth has been expanded to 1.56 times compared to a single unit, and the signal radiation bandwidth has been expanded to 1.47 times. This work provides a valuable reference for the future larger-scale arraying of ME antennas.