A Miniaturized, Low-Frequency Magnetoelectric Wireless Power Transfer System for Powering Biomedical Implants
Dibyajyoti Mukherjee, Simran Kaur Rainu, Neetu Singh, Dhiman Mallick
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> W/kg. The fabricated device is characterized with low-intensity AC magnetic field up to 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> T without using any DC bias, resulting in 0.4 V output voltage and 6.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> W power across 8 k <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> area. The overall PMC has intrinsic current consumption less than 550 nA with peak power conversion efficiency higher than 85 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$in$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$vitro$</tex-math></inline-formula> 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.