Effect of Demagnetizing Fields and Encapsulation on Wireless Magnetoelectric Output for Medical Devices

This work comprehensively analyses the dependency of voltage transfer gain and magnetoelectric (ME) output voltage coefficient on the encapsulation and geometry of ME laminates. By modulating the internal demagnetizing fields through geometric adjustments, the study demonstrates the capability to effectively tune both the piezoelectric voltage output and the required magnetic bias field. The study systematically investigates the experimental and analytical influence of demagnetizing fields and encapsulation conditions on the ME laminate's voltage output performance. To validate practical applicability, an energy harvesting circuit designed specifically for wearable coil excitation is developed and tested. Measurements of magnetoelectric voltage coefficients are carried out under various conditions—without damping, with encapsulation, and following implantation inside lamb brain tissue—to isolate and quantify their respective impacts on resonance frequency and voltage output. Moreover, this work evaluates the influence of device surface area and internal demagnetising fields on the necessary bias magnetic field, providing crucial insights for optimizing the design towards device miniaturization, that has not been previously investigated. Finally, the harvested energy is successfully rectified to drive a transcranial magnetic stimulation coil, modulated by the internal demagnetising field, and simulations conducted <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in silico</i> using a quasi-static human phantom head model to underscore the viability and effectiveness of ME further laminates for advanced wearable wireless power transfer technologies.