Design and Characterization of Miniaturized Magnetoelectric Antennas for Efficient Wireless Power Transfer in Implantable Medical Devices

Miniaturized, multi-functional implantable medical devices provide continuous health monitoring but encounter significant power supply challenges. Wiring is impractical due to infection risks and bulk, while batteries have limited lifespans and potential health risks if they leak. Therefore, an optimal power solution must ensure tissue safety, deliver sufficient energy, and minimize size to make the device less invasive. Wireless power transfer methods, including radio frequency, inductive coupling, ultrasound, and capacitive coupling, offer potential solutions but face hurdles such as receiver size constraints, sensitivity to misalignment, transmission loss, and safe power delivery through biological tissues. Magnetoelectric (ME) technology is emerging as a powerful solution for wirelessly powering devices deep within the body offering several key advantages, including high efficiency in a compact form factor and excellent performance against misalignment. ME antennas utilize the combined principles of piezoelectricity and magnetostriction, where incoming electromagnetic waves are converted into RF voltage through an energy transduction process. ME antennas break the conventional link between receiver size and wavelength, allowing for significant size reduction and efficient performance even in weak magnetic fields. In this thesis, the design, development, and optimization of a wireless power transfer system utilizing a magnetoelectric antenna are thoroughly explored. The research begins with an in-depth investigation to identify the most suitable materials for the ME antenna, followed by a detailed analysis of the optimal antenna configuration. This is achieved through a comprehensive approach that integrates Finite Element Analysis, analytical modeling and experimental validation ensuring a robust characterization of the system’s performance. The study further explores the impact of miniaturization on the output voltage generated by magnetoelectric (ME) antennas. Three different antenna sizes were tested: 27.6 x 8.15 x 0.085 mm³, 100 x 100 x 16 μm³ and 10 x 10 x 16 μm³ yielding output powers of 32.5 μW , 0.158 nW, and 1.52 pW, respectively. These results emphasize the trade-off between antenna efficiency and size reduction, however, while the output voltage decreases, it does not scale proportionally to the reduction in size, demonstrating the ME antennas’ effective performance in miniaturization. Nonetheless, as the antenna size decreases, the resonance frequency increases from 52 kHz to 18 MHz and 182 MHz, respectively. thus enhancing tissue absorption and lowering performances. To effectively excite the optimized ME antenna and ensure efficient power transfer with comprehensive coverage of the human head, an Birdcage Coil has been designed and tuned to resonate at the ME antenna’s operational frequency. Subsequently, a comprehensive safety assessment and in-body path loss analysis were conducted to evaluate the impact of implanting the ME antenna within the gray matter. Results indicate that the instantaneous SAR complies with regulatory limits for short-duration exposure, confirming safe operation under these conditions. The analysis also shows that when tissue attenuation is taken into account, the output power decreases by nearly five order of magnitude compared to the case where tissue effects are disregarded. These combined efforts highlight the potential of ME antennas as a breakthrough solution for wireless power transfer in miniaturized biomedical implants.