Implantable bioelectronics hold immense potential in transforming clinical therapies by enabling precise targeting of specific regions within the neural system, brain, and organs. To meet the demands for enhanced safety, simplified surgical procedures, minimal disruption to normal behaviors, and long-term operation, it is crucial for these bioelectronic implants to be wireless, battery-free, and highly miniaturized on a millimeter scale. Furthermore, these bio-implants should exhibit robust and efficient operation and deliver advanced bio-functionalities with utmost precision to ensure safe and effective therapies. Despite significant advancements in the development of millimeter-scale wireless battery-free bio-implants, several critical challenges remain. These challenges include establishing reliable, safe, and efficient wireless power transfer mechanisms, enabling bi-directional communication with high efficiency and bandwidth, integrating the implants into distributed wireless networks, and realizing effective and advanced biomedical functionalities.

To address the challenges and drive advancements in the field of implantable bioelectronics, my research encompassed multidisciplinary studies integrating advanced integrated circuit (IC) design, hardware platform development, and exploration of magnetoelectric (ME) wireless technologies. This paper presents three key components of my research in this domain.

First, this thesis presents wireless neural implants at the millimeter scale that exploit ME power and data transfer. The study demonstrates the superior advantages of the emerging magnetoelectric power transfer technique for millimeter-scale bio-implants, including high efficiency, robustness against misalignment, and low tissue absorption. The magnetoelectrically powered and programmable implants demonstrate reliable operation within the body, providing fully customizable stimulation. The effectiveness and significant advancements of these implants were extensively validated through successful minimally invasive endovascular stimulation of peripheral nerves in pigs.

The second focus is the development of low-power ME backscatter communication for millimetric bio-implants. It introduces a first-of-its-kind ME backscatter technology and demonstrates the first bio-implant platform that exploits converse ME effects for uplink telemetry. The implant achieves data modulation by creatively manipulating the ME resonance frequency through a custom IC. Moreover, we presents an innovative pulse-width modulation technique to enhance the robustness and bandwidth of the ME backscatter communication. These innovations enable ME implants to receive power and engage in bidirectional communication using a single transducer, significantly facilitating their miniaturization and expanding their applicability for closed-loop operations.

Lastly, this thesis showcases significant contributions in the realm of wireless networks comprising millimeter-sized bio-implants. Notably, a wireless coordinated multisite stimulation system is presented, where multiple implants are magnetoelectrically powered and individually programmed by a single transmitter. This system represents a significant step forward in the field, providing evident advantages, including improved system efficiency, a highly scalable and leadless architecture, flexible deployment options, and enhanced synchronization capabilities. Additionally, the thesis presents a distributed wireless network incorporating adaptive power transfer and innovative multi-access bidirectional telemetry techniques. These advancements effectively overcome the challenges associated with powering, communication, and the realization of precise and coordinated bio-functionalities within the bio-implant network.