MEMS-Based Ultrasonic Energy Harvesting Platform Enabling Sustained In Vivo Operation of Implantable Microdevices

Implantable microdevices capable of autonomous operation over extended lifetimes are promising enablers for minimally invasive diagnostics and therapy. Microelectromechanical systems (MEMS)-based piezoelectric ultrasonic energy harvesters (PUEH) have emerged as a compelling approach for powering implantable microdevices, where both miniaturization and efficient wireless energy transfer are essential. Here, we present a highly miniaturized (5 x 5 x 5 mm3) ultrasonic energy-harvesting platform enabling sustained in vivo operation of implantable microdevices. The platform integrates a MEMS-PUEH, a high-efficiency power management system, an energy storage element, and representative functional electronics. We first investigate the effect of backside cavity boundary conditions on MEMS-PUEH performance and show that a sealed air-filled chamber significantly outperforms an open water-filled cavity, yielding a 46% increase in root-mean-square output voltage and a 117% increase in average output power across a 2 k{Omega} resistive load under identical incident acoustic intensity at the respective optimal operating frequencies. We then demonstrate system-level integration and characterization. In a tissue-mimicking phantom, under an incident acoustic intensity of approximately 257 mW/cm2, the device charges an 11.5 mF supercapacitor, a 5 {micro}Ah solid-state microbattery, and a 100 {micro}F capacitor to their nominal voltages in less than 5 min, 3 min, and 20 s, respectively. Finally, in vivo validation demonstrates fully autonomous operation of representative functional electronics following ultrasonic charging of the onboard energy storage element. These results establish a highly miniaturized and fully integrated ultrasonic energy-harvesting platform that advances MEMS-based power solutions for implantable biomedical microdevices.