A Parallel-Input Energy-Recycling Power Management Unit with Continuous MPPT for Magnetoelectrically Powered mm-Scale Bio-Implants

Implantable medical devices (IMDs) offer transformative tools to substantially improve medical outcomes for cardiovascular diseases [1], pain relief [2], and neurological disorders [3]. To realize minimally invasive implants with miniaturized volume and weight, wireless power transfer (WPT) has been extensively studied to replace bulky batteries that dominate the volume of traditional IMDs and require surgical replacements [4]. Inductive coupling, a prevalent WPT method for IMDs, benefits from advanced power management, such as resonant regulating rectifiers, to enhance efficiency [5], [6], but is limited by large cm-scale RX coil [5] or high body absorption at higher carrier frequency [6]. Ultrasonic (US) [7], [8] and magneto-acoustic-electrical (ME) [9]–[11] WPT modalities, that leverage low-frequency (100s of kHz to MHz) acoustic waves for energy transduction, become viable solutions for mm-scale receivers. In addition, ME WPT avoids US WPT's reflection issue at the boundaries between air, tissue, and bones. Due to the higher impedance and stronger electromechanical coupling of these transducers, PMUs developed for inductive WPT and piezoelectric energy harvesting are not directly applicable [12], and recently demonstrated ME/US IMDs only adopt basic rectifier-(DCDC)-LDO PMU topologies [7]–[11]. However, the basic PMUs exhibit critical limitations in efficiency and reliability, which motivates us to develop PMUs specifically for ME/US WPT.