Scaling of ultrasound-powered receivers for sub-millimeter wireless implants

We investigate scaling of ultrasound-powered wireless receivers for efficient, miniaturized implantable medical devices. Single crystalline piezoelectric material, PMN-PT, is chosen in this study as it has low resonance frequency with scaled dimensions. For accurate modeling of sub-mm-sized receivers, we perform simulations using the finite element method, followed by validation with measurements. Results are presented for scaling of the resonance frequency, resistance at resonance, and aperture efficiency of PMN-PT receivers with thickness of 0.5 mm and widths ranging from 0.3 mm to 1.0 mm. Since optimizing the overall harvesting efficiency of an implant requires not only an efficient receiver but also an efficient interface to the power electronics, we analyze impedance matching efficiency between the receivers and the power electronics using optogenetic stimulation as an example application. Finally, we show the measurement of prototype implants with scaled receivers and discuss the trade-off between size and power harvesting efficiency of sub-mm wireless implants.