Ultrasonic Power Transfer based on Aluminium Nitride Piezoelectric Diaphragm Architectures for Deep Wireless Powering of Sub-Millimetre Biomedical Implants

Description

This proposal aims to enable miniaturization of ultrasonic power transfer (UPT) links that can wirelessly power sub-millimetre (mm) biomedical devices implanted deep in the body (>5cm). The increasing financial burden to fund healthcare in much of the developed world is reaching a breaking point. Proposed solutions include personalized healthcare management particularly for chronic conditions using modern technology (e.g. biomedical implants).But powering biomedical implants remains a challenge. Wireless power transfer (WPT) avoids the need for regular surgery to replace batteries or electrical wires going through the skin. But conventional WPT methods based on inductive-coupling (IPT) of electromagnetic (EM) waves are fundamentally unable to deliver enough power at very small scales (e.g. millimetre (mm)). Hence although we now have the capability to realize mm-size integrated circuits and sensors, WPT links at such small scales remain the bottleneck.Ultrasonic power transfer (UPT), based on ultrasonic waves, is fundamentally more efficient than IPT when the target spot size is much smaller than the transmission range; such is the case of mm-size implants located deep in the body. Recent research has demonstrated the feasibility and advantages of UPT for mm-size implants based on well-established materials (e.g. PZT) and piezoelectric receiver (RX) architectures (e.g. bulk architecture). Though small, these mm3 devices are still not chip-scale. Scaling systems below mm3 to deliver chip-scale solutions requires alternative RX architectures that scale more favourably than the conventional bulk architecture in terms of power conversion efficiency (PCE). Besides, PZT contains lead (Pb). To increase probability of patient adoption, Pb-free materials (e.g. Aluminium Nitride (AlN)) must be explored.This project aims to probe the limits of UPT at the sub-mm scale using piezoelectric diaphragm structures based on AlN by levering our expertise in microsystems and piezoelectric devices. Objective 1 focuses on the RX end of the UPT-link, examining the relation between device geometry, size, and harmonic mode on PCE. We aim to demonstrate mW power levels with incident power intensity levels below regulatory limits for ultrasound. Objective 2 focuses on the transmitting (TX) end, aiming to demonstrate highly-directed beams targeting sub-mm implant spot size to increase transmission efficiency and reduce peripheral exposure. The 3rd objective focuses on matching circuit networks interfacing the receiver and implant load, including tuning methods for matching a range of implant loads.At the end of this project, we aim to demonstrate ultrasonic powering of a μm-scale sensor co-fabricated on the same chip with the UPT-receiver.