Electrical and Electronic Engineering, Imperial College London
Doi
Abstract
Advances in miniature devices for biomedical applications are creating ever-increasing
requirements for their continuous, long lasting, and reliable energy
supply, particularly for implanted devices. As an alternative to bulky
and cost inefficient batteries that require occasional recharging and replacement,
energy harvesting and wireless power delivery are receiving increased
attention. While the former is generally only suited for low-power diagnostic
microdevices, the latter has greater potential to extend the functionality to
include more energy demanding therapeutic actuation such as drug release,
implant mechanical adjustment or microsurgery.
This thesis presents a novel approach to delivering wireless power to remote
medical microdevices with the aim of satisfying higher energy budgets
required for therapeutic functions. The method is based on ultrasonic power
delivery, the novelty being that actuation is powered by ultrasound directly
rather than via piezoelectric conversion. The thesis describes a coupled mechanical
system remotely excited by ultrasound and providing conversion
of acoustic energy into motion of a MEMS mechanism using a receiving
membrane coupled to a discrete oscillator. This motion is then converted
into useful stepwise actuation through oblique mechanical impact.
The problem of acoustic and mechanical impedance mismatch is addressed.
Several analytical and numerical models of ultrasonic power delivery
into the human body are developed. Major design challenges that have
to be solved in order to obtain acceptable performance under specified operating
conditions and with minimum wave reflections are discussed. A novel
microfabrication process is described, and the resulting proof-of-concept devices
are successfully characterized.Open Acces