Micromechanical Actuators Driven by Ultrasonic Power Transfer

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 batteries, energy harvesting and wireless power delivery are receiving increased attention. Although the former is generally only suited for lowpower diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding actuation such as drug release or mechanical adjustment of prosthetic devices. With this aim, we present an ultrasonic method of wireless power delivery for actuation, the novelty being that the actuation is powered by ultrasound directly, rather than via piezoelectric conversion. This paper describes a coupled mechanical system remotely excited by ultrasound at 200 kHz and providing conversion of acoustic energy into motion of a micromechanical mechanism using a receiving membrane coupled to a discrete oscillator. We address the problem of acoustic and mechanical impedance mismatch and simulate harmonic and frequency response of the system. The fabrication method is described, and the resulting devices are characterized, revealing hysteresis in their frequency response that is related to nonlinear behavior in the membrane-oscillator coupling. The experimental samples were successfully driven by an ultrasonic source, at various separations, and demonstrated maximum oscillator vibration amplitudes in the range of 9.6-9.9 μm. This provided a mechanical amplification with respect to the membrane in the range of 240-250.