Acoustic Energy Transfer for Integrated Sensor Systems

Powering embedded sensors in metal-enclosed environments poses significant challenges such as structural constraints, battery dependency, and electromagnetic shielding. This work investigates using acoustic energy transfer (AET) as a viable approach and explores key factors influencing performance. A parametric study examines various parameters affecting energy transfer, which is followed by an experimental demonstration in a sensor-integrated bolt. Results indicate that electrical impedance matching greatly enhances power transfer but also alters the optimal transmission frequency. Elevated temperatures reduce the transducers' resonance frequency. This potentially impacts performance if only a single transducer is subjected to a temperature gradient, which can be caused by nearby machinery, exposure to hot industrial processes or self-heating due to inefficiencies. Pure sine wave excitation increases power transfer up to 2.5 times over pulse-width modulation at the expense of increased circuit complexity. Given that multiple parameters influence not only peak output power but also its frequency, active resonance tracking is essential for optimal energy transfer. Ultrasonic communication enables receiver-side frequency tracking, improving efficiency and adaptability in dynamic conditions. The final bolt-integrated setup achieves an output power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rm{0.38}\,\rm{mW}$</tex-math></inline-formula>, demonstrating the feasibility of AET while also revealing size-related inefficiencies in embedded sensors.