Evaluation of Acoustic Energy Transfer Through Bolted Connections for Sensor Integrating Machine Elements

Monitoring machines and critical infrastructure with embedded sensor systems can increase reliability and decrease downtime. Sensor-Integrating Machine Elements (SiMes) can be used to enable in situ measurements of various parameters while maintaining structural integrity and compatibility with standard designs. Such devices integrate a sensor directly into a standardized machine element while maintaining its original dimensions and complying with strength requirements (e.g., a bolt with an integrated force sensor). This enables interchangeability. Challenges to power such a device arise from the limited integration volume, accessibility and retro fitting capability with existing machines. In this paper we discuss the possibility of using acoustic energy transfer to power a sensor integrating M20 bolt. We analyze losses due to the geometry of the SiMe, the bolt connection and misalignment by comparing it to a reference energy transfer channel. We assess various approaches to energize the system via Ultrasonic Power Transfer (UPT) through the bolt connection and an Aluminum bar, allowing for adaptable positioning of the SiMe. Finally, we present a concept for powering a sensor integrated into a machine element using UPT. We demonstrate the transmission through a 300 mm Aluminum bar into a bolt, aligned to the acoustic path, with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$578 \mu ~\mathrm{W}$</tex> received power and through a perpendicularly aligned bolt connection with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$141 \mu ~\mathrm{W}$</tex> respectively.