On the Electrodynamics of a Non-Contact Inductive Sensor for High-Accuracy Tip Deflection Measurements of Piezoceramic Bending Actuators and its Application for Energy Harvesting Purposes

Abstract

Piezoelectric bending actuators provide deflections of several hundred micrometers and are used in electrical and mechanical engineering, acoustics, automation, automotive technology and healthcare. Highly efficient, low-cost piezoceramics offer a wide range of technical solutions. Their highpiezoelectric coefficients enable large strains at low electric field strengths. However, hysteresis, drift and creep impair positioning accuracy. Precise switching and positioning require compensation for these material-related effects, as well as varying mechanical loads and vibrations. A non-contact inductive proximity sensor is therefore combined with high-precision electronic circuit. Within a closed-loop control system, this sensor-actuator arrangement detects disturbances and enables their compensation, allowing highly efficient piezoceramics to be used for high-accuracy positioning. This paper investigates the electrodynamics of a specially developed eddy-current-based proximity sensor suitable for integration into confined spaces. A theoretical description explains its physical operating principle and enables analytical determination of the relative change in inductance as a function of actuator tip deflection. Experimental measurements validate the electrodynamic approach. The paper also considers energy harvesting applications. Measuring tip deflection allows the power dissipated in the piezoelectric transducer to be determined. The sensor system thus provides a basis for investigating and evaluating the performance of piezoelectric energy harvesters.