Comparison of Interferometric and Electrical Analyses for the Spectral Dynamic Characterization of a Suspended Piezo-Actuated Panel

Flat piezoelectric speakers are emerging as a promising alternative for next-generation loudspeaker technologies thanks to their shrunk size, reduced thickness and improved efficiency. Although a full electro-mechano-acoustic characterization of these devices is ultimately required, preliminary experimental investigations aimed at a comprehensive understanding of their electromechanical behavior are essential. In this work, we adopted two complementary techniques to investigate the spectral dynamic response of a suspended Plexiglas® panel driven by a piezoceramic actuator: laser diode feedback interferometry for direct vibration measurements across different locations on the panel surface, and electrical impedance analyses of the transducer. Whereas optical testing was performed by driving the actuator with electrical white noise, electrical measurements were conducted by sinusoidally exciting the actuator with a frequency-swept signal. An extremely good matching was found among the frequency positions of the peaks in the photodetected spectral signals and of the local minima in the impedance response, in the frequency range from 0 Hz up to 5 kHz. This comparison demonstrates the possibility to use the same piezoceramic module for both actuation and resonance sensing. Moreover, spatially resolved vibration monitoring can be reliably and efficiently implemented with the almost self-aligned configuration and easily movable sensing head of the feedback interferometer. The use of optical and impedance-based techniques provides a comprehensive framework for the analysis of medium-size lightweight structures, for next-generation piezoelectric flat speakers with applications ranging from consumer electronics to automotive interior panels, where performance, form factor, and energy efficiency are increasingly demanded.