Precision piezoelectric acoustic position detector

A piezoelectric acoustic position detector has been fabricated using a piezoelectric bimorph ring and an acoustic sensor. The disk type piezoelectric bimorph with a center-opening and the acoustic sensor are placed at each end of a small plastic cylindrical cavity and act as the driving element and the detecting element, respectively. When the driving element vibrates at the cavity's resonance frequency, the air filled plastic cavity will be excited into a resonance state. The resonance frequency can be estimated by using a Helmholtz resonator theory. When an object obstructs the sound beam, the acoustic field would be changed. This thus leads to a variation in the state of the sound resonance. A lock-in amplifier is used to monitor the output voltage and phase change of the acoustic sensor. The experimental results show that the position detector has a linear phase change of 0.017° μm−1 and a linear voltage change of 51.2 μV/μm to small displacement along the acoustic radiation direction.