An acoustic position sensor, based on a piezoelectric-sound-resonance cavity (PSRC), is reported in which a resonance acoustic field is used as the sensing mechanism. It has been discovered that an inserted object or an object motion in the sound radiation field results in changes in the resonance state of the PSRC. Experiments have demonstrated a high position resolution in the axial direction, and also good sensitivity in the transverse. (C) 2003 American Institute of Physics.