High-Frequency Acoustic Wave Measurements in Air

Abstract

We have constructed focused and unfocused acoustic transducers for excitation of waves in air. These transducers operate at 1 and 2 MHz , respectively, and employ a quarter wavelength matching layer. we can transmit waves over distances of 1-40 cm . We have constructed systems for phase measurements and for pulse transit time measurements. At 1 MHz , the typical distance measuring a ccuracy is of the order of .5 mm over lengths of 2-40 cin , and improves considerably if several measurements are averaged. Our purposes are to use these t ypes of transducers and measurement systems for robotic applications and for profile measurements of solid materi a1 s. Although losses are high,