Range Finding and Surface Characterization Using High-Frequency Air Transducers

Abstract

The design and applications of high-frequency piezoelec- tric air transducers are described. Two types of thickness mode air transducers are designed and fabricated using newly synthesized acoustic matching layers with an acoustic impedance as low as 0.3 Mrayls. The insertion losses of these transducers are improved by 32- 45 dB compared to that of the transducer without a matching layer. Use of a l-MHz double matching layer transducer with a good RF pulse response for range finding has revealed that the measurement range accuracy is of the order of 0.1 mm. For surface profile and defect mea- surements of solid objects, a focused transducer with a single matching layer is found suitable due to its small focal spot diameter of 1.3 mm and range accuracy of 0.1 mm. Other applications described here are the analysis of a cloth surface state using the acoustic signals propa- gating along the cloth surface and passing through the cloth. air transducers mentioned above. This paper describes the design of these transducers and their applications to range finding, profile measurement of solid objects, and surface state measurement of cloth.