Masayuki Tone

Range Finding and Surface Characterization Using High-Frequency Air Transducers

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.

High-Frequency Ultrasonic Transducer Operating in Air

The design and application of high-frequency piezoelectric air transducers are described. By employing a double layer acoustic matching transformer to a ceramic thickness mode vibrator, an air transducer with low insertion loss (52 dB) and good RF pulse response (9 µs of -20 dB ring-down period) has been developed. Use of the transducer operating at 1 MHz for distance measurement in a range of 0~20 cm has revealed that the range resolution and the measurement accuracy are 1.5 mm and of the order of 0.1 mm, respectively. Other applications described here are the characterization of cloth surfaces and profile measurement of cloths.

1 MHz Ultrasonic Transducer Operating in Air

Conventional ultrasonic air transducers operating below 100 kHz have been utilized for position sensing in the range of 0.1–10m and provide several unique advantages. A typical application of an ultrasonic air transducer is to the wide range distance measurement of an optically transparent object placed “very close to” up to “relatively far from” the transducer. Additionally the real-time measurement can be done with simple signal processing. However, conventional air transducers have very wide beamwidths and relatively long pulse response characteristics which make it difficult to detect a small and nearby object.