High-Frequency Ultrasonic Transducer Operating in Air

Abstract

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.

Precise Displacement Measurements Using Phase Information of 40 kHz Ultrasonic Waves in Pinhole-Based Air-Coupled Ultrasonic System

“…14) The phase detection for CW allows a narrower bandwidth of the filter used in the phase detection, which accordingly improves the signal-to-noise ratio of ultrasonic wave signals. This is one of the advantages of this CW system over the often-adopted pulse-echo systems [5][6][7][8][9] that operate in a wide-band mode. When a continuous sinusoidal wave from a function generator (Agilent Technologies, 33250A) was applied to commercially available and low-cost transducers (Nippon Ceramic, R40-16), the ultrasonic wave was transmitted into the conical cavity in the CAP.…”

“…The use of MHz-range air-coupled ultrasonic waves has previously been studied, [5][6][7][8][9][10][11] and a few air-coupled ultrasonic transducers with frequency ranges of up to 11 MHz have recently been developed. 8) However, the large acousticimpedance mismatch and the increasing attenuation of ultrasound with increasing frequency, which are described above, decrease the signal-to-noise ratio of ultrasonic wave signals.…”

Ultrasonic Presence Sensors with Wide Range and High Local Resolution

“…The radiative efficiency can be improved significantly by the use of a quarter-wave matching layer of a material with smaller acoustic impedance. For this silicon rubber [5], [6] is used and even multiple coatings had been reported [7]. By systematic research, an extremely rugged material [8] was found having a rather low acoustic impedance.…”

“…The signal level reserve depends on the frequency because of the decreasing maximum power (7) and the increase of noise power with bandwidth B (constant Q factor). Thus…”

Range Finding and Surface Characterization Using High-Frequency Air Transducers

“…In the present study, thickness-driven piezoelectric air transducers operating at 1 MHz have been developed utilizing newly synthesized low-acoustic-impedance-matching materials [6]. The insertion losses of these transducers have been improved by more than 15 dB compared to the air transducers mentioned above.…”