Air Ultrasonic Transducers Combining High Sensitivity, Large Bandwidth and Wide Beamwidth

Abstract

An ultrasonic Doppler instrument was developed to measure the 3D velocity vector of small particles (diameter 1.5-3 mm) traveling in air at high speeds (up to 70 m/s) (Hofstee, 1996). The transducer configuration for this instrument consists of a sensor head with one convex, circular diameter piezoelectric transmitting transducer and three piezoelectric receiving transducers with a flat circular aperture. In passing it, a particle is illuminated by a diverging, monochromatic ultrasonic beam radiated by the transmitting transducer. The Doppler shifted ultrasonic signal backscattered by the particle is recorded simultaneously by all three receiving transducers. The velocity vector is computed from the Doppler shifts of the received signals while the particle diameter is estimated from the amplitude of the signals.