Acoustic touchless sensor using the flexural vibration of a plate

Abstract

Abstract This paper investigates a method to detect the position of an object in front of an ultrasonic vibrator using changes in the radiation impedance. This acoustic touchless sensor is composed of a rectangular vibrating plate (width: 30 mm; length: 200 mm; thickness: 3 mm) and two bolt-clamped Langevin-type transducers with stepped horns. The sensor configuration was determined based on the results of a finite element analysis simulation. When a stripe flexural vibration mode excited on the plate was generated an acoustic standing-wave field in the air, the electrical impedance of the ultrasound transducers changed dramatically, thus indicating that the radiation impedance of the sensor was dependent on the object position. By measuring the amplitude of the input current to the transducers and the phase difference between the input current and the voltage applied to the sensor, the 40 mm long object’s position could be determined uniquely within a two-dimensional area of 160 × 7 mm2.