A non-contact acoustic sensing system using changes in the radiation impedance was proposed to detect the position of an object in front of an ultrasonic vibrator. The sensor is composed of a rectangular vibrating plate (20 × 100 × 1 mm3) and a PZT transducer (20 × 20 × 2 mm3). The sensor configuration was determined based on the results of a finite element analysis simulation. The flexural vibration modes were excited on the plate at two resonance frequencies, 29.7 and 46.2 kHz. The radiation angle of ultrasound from the sensor and the acoustic field between the object and the plate were compared at the two frequencies to investigate the detection characteristics. When an acoustic standing-wave field was generated in the air, the electrical impedance of the ultrasound transducers dramatically increased, 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 object position could be determined uniquely within a two-dimensional area.

This paper investigates a thin sensor used to detect the position of an object in front of an ultrasonic transducer using changes in the radiation impedance. The sensor consists of a rectangular plate and a piezoelectric transducer, and the configuration is determined based on the results of a finite element analysis simulation. Stripe flexural vibration modes are generated on the plate, radiating sound waves into the air between the plate and the object. The radiation angle of these sound waves is dependent on the driving frequency, resulting in a change in the sound field and the electrical admittance characteristics. The sensing performance is examined using two resonant vibration modes. The sensor can determine the position of an object uniquely within a two-dimensional area, and the lower resonant mode gave a wider measurable range. The sensitivity is improved six-fold over that of our conventional sensor using the same sensing mechanism.

In an acoustic standing wave generated in the air between a vibrator and a reflector, a small object is levitated near the nodal positions of the sound pressure where the acoustic radiation force and the gravity are balanced. By controlling the sound field spatially and temporally, the object can be transported without contact. In this report, we experimentally investigated the non-contact high-speed rotation of a small object using ultrasound, which can be applied to measurement techniques of the physical properties of liquids. The experimental system consists of a vibrating disc with four bolt-clamped Langevin-type transducers and a reflector, and an acoustic standing wave is generated between them. The effects of the tilt angle of the reflector with respect to the vibrator on the rotation speed of the object and the acoustic field were investigated. When the tilt angle was around 1.2°, the object was trapped in the air at 31.5 kHz by the standing-wave component in the vertical direction and rotated by the traveling-wave component propagating in the horizontal direction. The maximum sound pressure amplitude and the rotation speed of the object were changed with the tilt angle, and a larger sound pressure amplitude gave a larger rotation speed.

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 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 mm×7 mm