Development of a capacitive ultrasonic sensor having parylene diaphragm and characterization of receiving performance of arrayed device

The present paper reports the development of a capacitive ultrasonic sensor having Parylene diaphragm. Parylene diaphragm is flexible and non-brittle, allowing good sensitivity and durability. The resonant frequency under the tensile stress of Parylene and the influence of the number and the radius of acoustic holes on damping ratio are investigated by FEM (finite element method) simulation. Practical sensor devices are fabricated. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge. The ranging system using this sensor can detect the distance up to 1 m with the error less than 1 mm. The developed sensor can be approximated to be non-directional. An arrayed sensor device comprising 5 × 5 developed sensors is fabricated, and its receiving performance is characterized. It is proven that the electric scanning of directivity based on delay-and-sum principle is possible.