A novel dynamic calibration method using polyvinylidene fluoride piezoelectric film for ultrasonic vibration sensing application

Abstract

Ultrasound has a wide range of applications in many fields. It has great significance in measuring the ultrasonic signal generated in process applications, such as ultrasonic vibration cutting and ultrasonic testing. However, its high frequency characteristics make it difficult to measure the ultrasonic signal. A novel sensor is proposed herewith, exhibiting excellent qualities such as good flexibility and quick response using polyvinylidene fluoride (PVDF), suitable for measuring ultrasonic frequency bands. The piezoelectric constant is a vital factor, influencing the accuracy of the measurement. The frequency of existing calibration methods for the piezoelectric constant is below 1 kHz. At present, as per our literature reviews, there is no existing or suitable method for calibrating PVDF under ultrasonic frequency. In this paper, a novel calibration method of the piezoelectric constant based on the ‘falling ball’ is presented, which could calibrate the constant dynamically at about 2.5 kHz. A steel ball is released from a static state, then it falls onto a thin rod placed on a dynamometer. By loading the mass of the steel ball with different masses at the falling height, different frequencies of the vertical dynamic impact can be produced. The calibration result of is 20.80 pC N−1 with a relative uncertainty of 1.28%, and the responsivity is 1.600 pC/ with a relative uncertainty of 1.896%. Finally, taking an ultrasonic transducer and horn as an example, the strain produced by the horn is measured with the calibrated PVDF film at ultrasonic frequency. It is proven that the piezoelectric constant calibrated by this method is suitable for ultrasonic frequency measurement.