Higher order modal dynamics of the flexural ultrasonic transducer

The flexural ultrasonic transducer (FUT) consists of a piezoelectric ceramic bonded to an edge-clamped elastic plate, for both generation and detection of ultrasound waves. It is typically employed for proximity measurement, such as in automotive parking systems, and for fl ow measurement in gases and liquids. Conventional industrial applications have generally incorporated FUTs with resonance frequencies up to around 50 kHz. However, there have been recent advances in the understanding of the FUT, both in terms of fabrication and operation, enabling the potential for measurement in a wider range of applications, including those of elevated pressure, temperature, and requiring multiple operating frequencies. Ultrasound measurement with FUTs at frequencies greater than 50 kHz is desirable in a range of applications, including gas and water metering in petrochemical plants, district heating, and power industries. The major restricting limitation of designing transducers to operate at these higher frequencies has been a relatively poor understanding of these transducers work, including optimisation of design and performance, and the few reports into how different modes of a FUT can be utilised for practical and reliable measurement. In this study, the higher order modal dynamics of the FUT are investigated through measurement of high frequency ultrasound waves in air, for different fundamental operating modes. A combination of experimental techniques is applied, comprising electrical impedance analysis and laser Doppler vibrometry. The experimental research is supported by analytical solutions to reveal complex higher order modal dynamics of the FUT. This investigation represents further development in widening the industrial application potential of the FUT.