Abstract
Flexural ultrasonic transducers are a widely available type of ultrasonic sensor used for flow measurement, proximity, and industrial metrology applications. The flexural ultrasonic transducer is commonly operated in one of the axisymmetric modes of vibration in the low-kilohertz range, under 50 kHz, but there is an increasing demand for higher frequency operation, towards 300 kHz. At present, there are no reports of the measurement of high-frequency vibrations using flexural ultrasonic transducers. This research reports on the measurement of high-frequency vibration in flexural ultrasonic transducers, utilizing electrical impedance and phase measurement, laser Doppler vibrometry, and response spectrum analysis through the adoption of two flexural ultrasonic transducers in a transmit–receive configuration. The outcomes of this research demonstrate the ability of flexural ultrasonic transducers to measure high-frequency ultrasound in air, vital for industrial metrology.
Highlights
T HE accurate detection of high frequency vibrations in industrial flow and measurement ultrasound systems is essential, especially at relatively low power with high efficiency
The geometrical approximation for the behaviour of the flexural ultrasonic transducer cap membrane has previously been considered as an edge-clamped plate [7], [9], and estimations of the vibration modes can be produced using Bessel functions, which have been detailed in the literature and are not repeated here [7]
The cap membrane is modelled as an edge-clamped plate, which will not precisely represent the dynamics of the flexural ultrasonic transducer in practical application
Summary
T HE accurate detection of high frequency vibrations in industrial flow and measurement ultrasound systems is essential, especially at relatively low power with high efficiency. Throughthickness or radial modes of piezoelectric transducer vibrations have been used in many commercial transducers [1], often using matching layers to improve coupling efficiency into gas because of the high acoustic impedance mismatch between the piezoelectric material and the gas [2] These sensors are capable of operating up to frequencies of 5 MHz, but generally require high voltages, in the region of 20 V or higher, and have at least part of their radiating face made from a polymer or other non-robust material. MEMS-type fabrication approaches have been used to manufacture CMUT [3] and PMUT [4] type sensors, both of which can be small, robust devices that can require high voltages to drive them, and in the case of a CMUT a large biasing voltage These MEMStype devices are capable of generating or detecting ultrasonic waves in gas up to MHz frequencies
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