Abstract
Recent studies of the electro-mechanical behavior of flexural ultrasonic transducers have shown that their response can be considered as three distinct characteristic regions, the first building towards a steady state, followed by oscillation at the driving frequency in the steady state, before an exponential decay from the steady state at the transducer's dominant resonance frequency, once the driving force is removed. Despite the widespread industrial use of these transducers as ultrasonic proximity sensors, there is little published information on their vibration characteristics under different operating conditions. Flexual transducers are composed of a piezoelectric ceramic disc bonded to the inner surface of a metallic cap, the membrane of which bends in response to the high-frequency ceramic vibrations of the ceramic. Piezoelectric devices can be subject to nonlinear behavior, but there is no reported detail of the nonlinearity in flexural transducers. Experimental investigation through laser Doppler vibrometry shows strong nonlinearity in the vibration response, where resonance frequency reduces with increasing vibration amplitude.
Highlights
The flexural ultrasonic transducer (FUT) is commonly applied as an air-coupled sensor, for example, in non-destructive evaluation or proximity sensing applications [1]
The electrical characteristics of each FUT, all with a nominal resonance frequency of around 40 kHz, have been measured to provide information regarding the resonance of the FUTs which can be correlated with the nonlinear characterisation measurements, and the quality factor of the devices
An explanation for the discrepancy is that the vibration response of the FUT membrane is measured optically through LDV, which is not the case with electrical impedance analysis, and since the vibration of the FUT membrane is not instantaneously sinusoidal [2], there will be a discrepancy between the resonance frequency detected by different measurement systems
Summary
The flexural ultrasonic transducer (FUT) is commonly applied as an air-coupled sensor, for example, in non-destructive evaluation or proximity sensing applications [1]. The increase in resonance frequency, termed a hardening nonlinearity [4], [6], is exhibited by the dotted curve, where fN approaches fH, the nonlinear hardening resonance frequency This investigation first analyses the electrical characteristics of a set of five commercially-available FUTs, where dynamic properties including electro-mechanical coupling factor, resonance frequency, and quality factor, are measured. This information is used to configure the experimental setup for the measurement of dynamic nonlinearity in the vibration response of all five FUTs, which is undertaken using single-point laser Doppler vibrometry
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