Detection of nonlinear Lamb wave using a PVDF comb transducer

Abstract

The detection of the nonlinear Lamb wave using a PVDF comb transducer is described in this research. The construction features of the PVDF comb transducer is firstly described. Then, the harmonic-frequency characteristic of PVDF comb transducer as the receiver in the nonlinear Lamb wave inspection is qualitatively investigated by the output-vector addition method. The theoretical result shows that, when the wavelength of the fundamental Lamb wave is equal to the PVDF comb transducer's finger spacing, the transducer can receive the fundamental wave. When the frequency of the higher-harmonic Lamb wave is integral multiple of the frequency of the fundamental one, the PVDF comb transducer can also receive the higher-harmonic Lamb wave. In order to verify the harmonic-frequency characteristic of the PVDF comb transducer, we conducted an experiment based on the cumulative effect of the nonlinear Lamb wave. That is, the value of the relative nonlinearity parameter will grow higher when the propagation distance increases. In order to receive the fundamental and second-harmonic Lamb waves, a PVDF comb transducer with special finger spacing was made and pasted on an aluminum plate surface. The desired Lamb-wave mode was generated by a wedge transducer. It had been observed that the value of relative nonlinearity parameter increased with the wave propagation distance. That means that the PVDF comb transducer had received both the fundamental and the second-harmonic Lamb waves. Both the theoretical and experimental results show that, because of the PVDF comb transducer's simultaneous response to the fundamental and second-harmonic signals, the nonlinear Lamb wave can be detected using a PVDF comb transducer.