• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.4
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• pp.277-282
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• 2014

Recently, much attention has been paid to nonlinear ultrasonic technology as a potential tool to assess hidden damages that cannot be detected by conventional ultrasonic testing. One nonlinear ultrasonic technique is measurement of the resonance frequency shift, which is based on the hysteresis of the material elasticity. Sophisticated measurement of resonance frequency is required, because the change in resonance frequency is usually quite small. In this investigation, the nonlinear electromagnetic acoustic resonance (NEMAR) method was employed. The NEMAR method uses noncontact electromagnetic acoustic transducers (EMATs) in order to minimize the effect of the transducer on the frequency response of the object. Aluminum plate specimens that underwent three point bending fatigue were tested with a shear wave EMAT. The hysteretic nonlinear parameter ${\alpha}$, a key indicator of damage, was calculated from the resonance frequency shift at several levels of input voltage. The hysteretic nonlinear parameter of a damaged sample was compared to that of an intact one, showing a difference in the values.

• The Journal of the Acoustical Society of Korea
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• v.26 no.2
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• pp.80-86
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• 2007

We have investigated on the development of 2-2 type piezocomposites that have better piezoelectric activity and lower acoustic impedance than those of conventional piezoceramics. In this study, we have investigated the piezoelectric and acoustic properties of 2-2 type piezocomposites sensor which was fabricated using dice-and-fill technique for the different volume fraction of PZT. The specific acoustic impedance of 2-2 type piezocomposites decreased linearly when PZT volume fraction was decreased. The resonance characteristics measured by an impedance analyzer(HP4194A) were similar to the analysis of finite element method (FEM). The resonance characteristics and the electromechanical coupling factor were the best when the volume fraction PZT was 0.6. It also showed the highest result from the standpoint of sensitivity, bandwidth and ring-down property and so on at the same condition. The specific characteristics show that the 2-2 type piezocomposites turned out to be superior to the ultrasonic sensor composed by single phase PZT.