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Application of pulse compression signal processing techniques to electromagnetic acoustic transducers for noncontact thickness measurements and imaging

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4 Author(s)
Ho, K.S. ; School of Engineering, University of Warwick, Coventry, CV4 7AL, United Kingdom ; Gan, T.H. ; Billson, D.R. ; Hutchins, D.A.

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A pair of noncontact Electromagnetic Acoustic Transducers (EMATs) has been used for thickness measurements and imaging of metallic plates. This was performed using wide bandwidth EMATs and pulse-compression signal processing techniques, using chirp excitation. This gives a greatly improved signal-to-noise ratio for air-coupled experiments, increasing the speed of data acquisition. A numerical simulation of the technique has confirmed the performance. Experimental results indicate that it is possible to perform noncontact ultrasonic imaging and thickness gauging in a wide range of metal plates. An accuracy of up to 99% has been obtained for aluminum, brass, and copper samples. The resolution of the image obtained using the pulse compression approach was also improved compared to a transient pulse signal from conventional pulser/receiver. It is thus suggested that the combination of EMATs and pulse compression can lead to a wide range of online applications where fast time acquisition is required.

Published in:

Review of Scientific Instruments  (Volume:76 ,  Issue: 5 )