A pair of non-contact 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 (SNR) for non-contact 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 non-contact ultrasonic imaging and thickness gauging in a wide range of metal plates. Advantages over conventional transient or tone-burst excitation will be discussed.

A continuous wavelet transform has been used to analyse multi-mode Lamb wave propagation. This was applied to experimental data from non-contact electromagnetic acoustic transducers (EMATs) in thin metal plates. The technique was able to identify the presence of s 0 , a 0 , a 1 , s 1 and s 2 modes in an aluminium plate from a single waveform, and hence to separate the modes. The technique has been applied to tomographic reconstruction of artificial defects in plates from individual modes to illustrate the usefulness of the approach.

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