Excitation and deconvolution in ultrasound nondestructive testing systems

The pulse-echo (PuE) model based on short pulses is introduced as a starting point. Its limits in terms of signal-to-noise ratio (SNR) are reviewed, together with the tradeoff between the excitation energy and the time resolution. It is shown how signal processing can improve the overall performance in terms of system sensitivity and resolution as long as the exciting waveform is chosen taking into account the system characteristics and is in agreement with the adopted processing techniques. The degrees of freedom on which one can operate are the time evolution law of the excitation signal and the processing technique adopted on the receiving end. In their exploitation, the designer should consider the physical characteristics of the hardware devices being employed in order to optimize the overall performance. The importance of introducing merit factors is discussed. By offering a quantitative measure of system performance, they are indispensable tools to drive formal optimization strategies and for comparing different approaches. Application-related merit factors are introduced for trying to overcome some current limitations and to prepare the ground for the extension of ultrasonic techniques to multiple input, multiple output (MIMO) systems, which are considered in the following chapter.