Fig. 4 shows echoes calculated, by using the model of Fig. 3, for the driving conditions of Fig. 2, in the case of a normal reflection through water from a plain steel target situated in the near field of the transducer. The negative effects on the echo signal of removing the rectifier sets RC can be clearly seen, in comparison to the echo where the direct effect of RC prevents the lengthening of the echoes. Without RC the echo amplitude had been reduced near to the half value and the signal length had notably increased, which is very harmful for NDE purposes. Therefore these non-linear effects from driver devices, RI C and RII C, bring advantages as regards the bandwidth and the echo amplitude, and should not be ignored in any modelling process.