Improved ultrasonic near-field scanning using dual-channel digital cancellation network

A digital cancellation network is proposed to improve wide band ultrasonic scanning of targets very close to the transducer surface. The presented network, designed to reduce the capacitive current during transmission according to a predescribed model, is investigated experimentally in a pulse-echo test bed. By using both two and four parametric models on a polyvinylidene fluorid sensing element, it is shown that the received main bang can be suppressed with as much as by 32.7 and 49.2 dB, respectively, without distorting the shape of the ultrasonic UWB pulse significantly.