Improvement in transient piezoelectric responses of NDEtransceivers using selective damping and tuning networks

摘要

NDE ultrasonic applications for quality control purposes, based onnpiezoelectric devices working as pulsed ultrasonic probes, usuallyninclude some tuning circuit either across the pulser output connectorsnor close to the piezoelectric probe electrodes. Classic criteria tondetermine tuning parameters in ultrasonic transducers do not performnvery well in transient regime under the typical electrical conditionsnand peculiar output impedances of the required high-voltage pulsers. Innmost practical situations, the tuning values are manually adjusted innspecific circuits for each NDE case, testing each channel of anmultiprobe inspection system to find the best sensitivity. In thisnpaper, the positive influences of certain selective damping and tuningnnetworks on the time and frequency behaviors of NDE piezoelectricntransceivers are analyzed in detail. Different waveforms and spectra ofnreceived ultrasonic signals are comparatively evaluated for differentnreal tuning conditions, after passing through two ultrasonic processesnlinked in cascade: a transmitter of industrial type and a broad-bandnultrasonic receiver. Piezoelectric transducer impedances, transductionntransfer functions, and HV output spikes from a piezoelectrically loadednNDE pulser, are computed, to identify separately the influence of eachnstage. In order to improve amplitude and axial resolution in thenreceived transient responses, relative contributions from emission andnreception tuning networks are individually evaluated for a particularnNDE two-stage piezoelectric channel. Also shown are the finalnexperimental results relative to the ultrasonic test pulse and detectednin a through-transmission NDE configuration, gradually improved by usingndistinct tuning levels