The purpose of this project has been to investigate means for obtaining improved characterization of the size@ shape and location of subsurface discontinuities in metals. This has been done by applying computerized data processing techniques to the signal obtained in conventional ultrasonic pulse-echo syslems. The principal benefits are improved signal-to-noise ratio@ and resolution. The received ultrasonic pulse from a discontinuity is combined with a reference function in order to preserve both the phase and amplitude of the received pulse. Processing is performed on the power spectrum of the resultant signal. The reference function is also used to compensate for some of the frequency dependent scattering caused by the material microstructure. During data acquisition@ analog signal averaging improves the signal-to-noise ratio (SNR). After data acquisition@ a digital deconvolution procedure improves the transducer longitudinal resolution. An analysis of a mathematical model of the combined ultrasonic and data processing system shows that the system provides an order of magnitude increase in the longitudinal resolution and a 37 dB increase in the signal-to-noise ratio over that expected from a conventional pulse echo system. Experimental data demonstrate a factor of five improvement in resolution and a 28 dR increase in the SNR. The results also show that the computer processed data are virtually independent of the transducer used in the ultrasonic system. A theoretical analysis of the model also shows that the final output format is ideally suited to the formation of a synthetic transducer array designed to increase the lateral resolution.
BULLETIN 185-1973 history
1973BULLETIN 185-1973 IMPROVED DISCONTINUITY DETECTION USING COMPUTER-AIDED ULTRASONIC PULSE-ECHO TECHNIQUES