PHY01 Basics of pulse echo method (A-Scan)

The pulse echo method forms the basis of many imaging methods in non-invasive medical diagnostics and non-destructive testing. In this method, electrical pulses are transformed into mechanical vibrations by an ultrasonic probe. These are coupled into the sample being examined and pass through it as sound waves. Waves that are reflected on discontinuities return to the probe and are converted back into an electrical signal. The chronological recording of the amplitude of this signal (amplitude scan) is graphically imaged as a so-called ultrasonic A-Scan image. Based on the reflection echoes in the A-Scan image, times of flight can be determined, the sound velocity in the material calculated and discontinuities in the sample detected.

PHY01 Schematic side view of the test block

Screenshot of the AScan software showing an amplitude scan with echo peaks and the TGC setup

The screen shot of the measurement software shows a typical ultrasonic A-Scan image of the test block. One can observe: the initial echo, the echo of a discontinuity and the bottom echo at the material-air boundary at the opposite end of the sample. The value to be determined for the sound velocity in the test block (acrylic) is around 2700 m/s. From the ascertained sound velocity and the measured times of flight of the reflection echoes of the discontinuities, their depth in the sample can be established.