Using ultrasonic sound frequencies that can’t be heard by the human ear is the basis of ultrasound testing. Ultrasonic Non-destructive testing measures sound waves as they bounce off different materials. In most common UT applications, very short ultrasonic pulse-waves with center frequencies ranging from 5-15 MHz are transmitted into materials to detect internal flaws or to characterize materials. Any change in a material consistency will change the rate at which the sound bounces back. By measuring this echo, many potential defects can come to light.