Ultrasonic testers send short ultrasonic pulse-waves with frequencies ranging from 0.1-15 MHz up to 50 MHz into material to determine the thickness of the test object, for example, to monitor pipework corrosion.

Ultrasonic testing is often performed on steel and other metals where access is limited & it can be used on concrete, wood and composites, albeit with less resolution. It is a form of non-destructive testing used in many industries including aerospace, automotive, marine & oil.