The properties of the test surfaces must be such that a proper coupling of the test probes used is ensured. The ultrasonic test is to be performed by the Impulse-Echo-Method with normal probes. The use of a testing frequency of 2 MHZ and an oscillating probe diameter of approx.25 mm is preferred. Testing frequencies of 1 and 4 MHz are also acceptable.
For material thicknesses>300 mm, probes with an extremely wide frequency spectrum may be use(coarse-grain probes).