Detecting internal defects – gently and precisely
Ultrasonic testing utilizes the physical propagation of high-frequency sound waves in solid materials. Short ultrasonic pulses are coupled into the component via a suitable probe. To ensure reliable sound transmission, a coupling medium – such as a gel or liquid – is applied between the probe and the component surface.
The coupled sound waves propagate directionally through the material. As long as the material is homogeneous, sound propagation is uniform. However, if the sound pulse encounters an interface with different acoustic properties – such as between the base material and an air pocket, at an internal crack, or at a material separation – part of the sound energy is reflected and sent back to the probe as an echo.
The testing device detects these echoes and displays them as a function of time and amplitude. The position of the reflecting structure within the component can be determined from the measured transit time, since the speed of sound propagation in the respective material is known. The signal amplitude provides information about the size and nature of the defect.
Depending on the inspection task, different testing methods are used. The most common is the pulse-echo technique, in which a single probe both transmits and receives. For certain applications, the through-transmission method can also be used, in which the transmitter and receiver are arranged separately.
This approach allows ultrasonic testing to provide a volumetric examination of the component. In contrast to purely surface-oriented methods, this enables even internal irregularities to be reliably detected and evaluated without mechanically damaging the component.
