Ultrasonic Transducers, contact dual element
Dual crystal probes are a special class of transducers. Mostly, one element transmits, the other receives. There is an area where the beam of both elements overlap, which makes the probe selection dependent on the application at hand.
To increase signal to noise ratio, probes with seperate transmitter and receiver are used (for example TRL-probes or TRT-probes).
Tandems are also an example of dual crystal probes. Information about tandems can be found under Specials.
Inspection of materials with high material scattering (for example: coarse grained austenitic materials) can be done with probes which use longitudinal waves.
High angled longitudinal wave probes are able to generate creeping waves. High angled transversal wave probes generate Rayleigh waves. Creeping waves and Rayleigh waves can be used for the detection of (near-)surface defects.
These probes are available in frequencies from 0,5 to 15MHz, with bandwidth low, medium or high. All designs of housings are possible as long as all necessary components will fit in.