In order to provide a reliable reference signal, the flaw used as reference for calibration has to:
- Interact with the beam in a specular or pseudo-specular way
- Be located in the far field if using a non focused probe
- Be located in the focal zone or further if using a focused transducer
- Be lighted by the beam during a bounded time
- Be large enough (wavenumber.radius=k.a>1.5 for a FBH , 1.5<k.a<20 for a SDH).
As soon as they respect this criteria and provided that the corresponding signals are also considered as reliable in the real inspection setup (repeatability, etc.), different type of defect (SDH, FBH, flat surface…) and different ultrasonic modes (P0°, SV45°…) can be considered. In Civa defect response, typically, Ø2 or Ø3 mm SDH reflectors can be used then usually 1.5<k.a<20 as soon as the frequency is higher than 1 MHz.
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