An angle-beam probe sends sound into the steel at an angle. Follow the sound through a 1 inch plate, see why a plain plate gives no echo, compare the skip for three wedges, and find the one place the plate sends the sound back.
Drag the probe along the plate. Change the wedge with the buttons. The probe stays the same; only the wedge changes the angle: the sound leaves the probe at a shallow angle in the wedge and bends (refracts) to the steeper angle as it enters the steel.
Key points
- The angle comes from the wedge. A 45° wedge sends the sound into the steel at 45°; the probe on top can be the same for every wedge.
- Leg 1 runs from the top surface down to the back wall. Leg 2 runs from the back wall back up to the top surface. Where the sound reaches the top surface again is one skip.
- In a 1 inch plate, one skip is 2.000″ with a 45° wedge, 3.464″ with a 60° wedge and 5.495″ with a 70° wedge. The bigger the angle, the flatter the sound travels and the longer the skip.
- In a plate with smooth surfaces and no flaws, the sound zig-zags away from the probe until it dies down due to attenuation. It never comes back: no echo.
- A corner (back wall meeting the end of the plate) sends the sound straight back to the probe. That's a corner trap. You can catch it with leg 1 or, farther back, with leg 2.