In angle beam ultrasonic testing, how does the refracted energy respond when the incidence angle is varied?

In angle beam ultrasonic testing, how does the refracted energy respond when the incidence angle is varied?

• A. It changes direction according to Snell's Law
• B. It changes the wavelength but not direction
• C. It remains along the interface
• D. It disappears

Answer: (D)

In angle beam ultrasonic testing, the direction of the refracted energy follows Snell’s law. When the wave crosses from the wedge or couplant into the test material, the path bends so that sin of the incidence angle divided by the wave speed in the first medium equals sin of the refracted angle divided by the wave speed in the second medium. So, as you adjust the incidence angle, the refracted angle in the test material changes accordingly, keeping the frequency the same. The wavelength in the test material is set by the material’s speed and the wave’s frequency (lambda = v2/f), so it does not stay constant while the angle changes — it changes with the material, not with the incidence angle. The idea that the refracted energy would change wavelength but not direction isn’t correct. The only situation where you don’t get a propagating refracted beam is when the incidence angle exceeds the critical angle for the boundary, in which case the transmitted energy becomes evanescent and is effectively not propagating into the bulk. In normal operation within propagating angles, the refracted energy clearly changes direction according to Snell’s law.

In angle beam ultrasonic testing, the direction of the refracted energy follows Snell’s law. When the wave crosses from the wedge or couplant into the test material, the path bends so that sin of the incidence angle divided by the wave speed in the first medium equals sin of the refracted angle divided by the wave speed in the second medium. So, as you adjust the incidence angle, the refracted angle in the test material changes accordingly, keeping the frequency the same. The wavelength in the test material is set by the material’s speed and the wave’s frequency (lambda = v2/f), so it does not stay constant while the angle changes — it changes with the material, not with the incidence angle. The idea that the refracted energy would change wavelength but not direction isn’t correct. The only situation where you don’t get a propagating refracted beam is when the incidence angle exceeds the critical angle for the boundary, in which case the transmitted energy becomes evanescent and is effectively not propagating into the bulk. In normal operation within propagating angles, the refracted energy clearly changes direction according to Snell’s law.