Which of the following affects the amplitude of ultrasonic signals?

The amplitude of ultrasonic signals is significantly influenced by the grain size of the material being tested. When the grain size of a material increases, it can lead to a reduction in the amplitude of the ultrasonic signals due to increased scattering and attenuation. Larger grain sizes can cause the ultrasonic waves to be scattered in different directions rather than traveling through the material uniformly. This scattering diminishes the intensity or amplitude of the reflected signals received by the transducer.

In comparison, changing the frequency or using a longer transducer may influence other aspects of the ultrasonic inspection, such as resolution or penetration depth, but they do not directly relate to how the amplitude of the signal is affected in the same way. Additionally, the angle of incidence might affect the intensity of the wave entering the material and could alter the path, but it generally does not have the same profound impact on amplitude as grain size does. Thus, understanding the relationship between grain size and signal amplitude is key in ultrasonic testing assessments.