The sound velocity of a shear wave in a given material is usually one-half of a longitudinal wave and about 1.1 times that of a surface wave. The sound velocity through a given material is the distance that sound energy will propagate in that material in a given time and is a function of material density, material's acoustic impedance, and its temperature.īecause sound velocities are relatively high, most expressions are in meters or feet per second. Understanding the variables associated with ultrasonic testing The amplitude of the sound is also higher at its centerline, and it gradually dies down on the outer edges. These calculations use simple centerline of the beam as input the actual application, however, is more complex as the sound beam has width and divergence. This angle of the medium is called First Critical Angle.Īs the incident angle is further increased, the shear angle e also increases until it becomes 90 degrees, and at this point the entire shear wave in the second medium is transformed into the surface wave. This longitudinal angle d also increases until it reaches 90 degrees, and at that point, no more longitudinal waves enter the second medium. We note that, as the incident angle is increased from normal, this results in only the longitudinal wave. Sin a shear / sin c long = Shear velocity in medium - 2 / Longitudinal velocity in medium - 2.