Which wave modes propagate through solids?

Which wave modes propagate through solids?

• A. Longitudinal only
• B. Transverse only
• C. Longitudinal, Transverse, and Surface
• D. Surface only

Answer: (C)

In solids, there are three ultrasonic wave modes because the material has both compressive stiffness and shear rigidity, and a boundary can support waves along the surface. Longitudinal waves move particles in the same direction as the travel and involve compression and expansion; they can propagate through the solid (and also through fluids, where shear is not supported). Transverse waves involve particle motion perpendicular to the travel direction and require the solid’s shear strength, so they propagate in solids. Surface waves, like Rayleigh waves, travel along the surface and decay with depth, formed by the interaction of the material’s P and S motions near the boundary. So the waves that propagate through solids are longitudinal, transverse, and surface. While a choice might omit one of these modes, solids inherently support all three, unlike fluids which cannot sustain shear to support transverse waves.

In solids, there are three ultrasonic wave modes because the material has both compressive stiffness and shear rigidity, and a boundary can support waves along the surface. Longitudinal waves move particles in the same direction as the travel and involve compression and expansion; they can propagate through the solid (and also through fluids, where shear is not supported). Transverse waves involve particle motion perpendicular to the travel direction and require the solid’s shear strength, so they propagate in solids. Surface waves, like Rayleigh waves, travel along the surface and decay with depth, formed by the interaction of the material’s P and S motions near the boundary.

So the waves that propagate through solids are longitudinal, transverse, and surface. While a choice might omit one of these modes, solids inherently support all three, unlike fluids which cannot sustain shear to support transverse waves.