When ultrasound waves hit bone, what happens to the wave type according to the material?

When ultrasound waves hit bone, what happens to the wave type according to the material?

• A. Longitudinal waves turn into transverse waves
• B. They pass through unchanged
• C. They reflect completely
• D. They disappear

Answer: (A)

When ultrasound enters bone, the fact that bone is a solid allows it to support both compressional (longitudinal) and shear (transverse) waves. At the interface, especially when the incidence is not perpendicular, the boundary conditions for stress and displacement enable energy to couple from the incoming longitudinal mode into a shear (transverse) mode inside the bone. In other words, the wave type can change from longitudinal to transverse within the material. This mode conversion is a consequence of the solid’s properties and the impedance difference with surrounding tissue. It doesn’t simply pass through unchanged, and it isn’t guaranteed to be completely reflected or disappear—the key idea is that the wave type can convert to a transverse wave in bone.

When ultrasound enters bone, the fact that bone is a solid allows it to support both compressional (longitudinal) and shear (transverse) waves. At the interface, especially when the incidence is not perpendicular, the boundary conditions for stress and displacement enable energy to couple from the incoming longitudinal mode into a shear (transverse) mode inside the bone. In other words, the wave type can change from longitudinal to transverse within the material. This mode conversion is a consequence of the solid’s properties and the impedance difference with surrounding tissue. It doesn’t simply pass through unchanged, and it isn’t guaranteed to be completely reflected or disappear—the key idea is that the wave type can convert to a transverse wave in bone.