The strength of the received signal from a specular reflector depends on two factors?

• A. Difference in acoustic impedance and angle of incidence.
• B. Difference in acoustic velocity and interface size.
• C. Angle of incidence and tissue temperature.
• D. Difference in acoustic velocity and motion of reflector.

Answer: (A)

In a specular (mirror-like) reflection, the amount of energy that returns to the transducer is shaped by two things: how strongly the boundary reflects sound, and the direction in which that reflection is sent.

First, the strength of the reflection is governed by the acoustic impedance difference between the two media. Acoustic impedance Z is the product of density and speed of sound (Z = ρc). A larger mismatch between Z1 and Z2 produces a larger reflection coefficient, so more of the incident energy is reflected back toward the transducer.

Second, the angle of incidence determines how that reflected energy is oriented. For a smooth surface, the angle of reflection equals the angle of incidence, so the geometry dictates how much of the reflected energy travels back toward the transducer. If the beam strikes at a steeper angle, less energy returns to the transducer, reducing the received signal, even if the impedance difference is the same.

Thus, the two factors are difference in acoustic impedance and angle of incidence.