What are the two functions of the matching layer?

• A. Increases the efficiency of sound energy transfer between the active element and the body
• B. Protects the active element
• C. Reduces the impedance mismatch
• D. Increases the efficiency of sound energy transfer between the active element and the body and Protects the active element

Answer: (D)

The matching layer sits between the active element and the body to bridge the large impedance difference between them. By presenting an intermediate acoustic impedance, it reduces reflections at the crystal–layer and layer–tissue interfaces, so more acoustic energy is transmitted into the body. In practice, it’s often designed to be a quarter-wavelength thick at the center frequency, which further enhances forward energy transfer by minimizing boundary reflections. So the two functions are: reducing impedance mismatch and increasing the efficiency of sound energy transfer between the active element and the body. (Protection of the active element is typically provided by a separate protective layer, not the matching layer.)