The matching layer ______ reflections at the PZT/skin boundary, thereby ______ the percentage of transmitted sound.

The matching layer ______ reflections at the PZT/skin boundary, thereby ______ the percentage of transmitted sound.

• A. Increases; Decreasing
• B. Decreases; Increasing
• C. Decreases; Decreasing
• D. Increases; Increasing

Answer: (B)

The matching layer works by impedance matching to reduce boundary reflections and increase transmission. At the PZT/skin interface, PZT has a much higher acoustic impedance than tissue, so a large portion of the ultrasound energy is reflected back and less enters the skin. Placing a matching layer between them provides an intermediate impedance, smoothing the transition and shrinking the impedance difference at the boundary. With less mismatch, the reflection is reduced and more sound energy is transmitted into the skin. So the matching layer decreases reflections and increases the percentage of transmitted sound.

The matching layer works by impedance matching to reduce boundary reflections and increase transmission. At the PZT/skin interface, PZT has a much higher acoustic impedance than tissue, so a large portion of the ultrasound energy is reflected back and less enters the skin. Placing a matching layer between them provides an intermediate impedance, smoothing the transition and shrinking the impedance difference at the boundary. With less mismatch, the reflection is reduced and more sound energy is transmitted into the skin. So the matching layer decreases reflections and increases the percentage of transmitted sound.