The matching layer's purpose is to improve impedance matching between the crystal and tissue.

• A. True
• B. False
• C. It increases backing
• D. It reduces bandwidth

Answer: (A)

Bridging the gap between the crystal and tissue is the job of the matching layer. The piezoelectric crystal has a much higher acoustic impedance than soft tissue, so when a wave reaches the crystal-tissue boundary, most of its energy would reflect back if nothing were added. The matching layer sits between them and has an intermediate impedance, which reduces the reflection and allows more energy to cross into the tissue. For optimal effect, this layer is typically designed to be about a quarter of a wavelength thick at the transducer’s center frequency, so reflections from its two interfaces interfere in a way that enhances forward transmission.

This is why the statement is true: the primary purpose of the matching layer is to improve impedance matching and energy transfer from crystal to tissue, boosting signal transmission and overall efficiency. The backing layer behind the crystal serves a different function—damping the pulse to widen bandwidth and shorten pulse length—not to improve the crystal-tissue impedance match.