Which factor is designed to minimize reflection at the crystal-tissue interface?

• A. A Matching Layer
• B. B Backing Material
• C. C Housing
• D. D Cooling System

Answer: (A)

Minimizing reflection at the crystal-tissue interface relies on acoustic impedance matching. When ultrasound hits a boundary where the impedances differ, part of the energy reflects back and part transmits forward; a larger mismatch means more reflection and less energy enters tissue. The matching layer provides a bridge between the crystal and tissue, with an impedance between the two so the transition is smoother. This reduces the reflection coefficient and increases transmitted energy, improving sensitivity and image quality. In practice, the matching layer is designed so its impedance is near the geometric mean of the crystal and tissue, and its thickness is often a quarter of the center wavelength to maximize transmission at the operating frequency. The backing material’s role is to damp the crystal’s vibrations to shorten the pulse, not to reduce boundary reflection, and the housing or cooling system mainly support protection and thermal management rather than interface impedance matching.