The matching layer thickness is equal to what fraction of the wavelength?

The matching layer thickness is equal to what fraction of the wavelength?

• A. 1/4
• B. 1/2
• C. 1
• D. 3/4

Answer: (A)

The matching layer acts as a quarter-wavelength transformer. Its job is to bridge the impedance gap between the piezoelectric crystal and the tissue, so more of the ultrasound energy reaches the tissue instead of being reflected back. If the matching layer thickness is one-quarter of the wavelength in that layer, the reflections from its outer and inner surfaces are 180 degrees out of phase and cancel each other out. This minimizes reflections at the interfaces and maximizes transmission into the tissue. The wavelength here is in the matching layer material, so the thickness is t = λ/4 = c_m / (4f), where c_m is the speed of sound in the matching layer and f is the frequency. Thus, the thickness is one-quarter of the wavelength.

The matching layer acts as a quarter-wavelength transformer. Its job is to bridge the impedance gap between the piezoelectric crystal and the tissue, so more of the ultrasound energy reaches the tissue instead of being reflected back.

If the matching layer thickness is one-quarter of the wavelength in that layer, the reflections from its outer and inner surfaces are 180 degrees out of phase and cancel each other out. This minimizes reflections at the interfaces and maximizes transmission into the tissue. The wavelength here is in the matching layer material, so the thickness is t = λ/4 = c_m / (4f), where c_m is the speed of sound in the matching layer and f is the frequency.

Thus, the thickness is one-quarter of the wavelength.