Which component is positioned in front of the PZT at the face of the transducer?

Which component is positioned in front of the PZT at the face of the transducer?

• A. Case
• B. Electrical shield
• C. Matching layer
• D. Acoustic insulator

Answer: (C)

The key idea is impedance matching between the crystal and the body. The PZT crystal has a much higher acoustic impedance than tissue, so a matching layer placed directly in front of the PZT serves as an intermediary that bridges that impedance gap. This layer reduces reflections at the crystal–tissue boundary, allowing more ultrasound energy to enter the body and improving both transmission efficiency and bandwidth, which leads to a stronger, clearer image. It’s typically a quarter-wavelength thick at the center frequency to optimize energy transfer. The other components serve different roles—case encloses the transducer, the electrical shield reduces interference, and the acoustic insulator dampens backward vibrations—whereas the matching layer’s purpose is specifically to match impedances at the face.

The key idea is impedance matching between the crystal and the body. The PZT crystal has a much higher acoustic impedance than tissue, so a matching layer placed directly in front of the PZT serves as an intermediary that bridges that impedance gap. This layer reduces reflections at the crystal–tissue boundary, allowing more ultrasound energy to enter the body and improving both transmission efficiency and bandwidth, which leads to a stronger, clearer image. It’s typically a quarter-wavelength thick at the center frequency to optimize energy transfer. The other components serve different roles—case encloses the transducer, the electrical shield reduces interference, and the acoustic insulator dampens backward vibrations—whereas the matching layer’s purpose is specifically to match impedances at the face.