Of the piezoelectric materials listed below, the most efficient sound receiver is:

• A. Quartz
• B. Barium titanate
• C. Lithium sulfate
• D. Silver oxide

Answer: (C)

When a piezoelectric receiver picks up an ultrasonic wave, the goal is to maximize how efficiently mechanical pressure turns into an electrical signal. That efficiency comes from the material’s piezoelectric coefficients and how well the crystal converts mechanical energy into charge (the electromechanical coupling) as well as how well its acoustic impedance matches the surrounding medium.

Lithium sulfate stands out because it offers a strong piezoelectric response with relatively low internal losses, which means a given acoustic pressure produces a larger electric signal. In comparison, quartz has excellent stability but a smaller coupling for reception, and barium titanate, while piezoelectric, tends to have higher losses and temperature sensitivity that reduce efficiency in practical usage. Silver oxide isn’t a piezoelectric material, so it can’t function as a piezoelectric receiver.

So, the lithium sulfate crystal provides the best combination of strong coupling and favorable energy transfer for receiving ultrasonic waves among the listed options.