Question

Among the piezoelectric materials, PZT crystals show better electro-mechanical conversion efficiency than Quartz crystals upto a frequency of about:

• A. \( 15 \text{ MHz} \)
• B. \( 25 \text{ MHz} \)
• C. \( 25 \text{ kHz} \)
• D. \( 15 \text{ kHz} \)

Hint:

Standard medical imaging operates between \( 2 \text{ MHz} \) and \( 15 \text{ MHz} \), which matches the sweet spot where PZT performs optimally before internal material stress degrades its efficiency.

Answer 1

The Correct Option is A

Concept: Piezoelectric materials convert mechanical stress into electrical energy and vice versa. Lead Zirconate Titanate (PZT) is a synthetic ferroelectric ceramic compound, whereas Quartz is a naturally occurring crystalline form of silicon dioxide.

Step 1: Comparing Material Performance.
PZT possesses a significantly higher coupling coefficient and higher piezoelectric voltage constant compared to Quartz, making it the preferred element for standard medical ultrasound imaging applications. It yields highly efficient electromechanical conversions, providing superb signal sensitivity.

Step 2: Identifying High Frequency Limitations.
As the operating frequency climbs into the high-frequency diagnostic domain (above \( 15 \text{ MHz} \)), synthetic ceramic materials like PZT suffer from sharp rises in internal dielectric losses, microstructural damping, and manufacturing limitations related to cutting fragile, thin ceramic wafers. Up to approximately \( 15 \text{ MHz} \), PZT maintains a dominant, superior conversion efficiency. Beyond this ceiling, alternative materials or single-crystal formulations are required. This satisfies Option (A).