Which component is the piezoelectric crystal itself (active element) that, in a simple probe, is coin-shaped and whose dimensions determine the emitted beam?

Which component is the piezoelectric crystal itself (active element) that, in a simple probe, is coin-shaped and whose dimensions determine the emitted beam?

• A. Case
• B. Electrical shield
• C. PZT or Active Element
• D. Matching layer

Answer: (D)

The active element is the piezoelectric crystal itself, the PZT disc. This coin-shaped piece is what actually converts electrical energy into mechanical vibration (and vice versa), and its physical dimensions set the emitted beam. The thickness of the crystal determines the resonant frequency (roughly f ≈ vp/2t, where vp is the wave speed in the crystal), while the diameter mainly influences the beam width and lateral resolution. The front-layer that touches tissue is a separate matching layer, added to improve acoustic impedance matching and bandwidth, not to generate the beam. The case and electrical shield are protective housing and shielding. So the component that is the crystal itself—the active element—is the PZT.

The active element is the piezoelectric crystal itself, the PZT disc. This coin-shaped piece is what actually converts electrical energy into mechanical vibration (and vice versa), and its physical dimensions set the emitted beam. The thickness of the crystal determines the resonant frequency (roughly f ≈ vp/2t, where vp is the wave speed in the crystal), while the diameter mainly influences the beam width and lateral resolution. The front-layer that touches tissue is a separate matching layer, added to improve acoustic impedance matching and bandwidth, not to generate the beam. The case and electrical shield are protective housing and shielding. So the component that is the crystal itself—the active element—is the PZT.