Which method of fixed focusing uses a curved active element?

Which method of fixed focusing uses a curved active element?

• A. External Focusing
• B. Dynamic Focusing
• C. Internal Focusing
• D. Acoustic Lens Focusing

Answer: (C)

Fixed focusing relies on shaping the emitted wavefront so it converges to a single point. When the active element itself is curved, its surface acts like a built‑in lens: the curvature imposes a varying phase across the aperture so all parts of the wavefront travel toward the same focal point. The result is a converging beam with a fixed focal depth determined by the element’s curvature. This built‑in curvature is why this method is called Internal Focusing. External focusing would require a separate lens in front of the element, and acoustic lens or dynamic focusing involve additional components or electronic delay, respectively.

Fixed focusing relies on shaping the emitted wavefront so it converges to a single point. When the active element itself is curved, its surface acts like a built‑in lens: the curvature imposes a varying phase across the aperture so all parts of the wavefront travel toward the same focal point. The result is a converging beam with a fixed focal depth determined by the element’s curvature. This built‑in curvature is why this method is called Internal Focusing. External focusing would require a separate lens in front of the element, and acoustic lens or dynamic focusing involve additional components or electronic delay, respectively.