Which is the most common form of fixed focusing?

• A. Phased array
• B. Mechanical focusing
• C. Internal focusing
• D. External focusing

Answer: (C)

Fixed focusing means the beam is designed to converge at one specific depth, with no adjustment during imaging. The way this fixed focus is achieved most often is by internal focusing, where the transducer’s own design provides the focusing. The active element itself is shaped or combined with an internal lens so that the waves naturally converge at a predetermined point inside the tissue. This approach is common because it keeps the device compact, robust, and cost-effective—there are no extra external lenses or moving parts to manage. External focusing would require an added lens outside the transducer, and mechanical focusing relies on physical changes to the element or an external component as well; while these can produce a fixed focus, they are less prevalent in everyday transducers. Phased-array designs, on the other hand, use electronic delays to adjust focus dynamically, which is not fixed.