What governs the electronic or linear scanning of a phased array probe?

The correct answer reflects the principle of how phased array technology allows for electronic scanning. When a single focal law is applied consistently across a group of active elements, it enables the generation of a focused ultrasound beam that can be directed at various angles. This process of multiplexing the same focal law across multiple elements is crucial for achieving effective linear scanning without the need for mechanical movement of the probe, providing rapid and accurate inspections.

In the context of phased array systems, using the same focal law means that the ultrasound beam is manipulated electronically, allowing for a more dynamic examination of the material under inspection. It results in a synchronous activation of multiple elements, which enhances the overall efficiency of the scanning process. This approach allows the inspection technician to produce detailed images and gather accurate data from different angles efficiently.

The other choices pertain to different aspects of phased array technology but do not directly relate to the core mechanism of electronic scanning. They involve concepts like varying focal depths or applying different focal laws to different element groups, which are relevant but do not specifically describe the process of using the same focal law across a group of elements for electronic scanning. This highlights the importance of understanding both the overall functionality and the specific mechanisms of phased array technology in ultrasonic testing.