Define "focal depth" in the context of Phased Array Ultrasonic Testing.

Focal depth refers to the specific point within the material where the ultrasound beam is concentrated to provide the highest resolution and sensitivity during inspection. In phased array ultrasonic testing, the transducer array can manipulate the angle and shape of the ultrasound beam through electronic means. By adjusting the array's timing and the excitation of individual elements, the focal depth can be precisely controlled.

This focusing capability enhances the inspector's ability to detect flaws and discontinuities at various depths within the material being examined. The best resolution at this focal point allows for clearer echoes and more accurate measurements of any defects present. Understanding focal depth is crucial because selecting the appropriate focal depth can significantly impact the quality of the inspection results, making it a fundamental concept in phased array ultrasonic testing.