Ultrasonic Phased Array Technology Introduction
Many people are familiar with the medical applications of ultrasonic imaging, in which high frequency sound waves are used to create highly detailed cross-sectional pictures of internal organs. Medical sonograms are commonly made with specialized multi-element transducers known as phased arrays and their accompanying hardware and software. But the applications of ultrasonic phased array technology are not limited to medical diagnosis. In recent years, phased array systems have seen increasing use in industrial settings to provide new levels of information and visualization in common ultrasonic tests that include weld inspection, bond testing, thickness profiling, and in-service crack detection. This paper provides a brief introduction to how phased array systems work and how they can be employed in industrial ultrasonic nondestructive testing.
What is a phased array system?
Conventional ultrasonic transducers for NDT commonly consist of either a single active element that both generates and receives high frequency sound waves, or two paired elements, one for transmitting and one for receiving. Phased array probes, on the other hand, typically consist of a transducer assembly with from 16 to as many as 256 small individual elements that can each be pulsed separately. These may be arranged in a strip (linear array), a ring (annular array), a circular matrix (circular array), or a more complex shape. As is the case with conventional transducers, phased array probes may be designed for direct contact use, as part of an angle beam assembly with a wedge, or for immersion use with sound coupling through a water path. Transducer frequencies are most commonly in the range from 2 MHz to 10 MHz. A phased array system will also include a sophisticated computer-based instrument that is capable of driving the multi-element probe, receiving and digitizing the returning echoes, and plotting that echo information in various standard formats. Unlike conventional flaw detectors, phased array systems can sweep a sound beam through a range of refracted angles or along a linear path, or dynamically focus at a number of different depths, thus increasing both flexibility and capability in inspection setups.