An array transducer is simply one that contains a number of separate elements in a single housing, and phasing refers to how those elements are sequentially pulsed. A phased array system is normally based around a specialized ultrasonic transducer that contains many individual elements (typically from 16 to 256) that can be pulsed separately in a programmed pattern. These transducers may be used with various types of wedges, in a contact mode, or in immersion testing. Their shape may be square, rectangular, or round, and test frequencies are most commonly in the range from 1 to 10 MHz.
Phased array systems pulse and receive from multiple elements of an array. These elements are pulsed in such a way as to cause multiple beam components to combine with each other and form a single wave front traveling in the desired direction. Similarly, the receiver function combines the input from multiple elements into a single presentation. Because phasing technology permits electronic beam shaping and steering, it is possible to generate a vast number of different ultrasonic beam profiles from a single probe assembly, and this beam steering can be dynamically programmed to create electronic scans.
This enables the following capabilities:
• Software control of beam angle, focal distance, and beam spot size. These parameters can be dynamically scanned at each inspection point to optimize incident angle and signal-to-noise for each part geometry.
• Multiple-angle inspection can be performed with a single, small, multi-element probe and wedge, offering either single fixed angles or a scan through a range of angles.
• These capabilities provide greater flexibility for inspection of complex geometries and tests in which part geometry limits access.
• Multiplexing across many elements allows motionless high-speed scans from a single transducer position. More than one scan may be performed from a single location with various inspection angles.
Advantages:
Ultrasonic phased array systems can potentially be employed in almost any test where conventional ultrasonic flaw detectors have traditionally been used. Weld inspection and crack detection are the most important applications, and these tests are done across a wide range of industries including aerospace, power generation, petrochemical, metal billet and tubular goods suppliers, pipeline construction and maintenance, structural metals, and general manufacturing. Phased arrays can also be effectively used to profile remaining wall thickness in corrosion survey applications.
The benefits of phased array technology over conventional UT come from its ability to use multiple elements to steer, focus and scan beams with a single transducer assembly. Beam steering, commonly referred to sectorial scanning, can be used for mapping components at appropriate angles. This can greatly simplify the inspection of components with complex geometry. The small footprint of the transducer and the ability to sweep the beam without moving the probe also aids inspection of such components in situations where there is limited access for mechanical scanning. Sectorial scanning is also typically used for weld inspection. The ability to test welds with multiple angles from a single probe greatly increases the probability of detection of anomalies. Electronic focusing permits optimizing the beam shape and size at the expected defect location, as well as further optimizing probability of detection. The ability to focus at multiple depths also improves the ability for sizing critical defects for volumetric inspections. Focusing can significantly improve signal-to-noise ratio in challenging applications, and electronic scanning across many groups of elements allows for C-Scan images to be produced very rapidly.
