Phased array ultrasonics (PA) is an advanced method of ultrasonic testing that has applications
in medical imaging and industrial nondestructive testing. Common applications are
to noninvasively examine the heart or to find flaws in manufactured materials such as welds. Singleelement (non-phased array) probes, known technically as monolithic probes, emit a beam in a fixed
direction. To test or interrogate a large volume of material, a conventional probe must be physically
scanned (moved or turned) to sweep the beam through the area of interest. In contrast, the beam
from a phased array probe can be focused and swept electronically without moving the probe. The
beam is controllable because a phased array probe is made up of multiple small elements, each of
which can be pulsed individually at a computer-calculated timing. The term phased refers to the
timing, and the term array refers to the multiple elements. Phased array ultrasonic testing is based
on principles of wave physics, which also have applications in fields such as optics and
electromagnetic antennae.
Contents
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1Principle of operation
2Phased array use in the industry
3Features of phased array
4Standards
5See also
6References
7Books
8External links
Principle of operation[edit]
The PA probe consists of many small ultrasonic transducers, each of which can be pulsed
independently. By varying the timing, for instance by making the pulse from each transducer
progressively delayed going up the line, a pattern of constructive interference is set up that results in
radiating a quasi-plane ultrasonic beam at a set angle depending on the progressive time delay. In
other words, by changing the progressive time delay the beam can be steered electronically. It can
be swept like a search-light through the tissue or object being examined, and the data from multiple
beams are put together to make a visual image showing a slice through the object.
Phased array use in the industry[edit]
Phased array is widely used for nondestructive testing (NDT) in several industrial sectors, such
as construction, pipelines, and power generation. This method is an advanced NDT method that is
used to detect discontinuities i.e. cracks or flaws and thereby determine component quality. Due to
the possibility to control parameters such as beam angle and focal distance, this method is very
efficient regarding the defect detection and speed of testing.[1] Apart from detecting flaws in
components, phased array can also be used for wall thickness measurements in conjunction
with corrosion testing.[2][3] Phased array can be used for the following industrial purposes:
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Inspection of welds[4]
Thickness measurements
Corrosion inspection
PAUT Validation/Demonstration Blocks[5]
Rolling stock inspection (wheels and axles)
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PAUT & TOFD Standard Calibration Blocks
Features of phased array[edit]
At a construction site, a technician tests a pipeline weld for defects using an ultrasonic phased array
instrument. The scanner, which consists of a frame with magnetic wheels, holds the probe in contact with the
pipe by a spring. The wet area is the ultrasonic couplant that allows the sound to pass into the pipe wall.
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The method most commonly used for medical ultrasonography.
Multiple probe elements produce a steerable and focused beam.[6]
Focal spot size depends on probe active aperture (A), wavelength (λ) and focal length
(F).[7] Focusing is limited to the near field of the phased array probe.
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Produces an image that shows a slice through the object.
Compared to conventional, single-element ultrasonic testing systems, PA instruments and
probes are more complex and expensive.
In industry, PA technicians require more experience and training than conventional UT
technicians.