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Phased Array

- History


Phased Array Ultrasonic technology moved from the medical field to the industrial sector at the beginning of the 1980s. By the mid-1980s, piezocomposite materials were developed and made available in order to manufacture complex shaped phased array probes.


By the beginning of the 1990s, phased array technology was incorporated as a new NDE method in ultrasonic handbooks and training manuals for engineers. The majority of the applications from 1985 to 1992 were related to nuclear pressure vessels (nozzles), large forging shafts, and low-pressure turbine components.


- Principle


The Phased Array concept concerns multi-element transducers. Each element of these transducers is connected to a different electronic channel, either directly or through multiplexers, according to electronic device performances.

Each element can be activated or not for each shot. The size and the location of the active aperture of a phased array transducer depends on the activated elements.

An electronic delay can be applied to each electronic channel when emitting and receiving the signal to/from the transducer elements. The setup corresponding to all the delays of a given shot is called Delay Law. Each delay law defines a different acoustic beam with particular direction, focusing distance and lateral resolution.

This technique requires probes with very low acoustic and electric cross coupling  between the elements, so that all the elements could be fired independently.


Electronic Scanning


The beam is electronically translated by alternatively firing a given number of elements of a linear or circular array phased array transducer. This technique is an alternative to mechanical translation of a single element probe


The advantages are
    - Faster inspection
    - No mechanical movement required, or reduction of scan line number
    - Possibility of combining with electronic focusing and beam steering


Beam Focusing


The beam is electronically focused by applying symmetrical delay laws to the different elements of a linear or annular phased array transducer. This technique is an alternative to using several transducers to focus at different depths.


The advantages are
    - Only one probe can focus at each depth
    - Faster inspection of complete volume of thick pieces with dynamic focusing
    - Electronic focusing can compensate focusing aberrations due to cylindrical interfaces


Beam Steering


The beam is electronically deflected by applying delay laws to different elements of a linear, circular or matrix array. Linear and circular arrays allow for 2D beam steering, while matrix arrays allow for 3D beam steering. This technique is an alternative to using different angled transducers.


The advantages are
    - Only one transducer required for inspection at variable angle
    - Faster inspection of complex geometry pieces
    - The advantage of this technique can be combined with the advantages of electronic focusing