Beam Deflection of Phased Array Probes
2019-11-26
Industry Information
Beam deflection and sector scanning are important factors to distinguish UT and phased array. And the performance of acoustic beam
deflectionplays an important role in the reliability of phased array inspection.In order to research the effects of frequency and chip size on acoustic
beam diffusion, we use a sound field simulation view to visualize.
The lower the frequency, the greater the diffusion Angle.
The smaller the size, the larger the diffusion Angle
As you can see from the picture above, the method to obtain a beam with a large diffusion angle is to reduce the frequency and
single e lement size. If every single e lement in the phased array is regarded as a conventional ultrasonic probe, the diffusion angle of UT
probe corresponds to the deflection angle of the phased array. By introducing the above conclusion into the phased array, we can get
the factorsthat affect the deflection angle of the phased array, that is,lower frequency and small single e lement size produce larger
diffusion angle.
Limit of Deflection Angle
The industry standard takes -6db as the beam diffusion boundary of phased array probe .Although there are also sound wavesbeyond this boundary, the energy is very weak. In order to compensate for the difference caused by different angle sound beams we
usually use a flaw detector to calibrate the sensitivity before phased array detection .If calibration can be achieved on the instrument, it
indicates that the angle deflection we set is appropriate. If it is difficult to achieve calibration for a large angle direction, or the
signal-to-noise ratio is too low after calibration, it indicates that the angle deflection may be beyond the available range.
Conclusion
The frequency of the phased array probe and transducer size (or pitch) is the main factor affecting the deflection angle. When testing a
thin plate weld or thin-wall tube weld, we usually use the oblique incidence of the sound beam with large deflection angle to cover the weld
area. A good choice is to select the probe with small size or pitch (0.1≤pitch≤0.5mm). Besides, the method of reducing frequency
is generally not adopted for thin-wall welds, because reducing frequency will affect the detection ability of minor defects.
