Phased Array Leseprobe

2 Ultrasonic phased array principles and design
2.1 Ultrasonic phased array instruments
Conventional ultrasonic instruments have a single pulser, driving a probe with a single transmit
element. By comparison, phased array instruments have multiple pulsers that drive multiple array
probe transmit elements. The number of elements that can be pulsed simultaneously is a way to
classify phased array instruments. The more pulser channels an instrument has, the more complex
and costly it is to build. Portable phased array instruments typically have 16 or 32 pulser channels
while fixed systems may have 128 channels or more. Instruments with higher channel counts
allow an inspector to configure larger virtual probes, which are more suitable for applications
requiring deeper focusing in the inspection material. A virtual probe is a group of individual array
elements that are pulsed to create the desired acoustic aperture.
Array elements may be pulsed individually or in virtual probe groups to match the ultrasonic
inspection requirements. There are several physical configurations for industrial phased array
probes; the more common ones are discussed in Section 2.4.1, Phased Array Probe Configurations.
Figure 2-1 shows a block diagram of an eight channel phased array instrument. Eight individual
pulsers activate eight array elements. The resulting acoustic wave travels through the test material
and is received by eight separate receiver elements. For simplicity, this example depicts a through
transmission set-up but the same concept applies to pulse echo.
Figure 2-1: Diagram of phased array instrument (through transmission)
2.2 How phased array probes work
Phased array probes have numerous individual acoustic elements. For industrial ultrasonic
inspection, the acoustic elements are typically manufactured from piezocomposite material.
Piezoelectric materials convert electrical energy to mechanical energy and vice versa. A short
duration high voltage pulse is applied to individual elements, which in turn, creates a mechanical
vibration or acoustic wave. When multiple elements are pulsed simultaneously their individual
acoustic waves interfere to generate an ultrasonic sound field that behaves in a manner similar to
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