Phased array ultrasonics





Phased Array (PA) ultrasonics is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing, originally pioneered by Albert Macovski of Stanford University. In medicine a common application of phased array is the imaging of the heart (images of the fetus in the womb are usually made by curvilinear array, a multi-element probe that does not actually phase the signals). When applied to steel the PA image shows a slice that may reveal defects hidden inside a structure or weld.

Principle of operation
The PA probe is comprised of many small ultrasonic elements, each of which can be pulsed individually. By varying the timing, for instance by pulsing the elements one by one in sequence along a row, a pattern of interference is set up that results in a beam at a set angle. In other words, the beam can be steered electronically. The beam is 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.

Features of phased array

 * The method most commonly used for medical ultrasonography.
 * Multiple probe elements produce a steerable, tightly focused, high-resolution beam.
 * Produces an image that shows a slice through the object.
 * Compared to conventional, single-element ultrasonic inspection systems, PA instruments and probes are more complex and expensive.
 * In industry, PA technicians require more experience and training than conventional technicians.

Books

 * Introduction to Phased Array Ultrasonic Technology Applications, R/DTech Inc. (now Olympus NDT), 2004.
 * Automated Ultrasonic Testing for Pipeline Girth Welds, R/DTech Inc. (now Olympus NDT).
 * ASME Boiler and Pressure Vessel Code. American Society Of Mechanical Engineers, 2004. Section V — Nondestructive Examination. [See Article 4 — Ultrasonic Examination Methods for Welds. Para E-474 UT-Phased Array Technique]
 * ASME Code Case 2235-9, Use of Ultrasonic Examination in Lieu of Radiography — Section I and Section VIII, Divisions 1 and 2. American Society Of Mechanical Engineers, Approval Date: October 11, 2005. [See page 1, footnote 1 on phased array] (PDF here)