Phased array ultrasonics

From Wikipedia, the free encyclopedia

Principle of operation of phased array (PA). The PA probe consists of many small elements, each of which can be pulsed separately. In the figure the element on the right is pulsed first, and emits a pressure wave that spreads out like a ripple on a pond (largest semi-circle). The second to right element is pulsed next, and emits a ripple that is slightly smaller than the first because it was started later. The process continues down the line until all the elements have been pulsed. The multiple waves add up to one single wave front travelling at a set angle. In other words, the beam angle can be set just by programming the pulse timings.
Principle of operation of phased array (PA). The PA probe consists of many small elements, each of which can be pulsed separately. In the figure the element on the right is pulsed first, and emits a pressure wave that spreads out like a ripple on a pond (largest semi-circle). The second to right element is pulsed next, and emits a ripple that is slightly smaller than the first because it was started later. The process continues down the line until all the elements have been pulsed. The multiple waves add up to one single wave front travelling at a set angle. In other words, the beam angle can be set just by programming the pulse timings.
Weld examination by phased array. TOP: The phased array probe emits a series of beams to flood the weld with sound. BOTTOM: The flaw in the weld appears as a red indication on the instrument screen.
Weld examination by phased array. TOP: The phased array probe emits a series of beams to flood the weld with sound. BOTTOM: The flaw in the weld appears as a red indication on the instrument screen.

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.[1] 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.

Contents

[edit] Principle of operation

The PA probe consists 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.

[edit] 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.
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.
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.

[edit] Further reading

[edit] External links

[edit] Books

[edit] See also

[edit] References

  1. ^ Inventor of the Week: Albert Macovski, Medical Imaging Systems. web.mit.edu/invent (2000-08). Retrieved on 2007-03-11.