where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

KARL DEUTSCH
INSTRUMENTS AND SYSTEMS FOR NON-DESTRUCTIVE TESTING OF MATERIALS
1011 views
Technical Discussions
Stan
NDT Inspector,
Canada, Joined Jan 2009, 31

Stan

NDT Inspector,
Canada,
Joined Jan 2009
31
16:44 Jul-07-2009
PA probe focusing

Hi:
I am hoping that some one will help me out here.
I was taught that with a traditional probe, if focusing is applied to it, the focal point must be less than the distance to the near zone, that is, focusing can only bring the focal point closer to the probe, you cannot focus the probe farther away from the probe than the near zone.
I was also taught that a phased array probe of a given virtual aperture has the same properties as a conventional probe of the same size. To me this implies that the probes focusing properties should be similar to those of a conventional probe, however, perhaps when using the phased array focusing this is not the case. Is it possible to focus a phased array probe farther from the probe than the end of the near zone? If so, what effect does this have on the size of the focal spot? Generally, the farther the focal distance is from the probe, the larger the focal spot size.
Will someone enlighten me here.
Thanks
Stan

 
 Reply 
 
Roger Duwe
NDT Inspector, API-510, 570, 653
MISTRAS, USA, Joined Jan 2009, 148

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
20:21 Jul-07-2009
Re: PA probe focusing
In Reply to Stan at 16:44 Jul-07-2009 (Opening).

A PA probe dows not have the 'same properties' as a conventional 'ducer. The focus depth of the PA 'virtual probe' can be varied based on material thickness, and should be refocused for actual indications found [assuming that the defect was not readily apparant and easily 'diagnosed' during the initial scan]. Additionally, PA is at its best in the nearfield, where conventional shearwave works best past nearfield zone.

The conventional probes that are focused are typically duals or straight-beam. Using PA as a straight scan, without any sectoral sweeping, seems to me like using an elephant gun to hunt mice. It works just fine, but simpler & cheaper methods work just as well.

Where PA 'shines' is with a 32- or 64-element probe, running a sectoral sweep, focused at [or just beyond] anticipated defects and simultaniously scanning for laminations and pitting [or crack tips, scanning at 45 deg's] by using a series of parallel beams generated by a series of 8-to-16 element 'virtual' probes. A linear 64-element transducer can generate up to 49 16-element 'virtual' probes all performing a 'ladder shaped' series of linear scans [64-16, +1]. It is all in "the power of the number of elements"

 
 Reply 
 
TomNelligan
Engineering,
retired, USA, Joined Nov 1998, 390

TomNelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
22:30 Jul-07-2009
Re: PA probe focusing
In Reply to Stan at 16:44 Jul-07-2009 (Opening).

A phased array transducer cannot be focused beyond its near field, and in the case of common square and rectangular probes, focusing occurs in the steering direction only. You can find some further information in the focusing section of our phased array tutorial at

http://www.olympus-ims.com/en/ndt-tutorials/transducers/focusing/

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1300
23:52 Jul-07-2009
Re: PA probe focusing
In Reply to Stan at 16:44 Jul-07-2009 (Opening).

Stan:
There was a thread last month about a similar topic.
http://www.ndt.net/forum/thread.php?admin=&msgID=31403&rootID=8596#31403
The discussion related to where the near field was on a rectangular probe (which most linear phased-array probes used today are duplicating).
The principles involved in focusing are still valid (i.e. only in the near field and the focal spot gets smaller as the focal point is brought closer to the probe). There have been some really nice results (especially for zonal discrimination techniques) whereby the passive aperture axis is curved and the active aperture focused in the normal fashion for a phased-array.
See http://www.ndt.net/article/ecndt2006/doc/Fr.1.1.1.pdf
and http://www.ndt.net/article/panndt2007/papers/146.pdf

 
 Reply 
 

Product Spotlight

Ultrasonic Squirter/Gantry System

TecScan’s NDT Ultrasonic Gantry Systems are industrial Squirter scanners designed for non-destru
...
ctive quality testing and raster scanning of large structures and parts. The Gantry Systems are usually composed of an Industrial Mechanical Scanner and a Control Room with System Workstation.
>

GUL Subsea Solutions - Screeening & Monitoring

To inspect new and existing subsea lines, you need proven technology and experience. GUL offers it's
...
technology to solve this challenge: GUL Subsea and gMAT Transducer Rings.
>

iProbe - USB Phased Array Probe

Turn your PC, Laptop or Tablet into a powerful 32:64 Phased Array system with our USB powered Phas
...
ed Array iProbe and inspection software package. Perform affordable weld inspection and corrosion mapping inspections with this powerful but small system. The probe has a 100V pulser, 8K PRF, dual axis encoder input and achieves outstanding signal quality.
>

IRIS 9000Plus - Introducing the next generation of heat exchanger inspection.

Representing the seventh generation of the IRIS system, the IRIS 9000 Plus has nearly 200 years of c
...
ombined field inspection experience incorporated in its design. This experience combined with a strong commitment to quality and a history of innovation has made Iris Inspection Services® the undisputed leader in IRIS technology.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window