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Technical Discussions
Chad
Chad
07:30 Jun-07-2006
Beam Profile

How do you determine beam profile of a transducer?


    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1218

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1218
01:03 Jun-07-2006
Re: Beam Profile
Chad:
The typical contact probe assessment uses an IOW block. It has a series of side drilled holes at varying depths that you direct the beam at and maximise the signal. Mark the block with a pencil line at the exit point of the probe. Then move the probe in a direction perpendicular to the SDH axis until the amplitude drops to a the level you want profiled (typically this is either 6dB or 20dB down). Again, mark the block with a pencil at the exit point that the probe has moved to. Move the probe back to the peak position and then move the probe in the opposite direction until the signal again driops to the desired level with respect to the peaked value and mark the exit point on the block. This series of 3 exit points is repeated for at least 3 of the holes in the IOW block. The results are then usually transferred from the block to a plastic overlay. A good description with images is to be found in J. C. Drury's book "Ultrasonic Flaw Detection for Technicians" (Chapter 16).

Alternatively, for immersion work a motorised data acquisition system can be used to map the entire pressure field.

More information can be found at http://www.ndt.net/article/ginzel/hotchkis/hotchk2.htm

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: How do you determine beam profile of a transducer?
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Neil Burleigh
Sales
Krautkramer Australia Pty Ltd, Australia, Joined Dec 2002, 151

Neil Burleigh

Sales
Krautkramer Australia Pty Ltd,
Australia,
Joined Dec 2002
151
01:57 Jun-08-2006
Re: Beam Profile
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: How do you determine beam profile of a transducer?
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The theoretical formula for the determination of beam spread of a transducer is as follows:

Y = arc sin(K x wavelength/D)

Where
Y is the angle for beam spread from the perpendicular axis of transducer. (2Y gives you the beam spread)
D is the diameter or side (for square or rectangular) of the crystal of the transducer.
K is a constant which is different for which edge of the beam you are trying to determine. See below for examples.
Wavelength is the wavelength of the sound wave in the material. The wavelength is a function of the frequency of the transducer and the velocity of sound in a given material.

Constant K in the determination of beam spread for circular crystals.
K Description
1.22 Infinite edge of beam
1.08 20dB edge in thru transmission mode
0.87 20db edge in pulse echo mode
0.51 6dB edge in pulse echo mode.

Further details can be found in "Ultrasonic Testing of Materials" by the brothers Krautkramer.

Hope this helps
regards

Neil Burleigh


    
 
 
Godfrey Hands
Engineering,
PRI Nadcap, United Kingdom, Joined Nov 1998, 286

Godfrey Hands

Engineering,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
286
00:57 Jun-08-2006
Re: Beam Profile
----------- Start Original Message -----------
: How do you determine beam profile of a transducer?
------------ End Original Message ------------

Chad,
Neil has given you formulae for calculation, and Ed has described how you measure on a standard calibration block for a contact probe. He also suggested motorized mapping for immersion probes.

If you need to test immersion probes, there is a device manufactured by Santec Systems in Illinois which can directly image an immersion beam, almost in real time, and you can set the probe up on the imager and view the beam as the probe is moved towards or away from the imaging screen.
NDT Consultants Ltd. markets this in Europe, but contact Santec directly in the USA.
Regards,
Godfrey Hands



    
 
 

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