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Technical Discussions
Frederic Brossard
Frederic Brossard
03:31 Mar-14-1999
Optical Beam Deflection method

I'm involved in developing for my thesis a simple and cheap
technology(a dream)to detect small defects in aluminium and
glass samples using laser ultrasound.
The optical beam deflection technique using a laser diode and a
photodiode to monitore the generated lamb waves seems to be the
best adapted but i'm still worried about the advantages of such
technique compared with EMAT.(spatial time domain...)
I'm looking for information/references/advices about OBD and its
performance compared with electromagnetic transducers.
Any assistance to achieve my objective would be greatly appreciated!


 
 Reply 
 
Robert (Rocky) A. Day
Engineering
Milky Way Jewels, USA, Joined Nov 1998, 40

Robert (Rocky) A. Day

Engineering
Milky Way Jewels,
USA,
Joined Nov 1998
40
03:02 Mar-15-1999
Re: Optical Beam Deflection method

The optical beam deflection method is fairly cheap to instrument and reasonably versatile. It usually features a differential technique using two photodiode which are nulled against each other in the quiescent state. When the beam is deflected the diodes are no longer nulled and each reads in opposite sense which increases the signal. I have used the method on surface waves and seen it used in water for bulk waves. Bandwidth is excellent but it is not a high sensitivity method and signal averaging is used in most NDT cases to get a good signal-to-noise ratio. I have put a diagram of a typical beam deflection system on my web site at http://www.xdcr.com/beam.gif

: I'm involved in developing for my thesis a simple and cheap
: technology(a dream)to detect small defects in aluminium and
: glass samples using laser ultrasound.
: The optical beam deflection technique using a laser diode and a
: photodiode to monitore the generated lamb waves seems to be the
: best adapted but i'm still worried about the advantages of such
: technique compared with EMAT.(spatial time domain...)
: I'm looking for information/references/advices about OBD and its
: performance compared with electromagnetic transducers.
: Any assistance to achieve my objective would be greatly appreciated!




 
 Reply 
 
Liviu Singher
R & D,
Technion, Israel, Joined Nov 1998, 11

Liviu Singher

R & D,
Technion,
Israel,
Joined Nov 1998
11
04:46 Mar-25-1999
Re: Optical Beam Deflection method
The optical beam deflection method or otherwise
known also as "optical triangulation" is one of
the less sensitive optical methods to detect
minute displacements. To compare with EMAT, it
is advisable to use an optical interferometric
technique.

: I'm involved in developing for my thesis a simple and cheap
: technology(a dream)to detect small defects in aluminium and
: glass samples using laser ultrasound.
: The optical beam deflection technique using a laser diode and a
: photodiode to monitore the generated lamb waves seems to be the
: best adapted but i'm still worried about the advantages of such
: technique compared with EMAT.(spatial time domain...)
: I'm looking for information/references/advices about OBD and its
: performance compared with electromagnetic transducers.
: Any assistance to achieve my objective would be greatly appreciated!




 
 Reply 
 
Michael Fisch
Michael Fisch
00:41 Jun-11-1999
Re: Optical Beam Deflection method
Hello, i have designed several beam-deflection systems for looking at disk surfaces. My first design was with Robert Bruce back in 1986




 
 Reply 
 

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