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KARL DEUTSCH
INSTRUMENTS AND SYSTEMS FOR NON-DESTRUCTIVE TESTING OF MATERIALS.

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Technical Discussions
Kwok
Kwok
07:18 Aug-12-2004
Ultrasonic interference, acoustic noise

Are there any publication, to describe a method to eliminate or minimise an unwanted acoutic signal (i.e. Lamb) while maintaining an useful signal (i.e. shear or longitudinal)?


    
 
 
Balachander L
Balachander L
09:30 Aug-13-2004
Re: Ultrasonic interference, acoustic noise
----------- Start Original Message -----------
: Are there any publication, to describe a method to eliminate or minimise an unwanted acoutic signal (i.e. Lamb) while maintaining an useful signal (i.e. shear or longitudinal)?
------------ End Original Message ------------

What kind of structure are you interested in? In general, Lamb modes are generated only if the lateral dimension is comparable to the wavelength of the wave propagating. Is this a spot measurement or are you pulsing between sensors separated by a distance? If its the latter, and you want pure longitudinal or shear waves in such a structure, you need to control your phase velocity (and make sure you are sensitive to high Vp, meaning low Vg... possibly even contact transducers, although source influence effects will have to be looked at) by varying wedge angle etc. You basically get through-thickness resonances, which you can then easily detect by frequency content analysis. Further processing for appropriate signal analysis, of course, is by simple bandpass filtering, ensuring temporal selectivity of received modes. It depends on your test situation.


    
 
 

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