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- since 1996 -
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Technical Discussions
manish
manish
07:39 Jul-30-2008
Sensitivity in UT

I want more details about sensitivity in UT.

we know that ( S = 1/2 lambda)
any supporting information / explaination about it will help me in understanding the equation better.

Thank you.




 
 Reply 
 
tj
tj
03:41 Jul-31-2008
Re: Sensitivity in UT
----------- Start Original Message -----------
: I want more details about sensitivity in UT.
: we know that ( S = 1/2 lambda)
: any supporting information / explaination about it will help me in understanding the equation better.
: Thank you.
------------ End Original Message ------------

Manish,

When you increase your test frequency you also decrease your wavelength. Smaller wavelength can detect smaller discontinuities. Your wavelength will also change with mode type and medium traveled.


 
 Reply 
 
Nathan
Nathan
04:05 Jul-31-2008
Re: Sensitivity in UT
----------- Start Original Message -----------
: I want more details about sensitivity in UT.
: we know that ( S = 1/2 lambda)
: any supporting information / explaination about it will help me in understanding the equation better.
: Thank you.
------------ End Original Message ------------

I am not too familiar with the sensitivity equation, but you asked for an explanation about it. I am assuming S = sensitivity. Lambda usually is the wavelength of the sound wave. The wavelength is inversely proportional to the frequency of the sound wave by lambda = a/nu where a is the speed of sound of the medium and nu is the frequency.

Therefore, S = a/(2*nu) which makes sense if the speed of sound in the medium goes up (or the more dense the medium) the higher the sensitivity needs to be. Conversely, the higher the frequency, the lower the sensitiviy needs to be.

If lambda in this case is not wavelength, please disregard this message, but usually when ultrasound and sound waves are discussed, lambda is the wavelength. I hope this helps.


 
 Reply 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 161

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
161
06:18 Jul-31-2008
Re: Sensitivity in UT
I was taught S = 1/2 lambda about 40 years ago, and it was probably about right with the equipment we had available then. It means that the smallest defect you can expect to detect is one with a dimension (length or diameter) equal to one half of the wave length in the test material at the test frequency used. The reasoning behind this has to do with constructive/destructive interference at 1/4 and 1/2 wavelength and can be found in some training material. Since there is no such thing as operating at just one single frequency this could only be an approximation. The actual limit is quite different for different types of techniques and can be less than 1/10 wavelength for some immersion tests with a focused transducer. It can be limited by "noise" reflections from some grain structures. When it is really necessary to know the smallest detectable reflector the only way to estimate this is with a range of reference reflector (FBH, Side-drilled hole, notch) sizes. And always remember that the smallest thing you can find is larger than the largest defect you might miss.--

--------- Start Original Message -----------
: : I want more details about sensitivity in UT.
: : we know that ( S = 1/2 lambda)
: : any supporting information / explaination about it will help me in understanding the equation better.
: : Thank you.
: I am not too familiar with the sensitivity equation, but you asked for an explanation about it. I am assuming S = sensitivity. Lambda usually is the wavelength of the sound wave. The wavelength is inversely proportional to the frequency of the sound wave by lambda = a/nu where a is the speed of sound of the medium and nu is the frequency.
: Therefore, S = a/(2*nu) which makes sense if the speed of sound in the medium goes up (or the more dense the medium) the higher the sensitivity needs to be. Conversely, the higher the frequency, the lower the sensitiviy needs to be.
: If lambda in this case is not wavelength, please disregard this message, but usually when ultrasound and sound waves are discussed, lambda is the wavelength. I hope this helps.
------------ End Original Message ------------




 
 Reply 
 
T.J
T.J
02:43 Aug-01-2008
Re: Sensitivity in UT
Sensitivity for a circular reflector is Lambda/2(usual in case of side drilled holes which is a circular reflector), with respect to Linear reflectors it can be upto Lambda/6 to L/10.




 
 Reply 
 

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