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Technical Discussions
bram desmet
bram desmet
02:31 Oct-26-2000
ultrasonic sound refraction

A question: does sound have a perfect reflection when the attack angle to a surface becomes to big, just like light(according to the refraction law of Snellius-Descartes)?


 
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Michael Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 141

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
141
06:50 Oct-26-2000
Re: ultrasonic sound refraction
: A question: does sound have a perfect reflection when the attack angle to a surface becomes to big, just like light(according to the refraction law of Snellius-Descartes)?

My answer would be no. Your post is titled ultrasonic sound refraction but your question is regarding perfect reflection.

With reflection the surface roughness is one factor to be considered, rougher surfaces widen the sound wave front resulting in a loss of energy.

With refraction different modes of propagation (in a solid) can occur ie surface, longitudal, shear which all have different velocities. Now the velocities for the refracted into the material are different from what is transmitted in there fore energy loss occurs.

So in both cases it cannot be perfect, even if light was put on a mirror a perfect mirror does not exist.

If I may can I ask you a question? Where did you find the reference to Snellius-Descartes? This topic was broached here a long time ago as some text I saw stated the law we commonly call Snell’slaw was actually prescribed by Descartes first. Snellius was doing similar research but expressed his formula differently.


Kindest Regards

Michael Trinidad





 
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bram desmet
bram desmet
03:08 Oct-26-2000
Re: ultrasonic sound refraction
At our University, the law "sin a1/sina2 = c1/c2" is commonly known as the law of "Snellius-Descartes". I should ask my professor, why he calls it that way.

Concerning my question now. If we consider a perfectly smooth surface, above a certain angle of attack, called Bragg's angle (which depends from the two sound speeds, or refraction modulifor light), this equation isn't valuable anymore, because it would cause one of the two sinusses in the formula to be bigger than one. In terms of light, we then have perfect reflection. But what with sound. Does it have the same effect?


 
 Reply 
 
Michael Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 141

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
141
07:45 Oct-27-2000
Re: ultrasonic sound refraction
: At our University, the law "sin a1/sina2 = c1/c2" is commonly known as the law of "Snellius-Descartes". I should ask my professor, why he calls it that way.

: Concerning my question now. If we consider a perfectly smooth surface, above a certain angle of attack, called Bragg's angle (which depends from the two sound speeds, or refraction modulifor light), this equation isn't valuable anymore, because it would cause one of the two sinusses in the formula to be bigger than one. In terms of light, we then have perfect reflection. But what with sound. Does it have the same effect?

Ok the law we use for Ultrasonic testing is what we call Snell's law "sin a1/sina2 = v1/v2" 'v' being the velocity of sound in the material.

Strange enough the ASNT hanbook does not mention Braggs law for either UT (Ultrasonic Testing) or VT (Visual Testing), it does mention Braggs law in the RT (Radiographic Testing) section. I did find a reference to Knott's Equation which is stated to be used additionally to Snell's law for reflected ultrasonic shear waves. I hope this may be of some use to you.

Kindest Regards

Michael Trinidad




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

Liviu Singher

R & D,
Technion,
Israel,
Joined Nov 1998
11
09:21 Oct-29-2000
Re: ultrasonic sound refraction
Regarding perfect reflection, sound will behave exactly the same as does light, meaning that for certain values of velocity, and about a certain angle, you get "perfect reflection". There are two differences though:
(1) The terms usually used are different than the one you presented (with light as well). "Perfect reflection" is known as "Total Reflection" and the "Bragg angle" is knows as "Critical angle".
(2)In sound, compared with light, there are two critical angles, one for the L wave and one for the T wave.

Hope that helps.

Liviu Singher


: At our University, the law "sin a1/sina2 = c1/c2" is commonly known as the law of "Snellius-Descartes". I should ask my professor, why he calls it that way.

: Concerning my question now. If we consider a perfectly smooth surface, above a certain angle of attack, called Bragg's angle (which depends from the two sound speeds, or refraction modulifor light), this equation isn't valuable anymore, because it would cause one of the two sinusses in the formula to be bigger than one. In terms of light, we then have perfect reflection. But what with sound. Does it have the same effect?




 
 Reply 
 
alanktop
alanktop
02:38 Apr-16-2001
Re: ultrasonic sound refraction
hiii, i wanna know much about this topics, where i can find free books


 
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