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16:24 Nov-02-2018
First Critical Angle of reflection Formula

Can anyone let me have the velocity formula for first critical angle of reflection? (Not Refraction)

19:21 Nov-02-2018
Re: First Critical Angle of reflection Formula

I am a student, a newbie in this field, and am curious as well. I looked over my notes briefly and was under the impression the velocity was given or determined by the type of material being used and the type of wave. For instance, if I was using steel it would be .230 u/s for compression wave but if I was using a shear wave it is half this amount. If I am wrong or this is not your answer to your problem then I am interested in the velocity formula as well.

20:11 Nov-02-2018
Re: First Critical Angle of reflection Formula

Hi Ed, Probably not explained myself well. We understand refraction but do not appear to address total reflection angles of incidence. Take a steel X to steel Y interface coupled by a water interface with an incident compressional angle A degrees in steel X. As A increases from 0 degrees, there comes an angle of incidence where the compressional beam totally reflects and no energy enters the water and therefore cannot enter the steel Y.

This phenomena is commonly discussed in optics but not in ultrasonics. I am looking for the related formula?

20:23 Nov-02-2018
Re: First Critical Angle of reflection Formula

George,
by imposing 90 ° to the angle of refraction of the shear wave in Snell's equation we obtain the limit incidence angle, beyond which there is no longer a refracted wave but only reflection. If you mean this.
If the interface is water-solid we only have longitudinal wave type reflection; in the solid-solid case the reflection is mixed, that is both longitudinal wave and shear (for angles both follow the snell law).
greetings
mario

10:14 Nov-03-2018
Re: First Critical Angle of reflection Formula

Hi Ed, Thank you for your detailed response. Let me first say I much appreciate what you do here on this forum. Sharing your knowledge, not only for me but for many others as well.
May I further impose on you to use Civa with a 68-degree longitudinal incidence only in the first steel to water interface? I am interested to see what longitudinal energy if any, enters the second steel after the water gap.
I am experimenting practically to locate cross-drilled holes in the second steel after the water gap with a steel 'shoe' on an L probe (The first steel) angled at 68 degrees to give the same 68 degrees L beam in the second steel. In theory, I would expect to obtain a far stronger compressional wave in the second steel then using say an acrylic shoe below the first critical angle of incidence as mode conversion in minimised.

09:51 Nov-05-2018
Re: First Critical Angle of reflection Formula

George,
I misunderstood your post. I do not know how, at the beginning I thought that your request was focused on everything that comes back in reflection between the first and second medium, when there is nothing in refraction. After Ed's simulations I realized that in your second post the request was clearly formulated but for some reason I had continued to keep this initial strangeness in my mind. I apologize for going off topic, what might have been avoided.
Ed, I associate myself so much with the beautiful words of George.
Greetings
Mario

19:02 Nov-05-2018
Re: First Critical Angle of reflection Formula

Ed, It would appear from the Civa simulation that there probably are a lot of reflective losses not shown in the first steel wedge and a much more reduced longitudinal wave in the second steel than apparent from the simulation. As Civa suggests -53dB. But this assumes no losses at the wedge interface. This reinforces the reasons the poor result I had with a physical experiment using a 68-degree steel wedge and an oil couplant. I may be better advised to produce the 68-degree compressional wave in the second steel using an acrylic wedge and live with an accompanying strong shear wave losses producing multiple return echoes. My target is normal to a 68 degreee compressional beam a through a further wetted interface and I can make the path length to coincide with the near field distance at the target interface to maximise compressional transmission. The shear wave noise is being removed by signal processing so my main issue is how well the processor works once I have achieved maximum transmission at the target!
Thank you again for your interest and support.