Acoustic Impedance - Ultrasound Propagation in Tissue

[Jimmy87]

Hi, I was just wondering why, when the acoustic impedance mismatch is so high between two boundaries at an interface, most of the ultrasound is reflected back. I was just wondering why this happens which I can't seem to find much of an answer to. The only thing I can think of is refraction and snells law. For example, if medium 2 has a much higher speed of sound than medium 1 then more of the transmitted wave will bend away from the normal. If the materials have a very big difference then you would get total internal reflection. Is this right or is this completely wrong? What I'm basically trying to say is that when the impedance mismatch is high is the reason why most of it is reflected is because you get total internal reflection of the ultrasound wave due to refraction?

 

[Doug Huffman]

The dominant phenomenon may be absorption.
https://en.wikipedia.org/wiki/Acoustic_impedance

I used US NDT to find the actual liquid level of a 2000 psi steam drum.