The discussion of ultrasonic refraction and wave transformation

We are so familiar with Snell’s law ,but most of people don’t deeply research why sound beam oblique incidence heterogenous interface will cause refraction?

In neurogen 1,sound beam oblique incidence,in neurogen 2,sound beam reflected,we all know transverse wave is mechanical vibration that direction of the particle vibration vertical to direction of sound waves.Particle A we can isolate a “horizontal force”to cause transverse shift,a “longitudinal force”causes longitudinal shift,to show movement of particle A.When sound beam up to medium 2,due to longitudinal modulus of medium 2 and transverse modulus don’t equal to medium 1,to be precise,the two materials don’t have same NUXY ,lead transverse deviation of particle B is lower than particle A,and longitudinal deviation is bigger than particle A.So motion curve of particle B is not parallel to particle A,so it will happen reflect.