We are going to explain the reflection of electromagnetic waves (is equivalent for acoustic waves)
caused by a mismatch on the impedance value of the propagation medium
We suppose an incident wave travelling in the +x axis following a sinusoidal form (blue)
When the incident wave arrives to the end of the medium, we must calculate the reflection coefficient, which depends on the relationship of the two medium impedances.
If this reflection coefficient is equal to -0.35 the reflected wave (red) is going to have an amplitude 0.35 times the amplitude of the incident wave and a phase shift of 180 degrees.
The resulting (total, stationary) wave is the sum of the two waves (green)
Now we animate the two waves and we see what really happens with a set of different reflection coefficients
For a reflection coefficient of -1 all the incident wave is reflected with a phase shift of 180 degrees
This causes that the stationary wave takes value from 0 to 2 times the incident wave peak)
As we can see the positions of the maximums and minimums (nulls) are fixed
For a reflection coefficient of -0.5 half of the incident wave is reflected with a phase shift of 180 degrees
Now the interference of the two waves don't cause nulls and maximums with two times the incident wave peak value
For a reflection coefficient of 0 the mismatch doesn't exist, so there isn't reflected wave and the incident wave is directly the stationary wave (blue and green waves are overlapping)
Of course the maximum value is the same across all the distance
For a reflection coefficient of 0.5 half of the incident wave is reflected with no phase shift between them.
Is equivalent to the -0.5 case. The unique changes are the positions of maximum and minimum values of the stationary wave.
For a reflection coefficient of 1 all the incident wave is reflected with no phase shift between them.
Is equivalent to the -1 case. The unique changes are the positions of maximum and minimum values of the stationary wave.
Thanks for watching