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• 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

We are going to explain the reflection of electromagnetic waves (is equivalent for acoustic waves)

B2 中上級

# 立つ（据置）波動レッスン（動画あり (Standing (Stationary) Waves Lesson with Animation)

• 45 0
Weihao Lu に公開 2021 年 01 月 14 日