电磁驻波

Standing electromagnetic waves form when an incident electromagnetic wave strikes a perfect conductor and reflects back. The superposition of the incident and reflected waves, which travel in opposite directions with equal amplitude and frequency, creates the standing wave pattern. This is analogous to standing waves formed on a stretched string.

The electric field must be zero everywhere on and inside a perfect conductor's surface. The incident wave induces oscillating currents on the conductor, generating an additional electric field that cancels the incident field. The vector sum of these fields results in zero net electric field at the conductor.

Nodes are points where the magnitudes of electric or magnetic fields are zero, forming nodal planes. Antinodes are points where field amplitude reaches maximum positive or negative displacement. In standing electromagnetic waves, electric field nodes coincide with magnetic field antinodes, and vice versa.

The total electric field follows a sine function while the total magnetic field follows a cosine function in standing electromagnetic waves. This 90-degree phase difference contrasts with traveling waves, where electric and magnetic fields are in phase. The phase offset means maximum electric field occurs where magnetic field is zero.

The superposition principle states that the total electromagnetic field at any point is the vector sum of incident and reflected wave fields. Both electric and magnetic fields obey this principle independently. This allows incident and reflected waves to combine and generate standing wave patterns with distinct nodal and antinodal regions.

The reflected wave has the same frequency and amplitude as the incident wave but travels in the opposite direction. When a linearly polarized electromagnetic wave strikes a perfect conductor, the induced surface currents produce this reflected wave. The two waves together create the standing wave through their superposition.

Antinodal planes are located midway between any two adjacent nodal planes, representing regions of maximum field amplitude. At these planes, the electric field reaches its maximum positive or negative displacement. Antinodal planes for the electric field coincide with nodal planes for the magnetic field.