proximity effect
The proximity effect, like the skin effect, is a phenomenon of current displacement. This phenomenon is based on eddy currents and is limited to closely spaced conductors in which alternating currents flow in opposite directions.
According to the proximity effect, which is particularly pronounced at higher frequencies, high- frequency currents tend to flow as close together as possible. The current flow is concentrated in the area where the two conductors are close together.
The proximity effect can be problematic for conductors and printed circuit boards because their effective conductor cross-section is further restricted. As a result, their AC resistance increases.
The proximity effect also exists as a proximity effect in audio technology for microphones. This effect drastically increases a microphone's sensitivity to low frequencies when it is placed very close to a sound source. It only affects directional microphones. Omnidirectional microphones are immune to it. For cardioid microphones, the proximity effect can be cancelled if the close sound source is placed 90 degrees off-axis.