The proximity effect is a phenomenon observed in conductors, particularly when alternating current (AC) flows through them. It refers to the non-uniform distribution of current within a conductor, resulting from the interaction between the magnetic fields generated by the current and the conductor's geometry. This effect becomes more pronounced as the frequency of the AC increases.
When AC flows through a conductor, it generates a magnetic field around the conductor according to Ampere's law. This magnetic field, in turn, induces currents within the conductor itself, known as eddy currents. The interaction between the original current and the induced eddy currents leads to the proximity effect.
The proximity effect can be explained using the skin effect as a starting point. The skin effect is the tendency of AC to concentrate its current flow near the surface of a conductor, as opposed to distributing it evenly across the entire cross-section of the conductor. This is due to the self-inductance of the conductor, which opposes changes in current flow. At higher frequencies, the skin effect becomes more pronounced, causing the current to flow primarily in the outer layers of the conductor, while the inner portions carry less current.
The proximity effect takes this concept a step further. In addition to the skin effect, the presence of nearby conductors or changes in the shape of the conductor can influence the distribution of current. When multiple conductors are placed close to each other, their magnetic fields interact, causing the current to concentrate more in the regions where the magnetic fields reinforce each other and to decrease in the regions where they oppose each other. This non-uniform distribution of current can lead to higher current density and heating in certain parts of the conductor, potentially causing issues like increased power losses, reduced efficiency, and even overheating.
The proximity effect is particularly important in applications involving high-frequency AC, such as power transmission, transformers, and high-frequency circuitry. Engineers and designers must take this effect into account when designing conductors and circuits to ensure that current distribution remains as uniform as possible to minimize power losses and other undesirable consequences.
In summary, the proximity effect in conductors is a phenomenon where the distribution of AC current becomes non-uniform due to the interaction between the magnetic fields generated by the current and the geometry of nearby conductors. This effect is a result of the skin effect combined with the influence of neighboring conductors and can have significant implications for the performance and efficiency of electrical systems.