In radio frequency (RF) bands, eddy currents, induced by changing magnetic fields, exhibit distinct behaviors impacting various applications. The skin effect is prominent, causing eddy currents to concentrate near the surface of conductive materials at higher frequencies. This phenomenon affects the depth of penetration and leads to increased resistive losses and surface heating. For instance, in RF induction heating, eddy currents generated in a metal object heat its surface efficiently due to the skin effect. Additionally, conductive materials can act as shields against RF electromagnetic fields by inducing eddy currents that counteract the incoming radiation. However, these currents can also lead to RF losses in materials, affecting signal transmission and component performance. Proper design considerations, material selection, and safety measures are imperative to harness the beneficial aspects of eddy currents and mitigate their potential drawbacks in RF systems.

Eddy currents in radio frequency bands (from some hundreds of MHz) exhibit the following behaviors:

• The skin effect is prominent. This means that eddy currents tend to concentrate near the surface of conductive materials at higher frequencies. This is because the resistance of a conductor to AC current increases with frequency, and the skin depth (the depth at which the eddy currents have decayed to 1/e of their surface value) decreases with frequency.
• The eddy current losses increase. This is because the eddy currents are concentrated in a smaller volume, and the resistance of the material is higher at higher frequencies.
• The eddy currents can cause heating. This is because the eddy currents dissipate their energy as heat in the material.
• The eddy currents can be used for a variety of applications, such as induction heating, non-destructive testing, and electromagnetic shielding.

Here are some specific examples of how eddy currents are used in radio frequency bands:

• Induction heating: Induction heating is a process that uses eddy currents to heat conductive materials. A radio frequency coil is placed near the material, and an alternating current is applied to the coil. The alternating current creates a changing magnetic field, which induces eddy currents in the material. The eddy currents heat the material by Joule heating.
• Non-destructive testing: Non-destructive testing (NDT) is a method of inspecting materials for defects without damaging them. Eddy current testing is a type of NDT that uses eddy currents to detect defects in conductive materials. A radio frequency coil is placed near the material, and an alternating current is applied to the coil. The alternating current creates a changing magnetic field, which induces eddy currents in the material. The eddy currents are disturbed by defects in the material, which can be detected by the coil.
• Electromagnetic shielding: Electromagnetic shielding is a method of preventing electromagnetic radiation from entering or leaving a space. Conductive materials can be used to shield electromagnetic radiation. When an electromagnetic wave encounters a conductive material, the wave induces eddy currents in the material. These eddy currents dissipate the energy of the wave, preventing it from passing through the material.

Eddy currents can be a beneficial or harmful phenomenon, depending on the application. In some cases, they can be used to create useful effects, such as induction heating and non-destructive testing. In other cases, they can cause unwanted effects, such as heating and electromagnetic interference. It is important to consider the behavior of eddy currents when designing and using radio frequency systems.