Tru Physics

Electromagnetic Interference

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Tru Physics
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Introduction

Electromagnetic interference (EMI), also referred to as radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit via electromagnetic radiation or induction. EMI can cause a range of problems, from minor annoyances like a noisy radio signal, to significant malfunctions in critical technology.

Sources of EMI

Electromagnetic interference can be caused by both natural and man-made sources. Natural sources include solar flares and electrical storms, while man-made sources can include electrical circuits, power lines, broadcast towers, and more.

Faraday’s Law

The principle that underlies electromagnetic interference is Faraday’s law of electromagnetic induction, which can be written as:

\varepsilon = - \dfrac{d\Phi_B}{dt}

where \varepsilon is the electromotive force (EMF), and \Phi_B is the magnetic flux. Essentially, a changing magnetic field induces an electric current, which can interfere with the operation of nearby electrical circuits.

EMI Shielding

To protect against EMI, devices and systems are often shielded with metallic enclosures that can absorb or reflect the interfering signals. This shielding relies on the principle of electromagnetic radiation reflection and absorption, which can be described with the skin depth equation:

\delta = \sqrt{\dfrac{2}{\omega \mu \sigma}}

where \delta is the skin depth, \omega is the angular frequency of the electromagnetic wave, \mu is the permeability of the material, and \sigma is the conductivity of the material. The skin depth is the depth at which the intensity of the electromagnetic radiation inside the material falls to about 37% of its original value.

Conclusion

Electromagnetic interference can pose serious challenges to the operation of electronic devices, especially in our increasingly connected world. However, with proper shielding and design, these effects can be minimized, ensuring the reliable operation of our technology.

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