Analogy is one of the best ways to demonstrate or explain an abstraction. Electromagnetic interference, or EMI, is not necessarily an abstraction, but it can be a difficult concept to grasp, especially for people without backgrounds in electrical engineering or physical sciences generally. One of the analogies that I’ve come to use to help myself understand the concept comes from American football. One of the most frustrating penalties in football is defensive pass interference, which is called when a player commits disruptive contact with a pass receiver before that player has a chance to make a catch attempt.

Here’s the analogy to EMI. Even when defensive pass interference is committed, there is still a chance that a pass completion can be made. When EMI disrupts the transmission of an electrical signal, there are varying degrees to which the interference can disrupt transmission. In any case, the disruption in passage, both of the ball and of the signal, is caused by an interfering third party. EMI shields are meant to reduce the ability of the interference to disrupt signal transmission. The analogue in football to an EMI shield would be an offensive lineman, who restricts the motion of defenders trying to disrupt or intercept a pass. Just like in the case of EMI shielding, the shield and the blocker don’t make the interference go away; instead, they redirect or block it. It is physically impossible to make EMI simply disappear or to absorb it, just as it is physically impossible to make defenders disappear.

The analogy begins to fail, of course, when it comes to explaining the specifics of what an EMI shield is and does. Composition, positioning and the type of interference being blocked determine what kind of shield will be necessary, what it must be made of, its size and other physical properties. But the basic analogy fits the interference-shield dynamic nicely.