Electromagnetic Pulse (EMP) Weapons Explained: How Do They Work?

Today, not many people may be familiar with a U.S. military operation from the early 1960's called "Starfish Prime." The details are fascinating, but here's the short version: over a remote National Wildlife Refuge in the Pacific Ocean, they launched a 1.4 megaton thermonuclear warhead and detonated it at roughly the altitude where today the ISS orbits the Earth (of course, the ISS wasn't built yet, but many early satellites sustained damage).

Close to 1,000 miles away, people in Hawaii experienced telephone disruptions as hundreds of street lights went out and other electrical systems behaved erratically. The U.S. had inadvertently attacked itself with an electromagnetic pulse, or "EMP."

It was an important learning moment. Nuclear weapons create an EMP, but with conventional use, the area affected by the pulse would also be immediately destroyed by the explosive blast. Starfish Prime demonstrated that a high-altitude nuclear device could create an EMP with a tremendous area of affect, and — crucially — without decimating a populated area in the process.

Two significant things have happened in the decades since: First, the world has become increasingly reliant on electronic devices. Second, researchers have figured out how to create an EMP without using a nuclear weapon at all. So how does it all work?

Electromagnetism is a single force responsible for phenomena including electric charge and the push-and-pull of magnets. In simple terms, the flow of electricity can generate a magnetic field, and a changing magnetic field can generate an electric current. An EMP is essentially a very powerful and directed magnetic field that passes over an area. As it passes, it interacts with conductive materials and causes short-circuits and power surges.

Many things can be included under the umbrella of "conductive materials." Semiconductors are an obvious example. These chips — which are critical for controlling everything from phones and cars, to guided missiles and the power grid — have grown ever smaller, relying on thinner and more delicate precision components to function. An EMP can overwhelm these components, destroying them outright.

Other conductive materials of import may be less obvious. Buried critical infrastructure like power lines, pipes, and conduit can all become charged from an EMP. This charge will then flow down the path of least resistance until its fully discharged, which could mean overloading things like generators that weren't even within the range of the EMP blast radius.

While there are ways to shield against an EMP blast, these methods are generally expensive, impractical, or both for most everyday applications. Even though EMP weapons are sometimes touted as non-destructive and non-lethal alternatives, the reality is that the chaos they would unleash — hospitals without electricity, no traffic lights, midflight loss of airplane controls — would be devastating.

The first EMP weapons were nuclear weapons, with the pulse being more of a side effect than the main purpose. When a nuclear device detonates, it generates — among other things — an incredible amount of high-energy radiation called gamma rays. These energetic waves fly outward from the blast and start knocking the electrons off of the air molecules in the surrounding atmosphere. This ionized bubble of air then generates a powerful magnetic pulse that shoots away at lightspeed, causing havoc on electronics.

A non-nuclear EMP can be a much smaller device, as it does away with the gamma radiation and the ionizing of the atmosphere. Instead, picture a closed metal tube with a stick of dynamite inside. Wrapped around the tube, but not touching it, are coiled wires with a constant electric current provided by capacitors. When the dynamite explodes, the pieces of the metal tube come into contact with the wires, interrupting the current. 

Of course, the reality of a larger EMP is slightly more complicated, but when this detonation can be properly controlled and directed, it will result in an EMP blast. EMPs might sound like action blockbuster fare — they did appear in "GoldenEye" and "Ocean's Eleven" — but the science behind them is sound. Just like truck-mounted lasers, these sci-fi weapons are real, and they're devastating.