One of the themes of the modernization of high-style warfare is the continuing introduction of more and more electronic equipment onto and around the battlefield. Soldiers are carrying more electronic gear; vehicles carry complex electronics both as mission payload and as vehicle systems, and command and control systems meant for use in fixed positions contains even more electronics. Combatants are tied together by electromagnetic links of increasing complexity and importance. Naturally, one of the first questions a savvy warrior asks is "how can I disrupt my opponent's electronics and communications?" There are several ways to do this on an ongoing basis, of course. But what if you wanted to go for the real knockout punch? What if you wanted to be able to make your foe's electronics fizzle and emit the magic smoke at your command?
To do that, you'll need that (so far) staple of video game warfare, the EMP grenade. Ideally, one that works without any bothersome nuclear detonations. The question then becomes an engineering one: how do you store enough energy in the grenade to allow it to push out a high-power enough pulse, fast enough, to damage electronics?
One answer is the explosively-compressed solenoid.
The humble solenoid has been around for <Obi-wan Kenobi voice> oh...a long time.</Obi-wan> They are used whenever an engineer needs to allow electricity to perform a small, repeatable (and ideally linear) motion. One example: the electronic door locks in cars. See the solenoid node for more details.
But solenoids, involving (as they do) electricity and magnetism, have an interesting trait - they're reversible. That is, if you can use a solenoid to turn electricity into a small mechanical motion, then if you provide mechanical motion to the solenoid, you can get a small amount of electricity back out of it.
I'm sure you can see where this is going.
High explosives remain one of the most efficient and stable ways that humans have come up with to produce large, fast energy outputs on demand. The problem is that most of the energy they produce is thermodynamic and kinetic, and the output lasts for fractions of a second at very high levels. Hm...wait...perfect! Yep, if you build a solenoid with a plunger or actuator that is paired with an explosive charge, you can (upon detonating the explosive) produce a proportionately large pulse of electricity through the coils of the solenoid. That pulse of electricity can then be used to make mischief.
Now, there are limits to this, mostly imposed on the design by the fact that a large enough explosive charge combined with a mechanism small enough to be carried means that using it will destroy the mechanism. Using a linear solenoid design isn't really practical, and the limited strength of the magnet on the actuator limits the amount of power that can be extracted. As a result, this idea led (very quickly) to the development of a whole new class of devices known as explosively pumped flux compression generators. But that's another node.