If you are unfamiliar with initiators, when you hear the phrase “exploding-bridgewire” you may picture a bridge blowing up and the hero running away from it in the nick of time, like an action movie cliché. But these devices are not about “burning bridges” like the demo video below:
Exploding-bridgewires (EBW’s) have a slug/header with wire going through it, a very thin wire which connects the slug/header to the low and high density, high explosive.
The thin wire is the bridgewire. This is placed next to a low density pressed explosive (PETN, for example), which is placed next to a higher density explosive which is what provides the output. A capacitor is dumped through this electrical circuit, and the amount of current going through is so large that the very thin wire (in other words, the EBW) explodes. Old style flash bulbs were like this—light bulbs that had very fine aluminum wire with oxygen, and you would dump capacitor through it, aluminum would explode and get so hot it would burn very brightly. That is what we used for illumination in photography before strobes became widely available. In explosives, this generates shockwave in pellet. Because there is confinement there, and there is confinement in the edges, when the low density explosive begins burning, it turns to a detonation through deflagration to detonation (DDT) process. Detonation then hits the higher density pellet and propagates the detonation accelerated, gains pressure because CJ pressure of high density pellet is greater than the low density pellet. Then what comes out of front end its higher pressure detonation wave, which is what you drive into explosive you are trying to send off.
Some authors state that the key mechanism is shock-to-detonation while others maintain it is more thermal in nature, or a complex combination of both [1]
An an easy-to-follow example of how an EBW can be made can be seen in the video below:
Other common mechanisms for initiation include direct lasers and slapper detonators, which will be discussed in future posts.
References:
[1] Rae P. J. and Dickson P. M. A review of the mechanism by which exploding bridge-wire detonators function 475 Proc. R. Soc. A. http://doi.org/10.1098/rspa.2019.0120
It Goes Boom 