Reference: EMP
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EMP stands for Electromagnetic Pulse.

The general idea is the same that is used in transformers, power adapters: a varying magnetic field creates a current in materials that conduct electricity. The greater the field and faster the change, the greater the voltage. The general principle of an EMP-bomb is that at the peak current of an electrical coil the coil is exploded with some fast-exploding explosive. During the explosion and before the electrical circuit within the coil breaks the diameter of the coil expands very rapidly, changing the inductance of the coil very rapidly. Rapidly changing inductance combined with roughly constant current produces a rapidly changing magnetic field, which induces current in materials that conduct electricity, including the wires within the electronic equipment that is being attacked. To maximize the current during the explosion, the explosion must be timed according to the chart that describes how the current of discharging capacitors that feed the coil depends on time.

The damage of an EMP-bomb is based on the permanent destruction of electronic components. The smaller the components within microchips are, the less voltage it takes to create a discharge. That explains, why the specified maximum operating voltage of microchips has fallen while smaller and smaller on-chip-components have been taken to use.

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