Being able to generate a Electromagnetic Pulse (EMP) in a handhold devise that does not require a substantial explosion could be a very effective non lethal weapon. We are not there yet, but research has put us on a promising path.
"The device borrows a technique invented in 2004 for audio signal processing by French physicist Mathias Fink, known as Time Reversal Signal Processing. The technique uses a Time Reversal Mirror to receive a short pulse of electromagnetic energy at an antenna and then shoot back toward the initial transmitter the same signal, but with its wave-form reversed in time. The technique is enabled by the use of an Arbitrary Waveform Generator, which can generate any waveform you like, including a backwards version of the waveform an antenna just received. It's a bit like responding to a given signal by playing the same signal backward, although it happens in milliseconds.
Using this setup, the researchers discovered a linear relationship between the number of antennas (from one to eight) used in their time reversal mirror and the resulting amplitude of the microwave pulse they generated.
Further amplification of the signal before retransmission by the mirror, using a technique called "one-bit time reversal," allowed the team to achieve 46 dB of amplification. Because decibels are represented on a logarithmic scale, that corresponds to amplification of the original signal by a factor of more than 10,000.
It's clear that this work is early-stage because the paper did not make explicit the power requirements of the device or the destructive capacity of the resulting amplified electromagnetic signal, if any. However, as our infrastructure and our military becomes ever more dependent on microchips and electronics in general, any developments in the ease with which an EMP can be developed should be of considerable interest to military and security professionals, or even, if this device is as straightforward as it appears to be, enterprising attendees of next year's Maker Faire."