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Microwave Amps Use 'Time Reversal Mirror'
6/10/2010


It may sound like science fiction, but the MIT Technology Review reports that a technique borrowed from acoustics could lead to a super-powerful amplifier of microwave radiation. The output of this device would be used to generate non-nuclear electromagnetic pulses (EMPs). EMPs are a strong shock wave of electromagnetic radiation that can be used to damage electronic circuits, stop cars by interfering with their electronic systems, disable satellites and destroy aircraft. EMPs can be generated by nuclear explosions and strong, nearby lightning discharges.

The MIT article points out that in the past, an explosion would be required to produce an EMP of sufficient power to disable vehicles or infrastructure. Earlier this year the French Ministry of Defense published a description of an early prototype of what the researchers called a potential "electromagnetic bazooka." The researchers were able to achieve a gain of 46 dB in the system. With this amount of gain, a 10 Watt input signal would result in an output of almost 400,000 Watts.

This amplification is achieved by using Time Reversal Signal Processing. A Time Reversal Mirror receives a short pulse of electromagnetic energy at an antenna, reverses it in time by using an "arbitrary waveform generator," and then sending it back to the original transmitter.

According to the article:

"When used on either audio signals or electromagnetic waves, a Time Reversal Mirror allows engineers to exploit what's known as the 'pulse compression property' of time reversal to create an amplified version of the signal at a point outside the reverberation chamber housing the transmitter and the time reversal mirror."

It further explains that at some distance away from the device, a "significantly amplified" version of the original signal is then generated.

The Time Reversal Signal Processing technique was invented by Mathias Fink in 2004 for audio signal processing, but has been extended for use into radio frequencies.

I did some research on this and found a paper which listed Mathias Fink as a contributor Time-reversal signal processing can boost wireless comms.

The paper explains how the technique can be used to increase wireless data bandwidth using multiple antennas spaced much closer than the one-half wavelength spacing typically required for MIMO systems.

A good summary of the technique, complete with graphs and formulas, is contained in the paper "The Time reversal method according to Mathias Fink" (LOA ESPCI Paris)[PDF] by C. Bardos. Interested readers should also see Mathis Fin's article on Time-reversal acoustics in the Journal of Physics Conference Series Volume 110, Number 1.

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