Generation of plasmas in air at atmospheric pressure using time-reversal of microwaves

Currently, most aircraft engines rely on spark plugs to ignite the fuel/air mixture. However, they are not without problems. Among them is the fixed location of the spark plug on the combustion chamber wall. This work is part of a project whose goal is to develop a new igniter with the ability to precisely target where and when the spark, or plasma, is created in the combustion chamber. This has traditionally been hard to achieve due to the high breakdown voltage of air at atmoshperic pressure. The ability of time reversal to focus microwaves, in space and in time, and therefore generate high intensity electric fields makes it interesting for these applications. With the correct initiators located at the focus point, the electric field could be increased even more and reach gas breakdown.

In this study, we show that plasmas can indeed be generated in atmospheric condition this way. More precisely, nanoseconds micro-wave pulses are refocused through time-reversal on Split-Ring-Resonators (SRR) initiators and micro-plasmas are generated in the SRR gap. In particular, we show some of the limits of this method, such as the minimum pulse duration and power, carrier frequency of the pulse relative to the SRR resonant frequency, … The signature of the resulting plasma and its effect on time reversal is also briefly investigated. Finally, we show some preliminary results on the dynamics of the plasma creation through the use of a high-speed camera.