What is it about?

There are limits to how much energy can be absorbed within a given region of space, but these limits do not apply to absorbers that include a second source of energy. This paper demonstrates that a pulse of energy sent into a cavity can be completely withdrawn by sending a second pulse into the cavity. Although this may sound counter-intuitive, this result is shown theoretically and experimentally.

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Why is it important?

Active absorption of pulses has been addressed using time-reversal techniques. Here, we have shown a different method that relies on the geometry of the cavity and shape (modulation) of the pulse, but is not time-reversal.


Although it may seem counter-intuitive that you can pump more energy into a box to retrieve the energy within it, that is what this work shows! It depends on the resonances within the cavity and the location of the "ports", of course: you either have to use the same port for input and output, or they must be symmetrically positioned, so that the ports couple to the same modes in the cavity.

Dr Robert N Foster
University of Birmingham

Read the Original

This page is a summary of: Active absorption of electromagnetic pulses in a cavity, New Journal of Physics, May 2015, Institute of Physics Publishing, DOI: 10.1088/1367-2630/17/5/053050.
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