Three focus rings of time-reversal electromagnetic fields in parallel-plate waveguide: Theory and simulation

In a parallel-plate waveguide, we find three time-reversal (TR) focus rings unlike familiar punctiform focus, including one Main Focus Ring (MFR) and two mirror Focus Rings (mFR). The two mFR come from the mirror symmetry and the annularity comes from the rotational symmetry. Theoretical and numerical results consistently show that the three rings have a uniform size and the TR focus gain in MFR is about twice that in mFR. These continuous rings have discounted the quality of TR imaging and detecting. However, these high gain focus rings have the potential to develop into new electromagnetic tweezers.