Robust Wireless Power Transfer with Minimal Field Exposure Using Parity-Time Symmetric Microwave Cavities

Wide-range robust wireless power transfer using heterogeneously coupled and flippable neutrals in parity-time symmetry

“…By self-adjusting the operational frequency, the voltage gain is kept high up to ~10-mm displacement but begins to decrease when the system becomes PT asymmetric false(trueĤnormalPT≠normalPTtrueĤfalse), where the gain is not balanced with the loss (gs≠γl′) and the eigenfrequencies degenerate (Fig. 2H) ( 8 , 9 , 13 , 19 , 20 , 39 ). Hence, although the dimer system is effective because of self-adjustment tuning, there is a significant need for further improvement to achieve robust WPT under lateral displacements.…”

“…The resonance maximizes the induced voltage across the rectifier at the load, improving the rectifier efficiency as well. Therefore, resonance has been applied widely in various types of wireless operation, such as in near-field WPT using coils ( 2 , 11 , 12 ) and cavities ( 13 , 14 ), including the industrial standards of Qi ( 3 ) and AirFuel ( 4 ), as well as midrange WPT using magnetic resonances ( 1 , 6 ).…”

“…Recently, a WPT mechanism that eliminates the need for active tuning has been proposed. It used a pair of transceivers (dimer) in parity-time (PT) symmetry to ensure WPT operation at resonant frequencies, which appear as real eigenvalues of the Hamiltonian operator describing the system dynamics ( 8 , 9 , 13 , 19 , 20 ). Note that while the Hamiltonian operator of a WPT system cannot be Hermitian because the system is not closed (e.g., energy goes in and out of the system), the reported systems, nevertheless, have the real eigenvalues.…”

“…This phase is referred to as unbroken PT symmetry, as opposed to broken PT symmetry in which the eigenvalues can be complex numbers even though trueĤnormalPT=normalPTtrueĤ. Although the concept of PT symmetry originated from quantum physics ( 21 ), the similarity of the Schrodinger and electromagnetic wave equations broadened its applications into the fields of optics and electronics to unveil several exotic features, such as optical nonreciprocity ( 22 , 23 ), intrinsically single-mode lasers ( 24 , 25 ), unidirectional scattering ( 26 , 27 ), ultrasensitive sensors ( 28 – 30 ), and robust WPT ( 8 , 9 , 13 , 19 , 20 ).…”