Exceptional point degeneracies, occurring in non-Hermitian systems, have challenged many well established concepts and led to the development of remarkable technologies. Here, we propose a family of autonomous motors whose operational principle relies on exceptional points via the opportune implementation of a (pseudo-)PT-symmetry and its spontaneous or explicit violation. These motors demonstrate a parameter domain of coexisting high efficiency and maximum work. In the photonic framework, they can be propelled by thermal radiation from the ambient thermal reservoirs and utilized as autonomous self-powered microrobots, or as micro-pumps for microfluidics in biological environments. The same designs can be also implemented with electromechanical elements for harvesting ambient mechanical (e.g., vibrational) noise for powering a variety of auxiliary systems. We expect that our proposal will contribute to the research agenda of energy harvesting by introducing concepts from mathematical and non-Hermitian wave physics.
Exceptional points (EP) are non-Hermitian spectral degeneracies where both eigenvalues and their corresponding eigenvectors coalesce [1][2][3][4] . Recently, EPs have attracted a lot of attention as a means to enhance the responsivity of sensors, via the abrupt resonant detuning occurring in their proximity [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . In many cases, however, the EP implementation is accompanied by noise enhancement leading to the degradation of the signal-to-noise performance of the sensor [15][16][17][18][19][20] . The excess noise can be of fundamental nature (due to the eigenbasis collapse) or of technical nature associated with the use of amplification mechanisms utilized for the realization of EPs. Here we show, using an EP-based PT -symmetric 21,22 electromechanical accelerometer, that the enhanced technical noise can be surpassed by the enhanced responsivity to applied accelerations. The noise due to eigenbasis collapse is mitigated by exploiting the detuning from a transmission peak degeneracy (TPD), which forms when the sensor is weakly coupled to transmission lines, as a sensitivity measurant. These TPDs occur at a frequency and controlled parameters for which the bi-orthogonal eigen-basis is still complete
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