Extraordinary acoustic scattering in a periodic PT-symmetric zero-index metamaterials waveguide

Abstract

We propose an acoustic waveguide consisting of periodic parity-time-symmetric zeroindex metamaterials separated by layers of passive medium. Consistent analytical derivations and numerical simulations show that a rich variety of extraordinary scattering effects can be achieved. For example, unidirectional transparency is found to occur at an exceptional point. At singular points, the system behaves as an acoustic coherent perfect absorber (CPA) laser. Bidirectional transparency, induced by the Fabry-Pérot resonance or balanced dissipation and amplification, is also observed. In contrast to the previous scheme without structural periodicity, the proposed periodic structure allows a greater number of conditions under which the CPA laser behavior and bidirectional transparency can be achieved, which may facilitate the experimental realization of such extraordinary effects.

Acoustic Equivalent Lasing and Coherent Perfect Absorption Based on a Conjugate Metamaterial Sphere

“…Thus, the scattering system works as an acoustic equivalent laser at this frequency, which produces coherent outgoing waves with extensive intensities. The time-reversed counterpart to this lasing mode is a CPA mode [38][39][40][41][42][43][44][45][46], where the acoustic and geometric parameters of the scatterer are the same as those in the lasing mode, except that the gain is replaced with loss with equal magnitude.…”

“…Now, the scattering system works as an acoustic coherent perfect absorber at this frequency, which could totally absorb a specific coherent incident wave pattern determined by the eigenstate. An acoustic system with effective loss (gain) could realize only the CPA (AEL) effect [38], while the simultaneous realization of AEL and CPA effects requires a system consisting of both gain and loss, which has been proposed based on an acoustic parity-time symmetric system [39] and an anti-parity-time symmetric system [40]. Besides, previous studies focused on one-dimensional (1D) and two-dimensional (2D) systems.…”

“…Besides, previous studies focused on one-dimensional (1D) and two-dimensional (2D) systems. In 1D systems, the AEL and CPA effects were demonstrated for plane normal incidence [39,40]. In a 2D panel system, such effects could be realized for plane oblique incidence [37].…”

Laser intensity affects the electron's optimal position and the spatial radiation characteristics in linearly polarized tightly focused laser field

“…Since the late 1980s, the field of high-power lasers and matter interaction has flourished due to the emergence of Chirped Pulse Amplification (CPA) technology [1][2][3][4] . Consequently, the research on relativistic nonlinear Thomson scattering (RNTS) as a promising X-ray 5 and γ-ray source 5 has attracted increasing attention in the field of ultrafast laser physics [6][7][8] .…”

Parity–time symmetric acoustic system constructed by piezoelectric composite plates with active external circuits

“…[12][13][14] In the meantime, PT-symmetric acoustics [15] also has attracted intense attention after being proposed by Zhu et al Since it is difficult to find the natural gain material in acoustics, [16] passive PT-symmetric systems [17][18][19] that consist of purely dissipative elements inspire the diverse designs of the acoustic PTsymmetric system. Moreover, the intriguing effects of exceptional points (EPs) corresponding to the PT phase transition points can also be observed in a passive PT-symmetric system, such as unidirectional invisibility, [20][21][22][23][24] anomalous reflection and refraction, [25][26][27][28] unidirectional sound focusing effect, [29] acoustic negative refraction [30] and sound absorption. [31] However, it is still difficult to construct a gain part for an active PT symmetry in the acoustic system, as the gain parts reported always consist of properly controlled loudspeakers, [32,33] interdigital transducers, [34] etc.…”