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Multi-reflection interference of sound waves is ubiquitous in our daily life, and suppressing any such distortions of a wave’s free propagation and achieving counter-directional adaptation is a challenging task, with many applications in acoustics. Here, we propose a non-Hermitian Fabry–Perot resonance unit, which demonstrates unidirectional invisibility in opposite directions at the so-called exceptional points by adjusting its geometric configuration and intrinsic acoustic parameters. Then, we extend the principle and design a waveguide containing six inclusion–membrane pairs in which a unique property of step-wise constant-amplitude waves in two opposite directions has been realized, irrespective of whether the distribution of inclusions is periodic or random. Our method breaks through the limitation of the impedance, amount, position of the inclusions, and the incident direction of the waves, revealing potential applications in acoustic sensing, noise control engineering, and other related wave disciplines.

In this paper, the performance analysis is carried out for farfield wideband beamformers with microphone mismatches, from the perspective of variance analysis of array response. Some insightful properties on farfield wideband beamformers have been revealed, which are helpful to better understand the robustness of farfield wideband beamformers. The comparative study is performed, regarding the effects of microphone position errors, and of microphone gain and phase errors on farfield wideband beamformers. It is found that the effects of microphone position errors depend on source angle of arrival as well as the temperature in homogeneous environments, while these factors have little impact on the effects of microphone gain and phase errors. Several numerical examples are presented to further confirm the theoretical results.Index Terms-Microphone array, wideband beamformer, robustness, microphone mismatches.

The pursuit of artificial structures exhibiting unusual acoustic properties is a major scientific endeavor, in which anti-parity-time (PT) symmetry has been coming into view recent years. At the same time, with the emergence of new acoustic metamaterials, the classical Fabry–Perot resonance mode also exhibits fascinating scattering features similar to those of the anti-PT-symmetric system. We derive the generalized relation for the scattering parameters of an acoustic anti-PT-symmetric system with a transfer matrix, including conjugate bidirectional reflection coefficients and pure real feature of transmission coefficient. In the absence of the real or the imaginary (representing gain/loss) part of the refractive index, the anti-PT-symmetric system degrades into a pair of complementary media, resulting in the bidirectional total transmission. Moreover, a Fabry–Perot resonance mode exhibiting conjugate bidirectional reflection coefficients and a pure imaginary transmission coefficient has been demonstrated. Our results are meaningful for guiding the experimental test of an acoustic anti-PT-symmetric system and the design of associated bidirectional response prototype devices.