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Researchers Propose an Acoustic Asymmetric Diffraction Grating Based on Passive Parity-Time-Symmetric Medium

Oct 11, 2019

Acoustic asymmetric transport is important in the noise control and communication acoustics. Theoretical research and experimental verification of acoustic asymmetric transport have attracted much attention. Recent progress on non-Hermitian systems has yielded a scheme to realize asymmetric transport without nonlinear effects or mode conversion. 

Researchers from the Institute of Acoustics (IOA) of the Chinese Academy of Sciences (CAS) proposed an acoustic asymmetric diffraction grating based on passive parity-time-symmetric medium and experimentally verified the asymmetric diffraction phenomenon in a two dimensional waveguide. 

The study was published online in Physical Review Applied on September 19, 2019. 

The researchers studied in the experimental realization of an asymmetric diffraction grating based on a cleverly designed passive PT-symmetric medium, in which the loss was introduced as an extra modulation factor, and the energy distribution could be adjusted more freely.

The proposed passive PT-symmetric medium was composed of additional cavities and leaked holes. By skillfully combining these two unit cells, the composite unit cell could modulate the real and imaginary parts of refractive index simultaneously. When the modulation amplitudes of real and imaginary parts were equal, asymmetric diffraction was observed in both simulated and experimental results at exceptional point. The designed structure was helpful for further research on non-Hermitian acoustic systems. 

 

Fig. 1. Distribution of refractive index, experimental structure and asymmetric diffraction sound pressure fields. (Image by IOA)  

Experimental results showed that the asymmetric diffraction effect of the designed passive PT-symmetric grating was available in a broad frequency band. In the measured sound pressure fields displayed in Fig. 2. (a), all the +1st-order diffractions with negative incident angle (left panel) were much weaker than the -1st-order diffractions with positive incident angle (right panel). The asymmetric diffraction in a wide frequency band (2.7-3.3 kHz) could be observed in both simulated result [Fig. 2. (b)] and experimental result [Fig. 2. (c)]. 

This work was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association CAS, and the IACAS Young Elite Researcher Project. 

 

Fig. 2. Asymmetric diffraction in a wide frequency range: (a) The measured +1st-order diffractions and -1st-order diffractions are shown in left panel and right panel, respectively; (b) The simulated diffraction intensity contrast; (c) Corresponding intensity bars of measured sound fields. (Image by IOA)

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ZHOU Wenjia

Institute of Acoustics

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Experimental demonstration of an acoustic asymmetric diffraction grating based on passive parity-time-symmetric medium

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