Subwavelength acoustic valley-hall topological insulators using soda cans honeycomb lattices

Topological valley-contrasting physics has attracted great attention in exploring the use of the valley degree of freedom as apromising carrier of information. Recently, this concept has been extended to acoustic systems to obtain nonbackscattering soundpropagations. However, previous demonstrations are limited by the cut-of frequency of 2D waveguides and lattice-scale sizerestrictions since the topological edge states originate from Bragg interference. Here we engineer topologically valley-projected edgestates in the form of spoof surface acoustic waves that confne along the surface of a subwavelength honeycomb lattice composedof 330-mL soda cans. Te inversion symmetry is broken through injecting a certain amount of water into one of the two cansin each unit cell, which gaps the Dirac cone and ultimately leads to the topological valley-Hall phase transition. Dual-frequencyranges of the valley-projected edge states below the sound line are observed, which originate from the frst-order and second-orderresonances, respectively. Tese results have the potential to enable promising routes to design integrated acoustic devices based onvalley-contrasting physics.This work was supported by National Key R&D Program of China (2017YFA0303702), NSFC (11834008, 11874215, 11674172, and 11574148), Jiangsu Provincial NSF (BK20160018), the Fundamental Research Funds for the Central Universities (020414380001), and Nanjing University Innovation and Creative Program for PhD candidate (CXCY17-11). Zhiwang Zhang acknowledges the support from the China Scholarship Council. Johan Christensen acknowledges the support from the European Research Council (ERC) through the Starting Grant 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant no. RYC-2015-17156).Publicad

Reconfigurable sound anomalous absorptions in transparent waveguide with modularized multi-order Helmholtz resonator

Abstract Helmholtz resonators offer an ideal platform for advanced sound absorbers, but their utility has been impeded by inherent frequency range limitations and the lack of function reconfiguration. Here, we introduce a multi-order Helmholtz resonator (MHR) that allows multiple monopolar resonant modes theoretically and experimentally. The combination of these modularized MHRs further creates reconfigurable multi-band anomalous absorbers in a two-port transparent waveguide while maintaining undisturbed air ventilation. In asymmetric absorption state through coupling of artificial sound soft boundary with preposed MHR, sound energy is almost totally absorbed in multiple frequency ranges when sound waves are incident from one side while it is largely reflected back from the opposite side. Interestingly, the original asymmetric absorber would turn into symmetric bidirectional absorber if one post MHR concatenates after the soft boundary. Using combination of identical MHRs, we demonstrate function selective asymmetric/symmetric absorber in multi-bands, highlighting the potential to use MHRs in the design of diverse devices for more versatile applications

Deep-subwavelength holey acoustic second-order topological insulators

Higher-order topological insulators (HOTIs) belong to a new class of materials with unusual topological phases. They have garnered considerable attention due to their capabilities in confining energy at the hinges and corners, which is entirely protected by the topology, and have thus become attractive structures for acoustic wave studies and control. However, for most practical applications at audible and low frequencies, compact and subwavelength implementations are desirable in addition to providing robust guiding of sound beyond a single-frequency operation. Here, a holey HOTI capable of sustaining deeply confined corner states 50 times smaller than the wavelength is proposed. A remarkable resilience of these surface-confined acoustic states against defects is experimentally observed, and topologically protected sound is demonstrated in three different frequency regimes. Concerning this matter, the findings will thus have the capability to push forward exciting applications for robust acoustic imaging way beyond the diffraction limit.This work was supported by the National Key R&D Program of China (2017YFA0303702), NSFC (11922407, 11834008, 11874215, 11674172, and 11574148), Jiangsu Provincial NSF (BK20160018), the Fundamental Research Funds for the Central Universities (020414380001), and Nanjing University Innovation and Creative Program for Ph.D. candidate (CXCY17-11). Z.Z. acknowledges the support from the China Scholarship Council. J.C. acknowledges the support from the European Research Council (ERC) through the Starting Grant 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant No. RYC-2015-17156)

Deep‐Subwavelength Holey Acoustic Second‐Order Topological Insulators

Higher-order topological insulators (HOTIs) belong to a new class of materials with unusual topological phases. They have garnered considerable attention due to their capabilities in confining energy at the hinges and corners, which is entirely protected by the topology, and have thus become attractive structures for acoustic wave studies and control. However, for most practical applications at audible and low frequencies, compact and subwavelength implementations are desirable in addition to providing robust guiding of sound beyond a single-frequency operation. Here, a holey HOTI capable of sustaining deeply confined corner states 50 times smaller than the wavelength is proposed. A remarkable resilience of these surface-confined acoustic states against defects is experimentally observed, and topologically protected sound is demonstrated in three different frequency regimes. Concerning this matter, the findings will thus have the capability to push forward exciting applications for robust acoustic imaging way beyond the diffraction limit.This work was supported by the National Key R&D Program of China (2017YFA0303702), NSFC (11922407, 11834008, 11874215, 11674172, and 11574148), Jiangsu Provincial NSF (BK20160018), the Fundamental Research Funds for the Central Universities (020414380001), and Nanjing University Innovation and Creative Program for Ph.D. candidate (CXCY17-11). Z.Z. acknowledges the support from the China Scholarship Council. J.C. acknowledges the support from the European Research Council (ERC) through the Starting Grant 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant No. RYC-2015-17156)