Topological vortices for sound and light

Localized zero-energy fermionic states can bind to topological defects such as two-dimensional vortices, which can be realized in the bulk of artificial acoustic and optical lattices

Topological sound pumping of zero-dimensional bound states

Topological phases have spurred unprecedented abilities for sound, light and matter engineering and recent progress has shown how waves not only confine at the interfaces between topologically distinct insulators, but in the form of zero-dimensional non-propagating states bound to defects or corners. Majorana-like bound states have recently been observed in man-made Kekul\'e textured lattices. We show here how the acoustic version of the associated Jackiw-Rossi vortex embodies a Thouless pumping process, in which the spectral flow of corner states adiabatically merge with the said Majorana-like state. Moreover, we argue how the chirality of the Kekul\'e vortex additionally maps into a 2D quantum-Hall system comprising spatially separated sonic hotspots. We foresee that our findings should provide novel exotic tools to enable contemporary control over sound

Non-Hermitian elastodynamics in gyro-odd continuum media

Linear elasticity has long been considered a well-established research area using conservative field theory. However, the discovery of odd-elasticity challenges the essential energy conservation assumption, which together with gyroscopic ingredients compromise the fundamental theory of elasticity, but to the same effect, enable new directions in active elastodynamics. Here, we consider two-dimensional continuum mechanics in a more general framework containing active constituents from both gyroscopic and odd-elastic effects, which gives rise to non-reciprocal and non-Hermitian elastic waves in a highly unconventional guise. We discuss how these unusual media can extract energy from odd-elastic engine cycles comprising remarkable features of stability transitions, in which the energy exchange process reverses. Beyond bulk waves, akin to the unidirectional characteristics of a 2D quantum-Hall insulator, we demonstrate the existence of non-Hermitian Rayleigh surface waves which, in contrast to the classical ones in passive solids, display one-way and interference-free transport characteristics, which even remain resilient in finite sharp or curved geometries. The findings reported here may provide new possibilities to manipulate elastic waves in unusual ways.J.C. acknowledges the support from the European Research Council (ERC) through the Starting Grant No. 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant No. RYC-2015-17156). Y.Q. acknowledges the support from the National Natural Science Foundation of China (Grant Nos. U2141244, 11922208, 11932011, 12121002) and the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University (Grant No. SL2021ZD104). P.G. acknowledges the support from the National Natural Science Foundation of China (Grant No. 12202267), Shanghai Pujiang Program (Grant No. 22PJ1405300) and the Starting Grant of Shanghai Jiao Tong University (Grant No. WH220402014)

Anomalous topological edge states in non-Hermitian piezophononic media

The bulk-boundary or bulk-edge correspondence is a principle relating surface confined states to the topological classification of the bulk. By combining non-Hermitian ingredients in terms of gain or loss with media that violate reciprocity, an unconventional non-Bloch bulk-boundary correspondence leads to unusual localization of bulk states at boundaries$-$a phenomenon coined non-Hermitian skin effect. Here we \textcolor{black}{numerically} employ the acoustoelectric effect in electrically biased and layered piezophononic media as a solid framework for non-Hermitian and nonreciprocal topological mechanics in the MHz regime. Thanks to a non-Hermitian skin effect for mechanical vibrations, we find that the bulk bands of finite systems are highly sensitive to the type of crystal termination, which indicates a failure of using traditional Bloch bands to predict the wave characteristics. More surprisingly, when reversing the electrical bias, we unveil how topological edge and bulk vibrations can be harnessed either at the same or opposite interface. Yet, while bulk states are found to display this unconventional skin effect, we further discuss how in-gap edge states in the same instant, counterintuitively are able to delocalize along the entire layered medium. We foresee that our predictions will stimulate new avenues in echo-less ultrasonics based on exotic wave physics

Poisson-like effect for flexural waves in periodically perforated thin plates

[EN] The Poisson-like effect, describing the redirection of waves by 90 degrees, is shown to be feasible for flexural waves propagating in perforated thin plates. It is demonstrated that the lowest order symmetric leaky guided mode (S0 mode) is responsible for the splitting of wave motion in two orthogonal directions. The S0 mode shows a feature of stationary waves containing standing wave modes in one and two orthogonal directions for smaller and larger holes, respectively. The former case is well understood thanks to the phenomenon of Wood's anomaly, which was first observed in optical gratings supposed to be transparent. On the contrary, the strong scattering caused by the larger holes leads to a mixed mode occurring when the incident wave is totally transmitted. The mixed mode easily couples with the incoming waves and, therefore, the Poisson-like effect activated under this mechanism is much stronger. Using the Poisson-like effect, a device is proposed in which about 82% of the incident mechanical energy is redirected to the perpendicular direction. Results obtained with arrays of free holes also apply to inclusions with parameters properly chosen. The findings may provide applications in beam splitting and waveguiding. (C) 2018 Acoustical Society of America.Work supported by the Ministerio de Economia y Competitividad of Spain and the EU Fondo Europeo de Desarrollo Regional under Project No. TEC2014-53088-C3-1-R, and the National Natural Science Foundation of China under Grants Nos. 11432004 and 11421091. P.G. acknowledges a scholarship with No. 201606120070 provided by China Scholarship Council.Gao, P.; Sánchez-Dehesa Moreno-Cid, J.; Wu, L. (2018). Poisson-like effect for flexural waves in periodically perforated thin plates. The Journal of the Acoustical Society of America. 144(2):1053-1058. https://doi.org/10.1121/1.5051648S10531058144

Single-phase metamaterial plates for broadband vibration suppression at low frequencies

[EN] By studying platonic crystals based on lattices of cavities containing N-beam resonators, we conclude that crystals made of 1-beam resonators easily produce low-frequency omnidirectional bandgaps. Based on this favorable property, hardly obtained for resonant cavities containing a higher number of beams N >= 2, we have designed single-phase metamaterial plates for the suppression of low frequency flexural waves in a broad range of frequencies. These metamaterials are obtained by using resonant cavities containing a multiple number M of identical 1-beam resonators uniformly distributed in the cavity. Square lattices of this type of resonators have been studied by using the impedance matrix approach and the multiple scattering method. This semi-analytical method has been employed to show the existence of complete bandgaps whose width can be optimized by increasing M. For the case M = 4, the largest number of resonators studied here, three complete bandgaps separated by two narrow passbands appear in the band structure. The formation of these complete bandgaps originates from the dynamic interaction between different local resonators as well as their interaction with the propagating waves in the host plate. By using composite structures consisting of platonic crystal slabs with complementary bandgaps, these separated bandgaps easily merge into a broadband wave attenuation region. The normalized width, defined as the percentage of the bandwidth to its central frequency, reaches 95.3%, representing an enhancement of about one order of magnitude compared with the absolute bandwidth obtained for the case of a single 1-beam resonator in the cavity. It is shown that the gaps can be easily tuned to lower frequencies by changing the geometrical parameters, such as the length of the beam, the radius and thickness of the smaller circular plate. Since the metamaterial is made of a single-phase material without attaching heavy masses, the work reported here provides a simple approach to construct low-cost structures with potential applications in aeronautic and astronautic industries for broadband vibration suppression at low frequencies. (C) 2018 Published by Elsevier Ltd.This work was supported by the Ministerio de Economia y Competitividad of the Spanish government and the European Union Fondo Europeo de Desarrollo Regional (FEDER) [Grant No. TEC2014-53088-C3-1-R], and the National Natural Science Foundation of China [Grant Nos. 11432004 and 11421091]. Penglin Gao acknowledges a scholarship provided by China Scholarship Council [Grant No. 201606120070].Gao, P.; Climente Alarcón, A.; Sánchez-Dehesa Moreno-Cid, J.; Wu, L. (2019). Single-phase metamaterial plates for broadband vibration suppression at low frequencies. Journal of Sound and Vibration. 444:108-126. https://doi.org/10.1016/j.jsv.2018.12.022S10812644

Theoretical study of platonic crystals with periodically structured N-beam resonators

[EN] A multiple scattering theory is applied to study the properties of flexural waves propagating in a plate with periodically structured N-beam resonators. Each resonator consists of a circular hole containing an inner disk connected to background plate with N rectangular beams. The Bloch theorem is employed to obtain the band structure of a two-dimensional lattice containing a single resonator per unit cell. Also, a numerical algorithm has been developed to get the transmittance through resonator slabs infinitely long in the direction perpendicular to the incident wave. For the numerical validation, a square lattice of 2-beam resonators has been comprehensively analyzed. Its band structure exhibits several flat bands, indicating the existence of local resonances embedded in the structure. Particularly, the one featured as the fundamental mode of the inner disk opens a bandgap at low frequencies. This mode has been fully described in terms of a simple spring-mass model. As a practical application of the results obtained, a homogenization approach has been employed to design a focusing lens for flexural waves, where the index gradient is obtained by adjusting the orientation of the resonators beams. Numerical experiments performed within the framework of a three-dimensional finite element method have been employed to discuss the accuracy of the models described here. Published by AIP Publishing.This work was supported by the Ministerio de Economia y Competitividad of the Spanish government and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC2014-53088-C3-1-R, and the National Science Foundation of China under Grant No. 11432004. Penglin Gao acknowledges a scholarship with No. 201606120070 provided by China Scholarship Council.Gao, P.; Climente Alarcón, A.; Sánchez-Dehesa Moreno-Cid, J.; Wu, L. (2018). Theoretical study of platonic crystals with periodically structured N-beam resonators. Journal of Applied Physics. 123(9). https://doi.org/10.1063/1.5009170S123

Structured sonic tube with carbon nanotube like topological edge states

A single-wall carbon nanotube can be viewed as a one-dimensional material created by rolling up a sheet of graphene. Its electronic band structure depends on the chirality, i.e., how the sheet has been rolled up, yet synthesizing the symmetry at will is rather challenging. We structure an artificial honeycomb lattice in both a zigzag and an armchair tube and explore their topological features for sound. Our findings reveal how armchair tubes remain gapless, whereas the zigzag counterparts host nontrivial edge states of non-zero quantized Zak phase, which are dictated by the circumferential number of units. Unlike man-made planar lattices whose underling symmetry must be broken to harvest quantum Hall and pseudospin phases, interestingly, the structured tubular lattice symmetry remains intact, while its nontrivial phase alone is governed by the chirality and the tube diameter. We foresee that our results, not only for sound, but also in photonics, mechanics and electronics will broaden future avenues for fundamental and applied sciencesThis work was supported by the National Basic Research Program of China (2017YFA0303702), NSFC (12074183, 11922407, 11834008, 11874215, 12104226, and 12225408), and the Fundamental Research Funds for the Central Universities (020414380181). Z.Z. acknowledges the support from the China National Postdoctoral Program for Innovative Talents (BX20200165), the China Postdoctoral Science Foundation (2020M681541), Jiangsu Planned Projects for Postdoctoral Research Funds (2021K054A), and Funds for Zijin Scholars of Nanjing University. 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)

Quantitative Evaluation of Chinese Herb Medicine in the Treatment of Sialorrhea and Frequent Nighttime Urination in Patients with Parkinson’s Disease

Aims. To evaluate the efficacy of Lian-Se formula (LSF), one Chinese herb formulation for treating sialorrhea and frequent overnight urination in patients with Parkinson’s disease (PD). Methods. 96 PD patients suffering from sialorrhea and/or frequent nighttime urination were divided into two groups: an LSF group (n = 48) treated with LSF for 6 weeks and a placebo group (n = 48) treated with a placebo formula whose appearance and taste were the same as LSF for 6 weeks. All patients were treated by standard antiparkinsonism medicine according to the PD guideline of China. The changes of the quantity of saliva (QS) (mL), frequency of nighttime urination (FNU) and early sleep activity (ESA), and nocturnal activity (NA) by analyzing actigraphic records as the primary results and the total score of unified Parkinson’s disease rating scale (UPDRS) and the Epworth Sleepiness Scale (ESS) as the secondary results were used to evaluate the clinical efficacy in both groups. Results. There were no significant differences in the baseline values of QS, FNU, NA, ESA, UPDRS total score, and ESS between the two groups. At the end of week 6, the QS, FNU, NA, and ESA in the LSF group showed superior results to those of the placebo group with no differences in the total UPDRS score between the two groups during the investigation. The ESS was significantly improved at the end of week 6 compared with the baseline and the placebo group. Laboratory test results indicated there were no side effects in either group. Conclusion. The findings of LSF treatment have clear clinical effects in patients with sialorrhea and frequent overnight urination. LSF thus appears to be a potential choice as an additional drug that can improve the sialorrhea and frequent overnight urination symptoms of PD patients