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The concept of birefringence, commonly treated as a property resulting from more than one polar-ization, is associated with different refractive indices, depending on polarization. Here, we propose a two-dimensional elastic metamaterial engineered to demonstrate birefringence of single polarization for flexural waves. By adopting a network of beams with "overpass" structures to upset the topology of unit cells from a conventional elastic plate, birefringence of single polarization at low frequencies can be real-ized , confirmed through measured band structures and double refraction of the flexural waves; this is further supported by full-wave simulations and models. Our approach can engineer birefringence at low frequencies in which the wavelength is at least a few times larger than the lattice constant, further allowing efficient control of beam splitting, filtering , multiplexing with applications for elastic wave devices.

Ao Li, Xiaozhao Zhang, Yihan Guo, Jingyi Wang, Yiran Hao, Yixuan Gu, Ying Jie Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, People’s Republic of ChinaCorrespondence: Ying Jie, Tel +86-13693572296, Fax +861058265900, Email jie_yingcn@aliyun.comAbstract: Dry eye is a disease that severely affects patients’ quality of life, increasing the global burden on public health and finance. There is growing evidence that a poor lifestyle is a significant risk factor for dry eye. Along with the development of society, sleep, as a way of life, is also constantly changing. The main manifestations of sleep disorders are reduced sleep time, circadian rhythm disturbances, and sleep breathing disturbances. Sleep disorders and their secondary systemic diseases have attracted wide attention in recent years. This review mainly explored the correlation between sleep disorders and dry eye, and found that sleep-related problems and other factors potentially leading from sleep disorders could be critical factors for dry eye. These results suggest that ophthalmologists should pay attention to the sleep health problems in patients with dry eye, and we hope that this paper can provide help for future research in this field.Keywords: circadian rhythm, sleep, sleep disorders, dry eye

Chao Yan,* Ao Li,* Yiran Hao, Xiaozhao Zhang, Yihan Guo, Yixuan Gu, Yinghui Wang, Ya Wen, Lei Tian, Ying Jie Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, People’s Republic of China*These authors contributed equally to this workCorrespondence: Ying Jie; Lei Tian, Tel +86-13693572296 ; +86-18600166885, Fax +861058265900, Email jie_yingcn@aliyun.com; tianlei0131@163.comPurpose: To explore the relationship between symptomatic dry eye and circadian typology in college students.Methods: This study included 269 students from 3 Chinese universities. All participants completed the ocular surface disease index (OSDI) questionnaire, the morningness-eveningness questionnaire (MEQ), and the Pittsburgh sleep quality index (PSQI) questionnaire. Participants were grouped into 3 types by the reduced MEQ (rMEQ) score:E-Type, N-Type, and M-Type. All these parameters were then analyzed for the effect on the severity of dry eye.Results: The occurrence rates of poor sleep quality (PSQI> 5) and symptomatic dry eye (OSDI > 13) in the college students were 53.2% and 40.2%, respectively. The distribution of the circadian typology differed significantly among the college students with different dry eye severities (χ2 = 59.44, P = 0. 000), and E-type was associated with the most severe dry eye symptoms. The OSDI and PSQI scores were both significantly different among college students with different chronotypes (F = 22.14, P = 0.000; F = 15.21, P = 0.000; respectively). For both scores, the E-type scored the highest, followed by N-type, and M-type was the lowest. The circadian typology was an independent factor for dry eye. The risk of E-Type was 6.99 times higher than that of M-Type (P = 0.000), and the risk of N-types was 3.23 times higher than that of M-Type (P = 0.000). Sleep quality was also an independent risk factor for dry eye (P = 0.000). Gender and awareness of dry eye were not risk factors for dry

Willis coupling has been recently realized for acoustic waves and elastic flexural waves as the analogy of bianisotropy originally in electromagnetism. For further extension, we investigate its formulation in water waves and other kinds of elastic waves. Possible designs and numerical formulation in extracting the effective media with Willis coupling will also be discussed. © 2023, META Conference. All rights reserved.

For mechanical waves, Willis coupling means a cross-coupling between stress and velocity or between momentum and strain. In contrary to its realization in acoustic and elastic waves, whether Willis coupling exists in water waves, as another kind of mechanical wave, is still unknown. Here, we propose and establish the concept of Willis coupling in water waves as the cross-coupling between the horizontal velocity at the free surface and the acceleration potential or between the vertical displacement of the water free surface and the flux. Thanks to the surface wave feature of water waves, the proposed metamaterial's resonating conditions can be tuned by using the wave shoaling effect. With a proper three-dimensional design, Willis coupling can still have significant effects with resonance in the long-wavelength regime. Furthermore, by adding loss in the Willis metamaterial, asymmetric reflectance and absorption can be achieved, which are useful for applications such as seismic isolation, coastal protection, water-wave energy-harnessing, and also for constructing non-Hermitian exceptional points. © 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.

Recently, higher-order topologies have been experimentally realized, featuring topological corner modes (TCMs) between adjacent topologically distinct domains. However, they have to comply with specific spatial symmetries of underlying lattices, hence their TCMs only emerge in very limited geometries, which significantly impedes generic applications. Here, we report a general scheme of inducing TCMs in arbitrary geometry based on Dirac vortices from aperiodic Kekulé modulations. The TCMs can now be constructed and experimentally observed in square and pentagonal domains incompatible with underlying triangular lattices. Such bound modes at arbitrary corners do not require their boundaries to run along particular lattice directions. Our scheme allows an arbitrary specification of numbers and positions of TCMs, which will be important for future on-chip topological circuits. Moreover, the general scheme developed here can be extended to other classical wave systems. Our findings reveal rich physics of aperiodic modulations, and advance applications of TCMs in realistic scenarios. © 2021 American Physical Society.

Transformation optics, which is generically applicable to other classical waves such as acoustic and elastic waves, provides an emerging design paradigm to manipulate waves. However, some lenses and optical-transformation devices require a singular refractive index; meeting this requirement is a significant challenge. A method called transmutation can relax some types of index singularity into finite anisotropy around the singularity. Here, we show that such lenses with a singularity for flexural waves can be obtained by approaching a near-zero thickness of the plate precisely at the location of the singularity. As examples, we demonstrate a series of Eaton lenses theoretically and experimentally by projecting the refractive index in space onto the thickness in plates and by working in a broad frequency range in which impedance mismatch is negligible. This framework offers an insight into feasible methods that can be used to develop singular devices such as cloaking devices on thin flexible curved plates and can be further extended to a general methodology for shaping elastic waves. We hope that this elastic platform can also be a test bed to indirectly study unprecedented phenomena enabled by gravitational and quantum fields in terms of analog models. © 2021 American Physical Society.