Multifunctional Material Systems: A state-of-the-art review

Resonant metamaterials have been proposed to reflect or redirect elastic waves at different length scales, ranging from thermal vibrations to seismic excitation. However, for seismic excitation, where energy is mostly carried by surface waves, energy reflection and redirection might lead to harming surrounding regions. Here, we propose a seismic metabarrier able to convert seismic Rayleigh waves into shear bulk waves that propagate away from the soil surface. The metabarrier is realized by burying sub-wavelength resonant structures under the soil surface. Each resonant structure consists of a cylindrical mass suspended by elastomeric springs within a concrete case and can be tuned to the resonance frequency of interest. The design allows controlling seismic waves with wavelengths from 10-to-100 m with meter-sized resonant structures. We develop an analytical model based on effective medium theory able to capture the mode conversion mechanism. The model is used to guide the design of metabarriers for varying soil conditions and validated using finite-element simulations. We investigate the shielding performance of a metabarrier in a scaled experimental model and demonstrate that surface ground motion can be reduced up to 50% in frequency regions below 10 Hz, relevant for the protection of buildings and civil infrastructures.

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Engineered metabarrier as shield from seismic surface waves.

Acoustic metamaterial plates for elastic wave absorption and structural vibration suppression

Acoustic multi-stopband metamaterial plates design for broadband elastic wave absorption and vibration suppression

Recently, with advances in acoustic metamaterial science, the possibility of sound attenuation using subwavelength structures, while maintaining permeability to air, has been demonstrated. However, the ongoing challenge addressed herein is the fact that among such air-permeable structures to date, the open area represents only small fraction of the overall area of the material. In the presented paper in order to address this challenge, we first demonstrate that a transversely placed bilayer medium with large degrees of contrast in the layers' acoustic properties exhibits an asymmetric transmission, similar to the Fano-like interference phenomenon. Next, we utilize this design methodology and propose a deep-subwavelength acoustic metasurface unit cell comprising nearly 60% open area for air passage, while serving as a high-performance selective sound silencer. Finally, the proposed unit-cell performance is validated experimentally, demonstrating a reduction in the transmitted acoustic energy of up to 94%. This ultra-open metamaterial design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among others.

Ultra-open acoustic metamaterial silencer based on Fano-like interference

Divergence exponents of the first-order quantum correction of a two-dimensional hard-sphere Bose atoms are obtained by an effective field theory method. The first-order correction to the ground-state energy density with respect to the zeroth-order is given by $\mathcal{E}_1/\mathcal{E}_0\sim |D-2|^{-\alpha}|\ln\gamma|^{-\alpha'}$, where D is the spatial dimension, and γ is the gas parameter (γ = naD). As D →2, α = α′ = 1. We show that the first-order quantum correction of the energy density is not perturbative in low dimensions of D < 2.2 regardless of any gas parameter which is much less than unity.

First-Order Quantum Correction to the Ground-State Energy Density of Two-Dimensional Hard-Sphere Bose Atoms

The ground-state energy density of an interacting dilute Bose gas system is studied in the canonical transformation scheme. It is shown that the transformation scheme enables us to calculate a higher order correction of order na3 in the particle depletion and ground-state energy density of a dilute Bose gas system, which corresponds to the density fluctuation resulting from the excited states. Considering a two-body interaction only, the coefficient of the na3 term is shown to be 2(π-8/3) for the particle depletion, and 16(π-8/3) for the ground-state energy density.

Ground-state energy density of a dilute Bose gas in the canonical transformation

The present disclosure relates to an exhaust gas after-treatment apparatus having improved durability, which includes: an exhaust gas oxidation catalyst part which oxidizes exhaust gas; an exhaust gas filtering part which is connected to the exhaust gas oxidation catalyst part, and filters the exhaust gas; a selective catalyst reducing part which is connected to the exhaust gas filtering part; and an ammonia oxidation catalyst part which is connected to the selective catalyst reducing part, in which a first gas detection sensor for detecting a generated amount of nitrogen compound in the exhaust gas flowing from the exhaust gas filtering part, and a selective catalyst reducing bypass valve for selectively blocking the exhaust gas from flowing into the selective catalyst reducing part are installed at a front side of the selective catalyst reducing part, and the exhaust gas after-treatment apparatus includes a control part which is electrically connected so as to control whether to operate the selective catalyst reducing bypass valve and the selective catalyst reducing part on the basis of a gas amount detection signal

Exhaust gas after-treatment apparatus having improved durability

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Erratum: “Acoustic imaging by three-dimensional acoustic Luneburg meta-lens with lattice columns” [Appl. Phys. Lett. 118, 091902 (2021)]

The macroscopic quantum states of a condensed neutral Bose gas in one-dimensional power-law traps are obtained by solving the Gross-Pitaevskii equation numerically. A suitable candidate for a trial wave function for the variational calculation of ground state energy is suggested, and shown that the suggested function produces a lower ground state energy than the conventional Gaussian trial wave function.

Sang-Hoon Kim

Papers

First-Order Quantum Correction to the Ground-State Energy Density of Two-Dimensional Hard-Sphere Bose Atoms

Ground-state energy density of a dilute Bose gas in the canonical transformation

Exhaust gas after-treatment apparatus having improved durability

Erratum: “Acoustic imaging by three-dimensional acoustic Luneburg meta-lens with lattice columns” [Appl. Phys. Lett. 118, 091902 (2021)]

Condensate wave function of neutral Bose atoms in power-law traps