Author
Sang-Hoon Kim
Other affiliations: Australian National University
Bio: Sang-Hoon Kim is an academic researcher from Mokpo National Maritime University. The author has contributed to research in topics: Bose gas & Lens (optics). The author has an hindex of 8, co-authored 37 publications receiving 309 citations. Previous affiliations of Sang-Hoon Kim include Australian National University.
Topics: Bose gas, Lens (optics), Ground state, Exhaust gas, Seismic wave
Papers
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TL;DR: In this article, a cylindrical shell-type waveguide composed of many Helmholtz resonators was constructed to convert a seismic wave into an attenuated one without touching the building that they want to protect.
Abstract: We developed a new method of an earthquake-resistant design to support conventional aseismic system using acoustic metamaterials. The device is an attenuator of a seismic wave that reduces the amplitude of the wave exponentially. Constructing a cylindrical shell-type waveguide composed of many Helmholtz resonators that creates a stop-band for the seismic frequency range, we convert the seismic wave into an attenuated one without touching the building that we want to protect. It is a mechanical way to convert the seismic energy into sound and heat.
80 citations
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TL;DR: In this paper, a cylindrical shell-type waveguide is constructed to create a stopband for the seismic wave, which converts the wave into an evanescent wave for some frequency range without touching the building.
Abstract: We have developed a new method of an earthquake-resistant design to support conventional aseismic designs using acoustic metamaterials. We suggest a simple and practical method to reduce the amplitude of a seismic wave exponentially. Our device is an attenuator of a seismic wave. Constructing a cylindrical shell-type waveguide that creates a stop-band for the seismic wave, we convert the wave into an evanescent wave for some frequency range without touching the building we want to protect.
73 citations
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TL;DR: In this paper, a soundproof window or wall which is transparent to airflow is presented, which consists of a three-dimensional array of strong diffraction-type resonators with many holes centered on each individual resonator.
Abstract: A soundproof window or wall which is transparent to airflow is presented. The design is based on two wave theories: the theory of diffraction and the theory of acoustic metamaterials. It consists of a three-dimensional array of strong diffraction-type resonators with many holes centered on each individual resonator. The negative effective bulk modulus of the resonators produces evanescent wave, and at the same time the air holes with subwavelength diameter existed on the surfaces of the window for macroscopic air ventilation. The acoustic performance levels of two soundproof windows with air holes of 20mm and 50mm diameters were measured. The sound level was reduced by about 30 - 35dB in the frequency range of 400 - 5,000Hz with the 20mm window, and by about 20 - 35dB in the frequency range of 700 - 2,200Hz with the 50mm window. Multi stop-band was created by the multi-layers of the window. The attenuation length or the thickness of the window was limited by background noise. The effectiveness of the soundproof window with airflow was demonstrated by a real installation.
59 citations
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TL;DR: In this paper, the authors developed a new method of earthquake-proof engineering to create an artificial seismic shadow zone using acoustic metamaterials, which is a mechanical method of converting the seismic energy into sound and heat.
Abstract: We developed a new method of earthquake-proof engineering to create an artificial seismic shadow zone using acoustic metamaterials. By designing huge empty boxes with a few side-holes corresponding to the resonance frequencies of seismic waves and burying them around the buildings that we want to protect, the velocity of the seismic wave becomes imaginary. The meta-barrier composed of many meta-boxes attenuates the seismic waves, which reduces the amplitude of the wave exponentially by dissipating the seismic energy. This is a mechanical method of converting the seismic energy into sound and heat. We estimated the sound level generated from a seismic wave. This method of area protection differs from the point protection of conventional seismic design, including the traditional cloaking method. The artificial seismic shadow zone is tested by computer simulation and compared with a normal barrier.
37 citations
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TL;DR: In this paper, the properties of the uniform Bose gas were studied within the optimized variational perturbation theory (Gaussian approximation) in a self-consistent way.
Abstract: The properties of the uniform Bose gas are studied within the optimized variational perturbation theory (Gaussian approximation) in a self-consistent way. It is shown that the atomic Bose-Einstein condensate with a repulsive interaction becomes unstable when the gas parameter $\ensuremath{\gamma}=\ensuremath{\rho}{a}^{3}$ exceeds a critical value ${\ensuremath{\gamma}}_{crit}\ensuremath{\approx}0.01$. The quantum corrections beyond the Bogoliubov-Popov approximation to the energy density, chemical potential, and pressure in powers of $\sqrt{\ensuremath{\gamma}}$ expansions are presented.
22 citations
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TL;DR: An overview of the topic is presented in this article, including state-of-the-art review and future directions to increase innovation in developing both these materials and structures, as well as future directions for developing these materials.
222 citations
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TL;DR: The shielding performance of a metabarrier is investigated in a scaled experimental model and surface ground motion can be reduced up to 50% in frequency regions below 10 Hz, relevant for the protection of buildings and civil infrastructures.
Abstract: 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.
174 citations
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TL;DR: In this paper, the authors present the design and modeling techniques and design guidelines of acoustic metamaterial plates for elastic wave absorption and structural vibration suppression, and reveal the actual working mechanism.
153 citations
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TL;DR: In this paper, an acoustic multi-stopband metamaterial plate is designed by integrating two-degree of freedom (DOF) mass-spring subsystems with an isotropic plate to act as vibration absorbers.
122 citations
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TL;DR: In this article, 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.
Abstract: 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.
117 citations