We have fabricated sonic crystals, based on the idea of localized resonant structures, that exhibit spectral gaps with a lattice constant two orders of magnitude smaller than the relevant wavelength. Disordered composites made from such localized resonant structures behave as a material with effective negative elastic constants and a total wave reflector within certain tunable sonic frequency ranges. A 2-centimeter slab of this composite material is shown to break the conventional mass-density law of sound transmission by one or more orders of magnitude at 400 hertz.

http://science.sciencemag.org/content/sci/289/5485/1734.full.pdf

Locally Resonant Sonic Materials

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

저작근 근전도에 관한 정상교합자와 ii급 부정교합자의 비교 연구

The present study demonstrates the creation of a stable, superhydrophobic surface using the nanoscale roughness inherent in a vertically aligned carbon nanotube forest together with a thin, conformal hydrophobic poly(tetrafluoroethylene) (PTFE) coating on the surface of the nanotubes. Superhydrophobicity is achieved down to the microscopic level where essentially spherical, micrometer-sized water droplets can be suspended on top of the nanotube forest.

/pdf/superhydrophobic-carbon-nanotube-forests-4wzbqm5f24.pdf

Superhydrophobic Carbon Nanotube Forests

The emergence of artificially designed subwavelength electromagnetic materials, denoted metamaterials, has significantly broadened the range of material responses found in nature. However, the acoustic analogue to electromagnetic metamaterials has, so far, not been investigated. We report a new class of ultrasonic metamaterials consisting of an array of subwavelength Helmholtz resonators with designed acoustic inductance and capacitance. These materials have an effective dynamic modulus with negative values near the resonance frequency. As a result, these ultrasonic metamaterials can convey acoustic waves with a group velocity antiparallel to phase velocity, as observed experimentally. On the basis of homogenized-media theory, we calculated the dispersion and transmission, which agrees well with experiments near 30 kHz. As the negative dynamic modulus leads to a richness of surface states with very large wavevectors, this new class of acoustic metamaterials may offer interesting applications, such as acoustic negative refraction and superlensing below the diffraction limit.

Ultrasonic metamaterials with negative modulus

Bound states in the continuum (BICs) have received increasing attention from researchers because of their potential applications in photonic crystal fibers, as well as in lasing, sensing, and surface acoustic wave devices. BICs have been experimentally observed in acoustic resonators, photonic crystal slabs, and optical waveguides. Herein, we constructed a topological inductor–capacitor (LC) circuit to observe BICs; the circuit consists of two identical LC Su–Schrieffer–Heeger chains coupled using a middle chain with capacitors. In addition, a BIC in a non-Hermitian system was also experimentally observed by adding different resistances to the original LC circuit. Our experimental and simulation results thus prove that an electrical circuit could be used as a platform to realize BIC. Furthermore, we believe that such a circuit can be extended to two- and three-dimensional models and higher frequencies, making it suitable for electrical device applications, such as antennae, filters, and radio frequency devices.

Bound state in the continuum in topological inductor–capacitor circuit

Here we report an experimental observation of the self-organization effect of polystyrene particles formed by acoustically induced interaction forces. Two types of stable configurations are observed experimentally: one is mechanically equilibrium and featured by nonzero interparticle separations, and the other corresponds to a closely packed assembly, which is created by strong attractions among the aggregated particles. For the former case involving two or three particles, the most probable interparticle separations (counted for numerous independent initial arrangements) agree well with the theoretical predictions. For the latter case, the number of the final stable configurations grows with the particle number, and the occurrence probability of each configuration is interpreted by a simple geometric model.

Sound-mediated stable configurations for polystyrene particles.

Experimental investigation of negative refraction and imaging of 8-fold-symmetry phononic quasicrystals

Unlike the well-known Airy beams that can be deformed beyond paraxial angles, the half-Bessel (HB) Beams can bend to steeper angles. Here we propose an effective metasurface design for constructing two-dimensional acoustic HB beams. The design is based on an array of spatially varied coiling-slit units, each of which mimics the wave responses derived from the analytical expression of the acoustic HB beam. A tradeoff method is utilized here to simplify the variable amplitude responses. The full-wave simulations and experimental measurements consistently manifest the effectiveness of this design process. Potential applications, such as the large-angle bending transport of particles, can be anticipated.

https://iopscience.iop.org/article/10.7567/JJAP.55.110302/pdf

Zhengyou Liu

Papers

Bound state in the continuum in topological inductor–capacitor circuit

Sound-mediated stable configurations for polystyrene particles.

Experimental investigation of negative refraction and imaging of 8-fold-symmetry phononic quasicrystals

Making acoustic half-Bessel beams with metasurfaces

Highly directional liquid surface wave source based on resonant cavity