Joo Hwan Oh

It has been long believed that a total mode conversion between longitudinal and shear elastic waves can only be achieved at a certain incidence angle. Here, we show that a total mode conversion can be achieved for a broad range of incidence angles by a specially designed elastic metasurface, namely, transmodal metasurface. From the generalized reflection law, we found that the incident longitudinal wave can be totally converted to a reflected shear wave over a broad range of incidence angles if

Sub-wavelength imaging is possible if metamaterial lenses realizing hyperbolic or elliptic Equi-Frequency Contours (EFCs) are used. Theoretically, lenses exhibiting hyperbolic EFCs allow imaging with unlimited resolution, but only metamaterials of elliptic EFCs producing limited resolution have been so far realized in elastic field. Thus, an elastic metamaterial lens realizing truly hyperbolic EFCs can lead to superior-resolution ultrasonic imaging. This Letter presents the realization of an ela

Vibration shielding is a core concept in applications including precision manufacturing, vehicle design, and interfloor noise reduction in architecture. Blocking broad ranges of extremely low frequencies remains a challenging, unresolved problem. The authors present an elastic metamaterial based on the dual ideas of $r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n$ $s\phantom

Metamaterials realizing stop bands have attracted much attentions recently since they can break-through the well-known mass law. However, achieving the stop band at extremely low frequency has been still a big challenge in the fields of elastic metamaterials. In this paper, we propose a new metamaterial based on the idea of the zero rotational stiffness, to achieve extremely low frequency stop band for flexural elastic waves. Unlike the previous ways to achieve the stop band, we found that the z

This work presents the realization of one-sided wave transmission by using a specially engineered phononic crystal structure. It is an inverted bi-prism phononic crystal engineered for a horizontally incident elastic wave at a specific frequency. The incident wave along one direction is shown to be totally reflected by the bi-prism while the incident wave along the opposite direction transmitted through it with refraction, also evident from experiments. An application of the proposed bi-prism ma

Achieving total mode conversion from longitudinal to shear waves for a broad incident angle has been a big scientific challenge in elastic fields, which was impossible to be achieved in classical elastic wave theory. In this paper, we propose and realize a refractive transmodal elastic metasurface that can convert an incident longitudinal wave to a shear wave for a broad incident angle. Here, the total mode conversion is achieved via a sufficiently large phase gradient, while the full transmissi

In this paper, we explore an elastic metamaterial adjoining the frequency band of negative density and that of negative stiffness. If the band-adjoining occurs, a fully continuous widened stop band covering the entire ranges of the negative density and stiffness can form. The resulting stop band can be useful for various vibration applications such as vibration shielding. We show that the band-adjoining frequency is characterized by a standing wave with peculiar “unbalanced” motions. Experiments

By numerical simulations, we show that active wave-guiding can be realized in a stop band frequency range of a phononic crystal (PC) if piezoelectric inclusions in the PC are electrically controlled. The advantages of the wave-guiding are that no permanent geometry or material change is needed and that somewhat arbitrarily shaped waveguides can be formed actively in PC structures. The analysis with supercells consisting of piezoelectrically coupled and decoupled inclusions shows that symmetric w

This work investigates wave attenuation and dissipation mechanisms in viscoelastic phononic crystals (VPCs) having different inclusion types in a long-wavelength regime. After investigating the intrinsic damping properties of VPCs for different inclusion sizes and materials, we carried out wave simulations revealing the energy dissipation by a finite VPC structure inserted inside an elastic medium. The simulations, supported by physical reasoning, showed that air- and metal-embedded VPCs can ind

Abstract Elastic metasurfaces are artificial thin layers composed of sub-wavelength structures designed to manipulate wave propagation such as anomalous refraction/reflection. Despite recent active researches, achieving a really thin metasurface has been a challenge, since it has been almost impossible to design a single unit to satisfy both the 2π phase span and the full transmission. In this paper, we revealed the way to achieve both conditions by a single unit so that a really thin elastic me

Generally, it has been known that the optical branch of a simple one-dimensional periodic structure has a negative group velocity at the first Brillouin zone due to the band-folding effect. However, the optical branch of the flexural wave in one-dimensional periodic structure doesn't always have negative group velocity. The problem is that the condition whether the group velocity of the flexural optical branch is negative, positive or positive-negative has not been studied yet. In consequence, w