Showing papers by "Yue-Sheng Wang published in 2018"

Continuously Tunable Acoustic Metasurface for Transmitted Wavefront Modulation

Abstract: Fixed properties are one thing, but the design of $t\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}e$ metasurfaces is significant for real-world applications, as an integrated, active control mechanism is much more resilient to the actual requirements of an ever-changing environment. However, design is often limited by the difficulty of finding a suitable tuning mechanism. The authors here design a tunable acoustic metasurface consisting of helical cylinders screwed into a circular plate. This screw-and-nut setup is used to obtain arbitrary phase profiles over a wide frequency range, and furthermore may inspire other sorts of designs.

Nonlinear vibration of piezoelectric nanoplates using nonlocal Mindlin plate theory

Abstract: This article investigates the nonlinear vibration of piezoelectric nanoplate with combined thermo-electric loads under various boundary conditions. The piezoelectric nanoplate model is developed by using the Mindlin plate theory and nonlocal theory. The von Karman type nonlinearity and nonlocal constitutive relationships are employed to derive governing equations through Hamilton's principle. The differential quadrature method is used to discretize the governing equations, which are then solved through a direct iterative method. A detailed parametric study is conducted to examine the effects of the nonlocal parameter, external electric voltage, and temperature rise on the nonlinear vibration characteristics of piezoelectric nanoplates.

Broadband single-phase hyperbolic elastic metamaterials for super-resolution imaging

Abstract: Hyperbolic metamaterials, the highly anisotropic subwavelength media, immensely widen the engineering feasibilities for wave manipulation. However, limited by the empirical structural topologies, the reported hyperbolic elastic metamaterials (HEMMs) suffer from the limitations of the relatively narrow frequency width, inflexible adjustable operating subwavelength scale and difficulty to further improve the imaging resolution. Here, we show an inverse-design strategy for HEMMs by topology optimization. We design broadband single-phase HEMMs supporting multipolar resonances at different prescribed deep-subwavelength scales, and demonstrate the super-resolution imaging for longitudinal waves. Benefiting from the extreme enhancement of the evanescent waves, an optimized HEMM at an ultra-low frequency can yield an imaging resolution of ~λ/64, representing the record in the field of elastic metamaterials. The present research provides a novel and general design methodology for exploring the HEMMs with unrevealed mechanisms and guides the ultrasonography and general biomedical applications.

Thermoelastic instability of functionally graded materials with interaction of frictional heat and contact resistance

Abstract: Both of the frictional heat and thermal contact resistance have a grave responsibility for the localized high temperature (hot spots) at the contact region, which is known as one of the most dangerous appearances in the brakes systems. In this paper, we study the thermoelastic instability (TEI) of a functionally graded material (FGM) half-plane sliding against a homogeneous half-plane at the in-plane direction. The interaction of the frictional heat and thermal contact resistance is taken into account in the TEI analysis. The material properties of the FGM half-plane are supposed to follow the exponential function along the thickness direction. The coupled TEI problem of FGMs is solved by using the perturbation method. The frictionally excited TEI of FGMs is also considered by neglecting the effect of the thermal contact resistance. The results show that the thermal contact resistance, sliding speed and gradient index have significant influence on the TEI. It is found that the variation of the gradient index of FGMs can increase the critical sliding speed and critical heat flux, and therefore improve the TEI of the sliding system.

Photonic and phononic surface and edge modes in three-dimensional phoxonic crystals

Abstract: We investigate the photonic and phononic surface and edge modes in finite-size three-dimensional phoxonic crystals. By appropriately terminating the phoxonic crystals, the photons and phonons can be simultaneously guided at the two-dimensional surface and/or the one-dimensional edge of the terminated crystals. The Bloch surface and edge modes show that the electromagnetic and acoustic waves are highly localized near the surface and edge, respectively. The surface and edge geometries play important roles in tailoring the dispersion relations of the surface and edge modes, and dual band gaps for the surface or edge modes can be simultaneously achieved by changing the geometrical configurations. Furthermore, as the band gaps for the bulk modes are the essential prerequisites for the realization of dual surface and edge modes, the photonic and phononic bulk-mode band gap properties of three different types of phoxonic crystals with six-connected networks are revealed. It is found that the geometrical characteristic of the crystals with six-connected networks leads to dual large bulk-mode band gaps. Compared with the conventional bulk modes, the surface and edge modes provide a new approach for the photon and phonon manipulation and show great potential for phoxonic crystal devices and optomechanics.

Two-Dimensional Frictionless Contact of a Coated Half-Plane Based on Couple Stress Theory

Abstract: Based on the couple stress theory, the size-dependent frictionless contact problem between a rigid punch and a homogeneous coated half-plane is investigated in this paper. This theory describes the size effect that emerges from the material microstructures by introducing the characteristic material length. With the aid of the Fourier transform method, the size-dependent contact problem of the rigid flat, cylindrical, parabolic and wedge punches is reduced to a Cauchy singular integral equation of the first kind. Subsequently, it is transformed into algebraic ones and solved numerically by using Gauss-Chebyshev integration formulas. Numerical results for the normal and in-plane contact stresses, contact width and indentation depth are given. The effect of the length scale parameters on the contact stress and indentation is predicted by the couple stress elasticity, which shows a strong dependence on the characteristic material length.

The coupled thermoelastic instability of FGM coatings with arbitrarily varying properties: in-plane sliding

Abstract: The hot spot caused by frictional heat and thermal contact resistance is one of the most important reasons for hot-cracks and brake failure in brake systems. This paper simulates the brake system as a functionally graded material (FGM) coated half-plane sliding against a homogeneous half-plane. The motivation of using the FGM coating is to improve the coupled thermoelastic instability (TEI) of the brake system due to the thermal contact resistance and frictional heat. The thermoelastic properties of the FGM coating are assumed to vary arbitrarily along the thickness direction. The homogeneous multi-layered model is employed to simulate arbitrary properties of the coating. The perturbation method and transfer matrix method are used to derive the characteristic equation of the coupled TEI problem. The effects of the thermal contact resistance, friction coefficient, heat generation factor and different gradient types of the FGM coating on the stability boundaries are discussed in detail. The results show that the stability boundary is sensitive to the varying thermal parameters of the FGM coating, and an appropriate gradient type can adjust the coupled TEI of the sliding system.

Evanescent-wave tuning of a locally resonant sonic crystal

Abstract: Locally resonant sonic crystals can support band gaps at low frequencies defined by resonances internal to the unit cell. Band gap frequencies are dictated by the choice of resonators and their interaction with the medium supporting acoustic wave propagation. We show that locally resonant band gaps can be tuned by engineering the dispersion of the evanescent waves appearing in the propagation medium at the resonator sites. Specifically, we experimentally consider a tubular waveguide filled with different levels of water and grafted with a periodic array of acoustic resonators. Water filling continuously tunes the dispersion of evanescent waves by changing the waveguide cross-section. Dispersion relations and transmission properties are obtained with a three-dimensional time-harmonic finite element model of wave propagation. Numerical and experimental results are found to be in good agreement. The present work is relevant to the practical design of tunable acoustic devices.

Liquid-assisted tunable metasurface for simultaneous manipulation of surface elastic and acoustic waves

Abstract: A tunable and multi-functional one-dimensional metasurface, which is formed by engraving periodic semi-ellipse grooves on the surface of an aluminum half-space, is proposed in this paper. One characteristic of the metasurface is the manipulation of multi-physical fields, i.e. it could be utilized to manipulate surface elastic and acoustic waves simultaneously. The dispersion curves of the elastic and acoustic waves can be effectively tuned by adding liquids into the grooves. Based on the tunability different applications can be realized by adding different volumes of different liquids into the grooves. As an example, simultaneous rainbow trapping of the surface elastic and acoustic waves is demonstrated in the metasurface. Moreover, a resonant cavity where the elastic and acoustic waves are highly confined is reported. The proposed metasurface paves the way to the design of multi-functional devices for simultaneous control of elastic and acoustic waves.A tunable and multi-functional one-dimensional metasurface, which is formed by engraving periodic semi-ellipse grooves on the surface of an aluminum half-space, is proposed in this paper. One characteristic of the metasurface is the manipulation of multi-physical fields, i.e. it could be utilized to manipulate surface elastic and acoustic waves simultaneously. The dispersion curves of the elastic and acoustic waves can be effectively tuned by adding liquids into the grooves. Based on the tunability different applications can be realized by adding different volumes of different liquids into the grooves. As an example, simultaneous rainbow trapping of the surface elastic and acoustic waves is demonstrated in the metasurface. Moreover, a resonant cavity where the elastic and acoustic waves are highly confined is reported. The proposed metasurface paves the way to the design of multi-functional devices for simultaneous control of elastic and acoustic waves.