Design and Modeling of Chiral Elastic Metamaterials

In this study, design and modeling of chiral elastic metamaterials are investigated to achieve subwavelength negative refraction of elastic waves while maintaining reasonable sample sizes. Negative effective mass density and elastic modulus occur simultaneously in the metamaterial owing to simultaneous translational and rotational resonances. We experimentally demonstrated negative refraction of the longitudinal elastic wave at the deep subwavelength scale in a stainless steel plate.

Active Metamaterials for Elastic Wave Control

The growing technological development in electro/magneto-mechanical couplings of smart materials introduced a controlling degree of freedom for passive elastic metamaterials. Active elastic metamaterials could allow fine control of the material physical behavior to induce new functional properties that cannot be introduced by the passive approaches. Two types of active elastic metamaterials with shunted piezoelectric materials and electrorheological elastomers are suggested. The active elastic metamaterialcould provide a new design methodology for adaptive wave filters, high signal-to-noise sensors and structural health monitoring applications.

Elastic Metamaterials with Multi-resonators and its Applications

We investigated dispersion curves and the band gap structure of a multi-resonator mass-in-mass lattice system. The unit cell of the lattice system consists of three separate masses connected by linear springs. It was demonstrated that the band gaps can be shifted by varying the spring constant and the magnitude of the internal masses. The promising application of the metamaterial for blast wave mitigation was also demonstrated.

Experimental Investigation of Elastic Metamaterials with Negative Mass Densities

A microstructure design of anisotropic resonant inclusions is investigated for the elastic metamaterial plate. Experimental validation is then conducted in the anisotropic metamaterial plate through both harmonic and transient wave testing, from which the anisotropic effective dynamic mass density, group and phase velocities are determined as functions of frequency. The strongly anisotropic mass density along two principal orientations is observed experimentally and the prediction from the experimental measurements agrees well with that from the numerical simulation.

Guided Wave Propagation in Anisotropic Metamaterial Plate

Both in-plane and out-of-plane guided waves in a thin plate with local resonators are studied numerically and experimentally. In the experiment, piezoelectric transducers were used to generate and receive guided wave signals. The results showed that the numerical predictions are in very good agreement with the experimental measurements. Specifically, the connection between the local resonance in the thin plate and its wave attenuation mechanism was discussed.

Coupled Vibroacoustic Modeling of Membrane-type Acoustic Metamaterials

The membrane-type acoustic metamaterial (MAM) has been demonstrated as a super absorber for low-frequency sound. A theoretical vibroacoustic model is developed to reveal sound energy reflection and absorption mechanism within the MAM under a plane normal incidence. The sound reflection and absorption of the MAM are obtained and discussed, which are also in good agreement with the prediction from the finite element method. The application of the membrane-type acoustic metamaterials for acoustic liner was also investigated.

Structural Health Monitoring of Honeycomb Composites

Due to the complex nature of such composite structures, understanding of the guided wave propagation mechanism in honeycomb composite panels with different frequencies inherently imposes many challenges. We conduct the experimental and numerical study to investigate the wave propagation mechanism in honeycomb sandwich structures using piezoelectric actuators/sensors and develop a multiple debonding detection technique based on the transmitted guided waves in the structure.

Surface Wave Monitoring of Civil Infrastructures

Concrete structures have been used widely in civil infrastructural systems. Due to the complex nature of its microstructure, nondestructive testing (NDT) of concrete inherently imposes many challenges, which can cause severe limitations to the resolution and the sensitivity of observed signals. In the study, a numerical simulation based on the Finite Element (FE) model was first performed to investigate surface wave generation and reception using piezoelectric actuators/sensors, especially at relatively higher frequency cases. The results provided a basic understanding of some features of the microstructure effects on the surface wave propagation. An experimental testing was also conducted to validate the numerical simulation.

Continuum Modeling of Dynamic Behavior of Nanowires

The continuum modeling of the mechanical behavior of nanowires has recently attracted much attention due to its simplicity and efficiency. However, there are still some critical issues to be solved. We demonstrated the importance of accounting for the effects of initial stresses in the nanowires that are caused by deformation due to surface stresses; we note that such initial stresses have previously been neglected in most existing continuum models.

Frequency-domain Reverse Wave Technique for Fast Damage Detection

The time-reversal technique was successfully used in structural health monitoring (SHM) for quantitative imaging of the damages. We study the technique in frequency-wavenumber (f-k) domain for fast real-time imaging of multiple damages in plate using scattered flexural plate waves. Based on Mindlin plate theory, the time reversibility of dispersive flexural waves in isotropic plate is theoretically investigated in f-k domain. A fast damage imaging technique is developed by using cross-correlation between the back-propagated scattered wavefield and incident wavefield in frequency domain.