P. A. Deymier

Acoustic metamaterials and phononic crystals

Introduction to Phononic Crystals and Acoustic Metamaterials.- Discrete One-Dimensional Phononic and Resonant Crystals.- One-Dimensional Phononic Crystals.- 2d-3d Phononic Crystals.- Dynamic Mass Density and Acoustic Metamaterials.- Damped Phononic Crystals and Acoustic Metamaterials.- Nonlinear Periodic Phononic Structures and Granular Crystals.- Tunable Phononic Crystals and Metamaterials.- Nanoscale Phononic Crystals and Structures.- Phononic Band Structures and Transmission Coefficients: Methods and Approaches.

Experimental evidence for the existence of absolute acoustic band gaps in two-dimensional periodic composite media

Transmission of acoustic waves in two-dimensional binary solid/solid composite media composed of arrays of Duralumin cylindrical inclusions embedded in an epoxy resin matrix is studied. The experimental transmission spectrum and theoretical band structure of two periodic arrays of cylinders organized on a square lattice and on a centred rectangular network are reported. Absolute gaps extending throughout the first two-dimensional Brillouin zone are predicted. The measured transmission is observed to drop to noise level throughout frequency intervals in reasonable agreement with the calculated forbidden frequency bands.

Two-dimensional phononic crystal with tunable narrow pass band: Application to a waveguide with selective frequency

We study theoretically the propagation of elastic waves in two-dimensional composite media composed of a square array of hollow steel cylinders embedded in water using the finite-difference time-domain method. These composite media constitute a class of acoustic band gap materials with narrow pass bands in their transmission stop bands. The frequency at which the pass band occurs is tunable by controlling the inner radius of the tubular steel inclusions. The effect of the tube inner radius on the transmission spectrum is semiquantitatively separable from the effect of the composite periodicity. A linear defect formed of a row of hollow cylinders in an array of filled cylinders produces an elastic waveguide that transmits at the narrow pass band frequency. We show that two of these tunable waveguides with different inner radii can be employed to filter and separate two specific frequencies from a broad band input signal.

Tunable magnetoelastic phononic crystals

The feasibility of tuning the band structure of phononic crystals is demonstrated by employing magnetostrictive materials and applying an external magnetic field. Band structures are calculated with a plane wave expansion method that accounts for coupling between the elastic behavior and the magnetic field through the development of elastic, piezomagnetic, and magnetic permeability effective tensors. We show the contactless tunability of the absolute band gaps of a two-dimensional phononic crystal composed of an epoxy matrix and Terfenol-D inclusions. The tunable phononic crystal behaves like a transmission switch for elastic waves when the magnitude of an applied magnetic field crosses a threshold.

Waveguiding in two-dimensional piezoelectric phononic crystal plates

We investigate the possibility of designing phononic crystal-based devices for telecommunication applications using materials commonly employed in microfabrication. We focus our attention on a phononic crystal made of a square array of cylindrical holes drilled in an active piezoelectric PZT5A matrix. Two different structures are considered, namely, a freestanding phononic crystal plate and a plate deposited on a silicon substrate. The geometrical characteristics of the phononic crystal plates (lattice parameter and thickness) were chosen to ensure the existence of an absolute band gap around 1.5GHz; a common frequency in radio frequency telecommunications. Computations of the dispersion curves of these active structures were conducted with the help of the finite element method. We demonstrate the existence of absolute band gaps in the band structure of the phononic crystal plates and, then, the possibility of guided modes inside a linear defect created by removing one row of air holes in the phononic cry...

Evidence of surface acoustic wave band gaps in the phononic crystals created on thin plates

Phononic structures and acoustic band gaps based on bulk materials have been researched in length in the past decades. However, few investigations have been performed on phononic structures in thin plates to form surface acoustic wave (SAW) band gaps. In this letter, we report a new type of phononic crystals manufactured by patterning periodical air-filled holes in thin plates. We confirmed the existence of SAW band gaps in the created phononic crystals through laser ultrasonics measurements. Wide multiple SAW band gaps and special structures, such as narrow pass bands within a band gap were observed experimentally.

Band gap tunability of magneto-elastic phononic crystal

The possibility of control and tuning of the band structures of phononic crystals offered by the introduction of an active magnetoelastic material and the application of an external magnetic field is studied. Two means to obtain large elastic properties variations in magnetoelastic material are considered: Giant magnetostriction and spin reorientation transition effects. A plane wave expansion method is used to calculate the band structures. The magnetoelastic coupling is taken into account through the consideration of an equivalent piezomagnetic material model with elastic, piezomagnetic, and magnetic permeability tensors varying as a function of the amplitude and orientation of the applied magnetic field. Results of contactless tunability of the absolute bandgap are presented for a two-dimensional phononic crystal constituted of Terfenol-D square rod embedded in an epoxy matrix.

Bulk elastic waves with unidirectional backscattering-immune topological states in a time-dependent superlattice

Recent progress in electronic and electromagnetic topological insulators has led to the demonstration of one way propagation of electron and photon edge states and the possibility of immunity to backscattering by edge defects. Unfortunately, such topologically protected propagation of waves in the bulk of a material has not been observed. We show, in the case of sound/elastic waves, that bulk waves with unidirectional backscattering-immune topological states can be observed in a time-dependent elastic superlattice. The superlattice is realized via spatial and temporal modulation of the stiffness of an elastic material. Bulk elastic waves in this superlattice are supported by a manifold in momentum space with the topology of a single twist Mobius strip. Our results demonstrate the possibility of attaining one way transport and immunity to scattering of bulk elastic waves.

Elastic and viscoelastic effects in rubber/air acoustic band gap structures: A theoretical and experimental study

The transmission of acoustic waves through centimeter-scale elastic and viscoelastic two-dimensional silicone rubber/air phononic crystal structures is investigated theoretically and experimentally. We introduce a finite difference time domain method for two-dimensional elastic and viscoelastic composite structures. Elastic fluid-solid phononic crystals composed of a two-dimensional array of cylindrical air inclusions in a solid rubber matrix, as well as an array of rubber cylinders in an air matrix, are shown to behave similarly to fluid-fluid composite structures. These systems exhibit very wide band gaps in their transmission spectra that extend to frequencies in the audible range of the spectrum. This effect is associated with the very low value of the transverse speed of sound in rubber compared to that of the longitudinal polarization. The difference in transmission between elastic and viscoelastic rubber/air crystals results from attenuation of transmission over a very wide frequency range, leaving...

Acoustic band gaps in fibre composite materials of boron nitride structure

We present elastic band-structure results for a new geometry of two-dimensional phononic crystals: the boron nitride- (BN-) like structure. This array is constituted of two kinds of infinite elastic parallel cylinder located at the vertices of a regular hexagon and surrounded by an elastic background. This geometry includes both the triangular and graphite structures as particular cases. The inclusions and matrix are either both fluids or both solids, the constituent materials being water and mercury, and carbon (or tungsten) and epoxy. We discuss the evolution of the band structure, and especially the existence of absolute band gaps, as a function of the ratio between the radii of the two cylinders in the BN geometry. We also discuss the existence of these gaps in relation to the physical parameters of the materials involved, and compare the results with those for square and triangular structures.