Subwavelength Metamaterial Unit Cell for Low-Frequency Electromagnetic Absorber Applications

Raman measurements were made on polycrystalline Bi2xPbxSr1:6Ln0:4CuO6 for Ln=fLa,Nd, Sm, Eug with various x and doping states. Our measurements suggest a signi cant Bicontribution to the 118cm1 mode but not to the 70cm1 mode which instead shifts to lowerfrequencies with increasing number of CuO2 layers in the Bi-based family. Shifts in the O(2)Srapical oxygen mode can be attributed to unit cell contraction within experimental error.

Download Full-text

Theoretical Modeling of the N-H and N-D Stretching Bands of Hydrogen-Bonded 1-Methylthymine Crystal and Its Deuterated Form

Computing Letters ◽

10.1163/157404006779194141 ◽

2006 ◽

Vol 2 (4) ◽

pp. 205-219

Author(s):

Marek Boczar ◽

Łukasz Boda ◽

Marek J. Wójcik

Keyword(s):

Hydrogen Bonds ◽

High Frequency ◽

Molecular Crystals ◽

Low Frequency ◽

Unit Cell ◽

Fermi Resonance ◽

Bending Vibrations ◽

Theoretical Simulation ◽

Stretching Vibrations ◽

Centrosymmetric Dimers

Theoretical model for vibrational interactions in the hydrogen bonds in molecular crystals with four molecules forming two centrosymmetric dimers in the unit cell is presented. The model takes into account anharmonic-type couplings between the high-frequency N-H(D) and the low-frequency N•••O stretching vibrations in each hydrogen bond, resonance interactions (Davydov coupling) between equivalent hydrogen bonds in each dimer, resonance interdimer interactions within an unit cell and Fermi resonance between the N-H(D) stretching fundamental and the first overtone of the N-H(D) in-plane bending vibrations. The vibrational Hamiltonian, selection rules, and expressions for the integral properties of an absorption spectrum are derived. The model is used for theoretical simulation of the νs stretching bands of 1-methylthymine and its ND derivative at 300 K. The effect of deuteration is successfully reproduced by our model.

Download Full-text

A computational study of the molecular and crystal structure and selected physical properties of octahydridosilasequioxane, (Si 2 O 3 H 2 ) 4 . II. Vibrational analysis

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2011.0473 ◽

2011 ◽

Vol 468 (2139) ◽

pp. 851-870 ◽

Cited By ~ 4

Author(s):

C. J. H. Schutte ◽

J. A. Pretorius

Keyword(s):

Ir Spectra ◽

Phonon Dispersion ◽

Computational Study ◽

Point Group ◽

Low Frequency ◽

Vibrational Analysis ◽

Unit Cell ◽

Molecular Spectra ◽

Vibrational Modes ◽

Free Molecule

A computational study of octahydridosilasequioxane, Si 8 O 12 H 8 , as a free molecule and when embedded in the unit cell R -3, Z =3, showed that the point group of the free molecule is indeed O h , but that its crystal symmetry is reduced to C 3i . Since the molecular and site-group symmetries influence the vibrational structure of a molecule, a full computational vibrational analysis of the isolated molecule and when embedded in the crystal lattice, is reported here. The analysis of the free molecular spectra given here agrees with that of its experimental infra-red (IR)-spectra and allows the assignment of all the vibrational modes, while the computed phonon dispersion of the crystal confirms the assignment of the internal vibrational modes of the molecule in the crystal. The computed and experimental IR spectra as well as Raman spectra show no indication of serious vibrational intermolecular coupling owing to the presence of multiple molecules in the unit cell. This may be the result of a weak intermolecular vibrational coupling in the solid state, which may feature in the low-frequency modes.

Download Full-text

Lattice Dynamical Model for Graphite-Bromine Intercalation Compounds

MRS Proceedings ◽

10.1557/proc-20-301 ◽

1982 ◽

Vol 20 ◽

Cited By ~ 4

Author(s):

R. Al-Jishi ◽

G. Dresselhaus

Keyword(s):

Brillouin Zone ◽

High Frequency ◽

Low Frequency ◽

Unit Cell ◽

Intercalation Compounds ◽

Dynamical Model ◽

Von Karman ◽

Zone Folding ◽

Von Kármán ◽

Brillouin Zone Center

ABSTRACTA Born-von Kármán lattice dynamical model for the graphite Br2 intercalation compounds is presented. The low frequency bromine branches are calculated using a commensurate (√3 × √13)R(30°, 13.9°) unit cell with two Br2 molecules/unit cell. In-plane zone folding is used to calculate the high frequency graphitic modes at the Brillouin zone center.

Download Full-text

Low-Frequency Electromagnetic Properties of an Alternating Stack of Thin Uniaxial Dielectric Laminae and Uniaxial Magnetic Laminae

Zeitschrift für Naturforschung A ◽

10.1515/zna-1991-0502 ◽

1991 ◽

Vol 46 (5) ◽

pp. 384-388

Author(s):

Reese Patrick S. ◽

Akhlesh Lakhtakia

Keyword(s):

Low Frequency ◽

Optic Axis ◽

Unit Cell ◽

Electromagnetic Properties ◽

Characteristic Matrix ◽

Vector Method

Abstract Analysis is carried out for an alternating arrangement of laminae which have either uniaxial permittivity or uniaxial permeability dyadics. The unit cell is constructed of two laminae such that the ones with the uniaxial permittivity dyadic alternate with the ones with the uniaxial permeability dyadic through the stack. It is assumed that both dyadics have the same optic axis. The 4-vector method is utilized to construct a characteristic matrix for the two-lamina unit cell. After assuming that each lamina is electrically thin, the properties of an equivalent medium are obtained: both the permeability and the permittivity dyadics of the equivalent medium are biaxial

Download Full-text

Flexible and elastic metamaterial absorber for low frequency, based on small-size unit cell

Applied Physics Letters ◽

10.1063/1.4885095 ◽

2014 ◽

Vol 105 (4) ◽

pp. 041902 ◽

Cited By ~ 94

Author(s):

Y. J. Yoo ◽

H. Y. Zheng ◽

Y. J. Kim ◽

J. Y. Rhee ◽

J.-H. Kang ◽

...

Keyword(s):

Low Frequency ◽

Metamaterial Absorber ◽

Unit Cell

Download Full-text

Broadband low-frequency noise reduction using Helmholtz resonator-based metamaterial

Noise Control Engineering Journal ◽

10.3397/1/376932 ◽

2021 ◽

Vol 69 (4) ◽

pp. 351-363

Author(s):

Jhalu Gorain ◽

Chandramouli Padmanabhan

Keyword(s):

Transmission Loss ◽

Low Frequency ◽

Helmholtz Resonator ◽

Broadband Noise ◽

Unit Cell ◽

Frequency Noise ◽

Noise Attenuation ◽

Low Frequency Noise ◽

Low Frequencies ◽

Pu Foam

Achieving broadband noise attenuation at low frequencies is still a significant challenge. Helmholtz resonators offer good low-frequency noise attenuation but are effective only over a narrow band; the cavity volume required at these frequencies is also larger. This article proposes a new broadband acoustic metamaterial (AMM) absorber, which uses polyurethane (PU) foam embedded with small-size resonators tuned to different frequencies. The AMM design is achieved in three phases: (1) develop a transfer-matrix-based one-dimensionalmodel for a resonator with intruded neck; (2) use this model to develop a novel band broadeningmethod, to select appropriate resonators tuned to different frequencies; and (3) construct a unit cell metamaterial embedded with an array of resonators into PU foam. A small-size resonator tuned to 415 Hz is modified, by varying the intrusion lengths of the neck, to achieve natural frequencies ranging from 210 to 415 Hz. Using the band broadening methodology, 1 unit cell metamaterial is constructed; its effectiveness is demonstrated by testing in an acoustic impedance tube. The broadband attenuation characteristics of the constructed unit cell metamaterial are shown to match well with the predicted results. To demonstrate further the effectiveness of the idea, a metamaterial is formed using 4 periodic unit cells and is tested in a twin room reverberation chamber. The transmission loss is shown to improve significantly, at low frequencies, due to the inclusion of the resonators.

Download Full-text

Classical homogenization to analyse the dispersion relations of spoof plasmons with geometrical and compositional effects

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2015.0472 ◽

2015 ◽

Vol 471 (2182) ◽

pp. 20150472 ◽

Cited By ~ 7

Author(s):

J.-F. Mercier ◽

M. L. Cordero ◽

S. Félix ◽

A. Ourir ◽

A. Maurel

Keyword(s):

Dispersion Relation ◽

Guided Waves ◽

Mass Density ◽

Low Frequency ◽

Unit Cell ◽

Real Problem ◽

Hard Material ◽

Effective Parameters ◽

Effective Medium Theories ◽

Spoof Plasmons

We show that the classical homogenization is able to describe the dispersion relation of spoof plasmons in structured thick interfaces with periodic unit cell being at the subwavelength scale. This is because the interface in the real problem is replaced by a slab of an homogeneous birefringent medium, with an effective mass density tensor and an effective bulk modulus. Thus, explicit dispersion relation can be derived, corresponding to guided waves in the homogenized problem. Contrary to previous effective medium theories or retrieval methods, the homogenization gives effective parameters depending only on the properties of the material and on the geometry of the microstructure. Although resonances in the unit cell cannot be accounted for within this low-frequency homogenization, it is able to account for resonances occurring because of the thickness of the interface and thus, to capture the behaviour of the spoof plasmons. Beyond the case of simple grooves in a hard material, we inspect the influence of tilting the grooves and the influence of the material properties.

Download Full-text

Homogenization and Equivalent In-Plane Properties of Hexagonal and Re-Entrant Honeycombs

Volume 10: Mechanics of Solids and Structures, Parts A and B ◽

10.1115/imece2007-42400 ◽

2007 ◽

Cited By ~ 2

Author(s):

Stefano Gonella ◽

Massimo Ruzzene

Keyword(s):

Equations Of Motion ◽

Low Frequency ◽

Unit Cell ◽

Numerical Code ◽

Continuum Models ◽

Propagation Characteristics ◽

Phase Velocities ◽

Lattice Unit ◽

Different Levels ◽

Plane Wave Propagation

The investigation of equivalent in-plane properties for hexagonal and re-entrant (auxetic) lattices can be carried out through the analysis of the partial differential equations associated with their homogenized continuum models. A homogenization technique is adopted based on the approximation of the discrete lattice equations according to the finite differences formalism. The technique can be used in conjunction with a finite element (FE) description of the lattice unit cell and therefore allows handling structures with different levels of complexity and various internal geometries within a general and compact framework that can be easily implemented in a numerical code. The in-plane wave propagation characteristics of honeycombs can be investigated with the proposed approach: approximate phase velocities can be calculated from the equations of motion for the low-frequency modes and compared with the exact values obtained through a Fourier analysis of the unit cell.

Download Full-text