Suppression of left-handed properties in disordered metamaterials

FerroelectricandpiezoelectricpropertiesoftungstensubstitutedSrBi2Ta2O9

ferroelectricceramics

IndraniCoondoo*,S.K.Agarwala,A.K.Jhab

aSuperconductivityandCryogenicsDivision,NationalPhysicalLaboratory,DrK.S.KrishnanRoad,NewDelhi110012,IndiabDepartmentofAppliedPhysics,DelhiCollegeofEngineering,BawanaRoad,Delhi110042,India

1.Introduction

Defectsincrystalssignificantlyinfluencephysicalandvarious

otherpropertiesofmaterials[1].Forinstance,asitiswellknown,

dopingbyotherelementsleadstosignificantchangesinthe

electricalpropertiesofsilicon.Historically,‘‘defectengineering’’

hasbeendevelopedinthefieldofsemiconductingmaterialssuch

ascompoundsemiconductorsaswellasindiamond,SiandGe

[2–4].Subsequently,theconceptofdefectengineeringhasbeen

appliedtootherfunctionalmaterials,andthesignificantimprove-

mentinmaterialpropertieshavebeenachievedinhightransition-

/ / 19 October 2006 / Page 1 / 10.1126/science.1133628 Recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We present here the first practical realization of such a cloak: in our demonstration, a copper cylinder is ‘hidden’ inside a cloak constructed according to the previous theoretical prescription. The cloak is constructed using artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreases scattering from the hidden object whilst at the same time reducing its shadow, so that the cloak and object combined begin to resemble free space. A new approach to the design of electromagnetic structures has recently been proposed, in which the paths of electromagnetic waves are controlled within a material by introducing a prescribed spatial variation in the constitutive parameters (1, 2). The recipe for determining this variation, based on coordinate transformations (3), enables us to arrive at structures that would be otherwise difficult to conceive, opening up the new paradigm of transformation optics (4, 5). One possible application of transform optics and transform media is that of electromagnetic cloaking, in which a material is used to render a volume effectively invisible to incident radiation. The design process for the cloak involves a coordinate transformation that squeezes space from a volume into a shell surrounding the concealment volume. Note that Maxwell’s equations are form invariant to coordinate transformations, so that only the components of the permittivity tensor, ε, and the permeability tensor, µ, are affected by the transformation (5), becoming both spatially varying and anisotropic. By implementing these complex material properties, the concealed volume plus the cloak appear to have the properties of free space when viewed externally. The cloak thus neither scatters waves nor imparts a shadow in the transmitted field—either of which would enable the cloak to be detected. Other approaches to invisibility either rely on the reduction of backscatter, or make use of a resonance in which the properties of the cloaked object and the cloak itself must be carefully matched (6, 7). It might be of concern that we are able to achieve two different solutions to Maxwell’s equations that both have, in principle, the exact same field distributions on a surface enclosing the region of interest. Indeed, the uniqueness theorem would suggest that these two solutions would be required to have the exact same medium within the surface. The uniqueness theorem, however, applies only to isotropic media (8, 9); the required media that result from our coordinate transformations are generally anisotropic. Such media have been shown to support sets of distinct solutions having identical boundary conditions (10, 11). The effectiveness of a transformation based cloak design was first confirmed computationally in the geometric optic limit (1, 5), and then in full-wave, finite-element simulations (12). Advances in the development of metamaterials (13), especially with respect to gradient index lenses (14, 15), have made the physical realization of the specified, complex material properties feasible. Here, we implement a two dimensional cloak, due to its simpler fabrication and measurement requirements. Recently, we have demonstrated the capability of obtaining detailed spatial maps of the amplitude and phase of the electric field distribution internal to two dimensional, negative index, metamaterial samples at microwave frequencies (16). Using this measurement technique, we confirm the working of our cloak by comparing our measured field maps to simulations. In both the cloaking simulations and the measurements presented here, the object being cloaked is a conducting cylinder at the inner radius of the cloak; this is the largest and most strongly scattering object that can be concealed in a cloak of cylindrical geometry. For the cloak design, we start with a coordinate transformation that compresses space from the cylindrical region 0rb<< into the annular region 'arb<<. A simple transformation that accomplishes this goal is the following, '''barrazzbθθ−=+== (1) where the primed and corresponding unprimed variables are

期刊

BIOMATERIALS

Acta Biomaterialia

Advanced Healthcare Materials

Journal of Materials Chemistry B

Biofabrication

DENTAL MATERIALS

Journal of Biomedical Nanotechnology

COLLOIDS AND SURFACES B-BIOINTERFACES

MACROMOLECULAR BIOSCIENCE

EUROPEAN CELLS & MATERIALS

Biomaterials Science

Materials Science & Engineering C-Materials for Biological Applications

Biomedical Materials

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A

Bioinspiration & Biomimetics

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS

Journal of the Mechanical Behavior of Biomedical Materials

JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE

Biointerphases

Artificial Cells Nanomedicine and Biotechnology

JOURNAL OF BIOMATERIALS APPLICATIONS

JOURNAL OF BIOMATERIALS SCIENCE-POLYMER EDITION

International Journal of Polymeric Materials and Polymeric Biomaterials

Title: Being Left-Handed in a Right-Handed World

In the predominantly right-handed world we live in, being left-handed

can often present challenges that many take for granted. From simple

daily tasks to the most basic social interactions, the right-handed bias is

evident. However, what does it mean to be left-handed in a right-handed

world?

Firstly, let's explore the biological aspect. Left-handedness is a result of

brain lateralization, where one side of the brain dominates over the

other for specific functions. In most people, the left side of the brain

controls language and fine motor skills, while the right side controls

spatial awareness and gross motor skills. However, in left-handers, this

pattern is often reversed. This means that left-handers have a different

way of processing information and performing tasks, often making them