The electric quadrupole contribution to the circular birefringence of nonmagnetic anisotropic chiral media: a circular waveguide experiment

Theron, I.P.; Cloete, J.H.

doi:10.1109/22.536028

Cited by 25 publications

(19 citation statements)

References 26 publications

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“…Although the current configuration is very similar for both polarizations, resembling standing waves with four (4 GHz) and six nodes (10 GHz), its intensity is significantly different which leads to the observed dichroism resonances. In the framework of multipole theory, the observed gyrotropy arises from the coupling of the electric and magnetic dipole moments, but can also include a contribution from the electric quadrupole moment, since the metamaterial is anisotropic [17,18]. In order to further investigate the metamaterial's response, we calculate the induced multipole moments [19] under plane wave illumination The multipole moments have been calculated by the following relations:…”

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confidence: 99%

Gyrotropy of a Metamolecule: Wire on a Torus

et al. 2009

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In this letter, we present the first experimental study of a new chiral metamaterial consisting of toroidal wire windings. We show that the metamaterial exhibits three bands of circular dichroism in the GHz range. We discuss the response of the structure in terms of multipole moments, including the (magnetic) toroidal dipole moment.Toroidal, doughnut-shaped structures are ubiquitous in nature, appearing on scales which range from the subatomic [1, 2] to the astronomical [3]. On the molecular level, the torus shape is preferred by numerous biological and chemical macromolecules, such as DNA condensates [4], proteins [5] and oligosaccharides [6], to name just a few. Toroidal symmetries are also encountered frequently in solid-state systems including carbon nanotubes [7] and ferroelectrics [8,9]. Although the behavior of such systems has been studied extensively, their interaction with electromagnetic radiation is not well understood. Indeed, within the framework of classical electrodynamics, unusual phenomena associated with violation of Lorentz reciprocity [10] and non-radiating configurations [11] have been predicted for toroidal structures and their interactions. Nevertheless, such phenomena are usually weak [12,13] and, therefore, experimental investigations are rare. In this letter, we study a new artificial chiral medium, originally suggested in [14], consisting of an array of toroidal wire windings in a metamaterial' configuration. We show that such a metamaterial exhibits strong gyrotropic response which is attributed to different terms of its multipole expansion.In contrast to artificial gyrotropic media, where handedness is usually associated with the direction of a "twist vector" following a cork-screw law along the helicity axis, the situation is more complicated when the structure possesses toroidal symmetry. Here, the twist vector rotates along the torus, and therefore a corresponding direction can not be defined. However, although no helicity axis exists, the structure has two well-defined enantiomeric forms, corresponding to different directions of the winding (see Fig. 1a). Based on this concept, we manufactured a chiral toroidal metamaterial with a unit cell consisting of four connected square loops that were formed by horizontal and vertical copper wire segments (see Fig. 1b). The resulting windings were embedded in dielectric bars with permittivity = 4.5 − 0.081i. The size of the unit cell was 15x15 mm rendering the metamaterial non-diffracting up to 20 GHz. Transmission experiments were performed at normal incidence, from 2 to 14 GHz, in an anechoic chamber using two broadband horn antennas (Schwarzbeck M. E. model BBHA 9120D). The transmission spectra were recorded with a vector network analyzer. The intensity and phase of the structure's response to right and left circularly polarized light are presented in Figs. 2a and 2b, respectively. As it can be seen in Fig. 2a, experimental results (solid line) are in good agreement with finite element numerical simulations (solid circles). Two resonan...

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Gyrotropy of a Metamolecule: Wire on a Torus

et al. 2009

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“…(Equations (48) and (50) can be inverted as in the step leading from (21) to (22).) One can readily verify that the space and time properties of (47)-(53) are those required in the HO decomposition (Sec.…”

Section: Realizations Of the Ho Decomposition For Homogeneous Mediamentioning

confidence: 96%

“…15 Agreement has been found between measured and theoretical values based on V (2) i j in (25). 22 3. Gyrotropic birefringence in magnetic crystals is associated with W i j .…”

Section: Property Tensors and Observablesmentioning

confidence: 99%

Multipole theory and the Hehl–Obukhov decomposition of the electromagnetic constitutive tensor

Lange

Raab

2015

Journal of Mathematical Physics

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The Hehl-Obukhov decomposition expresses the 36 independent components of the electromagnetic constitutive tensor for a local linear anisotropic medium in a useful general form comprising seven macroscopic property tensors: four of second rank, two vectors, and a four-dimensional (pseudo)scalar. We consider homogeneous media and show that in semi-classical multipole theory, the first full realization of this formulation is obtained (in terms of molecular polarizability tensors) at third order (electric octopole-magnetic quadrupole order). The calculations are an extension of a direct method previously used at second order (electric quadrupole-magnetic dipole order). We consider in what sense this theory is independent of the choice of molecular coordinate origins relative to which polarizabilities are evaluated. The pseudoscalar (axion) observable is expressed relative to the crystallographic origin. The other six property tensors are invariant (with respect to an arbitrary choice of each molecular coordinate origin), or zero, at first and second orders. At third order, this invariance has to be imposed (by transformation of the response fields)-an aspect that is required by consideration of isotropic fluids and is consistent with the invariance of transmission phenomena in dielectrics. Alternative derivations of the property tensors are reviewed, with emphasis on the pseudoscalar, constraint-breaking, translational invariance, and uniqueness. C 2015 AIP Publishing LLC. [http://dx.

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“…This was then compared with measurements on a 2 m long crystal constructed as discussed above with the result shown in Figure 5. Due to space limitations details of the waveguide analysis and experiment will be given in a separate paper [36]. Some of the error sources will also be discussed there.…”

Section: Measurementmentioning

confidence: 99%