Image theory for chiral bodies

Image theory for a chiral body over a perfect electric or magnetic conducting ground plane is developed using the chiral volume equivalence theorem and conventional image theory for electric and magnetic currents. It is shown that the image of the chiral body has the same material parameters as the original body, except that the chirality admittance of the image is the negative of the original. In essence the mirror image of a chiral object is that object, such as a helix, with the opposite handedness. Alternatively, the same results can be obtained using tensor analysis     

A finite element analysis on electromagnetic waves in rectangular dielectric chirowaveguide

A finite element algorithm on eigenvalue problem of the dielectric waveguide with chiral material is presented. The chiral material is defined by the constitution relations which make the electromagnetic coupling between the electric and magnetic fields by means of the chirality admittance. The chiral material has potential applications in the areas of infrared and mm-wave band. For different chirality admittance, the computation is developed for different structure of waveguides which are difficult for analytical calculation. From the eigenvalues and the eigenvectors, the dispersion curves, the modes and the field patterns are obtained. The maximum value of dispersion curves is obvious greater than that without chiral material. The main points of the results of finite element calculation are consistent with those of analytical approach.     

Distributed feedback lasers in chiral media

The combined effects of chirality and gain (or loss) on wave propagation and coupling in periodic structures is investigated here. The focus is on distributed feedback (DFB) lasers in a transversely unbounded periodic slab with spatially modulated electromagnetic parameters. The analysis uses a coupled-mode approach employing a canonical physical model of chiral materials to predict the effects of modulated chirality admittance on DFB lasers. Results for DFB laser behavior in chiral media are compared and contrasted to that in achiral media. It is found that, under certain circumstances, the electric and magnetic field coupling, which is characteristic of chiral materials, results in a lower threshold gain for DFB lasers in media with a given index of refraction and characteristic impedance. It is also found that chiral index-coupled or gain-coupled DFB lasers exhibit the same spectral mode properties as achiral DFB lasers     

Canonical sources and duality in chiral media [antenna arrays]

The authors examine the characteristics of antenna arrays embedded in unbounded chiral media using the Green's dyadic for electric sources and the Green's vector for magnetic sources. The purpose is to bring to light the new characteristics of sources, both point and extended, which interact with this medium and to examine general characteristics of sources located in a medium with handedness. Very simple quality relations are presented that are characteristic of chiral media when the results are written in terms of the circular eigenmodes. Appropriate measures of chirality such as the chirality admittance and impedance and a dimensionless chirality factor are introduced as needed. It is shown that, in the far field, both point and extended sources, whether electric or magnetic, radiate two electromagnetic eigenmodes which are of opposing handedness. Sources that access only one of the eigenmodes of the medium are demonstrated. Several applications of the results and array performance in chiral media are noted     

Propagation characteristics of a circular waveguide filled with a chiroferrite medium

A chiroferrite is made from chiral objects immersed in a magnetically biased ferrite. A waveguide including a chiroferrite is anticipated to possess some novel features due to the presence of chirality in combination with anisotropy. In this paper, the propagation characteristics of a circular metal waveguide filled with a chiroferrite medium are investigated by an analytical procedure. The equations of relations between the transverse components and the longitudinal ones of electromagnetic fields in general chiroferrite waveguides are derived in a cylindrical coordinate system. The coupled wave equations for the longitudinal electric and magnetic fields are decoupled into two Helmholtz equations which are then solved analytically. The characteristic equation is formulated for the circular chiroferrite waveguide. Propagation constants varying with the structural and material parameters have been calculated for several lower chiral modes. A number of interesting features have been revealed by the numerical results.     

A simple theory for optimizing finite width ELF magnetic fieldshields for minimum dependence on source orientation

The effectiveness of single layer, finite width, planar extremely low frequency (ELF) magnetic field shields is strongly dependent upon the orientation of the field sources. Since source information is difficult to obtain, the issue of designing shields which are independent of source orientation is important. Here, a simple analytic model for shielding by multiple layer, finite width, planar shields constructed from perfect electric and perfect magnetic material is presented. This is augmented by a study of conditions for which the perfect material approximation is valid. The simple model is used to determine strategies for designing shields which are independent of source orientation. It is found that two layer perfect electric/magnetic shields perform significantly better than single layer shields     

Power Reflection and Transmission Coefficients for Meander‐Line Polarizers with a Chiral Slab

This paper presents a theoretical investigation of power reflection and transmission coefficients for a meander‐line polarizer placed periodically on a chiral slab. It is assumed that a linearly polarized transverse magnetic wave is incident on a chiral slab from the air region. In the analysis, we derive the electric and magnetic fields in the modal form in the air and chiral regions. We obtain power reflection and transmission coefficients in a straightforward manner after matching the tangential components of the electric and magnetic fields at the boundaries. We present numerical results for the power reflection and transmission coefficients versus frequency and incident angle for different values of the chirality admittance. A meander‐line polarizer placed on a dielectric slab can convert a linearly polarized wave to a circularly polarized wave. The design parameters for a meander‐line polarizer are the dimensions of the meander‐line and the values of the dielectric slab. Replacing a dielectric slab with a chiral slab introduces a new independent parameter which controls the wave polarization.     

Faraday chiral media revisited. I. Fields and sources

Faraday chiral media, previously conceptualized as chiroplasmas or chiroferrites, are envisioned to combine the effects of Faraday rotation and chirality. Electromagnetic field representations for arbitrary sources are derived after the previous correct characterization of the constitutive relations of such media. The scalar Hertz potential (SHP) technique is employed and its applicability is thoroughly investigated. In particular, it is shown that all field components can be derived from one scalar Green function (plus so-called auxiliary source potentials) in source problems, whereas one scalar superpotential suffices for source-free problems. Expressions pertaining to radiation from electric and magnetic dipole sources are presented in a simple and compact form. Further generalizations of the results and the actual realizability of Faraday chiral media are discussed     

Analysis of a Metal-Coated Planar Dielectric Waveguide with Chiral Cladding

The propagation characteristics of a metal-coated planar waveguide with chiral media filled in the cladding are presented. The effects of chirality on cutoff, dispersion characteristics and field distributions of the waveguide are studied. The results show that cladding chirality brings phase chopping to the transverse electric field component of those modes with odd mode numbers.     

Chirality of Metal Nanoparticles in Chiral Mesoporous Silica

Chiroptical properties of pure inorganic material have been achieved by dispersing small amounts of achiral Ag nanoparticles into highly ordered chiral mesoporous silica. There are three types of chirality in chiral mesoporous silica: i) the helical hexagonal surface, ii) the helical pore orientation, and iii) the helical arrangement of aminopropyl groups on the surface of the mesopores, all of which impart plasmonic circular dichroism and have been investigated by introducing Ag nanoparticles into the as‐made, calcined and extracted chiral mesoporous silica, respectively. The three types of optical response originate from asymmetric plasmon‐plasmon interactions of achiral Ag nanoparticles in three types of chiral environments. Among the three sources of chirality, the helical pore orientation was considered to be predominantly responsible for the optical response owing to the high efficiency of nanoscale chirality. Interestingly, large Ag nanoparticles aggregation as a result of calcination still resulted in a strong optical activity, even the chiral mesostructure was destroyed completely. Rather than the pitch length, the length of helical channel was more effective for increasing the intensity of plasmonic circular dichroism due to longitudinal propagation of Ag nanoparticles along helical channel. Such novel chiral inorganic material will bring new opportunities in non‐linear optics, biosensors and chiral recognition.     

Calculation and measurement of the effective chirality parameter ofa composite chiral material over a wide frequency band

Materials that are effectively chiral at microwave frequencies can be fabricated by embedding identical, randomly oriented chiral inclusions, often metal helices, in a continuous matrix. We show that the chirality parameter can be calculated in the dilute limit using single scattering theory. The required tumble-averaged forward scattering by an individual inclusion is determined by the method of moments. Values of the effective chirality parameter are determined directly from the constitutive parameters of the matrix and the geometry and concentration of the inclusions. Comparisons are made with measurements previously reported in the literature. In addition, a chiral composite material was fabricated specifically to validate the calculations over frequencies including resonance. The measurements agree well with the calculations, providing quantitative values of the chirality parameter over a wide frequency band. It appears that the chirality parameter is appreciable only near the resonant frequencies of the inclusion. Finally, it is clear that an oscillator model can be used to describe the frequency dependence of the complex chirality parameter, and that therefore our results are consistent with the Kramers-Kronig relation     

Scattering and shielding properties of a chiral-coated fiber-reinforced plastic composite cylinder

A state-equation approach is developed to tackle a fiber-reinforced plastic composite (FRPC) cylinder coated by chiral media. This cylinder can be treated as consisting of multilayered bi-isotropic and anisotropic materials. As the chiral coating is properly designed, the backscattering of the linearly polarized plane wave almost disappears in some specific frequency bands. Numerical results of the monostatic echo widths show that a high invisible characteristic of the cylinder can be obtained by appropriately selecting the chiral layer thickness, chiral impedance, chiral nonreciprocity, chirality, and cylinder radius. It is also found that, with the presence of the chiral coating, the bistatic echo widths may be greatly reduced except in the forward scattering direction. However, cross-polarized penetrated fields occur owing to the chiral coating. Adding an interior metal coating is suggested to enhance the shielding performance without sacrificing the invisible property of the cylinder.     

手征球壳的低频电磁屏蔽效应分析

分析了手征介质球壳的低频电磁屏蔽效应，给出了一组手征电磁屏蔽球壳的设计曲线。比较了手征材料的一般电、磁屏蔽材料的不同之处，重点说明了该材料的特殊性。理论计算表明，这种新型材料是一种非常有前途的电磁屏蔽材料。     

A comprehensive study of discontinuities in chirowaveguides

We provide a comprehensive study of two- and three-dimensional discontinuities in chirowaveguides. The multimode coupled-mode method is an effective numerical approach to analyze this problem. After obtaining the coupled-mode equations, we diagonalize the coupling matrix to obtain a multimode scattering matrix rather than the usual two-mode approximation. We calculate the scattering properties of coaxial waveguides partially filled with lossy chiral media. Excellent agreement is observed between our results and those obtained by the mode-matching method. We also compare our results in the achiral case for dielectric material partially filled rectangular waveguide with experimental data and results obtained by the mode-matching method. Excellent agreement is again found. Based on our analysis, numerical and analytical results are displayed to provide physical insight into the problem. First, we discuss the effects of the chirality admittance on scattering properties and find that the sensitivity of the scattering parameters to chirality admittance increases as the chirality admittance increases. Second, we find the dielectric constant has a great influence on the scattering parameters. Third, we find the relative influence of height and width of chiral obstacles in rectangular waveguides.     

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

Constitutive relations which include electric quadrupole terms, in addition to electric and magnetic dipole terms, are used to describe the “optical activity”, in particular the circular birefringence, of an anisotropic chiral medium which is nonmagnetic. The resulting permittivity and chirality tensors are then used to predict the rotation of the polarization plane of a linearly polarized wave propagating in a circular waveguide filled with the medium. The numerical predictions were tested by measurements between 2.4 and 4 GHz on a 2 m long artificial crystal in a circular waveguide and it was found that the rotation of the polarization was within 13% of the predicted value-good agreement after considering the possible sources of error. It is thus established that the effect of electric quadrupoles must be included when modeling the optical activity of anisotropic chiral media in the long wavelength regime. The anisotropic chiral media which are dealt with here can be classified according to the crystallographic point groups to which they belong, and they may therefore also be considered to be artificial crystals     

Vector circuit method applied for chiral slab waveguides

Eigenvalue equations for the propagation constants of lightwaves in open chiral slab waveguides are derived. The analysis makes use of vector circuit modeling of a chiral slab, the method which has been previously applied for calculating reflection and transmission of electromagnetic waves in chiral multilayer structures. The general eigenvalue equation for the guide which is valid for arbitrary boundary impedance conditions on the slab interfaces is derived, and three special cases are analyzed in detail: an open chiral dielectric slab with dielectric half spaces of the opposite sides of the slab, a chiral slab on an ideally conducting surface, and a chiral slab on an ideal magnetic surface. The theory is visualized by calculated dispersion curves indicating the chirality effect on the wave propagation characteristics     

小型化宽带磁场探头仿真与设计

提出了一种近场磁场探头,可用于集成电路电磁辐射发射测量,对电子设备中的辐射源定位。探头采用四层印刷电路板设计,介质材料采用高性能、低损耗的Rogers 4350B 材料,确保结构简单和小型化。多层板结构可以有效屏蔽外部空间中的电场耦合。通过使用过孔栅栏和同轴过孔结构实现良好的阻抗匹配,并且提高工作频率。同时,屏蔽过孔能够形成屏蔽腔,有效抑制谐振,提高电场抑制性能。采用HFSS 仿真软件得到磁场探头的性能参数,并进行实物加工。实验结果表明,探头工作频带可达到12 GHz,空间分辨率为2 mm,有良好的电场抑制度,仿真与实测结果吻合良好。     

手征介质填充双平板中导模的反射和透射特性

用多模网络与严格模匹配相结合的方法,对纵向填充一层、两层和多层手征介质的双平板中导模的反射和透射特性进行了分析和求解.分析中在横截面采用等效传输线,在纵向采用多模传输线方法,并且利用结构的对称性使得问题简化.对各种不同情形进行了数值计算,讨论了手征参数和波导结构的尺寸对反射和透射特性的影响.     

Review of Circuit Approach to Calculate Shielding Effectiveness

The shielding effectiveness of an enclosure at low frequencies can be readily computed using a circuit approach. Not only does this technique include the effects of the properties of the shield material, but it also includes the details of the geometry of the enclosure. Furthermore, this approach allows a nonempirical consideration of mesh enclosures and the effects of resistive seams in enclosure walls. By working with the circuit analogue, penetration by transient fields can also be computed. Essentially the enclosure is viewed as an antenna. In the case of magnetic shielding effectiveness, the enclosure is viewed as a short circuited loop antenna. In the case of electric field penetration, the enclosure is viewed as a fat electric dipole. Using this characterization and exact solutions where available, the current distribution on the outside of the enclosure is first determined. Then, based on the current distribution, the penetrating fields are computed. The equations are developed in such a way as to preserve a lumped circuit analogue for the low-frequency region. The basic circuit equations for magnetic field penetration are rederived from a rigorous solution. Rules to estimate the rise-time, fall-time, and peak magnitudes of transient penetrating fields are developed. The electric shielding effectiveness is developed in a similar manner. In both cases the results of the circuit approach agree well with those based on rigorous solutions of the electromagnetic boundary conditions. The results also agree with published experimental data on both large and small enclosures.     

Controlling Chiral Spin States of a Triangular‐Lattice Magnet by Cooling in a Magnetic Field

Magnetic materials with a non‐collinear and non‐coplanar arrangement of magnetic moments hosting a nonzero scalar spin‐chirality exhibit unique magnetic and spin‐dependent electronic transport properties. The spin chirality often occurs in materials where competing exchange interactions lead to geometrical frustrations between magnetic moments and to a strong coupling between the crystal lattice and the magnetic structure. These characteristics are particularly strong in Mn‐based antiperovskites where the interactions and chirality can be tuned by substitutional modifications of the crystalline lattice. This study presents evidence for the formation of two unequal chiral spin states in magnetically ordered Mn_3.338Ni_0.651N antiperovskite based on density functional theory calculations and supported by magnetization measurements after cooling in a magnetic field. The existence of two scalar spin‐chiralities of opposite sign and different magnitude is demonstrated by a vertical shift of the magnetic‐field dependent magnetization and Hall effect at low fields and from an asymmetrical magnetoresistivity when the applied magnetic field is oriented parallel or antiparallel to the direction of the cooling field. This opens up the possibility of manipulating the spin chirality for potential use in the emerging field of chiral spintronics.