Magnetic Polarizability Research Articles

Magnetic Polarizability of Mesons

Using the similarity of mesons (qq¯ bound states) with Positronium (e+e−) and Muonium (μ+e−) we study the interaction of mesons with static magnetic fields. Assuming constituent quarks have magnetic moments we estimate the intrinsic magnetic polarizability of neutral and charged mesons. At the same time we suggest, that due to quantum superposition of (mz=0) spin-triplet and spin-singlet states of mesons in the external magnetic field, the lifetime and decay channels of hidden-flavour mesons J/Ψ and ϒ become modified. We apply our consideration also to light-mass mesons and we speculate on the enhancement of πo→e+e− decay rate in the magnetic field.

Hadron Structure in Chiral Perturbation Theory

We present our predictions for meson form factors for the SU(3) octet and investigate their impact on the pion electroproduction cross sections. The electric and magnetic polarizabilities of the SU(3) octet of mesons and baryons are analyzed in detail. These extensive calculations are made possible by the recent implementation of semi-automatized calculations in fully-relativistic chiral perturbation theory, which allows evaluation of polarizabilities from Compton scattering up to next-to-the-leading order.

Dynamical Casimir-Polder Force Between a Metallic Particle and a Perfectly Conducting Plate

For the first time, we have studied the impact of magnetic polarizability of a neutral metallic particle on the dynamical Casimir-Polder force, when the particle is uniformly moving with relativistic velocity parallel to the surface of an ideally conducting plate. The material properties of particle are taken into account within the Drude model approach.

Effective medium representation and complex modes in 3D periodic metamaterials made of cubic resonators with large permittivity at mid-infrared frequencies

We review some of the techniques that lead to the effective medium representation of a three-dimensional (3D) periodic metamaterial. We consider a 3D lattice of lead telluride cubic resonators at mid-infrared (MIR) frequencies. Each cubic resonator is modeled with both an electric and a magnetic dipole, through a method called the dual dipole approximation. The electric and magnetic polarizabilities of a cubic resonator are computed via full-wave simulations by mapping the resonator's scattered field under electric/magnetic excitation only to the field radiated by an equivalent electric/magnetic dipole. We then analyze the allowed modes in the lattice, with transverse polarization and complex wavenumber, highlighting the attenuation that each mode experiences after one free space wavelength. We observe the presence of two modes with low attenuation constant, dominant in different frequency ranges, able to propagate inside the lattice: this allows the treatment of the metamaterial as a homogeneous material with effective parameters, evaluated by using various techniques. We then show that the metamaterial under analysis allows for the generation of artificial magnetism (i.e., relative effective permeability different than unity, including negative permeability with low losses) at MIR frequencies.

Chiral discrimination via nuclear magnetic resonance spectroscopy

Calculations of nuclear magnetic shielding polarisabilities of cyclic C4H2X2 molecules, for X = O, S, Se and Te, have been carried out. Pseudoscalars of the nuclear magnetic shielding polarisability computed for the heavier nuclei are at least two orders of magnitude larger than those reported so far. Calculations of the rf voltage produced by the rotating chiral electric polarisation, induced by the permanent magnetic dipole moment of 77Se nucleus in 1,2-diselenin and 125Te nucleus in 1,2-ditellurin, are predicted to be ≈40 nV and ≈80 nV, respectively, detectable in principle with a proper experimental set-up. Also the chiral chemical shifts are evaluated and they are found near the experimental detection limit.

Polarizability tensor retrieval for magnetic and plasmonic antenna design

A key quantity in the design of plasmonic antennas and metasurfaces, as well as metamaterials, is the electrodynamic polarizability of a single scattering building block. In particular, in the current merging of plasmonics and metamaterials, subwavelength scatterers are judged by their ability to present a large, generally anisotropic electric and magnetic polarizability, as well as a bi-anisotropic magnetoelectric polarizability. This bi-anisotropic response, whereby a magnetic dipole is induced through electric driving, and vice versa, is strongly linked to the optical activity and chiral response of plasmonic metamolecules. We present two distinct methods to retrieve the polarizibility tensor from electrodynamic simulations. As a basis for both, we use the surface integral equation (SIE) method to solve for the scattering response of arbitrary objects exactly. In the first retrieval method, we project scattered fields onto vector spherical harmonics with the aid of an exact discrete spherical harmonic Fourier transform on the unit sphere. In the second, we take the effective current distributions generated by SIE as a basis to calculate dipole moments. We verify that the first approach holds for scatterers of any size, while the second is only approximately correct for small scatterers. We present benchmark calculations, revisiting the zero-forward scattering paradox of Kerker et al (1983 J. Opt. Soc. Am. 73 765–7) and Alù and Engheta (2010 J. Nanophoton. 4 041590), relevant in dielectric scattering cancelation and sensor cloaking designs. Finally, we report the polarizability tensor of split rings, and show that split rings will strongly influence the emission of dipolar single emitters. In the context of plasmon-enhanced emission, split rings can imbue their large magnetic dipole moment on the emission of simple electric dipole emitters. We present a split ring antenna array design that is capable of converting the emission of a single linear dipole emitter in forward and backward beams of directional emission of opposite handedness. This design can, for instance, find application in the spin angular momentum encoding of quantum information.

Classification of metallic targets using a single frequency component of the magnetic polarisability tensor

A k-nearest neighbour (KNN) classification algorithm has been added to a walk-through metal detection system which is capable of inverting the magnetic polarisability tensor of metallic targets at a frequency of 10 kHz. Pre-computed library data is used to determine the class of the object, e.g. 'knife' or 'mobile phone', and is consequently capable of determining if an object is considered a threat. The results presented show a typical success rate of 95%. An investigation into classification accuracy between different candidates is also presented to determine the significance of the body effect on the success of the classification.

Separation of Proton Polarizabilities with the Beam Asymmetry of Compton Scattering

We propose to determine the magnetic dipole polarizability of the proton from the beam asymmetry of low-energy Compton scattering based on the fact that the leading non-Born contribution to the asymmetry is given by the magnetic polarizability alone; the electric polarizability cancels out. The beam asymmetry thus provides a simple and clean separation of the magnetic polarizability from the electric one. Introducing polarizabilities in a Lorentz-invariant fashion, we compute the higher-order (recoil) effects of polarizabilities on beam asymmetry and show that these effects are suppressed in forward kinematics. With the prospects of precision Compton experiments at the Mainz Microtron and High Intensity Gamma Source facilities in mind, we argue why the beam asymmetry could be the best way to measure the elusive magnetic polarizability of the proton.

Computing simple models for scatterers in eddy current problems using a modal decomposition

Abstract A modal decomposition method for computing the solution to an eddy-current problem is presented. Modes are computed using the finite element method and the modes produced are simplified to a magnetic polarizability dyadic in the form of a singularity expansion. This reduced form is a very compact and easily-implemented model for the scatterer's reaction to an arbitrary magnetic field. Due to scaling properties, a single model can be applied to scatterers with different sizes and conductivities. The modal decomposition method could be used to compute a variety of parameterized simple models for canonical shapes to assist in algorithm design for clutter discrimination in buried object detection systems. The method is verified using analytically known formulas for the dyadic of a sphere and a loop. The code is then used to predict the behavior of cylinders with arbitrary conductivity and size, showing excellent agreement with a set of measured cylinders.

Quantum-mechanical description of spin-1 particles with electric dipole moments

The Proca-Corben-Schwinger equations for a spin-1 particle with an anomalous magnetic moment are added by a term describing an electric dipole moment, then they are reduced to a Hamiltonian form, and finally they are brought to the Foldy-Wouthuysen representation. Relativistic equations of motion are derived. The needed agreement between quantum-mechanical and classical relativistic equations of motion is proved. The scalar and tensor electric and magnetic polarizabilities of pointlike spin-1 particles (W bosons) are calculated for the first time.

Method to extract charged hadron properties from lattice QCD in magnetic fields

By analyzing the external field dependence of correlation functions, the magnetic properties of hadrons can be determined using lattice QCD in magnetic fields. To compute the magnetic moments and polarizabilities of charged hadrons, for example, one requires sufficiently weak magnetic fields. Such field strengths, however, lead to closely spaced Landau levels that are not straightforwardly resolved using standard lattice spectroscopy. Focusing on charged spinless hadrons, we introduce a simple projection technique that can be used to isolate the lowest Landau level. As the technique requires the explicit coordinate-space wave-function, we investigate the extent to which the continuum, infinite volume wave-function can be employed. We find that, in practice, the effects of discretization can be handled using a perturbative expansion about the continuum. Finite volume corrections are taken into account by using the discrete magnetic translational invariance of the torus. We show that quantized magnetic fields can lead to pernicious volume effects which depend on the magnetic flux quantum, rather than on the lattice volume.

Three-dimensional object location and inversion of the magnetic polarizability tensor at a single frequency using a walk-through metal detector

A tomographic metal detection and characterization system has been designed and built for recovering information about magnetic and/or conductive objects within the detector space. This information is gathered as a result of a ‘walk-through’ scan of a candidate in the same manner as for a typical security metal detector archway. Following the passage of the candidate, the system uses measurements from an array of coils to calculate the polarizability tensor, which describes the low frequency electromagnetic characteristic of a small metallic object when it interacts with an ac magnetic field. In addition to the magnetic polarizability dyadic tensor, the position of the perturbation is also determined as a product of the inversion algorithm. The system has been tested and is capable of inverting object tensors with <20% typical parameter variation, and determines three-dimensional object location with a typical error of less than ±3 cm. In this paper, results are shown from a set of four different test object examples, each with a different magnetic polarizability tensor. This object set consists of a ferrite sphere, a ferrite rod and phantom aluminium and steel handgun shapes.

Three-layered metallodielectric nanoshells: plausible meta-atoms for metamaterials with isotropic negative refractive index at visible wavelengths

A three-layered Ag-low-permittivity (LP)-high-permittivity (HP) nanoshell is proposed as a plausible meta-atom for building the three-dimensional isotropic negative refractive index metamaterials (NIMs). The overlap between the electric and magnetic responses of Ag-LP-HP nanoshell can be realized by designing the geometry of the particle, which can lead to the negative electric and magnetic polarizabilities. Then, the negative refractive index is found in the random arrangement of Ag-LP-HP nanoshells. Especially, the modulation of the middle LP layer can move the negative refractive index range into the visible region. Because the responses arise from the each meta-atom, the metamaterial is intrinsically isotropic and polarization independent. It is further found with the increase of the LP layer thickness that the negative refractive index range of the random arrangement shows a large blue-shift and becomes narrow. With the decrease of the filling fraction, the negative refractive index range shows a blue-shift and becomes narrow while the maximum of the negative refractive index decreases.

Magnetic susceptibility anisotropy: Cylindrical symmetry from macroscopically ordered anisotropic molecules and accuracy of MRI measurements using few orientations

White matter is an essential component of the central nervous system and is of major concern in neurodegenerative diseases such as multiple sclerosis (MS). Recent MRI studies have explored the unique anisotropic magnetic properties of white matter using susceptibility tensor imaging. However, these measurements are inhibited in practice by the large number of different head orientations needed to accurately reconstruct the susceptibility tensor. Adding reasonable constraints reduces the number of model parameters and can help condition the tensor reconstruction from a small number of orientations. The macroscopic magnetic susceptibility is decomposed as a sum of molecular magnetic polarizabilities, demonstrating that macroscopic order in molecular arrangement is essential to the existence of and symmetry in susceptibility anisotropy and cylindrical symmetry is a natural outcome of an ordered molecular arrangement. Noise propagation in the susceptibility tensor reconstruction is analyzed through its condition number, showing that the tensor reconstruction is highly susceptible to the distribution of acquired subject orientations and to the tensor symmetry properties, with a substantial over- or under-estimation of susceptibility anisotropy in fiber directions not favorably oriented with respect to the acquired orientations. It was found that a careful acquisition of three non-coplanar orientations and the use of cylindrical symmetry guided by diffusion tensor imaging allowed reasonable estimation of magnetic susceptibility anisotropy in certain major white matter tracts in the human brain.

Electromagnetic Modeling of a Magnetless Nonreciprocal Gyrotropic Metasurface

An analytical model of a recently invented magnetless nonreciprocal and gyrotropic traveling-wave ring metamaterial is developed. The metamaterial is, in fact, a metasurface, which consists of a 2D periodic array of pairs of broadside-parallel micro-rings loaded with a semiconductor-based unidirectional component. It emulates the operation of ferrites by inducing a rotating magnetic moment in the ring pairs. However, instead of requiring a magnetostatic bias, it operates with an electrostatic voltage bias, thus avoiding the classical issues related to permanent magnets in ferrites. The metamaterial has two modes of operation: a desired magnetic mode and a parasitic electric mode, which are related to the excitation of equal and opposite currents in the two rings of the pairs, respectively. The metamaterial exhibits these magnetic and electric responses when excited by a uniform magnetic and electric field, respectively. The magnetic response is analyzed through a transmission line model with a distributed voltage source that incorporates the voltage impressed in the rings by the external field. The magnetic moment and the subsequent magnetic polarizability are related to a traveling-wave resonance along the ring pair. For a perfectly matched unidirectional component, this resonance, and hence the magnetic polarizability, are lossless. However, in the presence of mismatch, the metamaterial becomes lossy, due to reflection and absorption of power at the ports of the component. Comparisons with full-wave simulations show the validity of the proposed model.

Compton scattering from the proton in an effective field theory with explicit Delta degrees of freedom

We analyse the proton Compton-scattering differential cross section for photon energies up to 325 MeV using Chiral Effective Field Theory and extract new values for the electric and magnetic polarisabilities of the proton. Our EFT treatment builds in the key physics in two different regimes: photon energies around the pion mass ("low energy") and the higher energies where the Delta(1232) resonance plays a key role. The Compton amplitude is complete at N4L0, O(e^2 delta^4), in the low-energy region, and at NLO, O(e^2 delta^0), in the resonance region. Throughout, the Delta-pole graphs are dressed with pi-N loops and gamma-N-Delta vertex corrections. A statistically consistent database of proton Compton experiments is used to constrain the free parameters in our amplitude: the M1 gamma-N-Delta transition strength b_1 (which is fixed in the resonance region) and the polarisabilities alpha and beta (which are fixed from data below 170 MeV). In order to obtain a reasonable fit we find it necessary to add the spin polarisability gammaM1 as a free parameter, even though it is, strictly speaking, predicted in chiral EFT at the order to which we work. We show that the fit is consistent with the Baldin sum rule, and then use that sum rule to constrain alpha+beta. In this way we obtain alpha=[10.65+/-0.35(stat})+/-0.2(Baldin)+/-0.3(theory)]10^{-4} fm^3, and beta =[3.15-/+0.35(stat)-/+0.2(Baldin)-/+0.3(theory)]10^{-4} fm^3, with chi^2 = 113.2 for 135 degrees of freedom. A detailed rationale for the theoretical uncertainties assigned to this result is provided.

THE FIELD OF A MAGNETIC DIPOLE AND THE POLARIZABILITY OF A SUPERCONDUCTING OBJECT EMBEDDED IN THE INTERFACE BETWEEN MAGNETIC MATERIALS

In this paper, a careful study is made of the magnetostatic potential and fleld of a magnetic dipole embedded in, and with dipole moment parallel to, the interface between two magnetic regions. Unlike the case of a magnetic dipole perpendicular to the interface, the detailed position of the current of the dipole relative to the location of the interface has a profound efiect on the value of the fleld produced away from the dipole. As a consequence, the question of deflning and determining the magnetic polarizability of a superconducting object partially embedded in a magnetic interface is examined. The results of this paper are important for the proper modeling of arrays of scatterers embedded in an interface, such as frequency-selective surfaces (FSSs) and metafllms.

Magnetic polarization in the optical absorption of metallic nanoparticles

We find remarkably strong absorption due to magnetic polarization in common colloidal and lithographic metallic nanoparticles. Our analysis is based upon a thorough examination of the dipolar electric and magnetic polarizabilities for representative combinations of nanoparticle composition, size, and morphology. We illustrate this concept by first discussing absorption in metallic spheres and then exploring ellipsoids, disks, and rings. Magnetic polarization reaches ~ 90% of the total absorption in 100 nm disks and rings for wavelengths above 1 μm under co-linear electric and magnetic irradiation. Our results demonstrate that the magnetic contribution to absorption cannot be naively overlooked, as it can largely exceed the contribution of electric polarization.

Limitations of the heavy-baryon expansion as revealed by a pion-mass dispersion relation

The chiral expansion of nucleon properties such as mass, magnetic moment, and magnetic polarizability are investigated in the framework of chiral perturbation theory, with and without the heavy-baryon expansion. The analysis makes use of a pion-mass dispersion relation, which is shown to hold in both frameworks. The dispersion relation allows an ultraviolet cutoff to be implemented without compromising the symmetries. After renormalization, the leading-order heavy-baryon loops demonstrate a stronger dependence on the cutoff scale, which results in weakened convergence of the expansion. This conclusion is tested against the recent results of lattice quantum chromodynamics simulations for nucleon mass and isovector magnetic moment. In the case of the polarizability, the situation is even more dramatic as the heavy-baryon expansion is unable to reproduce large soft contributions to this quantity. Clearly, the heavy-baryon expansion is not suitable for every quantity.

Use of Generalized Sheet Transition Conditions to Model Guided Waves on Metasurfaces/Metafilms

We use generalized sheet transition conditions (GSTCs) to investigate the existence of guided waves (both surface waves and complex modes) on a metafilm: a surface distribution of electrically small scatterers characterized by electric and magnetic surface susceptibilities. In this paper, excitation of a metafilm by both electric and magnetic line currents is investigated. The characteristics of the guided waves for both these polarizations are expressed in terms of the surface susceptibilities, which are directly related to the electric and magnetic polarizabilities of the scatterers composing the surface. We will show that the guided waves can have unique behaviors (not found in classical slab configurations) for judicious choices of the scatterers in the metafilm. For example, unlike a conventional dielectric slab, forward and backward surface waves as well as complex modes can be excited simultaneously on the metafilm, a direct consequence of engineering the properties of the constituent scatterers. Two different classes of modes (even and odd) are possible on the metasurface. The odd mode is analogous to the surface plasmon polariton seen on some metamaterials, and under certain conditions, the even mode is analogous to the classical dielectric slab surface wave. In order to validate the predictions presented here, we present numerical results for an electric-line source placed above a metafilm composed of spherical particles. We also show comparisons of propagation constants obtained from our model to other analytical results found in the literature. Finally, we show that the results from our formulation reduce to analytical results given in the literature for a thin dielectric layer.