Huygens Surfaces Research Articles

Identifying Interference From Multiple Noise Sources Using Only Magnetic Near Fields

As electronic products become increasingly more complicated, multiple noise sources are likely to simultaneously interfere with the radio frequency (RF) receiver. It will be very helpful if the dominant noise source can be identified when solving the RF interference issue in a complex system. This article proposes a method to separately calculate the contributions from multiple noise sources at their overlapped frequencies so that the worse noise source could be identified even when multiple sources radiate simultaneously. The proposed method creatively employs the decomposition method based on the reciprocity theory to calculate the interference contribution from different sources. Furthermore, in the interest of reducing the near-field scanning time and complexity, the magnetic field only scanning method is developed by using the finite-element method (FEM). In the proposed method, Huygens's surface is established for each source. The tangential magnetic near fields on each Huygens's surface were then applied to solve the corresponding tangential electric fields by the FEM. Subsequently, the sources are removed while the corresponding Huygens's surfaces are maintained. The victim structure is excited under these conditions to obtain the tangential magnetic fields on Huygens's surfaces, and a novel FEM procedure is applied to obtain the tangential electric fields. Finally, based on the electric and magnetic fields, the interference from each noise source can be separately estimated based on the reciprocity theory. This method is validated by a numerical example and measurement. This approach can assist engineers in identifying the contribution of coupling from different sources and in efficiently resolving electromagnetic interference issues.

Notice of Retraction: Identifying Interference From Multiple Noise Sources by Magnetic Near Fields Only

As electronic products become more and more complicated, multiple noise sources very likely interfere with the radio frequency receiver simultaneously. This paper proposes a method to identify the interference from different noise sources separately, even when they are radiating at the same time. This method converts magnetic fields to electric fields by the finite-element method (FEM) and employs the decomposition method based on reciprocity theory. In the proposed method, Huygens's surface will be set up for each source. The tangential magnetic near fields on each Huygens's surface are used to solve tangential electric fields correspondingly by the FEM. Then, the sources are removed but their Huygens's surfaces are kept. The victim structure is excited in this case to get the tangential magnetic fields on Huygens's surfaces. A creative FEM processing procedure is applied to obtain tangential electric fields in this situation. Finally, with these two groups of fields, the interference from each noise source can be estimated separately based on reciprocity theory. This method is validated by a numerical example. It is very helpful for engineers to be able to identify the contribution of the coupling from different sources and further solve the electromagnetic interference issues efficiently.

A new multilevels Huygens sub-gridding finite difference time domain based on a tree structure and object oriented programming

In this article, an efficient sub-gridding finite-difference time-domain is developed for the simulation of multiscaled electromagnetic problems. The proposed technique is based on using the Huygens surfaces for interfacing electromagnetic fields between different grids. The use of the Object Oriented Programming for modeling FDTD simulations facilitates the imbrication of multiple sub-grids. That heightens the spatial ratio without affecting the accuracy and stability of the sub-gridding technique. Spatiotemporal interpolation is used to evaluate the electromagnetic fields in Huygens surface location among the coarse grid. Results of numerical experiments prove that the use of imbricated sub-grids and spatiotemporal interpolation in the Huygens sub-gridding is more efficient than the use of a single sub-grid with only spatial interpolation.

A Broad-Band Huygens Surface Source Model for Near-Field to Near-Field Transformations

A broad-band Huygens surface method requiring only the measurement of the magnetic field for near-field to near-field transformations is presented. The proposed method is valid down to near dc and supports arbitrary shaped Huygens surfaces. The method relies on an augmented-integral equation formulation that is used to predict the electric field on the Huygens surface. The proposed formulation is discretized using a high-order locally corrected Nystrom method. The surface magnetic and electric fields can then be used to compute external electric and magnetic fields. The method is validated using electromagnetic fields radiated by a three-phase motor showing excellent results over several Fourier harmonics of the motor fields, including the zeroth harmonic. The method is also validated at high frequency for a dipole antenna array.

Role of loss in all-dielectric metasurfaces.

Arrays of dielectric cylinders support two fundamental dipole active eigenmodes, which can be manipulated to elicit a variety of electromagnetic responses in all-dielectric metamaterials. Dissipation is a critical parameter in determining functionality; the present work varies material loss to explore the rich electromagnetic response of this class of metasurface. Four experimental cases are investigated which span electromagnetic response ranging from Huygens surfaces with transmissivity T = 94%, and phase ϕS21 = 235°, to metasurfaces which absorb 99.96% of incident energy. We find perfect absorption to be analogous to the driven damped harmonic oscillator, with critical damping occurring at resonance. With high phase contrast, transmission, and absorption all accessible from a single system, we present a uniquely diverse all-dielectric system.

Singularity Problem With the One-sheet Huygens Subgridding Method

The Huygens subgridding (HSG) relies on the connection of two finite-difference time-domain (FDTD) grids by means of Huygens surfaces. An earlier work has presented that the Huygens surfaces can be reduced to one sheet of current in place of the usual two sheets. This letter shows that the resulting simplified HSG may be at the origin of inaccuracy in the computed results because of the singularity of the field at the edges of perfect electric or magnetic conductors. The difficulty can be easily overcome in two dimensions but not easily in three dimensions, where it is preferable to use the one sheet implementation only for the outer Huygens surface.

A regularised boundary element formulation for contactless SAR evaluations within homogeneous and inhomogeneous head phantoms

This work presents a Boundary Element Method (BEM) formulation for contactless electromagnetic field assessments. The new scheme is based on a regularized BEM approach that requires the use of electric measurements only. The regularization is obtained by leveraging on an extension of Calderon techniques to rectangular systems leading to well-conditioned problems independent of the discretization density. This enables the use of highly discretized Huygens surfaces that can be consequently placed very near to the radiating source. In addition, the new regularized scheme is hybridized with both surfacic homogeneous and volumetric inhomogeneous forward BEM solvers accelerated with fast matrix-vector multiplication schemes. This allows for rapid and effective dosimetric assessments and permits the use of inhomogeneous and realistic head phantoms. Numerical results corroborate the theory and confirms the practical effectiveness of all newly proposed formulations.

Polarization Control Using Tensor Huygens Surfaces

Controlling the polarization of the electromagnetic field is a crucial aspect of many communication and imaging systems. Building off of previous work on Huygens surfaces, which are surfaces used to manipulate wavefronts using electric and magnetic surface impedances, the concept of a tensor Huygens surface is introduced. A tensor Huygens surface consists of electric and magnetic surface impedances which are tensors as opposed to scalars. In this paper we show how the polarization can be modified from a given initial state to a desired state specifically using a tensor Huygens surface. We examine the fields at the surface to find the required impedance tensors to manipulate the polarization. We also come up with an equivalent circuit model which captures the behavior of the surface as well as its equivalent S-parameter representation. Furthermore, we examine how chiral functionality can be realized using two cascaded Huygens surfaces. We validate these results using a TLM solver as well. Finally, we demonstrate a possible implementation of a tensor Huygens surface made up of skewed dipoles and loops.

Discrete Green's function approach to disjoint domain simulations in 3D FDTD method

A discrete Green's function (DGF) approach to couple 3D FDTD subdomains is developed. The total-field/scattered-field subdomains are simulated using the explicit FDTD method whilst interaction between them is computed as a convolution of the DGF with equivalent current sources measured over Huygens surfaces. In the developed method, the DGF waveforms are truncated using the Hann's window. The error varies in the range − 65 to − 40 dB depending on the DGF length and positions of the subdomains. However, if the DGF length is equal to the number of iterations in a simulation, this approach returns the same results as the direct FDTD method.

Circuit Modeling of Huygens Surfaces

Huygens surfaces are a recently proposed way of manipulating electromagnetic wavefronts using a superposition of subwavelength electric and magnetic dipoles situated on a plane. This allows for interesting phenomena such as refraction, beam manipulation, and focusing using this planar screen. In this letter, a circuit model for the unit cells comprising a Huygens surface is proposed to further understand the functionality of this screen. The equivalent circuit is a lattice network whose constituent series and shunt impedances correspond to the impedances of the magnetic and electric dipoles, respectively. We demonstrate that the corresponding voltage and current terminal relations across the lattice network correspond exactly to the electromagnetic boundary conditions across the Huygens surfaces. We also show how this model can be used to design the required unit cells and, using a two-dimensional circuit solver, how these lattice cells can be used to model an entire Huygens surface.

APPLICATIONS OF THE DISCRETE GREEN'S FUNCTION IN THE FINITE-DIFFERENCE TIME-DOMAIN METHOD

In this paper, applications of the discrete Green's function (DGF) in the three-dimensional flnite-difierence time-domain (FDTD) method are presented. The FDTD method on disjoint domains was developed employing DGF to couple the FDTD domains as well as to compute the electromagnetic fleld outside these domains. Hence, source and scatterer are simulated in separate domains and updating of vacuum cells, being of little interest from a user point of view, can be avoided. In the developed method, the fleld radiated by an FDTD domain is computed as a convolution of DGF with equivalent current sources measured over two displaced Huygens surfaces. Therefore, the computed electromagnetic fleld is compatible with the FDTD grid and can be applied as an incident wave in a coupled total- fleld/scattered-fleld domain. In the developed method, the DGF waveforms are truncated using the Hann's window and windowing parameters assuring accuracy of computations are pointed out. The error of the fleld computations varies between i90dB and i40dB depending on the DGF length and excitation waveform. However, if the DGF length is equal to the number of iterations in a simulation, the presented DGF-based techniques return the same results as the direct FDTD method.

INVERSE EQUIVALENT SURFACE CURRENT METHOD WITH HIERARCHICAL HIGHER ORDER BASIS FUNCTIONS, FULL PROBE CORRECTION AND MULTILEVEL FAST MULTIPOLE ACCELERATION

An inverse equivalent surface current method working with equivalent electric and/or magnetic surface current densities on appropriately chosen Huygens surfaces is investigated. The considered model with triangular surface meshes is compatible with the models known from method of moments (MoM) solutions of surface integral equations. Divergence conforming current basis functions of order 0.5 and of order 1.5 are considered, where the order 0.5 functions are the well-known Rao-Wilton-Glisson basis functions. Known near-fleld samples typically obtained from measurements are mapped on the unknown equivalent surface current densities utilizing the radiation integrals of the currents as forward operator, where the measurement probe in∞uence is formulated in a MoM like weighting integral. The evaluation of the forward operator is accelerated by adaptation of the multilevel fast multipole method (MLFMM) to the inverse formulation, where the MLFMM representation is the key to full probe correction by employing only the far-fleld patterns of the measurement probe antennas. The resulting fully probe corrected algorithm is very ∞exible and e-cient, where it is found that the computation speed is mostly dependent on the MLFMM conflguration of the problem and not that much on the particular equivalent current expansion as long as the expansion is able to represent the currents su-ciently well. Inverse current and far-fleld pattern results are shown for a variety of problems, where near-fleld samples obtained from simulations as well as from realistic measurements are considered.

Solving inverse electromagnetic problems using FDTD and gradient-based minimization

Numerical simulation is an important tool in understanding the electromagnetic field and how it interacts with the environment. Different topics for time-domain finite-difference (FDTD) and finite-element (FETD) methods for Maxwell's equations are treated in this thesis. Subcell models are of vital importance for the efficient modeling of small objects that are not resolved by the grid. A novel model for thin sheets using shell elements is proposed. This approach has the advantage of taking into account discontinuities in the normal component of the electric field, unlike previous models based on impedance boundary conditions (IBCs). Several results are presented to illustrate the capabilities of the shell element approach. Waveguides are of fundamental importance in many microwave applications, for example in antenna feeds. The key issues of excitation and truncation of waveguides are addressed. A complex frequency shifted form of the uniaxial perfectly matched layer (UPML) absorbing boundary condition (ABC) in FETD is developed. Prism elements are used to promote automatic grid generation and enhance the performance. Results are presented where reflection errors below -70dB are obtained for different types of waveguides, including inhomogeneous cases. Excitation and analysis via the scattering parameters are achieved using waveguide modes computed by a general frequency-domain mode solver for the vector Helmholtz equation. Huygens surfaces are used in both FDTD and FETD for excitation in waveguide ports. Inverse problems have received an increased interest due to the availability of powerful computers. An important application is non-destructive evaluation of material. A time-domain, minimization approach is presented where exact gradients are computed using the adjoint problem. The approach is applied to a general form of Maxwell's equations including dispersive media and UPML. Successful reconstruction examples are presented both using synthetic and experimental measurement data. Parameter reduction of complex geometries using simplified models is an interesting topic that leads to an inverse problem. Gradients for subcell parameters are derived and a successful reconstruction example is presented for a combined dielectric sheet and slot geometry.