Electromagnetic Design of Dual Resonant Structures for Improved Sensitivity of Terahertz Label Free Bio-Sensing

A design is proposed exploiting full wave numerical simulation of a dual resonant structure with an aim to sense small amounts of chemical and biochemical materials. The structure is energized with free space radiation in the terahertz regime. Thanks to its asymmetric geometry two close resonances are excited. The interference between these two resonances produces a sharp change in the frequency response of the system. By selectively loading the structure with only small amounts of probe material, a relatively large shift in the frequency response may be achieved. The concept is demonstrated through simulation, while optimization of the structure and the analyte loading is attempted

Modelling of impulse loading in high-temperature superconductors. Assessment of accuracy and performance of computational techniques.

Purpose – The aim of this paper is to access performance of existing computational techniques to model strongly non-linear field diffusion problems. Design/methodology/approach – Multidimensional application of a finite volume front-fixing method to various front-type problems with moving boundaries and non-linear material properties is discussed. Advantages and implementation problems of the technique are highlighted by comparing the front-fixing method with computations using fixed grids. Particular attention is focused on conservation properties of the algorithm and accurate solutions close to the moving boundaries. The algorithm is tested using analytical solutions of diffusion problems with cylindrical symmetry with both spatial and temporal accuracy analysed. Findings – Several advantages are identified in using a front-fixing method for modelling of impulse phenomena in high-temperature superconductors (HTS), namely high accuracy can be obtained with a small number of grid points, and standard numerical methods for convection problems with diffusion can be utilised. Approximately, first order of spatial accuracy is found for all methods (stationary or mobile grids) for 2D problems with impulse events. Nevertheless, errors resulting from a front-fixing technique are much smaller in comparison with fixed grids. Fractional steps method is proved to be an effective algorithm for solving the equations obtained. A symmetrisation procedure has to be introduced to eliminate a directional bias for a standard asymmetric split in diffusion processes. Originality/value – This paper for the first time compares in detail advantages and implementation complications of a front-fixing method when applied to the front-type field diffusion problems common to HTS. Particular attention is paid to accurate solutions in the region close to the moving front where rapid changes in material properties are responsible for large computational errors. Keywords - Modelling, Numerical analysis, Diffusion, High temperatures, Superconductors Paper type - Research pape

Critical evaluation of numerical techniques for highly non-linear field diffusion modelling

Various numerical techniques have been applied to multidimensional field diffusion problems with front-type behaviour, moving boundaries and non-linear material properties. Advantages and implementation challenges of the methods are discussed with special attention paid to conservation properties of the algorithm and achieving accurate solutions close to the moving boundaries. The techniques are evaluated using analytical solutions of diffusion problems with cylindrical symmetry

Exploration versus Exploitation Using Kriging Surrogate Modelling in Electromagnetic Design

This paper discusses the use of kriging surrogate modelling in multiobjective design optimisation in electromagnetics. The importance of achieving appropriate balance between exploration and exploitation is emphasised when searching for the global optimum. It is argued that this approach will yield a procedure to solve time consuming electromagnetic design problems efficiently and will also assist the decision making process to achieve a robust design of practical devices considering tolerances and uncertainties

Analogies between finite difference and finite element methods for scalar and vector potential formulations in magnetic field calculations

Numerical 3D formulations using scalar ? and vector A potentials are examined for magnetic fields, with emphasis on the finite difference (FDM) and finite element (FEM) methods using nodal and facet elements. It is shown that for hexahedral elements the FDM equations may be presented in a form similar to the FEM equations; to accomplish this the coefficients defining volume integrals in FEM need to be expressed in an approximate manner, while the nodes in FDM require supplementary association with middle points of edges, facets and volumes. The analogy between a description of magnetic field sources arising from the classical mmf distribution approach and when expressed in terms of edge values of vector potential T0 is emphasized. Comparisons are made between results obtained using FDM and FEM for both scalar and vector potential formulations. Forces in systems containing permanent magnets and torques in permanent magnet machines are calculated and compared using both approaches for scalar and vector formulations. A unified form of the stress tensor has been applied to FDM and FEM

Numerical investigation of fano resonances in metamaterials with electric asymmetry

The excitation of high quality factor asymmetric Fano-type resonances on a double layer metafilm structure is investigated through numerical simulation. The paper demonstrates that it is possible to design simple structures capable to sustain a very high quality factor resonance by reducing their radiation losses. An equivalent circuit formed by two linearly coupled resonant RLC circuits is extracted in an attempt to explain the observed Fano resonance through classical circuit theory

Robust design optimisation of electromagnetic devices exploiting gradient indices and Kriging

Since uncertainties in variables are unavoidable, an optimal solution must consider the robustness of the design. The gradient index approach provides a convenient way to evaluate the robustness but is inconclusive when several possible solutions exist. To overcome this limitation, a novel methodology based on the use of first- and second-order gradient indices is proposed introducing the notion of gradient sensitivity. The sensitivity affords a measure of the change in the objective function with respect to the uncertainty of the variables. A Kriging method assisted by algorithms exploiting the concept of rewards is employed to facilitate function predictions for the robust optimisation process. The performance of the proposed algorithm is assessed through a series of numerical experiments. A modification to the correlation model through the introduction of a Kriging predictor and mean square error criterion allows efficient solution of large scale and multi-parameter problems. The three parameter version of TEAM Workshop Problem 22 has been used for illustration