Chris J. Railton

Experimental validation of a combined electromagnetic and thermal FDTD model of a microwave heating process

Microwave cooking, tempering, and pasteurizing of foods involves several complex and interacting physical phenomena. Although such processes are widely used, the interactions between the food product, packaging, and the microwave oven itself are particularly complicated, are not well understood, and applicable simulation tools are lacking. In this contribution we describe a combined finite difference time domain model for the electromagnetic and the heat transfer processes which include temperature dependence of the electrical and thermal properties of the food product. This model is validated by comparison to experiment. >

Analyzing electromagnetic structures with curved boundaries on Cartesian FDTD meshes

In this paper, a new finite-difference time-domain (FDTD) algorithm is investigated to analyze electromagnetic structures with curved boundaries using a Cartesian coordinate system. The new algorithm is based on a nonorthogonal FDTD method. However, only those cells near the curved boundaries are calculated by nonorthogonal FDTD formulas; most of the grid is orthogonal and can be determined by traditional FDTD formulas. Therefore, this new algorithm is more efficient than general nonorthogonal FDTD schemes in terms of computer resources such as memory and central processing unit (CPU) time. Simulation results are presented and compared to those using other methods.

An analytical and numerical analysis of several locally conformal FDTD schemes

The virtues of the finite-difference time-domain (FDTD) method for the electromagnetic analysis of arbitrary complex metal and dielectric structures are well known. Almost equally well known are the difficulties encountered by the technique when the material boundaries do not coincide with the Cartesian mesh. Until recently, there were few alternatives to the simple, but inaccurate, staircase approximation for these cases. However, over the past few years, there have been several solutions proposed, which maintain the simplicity and efficiency of the FDTD method while providing an accurate treatment of curved, offset, or sloping metallic boundaries. In this paper, analytical and numerical comparisons are presented and a clear recommended method is shown to emerge.

The incorporation of static field solutions into the finite-difference time domain algorithm MMIC structures modelling

The authors demonstrate how the accuracy, speed, and flexibility of finite-difference time-domain (FDTD) analysis can be improved for the modeling of MMIC structures. Correction factors, obtained from the known behavior of static fields close to discontinuities, can be incorporated into the algorithm for application in the regions of high field variation where errors would otherwise occur. Application is made to both enclosed and open microstrip structures. >

An analysis of microstrip with rectangular and trapezoidal conductor cross sections

The finite-difference time-domain (FDTD) technique is used to analyze boxed microstrip with both rectangular and trapezoidal cross sections. It is confirmed that the exact shape of the conductor has a marked effect on the effective permittivity of the microstrip. Results using this method are compared to the findings of K.A. Michalski et al. (1989) using the analytically more complicated boundary element method; very good agreement is observed. The effect of adding a thin passivation layer is also calculated and it is found that such an addition noticeably reduces the effective permittivity of the microstrip. It is shown that the FDTD technique is capable of treating microstrip with a general cross section and producing accurate results. >

The rigorous analysis of cascaded step discontinuities in microstrip

A rigorous analysis of boxed microstrip single-step discontinuities and cascades of strongly coupled discontinuities is presented. Use is made of a variational formulation involving the expansion of the transverse E field at the step in terms of suitable basis functions. Strongly coupled steps are analyzed using the concept of localized and accessible modes and making use of a network model. The method is applied to a five-section low-pass filter. >

Fast rigorous analysis of shielded planar filters

It is shown that realistically complex microstrip circuits can be rigorously analyzed on a small computer by means of the spectral domain technique in combination with precomputed basis functions and the use of the asymptotic forms of the Greens function and the fast Fourier transform (FFT) algorithm. The results compare well with published measurements and with calculations using finite-difference time-domain (FDTD) method. >

The Treatment of Thin Wire and Coaxial Structures in Lossless and Lossy Media in FDTD by the Modification of Assigned Material Parameters

It has been shown recently that the use of modified assigned material parameters (MAMPs) within the finite-difference time-domain (FDTD) method provides a systematic, readily extensible, accurate, and efficient approach to the electromagnetic analysis of microstrip structures. In this paper, it is shown that this technique can also be applied with equal effect to lossless and lossy coaxial lines, wires in a lossy medium such as earthing grids, and more complex structures which include coaxial feeds and shorting posts. The modified parameters are calculated directly from the known asymptotic fields near the wire and do not rely on the concept of equivalent radius. Results are given which show equal or superior performance compared to those obtained using other methods but with the added advantage of flexibility and rigor

Analysis of microstrip discontinuities using the finite difference time domain technique

The authors demonstrate the potential of the finite-difference time-domain technique for analyzing MMIC (monolithic microwave integrated circuit) structures of arbitrary complexity with moderate computational effort and for meeting the requirement for CAD (computer-aided design) tools capable of treating high-density MMICs. Results are presented for the propagation constant of a uniform microstrip, calculated using this method, which show excellent agreement with those obtained using the SDM (spectral domain method). Results are also presented for the parameters of structures containing a right-angle bend in microstrip and an abrupt termination in microstrip. The latter results are compared to those obtained by means of the SDM, and good agreement can be seen.<<ETX>>

A stable subgridding algorithm and its application to eigenvalue problems

In this paper, a new and stable subgridding algorithm is proposed for three-dimensional problems which provides subgridding in both space and time. The concept of an equivalent-circuit representation and a novel leapfrog time integration scheme is used to ensure that the algorithm is stable and efficient. Practical applications of this algorithm in the characterization of arbitrarily filled dielectric resonators are reported.