Wedge Diffracted Waves Excited by a Line Source: Method of Moments (MoM) Modeling of Fringe Waves

Abstract

Fig. 6. Effect of the value of on the output rise time of the pulse. is too fast for this FDTD grid.In the FCT case, the rise time of the pulse steepens from 75 ns to approximately 2 ns. In the FDTD case, the rise time steepens to about 20 ns, which is much larger than the value of . Using the standard FDTD update, the effect of different values of on the output rise time of the pulse is shown in Fig. 6.When is 1 ps, the pulse steepens to a rise time on the order of 1 ns, which is too steep for the grid, as shown by the resulting oscillations. The FCT algorithm is needed to remove the oscillations. The FCT algorithm with results in a shock wave that steepens to approximately the limit the grid can support. To model a steeper shock, a more refined grid must be employed. For FDTD and , 3 ps, and 4 ps, the output rise time is approximately 20 ns, 55 ns, and 80 ns, respectively. Since the input rise time is 75 ns, a shock wave is no longer forming when is 4 ps. The value of should be a property of the material being modeled, although measuring the value is apparently challenging because the rise time of a shock in the material differs greatly from the value of . IV. CONCLUSIONAn algorithm is presented for modeling non-linear ferro-electrics in FDTD. A polynomial fit is applied to the versus curve, and finite material response time can be modeled. If the material response time is sufficiently fast, very steep shock wave form, resulting in spurious grid oscillations. The flux corrected transport algorithm effectively removes these oscillations. Numerical results show the utility of the algorithm. ACKNOWLEDGMENTThe authors appreciate Dr. J. Hammond for editing the text and suggesting compact notation for equations. REFERENCES[1] R. E. Peterkin and J. W. Luginsland, "A virtual prototyping environment for directed-energy concepts," Comp. A. Muliana, "Time dependent behavior of ferroelectric materials undergoing changes in their material properties with electric field and temperature," Int. A new finite-difference time-domain algorithm for the accurate modeling of wide-band electromagnetic phenomena," IEEE Trans. Electromagn. Compat., vol. 35, pp. 215-222, 1993. [8] R. M. Joseph and A. Taflove, "FDTD Maxwell's equations models for nonlinear electrodynamics and optics," IEEE Trans. Antennas Propag., vol. 45, pp. 364-374, 1997. [9] M. M. Aziz, "Sub-nonosecond electromagnetic-micromagnetic dynamic simulations using the finite-difference time-domain method," Abstract-Method of moments (MoM) simulation of fringe waves generated by a line source that excites a perfectly reflecting wedge is introduced and compared with the exact physical theory of diffraction (PTD) fringe waves.Index Terms-Fringe wave, line source, physical optics (PO), physical theory of diffraction (PTD), method of moments (MoM), uniform currents, non-uniform currents, wedge.

Diffraction Modeling by a Soft--Hard Strip Using Finite-Difference Time-Domain Method

“…A 2-step method of moments (MoM) approach has been introduced in [12] for the generation and discrimination of diffracted waves on PEC wedges. Fringe waves which are a portion of diffracted fields have been re-visited in a couple of publications [13][14][15]. The procedures of the discrimination of diffracted waves from double edge structures using different numerical models have been given in [16,17].…”

Electromagnetic Scattering by Multiple Columns Partially Buried in a Ground Plane

“…Ultrawideband radar needs the wideband RCS of target to achieve long-range detection and tracking stability [7]. The methods of solving scattering problems are plenty, such as the Kirchhoff approximation (KA) [8], small perturbation method (SPM) [9], small slope approximation (SSA) [10], the Method of Moment (MoM) [11], the Finite-Difference TimeDomain (FDTD) [12], and finite element method (FEM) [13]. In previous studies, the composite scattering from the rough sea surface and single target under harmonic wave irradiation have been reported and various methods are used in these studies [14][15][16][17][18][19][20].…”

A Hybrid MLFMM–UTD Method for the Solution of Very Large 2-D Electromagnetic Problems

“…Field-based hybrid methods that combine the geometrical theory of diffraction (GTD) or the uniform theory of diffraction (UTD) with MoM can avoid the discretization of large scatterers completely [2]- [8]. The current-based physical theory of diffraction (PTD) is combined with MoM in [9]- [13]. The number of unknowns is reduced greatly on large smooth scatterers by only introducing MoM basis functions at discontinuities (points of diffraction).…”