Hybrid Algorithm Of Electromagnetic Transient Analysis Based On TD-FIT And TD-SBR

The interest in the analysis of transient wave phenomena has been growing primarily due to the many recent advances which are taking place in the development of ultra-wide band (or short pulse) radar and their associated antennas for remote sensing and target identification applications; in addition, there has always been significant interest in the effects of natural and man-made electromagnetic pulse (EMP) on complex radiating systems such as aircraft and spacecraft. It is natural to analyze transient electromagnetic (EM) wave phenomena directly in the time domain (TD). There are various numerical TD methods such as finite-difference time-domain (FDTD) or TD integral equation approaches, but these numerical solutions have in-herent difficulties with instability, interpolation error, and a need of extensive computer memory and CPU time to solve the problems involving large scattering objects. Recently, the use of hybrid methods combining these numerical methods and high-frequency asymptotic methods has been of interest. In this paper, a time-domain numerical hybrid method is developed by combining time-domain finite-integral technique (TD-FIT) and time-domain shooting and bouncing rays (TD-SBR) method to analyze the electromagnetic compatibility of the electric devices along with their supporting platforms. The author’s major work and contribution are as follow:·In the conventional time-domain physical optics (TD-PO) method, the far fields scattered by a metallic plate S of arbitrary shape have been described by a surface integral. However, the numerical evaluation of such a surface integral is time consuming, which becomes the crux of TD-PO technique. In this paper, a TD-PO integral is formulated under the incidence of plane waves and observation in the far-field region. Then the surface integral over S is reduced to a line integral around the boundary of S. When the shape of S is a polygon, the line integral is further reduced to a closed-form expression, which is very similar to the well-known Gordon formula in the evaluation of PO integral in the frequency domain. When S is arbitrarily shaped, the integral evaluation is also efficient once the polygon mesh is given.·An efficient TD-SBR method is developed to analyze the transient scattering responses from large perfectly conducting objects illuminated by a pulsed plane wave. Differing from the conventional TD-SBR method, a beam tracing (BT) technique, instead of the ray tracing (RT), is firstly employed in the time-domain SBR method, which provides much simpler procedure to avoid the divergence problem in the conventional SBR that happens when ray tubes intersecting discontinuous parts of the object. Applying a strategy of equiva-lent incident reference plane, alternative closed-form formulas are derived in the transient electromagnetic computations. Based on the closed-form representations, the characteristics of transition function and scat-tered fields are further investigated to show the physical phenomenon of scattering mechanisms. Due to the causality of transient fields, the proposed formulas are more efficient in electromagnetic calculations than the conventional frequency-domain formulas.·A time-efficient method is proposed to calculate the near-field TD-PO integral. It is shown that the TD- PO integral can be reduced to a close-form expression by introducing locally expanded Green-function approximations used in conjunction with the surface partitioning. As a result, the near-field TD-PO response to a general pulsed plane wave excitation is derived by a convolution of the excitation waveform with the TD-PO impulse response, which can be performed in a closed form. An novel adaptive subdivision algorithm is also developed for more efficient and robust near-field calculation in TD-SBR method.·A time-domain, near-field to near-field transformation, based on the Stratton-Chu representation, was his-torically presented for use with the FDTD method as well as the TD-FIT method. More recently, an alter-native near-field to near field transformation based on Kirchhoff’s surface integral representation (KSIR) was presented in the FDTD method. In this paper, this transformation is firstly introduced into the TD-FIT near-field calculations. The KSIR is very simple to implement and its distinct advantage is that the cal-culation of any of six field components depends on the value of the same field component over a closed surface. This avoids interpolation errors when using the popular Yee scheme for TD-FIT. In addition to its efficiency and simplicity of implementation, the KSIR leads to highly accuracy near fields that reduce the absorbing condition errors.·A new hybrid technique, entirely formulated in the time domain, has been developed to study small radi-ating sources close to large but finite scatters. It combines a rigorous method, time-domain finite-integral technique, with an asymptotic method, the time-domain shooting and bouncing rays method. When dealing with the EM coupling between TD-SBR region and TD-FIT region, a sequential transfer algorithm is de-veloped to achieve higher efficiency and less memory storage. Creatively, the optimization of the memory storage and the iteration is achieved by analysing the causality of transient EM fields.