Stroke is a dangerous disease with a high recurrence rate. Therefore, postoperative patients need timely monitoring of stroke conditions in their rehabilitation stage for early treatment. Recent studies in biomedical imaging have shown that strokes produce variations in the electric permittivity of brain tissues, which can be detected by microwave imaging techniques. Assuming that we have obtained the image of electromagnetic parameters in previous treatment, we can use differential imaging to detect the bleeding points when stroke recurs. However, the computational cost of traditional methods could be prohibitively large, as the bleeding points are small in the early stages of…

Planar periodic structures are widely utilized in microwave applications. The prism-based Discontinuous Galerkin time domain (DGTD) method is optimal to cope with the modeling challenges associated with these planar structures. In this work, we modified the prism based DGTD to take lossy materials into account. A ring-shaped frequency selective surface (FSS) is studied as a representative numerical example. When submerged into water, the operating frequency of the FSS is lowered dramatically. We test the algorithm with distilled and tap water of different conductivity. Results of both examples compare well with references of commercial software, which validates the accuracy of the…

The Discontinuous Galerkin Time-Domain (DGTD) method has gain great popularity for its capability of obtaining highly accuracy, flexibility, efficiency and parallel-computing. Different basis functions have their own merit in their advantageous applications. In this work, we focus on reseaches of DGTD’s basis functions and their advantageous applications. We firstly designed a nodal high-order based DGTD algorithm and studied its improvement on accuracy. As we known, an ultra-dense-mesh h-refinement will lead to the low-frequency breakdown which has been studied for decades. However, for highorder p-refinement, it is conventionally regarded that the accuracy is only limited by the basis orthogonality. While in…

Power integrity (PI) problem is essential when analyzing high speed signal passing through power ground. The fundamental mode in power ground is the zero-order parallel plate mode, which is capable for 2D simplification. However, in areas around anti-pads and other z-axis discontinuities, 3D algorithm has to be adopted to improve the accuracy. A hybrid 2D／3D discontinuous Galerkin time domain (DGTD) method has advantage on both accuracy and efficiency, thus is effective to cope with such full wave simulations. The 2D and 3D domains share the same triangular prism mesh. With appropriated basis functions, different domains can couple with each other…

Chiral mirrors are a class of metamaterials that reflect circularly polarized light of a certain helicity in a handedness-preserving manner, while absorbing circular polarization of the opposite handedness. However, most absorbing chiral mirrors operate only in a narrow frequency band, as limited by the causality principle. Instead of absorbing the undesired waveform, here we propose a transparent chiral mirror that allows undesired waves to pass through. In particular, the handedness-preserving band of the transparent chiral mirror is free of the causality limit, thus enabling broadband functionality. Furthermore, since electromagnetic waves outside the handedness-preserving band may transmit through the proposed chiral…

In this letter, we develop a prism-based discontinuous Galerkin time-domain (DGTD) algorithm with simplified periodic boundary conditions (PBCs) to analyze infinite doubly periodic frequency selective surfaces (FSS). Most FSS structures contain patterned planar conductive layers and supporting dielectric layers. These layers are very thin compared to the wavelength. Therefore, general tetrahedral discretization of space will unnecessarily increase the number of mesh elements, as well as the number of unknowns. Instead, we propose using prismatic elements, which are more optimal for planar structures, resulting in less unknowns, less memory usage, and higher efficiency. The accuracy of the proposed prism-based DGTD method…