Shiquan He

Finite-Element-Based Generalized Impedance Boundary Condition for Modeling Plasmonic Nanostructures

The superior ability of plasmonic structures to manipulate light has propelled their extensive applications in nanophotonics techniques and devices. Computational electromagnetics plays a critical role in characterizing and optimizing the nanometallic structures. In this paper, a general numerical algorithm, which is different from the commonly used discrete dipole approximation, the finite-difference time-domain, and the surface integral equation (SIE) method, is proposed to model plasmonic nanostructures. In this algorithm, the generalized impedance boundary condition (GIBC) based on the finite element method (FEM) is formulated and converted to the SIE. The plasmonic nanostructures with arbitrary inhomogeneity and shapes are modeled by the FEM. Their complex electromagnetic interactions are accurately described by the SIE method. As a result, the near field of plasmonic nanostructures can be accurately calculated. The higher order basis functions, together with the multifrontal massively parallel sparse direct solver, are involved to provide a higher order accurate and fast solver.

Finite-width gap excitation and impedance models

In this paper, we present a new method for the feed model for the method of moments (MoM). It is derived from a more accurate model with the realistic size of the excitation, in order to replace the commonly-used delta-gap excitation model. This new model is formulated around the electric field integration equations (EFIE) where the terms for magnetic current and magnetic field can be removed. Hence it is much simpler to implement and reduces the numerical complexity. In addition, a variational formulation is derived to provide second order accuracy of the input admittance calculation. Moreover, this new formulation can be easily extended such that one can insert passive load elements of finite size onto the distributive network, without complicated modification of the MoM analysis. This allows simulation of many realistic networks which include load elements such as resistors, capacitors and inductors.

Low-Profile Microstrip Antenna with Bandwidth Enhancement for Radio Frequency Identification Applications

Abstract Two low-profile microstrip antennas, which can be mounted on metallic objects for radio frequency identification applications, are proposed. By using a single-layer FR4 as the substrate, the thickness of the antennas is only 1.6 mm (about 1% dielectric wavelength at 900 MHz). In order to broaden the bandwidth, slots are added on the surface of the patch to excite two different modes. Compared to conventional microstrip antennas, the impedance bandwidth (voltage standing wave ratio < 3) of the design can reach 100 MHz, and the 3-dB gain bandwidth is about 50 MHz, which can satisfy most applications for UHF radio frequency identification systems. The size of the compact design is only 84 mm × 26 mm. Prototypes were fabricated and measured. The read range of the designed antennas can reach 4 m when mounted on metallic plates.

Compact Dual-Layer Bandpass Filter Using Novel Stepped-Impedance Resonators

ABSTRACT In this article, a compact third-order bandpass filter with high-frequency selectivity using novel dual-band stepped-impedance resonators is presented. In the proposed novel dual-band stepped-impedance resonator, the conventional low-impedance stub of the stepped-impedance resonator is replaced by a closed rectangular loop. The high-impedance stub is embedded in the closed loop for more compact structure. Multiple transmission zeros are introduced near the passband to improve the frequency selectivity and stopband performance. The proposed filter was designed, simulated, and fabricated to verify the validity of the proposed method. The measured results show that the center frequency is 2.83 GHz with a fractional bandwidth of 9.32%, and five transmission zeros were introduced near the passband, which are located at 1.76 GHz with 70.2-dB rejection, 2.53 GHz with 30.7-dB rejection, 3.95 GHz with 67.2-dB rejection, 8.85 GHz with 45.5-dB rejection, and 12.3 GHz with 34.5-dB rejection, respectively. The circuit only occupies 0.11λg × 0.08λg.

Compact Tri-Band Bandpass Filter with Multiple Transmission Zeros

Abstract In this article, a compact tri-band bandpass filter with high selectivity using novel tri-mode resonators is proposed. The novel tri-mode resonator consists of a modified λ/4 stepped-impedance resonator with a closed rectangular loop and two loaded open stubs. A pair of transmission zeros are generated at the lower and upper stopband of each passband for high selectivity and excellent band-to-band isolation. A 1.90/3.50/5.75-GHz tri-band experimental bandpass filter has been designed and fabricated to demonstrate the proposed method. The measured results show six finite transmission zeros near the passbands located at 1.65 GHz with 30.14-dB rejection (TZ1), 2.64 GHz with 51.35-dB rejection (TZ2), 3.06 GHz with 49.36-dB rejection (TZ3), 3.95 GHz with 43.76-dB rejection (TZ4), 5.40 GHz with 30.67-dB rejection (TZ5), and 6.16 GHz with 35.15-dB rejection (TZ6), respectively. The circuit only occupies 0.04 λg × 0.07λg.

Characterizing EMI radiation physics for edge-and broad-side coupled connectors

Electromagnetic radiation for a printed circuit board (PCB) midplane connector is studied in this paper. By applying integral-equation (IE) based method and characteristic mode (CM) analysis, the current is split into radiating and non-radiating ones. The radiated power from each part of the structure can be quantified using the radiating current. Therefore, the radiation hot spot can be identified for both edge-side coupled and broad-side coupled connectors. Furthermore, the radiation characteristics for these connectors are compared.

The Application of Higher-Order Basis Functions with Phase Description for Electromagnetic Simulation of Arbitrary Structures

Abstract In this article, a new set of high-order vector basis functions with phase descriptions, which are named traveling-standing-wave basis functions, is proposed for electromagnetic simulation with triangular patches. Such bases have an excellent capacity of describing the complicated standing-wave distribution and the rapid phase variation of the induced surface current. These basis functions were defined on electrically large patches so that the number of unknowns is lowered tremendously. A fast algorithm, such as the multilevel fast multiple algorithm, can easily be combined with the proposed basis functions to further reduce the computational complexity of numerical calculation. More importantly, the targets can be any convex, concave structures with any shape. Numerical experiments have demonstrated that reliable accuracy with the multilevel fast multiple algorithm–traveling-standing-wave scheme can be obtained even though the number of unknowns is reduced dramatically. Another benefit is that a fast convergence rate can be commonly achieved.

Numerical Solutions of the Integral Equation for Excitation-Transmission-Radiation in Aperture Antenna

Abstract The numerical method of the volume-surface integral equation has been used to model the electromagnetic excitation and propagation problems of the waveguide-fed aperture antenna. The mode-matching method has been used to describe the impedance marching situation at the exciting aperture. The excitation conditions were established based on the expansion of the waveguide modes and the equality principle of electromagnetics. The multi-level fast multi-pole algorithm is applied to speed up the matrix-vector multiplication and reduce the memory requirement of the method of moment. The numerical solutions of the electromagnetic transmission and radiation of an offset paraboloidal reflector antenna have been given. It has been demonstrated that the method proposed by this article is able to provide the valid and accurate numerical solution for the electromagnetic propagation and radiation problems of an aperture antenna with an arbitrary shape, composite metallic and material structure, and electrically large size.

Finite element based generalized impedance boundary condition for complicated EM calculation

In this paper, a finite element based generalized impedance boundary condition (FEM-GIBC) is proposed to solve complicated electromagnetic (EM) problems. Complex structures with arbitrary inhomogeneity and shapes are modeled with the finite element method, and their scattering contributions are transformed to generalized impedance conditions on their boundaries. For each sub-domain, a special GIBC can be established and it is only related to the structures in this domain. Hence, for finite periodic structures, a representative GIBC can be formulated at the boundary of a unit cell. After the GIBC at each boundary is established, the electromagnetic coupling between each impedance boundary can be calculated by the boundary integral equations (BIE) and accelerated with the multilevel fast multipole algorithm (MLFMA).