Anastasis C. Polycarpou

The finite-element method for modeling circuits and interconnects for electronic packaging

A full-wave finite-element method (FEM) is formulated and applied in the analysis of practical electronic packaging circuits and interconnects. The method is used to calculate S-parameters of unshielded microwave components such as patch antennas, filters, spiral inductors, bridges, bond wires, and microstrip transitions through a via. Although only representative microwave passive circuits and interconnects are analyzed in this paper, the underlined formulation is applicable to structures of arbitrary geometrical complexities including microstrip and coplanar-waveguide transitions, multiple conducting vias and solder bumps, multiple striplines, and multilayer substrates. The accuracy of the finite-element formulation is extensively verified by calculating the respective S-parameters and comparing them with results obtained using the finite-difference time-domain (FDTD) method. Computational statistics for both methods are also discussed.

Radiation and scattering from ferrite-tuned cavity-backed slot antennas: theory and experiment

A three-dimensional finite-element method hybridized with the spectral/spatial domain method of moments is presented for the analysis of ferrite-tuned cavity-backed slot antennas. The cavity, which is partially filled with magnetized ferrite layers, is flush mounted on an infinite ground plane with possible dielectric or magnetic overlay. The antenna operates primarily in the ultrahigh-frequency band. The finite-element method is used to solve for the electric-field distribution inside the cavity, whereas the spectral-domain approach is used to solve for the exterior region. An asymptotic extraction of the exponential behavior of the Greens function followed by a spatial evaluation of the resulting integral is used to improve computational speed. Radar cross section, input impedance, return loss, gain, and efficiency of ferrite-tuned cavity-backed slots (CBS) are calculated for various biasing conditions. Numerical results are compared with experimental data.

Multilayer effects on cavity-backed slot antennas

A hybrid technique of the finite-element method and the method of moments (FEM/ MoM) is used to analyze the effects of multilayered superstrates on cavity-backed slot (CBS) antennas. The spectral-domain approach is used to compute the MoM admittance matrix. An asymptotic extraction technique is applied to improve the computational efficiency of the convolution integrals. Effects on the input impedance, efficiency, gain, and radiation patterns are presented for different antennas. The numerical results are validated with measurements and published data.

Helicopter rotor-blade modulation of antenna radiation characteristics

This paper investigates rotor modulation on the gain and input impedance of an antenna mounted on a helicopters fuselage. The rotor blades, which are rotating about an axis with a given angular velocity, continuously modulate the signal transmitted by the antenna and adversely affect the established communication links. In this study, particular emphasis is placed on wire antennas operating within the HF and VHF bands. Specifically, the Doppler spectrum of the magnitude and phase of the radiated field from a vertical and a horizontal short dipole underneath the rotors is computed and analyzed. The variation of the corresponding antenna gain as a function of rotor angle and frequency is also investigated. The same type of analysis is then extended to a 14-ft towel-bar antenna mounted on the tail boom of a 10:1 scaled helicopter model. In addition to gain, the variation of input impedance versus angle and frequency is computed within the HF band. Finally, the bit error rate (BER) assuming a quadrature phase-shift keying (QPSK) modulation is evaluated assuming linearly and circularly polarized receiving antennas.

An optimized anisotropic PML for the analysis of microwave circuits

The anisotropic perfectly matched layer (PML) is implemented in the finite-element method (FEM) to evaluate the S-parameters of microwave integrated circuits (MICs). The PML region, which terminates the mesh over a range of frequencies, may exhibit either a uniform or nonuniform conductivity profile /spl sigma/(/spl rho/). The performance of the PML is strongly dependent on the choice of /spl sigma/(/spl rho/) as well as the mesh density inside the absorber. This observation is demonstrated numerically using a two-dimensional (2-D) finite-element analysis. The anisotropic PML is subsequently used in modeling three-dimensional (3-D) microwave integrated circuits. The accuracy and overall performance of the absorber is evaluated by computing the S-parameters of a low-pass filter.

Ferrite-loaded cavity-backed antennas including nonuniform and nonlinear magnetization effects

A method of analyzing both the electromagnetic and the magnetostatic phenomena involved in ferrite-loaded cavity-backed antennas is presented. The high-frequency modeling of the antenna is based on a hybrid of the finite element method (FEM) with the method of moments (MoM). The (magnetostatic) demagnetizing process of the finite ferrite loadings is modeled with the use of a nonlinear static FEM. The results of the magnetostatic analysis are used to compute the internal field of the ferrite samples. Through the use of an appropriate ferrite permeability tensor, the nonuniform internal bias field is incorporated into the high-frequency FEM/MoM analysis. The input impedance characteristics of two different ultrahigh-frequency (UHF) antennas are presented using different ferrite models. Results for the tuning range and sensitivity are presented for different bias directions. The numerical results are also compared with experimental data.

A two-dimensional finite element formulation of the perfectly matched layer

A perfectly matched layer (PML) is implemented using the finite element method (FEM) to successfully terminate the output port of a parallel-plate waveguide operating over a wide range of frequencies. The PML layer is modeled as a nonphysical anisotropic lossy material backed with a perfect electric conductor (PEC). Numerical results showing the reflection coefficient as a function of frequency, for both TEM and TM/sub 1/ propagation modes, demonstrate the effectiveness and accuracy of the PML concept as applied in the context of the FEM.

On the Design, Installation, and Evaluation of a Radio-Frequency Identification System for Healthcare Applications [Wireless Corner]

In this paper, we present the design, implementation, and testing of a radio-frequency identification (RFID) system for healthcare applications. The constantly growing passive RFID technology at ultra-high frequencies (UHF), in conjunction with current state-of-the-art information and communication technologies (ICTs), was used for the system design. The end product was installed at an oncology hospital in Cyprus, where it was thoroughly evaluated by medical staff and hospital administrators. This pilot project had three main objectives: a) automatic and error-free patient identification of in-hospital patients using RFID-enabled cards or wristbands; b) Real-time location service (RTLS) for locating and tracking medical assets and high-value equipment in the hospital ward; c) quick and hassle-free drug inventory management through the use of inexpensive smart labels and cost-effective stationary readers. Here, we present a detailed description of the three major subsystems of the pilot project, emphasizing the main features and capabilities of the system, important design and implementation issues, as well as system evaluation and testing. During the design stage of the project, special emphasis was placed on user friendliness, system capabilities, adequate coverage and tag readability, privacy and security of sensitive patient data, system reliability, and the daily practices of medical personnel and hospital administrators.

Finite element analysis of MMIC waveguide structures with anisotropic substrates

This paper presents an extended finite element formulation for a full-wave analysis of biaxial and transverse plane electric and magnetic anisotropic materials with application to monolithic microwave integrated circuits (MMICs). A convenient formulation of the characteristic impedance based on a power-voltage definition is developed using vector-based finite elements. The resultant generalized eigenvalue problem is solved using a numerically efficient algorithm based on a forward iteration, taking full advantage of the sparsity of the involved matrices. Numerical results are compared and agree well with existing published data for various MMIC configurations. Two specific coplanar waveguide structures, one with a conventional and the other with a suspended substrate, are examined using four common anisotropic materials. Principal axis rotations of the anisotropic substrates are also considered to improve dominant mode dispersion characteristics and minimize higher order mode interactions.

Full-Wave Scattering From a Grooved Cylinder-Tipped Conducting Wedge

The problem of full-wave electromagnetic scattering from a cylinder-tipped conducting wedge with either a sectoral or annular groove is formulated using the mode-matching technique. The mode expansion of the sector involves ratios of Bessel functions with large order as the order is inversely proportional to the inner angle of the sector. An asymptotic expansion of Bessel functions with large orders is introduced in order to overcome the numerical difficulty involved using a regular series expansion. Numerical results indicate good agreement with data obtained using the finite element method (FEM).