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Self-consistent solution to electromagnetic (EM)-circuit systems is of significant interest for a number of applications. This has resulted in exhaustive research on means to couple them. In time domain, this typically involves a tight integration (or coupling) with field and non-linear circuit solvers. This is in stark contrast to coupled analysis of linear/weakly non-linear circuits and EM systems in frequency domain. Here, one typically extracts equivalent port parameters that are then fed into the circuit solver. Such an approach has several advantages: 1) the number of ports is typically smaller than the number of degrees of freedom, resulting in cost savings; 2) is circuit agnostic; and 3) can be integrated with a variety of device models. Port extraction is tantamount to obtaining impulse response of the linear EM system. In time domain, the deconvolution required to effect this is unstable. Recently, a novel approach was developed for time domain integral equations (TDIEs) to overcome this bottleneck. We extend this approach to time domain finite element method, and demonstrate its utility via a number of examples; significantly, we demonstrate that self-consistent solutions obtained using either a fully coupled or port extraction is identical to the desired precision for non-linear circuit systems. This is shown within a nodal network. We also demonstrate integration of port extracted data directly with drift diffusion equation to model device physics. [ABSTRACT FROM AUTHOR]

In this paper, a volume integral equation (VIE)-based modeling method suitable for a patch or slot antenna on a thin finite dielectric substrate is developed and tested. Two new key features of the method are the use of proper dielectric basis functions and proper VIE conditioning, close to the metal surface, where the surface boundary condition of the zero tangential E-component must be extended into adjacent tetrahedra. The extended boundary condition is the exact result for the piecewise-constant dielectric basis functions. The latter operation allows one to achieve a good accuracy with one layer of tetrahedra for a thin dielectric substrate and thereby greatly reduces computational cost. The use of low-order basis functions also implies the use of low-order integration schemes and faster filling of the impedance matrix. For some common patch/slot antennas, the VIE-based modeling approach is found to give an error of about 1% or less in the resonant frequency for one-layer tetrahedral meshes with a relatively small number of unknowns. This error is obtained by comparison with fine finite-element method (FEM) simulations, or with measurements, or with the analytical mode matching approach. Hence it is competitive with both the method of moments surface integral equation approach and with the FEM approach for the printed antennas on thin dielectric substrates. Index Terms--Convergence, low order basis functions, method of moments (MoM), patch antennas, volume integral equation (VIE).

The dielectric properties of a curing diglycidyl ether of bisphenol A (DGEBA)/Jeffamine D-230 system have been studied over the temperature range of 20-90[degrees]C at 2.45 GHz. It was found that, generally, both the dielectric constant and the dielectric loss factor of the system increased with temperature and decreased as the reaction proceeded. The epoxy resins at different extents of cure exhibited the [gamma] relaxation, which can be described by the Arrhenius Rate Law. The relaxation is attributed to the motions of the dipolar groups associated with the reactants. The Davidson-Cole model can represent the temperature dependencies of the dielectric properties. The nature of the information yielded by dielectrometry on the dynamics of the system is discussed. The evolution of the parameters of the models during the polymerization was mainly affected by the decreasing number of the dipolar groups involved in the reaction and increasing medium viscosity. POLYM. ENG. SCI., 45:1576-1580, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Microwave processing of polymers has been studied as an attractive alternative to conventional thermal processing [1]. Dielectric properties of polymers are important for controlling microwave processing of the materials. [...]

A switchable frequency-selective surface (FSS) was developed at 30 GHz using RF microelectromechanical systems (MEMS) switches on a 500-[micro]m-thick glass substrate. The 3-in-diameter FSS is composed of 909 unit cells and 3636 MEMS bridges with a yield of 99.5%. The single-pole FSS shows a transmission loss of 2.0 dB and a -3-dB bandwidth of 3.2 GHz at a resonant frequency of 30.2 GHz with the MEMS bridges in the up-state position. The -1-dB bandwidth is 1.6 GHz. When the MEMS bridges are actuated to the down-state position, an insertion loss of 27.5 dB is measured. Theory and experiment agree quite well. The power handling is limited to approximately 25 W with passive air cooling and >150 W with active air cooling due to the increased temperature of the overall circuit resulting from the transmission loss (for continuous-wave operation with the assumed maximum allowable temperature of 80 [degrees]C), or 370 W-3.5 kW due to self-actuation of the RF MEMS bridges (for pulsed incident power). Experimental results validate that 20 W of continuous-wave power can be transferred by the RF MEMS FSS with no change in the frequency response. This is the first demonstration of a switched low-loss FSS at [kappa][alpha]-band frequencies. Index Terms--Frequency selective surface (FSS), microelectromechanical devices, quasi-optical, RF microelectromechanical systems (MEMS), tunable filters.

In this paper, the hybrid finite element-boundary integral (FE-BI) method appropriate for modeling conformal antennas on doubly curved surfaces is developed. The FE-BI method is extended to model doubly curved, convex surfaces by means of a specially formulated asymptotic dyadic Green's function. The FE-BI method will then be used to examine the effect of curvature variation on the resonant input impedance of a cavity-backed, conformal slot antenna and a conformal patch antenna recessed in a perfectly conducting, electrically large prolate spheroid surface. The prolate spheroid shape provides a canonical representation of a doubly curved mounting surface. The numerical results for conformal slot and patch antennas on the prolate spheroid are compared as a function of curvature and orientation. Index Terms--Boundary integral equations, conformal antennas, finite element method, microstrip antennas.

The feasibility of using the E-pulse technique to diagnose changes in the properties of simple layered materials is undertaken. Numerical results for a conductor-backed lossy slab and a Salisbury screen show that changes in permittivity, conductivity and thickness can be diagnosed in the presence of white Gaussian noise. Index Terms--Electromagnetic transient scattering, nondestructive testing, radar target recognition.

In this paper, the highly versatile finite element-boundary integral method is presented for accurate modeling of fields within cavities recessed in a perfectly conducting, infinite, elliptic cylinder. Properties of flush-mounted cavities and antennas are explored and compared with prior developments. This formulation represents a significant advancement over prior techniques since surface curvature variation, either across a single element or across an array of elements, is now accurately included into the antenna model. An advantage of this approach is the ability to model cavities with curvature varying from planar to the constant curvature of a circular cylinder. Computed eigenvalues for planar-rectangular and cylindrical-rectangular closed cavities will be compared with theoretical values. Eigenvalues will be presented for elliptic-rectangular cavities. Furthermore, the input impedance of a conformal cavity-backed patch antenna mounted on an elliptic cylinder will be presented and compared with a similar antenna on a circular cylinder. Index Terms--Conformal antenna, elliptic cylinder, finite element method.

Patch antennas on ferrite substrates allow for pattern control, frequency shifting, and scattering reduction. This is achieved by external magnetic field biasing coupled with the inherent magnetization of the ferrite substrate. Measurements and analytical studies based on the method of moments (MoM) have verified these attractive properties of ferrite substrates. However, verification of the analysis is difficult and, furthermore, previous models have relied on uniform biasing across the substrate. In this paper, we present a hybrid finite element-boundary integral (FE-BI) method, which permits modeling of the true nonuniform bias fields within the substrate for a more accurate prediction of the ferrite patch performance. After validation of the proposed simulation and a demonstration of the inherent properties of the ferrite patch, it is shown that nonuniform biasing is responsible for additional frequency shifts. We also identify the poor condition of the resulting matrix systems and relate this situation to the predictable occurrence of nonpropagating substrate modes. A more robust iterative solver with preconditioning is, therefore, proposed and applied to handle these situations. Index Terms - Anisotropic media, antennas, antenna theory, ferrites, finite-element methods, microstrip antennas.

Conformal arrays are popular antennas for aircraft, spacecraft, and land vehicle platforms due to their inherent low weight, drag, and observables. However, to date there has been a dearth of rigorous analytical or numerical solutions to aid the designer. In fact, it has been common practice to use limited measurements and planar approximations in designing such nonplanar antennas. In this paper, we extend the finite element-boundary integral method to scattering by cavity-backed structures in an infinite, metallic cylinder. In particular, we discuss the formulation specifics, such as weight functions, dyadic Green's function, implementation details, and particular difficulties inherent to cylindrical structures. Special care is taken to ensure that the resulting computer program has low memory demand and minimal computational requirements. Scattering results are presented and validated as much as possible.

For plane wave incidence, an integral equation is obtained for the magnetic current induced on a circular impedance insert in a perfectly conducting plane under the assumption that the radius is electrically small. This integral equation is solved numerically, and an analytical expression for the scattered field is determined. The complementary expression for a small disk is compared with a standard numerical code and conditions for the use of this expression are established. For a cavity-backed hole, the impedance of the insert is identified with the impedance looking into the hole as determined by a simple transmission line model and results are presented for a few cavity geometries.

An analysis is presented of the scattering by a resistive strip joined to a metallic half plane. Three different solutions are developed, one of which is based on the moment method/Green function approach. The other two are approximations, one of which improves as the resistive strip width decreases whereas the other does the same for large strip widths. Using the moment method solution as a reference, the accuracy of each approximation is examined and guidelines for using them are developed. It is found that the validity ranges of the two approximations overlap, making them suitable for computing the TM scattering of the configuration regardless of the strip's width and resistivity.

The mutual impedance between two rectangular patch antennas recessed in an elliptic cylinder is computed using a finite element-boundary integral method. Results show that the coupling between the antennas is dependent on the curvature of the cylinder surface. For H-plane coupling, the coupling decreases as the radius of curvature increases. For E-plane coupling, the strongest coupling occurs for a specific curvature. Index Terms--Antenna array mutual coupling, antenna theory, conformal antennas.

A tunable phase shifter at X band using single-crystal YIG film material grown on GGG substrates is fabricated. While the transmission phase can be sensitively tuned by applying a bias magnetic field, the insertion loss can be retained at a relatively constant low level.

A study was conducted to show that practical phase shifters operating at X band can be prepared using single-crystal YIG materials supporting a narrow ferromagnetic resonance linewidth. The performance of a phase shifter was characterized by numerical analysis. It was a fourth wavelength in the absence of a bias magnetic field. The insertion loss were shown to be retained at a relatively constant low level.

Green's function calculations have been applied to solve the radiation problem of circular microstrip patch antennas. The patch is fed by either a microstrip line or a coax line to be approximated as delta-function-like sources. The resultant Galerkin elements involve only one-fold Sommerfeld-type integrals. Resonant frequency, impedance, and far-field pattern have thus been calculated, which compared nicely with measurements. Index Terms--Antenna impedance, antenna radiation pattern, dyadic Green's function, microstrip patch antenna, Sommerfeld integral.

A phased array antenna containing four linear microstrip patch elements has been fabricated and tested. The elements were fed through single-crystal yttrium-iron-garnet (YIG) phase shifters. By varying the bias magnetic field, the input phases to the antenna elements can thus been tuned, resulting in steering of the radiation beam in one dimension. Measurements compared reasonably well with calculations. Index Terms--Ferrite phase shifter, magnetic microwave device, microstrip device, steerable phased array.

X-band phased array antenna containing four linear microstrip patch elements has been fabricated and tested. The elements were fed through single-crystal yttrium–iron–garnet phase shifters. By varying the bias magnetic field the input phases to the antenna elements can thus be tuned, resulting in steering of the radiation beam in one dimension. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A simple method to obtain high magnetic permeability ( μr), high dielectric permittivity ( ϵr), and low loss polymer composites with core/shell iron/metal oxide particles is developed. Magnetic iron (Fe0) particles with protective SiO2 shells are synthesized in aqueous environment at room temperature. The shells provide electrical insulting layers which decrease energy loss and also prevent the possibility of μr decrease due to Fe0 oxidation. Furthermore, Fe0 particles could also be coated with TiO2 shells which allow ϵr to be tuned. The ϵr and μr of the resulting polydimethylsiloxane composites are optimized for core-shell particle doping. The value of ϵr is up to 9.8 and most importantly, the μ is close to 2 at 1 GHz with 43 wt% doping of core-shell particles. The dielectric loss of the composites is less than 0.02. [ABSTRACT FROM AUTHOR]