摘要:

The transient field in a moving isotropic medium due to a current source of arbitrary time dependence is formulated and solved with the aid of an independent pseudo-time variable. The approach is similar to D'Alembert's method of solving the one-dimensional scalar wave equation, except that we are dealing with Maxwell's equations with two constitutive relations characterizing a moving medium. This new method appears to be simpler than the one used by Compton [1] who invoked a four-dimensional space-time differential operator and derived several new mathematical formulas covering both the spatial and the time domain simultaneously in order to solve the Maxwell-Minkowski equations. In our treatment, only conventional theorems in spatial domain are needed and the result is also cast in a more recognizable form.

ISSN:0920-5071    

DOI:10.1163/156939393X01047

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A novel NMR instrument to be used in holes drilled for geophysical exploration employs an unusual RF sensor which resembles one half of a coaxial cable that is split along its axis. The magnetic field and the efficiency of the sensor are computed by the method of moments.

ISSN:0920-5071    

DOI:10.1163/156939393X01056

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The reflection and transmission of waves on a nonuniform LCRG transmission line of finite length with frequency-dependent parameters are considered. A Green function technique combined with wave splitting is used both in the frequency domain and the time domain. In the frequency domain ordinary differential equations (ODEs) for the time-harmonic Green functions are obtained. In the time domain the transmission line model is established through a set of dispersion kernels. Partial differential equations (PDEs) for the time-domain Green functions are derived. Numerical results for transient reflected, transmitted and internal currents are presented. Furthermore, it is noted that a special case of the present formalism can be used to determine the reflected, transmitted and internal fields for normal plane wave incidence on a stratified dispersive and dissipative slab.

ISSN:0920-5071    

DOI:10.1163/156939393X01065

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A layer model is developed and applied to interpret radar backscattering coefficients at 5.3 GHz for a soybean canopy. The canopy is modeled as a random medium containing spheroidal scatterers for the leaves. The data were taken over an extended time period from early to late stage of the vegetation. The theoretical results and the experimental data are in good agreement. The lateral correlation length is observed to be highly correlated with the canopy fractional volume. With consideration of the interrelations among biophysical parameters, the model is then used to simulate backscattering coefficients under various conditions. The results provide sensitivity domains of radar responses to soil moisture and vegetation biomass for inversion assessment. Furthermore, the polarization signatures of the vegetation canopy are synthesized to illustrate structural information conveyed by polarimetric data.

ISSN:0920-5071    

DOI:10.1163/156939393X01074

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A point-matched time domain finite element method is proposed to analyze planar circuits of arbitrary shape. In this method, the wave propagation inside the circuit is simulated numerically by solving a boundary value problem at each time step starting from t = 0. To properly model ports with matched loads, absorbing boundary conditions are used. The excitation can be either a Gaussian pulse or a sinusoidal input. The method is illustrated with several examples of two-port circuits with results shown in both time and frequency domain.

ISSN:0920-5071    

DOI:10.1163/156939393X01083

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The method of moments is used to solve electromagnetic boundary value problems numerically. It is known that the choice of basis functions is crucial for the numerical efficiency. Fast convergence is achieved provided the basis functions efficiently approximate the unknown function. In this paper the far field (incl. RCS) of a thin conducting square plate is calculated. Basis functions with correct edge and corner singularities are shown to greatly enhance the convergence compared to ordinary "rooftop" functions. The calculations of the matrix elements as well as the right side of the matrix equation and the scattered field are simplified by the use of a multipole technique.

ISSN:0920-5071    

DOI:10.1163/156939393X01092

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Two configurations of broadband microstrip antennas are proposed and analyzed numerically by the full-wave spectral-domain method. One is a square Archimedean spiral microstrip antenna which yields circular polarization; the second configuration is a log-periodic patch microstrip antenna, which radiates linearly. In this paper, the definition of bandwidth of an antenna is redefined and is based on both VSWR and radiation pattern behavior. A 25% bandwidth for a square Archimedean spiral microstrip antenna and a 2:1 bandwidth for a log-periodic patch microstrip antenna are achieved using electrically thick (1/8λ to 1/4λ) substrates.

ISSN:0920-5071    

DOI:10.1163/156939393X01100

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Vector transmission-line theory is introduced for problems involving plane wave propagation, reflection and transmission in multilayered general bi-isotropic (BI) structures. The structure is replaced by a transmission line with vector voltage and current quantities and dyadic line parameters. The characteristic admittance and propagation factor are both dyadic quantities, which have different expressions for waves propagating in opposite directions along the transmission line. Vector circuit theory, developed earlier for plane-wave propagation and reflection problems in layered chiral and general BI structures, is formulated in terms of vector transmission line parameters. The theory is verified by checking special cases. It is claimed that, with the present formalism, analysis can be done more systematically, with less effort and particular results can be memorized more easily than when operating with scalar component quantities. Numerical examples show new and interesting results indicating possible applications of BI slabs.

ISSN:0920-5071    

DOI:10.1163/156939393X01119

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939393X01128

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939393X01137

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor