摘要:

Criteria are established for choosing the best way to formulate and implement a conjugate gradient FFT (fast Fourier transform) method. Also, the issues of speed and convergence are addressed in connection with the employed FFT. Higher order integration formulae are derived for improving the accuracy of the standard FFT, and a prime factor FFT is introduced for speed improvements when the data lengths do not coincide with a power of two. Finally, on the basis of the established criteria, a conjugate gradient FFT algorithm is presented for the solution of the scattering by a plate.

ISSN:0920-5071    

DOI:10.1163/156939389X00377

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The coupled-mode equations of six interacting modes in a dielectric slab waveguide having weak spatially-modulated multiperiodic interface corrugations are derived via the perturbation method of multiple scales and then solved numerically by means of a novel numerical method for two-point boundary-value problems. This numerical method is particularly useful for stiff systems of differential equations which is characteristic of mode coupling in a multiperiodic guide. The power reflection coefficient of a filter section is calculated for the cases of constant amplitude, tapered and chirped corrugations when conditions of simultaneous resonance are nearly satisfied. The method is also applied to a thin film having aperiodic refractive index perturbations and shown to be more efficient when compared with other numerical methods.

ISSN:0920-5071    

DOI:10.1163/156939389X00386

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The coupling of radio frequency power into a semi-infinite lossy tissue medium with an embedded lossy ferrite sphere is analysed. A magnetic loop near the surface of the lossy medium is taken as the external excitation source. The field induced inside the spherical ferrite implant is determined by solving an integral equation. The kernel of this integral equation is the Green's function of the semi-infinite medium and is expressed in terms of Sommerfeld type integrals. Absorbed power densities inside the ferrite spherical implant and the surrounding lossy medium are computed and are compared for several cases. The efficiency of using ferrite implants in hyperthermia applications is examined and conclusions are presented.

ISSN:0920-5071    

DOI:10.1163/156939389X00395

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The familiar physical optics (PO) approximation with current J = 2n x H is no longer valid when the perfectly conducting scatterer is coated with dielectric material. This paper reviews several possible PO formulations. By comparing the PO formulation with the moment method solution based on the impedance boundary condition for the case of the coated cone-sphere, a PO formulation using both electric and magnetic currents consistently gives the best numerical results. Comparisons of the exact moment method with the PO formulations using the impedance boundary condition and the PO formulation using the Fresnel reflection coefficient for the case of scattering from the cone-ellipsoid demonstrate that the Fresnel reflection coefficient gives the best numerical results in general.

ISSN:0920-5071    

DOI:10.1163/156939389X00403

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A multivariate K- distribution is proposed to model the statistics of fully polarimetric radar data from earth terrain with polarizations HH, HV, VH, and VV. In this approach, correlated polarizations of radar signals, as characterized by a covariance matrix, are treated as the sum of N n- dimensional random vectors; N obeys the negative binomial distribution with a parameter α and mean N. Subsequently, an n- dimensional K- distribution, with either zero or nonzero mean, is developed in the limit of infinite N or illuminated area. The probability density function (PDF) of the K- distributed vector normalized by its Euclidean norm is independent of the parameter α and is the same as that derived from a zero-mean Gaussian-distributed random vector. The above model is well supported by experimental data provided by MIT Lincoln Laboratory and the Jet Propulsion Laboratory in the form of polarimetric measurements.

ISSN:0920-5071    

DOI:10.1163/156939389X00412

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939389X00421

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor