An on-line microcomputing system for the acquisition and processing of data from a fourier spectrometer

A microcomputing system has been developed to provide on-line data acquisition and analysis for a Fourier transform spectrometer, and the interface between the spectrometer and the microcomputer is described in detail. The system has been equipped with software which includes a fast Fourier transform programme for use in either conventional or dispersive Fourier transform spectroscopy, and programmes for calculating the optical constants and dielectric functions of solids from complex spectra obtained by dispersive Fourier transform spectroscopy.     

Wideband measurement of microwave characteristics of soils

An in-situ method for measuring the bulk attenuation and dielectric constant of soils over the range of frequencies 0.3 GHz to 1.3 GHz has been devised. Very short pulse and fast Fourier transform techniques have been used to derive attenuation and dielectric constants.     

Variational Method for the Analysis of Microstrip Lines

This paper reports a method for computing the line capacitance of a microstrip line based on the application of Fourier transform and variational techniques. The characteristic impedance, guide wavelength, and the surface potential distribution in the microstrip line are obtained for a range of structure parameters and the dielectric constant. The results calculated from the expressions developed in the paper are compared with the theoretical results presently available in the literature and good agreement is found. Comparison with available experimental results is also made where feasible. Possible applications and limitations of the method are discussed.     

Metallization thickness in bilateral and unilateral Finlines

The theory and numerical results are presented to the effective dielectric constant and characteristic impedance of bilateral and unilateral finlines with metallization thickness. The full wave analysis of the transverse transmission line — TTL method is used to determine the electromagnetic fields of the structure in Fourier transform domain — FTD. Applying the suitable boundary conditions and the moment method, a homogeneous matrix system is obtained and the effective dielectric constant is extracted. The characteristic impedance is obtained using the relation between the voltage in slot and the transmitted power. Computational programs are developed to obtain numerical results to the effective dielectric constant and characteristic impedance.     

Application of the discrete Fourier transform method to thindielectric structures [EM scattering]

The discrete Fourier transform method is a numerical technique designed to take advantage of the convolution structure that often appears in the differential-integral equations arising from electromagnetic scattering. It used the fast Fourier transform (FFT) to compute both the derivatives and the convolution integrals. As a consequence, this method is easy to program, uses less computer memory than comparable methods, yields accurate predictions, and in general, offers a better rate of convergence. This technique, which is particularly suited for solving problems where the scatterer is made of a dielectric material and has a shape which can be approximated accurately by a rectangular grid, is applied to thin dielectric slabs with both electric and magnetic properties. It is shown that by choosing the conductivity sufficiently large, a thin dielectric slab behaves like a metallic plate. On the other hand, with a suitable choice of conductivity, a particular thin dielectric slab will act like a resistive plate     

Feed gap aperture field and input admittance of an infinitely longinsulated antenna

Expressions are derived for the input admittance and aperture electromagnetic fields in the feed gap of a solid insulated antenna of infinite extent. This is done by solving the boundary value problem where the fields are represented by Fourier series built up by superposition of basic sets of φ-independent cylindrical waves. Such waves are obtained from the solution of the Helmholtz equation governing the z-directed electric Hertzian potential. The axial aperture electric field in the gap is in the form of a Fourier-Bessel series and is used to find the input admittance. Results are plotted for the aperture fields and tabulated for the input admittances at different radii, insulating shell dielectric constants, and gap widths     

The far infrared optical properties of InP at 6 and 300 K

The amplitude and phase reflection spectra of InP have been determined in the far infrared at 6 and 300 K by dispersive Fourier transform spectroscopy and used to calculate values of the optical constants and dielectric functions in the region of the fundamental lattice resonance.     

Plasma-enhanced chemical vapour deposition of fluorinated silicon dioxide films using novel alkylsilanes

Deposition processes and film properties of plasma-enhanced chemical vapour deposition (PECVD) films derived from fluoroalkylsilanes are described. The fluorinated silicon dioxide (FSG) films have lower dielectric constants (3.3–3.7) than non-fluorinated silicon dioxide films (>4). With similar dielectric strengths, the reduced capacitance obtained with FSG films makes them useful as intermetal dielectrics (IMDs). The films are characterised using Fourier transform infrared spectroscopy, Auger electron spectroscopy, ellipsometry and capacitance-voltage measurements. Characterisation of the changes in FSG upon exposure to ambient conditions and a method for stabilising the films are presented     

基于化学物质释放的五点傅里叶变换求解泊松方程的方法

在电离层化学物质释放数值模拟中,傅里叶变换是一种有效的求解泊松方程的方法,但其仿真精度有待进一步提高.文章提出一种改进的傅里叶变换求解泊松方程的方法,对泊松方程的五点差分形式做傅里叶变换,并引入误差修正项,弥补二阶差分带来的误差,模型中给出了详细推导过程,并与常用方法进行了对比分析.研究结果表明,改进方法求得电势的均方误差（Mean Square Error,MSE）相对Birdsall方法和电势求导方法小6个量级,电势空间分布更加接近解析结果.文中所提方法满足化学物质释放数值仿真的要求,为等离子体粒子模拟中泊松方程的求解提供了一种新的方法.     

The Significance of Negative Frequencies in Spectrum Analysis

In EMC measurements spectra generated by pulsed signals are often measured. To calculate the spectra theoretically, Fourier methods are usually used. The Fourier transform yields a spectrum which contains positive and negative frequencies. The exponential form of the Fourier series also yields a spectrum which contains positive and negative frequencies. However, the trigonometric form of the Fourier series yields a spectrum containing only positive frequencies. Since there seems to be some doubt about the physical interpretation of negative frequencies, the relationship between the double sided spectrum of the exponential Fourier series and the single sided spectrum of the trigonometric Fourier series is shown. The reasoning is then extended to the Fourier transform to show the relationship between the double and single sided spectrum obtained by the Fourier transform. A method of obtaining spectral levels for positive frequencies only using the Fourier transform is shown.     

THz wave sensing for petroleum industrial applications

We present the results of terahertz (THz) sensing of gasoline products. The frequency-dependent absorption coefficients, refractive indices, and complex dielectric constants of gasoline and xylene isomers were extracted in the spectral range from 0.5–3.0 THz. The THz spectra of gasoline (#87, #89, #93) and related BTEX (benzene, toluene, ethylbenzene, and xylene) compounds were studied by using Fourier transform infrared spectroscopy (FTIR) in the 1.5–20 THz (50–660 cm^?1). The xylene isomers, which are used as antiknock agent in gasoline were determined quantitatively in gasoline in the THz range. Our investigations show the potential of THz technology for the petroleum industrial applications.     

Spectral Domain Analysis of Frequency Dependent Propagation Characteristics of Planar Structures on Uniaxial Medium

The propagation characteristics of single and multilayered uniaxial dielectric waveguides and planar structures on uniaxial medium can be determined by utilizing Hertzian potentials along the optical axis. The electric and magnetic Hertzian potentials, having components along the optical axis only, lead to TM and TE modes, respectively, with respect to that axis. The dyadic Green's function in Fourier transform domain (immittance matrix) required to solve for the propagation characteristics of planar structures on uniaxial medium are derived for all three orientations of the optical axis. The immittance matrix for all three cases is in the same form as that for the isotropic medium and hence the known Galerkin's method can be used to solve for the propagation characteristics of the structure.     

Study of TE0 and TM0 modes in dielectricresonators by a finite difference time-domain method coupled with thediscrete Fourier transform

An application of a numerical method of finite differences in the time domain (FDTD) coupled with the discrete Fourier transform is presented to determine the resonant frequencies of the TE₀ and TM₀ modes of axially symmetric dielectric resonators closed in a cavity. The technique is conceptually and computationally simple, and it allows access at once to information on the entire modal spectrum by means of the fast Fourier transform (FFT) applied to the time series. The cylindrical cavity dielectrically loaded at the base and the resonant frequency of the TE_01δ mode are analyzed in two systems: a cylindrical cavity with a cylindrical dielectric resonator of variable radius, and the shielded dielectric resonator on a microstrip substrate. The results obtained are compared with the rigorous (exact) theoretical solutions and with experimental results     

Spectral-Domain Calculation of Microstrip Characteristic Impedance

This paper presents a hybrid-mode solution for the characteristic impedance of microstrip on Iossless dielectric substrate. A solution to the hybrid-mode equations is obtained by applying the method of moments in the Fourier transform domain. Numerical results are presented showing the frequency dependence of both wavelength and characteristic impedance for single and coupled strips. These results are compared with those of other investigators in the low-frequency range.     

Scattering of plane waves by an anisotropic dielectric half-plane

Scattering of plane waves by a semi-infinite anisotropic thin dielectric layer is investigated, which can be considered as an example for electromagnetic energy absorbing materials. A pair of second-order boundary conditions is used to simulate an anisotropic thin dielectric layer as an infinitesimally thin sheet. Formulation is based on the Fourier integral transform technique, which reduces the scattering problem to two decoupled scalar Wiener-Hopf equations. Diffracted, reflected, and transmitted field terms are evaluated by using the Wiener-Hopf solutions that is obtained by the standard method. The uniqueness of the solution is satisfied by imposing an edge constraint in addition to the classical edge condition     

Electrostatic potential due to a potential drop across a slit

The electrostatic potential and charge density due to a potential drop across a slit in a thick conducting plane are obtained in analytic closed form. The Fourier transform, mode matching, and superposition are used to represent the potential in the spectral domain. The residue calculus is applied to represent the potential distribution in converging series form. Numerical computations are performed to illustrate the charge-density distribution through a slit     

基于STFT与G函数相结合的短波DFH跳检测方法

差分跳频利用频率的跳变携带信息,只要正确检测出每跳的频率,就可以恢复出信息.本文提出一种基于STFT的跳检测方法,并与G函数相结合来分析短波DFH信号在每跳时间间隔内的频率特性,以检测可能的跳频率.仿真结果表明,在短波信道几种可能的情况下,检测效果良好.     

The discrete Fourier transform method of solvingdifferential-integral equations in scattering theory

An accurate and efficient numerical method is presented for solving many differential-integral equations arising from electromagnetic scattering theory. It uses the discrete Fourier transform technique to treat both the derivatives and the convolution integrals which often appear in these equations. As a consequence, this method is extremely simple to implement, uses less computer memory than comparable methods, and yields accurate predictions. The differential-integral equation is recast into a periodic form conducive to application of the discrete Fourier convolution theorem. The differential operators are approximated by appropriate finite-difference and discrete-convolution operators. All these quantities are computed by using the fast Fourier transform. An approximate solution is obtained by using the conjugate gradient method. Results are compared to experimental data or analytical solutions for a 3λ×3λ metal plate (where λ is the wavelength), a homogeneous and a layered infinite circular dielectric cylinder, and a dielectric sphere. The accuracy of the method is further illustrated by comparing predictions with independent measurements by R.A. Ross (1966) on a 2λ×1λ metal plate at grazing incidence. In all cases, agreement is excellent     

利用PDMS纳米结构薄膜增强玻璃基板出光

以纳米压印技术为基础制备了具有纳米结构的聚二甲基硅氧烷(PDMS)薄膜.将纳米结构中间聚合物模板(IPS)薄膜覆盖在有PDMS溶液的玻璃基板上,真空加热后在玻璃基板上得到PDMS网格结构薄膜.这种方式得到的网格结构形状保持较好且厚度均匀无气泡,IPS薄膜不仅可以反复使用以减少Si母版的材料损耗,还可以缩短网格结构的制备...     

Radiation characteristics of dielectric-coated coaxial waveguideperiodic slot with finite and zero thickness

The leaky wave radiated from the dielectric-coated coaxial waveguide periodic slot with finite and zero thickness is investigated theoretically for the infinite and finite periodic structures. For the infinite periodic structure, mode-matching technique and integral equation method are applied to the analysis of finite and zero thickness slot cases, respectively. The integral equations are derived for the finite periodic structure by use of the Fourier transform and mode expansion and simultaneous linear equations are obtained. The effects of the slot thickness, the finite slot number and the dielectric coating are analyzed. Results for finite periodic slots are compared with those of the infinite extent structure and good agreement is found