用方波代替正弦波作傅里叶变换的一种算法研究

用方波替代正弦波进行离散傅里叶变换（DFT）的一种算法,以便能在一些计算能力不是很强的嵌入式系统内作傅里叶变换。此算法本身不存在变换误差。对方波的离散总是存在误差,但是随着奇次频项数的增加,误差逐渐减小。总体运算效率还是明显提高。     

正弦波辐照对无线电引信的作用机理研究

为了提出复杂电磁环境中降低无线电引信意外发火概率的防护对策,在简要介绍了实验装置与方法的基础上,研究了无线电引信的等幅正弦波辐照效应。确定了天线及弹体是造成引信意外发火的主要能量耦合通道,引信意外发火及作用机理是:引信天线及弹体接收正弦波信号,使引信高频电路工作状态发生变化,引信检波电压波动,最终导致引信意外发火。     

A Lamb wave device for a communication system with ternary logic

A new type of Lamb wave device for signal processing with ternary logic is presented. The transducer consists of a group of three electrodes deposited on two surfaces of a thin piezoelectric substrate. One is on the bottom surface as a common earth electrode. The other two are interdigital electrodes on the top surface. By using the device having two transducers, a communication system with ternary logic is demonstrated.     

Classical magnetoresistance of a two-component system induced by thermoelectric effects

Magnetotransport in a two-dimensional two-component system consisting of electrons and holes with the same concentrations is studied. Balance equations to describe charge carrier and heat transfer are derived from the classical kinetic equation. The charge-carrier density and temperature distributions and electric-current densities are calculated by solving the balance equations for a long strip sample. In a sufficiently high magnetic field, regions of increased and decreased charge-carrier density, temperature, and fluxes are formed near the sample edges. This leads to nontrivial positive magnetoresistance.     

Currents induced in a wire cross by a plane wave incident at an angle

The currents induced in a thin-wire cross with equal mutually perpendicular arms by an incident plane electromagnetic wave are determined when the normal to the wave front is perpendicular to the horizontal wire and is at an anglethetawith respect to the vertical wire; the direction of the electric vector in the wave front is arbitrary. The analysis is formulated in general terms but explicit formulas are obtained only for the zero-order currents which are generally adequate to determine the scattered field of very thin wires. The relatively simple formulas consist of even and odd parts for both the vertical and horizontal wires; they include components due to mutual coupling as well as those excited directly by the incident field.     

Mode selection in standing wave lasers by an induced gain grating

A novel method of overcoming spatial hole burning, in order to achieve narrow-band operation of a standing wave laser, is proposed. Frequency selection is obtained by the interaction between cavity modes and a grating induced in the active medium. A third-order Lamb theory analysis of the proposed system is made and the coefficients for net gain, self, and cross saturation obtained. These coefficients are used to examine the stability of the cavity modes. It is shown that, for the case of a transversely pumped dye laser, single-frequency selection should be possible using a suitable cavity arrangement.     

Early-time currents induced on a cylinder by a cylindricalelectromagnetic wave

An analytical study of the early-time current response of a perfectly conducting circular cylinder to a cylindrical electromagnetic wave, produced by a parallel filament carrying a unit-step current, is presented. Surface current density expressions for both the shadow and illuminated regions are obtained by applying the Watson transformation to the frequency-domain solution and then evaluating the corresponding integrals separately, in the shadow region by a residue series and in the illuminated region by using the saddle point technique. Analytical results obtained by using a double Laplace transform approach for the shadow region and the Luneberg-Kline expansion approach for the illuminated region are given. Numerical results illustrate the variation of the distribution of current density with time for different locations of the line current with respect to the cylinder, and also allows a comparison of the alternate methods applied by the authors, showing their corresponding range of validity. The response to an impulsive plane wave is derived as a special case     

入射波极化方向对毫米波天线罩瞄准误差的影响分析

当不同极化方向的电磁波入射时,采用射线追迹方法计算了Ka波段线极化单脉冲天线-天线罩系统中天线罩所引入的瞄准误差.给出了天线在空域扫描时天线罩引入的瞄准误差分布图,并总结了其随入射波极化方向变化的规律.结果表明,入射波极化方向改变对天线罩引入的共面瞄准误差不产生影响,对交叉面瞄准误差影响较小,而对偏离方位轴和俯仰轴的扫描位置上的瞄准误差影响较大,且整个扫描空域的瞄准误差分布图随入射波极化方向的旋转而缓慢旋转变化.     

电视机等电路中的正弦脉冲波

１ 正弦脉冲波及有关参数电视机及其它电路中常会遇到类似图１所示的波形,这可视为纯正弦波（如图２）在时间轴上横向压缩而成,姑且称其为“正弦脉冲波”。由此看来,纯正弦波形又恰恰成为正弦脉冲波的特例。为简化计算,对图１所示正弦脉冲波的分析和计算仅对其某半周期进行,解析表达式为ｕ（ｔ）＝其有效值Ｕｒ ｍ ｓ＝＝＝ ·（１）当Ｔ１＝Ｔ时, Ｕｒ ｍ ｓ＝为纯正弦波;当 Ｔ１＜Ｔ时,为正弦脉冲波,即为横向压缩比例,在计算有效值时必须计入这一因素。其平均值＝ｕ（ｔ）ｄｔ＝ｓｉｎｄｔ＝·（２）当Ｔ１＝Ｔ时,＝Ａ,为纯正…     

Measurement of the violation of the Madey theorem induced by a diverging wave

We have simultaneously measured the spectra of the gain and the forward spontaneous radiation in the Orsay free-electron laser so that we can extract the relative shift of these two curves. Our results are in agreement with the Madey theorem in the low divergence limit, and demonstrate the violation of the theorem produced as the Rayleigh range of the wave becomes comparable to or smaller than the length of the interaction region. We extend the single particle theory to account for the divergence of the wave to first order. The predictions from this linearized model are in reasonable agreement with the experimental results in view of the fundamental limitations on this kind of experiment.     

High-frequency surface currents induced on a perfectly conducting cylindrical sheet by an obliquely incident plane wave

Explicit expressions for the surface currents of different kinds induced on a perfectly conducting cylindrical sheet by an obliquely incident high-frequency plane wave are derived. The results are in such forms that they can both be used directly in numerical applications and permit us to understand the structure of the induced surface current. It is shown that the components due to the surface and edge diffractions propagate along certain geodesic lines on which the transfer coefficients as well as the attenuation constants are dependent only on the curvature radius.     

Analysis of the currents induced in a general wire cross by a plane wave incident at an angle with arbitrary polarization

Earlier analyses of the wire cross under restricted conditions are generalized, and a complete first-order solution is provided for the currents and charges per unit length in all four arms. These may have different and unrestricted lengths. The angles of incidence and polarization of the exciting plane wave are arbitrary. Detailed graphs are provided for the currents in and scattered fields of an equi-arm cross with electrical arm lengthskhup to 3.5 when the angle of incidence is45degand the electric vector is perpendicular to the horizontal wire. The included three resonances and the condition for a three-arm type of oscillation are treated. The critical effects of changes in the length of one of the vertical arms are examined for normal and nonnormal incidence.     

On reliability of a certain elementary safety system

The paper deals with the determination of reliability of an elementary safety system which consists of two identical elements used simultaneously (hot reserve) whereas for correct system operation is enough when one out of it is good. The operation time is so short that is assumed it is of zero length. Knowing the reliability of element, reliability of system is found.     

Attenuation by a lightning protection system of induced voltagesdue to direct strikes to a building

This paper deals with induced transient voltages on electric circuits inside a protected building due to direct lightning strikes. The prediction of these overvoltages is a mandatory requirement for every EMC design of the installations inside the stricken building. The maximum level of expected transients and the efficiency of their attenuation by different configurations of a lightning protection system (LPS) are evaluated by a new simplified approach. The results are compared with those obtained by a complete circuit prediction model. A loop transfer impedance is defined as the ratio between the open end voltage induced in metal loops and the injected lightning current. This impedance is used to set the upper and lower bounds of the frequency spectra of the voltages induced in the loops internal to the building. The results are helpful in locating critical positions of circuits and devices within the volume protected by a LPS     

Calculating the exact probability distribution of the pulse of a sine wave in narrow-band normal noise by means of infinite series (Corresp.)

The exact solution is provided for the probability distribution (PD) function of the modulo2piphase of a sine wave in narrow-band normal noise by means of several infinite series. Closed-form exact results are reported atpi/4and3pi/4.