Computation of the effect of a dielectric cylinder on the radiation pattern of a dipole

A method is given for calculating the effect on the horizontal radiation pattern of a dipole when it is enclosed in a dielectric cylinder. Results are shown which indicate that considerable pattern shaping can occur with cylinders of glass fibre when the radius is a wavelength or greater.     

Localization of the Interfaces of a Slab Hidden Behind a Wall

In this paper, a 1-D inverse-scattering problem laying within the framework of through-wall imaging is addressed. In particular, the problem of localizing the interfaces of a slab hidden behind an obstacle, another slab whose electromagnetic features and thickness are known, is considered. To this end, an approximate linear mathematical relationship between the scattered field and the unknown slab-interface positions is stated. Such an approximate relationship arises from neglecting the multiple-reflections between the two unknown slab's interfaces and between the slab and the obstacle. The unknown locations of the slab's interfaces are represented as the support of Dirac-delta functions, and the problem is cast as the inversion of a linear integral operator whose inversion is achieved by means of the Truncated-Singular-Value-Decomposition (TSVD) inversion scheme. The effect of the parameters of the obstacle on the inversion algorithm and the performances achievable by the solution approach are assessed by exploiting synthetic data. Furthermore, a comparison with the reconstructions obtained under the Born approximation and with the time-backscattered field is achieved. Finally, results obtained by employing experimental data collected owing to a stepped-frequency ground-penetrating radar system are also presented.     

Impedance of a monopole on the base of a large cone

This paper is concerned with the determination of the driving-point impedance of a monopole which is located at the center of the base of a perfectly conducting, right circular cone. The cone is assumed to be sufficiently large that it is valid to apply ray-optical theory. It is shown that the field which is reflected back to the monopole from the edge of the base may be pictured as arising from an equivalent magnetic current located at the base edge, the magnitude of which is determined by wedge-diffraction principles. Use of the induced electromotive-force (EMF) method then allows estimation of the change in the monopole impedance from its value on a ground plane of infinite extent. Proper account is taken of the edge curvature and of the more significant multiply diffracted rays. In the degenerate case in which the cone becomes an infinitely thin disk, the general result is shown to reduce to that obtained by a completely independent method. For this particular case, the theory is also compared with published experimental data and the agreement shown to be good for disks with a diameter exceeding one wavelength.     

Bounds for the resistance of a conductor of a given form

New upper and lower bounds for the resistance of a. conductor of given form are derived in a unified manner from the canonical theory of complementary extremum principles.     

Influence of a flatband-voltage variation along the channel on the drain characteristics of a TFT

The theoretical model for a thin film transistor (TFT) is extended to include the effect of a flatband-voltage variation along the channel as caused by the presence of mobile ions in the insulator and of slow surface traps in the semiconductor-insulator interface. The parameters determining the flatband-voltage in a common experimental situation are discussed. Finally, some approximations are given, resulting in a very simple model for the influence of mobile ions on the drain characteristics.     

Determination of the effective permittivity of a body in a waveguide from the reflection coefficient

The inverse problem of diffraction of the electromagnetic field by an inhomogeneous body placed in a rectangular waveguide with perfectly conducting walls is considered. The problem is reduced to a nonlinear volume singular integral equation. The integral equation is solved with the help of the iteration method. The permittivity is determined with the use of the reflection coefficient. Computation results for a figure of a complex shape are presented.     

On the recovery of a function on a circular domain

We consider the problem of estimating a function f (x, y) on the unit disk f {(x, y): x/sup 2/+y/sup 2//spl les/1}, given a discrete and noisy data recorded on a regular square grid. An estimate of f (x, y) based on a class of orthogonal and complete functions over the unit disk is proposed. This class of functions has a distinctive property of being invariant to rotation of axes about the origin of coordinates yielding therefore a rotationally invariant estimate. For-radial functions, the orthogonal set has a particularly simple form being related to the classical Legendre polynomials. We give the statistical accuracy analysis of the proposed estimate of f (x, y) in the sense of the L/sub 2/ metric. It is found that there is an inherent limitation in the precision of the estimate due to the geometric nature of a circular domain. This is explained by relating the accuracy issue to the celebrated problem in the analytic number theory called the lattice points of a circle. In fact, the obtained bounds for the mean integrated squared error are determined by the best known result so far on the problem of lattice points within the circular domain.     

On the design of a multiplexer with a common junction

Two sets of formulas for scattering parameters are presented for multiplexers having parallel and series configurations with a common junction. A new general design approach is developed for multiplexers having any response types and any number of channel filters of arbitrary degree, bandwidth, and interchannel spacing. By using these formulas and computer optimization techniques for all the element values in the channel filters, the design process results in a good match at the common input port over the transmission frequency band. Several examples including a contiguous multiplexer are given to demonstrate the design procedure.This work was supported by Air Force Systems Command under Contract F33615-84-K-1556.     

用望远系统移动法检测导轨不直度

本文研究望远系统在导轨上移动时光线的偏折引起莫尔条纹的位移来检测导轨。该法方便,精度高而可调。     

Studying the Influence of Temperature on the Operation of a Resonator of a Frequency Micromechanical Accelerometer

Russian Microelectronics - A micromechanical accelerometer (MMA) is used to measure the acceleration based on the change in frequency of the resonator when the acceleration is caused by the...     

Increasing the locking bandwidth of a waveguide-cavity oscillator through the use of a double-tuned circuit

The experimental 6 GHz Gunn oscillator consists of a TE101 waveguide cavity and a coupling slot, both being mechanically tunable in frequency. Fractional-bandwidth?voltage-gain products of approximately 0.2, corresponding to Qext = 10, were obtained. Comparison is made with other broadband injection-locked solid-state oscillators.     

An electric dipole on the surface of a half-space near the edge of a spherical segment

The 3D problem on the field of an electric dipole situated near the edge of a spherical irregularity projecting from a conducting half-space is solved in the quasi-static approximation. An analytical solution is obtained for the near field of the source in the case of rational angular points. For the spherical irregularity, the effect functions and their asymptotics taking into account the influence of the irregularity on the far field are studied.     

Probabilistic modeling of the states of a buffer in a productionflow system

Assembly line manufacturing systems and materials handling systems usually operate through a system of serially linked stages. In a serially dependent system of this type, the failure of any stage either causes a reduction or causes the complete shutdown of the system. The provision of buffers between stages can result in operation of the nonfailed stages even in the event of failure of a stage. The author presents a stochastic analysis of a buffered production system. The probability of the buffer being full is determined as a function of buffer capacity. This, in turn is used to make the decision on buffer size. Results of the analysis indicate that, over the range of buffer capacity from zero to infinity, the probability of the buffer-full-state exhibits monotonically decreasing behavior that approaches zero asymptotically as buffer size approaches infinity. This finding can be used to detect the range over which the probability of the buffer-full-state asymptotically approaches zero, and appropriately select a buffer size beyond which there is no significant gain in system availability to justify the incremental cost of the additional buffer capacity     

Synthesis of the fields of a transverse feed for a spherical reflector

The problem of designing a transverse feed for a spherical reflector is considered and a method is presented for synthesizing the fields on a surface of a sphere enclosing a feed that will produce a specified reflected field at the surface of a spherical reflector. The method identifies the reflector and a spherical surface enclosing the feed as a boundary value problem and uses a finite set of spherical waves to approximate the boundary conditions. A feed designed to excite this field will in turn produce the desired reflected field at the surface of the reflector, under the condition that that portion of the reflected field which is scattered by the feed may be neglected. It is shown that the feed need produce only a small part of the synthesized field to obtain an antenna efficiency of more than 70 percent. Some typical field distributions will be shown so as to indicate a method for designing a feed and to point out the correlation between the polarization of the synthesized field and the polarization of the reflected field at the surface of the reflector.     

About the localization of a converging spherical wave going through the plane boundary of a medium

The focusing properties of a converging spherical wave that passed the plane boundary of a medium are investigated in the ray approximation. Models of the medium of the two types are considered—ignoring and taking into account the wave energy loss in the medium. The dimensions of the localized volume spot of the field formed instead of the focusing point are estimated.     

Modeling the switching performance of a MOSFET in the high side of a non-isolated buck converter

This paper uses generic equations to model the switching performance of metal oxide semiconductor field effect transistors (MOSFETs). Two MOSFETs with different gate structures are analyzed and switching times are presented, which are compared against practical measurements. It is shown that it is possible to get a reasonable accuracy of the switching performance of a MOSFET in a nonsynchronous buck converter, but care must be taken to ensure the correct values of the parameters are used. It is also shown that the MOSFET with the thick bottom oxide gate provides a faster switching instant when compared to a conventional U-Trench gated MOSFET.     

Modulation of a helium-neon laser by the light of a helium discharge

A method of modulating laser intensity by optical action on the population mechanism of the upper level is given. Experiments have been made with a helium-neon laser using the 3s2?3p4 transition of neon (3.39 ?m line).     

Computational Optimization of a Thermoelectric Ice-Maker as a Function of the Geometric Parameters of a Peltier Module

The objective of this paper is to optimize a thermoelectric ice-maker installed in a no-frost refrigerator, by means of a computational model. This model provides the electric power consumption of the Peltier module and the ice production. The Peltier module is the most important part of the thermoelectric ice-maker; therefore, it must be optimized in order to obtain an efficient ice-maker. First of all, the length of the thermocouples of the Peltier module has been optimized in order to obtain the maximum ice production. It turned out that 3.5 kg per day could be achieved if 1.5-mm-long thermocouples were used. The coefficient of performance (COP) was 0.44. Second, the ice production was expressed as a function of the number of thermocouples of the Peltier module. Given a constant electric power consumption of the module, the results showed that the maximum ice production was achieved with a Peltier module with 254 thermocouples. However, if a module with 140 thermocouples was installed, the ice production would decrease by only 1%.     

Diffraction of a surface wave at the truncation of a dielectric structure

A numerical method to investigate the diffraction of a surface wave at the edges of a truncated dielectric structure is presented. The method is based on the equivalence principle. The current distribution is found from the relevant integral equation obtained from the condition of continuity of the tangential magnetic field. The diffraction pattern and the reflection coefficient of the surface wave are computed after the solution of the integral equation by the Galerkin method. The numerical results show the influence of the substrate's permittivity and thickness on the radiation parameters.     

Modal Analysis of a Doubly Clad Optical Waveguide Having a Cross-section of the Shape of a Lemniscate

In this paper, we choose a simple analytical method based on scalar wave approximation to study the modal behaviour of an unconventional doubly clad optical waveguide having a cross section of the shape of a lemniscate. We take the appropriate orthogonal coordinates for the proposed structure and impose the boundary conditions under the weak guidance approximation to get the modal eigen value equation. Using this equation we obtain numerical results in the form of dispersion curves and cutoff frequencies. An attempt has been made to estimate how the modal behaviour changes when a single cladded waveguide having a lemniscates of Bernoulli type core cross-section is changed to a waveguide having double cladded shape of a lemniscate. It is noted that the double cladded waveguide provides an additional degree of freedom to control the cutoff frequencies on our choice.