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1.
分析了一个用阱作为耐高压漂移区的LDMOS的导通电阻,提出了带有场极板的高阻漂移区导通电阻的计算公式,改进了双扩散沟道导通电阻的计算公式. 针对一个LDMOS的例子做了计算,并将其与相同参数情况下用MEDICI软件模拟的结果作了对比. 结果表明两者相差仅5%,这说明所得公式可用于该类型LDMOS的分析和设计.  相似文献   

2.
The problem of diffraction of a plane (cylindrical) wave by a perfectly conducting cylinder enclosed in a metamaterial shell is rigorously solved. The influence of the geometric dimensions of the shell, the value of the negative refractive index of the metamaterial medium, and the position of a cylindrical wave source on the field structure in the near zone of the scatterer is investigated. It is found that, in the quasi-optical range of the problem parameters, this structure does not exhibit ideal focusing. It is shown that, there are two types of caustics inside the shell. The first type is related with rays reflected by the surface of the interior cylinder and has one cusp point, and the second type is formed by the geometric-optics rays that are refracted by the outer boundary of the shell and do not fall on the surface of the interior perfectly conducting cylinder. The spatial distribution of the total field amplitude and of the equal-amplitude lines in the near zone of the scatterer is reported. The obtained numerical results are correctly interpreted from the physical viewpoint.  相似文献   

3.
This paper demonstrates the use of software radio techniques in the context of sensing, rather than communications. It describes code-division multiplexing (CDMA) and time-division multiplexing (TDMA) of a receiver channel in an electric field sensing system. The only hardware used is a front-end gain stage consisting of two opamps and a microcontroller. The modulation and demodulation operations are implemented entirely in the microcontroller software. Multiple coded waveforms are transmitted simultaneously, and induce a combined signal on a single receive electrode. The combined signal, after passing through a single analog front end terminating in an analog-to-digital converter, is separated into the four original component signals by a software demodulation operation. The signal-to-noise ratio (SNR) achieved by the code-division multiplexed system given a fixed measurement time is compared to the SNR achieved by a time-division multiplexed implementation given the same total measurement time. The paper also compares the scaling of TDMA and CDMA performance with the number of transmitted channels and the number of demodulated channels  相似文献   

4.
A rocket with removed access plate is simulated by a section of coaxial transmission line with a transverse elliptical slot cut in its sheath. The internal circuit consists of two arbitrary impedances in series with the inner conductor at its ends. The object is to find the currents in these impedances when the cylinder is illuminated from the outside by an electromagneticfield that enters the aperture and excites the internal circuit. The problem is solved by application of the reciprocal theorem. The current in a dipole antenna is determined when this is inthe far field maintained by the slotted coaxial line when driven by a generator in series with one of the load impedances. The field in the aperture is replaced by equivalent electric and magnetic dipoles. The reciprocal theorem gives the current in the load impedance when the distantdipole is driven. A numerical example is given.  相似文献   

5.
Transmission-Line Properties of a Strip on a Dielectric Sheet on a Plane   总被引:3,自引:0,他引:3  
The subject is a strip Iine formed of a strip and a parallel ground plane separated by a dielectric sheet (commonly termed "microstrip"). Building on the author's earlier papers all the significant properties are formulated in explicit form for practical applications. This may mean synthesis and/or analysis. Each formula is a close approximation for all shape ratios, obtained by a gradual transition between theoretical forms for the extremes of narrow and wide strips. The effect of thickness is formulated to a second-order approximation. Then the result is subjected to numerical differentiation for simple evaluation of the magnetic-loss power factor from the skin depth. The transition formulas are tested against derived formulas for overlapping narrow and wide ranges of shape. Some of these formulas are restated from the earlier derivations and others are derived herein. The latter include the second-order approximation for a narrow thin strip, and a close approximation for a narrow or wide square cross section in comparison with a circular cross section. Graphs are given for practical purposes, showing the wave resistance and magnetic loss for a wide range of shape and dielectric. For numerical reading, the formulas are suited for programming on a digital pocket calculator.  相似文献   

6.
Several cases of a compensation technique for a second order control system are described based on the idea of displacement of the equivalent Nyquist critical point during the system operation. The displacement of the Nyquist point is achieved by changing the characteristic of a nonlinear network constructed by means of a microprocessor. The time instants when the change occurs are properly selected so that the time response characteristics are improved.  相似文献   

7.
The scattered field from a hyperboloidal reflector is calculated by integrating the induced current density over the front of the hyperboloid. The resulting integral expressions for the fields possess a stationary term which, when evaluated, yields the geometrical ray-optics approximation to the scattering problem. The complete field, including diffraction effects, may be obtained by numerical evaluation of the integrals. The formulas are applied to a hyperboloid illuminated by an idealized, sharply cut off uniform feed pattern. Characteristic diffraction phenomena are reduced with increasingD/lambdauntil the geometrical ray-optics result is obtained in the limit of vanishing wavelength. Theoretical field patterns are also obtained for a horn-fed hyperboloidal subreflector in a Cassegrainian feed system; they indicate that for moderately large hyperboloidal reflectors spillover may be reduced to an acceptable level, but there is a tendency toward increased forward spillover. The results of 9600-Mc model tests compare favorably with the theoretical patterns.  相似文献   

8.
9.
垂直电偶极子在涂有介质层球形导电基底上的场   总被引:2,自引:1,他引:1  
利用解析方法导出了垂直电偶极子在涂履有介质层的球形导电基底上产生的电磁场的解析表达式。所得结果表明,当介质层达到一定的厚度时,与文献[1]中的平面导电基底情况相类似,垂直电偶极子同样能够在球形介质层的表面激励起吸附表面波(Trapped surface wave)。文中对具有特殊地貌情况下和有冰层的海面上的通信有新的指导意义。  相似文献   

10.
An analytical-numerical technique, for the solution of the two-dimensional electromagnetic plane-wave scattering by a finite set of perfectly conducting circular cylinders buried in a dielectric half-space, is presented. The problem is solved for both the near- and the far-field regions, for TM and TE polarizations. The diffracted field is represented in terms of a superposition of cylindrical waves and use is made of the plane-wave spectrum to take into account the reflection and transmission of such waves by the interface. The validity of the approach is confirmed by comparisons with results available in the literature, with very good agreement. The multiple interactions between two buried cylinders have been studied by considering both the induced currents and the scattered field diagrams. Applications of the method to objects of arbitrary cross-section simulated by a suitable configuration of circular cylinders are shown.  相似文献   

11.
The problem of wave propagation through a circular cylinder with a periodically interrupted dielectric lining is solved by a boundary value approach by considering the region between the corrugations as a medium with a tensor permittivity. The characteristic equation for the phase constant is derived by matching the field components. Solutions for the phase constant are obtained and the variation of the phase constant with the physical parameters is studied. The variation of the axial and circumferential electric field components in the transverse plane is also studied  相似文献   

12.
用实验方法测量了楔形光纤与锥形光纤的耦合效率,作出耦合效率随楔形光纤的半楔角及锥形光纤半圆锥角的变化曲线。从实验结果可以看出,楔形与锥形光纤的耦合效率随半楔角增加而增大。当半楔角由15.0°增大到30.3°,半楔角由44.9°增大到55.2°时,耦合效率曲线呈较快的上升趋势;当半楔角由30.3°增大到44.9°时,耦合效率曲线上升趋势变缓。当锥形光纤半圆锥角增加时,耦合效率也随着增大;并且随着楔形与锥形光纤的间距的减小而增大,在间距由0.10mm减小到0.03mm时,耦合效率曲线呈较快的上升趋势;在间距由0.03mm减小到0.01mm时,耦合效率曲线呈下降趋势。  相似文献   

13.
A capacitance-voltage (C-V) measurement is conducted on a series connection of a ferroelectric capacitor and a p-n diode. This series connection is found to have a threshold hysteresis (“memory window”) width of 2.7 V as observed by C-V measurement. The threshold hysteresis is the result of the remnant polarization of the ferroelectric capacitor. Because the series connection has a memory window, it is expected to serve as a new nonvolatile, nondestructive readout, ferroelectric memory. Moreover, this connection is expected to offer easy processing by conventional ultra large-scale integration (ULSI) methods  相似文献   

14.
A family of transmission lines is based on a round wire in a cylindrical shield of polygon cross-section. There is presented a simple formula which gives a smooth transition between the extremes of a small wire and a wire near contact. The same formula is adapted for different shapes by entry of different constants depending on the number of shield planes and the degree of symmetry. The formula is reversible for synthesis or analysis by explicit expression of either shape ratio or wave resistance in terms of the other. For comparison in the transition region, there is computed for each shape a close approximation by the method of images.  相似文献   

15.
在广义米理论的基础上,通过把入射高斯波束、散射场和内部场用适当的球矢量波函数展开,给出了一种求解手征涂覆球对高斯波束散射的解析方法。待定的展开系数可由从边界条件得到的线性方程组求出。对于波束的区域近似模型,给出了微分散射截面的数值结果。结果表明:与介质涂覆的情况相比,手征涂覆对微分散射截面和散色场的极化特性都产生了较大的影响。  相似文献   

16.
This paper presents an analysis of radiation from a horn with a superquadric aperture, modeled using a cascade of superquadric waveguides. Electromagnetic fields within each waveguide are expressed in terms of a set of orthogonal modes derived from polynomial functions based on a Cartesian coordinate system. The scattering matrix at the horn aperture is obtained by calculating the scattering matrix at each of the waveguide junctions using mode matching, and cascading them appropriately. Radiation patterns corresponding to both x- and y-polarizations of the input excitation are then obtained by integrating the aperture field. The computed numerical results are validated by comparing them with the corresponding results obtained from measurements.  相似文献   

17.
The fundamental interaction impedance for a helix surrounded by a dielectric medium and a conducting shield is computed and the result is found to be in good agreement with measurements on several TWT structures. Results obtained in this paper indicate that the addition of a conducting shield around a helix reduces the interaction impedance; this impedance reduction becomes more severe as the shield is brought closer to the helix and as γa, the ratio of helix circumference to guide wavelength, is made smaller. A sheath helix surrounded by a dielectric medium and a conducting shield is used to obtain a factor representing the impedance reduction caused by the shield. This impedance reduction factor is then combined with Tien's factors to compute the helix impedance.  相似文献   

18.
Electromagnetic fields in a rectangular waveguide containing a lossy dielectric cylinder are investigated by means of the orthogonal expansion method. The calculated results are provided by measurement. Resonance effects become visible through the frequency responses of the scattering parameters and understandable by patterns due to magnetic fields and Poynting vectors. The lowest resonance is nonsymmetric and can be used to realize tunable bandstop filters with a relative 3-dB bandwidth of about 0.04 and an attenuation of more than 40 dB  相似文献   

19.
A linear transport system, which is capable of reducing the weight of a moving carrier by separating power-supplying devices, is developed by using a new magnetic levitation technique. This system is designed to distribute a wafer between semiconductor fabrication process modules in clean rooms, because it can eliminate particles and oil contamination that normally exist in conventional transporter systems due to rubbing of mechanical components. The transport system consists of a wafer carrier, two levitation tracks, two stabilization tracks, and a propelling system. Levitation is achieved by using opposing forces produced between electromagnet tracks and permanent magnets. Stabilization is achieved by using a simple feedback control. The continuous propelling force is obtained by sending specific current patterns to the propulsion coils. The dynamic model of the transport system is presented, and it is verified by experiment. The system performance is experimentally investigated  相似文献   

20.
This paper presents an analysis of a human head response to impact by a foreign object. The analysis is accomplished via an integration of a head-striker contact force function with a 3-D finite-element (FE) head model. The contact force function developed by the authors is used to estimate the contact force between the solid striker and the human head. An explicit FE solver, implemented with the contact force function, is employed to predict the human head response to the contact impact. The analysis is verified by comparing the present results with the experimental data published by others. Based on the present solution, the effects of the different impact conditions on the intracranial pressure of the head are investigated.  相似文献   

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