浅层瞬变电磁法中全程瞬变场的畸变研究

浅层瞬变电磁法中,由于发射线圈为感性负载,实际激励信号是斜阶跃波,采用常规的后沿校正方法,探测时近地表仍然存在盲区,直接影响浅层探测的精度和分辨率.针对这一问题,研究了全程瞬变电磁场与斜阶跃波的关断时间与接收探头频率特性之间的关系,揭示了早期瞬变电磁场信号发生畸变和影响浅层瞬变电磁探测的根本原因,提出了当瞬变电磁测量系统在电流关断开始时刻记录全程瞬变响应和发射电流波形时,并且接收探头的位置和谐振频率已知,就可以通过数值计算方法从根本上剔除接收探头对早期瞬变信号的影响,从而实现浅层近地表探测,缩短探测盲区.通过对浙江舟山连岛工程的野外勘探数据进行数值剔除,验证算法的有效性.     

Experimental response of MOS devices to a fast linear voltage ramp

An experimental investigation is undertaken of the response of an MOS device to a linear voltage ramp of such speed as to take the device into non-equilibrium, but to allow sufficient generation to take place during the voltage sweep to provide structure in the C-V curves which can be analysed quantitatively. The main aim has been to investigate the effect of sweep rate per se, but additional data is presented which considers the voltage dependence of the space-charge width, the maximum sweep rate for quasi-equilibrium, and the effect of temperature. It is demonstrated that the technique provides quantitative information on bulk traps and a qualitative measure of the relative role of interface traps in the generation process. Transitions are observed between quasi-equilibrium and non-equilibrium which are a function of sweep rate. This is in contrast to the pulse technique, where the response is of a purely transient nature.     

Transient response of a p?n junction capacitor to a ramp signal

An analysis of the transient response of a step p?n junction capacitance to a linearly varying input signal is presented. The response has been found to be significantly bias-dependent and has some features not observed in linear capacitors. The essential transient parameters and their dependence on bias are given in a tabular form.     

Non-equilibrium response of MOS devices to a linear voltage ramp—I. Bulk discrete traps

A study is presented of MOS devices containing discrete bulk traps, subjected to a triangular voltage waveform, such that the rate of change of voltage is sufficiently high to take the device into the non-equilibrium mode of operation. Consequently, the dynamics of the system response are related to the parameters of the traps involved in the generation and recombination processes occurring within the device. The technique is in contrast with Kuhn's method in which the device, and hence the various generation and recombination processes, are always in quasi-equilibrium. Analytical parametric equations relating the current, and hence the small-signal capacitance and the gate voltage to the width of the depletion region, are obtained. From these equations current and small-signal capacitance vs gate voltage plots are obtained as a function of sweep rate and temperature, for both forward and reverse voltage sweeps. These plots are rich in structure, and physical discussion relating to the salient features of these plots is presented. Suggestions are made of how various device parameters such as generation rate and life-time, trap density, and capture cross-section, can be extracted from the theory.     

Transient response of coupled linear dipole antennas

Transient responses of coupled linear dipole antennas are measured for a basic understanding of coupling in the time domain. A very short pulse for excitation is used and it is shown that the measured data represent the quasi-impulse responses. For further investigation and comparison with the measured data, a simple formula of the impulse response of this configuration is derived by using the transmission line approximation. They suggest that the tips and feed points of each antenna have a significant role in the electromagnetic coupling.     

Transient response of linear antennas driven from a coaxial line

The initial transient response of straight wires connected to coaxial lines is studied theoretically for the case where a pulse is applied to the coaxial line. The wave form of the return pulse is first found approximately for the case of a pulse of zero rise time. Since this does not correspond to any feasible experimental situation, the effect of a finite rise time is considered in detail. Numerical results are obtained for several special cases.     

Substrate response of a floating gate n-channel MOS memory cell subject to a positive linear ramp voltage

A computer simulated substrate response of an n-channel MOS floating gate transistor to a positive linear ramping gate voltage was investigated. Device parameters, such as the channel length, effective electron mobility, substrate doping level and the gate voltage ramping rate were changed to see their effects on the substrate response. The substrate response was monitored by using the response of the surface potential at the mid-channel point. In the one-dimensional analysis it was found that the surface potential at the mid-channel point increased initially and dropped quickly after passing through its peak value and then decreased slowly. The mid-channel surface potential reached a higher peak value if the device had (1) a longer channel length, (2) a lower effective electron mobility, (3) a higher gate voltage ramping rate, or (4) a lower substrate doping level. Solutions show that the conditions for the mid-channel point to reach its peak surface potential faster are: (a) a shorter channel length, (b) a higher effective electron mobility, (c) a higher gate voltage ramping rate, and (d) a lower substrate doping level.     

Transient response of a microstrip line circuit excited by anexternal electromagnetic source

The transient voltages and currents induced by an external electromagnetic field along a microstrip line interconnecting active and/or passive components are studied by using a distributed-source transmission-line model. The influence of the angle of incidence as well as that of the microstrip geometrical and electrical parameters on the line response is analyzed. The instantaneous voltage and power induced on the loads by various types of pulse excitations are computed. Numerical results are obtained both for dispersive and nondispersive lines. A line feeding a transistor microwave amplifier is also considered. The results show the effects of the multiple reflections of the field inside the dielectric substrate and of the signal at the ends of the line. Indications of how to reduce the coupling between the external field and the considered structure are given     

Transient response of a distribution circuit recloser and controlunit to a high-altitude electromagnetic pulse (HEMP) and lightning

An analysis of the response of a power system distribution line recloser unit to a high-altitude electromagnetic pulse (HEMP) and a lightning direct-strike excitation is presented. From details of the configuration of the system, physical and mathematical models are developed, and a study of possible HEMP responses is conducted. Two voltage and two current responses at selected points within the system are studied for both the HEMP and lightning stresses. The possibility of simulating the HEMP responses is also discussed, with predicted and measured responses being provided for the advanced research EMP simulator (ARES). Based on a comparison of measured and predicted currents on one of the conductors, the model is shown to agree reasonably well with the measurement. With such a model, it is possible to perform parametric studies of the HEMP response of the system     

Transient response of a tunnel-diode trigger for linearly varying current pulses

The pertinent forward and reverse transient characteristics of a tunnel diode for a ramp input are analytically investigated. A comparison with the results of a step input shows that the slope of the trigger pulse greatly affects the initial development of the process. The results for a linear piecewise approximation are also presented to estimate the deviation from the actual results.     

Transient electromagnetic waves applied to prospecting

An argument based on a high-frequency filter can be used to show that the later stages of a transient are strongly controlled by the low-frequency component of its spectrum. In particular for a sphere of radius 50 m and conductivity 2 mho/m, frequencies greater than 3100 Hz are unimportant for times greater then 3 ms. For the later stages of the transient, where only low frequencies are important, it is possible to provide solutions for the transient response of spheres, cylinders, and dykes. These solutions have the attractive feature that the singular part of the Green's function is the most important term in this function for these calculations. The early stages of the transient are useful for depth estimations and for these times, different methods of calculation must be used. The various approaches to the problem of calculating transient electromagnetic responses utilize various singularities of the transfer function of the ground. This has shown that the contributions from the integration about poles as well as branch cuts of the transfer function must be considered. Alternatively, if the singularities are seen as specifying the structure, then deriving transient responses for frequency-domain data is likely to be a very ill-conditioned problem. A further conclusion is that care must be given to the choice of pulse shape and measuring time.     

两段式双稳半导体激光器下跳阈值点的确定

对Ｋｕｚｎｅｔｓｏｖ采用的速率方程加以修正，考虑了俄歇效应的影响，我们流子寿命不再作为常数处理，而写成载流子浓度的函数。由此导出了两段式双稳半导体激光器下跳阈值点载流子浓度所满足的隐函数解析表达式。通过该解析表达式确定出了器件存在双稳的必要条件。进而讨论了俄歇复合系数、吸收区偏置电流和长度等对双稳特性的影响。     

Broadband analytical magnetoquasistatic electromagnetic induction solution for a conducting and permeable spheroid

We use a hybrid model including asymptotic expressions of the spheroidal wave functions (SWFs) to obtain a reliable broadband solution for the electromagnetic induction (EMI) response from a conducting and permeable spheroid. We obtain this broadband response, valid in the magnetoquasistatic regime from zero to hundreds of kilohertz, by combining three different techniques, each applicable over a different frequency range. At low frequencies, the exact analytical solution is used. At midrange frequencies, asymptotic expressions for the angular and radial SWFs are incorporated into the exact solution in order to maintain a stable solution for the induced magnetic field. At higher frequencies, a small penetration approximation (SPA) solution is used when the SPA solution approaches the asymptotically assisted solution to within some predefined tolerance. Validation of this combined technique is accomplished through the comparison of the induced magnetic field predicted by our model to both a finite element/boundary integral (FE-BI) numerical solution and experimental data from various spheroids taken by an ultrawideband EMI instrument.     

Transient response of a thin wire to a moving charged particle

The transient current on a thin wire induced by a charged particle moving parallel to the wire axis is studied. An explicit analytical solution for the induced current is obtained by utilizing the natural-mode method in conjunction with the method of asymptotic expansion. It is found that the solution can be split into two parts: one part consists of damped sinusoidal oscillations and the other exhibits quasistatic-like behavior. Numerical results are presented and compared with some selected results obtained directly by numerically solving a spacetime domain integral equation for the induced wire current.     

Spectral and transient response of a circular disk to plane electromagnetic waves

Extensive theoretical far-field amplitude and phase data are presented for the monostatic scattering of an electromagnetic plane wave normally incident upon a thin circular metallic disk. These data are used to synthesize the impulse response of the disk. Comparisons are made with various approximate techniques in both the frequency and time domains.     

ULF/ELF electromagnetic fields produced in a conducting medium of infinite extent by a linear current source of finite length

A linear current source of finite length embedded in a conducting medium of infinite extent is considered. Assuming a sea-water medium, the components of the electric and magnetic fields are numerically evaluated for two frequencies in the ULF/ELF range (frequencies less than 3 kHz). Comparison is made between the electric field vectors produced at the two different frequencies, and curves are plotted for one of the frequencies showing the variation with distance of the amplitudes of the electric and magnetic field components. A parametric approach is outlined that generalizes the field data presented in the figures and which enables the data to be extended to conducting media other than sea water and to other frequencies in the ULF/ELF range. Some practical applications of the data are discussed.     

A methodology to extract the channel current of permeable gate oxide MOSFETs

A methodology to extract the channel current of MOS transistors in the presence of high gate leakage current is presented. The methodology is based on the partitioning of the gate current among the source and drain terminals and it is well suited for devices featuring ultrathin gate oxide and long channels, as those typically employed for mobility measurements. The proposed procedure is compared with the existing method based on a 50%-50% source/drain partition of the gate current, and the dependence of the extraction error associated with these two methods on channel length and bias conditions is studied in detail. It is found that the extraction error is weakly dependent on gate-source and drain-source voltages.     

Correlations between reverse recovery time and lifetime of p-n junction driven by a current ramp

When a p-n junction is switched from the forward to the reverse direction by a current ramp, the reverse recovery time trris found 1) either to be equal to the base lifetime τ if the ramp rateR ll I_{F} / tau, 2) to be equal to 0.79τ ifR approx I_{F} / tau, or 3) to be equal to 0.7 τ ifR gg I_{F} / tau. These results afford correlations between τrrand τ and also provide the basis for a useful method for measuring τ.     

Transient electromagnetic fields of a vertical magnetic dipole on a two-layer earth

The transient fields of a vertical magnetic dipole on a two-layer earth model are expressed in analytical form using two different approaches. In the first, the fields in the time domain are obtained as the inverse Laplace transforms of derived full wave time-harmonic solutions, while in the second, the concept of natural frequencies of the stratified earth is utilized. Comparison with a previously obtained approximate solution reveals that the latter is the late time part of the present solution. Important features in the waveforms of the surface fields due to step and pulsed current excitations are demonstrated by a variety of numerical examples. These features provide diagnostic means of sensing the earth's stratification, overburden thickness, and the ratio of conductivities of the layers.