Error analysis of image representations for sources near to a dissipative earth

Various image representations for sources above a dissipative earth are introduced. A criterion for assessing their accuracy is given. Some of these image representations comprise purely discrete images, a purely continuous image or a mixture of both types. It is shown that the error in any representation is a function of the height of the field point from the earth's surface. A mixture of a discrete image and a simple continuous image can lead to a negligibly small error for field calculations over a wide range of the height of the field point. This means that the image theory can offer simplicity and accuracy in many application such as geophysical prospecting of the earth.     

Transient response of an infinite cylindrical antenna in a dissipative medium

The transient solution of an infinite cylindrical antenna in a dissipative medium caused by an impulse excitation at a delta gap is obtained via an exact solution in the form of definite integrals and a simple asymptotic formula. This formula is used to obtain an integral for calculating the antenna current caused by a double exponential input voltage at the gap; furthermore, the resulting integral reduces to Sunde's classic result under the diffusion limit. These results are applied to the transient response of a buried wire subject to an electromagnetic pulse (EMP) or nearby lightning incident wave.     

Transient magnetic fields produced by a step-function-excited loop buried in the earth

Using a previously developed formalism, we obtain explicit results for the field waveforms observed on the Earth's surface for a small horizontal loop buried in a conducting halfspace. It is shown that the shape of the waveform is diagnostic of the relative location of the buried source. The results have possible application in mine rescue operations.     

New modal representation of electromagnetic waves supported by horizontal wire above dissipative earth

A new discrete mode that satisfies the radiation condition is found for the problem of a horizontal wire above an air-earth interface. It can be shown to be an important part of the total current distribution on the wire. It exhibits the nature of a fast wave and has a much smaller attenuation constant than the quasi-TEM mode.     

Image theory of a quasistatic magnetic dipole over a dissipative half-space

An analytical demonstration of image theory is given for the case where a vertical magnetic dipole is located over a dissipative half-space. It is shown that the image concept is valid, provided that distances are large with a skin depth in the ground yet small compared with the wavelength.     

Transient image theory for 2-D and 3-D conducting wedge problems

In the present paper, two- and three-dimensional transient scattering from a perfectly conducting wedge is studied. The exciting sources analyzed are an infinite impulsive line current parallel to edge of the conductor and an arbitrarily oriented electric dipole. The analysis presented is based on the time-harmonic image solution found for the scattered field. The frequency-domain image current corresponding to the field contribution from the wedge is an exact function expressed in terms of simple trigonometric functions. It is dependent only on the coordinates and the amplitude of the source, but it is independent of the observation point. It is shown that the transient scattering can be interpreted as arising from an image source by generalizing the time domain Green's function to complex source points     

Transient response of a transmission line excited by anelectromagnetic pulse

The transient response of a lossless transmission line of finite length excited externally by an electromagnetic wave of an arbitrary waveform is studied. By using the Laplace transformation, a solution of the transient current is obtained as a series of analytical functions. Inspection of the solution leads to the conclusion that the response currents at terminals of the line can be equivalently expressed by the components induced at both terminals, and, in addition, the multireflected wave when the line is mismatched. Furthermore, a new equivalent circuit for the coupling phenomenon is discussed     

Transient response of a rotor-AMBs system connected by a flexible mechanical coupling

In this paper, the effect of angular misalignment on the transient dynamics of a rotor-Active Magnetic Bearings (AMBs) system was examined with numerical analysis. A spatial model of a misaligned rotor mounted in two identical AMBs is setup to account angular misalignment with a flexible coupling having torsional and lateral flexibility. The driving rotor was powered by an electric motor in transient regime. Three models of AMBs were used with four; six and eight magnets. They were powered by bias and control current. The AMBs dynamics support parameters were modeled by stiffness and damping matrices. These were computed through an electromagnetic theory and derivation of the magnetic forces. The general equations of motion of the driven rotor were derived and solved using the Newmark time integration method. Simulation results were carried out to determine the frequency and transient responses in term of misalignment magnitude. Dynamic responses come to confirm a significant influence of the transient regime on the dynamic behavior of misaligned rotor. Simulated results also reveal that vibrations induced by angular misalignment were more important in the case of AMBs with four magnets. Spectral components of the system response were investigated, in sort to present diagnostic information about the signature of this kind of fault in transient regime.     

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.     

Transient response of a microwave beam amplifier

A model of a beam amplifier consisting of a chain of lightly-coupled cavities has been studied for initial time response with the aid of a computer. The beam flows through the center-holes of 20 cavities stacked together and coupled so the pass band width would be 5 per cent in an infinitely long chain. The intermediate cavities are externally loaded for stability. The electronic transit angle for each cavity is 3π/4,omega_{q}/omega = 0.1, and the beam-circuit coupling coefficient CBis small. Computations have been made of the steady-state input resistance, gain and bandwidth around the 3π/4 "cold" circuit phase shift frequency, as well as of the transient response for t ≥ 0. Results show 1) at the 3π/4 frequency the voltage in the output cavity overshoots the steady-state value, and reaches its first peak at a time almost exactly equal to the amplifier length divided by the group velocity; 2) at a frequency nearer to cutoff, for which the group velocity is smaller, the voltage does not overshoot, but approaches the steady-state value asymptotically, such that at a time equal to the amplifier length divided by the group velocity the voltage has about 80 per cent of its steady-state value.     

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 class of nonlinear systems

An algorithm is given to be used in conjunction with the parameter-plane method and the describing-function method for rapid calculation of transient oscillations in the design of a class of nonlinear systems.     

Transient response of a static VAr shunt compensator

A typical static VAr shunt compensator has been analyzed so that the step response and steady-state errors can be identified. The results show that the steady-state error is dependent upon the error in the measurement of the currents' phase alone. They also show that an unstable condition can occur, though it should rarely arise in practice. All the theory was verified on a low power (240 V, 3 A) system     

Transient response of a dipole over a circular ground screen

The time-domain response of a vertical electric dipole located over a circular ground screen is considered. The relevant time-harmonic solution is used as a starting point. By making a number of approximations a very simple formula is obtained for the transient response of the far field when the dipole current moment is a ramp function of time. It is shown that for early times, the pattern response appears as if the ground screen were of infinite extent, while at very long times, the response approaches that expected for a homogeneous flat ground.     

Image theory for electric dipoles above a conducting anisotropic earth

New image representations for vertical electric dipoles (VED) above an imperfectly conducting and axially anisotropic earth are developed. These include multidiscrete images at different depths below the air-earth interface and multipole image sources. It is shown that, in contrast with the available image representations in the literature, the developed ones predict the correct behavior of the fields in the far zone along the earth's surface. Extension to a layered earth's model is made. The theory is also extended to the horizontal electric dipole with similar conclusions to the case of the vertical dipole.     

Multimodal medical image fusion by cloud model theory

Image fusion can provide more extensive information since it combines two or more different images. Cloud model is a recently proposed theory in artificial intelligence and has the advantage of taking the randomness and fuzziness into account. In this paper, we introduce a novel multimodal medical image fusion method by cloud model theory. The proposed method fits the histograms of input images using the high-order spline function firstly and then divides intervals in line with the valley point of the fitted curve. On this basis, cloud models are generated adaptively through the reverse cloud generator. Finally, cloud reasoning rules are designed to achieve the fused image. Experimental results demonstrate that the fused images by proposed method show more image details and lesion regions than existing methods. The objective image quality assessment metrics on the fused images also show the superiority of the proposed method.     

Transient response of a peak voltage detector for sinusoidalsignals

A fast peak detector for constant frequency sinusoidal signals is proposed. This detector is based on the concept of the orthogonal function set. The theoretical response time of this detector is less than one-fourth of a cycle. When this detector is used, the transient response of the output voltage is different under different inception angles. The mathematical equations to describe transient phenomena are derived and simulated. Because its transient response performance is superior to the conventional sinusoidal amplitude detector used in an analog controller, it can improve the transient response performance of the controller. For practical applications, the effects of harmonics and frequency variation are also discussed, simulated, and tested     

Transient response of ARROW VCSELs

The transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is analyzed. It is found that under current modulation, the radiation loss of the transverse-leaky mode decreases during the state of the lasers but increases during the state. Numerical analysis shows that this variation in radiation loss is due to the carrier-induced refractive-index depression that arises from spatial-hole-burning of carrier concentration. It is noted that the increment in radiation loss during the state can be used to prevent net modal gain of the transverse-leaky mode from reacquiring threshold after turn-off. Hence, a new method to design ARROW, based on the variation in radiation loss, is proposed to eliminate the excitation of secondary pulsation in VCSELs. The influence of thermal lensing effects on the excitation of secondary pulsation during the state of the lasers is also investigated.     

Transient response of MS-DFB amplifier-filters

Time and spectral responses of a tunable three-contact distributed feedback (DFB) amplifier-filter obtained by feeding 50-ps optical pulses show the generation of a slow exponential falling tail (≈ 200 ps) in the output signal when the input pulses are spectrally narrowed. This phenomenon should limit the transfer bit rate of wavelength-filtered signals     

Transient response of vidicon photoconductors

An expression for the rise and decay times of vidicon photocurrents as a function of incident illumination is derived for a certain class of vidicon photoconductors. The approach taken is semiempirical in that certain parameters in the derived expression are obtained directly from vidicon manufacturer's data sheets. Regults compare well with the manufacturer's published results.