Coupling Maxwell's Equations to Full Band Particle-Based Simulators

In this work we utilize the Finite-Difference Time Domain (FDTD) Method coupled to a full band, particle-based simulator to solve for the total Lorentz force. Replacing a traditional Poisson solver with a more robust electromagnetics (EM) solver allows us to accurately account for radiated losses and provides a useful tool for investigating the near and far-field radiation patterns inherent in modern devices.     

An efficient electromagnetic-physics-based numerical technique for modeling and optimization of high-frequency multifinger transistors

We present a fast wavelet-based time-domain modeling technique to study the effect of electromagnetic (EM)-wave propagation on the performance of high-power and high-frequency multifinger transistors. The proposed approach solves the active device model that combines the transport physics, and Maxwell's equations on nonuniform self-adaptive grids, obtained by applying wavelet transforms followed by hard thresholding. This allows forming fine and coarse grids in the locations where variable solutions change rapidly and slowly, respectively. A CPU time reduction of 75% is achieved compared to a uniform-grid case, while maintaining the same degree of accuracy. After validation, the potential of the developed technique is demonstrated by EM-physical modeling of multifinger transistors. Different numerical examples are presented, showing that accurate modeling of high-frequency devices should incorporate the effect of EM-wave propagation and electron-wave interactions within and around the device. Moreover, high-frequency advantages of multifinger transistors over single-finger transistors are underlined through numerical examples. To our knowledge, this is the first time in the literature a fully numerical EM-physics-based simulator for accurate modeling of high-frequency multifinger transistors is introduced and implemented.     

Effect of number of spectral terms on convergence of spectral-domain calculations of E-plane structures

The effect of the number of spectral terms on the accuracy of the spectral-domain analysis of E-plane circuits is studied. The ability of the solution to reconstruct the gap field is related to the error in propagation constant and characteristic impedance.     

Electromagnetic and semiconductor device simulation usinginterpolating wavelets

A MESFET and a two-dimensional cavity enclosing a cylinder are simulated using a nonuniform mesh generated by an interpolating wavelet scheme. A self-adaptive mesh is implemented and controlled by the wavelet coefficient threshold. A fine mesh can therefore be used in domains where the unknown quantities are varying rapidly and a coarse mesh can be used where the unknowns are varying slowly. It is shown that good accuracy can be achieved while compressing the number of unknowns by 50% to 80% during the whole simulation. In the case of the MESFET, the I-V characteristics are obtained and the accuracy is compared with the basic finite difference scheme. A reduction of 83% in the number of discretization points at steady state is obtained with 3% error on the drain current. The performance of the scheme is investigated using different values of threshold and two types of interpolating wavelet, namely, the second-order and fourth-order wavelets. Due to the specific problem analyzed, a tradeoff appears between good compression, accuracy, and order of the wavelet. This represents the ongoing effort toward a numerical technique that uses wavelets to solve both Maxwell's equations and the semiconductor equations. Such a method is of great interest to deal with the multiscale problem that is the full-wave simulation of active microwave circuits     

Time-domain optical response of an electrooptic modulator usingFDTD

A time-domain analysis of an LiNbO₃ electrooptic modulator using the finite-difference time-domain (FDTD) technique is performed. This allows for the calculation of optical modulation and the time-domain optical response of an electrooptic modulator. The electromagnetic fields computed by FDTD are coupled to standard electrooptic relations that characterize electrooptic interactions inside the embedded Ti diffused LiNbO₃ optical waveguides. The electric field-dependent change in the index of refraction inside these optical waveguides and resulting minute phase shifts imparted to optical signals propagating along the device are determined in time, allowing for the simulation of optical intensity modulation. This novel approach to LiNbO₃ electrooptic modulators using a coupled FDTD technique allows for previously unattainable investigations into device operating bandwidth and data transmission speed     

Nonlinear analysis of microwave superconductor devices usingfull-wave electromagnetic model

This paper presents a full electromagnetic wave analysis for modeling the nonlinearity in high temperature superconductor (HTS) microwave and millimeter-wave devices. The HTS nonlinear model is based on the Ginzburg-Landau theory. The electromagnetic fields associated with the currents on the superconducting structure are obtained using a three-dimensional full wave solution of Maxwell's equations. A three-dimensional finite-difference time-domain algorithm simultaneously solves the resulting equations. The entire solution is performed in time domain, which is a must for this type of nonlinearity analysis. The macroscopic parameters of the HTS, the super fluid penetration depth and the normal fluid conductivity, are calculated as functions of the applied magnetic field. The nonlinear propagation characteristics for HTS transmission line, including the effective dielectric constant and the attenuation constant, are calculated, As the power on the transmission line increases, the phase velocity decreases and the line losses increase. The nonlinearity effects on the current distributions inside the HTS, the electromagnetic field distributions, and the frequency spectrum are also analyzed     

Active antennas incorporating tunnel diodes-large signal modelapproach

In this letter, a comprehensive dc and RF model of heterostructure interband tunnel diodes (HITDs) is extracted. Active antennas incorporating tunnel diodes are analyzed in the time domain using this tunnel diode model. The simulated and measured results are in good agreement in terms of oscillation frequencies of the active antennas. Phase noise of -114.67 dBc/Hz @1.0 MHz offset is achieved for injection-locked active antennas. The simulated injection locking range of a Ka band active antenna array is investigated     

Mach-Zehnder optical system as a sensitive measuring instrument

A laser interferometric measurement technique that uses a Mach-Zehnder interferometer is developed. This technique permits studies of the physical processes that involve a change in the refractive index with temperature to a high degree of accuracy. A theoretical derivation has been formulated to permit computation of the refractive index of transparent materials. The technique is particularly useful in studying slight changes in refractive index of various gases, solutions over a considerable region, and flow patterns in wind tunnels.     

Greetings from the 2010 President [Presidents Column]

It is a great honor for me to serve as the 2010 MTT-S president! It is a nice surprise too. As I sat down to write this column, I could not help but to reminisce about my first involvement with the MTT Society.     

Electromagnetic wave effects on microwave transistors using afull-wave time-domain model

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies