Md. Gaffar

Modeling of threshold voltage of a quadruple gate transistor

In this paper, a three dimensional analytical solution of electrostatic potential is presented for undoped (or lightly doped) quadruple gate MOSFET by solving 3-D Poissons equation. It is shown that the threshold voltage predicted by the analytical solution is in close agreement with TCAD 3-D numerical simulation results. For numerical simulation, self-consistent Schrodinger-Poisson equations, calibrated by 2D non equilibrium green function simulation, are used. This analytical model not only provides useful physics insight of effects of gate length and body width on the threshold voltage, but also serves as a basis for compact modeling of quadruple gate MOSFETs.

Modeling the illumination function of a cassegrain reflector for a corrugated horn feed and calculation of the far field pattern

A model of the illumination function of cassegrain reflector for a corrugated horn feed is presented here. A conical corrugated feed horn designed for a Ku band cassegrain reflector is simulated. The simulation data is compared to the illumination function. Comparison between the developed illumination function and the widely used quadratic on a pedestal function is also presented. Finally, the developed illumination function is used to calculate the radiation pattern of the cassegrain reflector by evaluating the aperture field integration.

Analysis of a conical corrugated horn operating in the K-band with low cross-polarization and high aperture efficiency, and observing its radiation patterns

In this paper, a simulation based design and analysis of a conical corrugated horn is performed. The design concentrated on reduction of cross-polarization. Optimizing the parameters for operation in a frequency band rather than a single frequency required multiple simulations and noting the effects of parameter variations. The optimized design along with the simulation results are presented here. The design can be further improved by making the corrugation length variable which could not be done here due to software limitations. Also a tapered feed can be attached to the horn to enhance its performance. The work can be extended by building a practical working model of the horn and observing its performance.

Optimization and analysis of a Ka band Pickett Potter horn antenna with low cross polarization

In this paper, a Pickett Potter horn antenna is designed and analyzed for Ka band operation. The dimensions of horn are optimized so that the cross polarization level is minimized for the operating frequency range. The design and optimization is done based on theoretical analysis of dual mode horn antennas and computer simulation. The copolarization and the cross polarization radiation pattern of the designed horn are analyzed at 32 GHz. The S11 parameter of the horn antenna for operating frequency range is obtained from simulation. Finally, maximum cross polarization level of the designed horn for Ka band frequencies is analyzed using theoretical analysis and simulation.

Quantum electrodynamic model of carbon nanotube photovoltaic device to assess its photo absorption

Quantum electrodynamic model is proposed for a recently reported efficient single-wall carbon nanotube (SWCNT) photovoltaic device. In this model, nanotube is presented to the simulator through a set of parameters that gives quantum mechanical description of a semiconducting nanotube, as used in the device. Electromagnetic simulation of this device is also performed using ray tracing method and FDTD method. An incident light beam of 600 THz with linear polarization has been used for illumination. Silvacos Atlas device simulator is used to simulate the proposed quantum model and also to perform electromagnetic simulation. Field intensity inside the device and its I-V characteristics are found from simulated results, which reflect photovoltaic effect of the device.

Approximate Closed-Form Expression of the Electric Field of a Conical Horn Antenna

In this paper, an approximate closed-form expression of the electric field of a conical horn with linear flare is formulated. Copolarization and cross polarization component of the electric field are calculated from the spherical field components using Ludwigs third definition of copolarization and cross polarization. The calculated field expression is found to be in close agreement with experimental results found in literature. The radiation characteristics of the conical horn are analyzed using the derived field expressions.

Sensitivity analysis of a circularly polarized U-slot microstrip antenna

In this paper, sensitivity models for centre frequency and maximum radiated power of a rectangular microstrip antenna at ϕ = 0 plane using Effective Length Theory have been developed. A wide operating bandwidth for a single-layer coaxially fed microstrip antenna is obtained by cutting a U shaped slot on the metal patch. The sensitivity of perturbation of different truncated slot and feed position for a microstrip antenna is a novel concept. An approximate sensitivity model is derived here using perturbation and variational method and confirmed by modified Haneishi model and hybrid FEM/MoM solver. The proposed sensitivity models provide better approximations for calculating shift of centre frequency and maximum radiated power of the microstrip antenna.

Design of an X band aperture matched horn antenna by optimization of back-lobe and cross-polarization level

In this paper, an aperture matched horn antenna is designed for operation in the microwave X band region. A conical horn is designed first, and the effect of additional aperture matching structure is studied to find the optimum dimension of the structure. The study is performed through computer simulation by Finite Element Method. Finally, the performance of the designed horn antenna for band operation is simulated. The obtained structure through simulation provides optimum performance in terms of backlobe level and cross polarization level.

Mechanical feasibility analysis of process optimized silicon microneedle for biomedical applications

In our previous work, we proposed a process optimized hollow silicon (Si) microneedle structure on a silicon chip, which had the highest aspect ratio (AR) reported so far. The 150 micrometer (µm) tall optimized microneedle structure with an AR of about 30∶1 was fabricated by reactive ion etch or RIE process on a p-type 500µm thick Si substrate for drug delivery applications. In this paper we have investigated mechanical properties of the process optimized hollow Si microneedle. More specifically, bending and buckling forces, Von Mises stress, tangential shear force, and effects of skin and/or tissue penetration pressure on the optimized microneedle have been analyzed by finite element method. Three dimensional solid stress and strain curves for the optimized structure have been reported. Both analytical and simulation results show that buckling force has the greatest influence on mechanical stability and that the force with the least mechanical impact is tangential shear force. The detailed analysis indicates that the optimized structure would be compatible with modern biomedical microsystems.

Modeling VHF air-to-ground multipath propagation channel and analyzing channel characteristics and BER performance

In this paper, a VHF air-to-ground multipath propagation channel model is proposed and channel characteristics and BER performance are analyzed. A tapped-delay line filter model with time-varying coefficients is used to model the channel. The taps represent signals with delay corresponding to their relative propagation time. Each delayed signal is modulated in amplitude and phase by independent baseband random functions of time that produces Rayleigh fading. Doppler frequency shift is also incorporated in the channel model. Channel characteristics are analyzed in terms of power delay profile, Doppler frequency shift and burst error occurrence probability. Finally, BER performance of the channel is analyzed using computer simulation and effect of interleaving and error correcting code on the performance is observed.