M. Rezwan Khan

Transmission line analogy of resonance tunneling phenomena: The generalized impedance concept

This paper presents a simple yet accurate method for solving the Schrodinger equation to calculate the quantum mechanical transmission probability across arbitrary potential barriers. It is based on the concept of wave impedance analogous to transmission line theory. The quantum mechanical transmission probability in a resonant tunneling device can be easily calculated using this method.

Calculation of the traversal time in resonant tunneling devices

Transmission line techniques are used to calculate the traversal time of electrons in resonant tunneling structures. It is suggested that the real part of the quantum‐mechanical wave impedance Re[(2ℏ/m*)ψ’/ψ], at resonance, can be used to calculate the electron traversal time. Furthermore, it is shown that for symmetric structures the lifetime and evolution time of electrons are the same. The sum of the lifetime and the evolution time equals the electron traversal time. Traversal time variations for the asymmetric well are discussed.

Efficient design of integrated antennas on Si for on-chip wireless interconnects in multi-layer metal process

In this study it has been shown that the transmission gain of an integrated dipole antenna on a Si chip used for an on-chip wireless interconnect is drastically reduced in a multi-layer metal interconnect scheme when a second metal layer is placed above the antenna at the usual interlayer metal distance. The best way to preserve high gain of the integrated antenna in such a multi-layer metal process is to design an antenna with excitation vertically through the Si substrate. In the presence of the upper metal layers, the vertically excited field mode propagating through the Si substrate does not cause any significant reduction in the power transmission of the antenna. Simulations of the structures have been carried out using the ANSOFT high frequency structure simulation (HFSS) program employing the three dimensional finite element method. A simple analytical model has also been developed, and the results are presented for comparison.

Energy cost calculations for a solar PV Home System

Energy costing for a Solar Home System has been presented here considering the main cost components. It has been identified that the cost of solar PV panels, bank interest rate, cost of battery and its longevity plays the most important role in determining the energy cost. Average solar insolation is also taken into consideration and the results show that contribution of the storage battery towards the total cost of energy is significantly higher than that of the solar PV panel.

Reducing signal-bias from MAD estimated noise level for DCT speech enhancement

This paper presents an improved thresholding technique for speech enhancement in the discrete cosine transform (DCT) domain. The signal-bias-compensated noise level is used as the threshold parameter. The probability of speech presence in the noisy DCT coefficients at the finest level is exploited for compensating the signal-bias. The performance of the proposed algorithm is evaluated on speech corrupted by background Gaussian white noise and real noise recorded inside a moving car. A relative comparison in the enhancement of the degraded speech is performed using the uncompensated and compensated noise levels for the same denoising filter. Both objective and subjective evaluations are presented to show improved performance for the case when the compensated noise level, estimated by the proposed algorithm, is used rather than the uncompensated noise level obtained using the median absolute deviation method. Simulation results are also given to show the superiority of the proposed method over a recently reported enhancement algorithm.

A Liquid Water Model That Explains the Variation of Surface Tension of Water with Temperaure

A model is presented that explains the variation of surface tension of liquid water with temperature. The presence of non H-bonding H (NHB H) atoms (defining surface of assumed clusters) together with H-bonding atoms, is considered in this treatment. A good agreement between the experimental and computed values suggests the validity of this model. The change in the number of NHB H atoms and density account for the variation of surface tension with temperature. Previously, the same model was applied to explain the anomalous variation of density of liquid water with temperature [A. Khan et.al.: Chem. Phys. Lett. 266 (1997) 473].

DC nanogrids: A low cost PV based solution for livelihood enhancement for rural Bangladesh

A concept paper, along with cost estimations, is presented proposing the development of very small sized solar PV grids, which we have termed nano-grids. These grids allow the incorporation of developmental activities such as irrigation, along with household usage of electricity. It is argued that the developmental activity should be chosen in such a way that it matches with the seasonal variation in insolation and load demand to keep the energy cost to a minimum.

Optimized Solar Home System package design: Bangladesh perspective

Bangladesh is experiencing a great success in Solar Home System rural electrification. Recently a study of a technical audit of SHS project shows non-uniformity in Solar Home System (SHS) packages in Bangladesh. A detail analysis of factors influencing the reliable design of SHS packages has been analyzed and finally optimized SHS package has been proposed for available PV system components considering the geographical, climate and socio-economic conditions in Bangladesh. Direct measured radiation data, the sun earth geometry, the variation of the solar insolation due to rotational and revolution of the earth around the sun has also considered in designing the standard package. The performance of the local SHS components has also considered in designing the proposed package.

Determination of electron trap distribution in the gate-oxide region of the deep submicron metal-oxide-semiconductor structure from direct tunneling gate current

The trap distribution inside the oxide layer of a metal–oxide–semiconductor device is studied via the direct tunneling gate current. Effects of traps are incorporated in the Schrodinger’s equation using an imaginary potential term. Different spatial distributions of traps have been considered to obtain a best fit between the simulated and the experimentally measured direct tunneling gate currents. Comparing our simulated current with experimental data, we have determined that the distribution of traps introduced during fabrication can be represented by a Gaussian function with its peak at the gate–electrode/oxide interface. This distribution is found to be independent of the gate–oxide thickness. Our results show that electric-field-induced traps, generated during tunneling, are proportional to the carrier density within the oxide layer and also to the traps introduced during fabrication.

A novel dehumidification technique using electric field

A completely new concept of dehumidification is presented. The polar nature of the electronic bond structure between oxygen and hydrogen atoms in a water molecule is utilized to attract them using an electric field. It is possible to single out and remove the water molecules from the air inside a room to make the room dehumidified. A theoretical formulation is developed and a simple experiment was performed to validate the theory. Unlike the conventional dehumidification process, this process does not involve any condensation of the moisture and hence requires a very small amount of power. The technique can also be very useful for air-conditioning as well.