Md. Saifur Rahman

Negative Refraction with Superior Transmission in Graphene-Hexagonal Boron Nitride (hBN) Multilayer Hyper Crystal

In this article, we have theoretically investigated the performance of graphene-hexagonal Boron Nitride (hBN) multilayer structure (hyper crystal) to demonstrate all angle negative refraction along with superior transmission. hBN, one of the latest natural hyperbolic materials, can be a very strong contender to form a hyper crystal with graphene due to its excellence as a graphene-compatible substrate. Although bare hBN can exhibit negative refraction, the transmission is generally low due to its high reflectivity. Whereas due to graphene’s 2D nature and metallic characteristics in the frequency range where hBN behaves as a type-I hyperbolic material, we have found graphene-hBN hyper-crystals to exhibit all angle negative refraction with superior transmission. Interestingly, superior transmission from the whole structure can be fully controlled by the tunability of graphene without hampering the negative refraction originated mainly from hBN. We have also presented an effective medium description of the hyper crystal in the low-k limit and validated the proposed theory analytically and with full wave simulations. Along with the current extensive research on hybridization of graphene plasmon polaritons with (hyperbolic) hBN phonon polaritons, this work might have some substantial impact on this field of research and can be very useful in applications such as hyper-lensing.

A theoretical model of GSM network based vehicle tracking system

This paper presents a novel idea of vehicle tracking system based on the existing GSM cellular networks. A software based system is proposed that sends specialized request to the GSM cellular networks to call any particular vehicle ID. The vehicle ID is actually a particular SIM kept in a special kit inside the vehicle that is capable of receiving a phone call automatically. As soon as the call is established, the particular cell information is available to the BSC which is then passed to the software. Based on the information collected, the software will initiate a forced handover of the call to another suitable cell and then receive the information of that cell too. Upon completion of two consecutive forced handovers, i.e., receiving cell information of the vehicle ID from three different cells and sending them to the software, it will automatically disconnect the call. The software will analyze the cell info and extract three timing advances (TA) data along with the GPS locations of the individual cells. An algorithm has been developed for this system, which then calculates the exact location of the vehicle. The accuracy of the vehicle right at the moment of the call establishment is expected to be within a circle of 200 meters radius.

Control of reflection through epsilon near zero graphene based anisotropic metamaterial

In graphene dielectric multilayer structure, a very interesting phenomena such as epsilon near zero property rises naturally. However, this epsilon near zero property (along with the proper control of chemical potential and gate voltage) of graphene multi-layer stack has not been used so far to make novel photonic switches. In this article, we have shown theoretically that in graphene-dielectric stack, which acts as an anisotropic metamaterial, full control of reflection and so transmission of light at a specific wavelength or frequency can be controlled very simply by external gate voltage. This external voltage tunes the chemical potential and so the parallel permittivity of the anisotropic structure. Our theoretical prediction may pave the way to novel voltage control photonic logic switches, which may play as an intermediate solution before entering into all optical commercial switches (as current silicon and electron based CMOS technology is facing a dead end).

Segmentation of printed bangla characters using structural properties of Bangla script

Some difficulties arise in segmentation of Bangla characters because of their unique structural properties, such as, having connectors adjoining two characters and vowel modifiers modifying either the top portion or the bottom portion of a character. This paper presents some ways to overcome these problems by taking into account these unique properties and thereby increases the accuracy of character segmentation of printed Bangla scripts that leads to greater accuracy of optical character recognition applications.

Channel Behavior of Residential Power Line Cable for the Broadband PLC

This paper considers residential power line as communication channel for high speed power line communication (PLC). Power line is analysed according to transmission line theory. Four channel parameters: attenuation constant, phase constant, phase velocity, and group velocity are formulated as a function of characteristic impedance. The high frequency characteristics of these parameters are simulated for a practical residential power line cable.

Block Faded Channel Estimation for Multiuser STBC-OFDM Systems

Accurate channel estimation is necessary to gain the advantage of space time coding for decoding purposes. Most of the previous work on orthogonal frequency division multiplexed (OFDM) channel estimation focused on single user systems. Hence, they are inappropriate in the multiuser communication systems. In this paper, we proposed a novel multiuser channel estimation technique based on simple blocked pilot grid for space time block coded (STBC)-OFDM systems. We simulated the proposed scheme for slowly faded quasi-static channel. LS and MMSE estimator performance for different number of users are also analyzed

Wavelet denoising spproach using fourth order moment to remove wireless random noise

Wavelet transform is used in signal processing to represent a statistical random signal in to various frequency components. The transform converts the signal into approximation coefficient and detail coefficients; the mean of each coefficient for a noiseless signal is ideally zero but the mean of the coefficients for a noisy signal is shifted from zero. The noise of a wireless channel can be reduced by using filter, equalizer, and antennal diversity techniques. The design complexity of filter and equalizer is increased with the data rate. Antenna diversity technique requires a comprehensive knowledge of channel property. In communication system of 3G, 4G and beyond, noise reduction is one of the main factors to cater for the high data rate. The thresholding of wavelet transform reduces the noise and interference at an acceptable level. Various denoising techniques have been proposed in recent work. The denoising approach using fourth order moments provides better signal reconstruction through a noisy channl among them. Fourth order moment-based denoising technique has been modified in this paper to obtain better result through a multipath fading channel. The simulation results show that our modified technique provides about 21% improvement of BER performance, compared to those in the literature.

Development of an automatic vehicle license plate detection and recognition system for Bangladesh

This paper describes the technique of extracting vehicle license-plate and interpretation of the registration code from a captured image in real-time. The developed algorithm is divided into three stages: extraction of vehicle license plate from captured image, segmentation of license plate components and recognition of the license plate characters for interpretation of vehicle registration code. A control algorithm is also developed to choose between the recognition processes and reconstruct the registration code from recognized characters. Most of the processes are implemented using mostly logical operations to achieve lower execution time.

Quasi-Static Channel Estimation for Multiuser STBC-OFDM Systems

This paper proposes multiuser channel estimation techniques for space time block coded-orthogonal frequency division multiplexing (STBC-OFDM) systems based on simple blocked pilot grid. The estimation of multiuser channels is based on least square (LS) and minimum mean square estimation (MMSE) schemes. Simulation results, for a slowly faded quasi-static channel, reveal that the estimated characteristics closely agree with the actual channel characteristics. Comparison of LS and MMSE performance for various number of users is performed and different Doppler fading effects on MMSE performance are also presented.

Tunable Fabry Perot filter using all-dielectric multilayer anisotropic metamaterial in the mid-infrared frequency range

In this article, we have theoretically proposed and numerically analysed a resonant wavelength tunable Fabry Perot (FP) filter without changing the physical length of the cavity in the mid-infrared range. The proposed FP filter consists of a multilayer cavity, which is constructed by alternately repeating two different sub-wavelength dielectric or semiconductor materials. Such a multilayer structure can behave as an anisotropic metamaterial. By varying the fill factor of the metamaerial, the effective refractive index of the cavity can be easily tuned. As the resonant wavelength of such a filter strongly depends on the cavity refractive index, the resonant wavelength of the filter can be easily tuned between a wide wavelength range of approximately 400nm by changing the fill factor. Distributed Bragg reflectors (DBRs) have been used as the high reflectivity mirrors. Both the DBRs and the cavity can be constructed by using only two materials, such as Silicon (Si) and SiO2. This device may find substantial applications in the fields of spectroscopy, color filtering, sensing etc.