Sayeed Shafayet Chowdhury

Dy doped BiFeO3: A bulk ceramic with improved multiferroic properties compared to nano counterparts

Abstract The synthesis as well as structural, multiferroic and optical characterization of Dy doped BiFeO3 multiferroic ceramic are presented. Bulk polycrystalline Bi 0.9 Dy 0.1 FeO 3 sample is synthesized by solid state reaction, while their nano counterparts are prepared using ultrasonic probe sonication technique. Significant improvement of phase purity in the as synthesized samples is observed after the doping of Dy both in bulk Bi 0.9 Dy 0.1 FeO 3 sample and corresponding nanoparticles as evidenced from Rietveld refinement. Magnetization measurements using SQUID magnetometer exhibit enhanced magnetic properties for Dy doped bulk Bi 0.9 Dy 0.1 FeO 3 ceramic compared to their nanostructured counterparts as well as undoped BiFeO3. Within the applied field range, saturation polarization is observed for Bi 0.9 Dy 0.1 FeO 3 bulk ceramic only. As a result, intrinsic ferroelectric behavior is obtained just for this sample. Optical bandgap measurements reveal lower bandgap for Dy doped bulk Bi 0.9 Dy 0.1 FeO 3 ceramic compared to that of corresponding nanoparticles and undoped BiFeO3. The outcome of this investigation demonstrates the potential of Dy as a doping element in BiFeO3 that provides a bulk ceramic material with improved multiferroic and optical properties compared to those of corresponding nanoparticles which involve rigorous synthesis procedure.

Real-time non-intrusive eye-gaze tracking based wheelchair control for the physically challenged

Driving and control of wheelchair by hand poses a great impediment for a physically challenged person with limited physical ability but a real time eye-gaze tracking based control system can go a long way in easing such cases. A robust scheme of pupil movement detection based on Recursive Circular Hough Transform (RCHT) is proposed in this paper. Despite CHT being a common technique for pupil detection, the requirement of a pre-defined contrast sensitivity and radius range of the target circular object limits its use in real time applications where both sensitivity and radius of the pupil may vary widely. Moreover, in different gazing modes, eyes may not appear to be circular either. Again, edge sensitivity reduction and relaxation of circular object detection criterion causes CHT to detect multiple objects other than just pupil in a given contrast sensitivity. To eliminate such problems, an RCHT technique is proposed which is able to automatically tune the sensitivity and radius. Thus, a robust performance without the usage of computationally expensive classifiers can be obtained. Very low resolution off-the-shelf cell phone camera has been used to capture images, from where pupil location detection has been performed. Effects of various changing conditions such as pupil color, camera position, speed of eye movement etc. have been analyzed too. Results assert that this computationally light approach provides satisfactory accuracy on the basis of correctly following the actual instructed direction in test cases and thus, it is suitable for real-time precise direction control for people with working eyes but very constrained physical abilities.

Real-Time Robust Heart Rate Estimation From Wrist-Type PPG Signals Using Multiple Reference Adaptive Noise Cancellation

Heart rate (HR) monitoring using photoplethysmographic (PPG) signals recorded from wearers’ wrist greatly facilitates design of wearable devices and maximizes user experience. However, placing PPG sensors in wrist causes much stronger and complicated motion artifacts (MA) due to loose interface between sensors and skin. Therefore, developing robust HR estimation algorithms for wrist-type PPG signals has significant commercial values. In this paper, we propose a robust HR estimation algorithm for wrist-type PPG signals using multiple reference adaptive noise cancellation (ANC) technique—termed here as “MURAD.” The main challenge of using ANC for MA reduction is to devise a qualified reference noise signal (RNS) to the adaptive filter. We propose a novel solution by using four RNSs, namely, the three-axis accelerometer data and the difference signal between the two PPG signals. For each RNS, we get a different version of the cleaned PPG signal. Then, a set of probable HR values is estimated using all of the cleaned PPG signals, and then, the value that is closest to the estimated HR of the previous time window is chosen to be the HR estimate of the current window. Then, some peak verification techniques are employed to ensure accurate HR estimations. The proposed technique gives lower average absolute error compared to state-of-the art methods. So, MURAD method provides a promising solution to the challenge of HR monitoring using PPG in wearable devices during severe MA conditions.

A theoretical model for determination of optimum metal thickness in Kretschmann configuration based surface plasmon resonance biosensors

Surface plasmon resonance (SPR) is one of the most exciting surface-sensitive methods for bio-molecular interaction analysis (BIA) currently available to researchers. It features surface-sensitive response, label-free detection, and real-time measurement capability. The most important characterizing parameter for an SPR biosensor is its sensitivity. A sensor with higher sensitivity is desired for detecting even minute changes in the sensing layer refractive index. However, sensitivity of SPR sensors based on Kretschmann configuration depends on some crucial parameters, thickness of the metal film being one of them. Thus, determination and choice of optimum metal thickness for the specific sensing conditions is pivotal for enhanced performance and reduction of false alarm occurrence. Hence, in this paper a comprehensive analytical model is developed for the optimization of metal thickness of an SPR bio-sensor. This theory provides the direct relationship between the performance characteristic of the sensor, minimum reflectance (Rmin) to the design parameter metal thickness. The proposed analytical model is verified using finite-difference time-domain simulations which match with the theoretical results with negligible error.

Detection of DNA mutation, urinary diseases and blood diseases using surface plasmon resonance biosensors based on Kretschmann configuration

Surface plasmon resonance (SPR) is one of the most attractive recent methods for surface-sensitive bio-molecular interaction analysis (BIA) and detection of various phenomenon. Its key advantages include surface-sensitive response, label-free detection, and real-time measurement capability and ability to detect even minute changes. As a result, one of the priority directions in the SPR biosensor research has been the development of SPR based sensors for detection of specific biological and chemical analytes related to the application areas such as medical diagnostics, environmental monitoring, food safety and security. Specially, medical diagnostics has been perceived as one of the most significant field for applications of SPR biosensor technology. Therefore, SPR biosensors for detection of molecules related to medical diagnostics are currently being widely researched. Here, we present the analysis of detection of three potentially threatening health conditions namely early detection of DNA mutation and some urinary and blood diseases, based on SPR biosensors of Kretschmann configuration. Experimental values of refractive indices corresponding to various conditions have been used from literature and finite-difference time-domain simulations have been performed to obtain the angle at which minimum reflectance (Rmin) occurs in an SPR sensor using Kretschmann configuration. The detection plausibility of varying normal as well as diseased cases has been analyzed observing the shifts in the resonance dip angle.

Inversion of symmetric matrices using unsymmetrical fault analysis

Matrix inversion is a fundamental operation in matrix algebra which is widely used in many electrical engineering applications. Although there are many inversion algorithms prevalent, a new method based on unsymmetrical fault analysis is presented here. The proposed approach highlights a wonderful analogy between mathematics and electrical circuits. It focuses on finding inverse of an invertible symmetric matrix purely based on techniques developed for line to line fault analysis. First, the elements of the given matrix are used to form a bus admittance matrix. Then, a line-to-line fault is assumed to simulate a real-life scenario and power system fault analysis is used to calculate the corresponding fault current. From the thus obtained results, the inverse of the matrix is computed. Simulation is used to validate the results which demonstrate that the method can be used to perform matrix inversion of symmetric matrices using the developed concepts of power system fault analysis.

Dy doped BiFeO 3 : A multiferroic with bulk structural and ferroelectric properties comparable with nano counterparts

The structural and ferroelectric properties of Dy doped BiFeO3 multiferroic materials are reported. The bulk polycrystalline Bi0.9Dy0.1FeO3 samples were synthesized using solid state reaction technique and their nano counterparts were prepared using ultrasonic probe sonication. XRD patterns demonstrated significant improvement of phase purity due to Dy substitution both in bulk sample and corresponding nanoparticles. Again, FESEM imaging was carried out to analyze the surface morphology of bulk sample as well as to determine the size and distribution of the synthesized nanoparticles. Furthermore, leakage current density measurements were performed where, interestingly, we found comparable performance for Bi0.9Dy0.1FeO3 bulk and its corresponding nanoparticles. Moreover, the polarization versus electric field measurements showed higher remanent polarization and coercive field for nanoparticles compared to their bulk samples which might be associated with leaky behavior generated from oxygen related defects of the nanoparticles. However, saturation polarization within the applied field range was observed for Bi0.9Dy0.1FeO3 bulk only indicating inherent ferroelectric behavior. Overall, this investigation provides evidence of Bi0.9Dy0.1FeO3 multiferroic having enhanced structural purity and ferroelectric properties over undoped BiFeO3. In particular, it opens up the pathway of a material with equivalent bulk and nano leakage current performance which may be useful in many applications.