Omar Usman Khan

Fast Magnetic Field Modeling for Shielding Systems

In this paper, a new iterative algorithm for the analysis of properties of magnetic shielding systems is proposed. Since such shielding systems for low frequency applications are composed of thin-walled shells with magnetic materials of high permeability, the thin shell approximation is adopted and a numerical integral formulation of the ensuing magnetostatic problem is obtained in the form of a convolution equation. This algebraic system is eventually solved iteratively by exploiting the convolution properties of the discrete Fourier transform. The convergence properties of the procedure are analyzed and tested on two case studies where isotropic and anisotropic magnetic shields are used.

Analysis of Fast Parallel Sorting Algorithms for GPU Architectures

Sorting algorithms have been studied extensively since past three decades. Their uses are found in many applications including real-time systems, operating systems, and discrete event simulations. In most cases, the efficiency of an application itself depends on usage of a sorting algorithm. Lately, the usage of graphic cards for general purpose computing has again revisited sorting algorithms. In this paper we extended our previous work regarding parallel sorting algorithms on GPU, and are presenting an analysis of parallel and sequential bitonic, odd-even and rank-sort algorithms on different GPU and CPU architectures. Their performance for various queue sizes is measured with respect to sorting time and rate and also the speed up of bitonic sort over odd-even sorting algorithms is shown on different GPUs and CPU. The algorithms have been written to exploit task parallelism model as available on multi-core GPUs using the OpenCL specification. Our findings report minimum of 19x speed-up of bitonic sort against odd-even sorting technique for small queue sizes on CPU and maximum of 2300x speed-up for very large queue sizes on Nvidia Quadro 6000 GPU architecture.

An Efficient Adaptive Window Size Selection Method for Improving Spectrogram Visualization

Short Time Fourier Transform (STFT) is an important technique for the time-frequency analysis of a time varying signal. The basic approach behind it involves the application of a Fast Fourier Transform (FFT) to a signal multiplied with an appropriate window function with fixed resolution. The selection of an appropriate window size is difficult when no background information about the input signal is known. In this paper, a novel empirical model is proposed that adaptively adjusts the window size for a narrow band-signal using spectrum sensing technique. For wide-band signals, where a fixed time-frequency resolution is undesirable, the approach adapts the constant Q transform (CQT). Unlike the STFT, the CQT provides a varying time-frequency resolution. This results in a high spectral resolution at low frequencies and high temporal resolution at high frequencies. In this paper, a simple but effective switching framework is provided between both STFT and CQT. The proposed method also allows for the dynamic construction of a filter bank according to user-defined parameters. This helps in reducing redundant entries in the filter bank. Results obtained from the proposed method not only improve the spectrogram visualization but also reduce the computation cost and achieves 87.71% of the appropriate window length selection.

Unsteady Squeezing Flow of Casson Fluid with Magnetohydrodynamic Effect and Passing through Porous Medium

An unsteady squeezing flow of Casson fluid having magnetohydrodynamic (MHD) effect and passing through porous medium channel is modeled and investigated. Similarity transformations are used to convert the partial differential equations (PDEs) of non-Newtonian fluid to a highly nonlinear fourth-order ordinary differential equation (ODE). The obtained boundary value problem is solved analytically by Homotopy Perturbation Method (HPM) and numerically by explicit Runge-Kutta method of order 4. For validity purpose, we compare the analytical and numerical results which show excellent agreement. Furthermore, comprehensive graphical analysis has been made to investigate the effects of various fluid parameters on the velocity profile. Analysis shows that positive and negative squeeze number have opposite effect on the velocity profile. It is also observed that Casson parameter shows opposite effect on the velocity profile in case of positive and negative squeeze number . MHD parameter and permeability constant have similar effects on the velocity profile in case of positive and negative squeeze numbers. It is also seen that, in case of positive squeeze number, similar velocity profiles have been obtained for , and . Besides this, analysis of skin friction coefficient has also been presented. It is observed that squeeze number, MHD parameter, and permeability parameter have direct relationship while Casson parameter has inverse relationship with skin friction coefficient.

A Mutual Demagnetizing Tensor for N-Body Magnetic Field Modeling

We introduce a mutual demagnetizing tensor for calculating the demagnetizing field in multiple magnetic bodies. Algorithms for magnetic simulations dealing with interactive n-bodies usually treat the simulation domain as a single magnetized body with embedded nonmagnetic regions. Doing so minimizes the number of variables used in the field calculations but the computation time and storage requirements can become very large. Our approach reduces memory consumption and shows a gain in performance for cases involving field calculation in patterned films. We have verified our results by performing simulation of dots in periodic grids and report a speed-up ranging between 3 × and 10 ×.

Computation of Two-Port Parameters in Magnonic Devices Through Circuit-Field Coupling

This paper presents a model for the computation of two-port parameters from the configuration of a typical Magnonic device involving two coplanar waveguides. A Permalloy thin film is saturated using an appropriate dc field. The first waveguide then performs the function of excitation of spin waves by superposition of an RF field. The second waveguide detects the excited wave vector in Damon–Eshbach mode at resonance frequency. The model is solved using the generalized mean residual method for a linearized approximation of the Landau–Lifshitz–Gilbert equation coupled with Maxwell equations. Complex impedance matrices from the two-port network are extracted for both uniformly saturated and non-uniform initial ground states. Findings report low absorption potential and shift in resonance frequency for highly non-uniform ground states. Validation of the model for uniformly saturated ground states is performed against experimental and semi-analytical findings, showing good agreement.

Computation of Demagnetization Tensors by Utilizing Fourier Properties

We describe a method for the computation of the discrete demagnetization tensor on regular cuboid grids. Assuming homogeneously magnetized cells, the tensor components can be calculated exactly by known analytical formulas. These integral-based expressions can be expensive due to their nested nature and difficult to code. The novelty of this paper is that parts of the tensor computation are moved to Fourier space, which simplifies the implementation. The main idea is that some nested sums, required for the computation of the tensor in real space, are replaced by simple multiplications with real factors in Fourier space. For regular grids, the demagnetization field is usually computed in Fourier space by application of the convolution theorem. Thus, computing the tensor in Fourier space in the first place does not introduce any drawbacks.

Improved Analysis for Squeezing of Newtonian Material between Two Circular Plates

This article presents a scheme for the analysis of an unsteady axisymmetric flow of incompressible Newtonian material in the form of liquid squeezed between two circular plates. The scheme combines traditional perturbation technique with homotopy using an adaptation of the Laplace Transform. The proposed method is tested against other schemes such as the Regular Perturbation Method (RPM), Homotopy Perturbation Method (HPM), Optimal Homotopy Asymptotic Method (OHAM), and the fourth-order Explicit Runge-Kutta Method (ERK4). Comparison of the solutions along with absolute residual errors confirms that the proposed scheme surpasses HPM, OHAM, RPM, and ERK4 in terms of accuracy. The article also investigates the effect of Reynolds number on the velocity profile and pressure variation graphically.

A comparative simulation based analysis of location based routing protocols in underwater wireless sensor networks

Underwater Wireless Sensor Network (UWSN) is newly emerged and developed branch of Wireless sensor technology. In UWSN small sensor nodes with limited battery and limited memory are deployed in underwater environment. Due to multiple differences from terrestrial Wireless Sensor Networks (WSN), radio waves cannot be used in underwater communication. Acoustic channels are used for communication in sea water. Acoustic channels has many communication constraints like low bandwidth, high end to end delay and high path loss. Therefore energy efficient communication in underwater networks has became uttermost need of wireless sensor technology. This paper has compared the three main Location based Routing protocols in UWSN. Such as Vector Based Forwarding(VBF), Hop by Hop- Vector Based Forwarding(HH-VBF) and Focused Beam Routing (FBR) has been compared using MATLAB simulation tool. These protocols has been compared on the basis of data delivery ratio, number of alive nodes, end to end delay and total consumed energy.

Comprehensive Theoretical and Experimental Analysis of Spin Waves in Magnetic Thin Film

Magnetic spin waves (SWs) have been induced and detected in a Ni80Fe20 thin film by two identical copper coplanar waveguides (CPWs). The dc fields up to 25 kA/m have been applied parallel to the CPWs, and magnetostatic surface SWs have been generated by applying voltages through the first CPW (source). The second CPW (pickup), 12 μm apart from the source, has been used to detect the ensuing SWs. Two independent setup and methods have been applied. Time domain SW measurements were performed by the application of voltage steps and the ensuing SW signal has been measured using a 16 GHz oscilloscope. Frequency domain SW spectroscopy was performed using a two-port vector network analyzer measurement in a frequency range from 10 MHz to 10 GHz. In addition, micromagnetic simulations were performed under the harmonic regime by assuming the induced SWs as perturbations of the saturated ground state excited by a small RF field. The numerically computed dispersion relation closely follows the Damon-Eshbach curve and is in good agreement with the experimental data.