Shafrida Sahrani

Numerical analysis of the electromagnetic wave scattering from a moving dielectric body by Overset Grid Generation method

This paper presents an alternative approach for the analysis of EM field with moving boundaries by FDTD method combined with Overset Grid Generation method, considering Lorentz transformation for the higher velocity cases. This approach has been previously proposed for the case of moving/rotating body with empty grids. Here, the approach is expanded to a moving dielectric body that moves linearly towards and against to the incident wave. The scattering of the EM fields when the incident wave hits the dielectric moving body with high velocity are analyzed. The numerical results are compared with the theoretical results and achieved good agreements between both results. This numerical approach may have numerous situations to which it can be applied. This may be involved with the design of the high-frequency devices such as microactuator, commutator and the others.

Electromagnetic radiation towards adult human head from 900MHz handheld mobile phone

Electromagnetic radiation produce by mobile phone and the relationship with the humans health is not a new issue nowadays. Since the used of mobile phone had increased rapidly over the past few years, people are becoming more concern with their health when dealing with the so-called electromagnetic radiation. This type of radiation would leads to heating of body tissue at specific rate called the thermal radiation. Thermal radiation depends on the frequency of the energy, the power density of the radio frequency field that strikes the body and the polarization of wave. This paper will discuss on the result collected from the thermal radiation generated by handheld mobile phone with frequency of 900 MHz towards adult human head. The analysis is conducted in a laboratory with average of 45 minutes talking hour with two different types of mobile phone, internal and external antenna. The results show an increased of heat especially at the place near the ear skull after 45 minutes of operation. When comparing both different types of mobile phone, mobile phone with external antenna produce more heat compared to mobile phone with internal antenna.

Preliminary Results on Estimation of the Dispersive Dielectric Properties of an Object Utilizing Frequency-Dependent Forward-Backward Time-Stepping Technique

In this paper, a Frequency-Dependent Forward-Backward Time-Stepping (FD-FBTS) inverse scattering technique is used for reconstruction of homogeneous dispersive object. The aim of the technique is to reconstruct the relative permittivity at infinite frequency, static relative permittivity and static conductivity of the homogeneous dispersive object simultaneously. The technique utilizes iterative finite-difference time-domain (FDTD) method for solving inverse scattering problem in time domain. The minimization of the cost functional is carried out utilizing Dai-Yuan nonlinear conjugate-gradient algorithm. The Frechet derivatives of the augmented cost functional are derived analytically with respect to scatterer properties. Numerical results for reconstruction of two-dimensional homogeneous dispersive illustrate the performance of the proposed technique.

A study of the accuracy in FDTD algorithm for solving EM field with rotating body

In this paper, FDTD method combined with Overset Grid Generation method is proposed to the analysis of the EM fields around a rotating body. We have previously proposed this numerical approach for a stationary and uniformly moving body. Lorentz transformation is combined to the analysis to comprise with the high relative velocities. The results of the numerical analysis show the modulations of the observed waveform when the incident wave hits the rotating body. The relativistic effects and its influence to the EM waveforms are presented. The modulations of EM fields in different radius length of observation point are also shown. The observed EM waveforms are compared with the theoretical results and achieved good agreements in high relative velocities, up to ν = 0.7c closed with the finite speed of light.

Integration of Image Segmentation Method in Inverse Scattering for Brain Tumour Detection

This paper presents a microwave imaging for brain tumour detection utilizing ForwardBackward Time-Stepping (FBTS) inverse scattering technique. This technique is applied to solve electromagnetic scattered signals. It is proven that this technique is able to detect the presence of tumour in the breast. The application is now extended to brain imaging. Two types of results are presented in this paper; FBTS and FBTS integrated with image segmentation as a pre-processing step to form a focusing reconstruction. The results show that the latter technique has improved the reconstructions compared to the primary technique. Integration of the image segmentation step helps to reduce the variation of the estimated dielectric properties of the head tissues. It is also found that the optimal frequency used for microwave brain imaging is at 2 GHz and able to detect a tumour as small as 5 mm in diameter. The numerical simulations show that the integration of image segmentation with FBTS has the potential to provide useful quantitative information on the head internal composition.

Profile Reconstruction Utilizing Forward-Backward Time-Stepping With the Integration of Automated Edge-Preserving Regularization Technique for Object Detection Applications

A regularization is integrated with Forward-Backward Time-Stepping (FBTS) method which is formulated in time-domain utilizing Finite-Difference Time-Domain (FDTD) method to solve the nonlinear and ill-posed problem arisen in the microwave inverse scattering problem. FBTS method based on a Polak-Ribiete-Polyak conjugate gradient method is easily trapped in the local minima. Thus, we extend our work with the integration of edge-preserving regularization technique due to its ability to smooth and preserve the edges containing important information for reconstructing the dielectric profiles of the targeted object. In this paper, we propose a deterministic relaxation with Mean Square Error algorithm known as DrMSE in FBTS and integrate it with the automated edge-preserving regularization technique. Numerical simulations are carried out and prove that the reconstructed results are more accurate by calculating the edge-preserving parameter automatically.

Numerical technique for wireless communication system with high speed movement

Numerical technique for the analysis of EM field with high speed moving dielectric body by using FDTD method with Overset Grid Generation method considering Lorentz transformation is presented. The characteristic of EM field when incident wave hits the moving dielectric body with high velocity value are analyzed. The accuracy of the proposed technique is validated. Good agreements are obtained between numerical results and theoretical results. The development of this numerical technique will give a great impact for many areas, particularly for the future high speed mobile communication systems used in transportation and aerial radar systems to detect the high speed motion of a moving boundary.

Iterative refinement in inverse scattering technique with median filter

This paper presents a preliminary study of integrating median filter in Forward-Backward Time-Stepping (FBTS) algorithm for single object detection. A two dimensional (2D) homogeneous numerical phantom image with significant contrast was utilized to represent an unknown object. Mean Squared Error (MSE) was used to evaluate the efficiency of the proposed technique in eliminating artifacts that exists in the reconstructed image due to strong nonlinearity and ill-posedness of inverse scattering method in FBTS method. Preliminary results shown that MSE of median filtered FBTS was significantly lower than FBTS.

The development of novel numerical technique for the analysis of the moving vehicle and moving source

The numerical technique for the analysis of the electromagnetic field with moving body or a moving source are required for the effective modeling of new optical devices or microwave devices and also mobile communication field. We have previously proposed the Overset Grid Generation method coupled with FDTD method for the analysis of the EM field with moving boundaries considering Doppler Effect. For higher velocity value, Lorentz transformation is applied to the FDTD method. The time components that were changed in Lorentz transformation are fixed by using linear interpolation scheme in the Overset Grid Generation method. This allows a coherent point in time component with the FDTD method, which is an important element of this proposed numerical technique.

FDTD analysis of EM field effected by the motion of source and vehicle

A numerical technique for the analysis of the electromagnetic (EM) fields by moving sources and moving bodies can be significantly important for the realization of next generation nano-electronic devices particularly for mobile communication system. However, most of the analysis were primarily focused on the stationary source. We have previously proposed the Overset Grid Generation method combined with the FDTD method for the analysis of the EM field with moving body. In this paper, this technique is applied for the analysis of the EM field in a street cross section from moving vehicle and moving source. Here, the Doppler effect is observed by the moving vehicle and moving source.