Theses and Dissertations

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    ItemOpen Access
    Microwave Imaging for Breast Cancer Detection using 3D Level Set based Optimization, FDTD Method and Method of Moments
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2019) Patel, Hardik Nayankumar; Ghodgaonkar, Deepak K.
    Microwave imaging is emerging as new diagnostic option for breast cancer detection because of non-ionizing nature of microwave radiation and significant contrast between dielectric properties of healthy and malignant breast tissues. Class III and IV breasts have more than 50% fibro-glandular tissues. So, it is very difficult to detect cancer in class III and IV breasts by using X-ray based mammography. Microwave imaging is very promising for cancer detection in case of dense breasts. Complex permittivity profile of breasts is reconstructed in three dimensions for microwave breast imaging. 3D level set based optimization proposed in this thesis is able to reconstruct proper shape and dielectric property values of breast tissues. Multiple frequency inverse scattering problem formulation improves computational efficiency and accuracy of microwave imaging system because complex number computations are avoided. Measurements of scattered electric fields are taken at five equally spaced frequencies in the range 0.5-2.5 GHz. Class III numerical breast phantom and Debye model are used in multiple frequency inverse scattering problem formulation. There are three unknowns per cell of numerical breast phantom due to Debye model. Linear relationships between Debye parameters are applied to get only static permittivity as unknown per cell of numerical breast phantom. Two level set functions are used to detect breast cancer in 3D level set based optimization. Pixel based reconstruction is replaced by initial guess about static permittivity solution in this modified four stage reconstruction strategy. Frequency hopping method is used to avoid local minima present at particular frequency in the 3D level set based optimization. 3D FDTD solves forward problem efficiently during each iteration of 3D level set method which leads to better reconstruction of static permittivity profile. 3D reconstruction problem is very challenging due to Ill posed system matrix and noisy scattered fields data. Tikhonov and total variation (TV) regularization schemes are used to overcome above challenges. The performance of TV regularization is better than Tikhonov regularization in 3D level set based optimization. TV regularization reconstructs shape and size of very small tumour but it fails to reconstruct exact location of very small tumour. Better 3D reconstruction is achieved by using regularized 3D level set based optimization for at least 20 dB SNR in electric field data. 3D FDTD method based electric field computation in heterogeneous numerical breast phantom is very efficient because it solves Maxwell's equations on grids by using an iterative process. Microwave imaging problem is solved with millions of cells because 3D FDTD is used. Method of moments is used to solve electric field integral equation (EFIE) which estimates complex permittivity of 2048 cell human breast model. Matrix formation and inversion time are reduced to allow large number of cells in breast model. Computational efficiency of the imaging system is improved by exploiting symmetry using group theory. Matrix formed by method of moments is ill posed due to presence of large number of buried cells in inverse scattering formulation. Ill posed system matrix and noise are two major challenges in the solution of inverse scattering problem. Levenberg-Marquardt method is used to solve above challenges.
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    ItemOpen Access
    Novel circular fractal antenna array
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2018) Chauhan, Rahul; Gupta, Sanjeev
    Traditional antennas work well only for one resonant frequency and using multiple antennas for different frequencies is a complex task, therefore multiband circular fractal antenna was designed which have a small size and multiple resonating frequencies for UltraWideband Applications (UWB). For designing and fabrication of the antenna the substrate used is FR4 which have dielectric constant 4.4 and whose dimensions are 48 96mm2. For the excitation of the antenna microstrip feed line of 50W is fed to the circular fractal patch for impedance matching. The UWB characteristics can be achieved using fractal concept. Also to increase the bandwidth, slots of different dimensions are etched out from the ground plane from the basic fractal configuration. Slots dimensions are adjusted in each iteration to achieve the desired results. In the later part of the work, different array configurations of the circular fractal antenna are analyzed. The various arrays design configurations are 1 2, 1 4, 2 2 and 2 4. The substrate used is FR4 whose dimension is varied according to the array configurations. Similar to basic antenna design a 50W microstrip feedline is used to excite the antenna for all the configurations. The antenna shows stable radiation patterns and good return loss values i.e better than 10dB at multiple frequencies. All the analysis is done in HFSS 2014.
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    ItemOpen Access
    Design and analysis of multiband fractal antenna
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2015) Dhoot, Vivek; Gupta, Sanjeev
    Miniaturized Multiband antenna design is an important and challenging task for communication industry. Several constraints like size, position of the antenna, feasibility, reflection coefficient, Specific absorption Rate (SAR), make it more difficult to design a multiband antenna. Current trend suggests that one device (Mobile, Tablet PCs etc.) should cover multiple communication applications (Like GSM, LTE, Bluetooth, Wi_ etc.). It implies that antenna design should not only satisfy the constraints but also cover wide multiband range. In this research work, design, analysis and measurement of fractal antennas, are carried out, for such multiband applications. Revised cantor geometry is proposed for antenna design, which produces more than 5 resonances in second iteration only (feasible design). The three dimensional Finite Difference Time Domain (3D-FDTD) Method is used for analyzing the reflection coefficient of the antenna. Revised cantor geometry based compact, low profile LTE fractal antenna is proposed here, for Mobile and Tablet PC applications. The proposed antenna is appropriately covering several wireless applications, including LTE 1.7-1.8 GHz band, 2.3 GHz, 2.6 GHz and 2.9 GHz applications, WLAN 2.4 GHz and 5.8 GHz applications, GSM, UMTS, DCS, ZigBee, PCS, applications. This antenna is designed and analyzed using MATLAB code based on 3D FDTD method. Antenna finger dimensions are optimized using observations in MATLAB and CST Studio Suite. Radiation Patterns show, for all the observed frequencies, Directivity between 7.72 dBi to 8.17 dBi and Radiation Efficiency, within the range of -0.98 dB to -1.95 dB. Experimental reflection coefficient results present accurate matching with theoretical results. Theoretically analyzed SAR is less than 1.6 W/kg for 10 g tissue, without mobile circuitry. SAR reduction technique is also been presented.

    In addition to this, fractal antenna on substrate with high dielectric constant, fractal antenna array design and integrated antenna designs, are also studied, as part of this work.

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    ItemOpen Access
    Performance of MIMO in correlated rayleigh flat fading channels
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2005) Jain, Alok; Jadhav, Ashish
    The recent interest in Multiple Input Multiple Output (MIMO) communication systems was initiated by the theoretical work of Telatar. The development in the field of random matrix theory is the basis of these studies. The assumption in the mathematical model for studying MIMO turned out to be too idealistic for realistic (correlated) channel condition. This lead to an exaggeration of performance of MIMO. This thesis deals with quantification of performance of MIMO in realistic channel conditions with the emphasis on study of working of MIMO receivers. Our definition of MIMO contains both diversity systems and spatial multiplexing systems. For the simulation of realistic channel conditions a correlated fading channel model with lack of rich scattering is used. To perform simulations for N transmit and M receive MIMO systems there is a need for having N x M correlated fading envelops. We propose a novel and simplified technique to extend the algorithm for two correlated fading envelops given by Richard and Jeffery. Various analytical studies on the effect of correlated multi-path channel on performance of spatial multiplexing have been done. These studies focus on capacity cumulative distribution function. Effect of various degree of correlation on other performance measures like diversity gain and error probability have been not done. This is due to lack of simple method of generation of correlated Rayleigh fading envelops. By making use of the extended algorithm we have been successful in carrying out simulation to observe the effects on the performance. Recently there is interest in extending the concept of MIMO in wireless communication for sensor networks. The motivation behind it is energy efficiency of sensor nodes. Our results have implications on this venture.