روشهاي وارون زماني در سنجش و تصوير برداري دو بعدي مايكروويو

چكيده انگليسي :

Time Reversal Techniques in 2 D Microwave Sensing and Imaging Mohammad Hossein Hosseini mh hosseini@ec iut ac ir Date of Submission 2012 3 10 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Dr Reza Safian rsafian@cc iut ac irAbstractThis thesis focuses on application and development of time reversal TR based signal processing techniquesusing ultrawideband electromagnetic waves in microwave sensing and imaging This fundamental symmetryof physics the time reversal invariance can be exploited in the domain of wave physics in acoustics andmore recently in electromagnetics leading to a huge variety of experiments and instruments both forfundamental physics and engineering applications TR techniques exploit the time reversal invariance of thewave equation to take advantage of the retransmitted time reversed fields for improved focusing andimaging This is because retransmitted signals propagate backwards through the same medium and undergosimilar reflection refraction and multiple scattering that they underwent during the forward propagation resulting in focusing around initial source locations The refocusing resolution can overcome the classicaldiffraction limit if multiple scattering occurs in intervening media With the success of initial TRexperiments in acoustics there has been a strong interest in the application of TR methods using radiofrequency electromagnetic waves Thanks to development of high speed digital electronics for signalacquisition and processing many applications including subsurface sensing non destructive evaluation medical imaging etc are reported by several research groups around the globe Here our motivation is todevelop TR techniques using ultrawideband electromagnetic waves for the problem of through the wallimaging We start by investigating the time reversal of electromagnetic waves theoretically This is done byusing both time and frequency domain analysis An integral equation for time reversal is introduced infrequency domain The results of theoretical analysis are demonstrated through numerical experiments Totake advantage of time domain representation we use the finite difference time domain FDTD method fornumerical analysis The effect of depolarization on time reversal focusing is also studied by two dimensionalexperiments using TE waves For the selective focusing on different scatterers in the problem domain themulti static data matrix MDM was constructed Time reversal operator is defined with the aid of the MDM Decomposition techniques such as singular value decomposition and eigenvalue decomposition is applied onthese matrices to separate the contribution of each scatterer Due to proportionality of singular values ofMDM to scattering strength of scatterers an extensive study was performed on singular values obtained fromMDM of various canonical scatterers to extract their features and characteristics With this method we areable to classify scatterers according to their intrinsic features Conductive targets lossless and lossy dielectrictargets and inhomogeneous targets can be treated as typical classes of scatterers Since knowledge about wallcharacteristics and the background Green s function is critical for detection and imaging of obscured targetsbehind walls we use this method to characterize different walls By inspecting the singular value spectrumobtained from brick and cinder block walls and with known constitutive parameters one can calculate thewall thickness This data is a key point in mitigating the large clutter introduced by walls With this cluttermitigation technique we are able to detect and image the obscured targets behind walls Key WordsTime reversal Microwave imaging Remote sensing Time reversal operator Radar target classification Through the wall imaging Time reversal array Singular value decomposition

حسيني، محمد حسين

روشهاي وارون زماني در سنجش و تصوير برداري دو بعدي مايكروويو

سنجش از راه دور , عملگر وارون زماني , دسته بندي اهداف راداري , آرايه وارون زماني