Recently, there is strong interest in the through-wall sensing capabilities of radar for use in law enforcement, search and rescue, and urban military operations. Due to the high attenuation of walls, through-wall radar typically operates in the low GHz frequency region, where resolution is limited. It is worthwhile to explore other means of propagating radar waves into and back out of a building’s interior for sensing applications. One possibility is through duct-like structures that are commonly found in a building, such as metal pipes used for plumbing or air conditioning ducts. The objective of this dissertation is to investigate techniques to acquire radar images of targets through a pipe. First, using the pipe as an electromagnetic propagation channel is studied. A modal approach previously developed for computing the radar cross-section of a circular duct is modified to compute the transmission through a pipe. This modal approach for transmission is validated against measured data. It is also shown that a pipe is a high-pass propagation channel. The modal analysis is then extended to two-way, through-pipe propagation for backscattering analysis. The backscattering from a target is observed through a pipe in simulation and measurement. Next, methods to form two-dimensional radar images from backscattering data collected through a pipe are explored. Four different methods previously developed for free-space imaging are applied to the problem of imaging through a pipe: beamforming, matched filter processing, MUSIC, and compressed sensing. In all four methods it is necessary to take into account the propagation through the pipe in order to properly generate a focused radar image. Each method is demonstrated using simulation and validated against measurement data. The beamforming and matched filter methods are found to suffer from poor cross-range resolution. To improve resolution, the MUSIC algorithm is applied and shown to give superior resolution at the expense of more complicated data collection. The final method, compressed sensing, is shown to achieve good cross-range resolution with simpler data collection. A comparison of the tradeoffs between the four methods is summarized and discussed. Two additional extensions are studied. First, a method for computing the transmission through an arbitrary pipe network using the generalized scattering matrix approach is proposed and implemented. Second, a new method for computing joint time-frequency distributions based on compressed sensing is applied to analyze the backscattering phenomenology from a pipe. / text

This thesis presents a simulation model of Stepped Frequency (SF) and Near Field BeamForming (NF BF) based stationary Through Wall Imaging (TWI) system to scan an object behind the wall for the reconstruction of 2D/3D image of it. The developed simulation model of TWI system requires neither the movement of the antenna array nor the object to reconstruct the image of the object behind the wall, thus overcoming the limitation of SAR/ISAR based TWI system. The simulation model of TWI system arrived at in this thesis facilitates the scan of the desired scenario in both azimuth and elevation to maximize the information available for more effective reconstruction of the Image of object behind the wall. The reconstruction of the image has been realized through conventional image processing algorithms which are devoid of inversion techniques to minimize the computational burden as well as the overall execution time of the TWI system. Contrary to the present TWI systems, the proposed simulation model has the capability for the reconstruction of the shape and contour of the object. In addition, the formulated simulation model of the TWI system overcomes the previously imposed constraints on the distances of separation between the object and the wall as well as the wall and the target. The simulation model of TWI of this thesis can handle arbitrary distances (far field or near field) between the antenna array and the wall as well as the wall and the object, which is not the case with the existing TWI systems. The thesis provides wave propagation analysis from the transmitting antenna array through the wall and the obstacle behind it and back to the receiver. Subsystems of TWI system like beamforming antenna arrays, wall and obstacles have been modeled individually. The thesis proposes a novel near field beamforming method that overcomes the usual requirement of 3D or volumetric near field radiation patterns of the beamforming array. Typical simulation results of NF BF with linear and planar arrays reveal the beam formation at a distance of one wavelength from the aperture of the array and which corresponds to the ratio of observation distance to aperture of array to be 0.2334. As a supplement to the presented NF BF a generic and versatile procedure to compute near field radiation patterns of antennas with prior knowledge of its either field or current distribution over the radiating aperture is also proposed. Examples of reconstruction of images of typical 2D and 3D objects are also illustrated in the thesis.

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Technological advances require novel solutions for contactless energy transfer. Many engineering applications require unique approaches to power electrical components without using physical wires. In the past decade, awareness of the need to wirelessly power electrical components spawned many forays into the field of wireless power transfer (WPT). WPT techniques include capacitive energy transfer, electromagnetic inductive power transfer, electromagnetic radiative power transfer, electrostatic induction, and acoustic energy transfer. Acoustic energy transfer (AET) has many advantages over other methods. These advantages include lower operating frequency, shorter wavelengths enabling the use of smaller sized receiver and transmitter, extended transmitter-to-receiver distance therefore more manageable design constraints, achieving lower attenuation, higher penetration depth, and no electromagnetic losses. Most AET systems operate in the ultrasonic frequency range and are more commonly referred to as ultrasonic acoustic energy transfer (UAET) systems. Through-wall UAET systems are constructed of a transmitter bonded to a transmission elastic layer, which in turn is bonded to a receiver. The transmitter and receiver layers are constructed of a piezoelectric material. Piezoelectric materials behave according to the piezoelectric effect, which is when a material generates an electric charge in response to mechanical strain. The transmitter utilizes the reverse of the piezoelectric effect. A sinusoidal input voltage is applied to the transmitter, inducing vibrations in the transmitter. The vibration-induced acoustic waves emanating from the transmitter travel through the initial bonding layer, the transmission layer, and the final bonding layer to the receiver. In turn, the acoustic waves cause the receiver to deform and undergo strain. This induces a flow of charge in the receiver, which is an electric current. The receiver feeds current to a resistive load. In this manner, energy is acoustically transferred between two transducers without wires. The performance of UAET systems can be evaluated based on power transfer efficiency, voltage magnification, and input admittance. UAET systems require extensive modeling before experimental assembly can be attempted. The analytical models of UAET are either based on the mechanics of the constitutive relations of piezoelectricity and solid mechanics or using equivalent circuit methods. The equivalent circuit method approximates the physics of the UAET system with electrical assumptions. The mechanics-based method is the most comprehensive description of the physics of all the intermediate layers in a UAET system. The mechanics-based method has been based on the assumption that the UAET system is operated in the thickness mode of vibration, i.e., piston-like vibration mode where the transmitter and receiver disks vibrate only in the thickness direction. This poses an issue for disks with aspect ratios between 0.1 and 20 because the piezoelectric transducers vibrate in both the radial and thickness modes. In addition to this assumption, most of the works on UAET models only have accounted for the piezoelectric and transmission layers. The effects of the bonding layers were not considered. Bonding the piezoelectric layers to the transmission layer introduces epoxy material with mechanical properties that are not accounted for. The epoxy layers are extra barriers to the transmission that introduce attenuation and alter the vibrational and acoustical behaviors of the UAET system. Investigations into UAET commonly focus on metal through-wall applications. Alternate transmission layer materials are not investigated and the impact of varying mechanical properties on the performance of a through-wall UAET system has not been comprehensively studied. Even with the metal transmission layers, the impact of the metal thickness has not been extensively investigated thoroughly. This work addresses the issues of the thickness-mode assumption in UAET modeling, the effects of epoxy layers, the impacts of the metal layer geometry, and the performance of UAET systems with alternate transmission layer materials. Particularly, (1) we showed that the thickness-mode assumption, that has been used in the UAET modeling leads to inaccurate results. (2) We modified the available acoustic electro- elastic theoretical modeling to include the effects of radial modes as well as the epoxy bonding layers. (3) We showed that the geometry of the elastic/metal layer requires optimization for peak system efficiency. (4) The results show that using alternate transmission layer materials impacts the performance of UAET systems. The results of this work were investigated using an improved 5-layer analytical model and finite element modeling in COMSOL Multiphysics. / Master of Science / Wireless power transfer (WPT) is an innovative solution to the problem of powering sophisticated technological applications. Such instances include the powering of implanted medical devices, recharging inaccessible sensor networks, and wireless powering of components in sealed containers. Acoustic energy transfer (AET) is a feasible WPT method that addresses these needs. AET is based on the propagation of acoustic waves to a piezoelectric receiver which converts the vibrations caused by incident acoustic waves into electrical energy. Most AET systems operate in the ultrasonic frequency range, and so AET can also be referred to as ultrasonic acoustic energy transfer (UAET). Through-wall UAET systems are constructed from a transmitter that is bonded to a transmission elastic layer. The transmission layer is bonded to a receiver. The transmitter and receiver are made of a piezoelectric material. This thesis addresses the modeling process of through-wall UAET systems. In previous works, the fundamental assumption has been that such systems vibrate purely in the thickness mode. Additionally, other investigations did not comprehensively analyze the effects of the bonding layers, ascertain the performance of non-metal transmission layers, or provide practical insight on the effect of the resistive loading on such systems. This work addresses all these issues with a mathematical framework and finite element modeling results.

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No description available.

L’objectif de cette thèse a consisté en l’étude des apports d’une architecture radar MIMO pour la détection d’êtres humains à l’intérieur des bâtiments. Pour ce faire, il a tout d’abord été mis en évidence sur un point théorique la supériorité d’une architecture radar MIMO comparée au SIMO, en terme de robustesse et de pouvoir discriminant de cibles rapprochées. Ensuite, les effets de la traversée du mur sur le signal radar furent décrits et une caractérisation quantitative de la transmission à travers un mur fut réalisée sur mesures expérimentales. Différents simulateurs de scénarii de détection à travers les murs ont été produits : un simulateur réaliste FDTD ainsi qu’un simulateur «comportemental» simplifié.La méthode de détection et de localisation retenue est l’imagerie radar.Ainsi, différents algorithmes d’imagerie radar pour une architecture MIMO furent développés. Des traitements incohérents (migration, multilatération),cohérents (filtrage adapté) et haute résolution (MVDR, MUSIC Time Reversal) furent détaillés. Enfin des considérations techniques (bilan de liaison, temps d’observation de la scène) ont été discutées et deux architectures radar MIMO ultra-large bande furent proposées. Une architecture radar MIMO avec 2GHz de bande et un multiplexage temporel pour l’adressage des antennes d’émission a été réalisée par le personnel du laboratoire. Des mesures expérimentales ont conduites permettant de réaliser la détection à travers les murs à l’aide du dispositif réalisé. / This thesis focused on the study of the contributions of MIMO radar systemfor human beings detection inside buildings. First, on a theoretical point, it was highlighted the superiority of MIMO systems compared with the SIMO, in term of robustness and discrimination abilities of close targets. Then, through the wall propagation effects were described and a quantitative characterization of the transmission through a wall wasrealised based on experimental measures. Various simulators of scenarios of detection through walls were produced : a full-wave FDTD simulator and a simplified «behavioral» one. The method of detection and localisation is the radar imaging. So, differents algorithms of radar imaging for MIMO system were developed. Among them, incoherent processings (migration,multi-lateration), coherent (matched filtering) and high resolution(MVDR, MUSIC Time Reversal) were detailed. Finally, technical considerations(link budget, observation time of the scene) were discussed and two ultrawide band MIMO radar architectures were proposed. A experimental bench of MIMO radar with 2GHz bandwidth and a temporal multiplexing was realized in the laboratory. Experimental measures allow to realize the detection through walls with the realized MIMO radar.