High Resolution Through-the-Wall and Subsurface Imaging Using Small Number of Transceivers on Moving Robotic Platforms

Imaging of visually obscured objects within buildings or buried under ground using low frequency EM waves have many military, security, civilian, and industrial applications. In imaging systems, range and cross-range resolution are important parameters that determine the ability of the system to resolve closely spaced objects. Range resolution generally depends on the signal bandwidth while the cross-range resolution depends on the antenna aperture size. In certain application such as through-the-wall imaging and detection of buried land mines and pipelines where the objects are closely spaced and/or located at far distance from the transmitter and receiver, the imaging system must have high cross-range resolution. Typically, this is achieved by using a large array of directive antennas with limited field of view and low mobility. In this research, new imaging methods based on synthetic aperture processing are presented to address low cross-range resolution, limited field of view, and low mobility of currently available imaging systems. For through-the-wall imaging applications, the large array of directive antennas used in current systems is replaced by a small number of omnidirectional transceivers mounted on moving robots. One or more receivers move and sample the scattered signal at different locations within the imaging area. By applying back-projection technique to the obtained samples, a large 2-D array is synthesized for high resolution imaging. Using omnidirectional antennas, images with a 360° field of view are generated in a short period of time. To suppress the effect of direct coupling between the transmitter and receiver and multiple reflections in the image, orthogonal circular polarizations are used for the transmitting and receiving antennas. In this research, a novel wideband circularly polarized omnidirectional antenna is presented for through-the-wall imaging applications. The antenna operates based on excitation of orthogonal field distributions similar to a circular waveguide TE21 mode. A bi-static FMCW radar system realizing the presented through-the-wall imaging method is designed and fabricated. The system is configured to account and completely compensate for the delays inherent to the circuits and errors in transmitter/receiver synchronization completely. Performance of the method is evaluated in different real-world scenarios using the fabricated radar system and the associated algorithms. Two new methods for image enhancement in through-the-wall imaging are developed. The first method enhances the range resolution and reduces the background noise in the image by detecting the locations of the reflections and forming the image only at those points. The second method discriminates wall surfaces from small size objects and detects the location and orientation of all wall surfaces within the imaging area. The second part of the dissertation describes a new method for subsurface imaging using the general idea developed for the through-the-wall imaging. The method utilizes bi-static ground looking transmitters and receivers mounted on moving robots to sample scattered fields at different locations. The samples are processed coherently to form a large 2-D synthetic array which provides high cross-range resolution 3-D images of the subsurface in a short period of time. This cannot be achieved using conventional ground penetrating radars. A new low profile wideband antenna is designed for the imaging of deeply buried targets or targets buried in soil with high losses. Performance of the designed antenna and the proposed imaging method have been tested through field measurements. The imaging results show high resolution 3-D imaging capability of the method.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/153344/1/byekta_1.pd

Physics-Based Coherent Modeling of Long-Range Millimeter-Wave Propagation and Scattering in Rain

Precipitation and in particular rain present a random medium with constituent particles having dimensions comparable to the wavelength at millimeter-wave frequencies. Due to considerable scattering of waves from such particles, significant signal attenuation and phase front aberration can take place which are important factors that must be considered in modern communication system or radar design. This paper presents a fast and accurate numerical method for phase coherent modeling of wave propagation and scattering in random media, like rain. In this approach, the random medium is divided into sufficiently large finite slabs and each slab is modeled as a network with multiple input/output ports where ports represent rays with different polarizations propagating in different directions entering and leaving the slabs. The cascaded networks of slabs can be used to find the response of the random medium to any arbitrary source. The proposed method considers multiple scattering among all scatterers and thus the entire physics of wave-particle interactions is accounted for. In addition, the method can model both the mean and the fluctuating parts of waves in the random medium. To demonstrate the applicability of the proposed method, it is used for the calculation of the specific attenuation in rain media as a function of rain rates and frequency within the millimeter-wave band. The results show a good match with the available rain attenuation data in the literature

Stress in Mothers of Hearing Impaired Children Compared to Mothers of Normal and Other Disabled Children

Background and Aim: Stress is associated with life satisfaction and also development of some physical diseases. Birth of a disabled child with mental or physical disability (especially deaf or blind children), impose an enormous load of stress on their parents especially the mothers. This study compared stress levels of mothers with hearing impaired children and mothers of normal children or with other disabilities.Methods: In this study, cluster random sampling was performed in Karaj city. 120 mothers in four groups of having a child with mental retardation, low vision, hearing impairment and with normal children were included. Family inventory of life events (FILE) of Mc Cubbin et al. was used to determine stress level in four groups of mothers.Results: The results of this research indicated a significant difference (p<0.05) between stress levels of mothers with hearing impaired children and mothers of other disabled and normal children in subscales of intra-family stress, finance and business strains, stress of job transitions, stress of illness and family care and family members "in and out''. There was no difference between compared groups in other subscales.Conclusion: Since deafness is a hidden inability, the child with hearing impairment has a set of social and educational problems causing great stress for parents, especially to mother. In order to decrease mother’s stress, it is suggested to provide more family consultation, adequate social support and to run educational classes for parents to practice stress coping strategies