A novel coherent ultra-wideband radar system operating in the 1-to 2-GHz frequency range has been developed recently at the University of Nebraska. The radar system transmits white Gaussian noise. Detection and localization of buried objects is accomplished by correlating the reflected waveform with a time-delayed replica of the transmitted waveform. Broadband dual-polarized log-periodic antennas are used for transmission and reception. A unique signal-processing scheme is used to inject coherence into the system by frequency translation of the ultrawideband signal by a coherent 160-MHz phase-locked source prior to performing heterodyne correlation. The system coherence allows the extraction of a target's polarimetric amplitude and phase characteristics. This paper describes the unique design features of the radar system, develops the theoretical foundations of noise polarimetry, provides experimental evidence of the polarimetric and resolution capabilities of the system, and demonstrates results obtained in subsurface probing applications.
A novel polarimetric ultra-wideband radar system operating in the 1-2 GHz frequency range for subsurface probing applications is currently under development at the University of Nebraska. The radar system transmits white Gaussian noise. Detection and localization of buried objects is accomplished by correlating the reflected waveform with a time-delayed replica of the transmitted waveform. Broadband dual-polarized log-periodic antennas are used for transmission and reception. A unique signal processing scheme is used to obtain the target's polarimetric amplitude and phase response by frequency translation of the ultra-wideband signal by a coherent 160 MHz phase-locked source. In addition, the radar system features high depth resolution, low bandwidth-duration product, as well as simplified signal processing. This paper describes the unique design features of the radar system, develops the theoretical foundations of noise polarimetry, and provides experimental evidence of the polarimetric and resolution capabilities of the system.
This study investigated the effect of cyclic tests on the shape memory performance of graphene oxide-carbon fiber (GO-CF) hybrid-reinforced shape memory polymer composite (SMPC). The shape memory performance was evaluated by four indexes: shape fixation rate, shape recovery rate, recovery time, and maximum recovery force. The results showed that the service life of the GO-CF hybrid-reinforced SMPC prepared by the vacuum infiltration hot-press forming experimental system process (VIHPS) was 16 cycles. After 16 repetitions, the shape fixation rate decreased by approximately 6.6% and the shape recovery rate decreased by approximately 14.0%. At this time, the shape recovery rate was lower than 90%. The recovery time increased by 62.2% and the maximum recovery force decreased by 70.1%. The maximum recovery force exhibited the highest performance attenuation. Scanning electron microscopy (SEM) was used to photograph and analyze the microstructures of the samples under various cyclic tests. It was concluded that the main factor affecting the shape memory performance of GO-CF hybrid-reinforced SMPC is the life of fiber bundle. During cyclic testing, the fiber was prone to kinks, tensile damage and other defects, which increased the probability of reducing the length of the fiber bundle. Therefore, the probability of fiber fracture was improved, and the shape memory performance of the GO-CF hybrid-reinforced SMPC was attenuated.
Random noise polarimetry is a new radar technique for high-resolution probing of subsurface objects and interfaces. Detection of buried targets is accomplished by cross-correlating the reflected signal by a time-delayed replica of the transmitted waveform. A unique signal processing scheme is used to inject coherence in the system to permit extraction of the wideband polarimetric scattering response of the buried object. This facilitates computation of the Stokes matrices of the target response which enhances the detection and identification process. Random noise polarimetry also possesses additional desirable features for subsurface probing such as immunity from detection and jamming. The paper discusses the theoretical foundations of random noise polarimetry and presents data acquired from various targets using a 1-2 GHz radar system fabricated by the University of Nebraska under contract to the U.S. Army Waterways Experiment Station. In addition, various signal processing algorithms used to analyze the polarimetric data are presented.
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