The Experts below are selected from a list of 11913 Experts worldwide ranked by ideXlab platform
Gerhard Krieger - One of the best experts on this subject based on the ideXlab platform.
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cebras cross elevation beam range ambiguity suppression for high resolution wide swath and mimo sar imaging
International Geoscience and Remote Sensing Symposium, 2015Co-Authors: Gerhard Krieger, Michelangelo Villano, Marwan Younis, Sigurd Huber, Tobias Rommel, Lopez P Dekker, Queiroz F De Almeida, Alberto MoreiraAbstract:In this paper we propose a new hybrid technique to suppress range ambiguities in spaceborne SAR systems with multiple elevation beams. First, conventional scan-on-receive (SCORE) is performed in real-time onboard the satellite by employing a set of dispersive beams that maximize the collected signal energy for each Transmitted Pulse. The range ambiguities are then removed in a second step by a joint processing of the signals collected by the multiple elevation beams. The suggested two-stage approach has the advantage that a more robust range ambiguity suppression, which may involve advanced nulling techniques to account for local topography as well as satellite attitude and instrument phase errors, can be performed on ground without tremendously increasing the onboard processing demands or the data downlink volume.
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azimuth phase center adaptation on transmit for high resolution wide swath sar imaging
IEEE Geoscience and Remote Sensing Letters, 2009Co-Authors: Nicolas Gebert, Gerhard KriegerAbstract:Synthetic aperture radar (SAR) systems with multiple receive channels allow for high-resolution wide-swath imaging thus overcoming a fundamental limitation of conventional single-aperture SAR. By using multiple apertures in azimuth, additional samples are received for each Transmitted Pulse. This allows for a reduced Pulse repetition frequency (PRF) thereby enabling a wider swath. However, a nonoptimum PRF is associated with a nonuniform sample spacing in azimuth and needs to be compensated by a multichannel reconstruction algorithm. For strong deviations from the optimum PRF, the inverse character of such an algorithm might result in a degraded performance. This can be overcome by an innovative advanced transmit antenna architecture which allows for a Pulse-to-Pulse shift of the phase center. Such an antenna enables the adaptive adjustment of the system's phase center positions to the respective PRF, thereby ensuring constant performance over a clearly extended PRF range. In particular, in combination with conventional multichannel processing strategies, this technique represents the next step toward a fully active multiple-input multiple-output (MIMO) SAR and has a great potential for future systems.
Andrew N Norris - One of the best experts on this subject based on the ideXlab platform.
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non reciprocal wave transmission in a bilinear spring mass system
arXiv: Computational Physics, 2019Co-Authors: Andrew N NorrisAbstract:Significant amplitude-independent and passive non-reciprocal wave motion can be achieved in a one dimensional (1D) discrete chain of masses and springs with bilinear elastic stiffness. Some fundamental asymmetric spatial modulations of the bilinear spring stiffness are first examined for their non-reciprocal properties. These are combined as building blocks into more complex configurations with the objective of maximizing non-reciprocal wave behavior. The non-reciprocal property is demonstrated by the significant difference between the Transmitted Pulse displacement amplitudes and energies for incidence in opposite directions. Extreme non-reciprocity is realized when almost-zero transmission is achieved for the propagation from one direction with a noticeable Transmitted Pulse for incidence from the other. These models provide the basis for a class of simple 1D non-reciprocal designs and can serve as the building blocks for more complex and higher dimensional non-reciprocal wave systems.
Mahbub Hassan - One of the best experts on this subject based on the ideXlab platform.
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Direction of Arrival and Center Frequency Estimation for ImPulse Radio Millimeter Wave Communications.
arXiv: Signal Processing, 2018Co-Authors: M Shree Prasad, Trilochan Panigrahi, Mahbub HassanAbstract:The 30-300GHz millimeter wave (mmWave) band is currently being pursued to combat the rising capacity demands in 5G, WiFi, and IoT networks. Due to the high frequency, imPulse radio (IR) in this band is better suited for positioning than other existing low-frequency bands. Besides precision positioning, the exceptionally wide bandwidth also enables concurrent use of multiple center frequencies in the same application, which opens up additional avenues of information encoding in IR mmWave networks. In this paper, we propose a new mmWave IR framework that can simultaneously detect direction of arrival (DOA) as well as the center frequency of the Transmitted Pulse. Based on the emerging graphene-based transceivers, we evaluate the performance of the proposed framework in the higher frequency region of mmWave band (100-300GHz). Numerical experiments demonstrate that the proposed framework can detect the DOA of a 0.1 $\mu$Watt mmWave Pulse within 1 degree of precision at 20 meters, and classify three different center frequencies with 100% accuracy from a distance of 10 meters. These performances could be further improved by trading off the Pulse rate of the system.
Nicolas Gebert - One of the best experts on this subject based on the ideXlab platform.
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azimuth phase center adaptation on transmit for high resolution wide swath sar imaging
IEEE Geoscience and Remote Sensing Letters, 2009Co-Authors: Nicolas Gebert, Gerhard KriegerAbstract:Synthetic aperture radar (SAR) systems with multiple receive channels allow for high-resolution wide-swath imaging thus overcoming a fundamental limitation of conventional single-aperture SAR. By using multiple apertures in azimuth, additional samples are received for each Transmitted Pulse. This allows for a reduced Pulse repetition frequency (PRF) thereby enabling a wider swath. However, a nonoptimum PRF is associated with a nonuniform sample spacing in azimuth and needs to be compensated by a multichannel reconstruction algorithm. For strong deviations from the optimum PRF, the inverse character of such an algorithm might result in a degraded performance. This can be overcome by an innovative advanced transmit antenna architecture which allows for a Pulse-to-Pulse shift of the phase center. Such an antenna enables the adaptive adjustment of the system's phase center positions to the respective PRF, thereby ensuring constant performance over a clearly extended PRF range. In particular, in combination with conventional multichannel processing strategies, this technique represents the next step toward a fully active multiple-input multiple-output (MIMO) SAR and has a great potential for future systems.
Nakhiah C. Goulbourne - One of the best experts on this subject based on the ideXlab platform.
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high strain rate response and deformation mechanisms in polycrystalline ti2alc
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Riddhiman Bhattacharya, Miladin Radovic, Rogelio Benitez, Nakhiah C. GoulbourneAbstract:Abstract Ti2AlC is a representative member of MAX phase materials, which are known to exhibit a unique combination of properties observed in conventional ceramics and metals. In this paper, experimental protocols for the high strain-rate compressive response (up to ~4700 s−1) using a Split Hopkinson Pressure Bar (SHPB) is developed. The optimized specimen geometry for Ti2AlC, derived in this work, ensures dynamic equilibrium and minimizes dispersion in the Transmitted Pulse. A modification of the conventional SHPB experimental set-up involves in situ high speed imaging, which facilitates identification of real strains free of macroscopic crack artifacts. Characteristics of the high strain-rate response of polycrystalline Ti2AlC, associated deformation mechanisms and micro-scale origins are presented. The results show that Ti2AlC shows significant inelastic deformation and strain softening before fracture, even at very high strain-rates. Post-fracture microstructures are analyzed to determine dominant deformation mechanisms which reveal simultaneous coexistence of kink bands and delamination, grain-pullouts and trans-granular cracks induced by high strain-rate loading. These deformation characteristics – also active under quasi-static loading, are responsible for the exceptional damage tolerance of Ti2 AlC and provide experimental evidence for high rate kink banding in MAX phases.
