356 research outputs found
Generating Information-Diverse Microwave Speckle Patterns Inside a Room at a Single Frequency With a Dynamic Metasurface Aperture
We demonstrate that dynamic metasurface apertures (DMAs) are capable of generating a multitude of highly uncorrelated speckle patterns in a typical residential environment at a single frequency. We use a DMA implemented as an electrically-large cavity excited by a single port and loaded with many individually-addressable tunable metamaterial radiators. We placed such a DMA in one corner of a plywood-walled L-shape room transmitting microwave signals at 19 GHz as we changed the tuning states of the metamaterial radiators. In another corner, in the non-line-of-sight of the DMA, we conducted a scan of the field generated by the DMA. For comparison, we also performed a similar test where the DMA was replaced by a simple dipole antenna with fixed pattern but generating a signal that spanned 19-24 GHz. Using singular value decomposition of the scanned data, we demonstrate that the DMA can generate a multitude of highly uncorrelated speckle patterns at a single frequency. In contrast, a dipole antenna with a fixed pattern can only generate such a highly uncorrelated set of patterns when operating over a large bandwidth. The experimental results of this paper suggest that DMAs can be used to capture a diversity of information at a single frequency which can be used for single frequency computational imaging systems, NLOS motion detection, gesture recognition systems, and more
Experimental Synthetic Aperture Radar with Dynamic Metasurfaces
We investigate the use of a dynamic metasurface as the transmitting antenna
for a synthetic aperture radar (SAR) imaging system. The dynamic metasurface
consists of a one-dimensional microstrip waveguide with complementary electric
resonator (cELC) elements patterned into the upper conductor. Integrated into
each of the cELCs are two diodes that can be used to shift each cELC resonance
out of band with an applied voltage. The aperture is designed to operate at K
band frequencies (17.5 to 20.3 GHz), with a bandwidth of 2.8 GHz. We
experimentally demonstrate imaging with a fabricated metasurface aperture using
existing SAR modalities, showing image quality comparable to traditional
antennas. The agility of this aperture allows it to operate in spotlight and
stripmap SAR modes, as well as in a third modality inspired by computational
imaging strategies. We describe its operation in detail, demonstrate
high-quality imaging in both 2D and 3D, and examine various trade-offs
governing the integration of dynamic metasurfaces in future SAR imaging
platforms
Prevalence and risk factors of HIV, hepatitis B virus and hepatitis C virus infections in drug addicts among Gorgan prisoners
The objective of the present study is to determine the prevalence of HIV, HBV and HCV in the addict prisoners in Gorgan city. In this cross-sectional study conducted between 2002-2003, a randomized sampling was done on 121 drug addict prisoners. A blood sample was taken from each case and serologic tests for HBV, HCV and HIV were done, then complementary tests for HIV (ELISA and Western-blot) were done. Physical examinations and face-to-face interviews were done. Chi-square and Exact-Fisher test were used for data analysis and relationships between factors. The prevalence of HIV, HCV and HBV were 5.8, 23.1 and 4.1%, respectively. Injection was the most common route of drug use. Marital status was significantly related to HIV and HCV infection. Tatooing and shared syringe use were significantly related to all these infections. Because of the high prevalence of HIV, HCV and HBV in the studied cases and tending to the high risk behaviors among the prisoners, it seems that more educational and preventive programs are needed to control the spread of these infections in the population
Systematic Physics-Compliant Analysis of Over-the-Air Channel Equalization in RIS-Parametrized Wireless Networks-on-Chip
Wireless networks-on-chip (WNoCs) are an enticing complementary interconnect
technology for multi-core chips but face severe resource constraints. Being
limited to simple on-off-keying modulation, the reverberant nature of the chip
enclosure imposes limits on allowed modulation speeds in sight of inter-symbol
interference, casting doubts on the competitiveness of WNoCs as interconnect
technology. Fortunately, this vexing problem was recently overcome by
parametrizing the on-chip radio environment with a reconfigurable intelligent
surface (RIS). By suitably configuring the RIS, selected channel impulse
responses (CIRs) can be tuned to be (almost) pulse-like despite rich scattering
thanks to judiciously tailored multi-bounce path interferences. However, the
exploration of this "over-the-air" (OTA) equalization is thwarted by (i) the
overwhelming complexity of the propagation environment, and (ii) the non-linear
dependence of the CIR on the RIS configuration, requiring a costly and lengthy
full-wave simulation for every optimization step. Here, we show that a
reduced-basis physics-compliant model for RIS-parametrized WNoCs can be
calibrated with a single full-wave simulation. Thereby, we unlock the
possibility of predicting the CIR for any RIS configuration almost
instantaneously without any additional full-wave simulation. We leverage this
new tool to systematically explore OTA equalization in RIS-parametrized WNoCs
regarding the optimal choice of delay time for the RIS-shaped CIR's peak. We
also study the simultaneous optimization of multiple on-chip wireless links for
broadcasting. Looking forward, the introduced tools will enable the efficient
exploration of various types of OTA analog computing in RIS-parametrized WNoCs.Comment: 10 pages, 7 figures, submitted to an IEEE Journa
Generating Information-Diverse Microwave Speckle Patterns Inside a Room at a Single Frequency With a Dynamic Metasurface Aperture
We demonstrate that dynamic metasurface apertures (DMAs) are capable of generating a multitude of highly uncorrelated speckle patterns in a typical residential environment at a single frequency. We use a DMA implemented as an electrically-large cavity excited by a single port and loaded with many individually-addressable tunable metamaterial radiators. We placed such a DMA in one corner of a plywood-walled L-shape room transmitting microwave signals at 19 GHz as we changed the tuning states of the metamaterial radiators. In another corner, in the non-line-of-sight of the DMA, we conducted a scan of the field generated by the DMA. For comparison, we also performed a similar test where the DMA was replaced by a simple dipole antenna with fixed pattern but generating a signal that spanned 19-24 GHz. Using singular value decomposition of the scanned data, we demonstrate that the DMA can generate a multitude of highly uncorrelated speckle patterns at a single frequency. In contrast, a dipole antenna with a fixed pattern can only generate such a highly uncorrelated set of patterns when operating over a large bandwidth. The experimental results of this paper suggest that DMAs can be used to capture a diversity of information at a single frequency which can be used for single frequency computational imaging systems, NLOS motion detection, gesture recognition systems, and more
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