47 research outputs found
Phaseless computational imaging with a radiating metasurface
Computational imaging modalities support a simplification of the active
architectures required in an imaging system and these approaches have been
validated across the electromagnetic spectrum. Recent implementations have
utilized pseudo-orthogonal radiation patterns to illuminate an object of
interest---notably, frequency-diverse metasurfaces have been exploited as fast
and low-cost alternative to conventional coherent imaging systems. However,
accurately measuring the complex-valued signals in the frequency domain can be
burdensome, particularly for sub-centimeter wavelengths. Here, computational
imaging is studied under the relaxed constraint of intensity-only measurements.
A novel 3D imaging system is conceived based on 'phaseless' and compressed
measurements, with benefits from recent advances in the field of phase
retrieval. In this paper, the methodology associated with this novel principle
is described, studied, and experimentally demonstrated in the microwave range.
A comparison of the estimated images from both complex valued and phaseless
measurements are presented, verifying the fidelity of phaseless computational
imaging.Comment: 18 pages, 18 figures, articl
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
Computational polarimetric microwave imaging
We propose a polarimetric microwave imaging technique that exploits recent
advances in computational imaging. We utilize a frequency-diverse cavity-backed
metasurface, allowing us to demonstrate high-resolution polarimetric imaging
using a single transceiver and frequency sweep over the operational microwave
bandwidth. The frequency-diverse metasurface imager greatly simplifies the
system architecture compared with active arrays and other conventional
microwave imaging approaches. We further develop the theoretical framework for
computational polarimetric imaging and validate the approach experimentally
using a multi-modal leaky cavity. The scalar approximation for the interaction
between the radiated waves and the target---often applied in microwave
computational imaging schemes---is thus extended to retrieve the susceptibility
tensors, and hence providing additional information about the targets.
Computational polarimetry has relevance for existing systems in the field that
extract polarimetric imagery, and particular for ground observation. A growing
number of short-range microwave imaging applications can also notably benefit
from computational polarimetry, particularly for imaging objects that are
difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure
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
Algorithme de projection pour l’imagerie microonde à haute résolution en temps réel
National audienceUne technique de calcul de projection 2D d'images radar est présentée dans cet article. Dans de nombreux cas tels que les scanners d'aéroport, une projection d'image 3D est suffisante pour détecter les éléments visés et ap-porte plus d'informations qu'une simple coupe 2D, no-tamment lorsque la distance de l'objet n'est pas connue précisément. En réalisant une projection des voxels à re-construire sur un plan, il est possible de diminuer le temps de calcul et la mémoire nécessaires à l'obtention des images. Le principe théorique de cette méthode est dé-veloppé dans ce papier suivi de résultats issus de simulations. Enfin, les gains apportés en termes de temps de calcul sont présentés
Measurement of photon sorting at microwave frequencies in a cavity array metasurface
PublishedJournal ArticleWe present experimental results demonstrating the spatial sorting of incoming radiation in two spectral ranges. A metasurface composed of a periodically patterned metal of subwavelength thickness with dielectric inclusions concentrates and localizes electromagnetic fields near the surface. Light of the separate spectral bands is channeled into different geometrically tuned cavities within each spatially repeating unit cell. Excitation of cavity modes facilitates this simultaneous spatial- and spectral-selective absorption. The measured reflection and field profiles are presented and the spectral and spatial selectivity are shown. A method to apply these concepts to split radiation into three spectral bands is also proposed.This work was supported in part by the AFOSR Bioenergy project (FA9550-10-1-0350), in part by the NSF Industry/University Cooperative Research Center for Metamaterials (IIP-1068028), and in part by the EPSRC, U.K. funding through the QUEST project (ref: EP/I034548/1)
Computational Microwave Imaging Using 3D Printed Conductive Polymer Frequency-Diverse Metasurface Antennas
A frequency-diverse computational imaging system synthesized using
three-dimensional (3D) printed frequency-diverse metasurface antennas is
demonstrated. The 3D fabrication of the antennas is achieved using a
combination of PolyLactic Acid (PLA) polymer material and conductive polymer
material (Electrifi), circumventing the requirement for expensive and
time-consuming conventional fabrication techniques, such as machine milling,
photolithography and laser-etching. Using the 3D printed frequency- diverse
metasurface antennas, a composite aperture is designed and simulated for
imaging in the K-band frequency regime (17.5-26.5 GHz). The frequency-diverse
system is capable of imaging by means of a simple frequency-sweep in an-all
electronic manner, avoiding mechanical scanning and active circuit components.
Using the synthesized system, microwave imaging of objects is achieved at the
diffraction limit. It is also demonstrated that the conductivity of the
Electrifi polymer material significantly affects the performance of the 3D
printed antennas and therefore is a critical factor governing the fidelity of
the reconstructed images.Comment: Original manuscript as submitted to IET Microwaves, Antennas &
Propagation (2017). 17 pages, 8 figure