A Reconfigurable Chaotic Cavity With Fluorescent Lamps for Microwave Computational Imaging

Abstract

Several computational imaging systems have recently been proposed at microwave and millimeter-wave frequencies enabling a fast and low cost reconstruction of the scattering strength of a scene. The quality of the reconstructed images is directly linked to the degrees of freedom of the system which are the number of uncorrelated radiated patterns that sequentially sample the scene. Frequency diverse antennas such as leaky chaotic cavities and metamaterial apertures take advantage of the spectral decorrelation of transmitted speckle patterns that stems from the reverberation within a medium. We present a reconfigurable chaotic cavity for which the boundary conditions can be tuned by exciting plasma elements, here commercial fluorescent lamps. The interaction of electromagnetic waves with a cold plasma is strongly modified as it is ionized. Instead of being transparent to incident waves, it behaves theoretically as a metallic material. The independent states of the cavity obtained using a differential approach further enhance the degrees of freedom. This relaxes the need of a cavity with a large bandwidth and/or high quality factor. Experimental results validate the use of fluorescent lamps, and its limitations are discussed. Images of various metallic objects are provided to illustrate the potentialities of this promising solution.

Frequency‐Controlled Focusing Using Achromatic Metasurface

“…[23][24][25][26] Focus-scanning technology realized by an individual metadevice has important applications, such as multiple modes of phased-array radar scanning, [27] synthetic aperture radar (SAR) imaging, [28][29][30][31] sensing, and communications. [32,33] However, the reported focusing meta-devices [34,35] usually work only at a target frequency or a particular range of frequencies; therefore, these cannot achieve a high broad bandwidth performance. [11,24,36,37] Besides, the focal plane of such designs cannot be effectively controlled over the entire operating frequency band.…”

Coherence Reduction of the Measurement Matrix in Microwave Computational Imaging by Introducing Polarization Diversity

“…In conventional configurations, the aperture elements are unitarily polarized, making θ cell fixed to 0. This makes P equivalently independent of the illumination polarization, because the alteration ofp inc only contributes to a factor that is ignorable due to its invariance in space:c By comparison with Equation (13), Equation (15) shows that the two sets of uncorrelated functions degenerate whenP evolves to a function unrelated top inc . In other words, the additional degree of freedom in the generation of h disappears together with the PD.…”

“…Before ending up this section, it is worth briefly discussing the limitation of the proposed formulation. Due to the presence of the convolutions in k-space, a further decomposition of Equations (14) and (15) seems to be quite difficult. Hence, it fails to isolate P and give an explicit formulation on how the mutual coherences in Equation (2) are reduced by introducing PD to aperture elements.…”

“…This illuminating work implies that mechanical rotations can be a practicable approach to the coherence reduction at an acceptable cost. Recently, a very innovative aperture with reconfigurable chaotic cavity was proposed, in which the boundary of the cavity is tuned by switching on/off the fluorescent lamps inserted into the cavity as reconfigurable plasma scatters [15]. The switching status of the lamps brings additional degrees of freedom in the generation of the excitation diversity, which therefore relaxes the requirement of high Q factors.…”

Ghost Image Removal Using Physical Layer Spatial Asymmetry in Frequency-Diverse Computational Imaging

“…Computational imaging is the process through advanced processing algorithms to reconstruct images from a set of indirect measurements [1][2][3][4][5][6][7][8]. In contrast to conventional imaging modalities with a limited data acquisition speed, such as synthetic aperture radar [9][10][11], and a complex hardware layer, such as phased arrays [12,13], frequencydiverse computational imaging has recently emerged as a promising alternative [14][15][16][17][18][19][20][21].…”