The future of mobile communications looks exciting with the potential new use cases and challenging requirements 6th generation (6G) beyond wireless networks. Since beginning modern era communications, propagation medium has been perceived as a randomly behaving entity between transmitter receiver, which degrades quality received signal due to uncontrollable interactions transmitted radio waves surrounding objects. recent advent reconfigurable intelligent surfaces in enables, on other hand,...

Reconfigurable intelligent surfaces (RISs) are an emerging transmission technology for application to wireless communications. RISs can be realized in different ways, which include (i) large arrays of inexpensive antennas that usually spaced half the wavelength apart; and (ii) metamaterial-based planar or conformal whose scattering elements have sizes inter-distances much smaller than wavelength. Compared with other technologies, e.g., phased arrays, multi-antenna transmitters, relays,...

Future wireless networks are expected to constitute a distributed intelligent communications, sensing, and computing platform, which will have the challenging requirement of interconnecting physical digital worlds in seamless sustainable manner. Currently, two main factors prevent network operators from building such networks: (1) lack control environment, whose impact on radio waves cannot be customized, (2) current operation radios, consume lot power because new signals generated whenever...

Reconfigurable intelligent surfaces (RISs) have the potential of realizing emerging concept smart radio environments by leveraging unique properties metamaterials and large arrays inexpensive antennas. In this article, we discuss applications RISs in wireless networks that operate at high-frequency bands, e.g., millimeter wave (30-100 GHz) sub-millimeter (greater than 100 frequencies. When used networks, may a manner similar to relays. The present paper, therefore, elaborates on key...

We present an approach for subwavelength focusing of microwaves using both a time-reversal mirror placed in the far field and random distribution scatterers near point. The far-field is used to build time-reversed wave field, which interacts with medium regenerate not only propagating waves but also evanescent required refocus below diffraction limit. Focal spots as small one-thirtieth wavelength are described. one example application telecommunications, shows enhancement information...

We report the first experimental demonstration of time-reversal focusing with electromagnetic waves. An antenna transmits a $1\mathrm{\text{\ensuremath{-}}}\mathrm{\ensuremath{\mu}s}$ pulse at central frequency 2.45 GHz in high-$Q$ cavity. Another records strongly reverberated signal. The time-reversed wave is built and transmitted back by same acting now as mirror. found to converge its initial source compressed time. quality determined bandwidth spectral correlations field within

In this paper, we introduce a physics-consistent analytical characterization of the free-space path-loss wireless link in presence reconfigurable intelligent surface. The proposed approach is based on vector generalization Green's theorem. obtained model can be applied to two-dimensional homogenized metasurfaces, which are made sub-wavelength scattering elements and that operate either reflection or transmission mode. formulated terms computable integral depends distances, polarization radio...

With the development of next generation mobile networks, new research challenges have emerged, and technologies been proposed to face them. On one hand, reconfigurable intelligent surface (RIS) technology is being investigated for partially controlling wireless channels. RIS a promising improving signal quality by propagation electromagnetic waves in nearly passive manner. other ambient backscatter communications (AmBC) another that tailored address energy efficiency requirements Internet...

In recent years, time-reversal (TR) mirrors have been developed that create TR waves for ultrasonic transient fields propagating through complex media. A wave back propagates and refocuses exactly at its initial source. However, because of diffraction, even if the source is pointlike on a spot size cannot be smaller than half wavelength. Here, by using interpretation this limit, we show latter limitation can overcome replaced image. This new device acts as an acoustic sink absorbs wave. Here...

We introduce the resonant metalens, a cluster of coupled subwavelength resonators. Dispersion allows conversion wave fields into temporal signatures while Purcell effect permits an efficient radiation this information in far field. The study array wires using microwaves provides physical understanding underlying mechanism. experimentally demonstrate imaging and focusing from field with resolutions below diffraction limit. This concept is realizable at any frequency where resonators can be designed.

We present an experimental demonstration showing that, contrary to first intuition, the more scattering a mesoscopic medium is, information can be conveyed through it. used multiple input-multiple output configuration: multichannel ultrasonic time-reversal antenna is transmit random series of bits simultaneously different receivers which were only few wavelengths apart. Whereas transmission free error when occurs in propagation medium, rate huge homogeneous medium.

The theory of monochromatic time-reversal mirrors (TRM) or equivalently phase conjugate is developed for electromagnetic waves. We start from the fundamental time-symmetry Maxwell's equations. From this symmetry, a differential expression similar to Lorentz reciprocity theorem deduced. radiating conditions on TRM are expressed in terms 6-dimension Green's functions. To predict time reversal focusing antenna arrays, formalism that involves impedance matrix developed. show coupling can...

Reconfigurable intelligent surfaces (RISs) are an emerging field of research in wireless communications.A fundamental component for analyzing and optimizing RIS-empowered networks is the development simple but sufficiently accurate models power scattered by RIS.By leveraging general scalar theory diffraction Huygens-Fresnel principle, we introduce formulas electric RIS that modeled as a sheet electromagnetic material negligible thickness.The proposed approach allows us to identify conditions...

Multimode optical fibers (MMFs) have gained renewed interest in the past decade, emerging as a way to boost communication data rates context of an expected saturation current single-mode fiber-based networks. They are also attractive for endoscopic applications, offering possibility achieve similar information content multicore fibers, but with much smaller footprint, thus reducing invasiveness procedures. However, these advances hindered by unavoidable presence disorder that affects...

In this letter, time reversal is applied to wideband electromagnetic waves in a reverberant room. To that end multiantenna mirror (TRM) has been built. A 150MHz bandwidth pulse at central frequency of 2.45GHz radiated by monopolar antenna, spread due reverberation, recorded the TRM, reversed, and retransmitted. The time-reversed wave converges back its source focus both space. compression studied versus number antennas TRM bandwidth. focal spot also measured thanks an eight-channel receiving array.

We derive a general expression of the electric dyadic Green function in time-reversal cavity, based on vector diffraction theory frequency domain. Our gives rigorous framework to experiments using electromagnetic waves and suggests methodology design structures generating subwavelength focusing after time reversal.

Performing linear operations using optical devices is a crucial building block in many fields ranging from telecommunication to analogue computation and machine learning.For of these applications, key requirements are robustness fabrication inaccuracies reconfigurability.Current designs custom-tailored photonic or coherent circuits only partially satisfy needs.Here, we propose way perform by complex media such as multimode fibers thin scattering layers computational platform driven wavefront...

Sixth generation (6G) mobile networks may include new passive technologies, such as ambient backscatter communication or the use of reconfigurable intelligent surfaces, to avoid emission waves and corresponding energy consumption. On one hand, a surface improves network performance by adding electronically controlled reflected paths in radio propagation channel. other an system, device, named tag, communicates towards reader backscattering source (such TV tower). However, tag's backscattered...

Abstract The seismic waves emitted during granular flows are generated by different sources: high frequencies interparticle collisions and low global motion large scale deformation. To unravel these mechanisms, an experimental study has been performed on the dry, dense, quasi‐steady flows. were recorded using shock accelerometers flow dynamics captured with a fast camera. mechanical characteristics of particle analyzed, along intervals between correlations in particles' motion....

We show that all the spatiotemporal degrees of freedom available in a complex medium can be harnessed and converted into spatial ones. This is demonstrated experimentally through an instantaneous inversion, using broadband ultrasonic waves multiple scattering sample. theoretically inversion convergence governed by total number for fixed bandwidth demonstrate its use media investigation. believe our approach has potential sensing, imagery, focusing, telecommunication.

Abstract We develop a network‐based method for detecting and classifying seismovolcanic tremors. The proposed approach exploits the coherence of tremor signals across network that is estimated from array covariance matrix. applied to four half years continuous seismic data recorded by 19 permanent stations in vicinity Klyuchevskoy volcanic group Kamchatka (Russia), where five volcanoes were erupting during considered time period. compute analyze daily matrices together with their eigenvalues...

Abstract The seismic signals generated by rockfalls can provide information on their dynamics and location. However, the lack of field observations makes it difficult to establish clear relationships between characteristics signal source. In this study, scaling laws are derived from analytical impact models relate mass speed an individual impactor radiated elastic energy frequency content emitted signal. It appears that frequencies decrease when is viscoelastic or elastoplastic compared case...

Modern seismic networks are recording the ground motion continuously at Earth's surface, providing dense spatial samples of wavefield. The aim our study is to analyse these records with statistical array-based approaches identify coherent time-series as a function time and frequency. Using ideas mainly brought from random matrix theory, we coherence wavefield width covariance eigenvalue distribution. We propose robust detection method that could be used for analysis weak emergent signals...