Diffuse field cross-correlations: Scattering theory and electromagnetic experiments

The passive estimation of impulse responses from ambient noise correlations arouses increasing interest in seismology, acoustics, optics and electromagnetism. Assuming the equipartition of the noise field, the cross-correlation function measured with non-invasive receiving probes converges towards the difference of the causal and anti-causal Green’s functions. Here, we consider the case when the receiving field probes are antennas which are well coupled to a complex medium – a scenario of practical relevance in electromagnetism. We propose a general approach based on the scattering matrix formalism to explore the convergence of the cross-correlation function. The analytically derived theoretical results for chaotic systems are confirmed in microwave measurements within a mode-stirred reverberation chamber. This study provides new fundamental insights into the Green’s function retrieval technique and paves the way for a new technique to characterize electromagnetic antennas.French Agence Nationale de la Recherche (reference ANR-17- ASTR-0017); European Union (European Regional Development Fund (ERDF)), French region of Brittany and Rennes Métropole (CPER Project SOPHIE/STIC & Ondes); Institut Universitaire de France (IUF)

Reconfigurable Intelligent Surfaces for Rich Scattering Wireless Communications: Recent Experiments, Challenges, and Opportunities

Recent advances in the fabrication and experimentation of reconfigurable intelligent surfaces (RISs) have motivated the concept of the smart radio environment, according to which the propagation of information-bearing waveforms in the wireless medium is amenable to programmability. Although the vast majority of recent experimental research on RIS-empowered wireless communications gravitates around narrowband beamforming in quasi-free space, RISs are foreseen to revolutionize wideband wireless connectivity in dense urban as well as indoor scenarios, which are usually characterized as strongly reverberant environments exhibiting severe multipath conditions. In this article, capitalizing on recent physics-driven experimental explorations of RIS-empowered wave propagation control in complex scattering cavities, we identify the potential of the spatio-temporal control offered by RISs to boost wireless communications in rich scattering channels via two case studies. First, an RIS is deployed to shape the multipath channel impulse response, which is shown to enable higher achievable communication rates. Second, the RIS-tunable propagation environment is leveraged as an analog multiplexer to localize non-cooperative objects using wave fingerprints, even when they are outside the line of sight. Future research challenges and opportunities in the algorithmic design and experimentation of smart rich scattering wireless environments enabled by RISs for sixth generation wireless communications are discussed. © 1979-2012 IEEE

Beyond CPA: A General Theory of Reflectionless Scattering

International audienceCoherent Perfect Absorption is one form of reflectionless scattering, involving transduction of an adapted input field. We present a general theory of reflectionless scattering, which includes CPA, based on choosing a subset of input channels and requiring no backscattering into them. We show that infinitely many such solutions exist at complex frequency, can be calculated efficiently, and can be made accessible via tuning a single structural parameter. Optimization of a parameterized structure can achieve high quality signal routing. © 2023, META Conference. All rights reserved

Beyond CPA: A General Theory of Reflectionless Scattering

International audienceCoherent Perfect Absorption is one form of reflectionless scattering, involving transduction of an adapted input field. We present a general theory of reflectionless scattering, which includes CPA, based on choosing a subset of input channels and requiring no backscattering into them. We show that infinitely many such solutions exist at complex frequency, can be calculated efficiently, and can be made accessible via tuning a single structural parameter. Optimization of a parameterized structure can achieve high quality signal routing. © 2023, META Conference. All rights reserved