Diffuse field cross-correlation in a programmable-metasurface-stirred reverberation chamber

Abstract

Programmable metasurfaces can endow complex scattering environments with reconfigurability. Here, we make use of these configurational degrees of freedom to retrieve the impulse response between two passive antennas via cross-correlation techniques. An ensemble of stirred chaotic wave fields in a reverberation chamber (RC) can play the role of thermal noise in passive Green's function retrieval. Instead of using a conventional mechanical mode stirrer, we generate the ensemble of RC configurations with random configurations of a programmable metasurface. We adapt the data processing of the diffuse field cross-correlation technique to this stirring mechanism, which is, given the size of the RC, nominally inefficient, and we investigate the convergence of the cross-correlated signals toward the impulse response. Finally, we apply our scheme to phaseless imaging in complex propagation environments, with potential applications in indoor context-awareness.

Experimentally realized physical-model-based frugal wave control in metasurface-programmable complex media

“…Our GFR-model’s ability to retrieve all essential information about unseen Green’s functions is reminiscent of algorithmically very different techniques that cross-correlate two time-domain recordings of a diffuse wave field at different receivers to recover the Green’s function between these receivers 48 , 49 . The noise can be emulated via different realizations of disorder in a chaotic cavity 50 , which has even been realized by randomly configuring a programmable metasurface 51 . These cross-correlation techniques require by construction broadband calibration data and typically only retrieve information about short (i.e., few-bounce) paths.…”

Passive Antenna Characterization Through Impedance Correlations in a Diffuse Field

“…A first experimental demonstration of electromagnetic Green's function retrieval in the microwave range has been performed in anechoic and reverberant cavities by computing the average cross-correlation of noise signals generated by a wideband diffuse thermal radiation, and the ability to detect and locate a scattering object solely using this thermal ambient has been demonstrated [7]. To increase the field intensity, an emitting antenna has then been used as a source; the equipartitioned field has been obtained while performing measurement within a reverberation chamber (RC) inducing field multiple scattering for different cavity configurations thanks to the mode-stirrer rotation [8] or a programmable metasurface [9]. The influence of antenna properties on the cross-correlation result has been highlighted using an antenna and an electrooptical probe as sensors [8].…”

Diffuse field cross-correlations: scattering theory and electromagnetic experiments

“…GFR is nowadays routinely applied to ambient noise measurements in seismology for surface wave tomography and landslide monitoring [13][14][15][16]. The GFR approach also opens the door to passive imaging with sound [17,18], microwaves [19,20] and light [21]. In disordered media, including chaotic cavities, multiple scattering of waves enhances the convergence of the crosscorrelation since the field illuminating the two probes is ideally a superposition of random plane waves with statistically homogeneous coefficients [7,11,22,23].…”

“…In disordered media, including chaotic cavities, multiple scattering of waves enhances the convergence of the crosscorrelation since the field illuminating the two probes is ideally a superposition of random plane waves with statistically homogeneous coefficients [7,11,22,23]. Because GFR is a self-averaging technique, a single or a few sources are therefore sufficient to recover the ballistic components of the broadband impulse response between two receivers [3,4,12,20,24].…”

“…Statistical approaches based on the energy conservation principle enable the extraction of the radiation efficiency or the directivity pattern of transmitting or receiving antennas [47]. In this context, GFR is a technique of potentially great interest to extract the coupling coefficient between two purely receiving antennas [3,20]. This approach could also accelerate measurements of the coupling coefficients between antennas of a large array since the technique avoids the requirement of turning each antenna successively into its transmitting and receiving modes.…”