Time-varying Metasurfaces for Broadband Spectral Camouflage

Abstract

The possibility of making an object invisible for detectors has become a topic of considerable interest over the past decades. Most of the studies so far focused on reducing the visibility by reshaping the electromagnetic scattering in the spatial domain. In fact, by manipulating the electromagnetic scattering in the time domain, the visibility of an object can also be reduced. Importantly, unlike previous studies on phase-switched screens and time-varying metasurfaces, where the effect is narrow band due to the dispersive resonance, for microwave frequency range, we introduce a broadband switchable metasurface integrated with PIN diodes. The reflection phase of the metasurface can be changed by approximately π over a fractional bandwidth of 76%. By modulating the metasurface quasi-randomly in the time-domain, the incident narrow-band signal is spread into a white noise-like spectrum upon reflection, creating a spectral camouflage. The broadband feature of the proposed time-varying metasurface can provide practical insight for various applications including radar stealth and ultrawide-band wireless communication.

Smart Doppler Cloak Operating in Broad Band and Full Polarizations

“…Recently, time-modulated metasurfaces have been verified that can be used to control dynamically the spectrum distribution of EM waves. [23][24][25][26][27][28][29][30] In particular, when the modulation waveform enables continuously linear variation of the reflection phase of metasurface in one modulation period T m , the incident frequency f i will be converted efficiently to a new frequency component f r upon reflection, and thus create a frequency shift Δf t = f r -f i (f r is the frequency of reflected waves). Under this modulation, the linearly varying reflection phase ϕ(t) of the metasurface is described as…”

Joint Multi‐Frequency Beam Shaping and Steering via Space–Time‐Coding Digital Metasurfaces

“…We showed that the switching, described by a space–time‐coding matrix, could be designed and optimized so as to attain simultaneous field manipulations in both the space and frequency domains, including harmonic beam steering and scattering‐signature reduction/control. This idea has resonated in the research community, and has already found a variety of applications, including programmable and reconfigurable nonreciprocity, [ 26 ] harmonic manipulations, [ 34,35 ] broadband spectral camouflaging, [ 36 ] wireless communications, [ 37 ] and analog computing. [ 38 ] Although most experimental validations to date are restricted to the microwave range, with the advent of increasingly faster switching schemes, for example, based on graphene [ 39,40 ] and vanadium dioxide, [ 41,42 ] applications to the terahertz range should be within reach.…”

Time-varying optical vortices enabled by time-modulated metasurfaces

“…Space-time coding has also been recently adopted to develop digital metasurfaces capable of light manipulation in space and frequency while offering nonreciprocity [56][57][58][59]. In addition to nonreciprocity, TMMs hold a great potential for a wide range of applications such as wavefront engineering [60][61][62][63], extreme energy accumulation [64], spectral camouflaging [65,66], wide band impedance matching [67,68], signal amplification [69], pulse shaping [70][71][72], and providing multiple access through multiplexing and multicasting [73,74]. A fundamental property of a TMM is frequency mixing which leads to conversion of an incident frequency (f 0 ) into higher-order frequency harmonics.…”