Smart control is an attracting and important function for modern electromagnetic wave absorber. This paper presents the design, fabrication, and measurement of a frequency and bandwidth tunable metamaterial absorber (MA) in X-band. The unit cell of the MA consists of a microstrip resonator loaded with the varactors. Simulation and measurement results show that by tuning the bias voltage on the varactors, the peak absorption frequency can be tuned by 0.44 GHz with the peak absorption greater than 95%. Field and circuit model analysis is conducted to reveal the working mode and predict the absorbing frequency. After that, by specially designing the bias circuit so as to adjust the bias voltage on neighboring unit cells separately, dual resonance and absorption peaks occur, and the overall absorption bandwidth can thus be tuned conveniently by controlling the difference of the two resonance frequencies. The center absorbing frequency can also be tuned. Simulation and experiment results show that the 75% absorption (À6 dB reflection) bandwidth can be tuned from 0.40 GHz to 0.74 GHz, which is a two-fold tuning range. This work is believed to improve the state-of-the-art smart metamaterial absorber. V C 2015 AIP Publishing LLC.

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Recently, compressive sensing has been introduced to confocal Raman imaging to accelerate data acquisition. In particular, unsupervised compressive imaging methods do not require a priori knowledge of an object’s spectral signatures, and they are thus applicable to unknown or dynamically changing systems. However, the current methods based on either spatial or spectral undersampling struggle between spatial and spectral fidelities at high compression ratios. By exciting a sample with an array of focused laser beams and randomly interleaving the projection locations of the scattering, we simultaneously demonstrate a single-acquisition confocal Raman hyperspectral imaging with a high fidelity and resolution in spatial and spectral domains, at a compression ratio of 40–50. The proposed method is also demonstrated with suppressed noise and a smooth transition at the boundaries.

In this paper, an optically transparent and wideband absorber/reflector with switchable states and tunable frequency spectrum is presented. The proposed structure consists of a Polydimethylsiloxane (PDMS) layer with microchannel structures and an Indium Tin Oxide (ITO) layer as the metal panel. The switching function is implemented by controlling the injection and discharge of pure water, and the switchable frequency band of the absorbing and reflecting states ranges from 7.9 to 34.4 GHz with a fractional bandwidth of 125.2%. The tunable properties are achieved by changing the concentration of the injected saline water. In addition, the distributions of the electric field, the magnetic field and the power loss density are used to further understand the physical mechanism of the structure. Moreover, it also performs well under different polarizations and incident angles. For validation, a transparent and wideband absorber/reflector is fabricated and tested, and the simulated and measured results are consistent with each other.

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A reconfigurable absorber/reflector, which has optical transparency and broadband switching function, is developed based on structured water medium. The conductive indium tin oxide (ITO) coating is deposited on a thin polyethylene terephthalate (PET) film to act as the reflective backplane. Pure water is encapsulated by polydimethylsiloxane (PDMS) materials to construct structured water. The average optical transmittance is about 61.88%/56.44% in the visible spectrum of 380 – 760 nm with/without pure water. Based on the super-element configuration and the stacking technique, an obvious switching function from broadband absorption (12.47 – 28.43 GHz) to broadband reflection (12 – 30 GHz) can be attained under normal incidence through the injection and discharge of pure water,. Besides, the broadband switchable characteristics of the proposed structure remain effective for TE and TM modes when illuminated by oblique incident waves up to 45°. Moreover, the proposed switchable absorber/reflector shows good temperature stability and can work under different liquid temperatures. Furthermore, the excellent performance of the proposed design is demonstrated by both simulated and experimental results, exhibiting great potential as transparent smart windows in large-scale ground-based stealth systems.