Achieving the broadband response of metamaterial absorbers has been quite challenging due to the inherent bandwidth limitations. Herein, the investigation was made of a unique kind of visible light metamaterial absorber comprising elliptical rings-shaped fractal metasurface using tungsten metal. It was found that the proposed absorber exhibits average absorption of over 90% in the visible wavelength span of 400-750 nm. The features of perfect absorption could be observed because of the localized surface plasmon resonance that causes impedance matching. Moreover, in the context of optoelectronic applications, the absorber yields absorbance up to ~ 70% even with the incidence obliquity in the range of 0°-60° for transverse electric polarization. The theory of multiple reflections was employed to further verify the performance of the absorber. the obtained theoretical results were found to be in close agreement with the simulation results. in order to optimize the results, the performance was analyzed in terms of the figure of merit and operating bandwidth. Significant amount of absorption in the entire visible span, wide-angle stability, and utilization of low-cost metal make the proposed absorber suitable in varieties of photonics applications, in particular photovoltaics, thermal emitters and sensors. In recent years, optical metamaterials have gained considerable attention in both the engineering and scientific lexicons owing to the exotic electromagnetic (EM) response, that led to varieties of technological applications 1-6. As has been in reports, these artificially engineered materials allow the versatile utility to manipulate the amplitude, phase, and polarization of the incidence radiation at a deep subwavelength scale 7. Metamaterials are generally comprised of nano-resonators, scatterers and meta-molecules of different size, shape, geometry, orientation, and arrangement. Within the context, the negative refractive index (RI)-based metasurfaces enable intriguing applications in super lensing 8 , planar filters 3 , optical cloaking 9,10 , wavefront manipulation 11,12 , optical chirality 13 , medical imaging 14 , and perfect absorption 15-17. These are also tremendously exploited in various other EM applications, namely asymmetric transmission, plasmon-induced transparency, holography, and bio-sensing 6,17-19. Extensive studies have been reported on metamaterial absorbers operating in different frequency regimes 20-22 owing to the prevalent applications in bolometer, holograms, stealth technology, solar energy harvesting, wireless communications, and sensors 15-17,23-27. From the perspective of absorption bandwidth, the narrowband metamaterial absorbers covering the visible and infrared (IR) regimes find applications, such as thermal emission manipulation, nano-antennas, sensors, and resonators 28,29. On the other hand, wideband absorbers have potentials in solar energy converters, artificial colors, thermal emitters, and many other optoelectronic applications 30,31. Within the context, photovoltaics have im...

be switched between an opaque and transparent state with the application of a voltage. Furthermore, their compatibility with cost-effective production processes such as roll-to-roll processing has ensured their successful deployment as a "smart window" technology. In contrast to multilayered electrochromic devices, PDLC technology is typically based upon a single-layered film that consists of liquid crystal (LC) droplets suspended in a polymer matrix. [6][7][8] The most common process employed to manufacture PDLC films involves the phase separation of a homogeneous mixture of LC and prepolymer, typically through a photopolymerization-induced phase separation technique (PIPS). This process can be used to form large area PDLCs films, which typically allows for a wide degree of control over droplet size and shape when compared to emulsification or thermal/solvent-induced phase separation techniques. [9][10][11][12] For smart glass and window applications, the size of the LC droplet after phase separation is generally within the range of 1-20 µm. [13,14] These LC droplets lack any preferential macroscopic orientation between LC domains. By matching the refractive index of the polymer matrix to one of the refractive indices of the LC, typically the ordinary refractive index, then a transparent state can be obtained by reorienting the LC director with an applied electric field so that the refractive indices of the LC droplets and the polymer binder match. [11,15] Even though the PIPS technique provides flexibility in terms of the phase separation process, a drawback lies in the inherent homogeneity that results from the mixing and coating procedures, which produces films consisting of a single LC and polymer formulation. To obtain PDLC films with spatially varying properties, the photopolymerization process has to be performed with the aid of a photomask or hologram to create patterns or variations in the film morphology. [16,17] Patterned PDLCs have attracted interest in recent years and several attempts have been made to manufacture them. Among the fabrication processes reported, irradiation of the material with coherent light allows for the use of holographic masks, which enables light with a structured intensity to be applied to the films. [17][18][19][20] Additionally, if the LC host is doped with an azo dye the use of a linearly polarized light source during the photopolymerization process can cause the LC director to adopt a preferential microscopic orientation following phase separation and the formation of a polymer binder. [21,22] Another method Conventional polymer dispersed liquid crystal (PDLC) films have been successful as electrically-switchable screens for privacy applications. However, spatial patterning of the films so as to generate a visually appealing design, logo, or image typically requires intricate fabrication processes, such as the use of prefabricated photomasks that do not allow for on-demand designs. Herein is reported on the fabrication and characterization of spatially patterned PDLC "pix...

In this communication, the fabrication of electrically tunable bifocal liquid crystal (LC) microlenses using drop‐on‐demand inkjet printing is demonstrated. By treating the glass substrate with a homeotropic alignment layer, the printed droplets are found to form plano‐convex lenses with focal lengths in the range of 220–463 µm, depending upon the number of droplets deposited at each location on the substrate. The precision of the process allows for the microlenses to be deposited in between in‐plane indium tin oxide electrodes. In the presence of a high amplitude electric field, the director within the LC droplets is observed to align with the direction of the applied field, but without any accompanying distortion in the droplet profile. However, these changes in the LC director alignment are found to result in a bifocal behavior rather than a continuous change in the focal length. It is also found that there exists a range of voltages for which two focal planes are observed.

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Temperature sensors based on the principle of a change of resistance are fabricated on polyethylene terephthalate (PET) substrates using a silver nanoparticles (AgNPs)-based ink using a bespoke drop-on-demand (DoD) electrohydrodynamic (EHD) printer. Two sensors consisting of either a single or double layer of silver were deposited using EHD printing and were found to exhibit an internal resistance of a few hundred ohms for the double-layer sensor compared to 1 kΩ for the single-layer sensor. The achieved pattern width was almost half the size of nozzle internal diameter (160 μm), and printed without treatment of substrate and nozzle. The sensors were characterized over a temperature range of 20°C to 110°C. Both sensors showed a linear behavior with low hysteresis within the temperature ranges considered in this study and are found to recover the nominal resistance value with good reproducibility. The double-layer sensor showed high sensitivity with a temperature coefficient of resistance (TCR) of 3.4×10-3 ℃−1, which is an order of magnitude larger than that observed for the single-layered sensor with a TCR of 8.41×10-4 ℃−1. The sensors were also tested in a controlled humid environment and results are presented on the dependence of the internal resistance on the level of humidity. The proposed flexible printed sensors are promising for temperature monitoring systems and wearable technologies.