Holographic metasurfaces can sense and alarm toxic gases, with integration onto flexible surfaces such as safety glasses.

Metamaterials open up various exotic means to control electromagnetic waves and among them polarization manipulations with metamaterials have attracted intense attention. As of today, static responses of resonators in metamaterials lead to a narrow-band and single-function operation. Extension of the working frequency relies on multilayer metamaterials or different unit cells, which hinder the development of ultra-compact optical systems. In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO₂), with a metasurface. Before the phase transition, VO₂behaves as a semiconductor and the metasurface operates as a quarter-wave plate at 0.468 THz. After the transition to metal phase, the quarter-wave plate operates at 0.502 THz. At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light. This work reveals the feasibility to realize tunable/active and extremely low-profile polarization manipulation devices in the terahertz regime through the incorporation of such phase-change metasurfaces, enabling novel applications of ultrathin terahertz meta-devices.

A compact and low-profile wearable antenna is presented for on-body wireless body area network (WBAN) applications. The proposed triangular patch antenna is designed using low-cost widely available vinyl polymer-based flexible substrate. The final antenna topology is obtained by the combination of Koch fractal geometry, meandering slits and defected ground structure, to achieve a novel hybrid structure with compact footprint, good structural conformability and enhanced impedance bandwidth to operate in the Industrial, Scientific, and Medical (ISM) band with center frequency at 2.45GHz. The fabricated prototype of the antenna has shown good agreement between numerical and experimental results. In comparison to state of the art prototypes, our design has more compact-form-factor of $\rm 0.318\lambda_o \times 0.318\lambda_o \times 0.004\lambda_o$ , along with 7.75% impedance bandwidth, a peak gain of 2.06dBi and overall radiated efficiency of 75%. For the assessment of Specific Absorption Rate (SAR) performance of our design, it is tested on realistic heterogeneous HUGO voxel model. Both numerical and experimental investigations revealed extremely good robustness to both human body loading and structural deformation, making it an ideal candidate for flexible and body-worn devices.

The focusing performance of a 40 nm-thick metasurface lens is experimentally demonstrated. The longitudinal multifoci flat metasurface lens is illuminated with a linearly polarized light (|LP>) beam at normal incidence. Three focal planes with circular polarization states (|L> and |R>) are observed. The theoretical intensity profile of the light behind the metalens in the y–z plane agrees well with theoretical predictions.