Functional plastic films:nano-engineered composite based flexible microwave antennas with near-unity relative visible transmittance

Microwave antennas are essential elements for various applications,such as telecommunication,radar,sensing,and wireless power transport.These antennas are conventionally manufactured on rigid substrates using opaque materials,such as metal strips,metallic tapes,or epoxy pastes;thus,prohibiting their use in flexible and wearable devices,and simultaneously limiting their integration into existing optoelectronic systems.Here,we demonstrate that mechanically flexible and optically transparent microwave antennas with high operational efficiencies can be readily fabricated using composite nanolayers deposited on common plastic substrates.The composite nanolayer structure consists of an ultra-thin copper-doped silver film sandwiched between two dielectric films of tantalum pentoxide and aluminum oxide.The material and thickness of each constituent layer are judiciously selected such that the whole structure exhibits an experimentally measured averaged visible transmittance as high as 98.94%compared to a bare plastic substrate,and simultaneously,a sheet resistance as low as 12.5Ω/sq.Four representative types of microwave antennas are implemented:an omnidirectional dipole antenna,unidirectional Yagi-Uda antenna,low-profile patch antenna,and Fabry-Pérot cavity antenna.These devices exhibit great mechanical flexibility with bending angle over 70°,high gain of up to 13.6 dBi,and large radiation efficiency of up to 84.5%.The proposed nano-engineered composites can be easily prepared over large areas on various types of substrates and simultaneously overcome the limitations of poor mechanical flexibility,low electrical conductivity,and reduced optical transparency usually faced by other constituent materials for flexible transparent microwave antennas.The demonstrated flexible microwave antennas have various applications ranging from fifth-generation and vehicular communication systems to bio-signal monitors and wearable electronics.

PTX-symmetric metasurfaces for sensing applications

In this paper,we introduce an ultra-sensitive optical sensing platform based on the parity-time-reciprocal scaling(PT^-symmetric non-Hermitian metasurfaces,which leverage exotic singularities,such as the exceptional point(EP)and the coherent perfect absorber-laser(CPAL)point,to significantly enhance the sensitivity and detectability of photonic sensors.We theoretically studied scattering properties and physical limitations of the PTX-symmetric metasurface sensing systems with an asymmetric,unbalanced gain-loss profile.The PTLY-symmetric metasurfaces can exhibit similar scattering properties as their Pr-symmetric counterparts at singular points,while achieving a higher sensitivity and a larger modulation depth,possible with the reciprocal-scaling factor(i.e.,X transformation).Specifically,with the optimal reciprocalscaling factor or near-zero phase offset,the proposed PTX-symmetric metasurface sensors operating around the EP or CPAL point may achieve an over 100 dB modulation depth,thus paving a promising route toward the detection of small-scale perturbations caused by,for example,molecular,gaseous,and biochemical surface adsorbates.

Chemical-sensitive graphene modulator with a memory effect for internet-of-things applications

Modern internet of things(IoTs)and ubiquitous sensor networks could potentially take advantage of chemically sensitive nanomaterials and nanostructures.However,their heterogeneous integration with other electronic modules on a networked sensor node,such as silicon-based modulators and memories,is inherently challenging because of compatibility and integration issues.Here we report a novel paradigm for sensing modulators:a graphene field-effect transistor device that directly modulates a radio frequency(RF)electrical carrier signal when exposed to chemical agents,with a memory effect in its electrochemical history.We demonstrated the concept and implementation of this graphene-based sensing modulator through a frequency-modulation(FM)experiment conducted in a modulation cycle consisting of alternating phases of air exposure and ethanol or water treatment.In addition,we observed an analog memory effect in terms of the charge neutrality point of the graphene,Vcnp,which strongly influences the FM results,and developed a calibration method using electrochemical gate-voltage pulse sequences.This graphenebased multifunctional device shows great potential for use in a simple,low-cost,and ultracompact nanomaterial-based nodal architecture to enable continuous,real-time event-based monitoring in pervasive healthcare IoTs,ubiquitous security systems,and other chemical/molecular/gas monitoring applications.