the utilization of wide-ranging renewable energy. An enlightening idea has arisen over the latest publications to harvest environmental energy through employment of various piezoelectric, pyroelectric, and triboelectric materials. [1,2] Thereinto, piezoelectric materials, possessing the ability to capture mechanical energy with different amplitudes and frequencies, have been intensively developed to harvest energy from the ambient environment. [3,4] Energy harvesting is becoming a major technological trend not only for pure and clean energy production but equal importantly for aiding the development of energy autonomous monitoring systems like large area wireless access networks [5] or body wearable sensors that form key parts of the future Internet of Things ecosystem. Piezoelectric materials act as energy transducers through generating charges on the surfaces in response to an applied force. [6] In the past reports, ZnO nanowires were considered to be the excellent materials for developing nanogenerators compared with other traditional piezoelectric materials. Nonetheless, drawbacks to the prevalent application of ZnO nanowire materials are obvious too, such as the relatively low piezoelectric coefficient. [7] Furthermore widely used piezo-ceramic materials, despite their mechanical robustness and relatively high electromechanical coupling coefficient, exhibit also certain intrinsic major drawbacks such as limited mechanical flexibility, high fragility, and usually high content In this work, a novel design of poly (vinylidene fluoride)/carbon quantum dots (PVDF/CQDs) based flexible poling-free hybrid material system able to efficiently convert small amounts of mechanical energy into electricity through the intrinsic piezoelectric nanostructures is reported. The PVDF/ CQDs composite is fabricated through solution casting followed by a highpressure crystallization process. The introduction of 3D quasi-spherical CQDs has in situ induced the self-assembly of polymorphic substructures in the PVDF crystallites at high pressure, and piezoelectric 3D nanosheet arrays, 1D nanometer small sticks, and 1D nanowires, respectively, are formed in situ with the increase of CQDs concentration. Without any electrical polarization treatment, the maximum open-circuit voltage output density of the durable composite system reaches 19.2 V cm −2 and short-circuit current output density of 550 nA cm −2 , both far exceeding that of pure PVDF. Simultaneously, owing to the successful incorporation of CQDs, the material shows excellent fluorescent effect with high stability, and its multicolor photoluminescence is well retained even after the endurance for a rigorous treatment at high pressure and high temperature. The as-developed environmental friendly PVDF/ CQDs compound may diversify niche applications in a new-generation of self-powered autonomous optoelectronic devices, biosensors, cell imaging, and so on.
Abstract-The performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry ( 2 1 ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should be optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet the stringent telecom specifications.
ferrous core-shell nanoparticles consisting of a magnetic γ-fe 2 o 3 multi-nanoparticle core and an outer silica shell have been synthesized and covalently functionalized with Rhodamine B (RhB) fluorescent molecules (γ-fe 2 o 3 /Sio 2 /RhB NPs). The resulting γ-fe 2 o 3 /Sio 2 /RhB nps were integrated with a renewable and naturally-abundant cellulose derivative (i.e. cellulose acetate, CA) that was processed in the form of electrospun fibers to yield multifunctional fluorescent fibrous nanocomposites. The encapsulation of the nanoparticles within the fibers and the covalent anchoring of the RhB fluorophore onto the nanoparticle surfaces prevented the fluorophore's leakage from the fibrous mat, enabling thus stable fluorescence-based operation of the developed materials. These materials were further evaluated as dual fluorescent sensors (i.e. ammonia gas and pH sensors), demonstrating consistent response for very high ammonia concentrations (up to 12000 ppm) and fast and linear response in both alkaline and acidic environments. The superparamagnetic nature of embedded nanoparticles provides means of electrospun fibers morphology control by magnetic field-assisted processes and additional means of electromagnetic-based manipulation making possible their use in a wide range of sensing applications. Nanoparticle-based systems containing more than one functional components represent an active research field having a great potential in numerous technological applications 1. Among others, magnetic core-shell nanoparticles offer new opportunities in the biomedical field, catalysis and sensing 2-10. In particular, fluorescent-functionalized silica-coated core-shell magnetic nanoparticles attract high attention in imaging and sensing applications. In such multifunctional nanomaterials the fluorescent dye can be covalently anchored either onto the silica surface or doped into the matrix of the silica shell 2,3,11-13. Electrospinning has been one of the most versatile methods employed for generating nano-and microfibers 14-16. Its simplicity, scalability and high versatility renders this method very attractive in many scientific fields. Electrospun polymer-based organic-inorganic fibrous nanocomposites have been developed by many research groups and further evaluated in various fields including biomedicine 17-19 , catalysis 20-22 , sensing 23 , energy 24,25 and environmental protection 26-29. However, only a few examples appear to date on the fabrication of nanocomposite electrospun fibers with embedded core-shell ferrous nanoparticles 30,31. In one such example, core-shell Fe/ FeO nanoparticles have been incorporated within polyimide fibers aiming to produce fibrous nanocomposites
We discuss the background and technology of planar Bragg grating sensors, reviewing their development and describing the latest developments. The physical operating principles are discussed, relating device operation to user requirements. Recent performance of such devices includes a planar Bragg grating sensor design which allows refractive index resolution of RIU and temperature resolution of . This sensor design is incorporated into industrialised applications allowing the sensor to be used for real time sensing in intrinsically safe, high-pressure pipelines, or for insertion probe applications such as fermentation. Initial data demonstrating the ability to identify solvents and monitor long term industrial processes is presented. A brief review of the technology used to fabricate the sensors is given along with examples of the flexibility afforded by the technique.
We report the fabrication of optical channel waveguides in congruent lithium niobate single crystals by direct writing with continuous-wave ultraviolet frequency-doubled Ar+ laser radiation (244 nm). The properties and performance of such waveguides are investigated, and first results are presented.
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