Systems For Numerous Applications Research Articles

Ultrahigh‐Output Triboelectric and Electromagnetic Hybrid Generator for Self‐Powered Smart Electronics and Biomedical Applications

AbstractBiomechanical energy harvesting shows great potential in the fields of smart electronics and biomedical Internet of Things. However, it is a significant challenge to develop a biomechanically driven energy harvester with high output power and fast charging as a sustainable power source for extended practical applications. Herein, an ultrahigh‐output triboelectric and electromagnetic hybrid generator (UHO‐TEHG) is developed to efficiently harvest biomechanical energy and provide self‐powered systems for numerous applications. The Halbach magnet array is used to concentrate additional magnetic flux in the coil and significantly enhance electromagnetic performance, while the novel poly(ethylene oxide) nanofibers enhance the triboelectric performance. Through the implementation of a mechanical spring‐mass model, and rational integration of electromagnetic and triboelectric generators, the UHO‐TEHG can provide an excellent output power of 1.02 W. Compared with existing mechanical energy harvesting devices, the fabricated device exhibits a much faster battery charging performance. Experimental results reveal remarkable performance related to biomechanical energy harvesting during walking, running, hiking, mountaineering, and self‐powered wireless human motion sensor. Real‐time charging of smartphones, smartwatches, Buds Live, and iTag via customized power management circuits is demonstrated. In addition, the fabricated UHO‐TEHG demonstrates the capability to power healthcare monitoring systems using a laser‐induced hierarchical carbon nanofiber‐based e‐tattoo sensor.

Optimization of Seebeck coefficients of strain-symmetrized semiconductor heterostructures

A nonmonotonic thermopower (S) as a function of the carrier concentration (ne) has been reported for III–V semiconductor superlattices (SLs), deviating from the Pisarenko relation. However, |S| has been shown to decrease with increasing ne in n-type Si/Ge heterostructures, the widely used systems for numerous applications. Here, we illustrate that S of a SinGem SL, with n Si and m Ge monolayers, can deviate from the Pisarenko relation depending on the period and the composition; for example, oscillations of S of a Si12Ge12 SL reach a peak |S|=540 μV/K at ne=1.3×1020 cm−3, 5.4 times higher than that of bulk Si at the same doping level. Additionally, S shows an interesting sign-change nature at certain carrier concentrations. We demonstrate the direct relationship between the electronic structure and S of strain-symmetrized Si/Ge SLs using two independent modeling approaches. We anticipate that this relationship will provide insight into fully exploiting S as a tool to control electronic properties of Si/Ge heterostructures as well as future technology-enabling materials. Furthermore, we expect that this analysis will encourage future investigations to enhance thermoelectric properties of a broad class of semiconductor SLs in the high-doping regime.

Effect of the modified silica on the conductivity and sensory properties of polyaniline nanocomposites

The introduction of nanosized fillers into composites with conductive polymers allows them to control physical and chemical characteristics of these polymers. Silica nanoparticles due to its remarkable properties, which include large ratio of surface area to volume, excellent chemical stability, low cost of synthesis, and low toxicity, especially convenient surface modification, have attracted much attention of researchers. Such materials may be as excellent platforms for development of smart sensing systems for numerous applications in analytical chemistry and bioanalysis, in medical diagnostics and therapy, environmental and food analysis, security. It is known that the presence of nanosized silica in the structure of hybrid polymeric composites can not only radically change the structure, but also lead to improved mechanical characteristics, sorption capacity, increase or decrease in specific conductivity. In this work the method of polymerization filling “in situ” was used for preparation of the hybrid composites of polyaniline with nanoparticles of silica modified by titanium (TAC-7) and phosphorus (F-2.1) compounds, studied their morphology, electrical and moisture absorption properties. Influence of the content of inorganic component in composites on their specific conductivity, activation parameters of conductivity and their changes under the action of moisture were studied. It is shown that the filler content of 1–4% increases the electrical conductivity of composites and the incorporation of modified nanoparticles F-2.1 helps stabilize the resistivity of nanocomposites at high humidity. The resistivity change less than 2% was observed throughout the whole range of possible moisture, therefore the obtained modified material can be recommended for using in the resistive sensors operating in the condition of high humidity. Moreover, F-2.1 enhances sensitivity of polymer matrix to hydrogen chloride vapors. So, the possibility of using chemically deposited thin films of polyaniline/modified silica nanocomposite for the optical gas sensors production for various purposes, including monitoring the state of environments in real conditions of atmosphere, is shown.

Mutual Exclusion in MANETs Using Quorum Agreements

The quorum agreement has been used in static distributed systems for numerous applications like mutual exclusion, distributed commit, and replication. The article proposes a framework to use quorum agreement in mobile ad hoc networks. The correctness proof, complexity analysis, and simulation measurements have also been presented.