In this study, it was aimed to increase the piezoelectric and pyroelectric properties of electrospun polyvinylidene fluoride (PVDF) nanofibers simultaneously by using specific nanofillers. Graphene oxide (GO), graphene, and halloysite nanotubes with different concentrations (0, 0.05, 0.4, and 1.6% wt/wt) were combined with PVDF solution and were fabricated in the form of nanofibers through electrospinning. Pyroelectric properties of samples were measured by submerging sealed samples in hot water (360°K) and ice (270°K). The piezoelectric properties of the samples were evaluated through bending tests. The microstructural, mechanical, and thermal properties of the electrospun PVDF nanocomposite were investigated using scanning electron microscope, Instron instrument, and thermogravimetric analysis, respectively. To further support the experimental observations for generating electric voltage in the bended nanogenerator, the PVDF nanogenerator (PNG) was also modeled by a finite element analysis based on the theory of linear piezoelectricity using COMSOL Multiphysics simulation software. Experimental results showed that adding nanofillers could improve the piezoelectric and pyroelectric properties of all samples, associated with the increment of β-phase in the nanofibers. It was concluded that adding nanofillers could increase pyroelectricity about 50% more than piezoelectricity in pristine PVDF nanofiber web. The PNG containing 1.6 wt% GO showed the highest efficiency in terms of piezoelectricity and pyroelectricity. In addition, the results showed that the ratio of piezoelectric to pyroelectric coefficients was constant (~1.5) and it was independent of the nanofiller type and content. The effect of external force and vibration frequency on the output voltage was also investigated. Increasing the compressive force and vibration frequency caused a greater output voltage. Finally, the fabricated nanogenerator was integrated on insole and elbow to investigate its energy harvesting capabilities from body movement.
In this paper, two bandpass-bandpass diplexers, based on L-, T-and rectangular-shaped resonators are designed and analyzed, which are used to design a novel hybrid power amplifier (HPA) in 5G applications. By using the designed diplexers, the presented hybrid power amplifier structure can operate at two desired frequencies in two desired classes of operation. The equivalent circuits and transfer functions are extracted to study the behavior of the filters responses.Query However, the proposed analysis can be used to locate transmission zeros at desired frequencies, which can ease the design procedures of the diplexers at any desired frequency. The proposed HPA and diplexers are designed at 1.5 GHz and 2.1 GHz operating frequencies. To verify the results, one of the proposed diplexers is fabricated, in which the obtained measured results are in good agreement with the simulated results. The insertion losses for the fabricated diplexer are less than 0.7 dB and the isolation value is achieved better than 27 dB in the operating frequencies. The overall sizes of the proposed diplexers are about (0.165k g 9 0.198k g ) and (0.75k g 9 0.07k g ). The results of the designed HPA show that the proposed HPA has desirable specifications. The drain efficiency (DE) and power added efficiency (PAE) of the proposed HPA are 60% and 53% at 1.5 GHz operating frequency while, the DE and PAE are 65% and 51.5% at 2.1 GHz respectively.
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