Electrowetting technique is an actuation method for manipulating position and velocity of fluids in the microchannels. By combining electrowetting technique and a freestanding mode triboelectric ...nanogenerator (TENG), we have designed a self-powered microfluidic transport system. In this system, a mini vehicle is fabricated by using four droplets to carry a pallet (6 mm × 8 mm), and it can transport some tiny object on the track electrodes under the drive of TENG. The motion of TENG can provide both driving power and control signal for the mini vehicle. The maximum load for this mini vehicle is 500 mg, and its highest controllable velocity can reach 1 m/s. Freestanding TENG has shown excellent capability to manipulate microfluid. Under the drive of TENG, the minimum volume of the droplet can reach 70–80 nL, while the tiny droplet can freely move on both horizontal and vertical planes. Finally, another strategy for delivering nanoparticles to the designated position has also been demonstrated. This proposed self-powered transport technique may have great applications in the field of microsolid/liquid manipulators, drug delivery systems, microrobotics, and human-machine interactions.
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Fiber alignment is a key factor that determines the physical properties of nanofiber mats. In this work, SiC nanofiber mats with or without fiber alignment are fabricated via electrospinning and the ...microwave electromagnetic properties of their silicone resin composites (5 wt %) are investigated in 2–18 GHz. By comparing with the composite containing SiC whisker, it is found that the nanofiber mats show superior dielectric loss and a minimal reflection loss (RL) of around −49 dB at 8.6 GHz and 4.3 mm thickness, associated with a broad effective absorption (<−10 dB) bandwidth (EAB) of about 7.2 GHz at 2.8 mm thickness. Moreover, the performance can be further enhanced (RL = −53 dB at 17.6 GHz and 2.3 mm thickness) by aligning the nanofiber in the plane of mat, accompanied by the shift of absorption peak to higher-frequency direction and broader EAB up to 8.6 GHz at 3 mm. In addition, the stacking ways of aligned SiC nanofiber mats (either parallel or perpendicular) are proved to have a negligible effect on their microwave properties. Compared with parallel stacking of the aligned mats, cross-stacking (perpendicular) only leads to a slight drop of the attenuation ability. It confirms that alignment of nanofiber in the mats offers a more effective approach to improve the microwave absorption properties than changing the ways of stacking. Furthermore, it is worth mentioning that the low loading fraction (5 wt %) is a great advantage to reduce the weight as well as the cost for large-scale production. All of these facts indicate that the aligned SiC nanofiber mats can serve as a great lightweight and broad-band microwave absorber.
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Tyres made of natural rubber (NR) filled with silica (SiO
2
) are usually called energy-saving tyres with excellent resistance to wet slip and low friction resistance. It’s noted that the tyres tend ...to aging and produce static electricity caused by poor electrical and thermal conductivity of NR and SiO
2
. Therefore, it’s urgent to prepare NR/SiO
2
composites with enhanced thermal conductivity and antistatic performance. Here, a simple, efficient, and green method is applied to obtain graphene nanosheets (GNs) compatible well with NR, and the influence of GNs dosage on the properties of SiO
2
/NR composites are explored. The results show that GNs are helpful to improve mechanical properties and solvent resistance of SiO
2
/NR composites. Outstandingly, the thermal conductivity and electrical conductivity of 2.0wt%GNs/SiO
2
/NR composites are increased by 60% and 5 orders of magnitude compared with SiO
2
/NR composites, reaching to 0.29W·m
-1
·K
-1
and 4.2×10
-8
S/m respectively. It’s expected that GNs can become a candidate for improving thermal conductivity and antistatic properties of energy-saving tyres.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Sensitive monitoring and real‐time foot pressure mapping have important applications for medical treatment/diagnostics, sports training, and even security. In this work, a facile plantar pressure ...mapping system with a large pressure detection range using piezoelectric nanogenerators serving as the sensor array to acquire pressure signals, and a self‐designed data acquisition (DAQ) circuit board to process and wirelessly send the signals to a mobile terminal, such as a smart phone, are developed. Working with an application program developed in Android, the whole system can accurately monitor and visually display the real‐time pressure distribution during walking. More importantly, by combining a hybridized triboelectric–electromagnetic nanogenerator, a self‐powered, continuous, and real‐time pressure distribution monitoring system is developed, which provides a feasible solution for sport/exercise biomechanics information acquisition, injury prevention, and ulceration prediction in the feet.
Using a hybridized triboelectric–electromagnetic nanogenerator as power source and piezoelectric nanogenerator as pressure sensor, a self‐powered insole plantar mapping system is developed. The acquired pressure signals can be processed and sent wirelessly to a mobile terminal by a self‐designed data acquisition circuit, enabling to reflect the pressure distribution, dynamic motion, and mapping in real time.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Fe/SiC hybrid fibers have been fabricated by electrospinning and subsequent high-temperature (1300 °C) pyrolysis in Ar atmosphere using polycarbosilane (PCS) and Fe3O4 precursors. It is found that ...the introduction of Fe has had a dramatic impact on the morphology, crystallization temperature, and microwave electromagnetic properties of the hybrid fibers. In addition, the Fe particles have acted as catalyst sites to facilitate the growth of SiCO nanowires on the surface of the hybrid fibers. As a result, the permittivity and permeability have been enhanced effectively, and the high reflection loss (RL) has been achieved at a low frequency band with a thin absorber thickness. At an optimal PCS/Fe ratio of 3:0.5, the hybrid fiber/silicone resin composite (35 wt %) with a 2.25 mm absorber thickness exhibits a minimal RL of about −46.3 dB at 6.4 GHz. The wide frequency band (4–9.6 GHz) and thin absorber thickness (1.5–3.5 mm) for effective absorption (<−20 dB) prove that the Fe/SiC hybrid fiber is a promising candidate to work as a highly efficient and lightweight absorber in the C band (4–8 GHz).
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Hafnium carbide (HfC) phase, with a high melting point, excellent strength, and high electrical conductivity, could be a suitable addition to enhance the microwave absorption properties of ...one-dimensional silicon carbide (SiC) nanomaterials without sacrificing its high-temperature thermal stability. In the present work, HfC/SiC hybrid nanofiber mats with different HfC loading contents are fabricated by electrospinning and high-temperature pyrolysis. HfC hybrids with sizes of 5–10 nm are embedded in the SiC nanofibers. As the HfC content increases from 0 to 6.3 wt %, the average diameter of the fibers drops from 2.62 μm to 260 nm. Meanwhile, the electrical conductivity rises from 7.9 × 10–8 to 4.2 × 10–5 S/cm. Moreover, the flexibility of the nanofiber mats is also greatly improved, according to a 200-times 180° bending test. Furthermore, compared with pure SiC fiber mats, the HfC/SiC nanofiber mats possess much larger dielectric loss because of higher electrical conductivity. At the optimal HfC content of 2.5 wt %, the HfC/SiC nanofibers/silicon resin composite (10 wt %) exhibits a minimal reflection loss (RL) of −33.9 dB at 12.8 GHz and a 3 mm thickness with a broad effective absorption bandwidth (RL < −10 dB) of 7.4 GHz. The above results prove that introducing HfC into SiC nanofiber mats is an effective way to enhance their flexibility, dielectric properties, and microwave absorption performance.
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Understanding the physical requirements for a broad bandwidth is vital for the design of high-efficiency microwave absorber. Our recent works on silicon carbide (SiC) fiber mats-based absorbers imply ...that metal modification (e.g., Fe or Hf) could benefit their bandwidth effectively. For verification, we fabricated a Co/SiC fiber mat via a similar electrospinning process and subsequent pyrolysis at 1400 °C in Ar atmosphere. The results indicate that after Co modification, the SiC fiber mats show elevated permittivity and tangent loss. With a proper amount of Co adding, the mats could exhibit a wide bandwidth of around 8 GHz (ranging from 10 to 18 GHz) for effective absorption (reflection loss (RL) less than −10 dB) at 2.8 mm thickness. This is similar to our previous findings, confirming that metal modification could be an effective approach to extend the bandwidth of SiC mat absorbers. Explanations can be found through theoretical analysis with the quarter wavelength (λ/4) cancellation theory. It suggests that the declining permittivity (with the increase of frequency) is the key to keep the wavelength in material (λm) nearly unchanged within a frequency range. As a result, in this range, λ/4 cancellation could still be satisfied without changing thickness, which could explain the reasons for the broad bandwidth of metal-modified SiC fiber mats. With this model, it is further predicted that the effective absorption bandwidth could be even extended to be around 12 GHz with appropriate tangent loss. It should be emphasized that the implications obtained in this study could also be applicable to other dielectric absorbers. The requirement of permittivity and the proposed approach could serve as guidelines to achieve a wide bandwidth on a dielectric absorber relying on the λ/4 cancellation principle.
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A triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) were hybridized to harvest the human mechanical energy. By an effective conjunction of triboelectrification and ...electromagnetic induction, the hybridized nanogenerator with a radius of 2 cm and height of 1.2 cm could charge a 1,000 μF capacitor to 5.09 V after 100 cycles of vibration. This mini-sized hybrid nanogenerator could then be embedded in shoes to serve as an energy cell. Typical outdoor applications—including driving with a Global Positioning System (GPS) device, charging a Li-ion battery and a cell phone—were successfully demonstrated, suggesting its potential application in smart wearable electronics and future suits of soldiers.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Graphene nanosheets (GNs) were prepared by supercritical solvent intercalation method and cyclic stripping method under high pressure and stress. This “non‐chemical method” reduces impurities and ...avoids the destruction of graphene's intrinsic structure. In order to decrease the secondary stacking in processing, firstly GNs were dispersed in natural rubber (NR) latex to prepare NR/GNs concentrated master batch, and then combined with solid NR by mechanical blending. Since GNs have good dispersion in rubber matrix, a strong intermolecular force is formed between GNs and NR. Tensile strength, elongation at break, stress at 100% strain, stress at 300% strain, and tear strength of NR/GNs nanocomposites with 2 wt% GNs are enhanced 59.53%, 17.85%, 67.07%, 80.12% and19.20% respectively compared with NR. With more GNs, the NR/GNs nanocomposites exhibit lower Tg and better thermal stability. When the content of GNs in NR/GNs nanocomposites reaches 2 wt%, the Tg of nanocomposites drops about 2°C, and the remaining carbon at 600°C of nanocomposites increase by 3.07%. Moreover, It is demonstrated that the NR filled with 2 wt% GNs possess excellent thermal conductivity of 0.24 W m−1 K−1，which is a 50% increment compared with pure NR. Meanwhile, the electrical conductivity of the composites increases by four orders of magnitude than that of pure NR. These results clearly indicate that GNs can be expected to be manufactured at large scale and utilized in heat‐conducting and antistatic rubber.
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Flexible Fe3Si/SiC ultrathin fiber mats have been fabricated by electrospinning and high temperature treatment (1400 °C) using polycarbosilane (PCS) and ferric acetylacetonate (Fe(acac)3) as ...precursors. The crystallization degree, flexibility, electrical conductivity, dielectric loss and microwave absorption properties of the hybrid fibers have been dramatically enhanced by the introduction of Fe. Fe3Si nanoparticles with a diameter around 500 nm are embedded in SiC fibers. As the Fe3Si content increases from 0 to 6.5 wt%, the related saturation magnetization (Ms) values increase from 0 to 8.4 emu g−1, and the electrical conductivity rises from 7.9 × 10−8 to 3.1 × 10−3 S cm−1. Moreover, the flexibility of Fe3Si/SiC hybrid fiber mats is greatly improved and remains intact after 500 times 180°-bending testing. Compared with pure SiC fibers, the Fe3Si/SiC hybrid fibers process higher dielectric and magnetic loss, which would be further advanced as more Fe3Si phase is introduced. At the optimal Fe3Si content of 3.8 wt%, the Fe3Si/SiC fibers/silicon resin composite (5 wt%) exhibits minimal reflection loss (RL) of −22.5 dB at 16.5 GHz and 2.5 mm thickness with a wide effective absorption bandwidth (EAB, RL < −10 dB) of 8.5 GHz. The microwave absorption performance can be further promoted by multi component stacking fiber mat composites which contain both low and high Fe3Si content layers. Furthermore, the position of the microwave absorption bands can also be simply manipulated by designing the stacking components and structure.
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