SiC Nanofiber Mat: A Broad-Band Microwave Absorber, and the Alignment Effect

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

All-Graphene-Based Highly Flexible Noncontact Electronic Skin

Noncontact electronic skin (e-skin), which possesses superior long-range and high-spatial-resolution sensory properties, is becoming indispensable in fulfilling the emulation of human sensation via prosthetics. Here, we present an advanced design and fabrication of all-graphene-based highly flexible noncontact e-skins by virtue of femtosecond laser direct writing (FsLDW). The photoreduced graphene oxide patterns function as the conductive electrodes, whereas the pristine graphene oxide thin film serves as the sensing layer. The as-fabricated e-skins exhibit high sensitivity, fast response–recovery behavior, good long-term stability, and excellent mechanical robustness. In-depth analysis reveals that the sensing mechanism is attributed to proton and ionic conductivity in the low and high humidity conditions, respectively. By taking the merits of the FsLDW, a 4 × 4 sensing matrix is facilely integrated in a single-step, eco-friendly, and green process. The light-weight and in-plane matrix shows high-spatial-resolution sensing capabilities over a long detection range in a noncontact mode. This study will open up an avenue to innovations in the noncontact e-skins and hold a promise for applications in wearable human–machine interfaces, robotics, and bioelectronics

Enhanced Flexibility and Microwave Absorption Properties of HfC/SiC Nanofiber Mats

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

All-Graphene-Based Highly Flexible Noncontact Electronic Skin

Noncontact electronic skin (e-skin), which possesses superior long-range and high-spatial-resolution sensory properties, is becoming indispensable in fulfilling the emulation of human sensation via prosthetics. Here, we present an advanced design and fabrication of all-graphene-based highly flexible noncontact e-skins by virtue of femtosecond laser direct writing (FsLDW). The photoreduced graphene oxide patterns function as the conductive electrodes, whereas the pristine graphene oxide thin film serves as the sensing layer. The as-fabricated e-skins exhibit high sensitivity, fast response–recovery behavior, good long-term stability, and excellent mechanical robustness. In-depth analysis reveals that the sensing mechanism is attributed to proton and ionic conductivity in the low and high humidity conditions, respectively. By taking the merits of the FsLDW, a 4 × 4 sensing matrix is facilely integrated in a single-step, eco-friendly, and green process. The light-weight and in-plane matrix shows high-spatial-resolution sensing capabilities over a long detection range in a noncontact mode. This study will open up an avenue to innovations in the noncontact e-skins and hold a promise for applications in wearable human–machine interfaces, robotics, and bioelectronics