Active carbons have unique physicochemical properties, but their conductivities and surface to weight ratios are much poorer than graphene. A unique and facile method is innovated to chemically ...process biomass by “drilling” holes with H2O2 and exfoliating into graphene‐like nanosheets with HAc, followed by carbonization at a high temperature for highly graphitized activated carbon with greatly enhanced porosity, unique pore structure, high conductivity, and large surface area. This graphene‐like carbon exhibits extremely high specific capacitance (340 F g−1 at 0.5 A g−1) and high specific energy density (23.33 to 16.67 W h kg−1) with excellent rate capability and long cycling stability (remains 98% after 10 000 cycles), which is much superior to all reported carbons including graphene. Synthesis mechanism for deriving biomass into porous graphene‐like carbons is discussed in detail. The enhancement mechanism for the porous graphene‐like carbon electrode reveals that rationally designed meso‐ and macropores are very critical in porous electrode performance, which can network micropores for diffusion freeways, high conductivity, and high utilization. This work has universal significance in producing highly porous and conductive carbons from biomass including biowastes for various energy storage/conversion applications.
A graphene‐like porous activated carbon derived from a biomass fabricated, rationally designed chemical process, followed by carbonization at high temperature, exhibits a specific capacitance of 340 F g−1 at 0.5 A g−1 and high specific energy density (23.33–16.67 W h kg−1), with excellent capacity retention after 10 000 cycles, superior to other carbon electrodes.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A compact self-isolated multiple-input–multiple-output (MIMO) antenna system is proposed. It is based on a quarter-mode substrate integrated waveguide (SIW) cavity where two edges are shorted by ...metallic vias and the other edges are open. A narrow slot with a rotated angle of 45° is utilised to divide the single cavity into two equal eighth-mode sub-cavities. These sub-cavities are fed by two coaxial ports to construct the proposed MIMO antenna system. A self-isolated mechanism that cavity energy inputted by one port is radiated into free space rather than transmitted to the other port is first observed. High isolation between two antenna elements can be obtained without additional isolating or decoupling networks although they are contacted with each other. A fabricated prototype operating at 3.5 GHz achieves the measured port isolation of higher than 18.5 dB, envelope correlation coefficient (ECC) of less than 0.04, the peak gain of 4.6 dBi, and maximum efficiency of 79.2%. With advantages of compact size, high isolation, low ECC, and good radiation performance, the proposed self-isolated MIMO antenna system is a good candidate for wireless communication.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A compact substrate-integrated-waveguide (SIW) cavity multiple-input–multiple-output (MIMO) antenna with enhanced bandwidth and high isolation is proposed. It is based on a triangle half-mode SIW ...cavity with one open edge and two edges shorted by metallic vias. By etching three slots, the single cavity can be divided into four eighth-mode sub-cavities. Two large sub-cavities with the same size are excited by two coaxial ports to construct two antenna elements and a wide slot between them is utilised as the de-coupler. Therefore, high isolation can be obtained. On the other hand, cavity energy can be coupled from the excited sub-cavities to the unexcited sub-cavities due to two narrow T-shaped slots serving as the couplers. Therefore, enhanced bandwidth can be achieved by merging two coupled modes into the required operating band. A fabricated prototype centring at 3.51 GHz has been measured. With a compact size of 0.59λ0 × 0.59λ0, enhanced bandwidth of 160 MHz, high isolation of 19.5 dB, the antenna gain of 4.9 dBi, and radiation efficiency of 72.8%, the proposed design has potential applications for fifth-generation communication.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A bandwidth-enhanced four-antenna multiple-input–multiple-output (MIMO) system based on a substrate-integrated-waveguide (SIW) cavity is proposed. By etching two long rectangular slots on the top ...plane of the cavity, four quarter-mode sub-cavities with the same size are constructed and then individually fed by a coaxial port to form a four-antenna MIMO system. Suitable port isolation is achieved by optimising the length and width of these slots. To enhance bandwidth, a pair of back-to-back L-shaped slots is cut to split each sub-cavity into three smaller parts. Three resonant modes are generated in these parts and merged into the operating band. A sample with the overall size of 0.58λ0 × 0.58λ0 × 0.02λ0 has been fabricated. Measured bandwidth is enhanced from 80 to 230 MHz and measured isolation is better than 15.0 dB. Owing to covering the band of 3.40–3.60 GHz, the proposed antenna system has potential applications for fifth-generation communication.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A half‐mode (HM) substrate‐integrated‐waveguide (SIW) cavity antenna is designed for tri‐band multiple‐input‐multiple‐output (MIMO) applications. Three cavity edges are shorted by metal posts while ...one aperture is open to radiate cavity energy into free space. To meet MIMO applications, a T‐shaped slot is etched to split the single HM cavity into two equal SIW subcavities and then they are excited by coaxial feeding ports to realize two antenna elements. To obtain tri‐band operations, four additional rectangle slots are cut, which introduces six quarter modes with different resonating regions. With the cavity size of 0.20λ0 × 0.40λ0, a fabricated prototype exhibits three operating bands with center frequencies of 3.33, 4.09, and 4.72 GHz and peak gain of 4.51, 4.05, and 3.93 dBi. Moreover, the measured port isolation is higher than 18.26 dB and the measured envelope correlation coefficient is below 0.05 within the frequency of interest.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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