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A facile method for preparing hierarchical carbon composites that contain activated carbon (AC), carbon nanospheres (CNSs), and carbon nanotubes (CNTs) for use as the electrode material in supercapacitors (SCs) was developed. The CNS/CNT network enabled the formation of three‐dimensional conducting pathways within the highly porous AC matrix, effectively reducing the internal resistance of an SC electrode. The specific capacitance, cyclability, voltage window, temperature profile during charging/discharging, leakage current, gas evolution, and self‐discharge of the fabricated SCs were systematically investigated and the optimal CNS/CNT ratio was determined. A 2.5 V floating aging test at 70 °C was performed on SCs made with various hierarchical carbon electrodes. Electrochemical impedance spectroscopy, postmortem electron microscopy, Raman spectroscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy analyses were conducted to examine the electrode aging behavior. A hierarchical carbon architecture with an appropriate AC/CNS/CNT constituent ratio could significantly improve charge‐discharge performance, increase cell reliability, and decrease the aging‐related degradation rate. [ABSTRACT FROM AUTHOR]

This article proposes a design of miniaturized high selectivity band‐pass filter by using a dual‐mode patch resonator with two pairs of uniform slots set in the four corners. The effect of the pairs of the slots on the resonant modes of the square patch resonator is investigated first. For filter design, the slots set in the four corners of the patch resonator are provided as the perturbation elements to tune the resonant modes and thus form the filter response. The pairs of the slots reduce the fundamental resonant frequency and thus miniaturize the filter size. The designed filter is simulated and measured at 1.95 GHz for the fifth generation applications with narrow bandwidth. High band selectivity is obtained due to the creation of transmission zeros near the passband edges. The filter performances are measured by network analyzer and the results are discussed. [ABSTRACT FROM AUTHOR]