Understanding the influences of defect states on gas adsorption on graphene is at the heart of developing graphene based gas sensors for practical applications. However, it has been challenging to experimentally discriminate the gas adsorptions induced by the defects on graphene, especially the charged impurities commonly found on the transferred graphene samples. Here, using a graphene transistor biased with the quasistatic gate voltage, this study experimentally measures the charge density and the scattering strength of the gas adsorbents on graphene and directly resolves the defect‐induced versus intrinsic gas adsorption processes on graphene for the first time. Furthermore, the elimination and the tuning of the defect‐induced gas adsorptions on graphene are also demonstrated via the chemical compensation process and the gate voltage technique, respectively. These findings provide critical experimental proofs and a versatile platform for understanding and manipulating the defect‐gas interactions on graphene, and could advance the developments of defect‐free and label‐free gas sensing applications using graphene transistors.

With the booming development of satellite applications, the giant constellations of low Earth orbit (LEO) satellites have introduced challenges for the data relay service. The multi-beam satellite not only offers concurrent access to a large number of objects, but can also meet the high data requirements toward specific coverage of the LEO constellation. However, the multi-beam satellite often faces the mismatch problem of spot allocation and data requirements, which can cause an overload traffic jam or a waste of resources. An optimization algorithm on spot beam allocation is necessary to automatically place the spot centers with appropriate beam widths in line with the density of the traffic demands and to realize the uniformity of the beam occupation. Compared with the conventional K-means algorithm, two adjustable parameters α and β are introduced: one for tuning the ratio of two components making up the distance matrix, and the other for setting the obligatory minimum number of objects per beam. In this paper, the whole process of the proposed method is demonstrated, including the establishment of the low-orbit satellite constellation model, the extraction of the distribution features, and the implementation and evaluation of the modified K-means algorithm. The results prove the validity of the proposed algorithm. A larger value of β with a relative smaller value of α tends to obtain the uniformity of beam occupation; the minimum standard deviation of objects per beam is achieved when α is 0.2 and β is 0.8. This demonstrates that the uniformity of objects per beam can be realized by adjusting the parameters of the distance determination matrix and the obligatory minimal number of objects in each beam. The impact of parameter range on the results is also analyzed.

This work demonstrates the design of an E-band waveguide duplexer and the fabrication process based on micromachining technology. To make the proposed solution practical, the error tolerance analysis and multipactor effect simulation were carried out. Compared with state-of-art technologies, three distinctive advancements have been achieved: (1) the design of a high-performance E-band duplexer and the corresponding fabrication process based on micromachining technology; (2) the demonstration of the RF performance simulation and the error tolerance analysis of the proposed fabrication process; and (3) the illustration of the multipaction phenomena and the counter measures to inhibit the effect. As such, the proposed portfolio of micromachining fabrication process and suppression scheme of multipaction can offer a practical approach for E-band waveguide duplexers.

This work marks the first performance analysis of structure optimization of piezoelectric disc antenna and its impact on the characteristics and performance. Compared with the state-of-art technology, three distinctive advances have achieved: (a) first demonstration of central perforation on piezoelectric disc to further reduce the resonance frequency of the acoustically driven antenna; (b) simulation results and discussion of the characteristic and performance of the proposed design; and (c) an outlook and feasibility analysis of spaceborne low-frequency telecommunication with acoustically driven antenna on satellites.