Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the graphene pressure sensor suffers a lot. This is one of the main obstacles towards graphene commercial applications. In this paper, we utilized polymethylmethacrylate (PMMA)/graphene heterostructure to isolate graphene from the ambient environment and enhance its strength simultaneously. PMMA/graphene pressure sensors, with the finite-depth cavities and the through-hole cavities separately, were made for comparative study. The through-hole device obtained a comparable sensitivity per unit area to the state of the art of the bare graphene pressure sensor, since there were no leaking cracks or defects. Both the sensitivity and stability of the through-hole sensor are better than those of the sensor with 285-nm-deep cavities, which is due to the sealed gas effect in the pressure cavity. A modified piezoresistive model was derived by considering the pressure change of the sealed gas in the pressure cavity. The calculated result of the new model is consistent with the experimental results. Our findings point out a promising route for performance optimization of graphene pressure sensors.

Virtual testability demonstration test has many advantages, such as low cost, high efficiency, low risk and few restrictions. It brings new requirements to the fault sample generation. A fault sample simulation approach for virtual testability demonstration test based on stochastic process theory is proposed. First, the similarities and differences of fault sample generation between physical testability demonstration test and virtual testability demonstration test are discussed. Second, it is pointed out that the fault occurrence process subject to perfect repair is renewal process. Third, the interarrival time distribution function of the next fault event is given. Steps and flowcharts of fault sample generation are introduced. The number of faults and their occurrence time are obtained by statistical simulation. Finally, experiments are carried out on a stable tracking platform. Because a variety of types of life distributions and maintenance modes are considered and some assumptions are removed, the sample size and structure of fault sample simulation results are more similar to the actual results and more reasonable. The proposed method can effectively guide the fault injection in virtual testability demonstration test.

Multidirectional monitoring is highly expectable for stretchable strain sensors by which the randomly orientated cracks or the maximum strain of all directions need to be accommodated. Many current types of research exploit laminated sensors and rosette designs to obtain the desired behavior in several discrete directions. However, this can lead to complex fabricating and resolving processes, as well as significant measurement errors. Our work proposes an isotropic stretchable strain (ISS) sensor that utilizes the in-plane curved sensing film from graphene/silver nanowires (AgNWs), which exhibits uniform sensitivity in all directions within 30 ^∘ and the potential extending to 360 ^∘ . The ISS sensor, whose curved shape is optimized based on splines and the quantitative sensing model, is fabricated by a flash stamp machine and followed by vacuum filtration. Experimental results show that the ISS sensor possesses equivalent sensing properties in 30 ^∘ with excellent linearity and durability. Thus our customized sensor is applied to multidirectionally monitor the stretchable surface without consideration for the sensor orientation and the resolving process. Most importantly, the ISS sensor and its design method provide an efficient route for future sensor design with expected properties, not limited to isotropy.

In aviation, aerospace, and other fields, nanomechanical resonators could offer excellent sensing performance. Among these, graphene resonators, as a new sensitive unit, are expected to offer very high mass and force sensitivity due to their extremely thin thickness. However, at present, the quality factor of graphene resonators at room temperature is generally low, which limits the performance improvement and further application of graphene resonators. Enhancing the quality factor of graphene resonators has emerged as a pressing research concern. In a previous study, we have proposed a new mechanism to reduce the energy dissipation of graphene resonators by utilizing phononic crystal soft-supported structures. We verified its feasibility through theoretical analysis and simulations. This article focuses on the fabrication of a phononic crystal soft-supported graphene resonator. In order to address the issues of easy fracture, deformation, and low success rate in the fabrication of phononic crystal soft-supported graphene resonators, we have studied key processes for graphene suspension release and focused ion beam etching. Through parameter optimization, finally, we have obtained phononic crystal soft-supported graphene resonators with varying cycles and pore sizes. Finally, we designed an optical excitation and detection platform based on Fabry–Pérot interference principle and explored the impact of laser power and spot size on phononic crystal soft-supported graphene resonators.

It is difficult to diagnose the faults, especially multiple faults, in redundant systems by traditional diagnostic strategies. So the problem of multiple fault diagnostic strategy for redundant system was researched in this paper. Firstly, the typical characters of multiple faults (minimal faults) were analyzed, and the problem was formulated. Secondly, a pair of two-tuples were applied to denote the possible and impossible diagnostic conclusion at different diagnostic stages respectively, and a multiple fault diagnostic inference engine was constructed based on Boolean logic. The inference engine can determine the system diagnostic conclusions after executing each test, and determine whether a repair action was needed, and further determine whether a next test was needed. Thirdly, a method determining the next best test was presented. Based on the proposed inference engine and test determining method, a multiple fault diagnostic strategy was constructed. Finally, a simulation case and a certain flight control system were applied to illustrate the proposed diagnostic strategy. The simulation and practical data computational results show that the presented diagnostic strategy can diagnose multiple faults in redundant systems effectively and it is of certain application value.