A great deal of engineering effort is focused on developing stretchable strain sensors for human motion monitoring and wearable devices. The ultrasensitivity and fast response under tiny strain (1%) while maintaining the working range remain the grand challenge. In this work, we propose an entirely stretchable strain sensor based on the sandwich sensing film, which is fabricated by vacuum filtration of silver nanowires (AgNWs)/ graphene/ AgNWs in sequence and the injection of liquid metal as electrodes. The novel sandwich sensing film endows the stretchable strain sensor high sensitivity under tiny strain (Gauge factor = 111.5 at 1%), fast response (<10 ms), relative large working range (0%–35%) with a maximum gauge factor of 1403.7, followed by good linearity, long-term durability, and the recovery property from being overstretched (>100%). The excellent performance is due to the slippage of the inner graphene under tiny strain, whereas the ‘sewing’ phenomenon of the outer AgNWs under larger strain. The sandwich structure illustrates a better combination of graphene and AgNWs than other hybrid methods, showing great potential in wearable devices and soft robotics.

Flexible strain sensors, as the core member of the family of smart electronic devices, along with reasonable sensing range and sensitivity plus low cost, have rose a huge consumer market and also immense interests in fundamental studies and technological applications, especially in the field of biomimetic robots movement detection and human health condition monitoring. In this paper, we propose a new flexible strain sensor based on thick CVD graphene film and its low-cost fabrication strategy by using the commercial adhesive tape as flexible substrate. The tensile tests in a strain range of [Formula: see text]30% were implemented, and a gage factor of 30 was achieved under high strain condition. The optical microscopic observation with different strains showed the evolution of cracks in graphene film. Together with commonly used platelet overlap theory and percolation network theory for sensor resistance modeling, we established an overlap destructive resistance model to analyze the sensing mechanism of our devices, which fitted the experimental data very well. The finding of difference of fitting parameters in small and large strain ranges revealed the multiple stage feature of graphene crack evolution. The resistance fallback phenomenon due to the viscoelasticity of flexible substrate was analyzed. Our flexible strain sensor with low cost and simple fabrication process exhibits great potential for commercial applications.

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Carbon fiber wound hydrogen tanks are widely used in the field of new energy, but their complex multilayer structure makes it difficult to conduct nondestructive testing/structural health monitoring (NDT/SHM). In this paper, electromagnetic tomography (EMT) is used for noncontact in situ defect detection on a carbon fiber wound hydrogen tank. According to its structural characteristics, an open U-shaped sensor array that fits the curvature of the tank body is designed. To improve the quality of reconstructed images, an iterative image reconstruction algorithm based on a composite sensitivity matrix (CSM) is proposed. To verify the performance of the method, the method in this paper is compared with linear back projection (LBP), Landweber iterative algorithm, and the Tikhonov regularization algorithm, and the image quality is evaluated by comparing the image relative error and correlation coefficient. Both simulated and experimental results show that the method proposed in this paper is more accurate in defect localization and higher in quality than traditional image reconstruction algorithms.