Skin-inspired flexible wearable acceleration sensors attract much attention due to their advantages of portability, personalized and comfortable experience, and potential application in healthcare monitoring, human–machine interfaces, artificial intelligence, and physical sports performance evaluation. This paper presents a flexible wearable acceleration sensor for monitoring human motion by introducing the island–bridge configuration and serpentine interconnects. Compared with traditional wearable accelerometers, the flexible accelerometer proposed in this paper improves the wearing comfort while reducing the cost of the device. Simulation and experiments under bending, stretching, and torsion conditions demonstrate that the flexible performance of the flexible acceleration sensor can meet the needs of monitoring the daily movement of the human body, and it can work normally under various conditions. The measurement accuracy of the flexible acceleration sensor is verified by comparing it with the data of the commercial acceleration sensor. The flexible acceleration sensor can measure the acceleration and the angular velocity of the human body with six degrees of freedom and recognize the gesture and motion features according to the acceleration characteristics. The presented flexible accelerometers provide great potential in recognizing the motion features that are critical for healthcare monitoring and physical sports performance evaluation.

Stretchable transparent thin-film electrodes that can tolerate high deformation and adhere to irregular surface is a key building block in these stretchable optoelectronic devices. One of the key research topics in this area has been how to develop stretchable transparent electrodes which can simultaneously achieve stable conductivity and high transparency under large tensile strain. [7][8] In recent decades, attempts to achieve these attributes have stimulated extensive research efforts on enhancing the tensile performance of transparent electrodes while attaining high and stable electrical properties. One strategy is based on coating solution-dispersed nanomaterials such as metal nanowires and carbon nanotube materials on an elastomer to form percolation networks. [9][10][11][12][13] However, the conductivity of these nanowires or nanotube network fluctuated greatly under external strains because of the sliding movements at the junctions. [14][15] To solve this problem, various methods of wielding the nanowire junctions were proposed to reduce the internanowire contact resistance. [12,15] Although those approaches have greatly improved the electrical connection, the conductivity of such percolation networks is lower than that of metals, and the large electrical change with strain is still generated.2D stretchable transparent electrodes (STE) are required to conform to non-flat complex 3D surfaces for next-generation stretchable optoelectronic devices. However, it is a great challenge to simultaneously maintain omnidirectional stretchability, high transmittance, and the least change in conductivity at large strain. In this work, omnidirectionally stretchable 2D transparent electrode is achieved by hybrid printed copper mesh embedded in an elastic material. The electrode displays exceedingly low sheet resistance down to 0.12 Ω sq −1 while still maintaining 80% of optical transparency. Two types of mesh geometries, the horseshoe-like and sinusoid-like shapes, are thoroughly investigated by simulations and experiments. By optimizing the key geometrical parameters of mesh structure, the copper mesh can endure stretching up to 130% with no fractures and no resistivity change. After 1000 stretch-and-release cycles at 10% strain, the copper mesh remains intact with negligible resistance variation. For 2D stretchability, the copper mesh is stretched in eight directions simultaneously and can maintain its initial conductivity up to 50% tensile deformation. As a demonstration of application, the copper mesh STE is employed in a stretchable electroluminescent device that maintained uniform lighting up to 120% stretching and 100 stretch-release cycles at 30% strain, showing its potential in stretchable and wearable optoelectronic applications.

Frequency selective surfaces (FSS) that can be tightly laminated to complex nondevelopable surfaces have a wide range of applications in many engineering areas. This paper presents a 3D flexible FSS prepared by mechanically guided 3D assembly, capable of being conformally adhered to complex surfaces, while maintaining stable frequency selective properties as well as transmission performance. The stretching strain applied to the prestrained ecoflex substrate can precisely tune and control the buckled 3D metal structures, which leads to the stretchability of the flexible FSS, introduces the increase of the inductance inside the metal cells, and expands the metal gap resulting in a reduction of the capacitance between the unit cells. The mutual correlation of capacitance and inductance ensures in the mechanism that the FSS transmission characteristics will not be significantly affected by the applied strain, as verified by calculations using the equivalent circuit method. Both the results obtained by the experiments and simulations indicate that the resonant frequency of the 3D flexible FSS is 5.7 GHz and the bandwidth at −10 dB is 0.94 GHz, while the resonant frequency shift will not exceed 0.45 Hz, and −10 dB bandwidth change will not exceed 0.32 GHz with applied strain of 17.8% in the ecoflex substrate. At the same time, the 3D flexible FSS maintains stable transmission performance for oblique incidence, with only 0.5 GHz frequency shift at 45° incidence. This stretchable flexible FSS with stable electromagnetic (EM) properties may find potential applications in EM shielding and spatial filtering due to its high flexibility, ready applicability, and cost‐effectiveness.

Epidermal electronic sensors (EESs) possess great advantages in the real-time and enduring monitoring of human vital information compared to the traditional medical device for intimately making contact with human skin. Skin strain is a significant and effective routine to monitor motion, heart rate, wrist pulse, and skin growth in wound healing. In this paper, a novel skin sensor combined with a ternary conductive nanocomposite (Carbon black (CB)/Decamethylcyclopentasiloxane (D5)/Silbione) and a two-stage serpentine connector is designed and fabricated to monitor skin strain. The ultrasoft (~2 kPa) and adhesive properties of the ternary conductive nanocomposite ensure the capacity of the EES to intimately couple with human skin in order to improve accuracy with a relative error of 3.39% at strain 50% as well as a large strain range (0~50%) and gauge factor (GF ~2.5). The millimeter scale EES (~5 mm × 1 mm × 100 μm), based on the micro-nano fabrication technique, consisted of a two-stage serpentine connector and screen print of the ternary conductive nanocomposite. EESs with high comprehensive performance (electrical and mechanical properties) are fabricated to confirm the analytical results and monitor the motion of a human hand. The good agreement between experimental and analytical results paves the way for bettering monitoring of skin growth during wound healing in order to avoid necrosis and scarring. This EES in monitoring the motion of a human exhibit presents a promising application for assisting prosthetic movement.