Flexible, anisotropic strain sensor based on interdigital capacitance for multi-direction discrimination

The direction information of strain plays a pivotal role in practical applications such as soft robots and human-machine interfaces. However, most of the multi-directional strain sensors studied before are integrated devices, which accomplish the strain direction discrimination through the signal difference of independent sensing units when they are stretched, thus increasing the complexity of the detection system. In this article, a multi-directional flexible strain sensor based on an interdigital capacitance structure is reported. The structure enables opposite variation of the capacitance changes in the orthogonal direction because the device exhibits different structural deformation depending on the direction of strain, thus detecting multiple direction strain by a single device. This sensor is fabricated by a one-step transfer method, which takes advantage of the excellent electrical conductivity of silver nanowires and the extremely low surface adhesion of the release film. The strain range of this sensor can be up to 60%. The influence of the structural parameters of the sensor on the gauge factor (GF) is explored to optimize capacitance structure parameters. The device shows good stability dynamic response (0.1–1.0 Hz). When the angle of strain direction changes from 0° to 90°, the GF changes from 1.1 to -0.56. Furthermore, owing to the high sensitivity and excellent stability of the sensor, human motion such as the bending direction of the wrist, can be accurately detected by this sensor.