Tailoring Auxetic Mechanical Metamaterials to Achieve Patterned Wire Strain Sensors with Controllable High Sensitivity

A novel design concept of auxetic mechanical metamaterials is proposed to achieve controllable high sensitivity as well as good stretchability and durability of wire strain sensors. Semi-auxetic and contractile architectures are derived from an auxetic architecture and collected as three master units. To achieve an adjustable structural Poisson's ratio (v), patterned wire strain sensors with six units are constructed. Sensitivity of wire strain sensors is tuned by tailoring the ratio and location of three master units. High sensitivity, good stretchability, and durability are related to continuous stretching and structural synergetic effects. Based on the results of finite element modeling and sensing performance, relationship between structural v, effective contributions, and sensitivity is presented. To evaluate the effectiveness of proposed scheme, wire strain sensors with different shapes and a 2D auxetic network sensor are fabricated. The analysis reveals that wire strain sensors with six auxetic units show high sensitivity (GF = 21.8 at ~ 80-130% strain), high stretchability (130%), excellent durability (up to 1000 r), and fast response time. Morphological evolution is tracked to explain the excellent durability. Because of controllable sensitivity, our sensors can be used for weight and displacement monitoring of objects with a small mass.