The Intrinsic Mechanism of the Sensitivity Improvement for Capacitive Strain Sensors and Its Trade-Off With Sensing Range

Capacitive strain sensors with high sensitivity are fundamental for many engineering applications. Previous studies mainly improved sensitivity with introducing microstructures or developing active materials. But it still lacks theoretical models to reveal the intrinsic mechanism of sensitivity improvement. In addition, it is well-known that the increase in sensitivity is often accompanied by a decrease in sensing range, which is the key challenge for sensors. In this study, a theoretical model of capacitive strain sensors was established to reveal the intrinsic mechanism of sensitivity improvement, as well as the tradeoff between sensitivity and sensing range. The strain amplification factor was defined to regulate sensitivity. To reveal the restriction of sensing range and sensitivity, a universal expression was further developed, which considers the material, nonlinear errors, and dimension. The validity of the theoretical model was also verified by simulation and experiment. For the two usually used methods to improve sensitivity, introducing microstructures and doped materials, we established a uniform expression, which indicates the sensitivity was determined by the mechanical and electrical properties of the sensor. This model indicates the inherent restriction to improve sensitivity, providing an insight and possible way to develop high-performance capacitive strain sensors.