Pre-Strain Method for Stretchable Strain Sensors With Linear Sensitivity Using Acrylic Elastomer and CNTs Powder

Stretchable sensors can measure large strains generated in the joints of the human body. Generally, in the characteristics of carbon nanotubes based stretchable resistive sensors, the reference resistance increases with repeated strain, and the gauge factor which indicates sensitivity is not constant. These characteristics are related to the rupture of the CNT networks. This study proposes a pre-strain method to produce the resistive strain sensor with linear sensitivity. In this method, since the CNT network is formed on a strained elastomer, we expected that the CNT networks withstand the strain. By observing the electrodes, we discovered that this method aligned the agglomerated CNTs, changed the density of the CNT, and strengthened the networks. The pre-strain method is simple because it requires just a brush and stretching jig without special equipment. The sensor is completed by applying CNT powder to an elastomer that has been pre-strained 47% in the uniaxial direction and then returning it to its initial state. In the strain from 0% to 100%, the GF of the sensor is 1.46 constantly, and the variance of the normalized change in resistance of the sensor is less than 0.06. Therefore, the sensibility of the sensor has strong linearity. This result solves the problem of non-linear sensitivity of sensors using CNT powder in previous research. These features of constant gauge factor and reference resistance are expected to simplify the system's data processing.