Practical and Durable Flexible Strain Sensors Based on Conductive Carbon Black and Silicone Blends for Large Scale Motion Monitoring Applications

Abstract

Presented is a flexible capacitive strain sensor, based on the low cost materials silicone (PDMS) and carbon black (CB), that was fabricated by casting and curing of successive silicone layers—a central PDMS dielectric layer bounded by PDMS/CB blend electrodes and packaged by exterior PDMS films. It was effectively characterized for large flexion-angle motion wearable applications, with strain sensing properties assessed over large strains (50%) and variations in temperature and humidity. Additionally, suitability for monitoring large tissue deformation was established by integration with an in vitro digestive model. The capacitive gauge factor was approximately constant at 0.86 over these conditions for the linear strain range (3 to 47%). Durability was established from consistent relative capacitance changes over 10,000 strain cycles, with varying strain frequency and elongation up to 50%. Wearability and high flexion angle human motion detection were demonstrated by integration with an elbow band, with clear detection of motion ranges up 90°. The device’s simple structure and fabrication method, low-cost materials and robust performance, offer promise for expanding the availability of wearable sensor systems.

Extending Porous Silicone Capacitive Pressure Sensor Applications into Athletic and Physiological Monitoring

“…The 0.51 GF of the report’s sensor lies within a common range for materials primarily intended for pressure measurement. Typically, pressure sensors have not been extensively characterized for durability, with ~1000 cycles of deformation common, compared with the 10,000 to 100,000 cycles sometimes reported for strain sensors [ 28 ]. The 10,000 strain and pressure cycles evaluated here are relatively high for capacitive pressure sensors.…”

“…Capacitive sensors, with their restriction of conductive elements to electrodes for interrogation of dielectric layers [ 3 , 24 ], have potential for mechanical robustness, particularly with large deformation. This class has demonstrated fast responsiveness [ 4 , 25 , 26 ], good linearity [ 4 , 5 , 25 , 26 ], low hysteresis [ 4 , 5 , 25 , 26 ], durability [ 4 , 27 , 28 ], and insensitivity to changes in temperature and humidity [ 28 , 29 ], but may lack sensitivity [ 20 , 22 ]. For wearable applications, where sensors are expected to undergo many high strain or compression cycles, and even impact, this robustness may be particularly important.…”

The effect of barium titanate ceramic loading on the stress relaxation behavior of barium titanate‐silicone elastomer composites

“…Recently, flexible and stretchable sensors have played a key role in a variety of applications, such as in robotics, electronic skins, diagnostic devices, and medical monitoring. [1][2][3][4][5] Strain sensors are a predominant member of the flexible sensor family, requiring both stretchability and reversibility; [6,7] examples of such sensors include Ecoflex and other soft silicones which are suitable for ultra-soft and skin-mountable strain sensors. [8][9][10][11][12] To increase the permittivity, and capacitance, of the Ecoflex silicone elastomer, barium titanate (BTO) ceramic nanoparticles are added.…”

Strain Sensing by Electrical Capacitive Variation: From Stretchable Materials to Electronic Interfaces

“…For example, Zhu et al. [ 170 ] developed a multi‐touch capacitive sensor that can identify multiple touches on different locations using only four independent channels. Their objective was to decry the number of connections and wires on the array systems by combining four capacitive sensors that have partially overlapping areas.…”