Highly Sensitive Multifunctional Flexible Capacitive Ionogel Sensor for Proximity, Pressure, and Temperature Perception

Flexible sensors with a single tactile sensing function have been extensively studied, however, the development of highly sensitive multifunctional sensors remains a significant challenge in the realm of wearable technology. In this paper, a multifunctional flexible capacitive sensor with integrated proximity, pressure and temperature perception is developed. The dielectric layer of the sensor is obtained by spontaneous polymerization of polyvinyl alcohol and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide at room temperature. The electrode structure is optimized by leveraging the capacitive fringing field effect, and the designed hole-circle shaped 4 × 4 electrode array achieves optimal proximity sensitivity with a maximal capacitance drop of 0.54 pF to human hand and a detection distance of 30 mm. Besides, the prepared microcone structure sensor exhibits high pressure sensitivity of 4.822 kPa<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>(0-5 kPa), rapid response time (<100 ms), a broad detection range (~200 kPa), and excellent stability over 3000 cycles of loading/unloading tests. By exploiting the temperature dependence of the ionic liquid, the sensor also exhibits high temperature sensitivity of 80.6%°C<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>(25-80°C). Finally, we verified the successful application of this sensor in dynamic finger trajectory recognition, multi-touch and robotic grasping state detection, paving the way for its use in artificial intelligence, healthcare, and intelligent robotics.