A Single-Channel Capacitive Sensor for Sequential Discrimination of Proximity, Pressure, and Shear With High Sensitivity in All Three

Emulating human skin tactile perception with pre-touch awareness would enable safer, more dexterous robotic manipulation, yet integrating proximity, pressure, and shear sensing into one device remains challenging. Here, we report an all-in-one Proximity-Pressure-Shear capacitive sensor: a porous CNT/Ecoflex nanocomposite (PNC) and an ultrathin insulating layer between coil-shaped electrodes. The electrodes project fringing fields outward for proximity detection, while lateral misalignment reduces overlap under shear. The CNT-doped PNC behaves as a lossy medium and the ultrathin insulating layer blocks this charge transport, triggering Maxwell-Wagner-Sillars interfacial polarization that markedly amplifies effective permittivity and pressure-induced capacitance change. Together, these coupled geometric and material effects yield high sensitivity across all three modalities: a proximity capacitance change of 0.46 pF, a pressure sensitivity of 0.44 kPa^{- 1} (0-10 kPa), and a shear response of ΔC/C₀ = 0.28 (γ  =  1, 50 kPa pressure). In a robotic manipulation cycle, the sensor sequentially identifies approaching, gripping, and lifting phases from the sign of a single capacitance output, which decreases upon approaching, increases upon gripping, and decreases again upon lifting. This sequential, sign-based logic leverages the known temporal order of manipulation rather than decoupling the three modalities independently.