Abstract: Soft capacitive sensors have prospective applications in the areas such as human-machine interaction, wearable devices, and soft robots because of their high flexibility and sensitivity. However, the measurement is vulnerable to the environmental disturbing electromagnetic fields. Therefore, a shielded soft capacitive sensor is presented. To detect the normal pressure and shear pressure simultaneously, a two capacitors structure with three electrodes is proposed. Meanwhile, a shielding layer is added separately on the upper and lower surface of the sensor to shield the external electromagnetic field. To reduce the influence of parasite capacitance which is caused by the deformation of the shielding layer on the measuring capacitance, a stiffness layered method is proposed. The dielectric sensing region between the electrodes uses a silicone sponge with a thickness of only about 0.6 mm, while solid silicone rubber is filled between the electrodes and the shielding layers. The special design ensures that the deformation of the sensing region is much larger than that of the shielding layer when pressing the sensor. The experimental results show that the sensor can simultaneously detect the changes of normal pressure and shear pressure, the normal sensitivity can reach 0.12 kPa^-1, and the capacitance change per shear pressure can reach 10 fF. Compared with the sensor without shielding layers, this sensor can reduce the noise caused by the external AC voltage (1400V) to 9%. This shielded sensor is promising in the scenarios with strong electromagnetic interference, such as electro adhesion skin, wearable medical devices, and soft robots.

Key words: capacitive sensor, shielded soft sensor, multi-axis force measuring, ultrathin silicone sponge