Sensitivity improvement strategies and applications for flexible and wearable capacitive pressure sensors

Çiçek, Melih Ögeday
Pressure sensors have attracted great interest in parallel with developments in wearable electronics, robotics, human-machine interface devices, and electronic skin. In this field, capacitive pressure sensors are gaining increasing research attention due to their high sensitivity, high stability, fast response/recovery times, and simple manufacturing routes. While capacitive pressure sensors have prominent features, there is still a long way to go before they become more common in wearable technology. Increasing the sensitivity of today's capacitive pressure sensors is one of the most critical priorities in this field. In the first chapter of this work, sensitivities of the capacitive pressure sensors were improved by employing facile fabrication methods and rational sensor designs. In that regard, the first part of the thesis proposes a low-cost, lightweight, parallel plate capacitive sensor with a unique monolithic design. This design allows the sensors to significantly improve their sensitivity. The monolithic capacitive sensor (MCS) with a density of as low as 10.78 mg/cm3 was fabricated using 3-D masking technique on a commercially available melamine sponge with silver nanowire electrodes and a protective thin layer of polydimethylsiloxane coating. In addition to its unique design, the MCSs showed high sensitivity (up to 1.28 kPa-1), fast response/recovery time (18 ms/54 ms), very low-pressure sensing ability (0.5 Pa) with ultra-high mechanical (42 000 cycles) and washing stabilities (10 cycles) along with high air permeability. Moreover, finite element analysis simulations were conducted to reveal deformation mechanism differences between the monolithic and classical design. Finally, in order to demonstrate their true potential, fabricated MCSs were utilized in real-time body motion monitoring, word and proximity detection. In the second part, a cellulose-based supramolecular bio-polymer gel that possesses high ionic conductivity (9.85 x 10-4 S cm-4 at 25 oC) and exceptional structural integrity was developed. An iontronic pressure sensor was fabricated with record sensitivity (1 475 000 kPa-1) using the supramolecular bio-polymer gel as a dielectric layer. The combination of in-situ 3D Bode and 3D areal capacitance analyses allowed a deep understanding of the record sensitivity and detection mechanism of the iontronic pressure sensors. A prototype smart glove was fabricated for object recognition from the tactile feedback of the sensors and an object classification accuracy of 90% is demonstrated with only 8 sensors.


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Citation Formats
M. Ö. Çiçek, “Sensitivity improvement strategies and applications for flexible and wearable capacitive pressure sensors,” M.S. - Master of Science, Middle East Technical University, 2022.