Wearable capacitive pressure sensor using interdigitated capacitor printed on fabric

Abstract

This paper presented a systematic approach to electro-textile pressure sensors dependent on interdigitated capacitors (IDCs) printed on fabric. In this study, we proposed a highly sensitive, broad-range pressure sensor based on the combination of porous Ecoflex, carbon nanotubes (CNTs), and interdigitated electrodes. Firstly, characterizations of the interdigitated capacitor using silver ink on Cotton and Polyester fabric were completed by precision LCR meter across the frequency range from 1 to 300 kHz. The effect of the fabric on the performance of sensor sensitivity was included. Secondly, estimating and optimizing the volume fraction of CNTs and air gaps on the properties of composites are included. The presence of volume fraction CNTs enhanced the bond strength of composites and improved sensor deformability. The robustness of the presented sensor was demonstrated by testing under high pressure at 400 kPa for more than 20,000 cycles. Thirdly, the combination of CNTs and porous dielectric achieved a broad detection range (400 kPa) with a sensitivity range from 0.035 (at 400 kPa) to 0.15 $${\mathrm{KPa}}^{-1}$$ KPa - 1 (at 50 kPa). Finally, the Cotton and Polyester substrate comparison demonstrates that selecting a suitable dielectric substrate affects sensor sensitivity and signal output.

Development of Embroidery-Type Sensor Capable of Detecting Respiration Using the Capacitive Method

“…Eco-flex (Smooth-on Inc., Macungie, PA, USA) was employed to create an ideal dielectric environment with and without air, which was used in the experiment to detect respiration motion. Eco-flex was chosen as the dielectric due to its low viscosity, making it simple to mix with other materials and causing no surface-level phenomena [ 20 ]. It is also safe for the human body and is easy to create in complex shapes.…”

“…In contrast, the dielectric constant and the distance between the electrodes ( vary under pressure in the case of a porous Eco-flex ( ), in which an air layer is produced by sugar. Additionally, even under the same pressure, the capacitance of the porous Eco-flex changes significantly, indicating that the shift in capacitance is substantial [ 20 ]. The effective dielectric constant of porous Eco-flex ( ), which may be explained by Formula (2) [ 21 ], increases when the pores are subjected to external pressure [ 22 ]: where indicates the volume fraction of air and is for the volume fraction of the immaculate Eco-flex, where and [ 23 ].…”

“…The compression causes the pores of the dielectric layer to close gradually, which lowers the volume percent of air and increases the volume fraction of Eco-flex. The greater dielectric constant of the silicone elastomer ( ) replaced the lower dielectric constant of the pores ( ), increasing the effective dielectric constant of the porous Eco-flex composite [ 20 , 24 ]. The sensitivity of the capacitance sensor can be increased by adding air gaps to this porous elastomer owing to increased deformability.…”

Highly Inductive Coil Spring Strain/Compress Sensors Integrated with Shape Memory Alloy and Shape Memory Polymers‐CNTs

“…Adding functional groups to the CNT surface through acid functionalization exfoliates these bundles by repulsive forces, which results in improved dispersibility in polar solvents. [ 21,22 ]…”

“…Adding functional groups to the CNT surface through acid functionalization exfoliates these bundles by repulsive forces, which results in improved dispersibility in polar solvents. [21,22] In the experiments, ultrapure HNO3 65% and H2SO4 98% (w/w) (from KH Chemicals in Korea) were employed. As can be seen in Figure 4a, The SWCNT (1-1.4 nm in diameter, 5-50 m in length, from KH Chemicals in Korea) with 60% weight was cleaned in Deionized (DI) water or distilled water before being treated with two acid concentrations of 3:1 solution of concentrated H2SO4 (98%): HNO3 (65%) by sonicating in a water bath for 24 h at 70 °C.…”