Development of Embroidery-Type Pressure Sensor Dependent on Interdigitated Capacitive Method

Abstract

Many studies have been conducted to develop electronic skin (e-skin) and flexible wearable textiles which transform into actual “skin”, using different approaches. Moreover, many reports have investigated self-healing materials, multifunctional sensors, etc. This study presents a systematic approach to embroidery pressure sensors dependent on interdigitated capacitors (IDCs), for applications surrounding intelligent wearable devices, robots, and e-skins. The method proposed a broad range of highly sensitive pressure sensors based on porous Ecoflex, carbon nanotubes (CNTs), and interdigitated electrodes. Firstly, characterizations of ICDs embroidering on a cotton fabric using silver conductive thread are evaluated by a precision LCR meter throughout the frequency range from 1 kHz to 300 kHz. The effect of thread density on the performance of embroidered sensors is included. Secondly, the 16451B dielectric test fixture from Keysight is utilized to evaluate the composite samples’ dielectric constant accurately. The effect of frequency on sensor performance was evaluated to consider the influence of the dielectric constant as a function of the capacitance change. This study shows that the lower the frequency, the higher the sensitivity, but at the same time, it also leads to instability in the sensor’s operation. Thirdly, assessing the volume fraction of CNTs on composites’ properties is enclosed. The presence of volume portion CNTs upgrades the bond strength of composites and further develops sensor deformability. Finally, the presented sensor can accomplish excellent performance with an ultra-high sensitivity of 0.24 kPa−1 in low pressure (<25 kPa) as well as a wide detection range from 1 to 1000 kPa, which is appropriate for general tactile pressure rages. In order to achieve high sensor performance, factors such as density, frequency, fabric substrate, and the structure of the dielectric layer need to be carefully evaluated.

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

“…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.…”

Classification of Breathing Signals According to Human Motions by Combining 1D Convolutional Neural Network and Embroidered Textile Sensor

“…where ε air = 1 and ε Eco-flex = 2.8 [38]. v air stands for the volume fraction of air and V Ecoflex for the volume fraction of the impeccable Eco-flex.…”

“…Furthermore, the capacitance of the porous Eco-flex varies considerably, even under the same pressure, demonstrating that the shift in capacitance is significant [ 35 ]. When the pores are subjected to external pressure, the effective dielectric constant of porous Eco-flex ( ε r ), which may be explained by Equation (2) [ 36 ], rises [ 37 ]: ε r = ε air V air + ε Eco f lex V Eco f lex , where ε air = 1 and ε Eco- flex = 2.8 [ 38 ]. v air stands for the volume fraction of air and V Ecoflex for the volume fraction of the impeccable Eco-flex.…”

Wearable humidity sensor embroidered on a commercial face mask and its electrical properties

“…Fabrication of sensors through modern embroidery technique provides numerous benefits including stretchability of sensors, high throughput and rapid manufacturing with great functionality, which are compatible for flexible electronics. Furthermore, embroidery offers an opportunity to integrate electrode patterns made up of threads into substrate to fabricate various kinds of sensors, majority of which can be utilized for biomedical applications [ 14 , 15 ]. The technique allows flexibility with respect to selecting a wide range of electrode, sensing/substrate materials and sensor design.…”