Seamless Monolithic Design for Foam Based, Flexible, Parallel Plate Capacitive Sensors

Abstract

range, low power consumption, cycling stability and fast response make capacitive sensors promising candidates for wearable electronics. [27][28][29][30] It was demonstrated that the capacitive pressure sensors can be attached or carried by the human body for human-machine interface. Alternatively, they can be used for collecting physiological signals for real-time healthcare monitoring. However, commercialized or recently developed capacitive pressure sensors are mainly composed of planar separate electrodes, [31,32] which lead to user movement restriction and aesthetic loss. In addition, rigid planar structure restricts the breathability of the body and disrupts user comfort during long periods of use. Wearable capacitive pressure sensors are desired to be designed as a comfortable platform while providing high sensitivity with a low-pressure detection ability and long-term durability. They should also minimize additional weight and physical constraints on the human body in motion.Improvement of the sensitivity of capacitive pressure sensors is achieved by various strategies. These include the use of micropatterned dielectric layers or electrode surfaces, [31] nanofibrous membranes, [6,33] dielectric layers with microspheres [34,35] and ionic-liquid active dielectric layers. [36][37][38] The capacitive pressure sensors based on micro/nano patterned or ionic-liquid activated structures show promising sensitivity and quick response to external stimuli. These methods are time consuming, expensive and involve complicated production steps, such as electrospinning, etching and photolithography. Alternatively, foam-like structures with a wide variety of polymeric materials like polyelefin, [39] polyurethane, [40] ecoflex, [41] and polydimethylsiloxane (PDMS) [42] can be used in wearable electronics. They are cost-effective, commercially available and can be used for large scale-fabrication. Porous structure of these dielectric layers allows capacitive pressure sensors to detect low-pressures and have high sensitivity. For example, Teo and co-workers have demonstrated a capacitive pressure sensor with a dielectric layer made by boron nitride/PDMS foam and verified that 3D network structure can detect very low-pressures (<1 Pa). [42] Park and co-workers have showed a capacitive pressure sensor from 3D microporous dielectric layer sandwiched between carbon nanotube -ecoflex electrode layers with a Capacitive pressure sensors received significant attention in line with advancements in wearable electronics. However, in the era of the wearable electronics, fabricated sensors fail to fulfill the absolute requirements. Significant portion of the previously reported capacitive pressure sensors suffer from excessive weight, lack of air permeability, and washing stability due to the use of separate electrode layers. A low-cost, lightweight, parallel plate capacitive sensor with a unique seamless monolithic design that allows sensors to circumvent aforementioned problems is hereby demonstrated. The seamless monolithic capacitive ...

Ionic Flexible Sensors: Mechanisms, Materials, Structures, and Applications

“…In addition to ionic fibers, recently researchers have also studied the preparation process of directly generating microporous structures inside the ionic gel membrane, such as foams, [243] sponges, [244] paper fibers, [36,245] and fabrics. [246] Pan et al prepared an IFS with an internal microstructure through a multiphase reaction.…”

Biologically Emulated Flexible Sensors With High Sensitivity and Low Hysteresis: Toward Electronic Skin to a Sense of Touch

“…[27][28][29] When detecting fastloading pressures, this type of pressure sensors is not competent for the pressure measurement function. [30][31][32] To address this issue, another type of pressure sensor based on multi-layer microstructures or other hard porous materials as the dielectric layer has been developed, which exhibits low hysteresis. Nevertheless, the sensitivity is relatively small, hence it is difficult to monitor subtle movements in human activities.…”

Recent Advances in Silver Nanowire Based Flexible Capacitive Pressure Sensors: From Structure, Fabrication to Emerging Applications

“…Besides that, utilization of printing paper, [44] flexible wood film, [45] cellulose tape, [46] polyurethane film [25] and PET film [47] have also been demonstrated in the literature. Additionally, porous materials such as wool fabric, [48] melamine sponge [49] and porous PDMS [50] have also been explored. Moreover, to add breathability function to the sensor, PVDF nanofiber membrane was employed as substrate material.…”

“…[23,25,48,[52][53][54] Natural materials such as bamboo leaf [55] and dried rose petal [46] have-on the other hand-been employed owing to their microstructured form and biodegradability. To increase the sensitivity, porous dielectric materials like melamine sponge [49] and nanofiber membrane, [26] and ionic dielectric materials [42,56] were also investigated. Another way to cause pressure-related capacitance changes is to implement AgNWs into the dielectric medium, since then the dielectric constant of the device can be modulated upon external pressure due to changing number density of AgNWs.…”

“…Numerous approaches have been developed to prepare flexible capacitive pressure sensor arrays, which require the patterning of AgNWs. Since the substrates should be flexible polymer materials, the patterning techniques should not include harsh [49] Copyright 2021, Wiley-VCH. b) Porous PDMS/AgNW electrode fabricated from sugar template.…”