Sacrificial Template Method to Fabricate Highly Sensitive Porous Capacitive Pressure Sensor for Full Pulse Waveform Detection

Abstract

Due to the recent advancements in sensing technology, skin mountable wearable devices have gained much attention due to their non-invasive usage and wearer comfort for health care monitoring. For instance, monitoring pulse waveform from the wrist arterial sites bears tremendous information about cardiovascular health and can show abnormalities such as hypertension or arterial fibrosis. Acquiring a high-quality pulse waveform from the wrist artery requires high-pressure sensitivity and fast response time. However, the need for building highly sensitive and low-cost fabrication of the sensors for subtle physiological monitoring is still challenging. Targeting these issues, this study presents a facile and cost-effective approach to realizing a flexible capacitive pressure sensor by sandwiching porous polydimethylsiloxane (PDMS) polymer functionalized by multi-walled carbon nanotubes (MWCNTs) fabricated by sacrificial template method for physiological monitoring. The fabrication steps for the dielectric layer involve mixing sucrose as the porogens and MWCNTs as the functionalizing material with PDMS followed by casting the mixture in a mold and curing of the PDMS. Subsequently, the sucrose particles are dissolved in water. The sucrose particles are easily dissolved in water leaving a highly uniform and porous structure behind. The dielectric layer is then sandwiched between two conductive textile based electrodes for physiological monitoring. The electromechanical tests were performed for different concentration of MWCNTs content in porous PDMS to obtain the best sensing performance. The champion sensor exhibits ultrahigh-pressure sensitivity of 2.41kPa-1 and a minimum detection limit of 1.4Pa in contrast to the sensor exhibiting only 0.31kPa-1 without addition of any MWCNTs. In addition, the pressure sensor shows a fast response time of 0.18s and excellent cyclic stability over 6000 cycles. The ultrahigh-pressure sensitivity comes from the addition of conductive MWCNTs filler that increases the dielectric permittivity. The highly porous structure of the polymer reduces the typical viscoelastic effects of polymer resulting in fast response time. The pressure sensor could detect arterial pulse waveform from the wrist artery with all the key characteristic points showing its promises for low-cost physiological monitoring. The detailed results will be discussed during the presentation.