Porous dielectric materials based wearable capacitance pressure sensors for vital signs monitoring: A review

Electrical transduction-based pressure sensors namely resistance, capacitance, piezoelectric, and triboelectric pressure sensors are deep-rooted in different applications. Resistance and capacitance pressure sensors are widely used in pressure, touch, and tactile sensing applications due to the simple output signal reader and small form factor. Whereas piezoelectric and triboelectric sensors are utilized in dynamic pressure sensing applications. Additionally, the latter two sensors are also used in electric potential generation applications. Recently, many researchers are exploring the possibilities of these sensors for biomedical applications such as vital signs monitor, and body language and motion. Vital signs give information about the homeostasis status which is essential for the human body. Body temperature (BT), heart rate (HR), blood pressure (BP), respiratory rate (RR), oxygen saturation (OSat), and electrolyte balance maintain homeostasis. Parallel plate capacitor (PPC) based pressure sensors are more broadly applied in vital signs monitor than interdigitated capacitor (IDC) architecture. To in-crease the sensitivity, response rate, and working range of PPC sensors, surface microstructure and porous microstructured dielectric sandwich materials are widely studied. Among these two, porous microstructured sandwich layers were exposed to superior sensitivity and an ample operating range. Recent literature on porous dielectric sandwich layer-based PPC sensors was reviewed and the key points were reported here. Many reports suggest that porous dielectric PPC sensors show high sensitivity due to simultaneous modification of A, d & epsilon values under external stimuli. Further, challenges in reproducibility of data, sensor design, porosity volume, cost of sensors, and ionic porous dielectric materials were discussed.