Highly Flexible Strain Sensors Based on CNT-Reinforced Ecoflex Silicone Rubber for Wireless Facemask Breathing Monitoring via Bluetooth

Abstract

Highly stretchable strain sensors based on carbon nanotube (CNT)reinforced Ecoflex silicone rubber are developed for breathing monitoring purposes. The addition of CNTs promotes an improvement in electrical conductivity and mechanical properties (Young's modulus and tensile strength) due to its good dispersion in Ecoflex. The evaluation of strain monitoring response, in both tensile and compression conditions, indicates a wide strain detection range and an ultrasensitive response at high strain levels, reaching a gauge factor of around 10 4 at 70% or 10 5 at 300% for 0.3 and 0.7 wt % CNT-reinforced sensors, respectively. They show a quite stable electrical response under 2000 cycling loads and different levels of frequencies. Moreover, the response and recovery times are in the range of milliseconds (∼600 and ∼800 ms, respectively). Finally, a proof-of-concept of wireless facemask breathing monitoring was carried out with Bluetooth Low Energy technology and a platform that has been developed to acquire, filter, visualize, and store the breathing signal. With this, the respiration rate can be unequivocally monitored as well as the difference between inspiration and expiration. Thus, this type of trial is proposed for breath monitoring in medical analysis, emergency teams, or first aid.

One Novel Hybrid Flexible Piezoresistive/Piezoelectric Double-Mode Sensor Design for Water Leakage Monitoring

“…From the more microscopic characterization in the inset of Figure d, it can also be seen that MWCNTs cover the surface of PDMS in a filiform manner to form conductive paths. Despite the challenge posed by the tendency toward agglomeration, the successful preparation of stable MWCNT suspension was achieved through the ultrasonic and mechanical shearing dispersion methods. , The combination of high volatile solvent and spray-coating method allowed for the distribution of a relatively uniform functional conductive layer composed of MWCNTs on the surface of PDMS. When the sandpaper mesh number increases from 180 to 400, the size of bumps and concave holes becomes smaller and denser, and the whole becomes flatter, which will lead to the reduction of the sensitivity of the piezoresistive sensor.…”

Recent Advances in Wearable Healthcare Devices: From Material to Application

“…Biocompatibility is a property of living tissue that reacts to an inactive material, generally referring to the compatibility between the material and the host, according to the International Standards Organization (ISO). Substrate is the key to sensor comfort and materials such as metal foil, polymer, silicone, rubber, and so on are commonly used [6,[19][20][21][22]. In general, the materials of biosensors can be divided into: (1) inorganic materials based on metal, carbon, and oxide materials; (2) organic materials such as polymers, small molecules, and natural biomaterials; (3) compound/mixed material in order to realize the function and structure of complementary properties [23].…”

Electromechanical Properties of Smart Vitrimers Reinforced with Carbon Nanotubes for SHM Applications

“…This may be due to the presence of unreacted hardener domains, as previously explained, which may cause material segregation into regions with CNT clusters and regions with lower nanoreinforcement content [48,49], although both are well dispersed without significant CNT agglomerations. The overall electromechanical behavior is governed by regions with a low CNT concentration, where tunneling mechanisms predominate over contact and intrinsic mechanisms of the regions with a higher CNT concentration [50]. These tunneling mechanisms present a higher sensitivity to mechanical deformation, which would explain the increasing GF.…”