Ultrasensitive Airflow Sensors Based on Suspended Carbon Nanotube Networks

Abstract

applications. Recently, bionic fluffy fabrics learning from many animals, such as crickets and spiders, were reported to fabricate airflow sensors but usually exhibited low sensitivity and slow response speed against different airflows. [9,10] Therefore, the rational design and controllable fabrication of airflow sensors are urgently needed to tackle their issues of poor performance.For piezoresistive materials, sufficient deformation under external forces is the prerequisite for causing resistance variations, which calls for the excellent flexibility of the component materials. Besides, lightweight materials are easy to change their states of motion due to their low inertia, ensuring a fast response to external stimuli. For composite-based sensors, the interfacial areas within the composites should also be reduced because the interfaces often behave like capacitors under external electrical fields, [11] which inevitably causes a decline in the response speed of sensors owing to the charging-discharging processes. Therefore, from the perspective of material selection, flexible and lightweight materials with small interfacial areas show more advantages in fabricating highly sensitive and responsive piezoresistive sensors.Carbon nanotubes (CNTs) are supposed to be ideal candidates for fabricating high-performance piezoresistive airflow sensors because of their intrinsic properties, such as nanosized diameters, high aspect ratio and flexibility, low density, and excellent mechanical and electrical properties, [12,13] which fully meet the requirements for airflow sensors. However, the previous attempts to incorporate CNTs with other materials for making airflow sensors usually produced mixed bulky structures with declined mechanical properties, thus degrading their performance as sensors. [14][15][16][17][18] For example, the response time of many CNT-based sensors generally ranges from one to several seconds, [9,[19][20][21] which is far inferior to the expected performance of individual CNT-based sensors. [22][23][24] In previous studies, carbonized silk fabric (CSF) decorated with fluffylike CNTs were developed as piezoresistive airflow sensors, of which the sensing performance was simultaneously determined by the properties of CSF and CNTs. [9] Although the CNT assembly with a foam-like structure was capable of sensing very mild airflows, its response time was ≈1.3 s, which could High-performance airflow sensors are in great demand in numerous fields but still face many challenges, such as slow response speed, low sensitivity, large detection threshold, and narrow sensing range. Carbon nanotubes (CNTs) exhibit many advantages in fabricating airflow sensors due to their nanoscale diameters, excellent mechanical and electrical properties, and so on. However, the intrinsic extraordinary properties of CNTs are not fully exhibited in previously reported CNT-based airflow sensors due to the mixed structures of macroscale CNT assemblies. Herein, this article presents suspended CNT networks (SCNTNs) as high-performance a...

Stable Ultrathin Ag Electrodes by Tailoring the Surface of Plastic Substrates for Flexible Organic Light-Emitting Devices

“…Although the most used indium tin oxide possesses excellent optoelectrical properties, it cannot match the basic requirements of FTEs since its inherent brittleness. At present, carbon nanotubes, , metal nanowires, , conductive polymers, , and ultrathin metal films , have been exploited to construct FTEs. Nevertheless, FTEs with both excellent optoelectrical properties and durable mechanical flexibility remain a challenge in applications of flexible optoelectronic devices.…”

Ultrasensitive, Fast-Responsive, Directional Airflow Sensing by Bioinspired Suspended Graphene Fibers

“…(h) Cycling performance of SLIGF-150 at airflow speed of 1.4 m/s. (i) Sensing performance comparison with the reported airflow sensors. ,,,,,,− The sensitivity (s/m) discussed in some literature is illustrated in the bracket.…”

“…Due to the lightweight and excellent mechanical and electrical properties, carbon nanotube (CNT), reduced graphene oxide (rGO), graphene materials, and their composites offer a new train of thought for developing airflow sensors. 7 Zhang's group synthesized suspended CNT on silicon substrates for ultrasensitive airflow sensors by floating catalyst chemical vapor deposition (CVD) method. The multiple junctions in the CNT networks enable a high sensitivity of 0.0124 s/m and a quick response speed of 0.021s.…”

“…The multiple junctions in the CNT networks enable a high sensitivity of 0.0124 s/m and a quick response speed of 0.021s. 7 Wang et al designed a bioinspired fluff-like CNTbased airflow sensor based on silk fabrics grown with CNT by the CVD approach. The fabric endows the device with flexibility, showing potential applications in smart textiles and wearable electronics.…”

“…Recent years have witnessed the explosive development of new-generation wearable electronics, − of which airflow sensors are the diagnostic source for breath monitoring. − Apart from wearable electronics, airflow sensors also play a key role in conventional mine work, aerospace industry, weather forecasting, and emerging biomedical engineering. , The working mechanism of current airflow sensors rely on the piezoresistive, ,, thermal (hot-wire, hot-film), , optical, , and calorimetric approach. The thermal-based airflow sensors are first heated, and the resistance variation due to heat transfer is recorded with flowing gas.…”