High-Sensitivity and Environmentally Friendly Humidity Sensors Deposited with Recyclable Green Microspheres for Wireless Monitoring

Abstract

The reliable, high-sensitive, wireless, and affordable requirements for humidity sensors are needed in high-precision measurement fields. Quartz crystal microbalance (QCM) based on the piezoelectric effect can accurately detect the mass changes at the nanogram level. However, water-capture materials deposited on the surface of QCM generally show disadvantages in either cost, sensitivity, or recyclability. Herein, novel QCM-based humidity sensors (NQHSs) are developed by uniformly depositing green microspheres (GMs) of natural polymers prepared by the chemical synthesis of the emulsification/inner gel method on QCM as humidity-sensitive materials. The NQHSs demonstrate high accuracy and sensitivity (27.1 Hz/% RH) owing to the various hydrophilic groups and porous nano-3D deposition structure. Compared with the devices deposited with a smooth film, the frequency of the NQHSs shows almost no changes during the cyclic test and exhibits long-term stability. The NQHSs have been successfully applied to non-contact sensing human activities and remote real-time humidity monitoring via Bluetooth transmission. In addition, the deposited humidity-sensitive GMs and QCM substrate are fully recycled and reused (72% of the original value). This work has provided an innovative idea to construct environmental-friendly, high-sensitivity, and wireless humidity sensors.

Impedance Analysis of Chitin Nanofibers Integrated Bulk Acoustic Wave Humidity Sensor with Asymmetric Electrode Configuration

“…Table 3 and Table 4 show the performance comparison of the ChNF-3 with some published humidity sensors. The ChNF integrated n-m electrode QCM humidity sensor is extremely competitive in terms of sensitivity, humidity hysteresis, and response/recovery times [ 11 , 19 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ].…”

Self-Powered Carbon Ink/Filter Paper Flexible Humidity Sensor Based on Moisture-Induced Voltage Generation

“…In the fields of wearable electronics, physiological health monitoring, and environmental monitoring, flexible humidity sensors have attracted a lot of attention as a device that can detect changes in air humidity and transmit signals while having excellent foldability and flexibility. − To date, various types of humidity sensors have been made that use signals such as frequency, capacitance, resistance, current, and colorimetry to achieve humidity response. For example, Ryosuke Nitta reported the preparation of a flexible resistive humidity sensor with CuO nanostructures on polyethylene terephthalate substrates via the spin–spray method, which offered a fast response/recovery time of 2 s/2.8 s and a sensitivity of 170% at an RH of 20–70% .…”

Degradable Bioinspired Hypersensitive Strain Sensor with High Mechanical Strength Using a Basalt Fiber as a Reinforced Layer

“…Meanwhile, a great number of reported strain sensors are made of synthetic polymer materials, including poly­(ethylene terephthalate) and poly­(dimethylsiloxane), which have limited biocompatibility and biodegradability, and may exacerbate the environmental crisis, threatening human health and impairing the sustained economic and social development. − To solve the electronic waste-caused environmental issue, sundry degradable or recyclable materials have been explored to substitute conventional materials to develop flexible electronics. , In specific, natural materials including silk protein and plant materials along with synthetic degradable materials (e.g., poly­(vinyl alcohol) (PVA) and poly­(glycerol sebacate) (PGS)) have been utilized to fabricate strain sensors . Nevertheless, most biodegradable wearable sensors proposed always exhibited rather limited mechanical properties and undesirable sensing performances .…”

“…36,37 In specific, natural materials including silk protein and plant materials along with synthetic degradable materials (e.g., poly(vinyl alcohol) (PVA) and poly(glycerol sebacate) (PGS)) have been utilized to fabricate strain sensors. 38 Nevertheless, most biodegradable wearable sensors proposed always exhibited rather limited mechanical properties and undesirable sensing performances. 39 Hence, the construction of a biodegradable, sensitive strain sensor with good mechanical properties that can maintain normal performances under external loads remains promising.…”