Carboxymethyl cellulose-MgCl2 composite based humidity sensor: self-powered, flexible, and multifunctional sensing applications
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摘要: 湿度传感器在农业、工业生产、精密仪器及人体健康监测等领域有着广泛的应用。针对湿度传感器需要外加电源驱动的问题，本文借鉴原电池原理，将具有湿敏特性的羧甲基纤维素和具有吸湿特性的MgCl2复合物作为敏感层，并用商品化的导电铜胶带和镍胶带作为正、负极，制备自驱动的柔性湿度传感器。通过SEM、EDS对传感器敏感层的微观形貌和表面元素进行表征，通过复阻抗谱分析其湿敏机制，并对其多功能应用进行探索。该传感器敏感层具有良好的亲水性，在接触环境中的水分子后可将其中的MgCl2离子化产生Mg2+、Cl−等载流子，并定向移动而形成输出电压，相对湿度从11%到95%时其响应值可达177%。该传感器可用于人体呼吸频率和呼吸类型检测、土壤湿度和尿不湿湿度检测、手指距离检测、提供电能，显示其在健康监测、环境湿度监测、非接触开关、供能领域的应用潜力。Abstract: Humidity sensors have been widely used in fields of agriculture, industrial production, precision instruments and human health monitoring. To address the problem that humidity sensors need to be driven by an external power source, a self-powered flexible humidity sensor based on the principle of primary battery was proposed in this paper. The carboxymethyl cellulose with moisture-sensitive properties and MgCl2 with moisture-absorbent properties were applied as the sensitive layer. And commercialized conductive copper and nickel adhesive tapes were used as the positive and negative electrodes. The micro-morphology and surface elements of the sensitive layer of the sensor were characterized by SEM and EDS, the moisture sensitivity mechanism was analyzed based on complex impedance spectroscopy, and the multifunctional applications of the sensor was demonstrated. The sensor sensitive layer has good hydrophilicity, which can ionize the MgCl2 in it to produce carriers such as Mg2+ and Cl− after contacting the water molecules in the environment. The directional movement of these carriers can generate output voltage. The response value can reach 177% when the relative humidity changes from 11% to 95%. The sensor can be used for human respiratory frequency and characteristic detection, soil moisture and urinary moisture detection, finger distance detection, and providing electrical energy. Experimental results show its potential for applications in health monitoring, environmental humidity monitoring, non-contact switching, and power-supply areas.
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Key words:
- humidity sensor /
- self-powered /
- multifunctional /
- carboxymethyl cellulose /
- flexible sensor
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图 1 自驱动柔性湿度传感器的制备过程示意图
Figure 1. Schematic diagram of the preparation process of the flexible sensor and humidity sensing measurement
图 2 (a)不同MgCl2含量的传感器在不同相对湿度下产生的电压值；(b)不同MgCl2含量的传感器在对不同相对湿度的响应-恢复曲线，(c)湿度滞回特性曲线(相对湿度均从11%至95%再到11%)
Figure 2. (a) Output voltage for the sensors with different MgCl2 contents at different relative humidities; (b) Response-recovery curves of sensors with different MgCl2 contents at different relative humidities; (c) Humidity hysteresis characteristic curves (relative humidity from 11% to 95% at to 11%)
图 3 (a)羧甲基纤维素(CMC)-MgCl2敏感膜表面的SEM图像；(b) CMC-MgCl2敏感膜表面的EDS图谱
Figure 3. (a) SEM image of the surface of carboxymethyl cellulose (CMC)-MgCl2 sensitive membrane; (b) EDS mapping of the surface of CMC-MgCl2 sensitive membrane
图 4 CMC-MgCl2基湿度传感器敏感层在20 s之内的接触角变化
Figure 4. Contact angle of the CMC-MgCl2-based sensitive layer of the humidity sensor within 20 s
图 5 (a) 传感器在不同相对湿度下的重复响应性能; (b)传感器对不同湿度的连续响应值
Figure 5. (a-e) Repeatability of the sensor response to different RHs; (b) Continuous response values of the sensor to different RHs
图 6 CMC-MgCl2基传感器正接合反接的情况下在RH从11%到54%的条件下输出的电压响应-恢复曲线
Figure 6. Response and recovery curve of the CMC-MgCl2-based humidity sensor at positive and negative connections
图 7 CMC-MgCl2基湿度传感器敏感层在RH为11%，54%和95%时的复阻抗曲线
Figure 7. The complex impedance spectroscopy plots of CMC-MgCl2-based sensitive layer under RH 11%, 54%, and 95%.
图 8 CMC-MgCl2基自驱动湿度传感器湿敏机制示意图
Figure 8. Schematic diagram of the sensing mechanism for the CMC-MgCl2-based self-powered humidity sensor
图 9 (a)传感器对不同类型鼻呼吸的电压响应曲线；(b)传感器对不同类型嘴呼吸的电压响应曲线
Figure 9. (a) Response curve under different nasal breathing conditions;(b) Response curve under different oral breathing conditions
图 10 (a)传感器对土壤湿度变化的电压响应曲线；(b)传感器对尿不湿表面湿度变化的电压响应曲线(插图为实验照片)
Figure 10. (a) Output voltage curve of the sensor to the soil humidity change; (b) Output voltage curve of the sensor to the diaper humidity change (the insert shows the digital photograph of the experiment)
图 11 手指距离感知的电压响应曲线(插图为实验照片)
Figure 11. Output voltage curve of the finger distance (the insert shows the digital photograph of the experiment)
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