Study On QCM Humidity Sensor Based On Modified Carbon Nanotubes

The detection of air humidity is closely related to human life.It has great significance in meteorology,biomedicine,industrial and agricultural production,storage,construction,forestry and other fields.In daily life,environmental humidity also has an important influence on human health.Therefore,it is very important to detect the high precision of environmental humidity.At present,resistance type and capacitance type humidity sensors are widely used,but the resistance type humidity sensors are difficult to detect due to high impedance in low humidity range,and the interchangeability of products are poor.And the capacitive type humidity sensors also have a series of problems,such as high moisture drift under high humidity,high requirement for environmental cleanliness and long term stability is not good,and so on.And these two kinds of traditional humidity sensors are difficult to achieve digital output,which restricts their development in a certain extent.QCM humidity sensor,a type of mass humidity sensor,which outputs frequency value,and it can realize the digital output.It has many advantages,such as high detection accuracy(up to ng order),high sensitivity and good stability.But QCM itself does not have the function of adsorption.It is necessary to prepare a layer of humidity sensitive film on the surface of QCM electrode to make it become a QCM humidity sensor.In this paper,the oscillating circuit of QCM was designed and manufactured,and the detection system of QCM humidity sensor was built.The QCM humidity sensors were made of modified carbon nanotubes as humidity sensitive material,and their humidity performance at room temperature was studied.First,the oscillating circuit of QCM was designed and manufactured.The detection system of QCM humidity sensor was built with QCM humidity sensor,self-made oscillation circuit,intelligent frequency meter,computer and humidity generator.Secondly,the MWCNTs material was modified by acid oxidation treatment method,made it as humidity sensitive material dispersion liquid.And a series of differe nt coating amount of sensitive material of QCM humidity sensors were prepared by dropping coating method.Finally,a series of tests about the properties of QCM humidity sensors were studied.Include humidity sensing properties,dynamic characteristics,we t hysteresis characteristics,repeatability,response / recovery characteristics,stability and long-term stability,and the sensitive mechanism of material was analyzed.The experimental results show that the MWCNTs after acid oxidation can be used as a humidity sensitive material on the QCM humidity sensor,and the response value is related to the coating quality of the sensitive membrane.Under the premise of meeting the Sauerbrey equation,the response value of QCM humidity sensor will increase with the increase of film quality,but other humidity sensitive properties may be affected,such as humidity hysteresis and response / recovery time increase.Among them,the QCM-8 humidity sensor shows a better comprehensive humidity sensitive characteristic within the range of 11%RH~95%RH,its response time is 49 s,the recovery time is 6 s,and the wet hysteresis is about 5%RH.