Research On QCM Gas Sensors Based On Polyaniline And Its Composites

Quartz crystal microbalance(Quartz Crystal Microbalance, QCM) gas sensor uses sensitive quartz crystal surface film as sensitive components and AT-cut quartz crystal as a transducing element. It realizes the detection of gas concentration by using the relationship between the quality of crystal and the frequency change. It converts the test gas concentration signal into a frequency signal to output.In this thesis, a quartz crystal microbalance gas sensor is deeply studied in order to monitor the fruit freshness in the process of storage, transportation and so on. The QCM gas sensor was developed with good sensitivity characteristics to bananas and apples. The ployaniline film doped with Toluene Sulfonic Acid(TSA) and SnO2 degree 10%, 20%, 50% of the PANI / SnO2 are synthesized by one-step in situ polymerization method. The sensitive film is coated on a quartz crystal with the fundamental frequency of 6MHz. The fruit QCM gas sensor samples are produced. The test platform is built which consists of start-up, plastic, difference frequency, F/V and data acquisition circuits. The response of the sensor to different days’ apple and banana releasing gas are tested at room temperature. The experiment results are compared and analyzed to select the sensors which have fast response, high sensitivity and good repeatability.Experiment results show that in a certain range, the doping concentration of TSA increases gas sensing performance of the sensor. The frequency variation of the sensor to the apple releasing gas placed on different days is dramatic increased. The sensor frequency change increases from fresh to rot. The sensor doped with 10% degree of SnO2 has the best sensitivity. The response to the three stages apple releasing gas are:581.49 Hz, 730.95 Hz and 1098.701 Hz respectively. The apples begin to rot when the frequency of the sensor reach 1058 Hz. Then the frequency variation of sensor begin to stabilize. The sensor frequency change to the banana releasing gas is sharply increased from fresh to mature. The frequency variation of the sensor begins to decrease when bananas start to rot. Finally it become stabilized. PANI sensor has the best sensitivity characteristics to banana releasing gas. The response to the three stages apple releasing gas are:1070.53 Hz, 2451.12 Hz and 1834.68 Hz respectively. It can be used to judge whether the bananas become mature. The bananas begin to mature when the frequency of the sensor reached 2309 Hz.Fruit releasing gas is mixed various ingredients after analyzed the three different levels of apples and bananas gas releasing with mass spectrometer. When the maturity degree of gas is different, the concentrations of each component gas is significantly different. Therefore the sensor shows different response characteristics to different days’ apple and banana releasing gas. The results show that the QCM fruits releasing gas sensor which the paper developed has the advantage of high sensitivity, good linearity, fast response and good repeatability. The researched sensor is expected to be applied in the fields of fruit storage and transportation.