Electronic Nose Based On A Wireless Acoustic Wave Sensor Array

Electronic nose(E-nose)is a kind of vapor detection and analysis instrument imitating the mammalian olfaction system.The E-nose uses data mining and pattern recognition algorithm to analyze the sensor array's response of analyte vapors.E-nose technology has developed rapidly over the past decades,which has attracted considerable attention and been applied widely in the fields of ambient air monitoring,biomedical diagnostics,food quality assurance and medicinal materials supervision for its advantages of fast testing,easy operation and low cost.The E-nose based on the traditional quartz crystal microbalance(QCM)has been researched and developed due to its high sensitivity,low cost and small size.However,the "sandwich" structure and self-excited oscillation mode of traditional QCM sensors have limited the possibility of a higher working sensitivity,a lower detection limit and a wider application scenarios.The technology of wireless and electrodeless QCM-D(WE-QCM-D)has effectively solved the limitations of traditional QCM in detection performance and application,and has the benefits of higher detection accuracy,lower cost,and non-contact measurement.Therefore,a new design of E-node based on WE-QCM-D sensor was proposed and implemented in a way of simpler fab-rication and lower cost.In this work,the hardware and circuit of the WE-QCM-D sensor array that works in time-division multiplexing mode was designed and a experiment software platform based on Lab VIEW was developed for automatic controlling of circuits and devices and online data collection,calculation,display and storage.Then,the vapor chamber and gas line part were designed and manufactured.Finally,three E-nose vapor detection systems based on physical sen-sor array(PSA),virtual sensor array(VSA)and hybrid sensor array(HSA)were designed and assembled.The E-nose based on WE-QCM-D PSA consists of four physical sensors,shared the most of hardware circuits and software through time division multiplexing.The E-nose system has the ability of discriminating five volatile organic gas(VOCs)of 50 ppm at the accuracy of 90.I%with k nearest neighbor(kNN),and even toluene and heptaldehyde could be completely classificated at multiple concentration(10 ppm-50 ppm).In addition,the analysis of experimental results proves that the functional groups and structures of gas molecules and sensitive membranes are important factors affecting the gas adsorption capacity.Through single quartz's working at different resonance frequencies,a E-nose based on WE-QCM-D VS A was fabricated,expanding the dimension of the sensor response in the frequency space.The E-nose based on WE-QCM-D VSA has achieved of the identification rate of 97.5%with kNN to 7 VOCs vapors in multiple concentration,which has the ability of observing the frequency and dissipation response simultaneously.The frequency response fingerprint pattern reveals the concentration distribution of gas molecules in the sensitive membrane and the phys-ical structure properties of the gas molecules.And it is observed from the dissipation response fingerprint pattern that the adsorption of gas molecules caused changes in sensitive membrane's structure and the gas molecules had a concentration distribution in the membrane thickness's di-rection.Therefore,it is conclude that the frequency expansion of the single WE-QCM-D sensor not only enhances the ability of gas identification but also facilitates analysis of the gas adsorption mechanism.Finally,an E-nose based on WE-QCM-D HSA was built through expand multiple harmonic channels in one physical sensor of WE-QCM-D PSA with four sensors.A set of gas experiments of headspace vapors discrimination for seven traditional Chinese medicine,a complex component gases discrimination,was designed to test the E-nose HSA system's ability.And finally the E-nose HSA system achieved a recognition rate of 95.2%based on support vector machine(SVM).It is proved that the expansion of VSA does help in improving the recognition rate of the E-nose system,and also helps to analyze the response mechanism.In summary,this work designed and implemented an E-nose system based on WE-QCM-D,and examined the performance of the E-nose system to VOCs vapors and Chinese medicine headspace vapors,which simplifies the E-nose system structure,reduces costs and improves the sensitivity,improves the classification accuracy,and expands the detection analysis abilities and application scenarios of the E-nose based on WE-QCM-D.