Font Size: a A A

Detection And Analysis Of Gas Mixtures Based On Micro-hotplate Gas Sensors

Posted on:2007-05-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:G F WeiFull Text:PDF
GTID:1118360182960774Subject:Mechanical and electrical engineering
Abstract/Summary:PDF Full Text Request
The micro-hotplate gas sensors have been an important achievement in MEMS field, due to their merits such as small size, low power and easy integration. However, their selectivity and stability are still very low, which confines their utilization and industrialization. This dissertation pays attention to the selectivity improvement methods of the tin oxide based micro-hotplate gas sensors. Starting from the fabrication and characterization technology of the gas sensors, systematical studies have been performed on the gas sensing mechanism, gas sensor array and temperature modulation techniques, as well as their applications into the detection and analysis of the carbon monoxide and methane gas mixtures.An automated gas sensor characterization and measurement system is firstly designed and constructed. A batch of micro-hotplate gas sensors are fabricated with the micromachining technology and their performances are systematically studied with the characterization and measurement system. According to the analysis of the material characterization results, the quantum mechanical ab initio method has been applied to simulate the physical chemical adsorption of CO, CH4 and O2 on the surface of the SnC>2 thin film. Combining with the surface barrier theory of semiconductors and the dynamic balance theory of the physical chemical adsorption, the SnO2 gas sensor's electronic response equation to CO and CH4 gas mixtures is deduced in detail and established, verified by the experimental data based on the multi-parameter optimization. The influence of ambient oxygen on sensor's sensitivity is also discussed.According to the model of sensor's response to gas mixtures, the selectivity improvement methods by using gas sensor array are investigated. The blind gas source separability is discussed based on the linear steady response and the Blind Source Separation (BSS) method is applied to analyze the gas mixtures. Associating with the practical data, the nonlinear Principal Component Analysis (NLPCA) and the Independent Component Analysis (ICA) methods are studied to identify and quantify the CO and CH4 gas mixtures, compared with the Principal Component Analysis (PCA) in common use, the mean absolute quantification errors of CH4 and CO are reduced about 200ppm and 7ppm respectively. The nonlinear steady responses areprocessed with NLPCA or combining the BSS techniques with the BP neural networks, which is efficient to improve the gas quantification accuracy.The gas sensor's dynamic response characteristics are also studied while the operating temperature is changed with some rule. The subtractive preprocessing method is proposed to restrain the strong signal caused by the temperature variation of the micro-hotplate and to extract the weak signal caused by the dynamic adsorption of gases on thin film surfaces at the temperature modulation modes. Combining with the Short Time Fourier Transform (STFT), the frequency feature method is applied to study the gas sensor's ability to recognize CO, CH4 and ethanol modulated with sine wave, rectangular wave, triangular wave and sawtooth wave at different periods and temperature ranges. To simplify the computation, virtual array method is proposed to detect and analyze the gas mixtures.Real-time gas detectors are developed with a single chip processor as the control and signal processing center for CO and CH4 gas mixutres, the two major flammable and explosive gases in coal mines. Experimental results verify the realization methods, which is useful and significative for developments of the electronic nose system on a chip.
Keywords/Search Tags:Micro gas sensor, Electronic nose, Blind Signal Separation, Gas mixture analysis, Temperature modulation
PDF Full Text Request
Related items