| As one of the key foundations of the modern information technology, the sensor technology has been held great attraction for people. Surface acoustic wave (SAW) sensor using the surface acoustic wave as the information sensing carrier is characterized by high sensing accuracy, short response time, wide range of application and small size. SAW sensors are very promising for meeting the needs of aerospace, food hygiene, environmental monitoring ,medical and chemical industry, process monitoring, military affairs and security services etc.. Especially, as chemical sensors for measuring high fatal chemical warfare agents in real time, SAW sensors exhibit technologies superiority. Now, SAW sensors have become the first choice of the military in every country.Although SAW sensors have such advantages as high sensing accuracy, short response time etc, the worse selection and weak anti-interference are the intrinsic shortcomings of SAW sensors due to the multi-parameter information sensing properties. At the complex conditions, especially at the detection environments of chemical warfare agents in real time, these intrinsic shortcomings have great limitations to the applications of SAW sensors. How to overcome these shortcomings of SAW sensors have become a study topic of general interest. Supporting by the subject of"Theory and Technology Study on SAW Chemical Sensors", the multi-parameter information sensing theory of SAW sensor and its key technology have been deeply studied. The physical process of the selection and anti-interference of SAW sensor have also been described in this paper.Based on the basic theory and the physical process of SAW sensor information sensing, the partition of the three physical processes of the information-signal mapping and its corresponding mathematical expressions have been proposed. The model of SAW sensor information sensing has been established. Using this information sensing model and on the basis of the SAW signal to electrical signal frequency parameter mapping mechanism of SAW oscillator, the signal processing model of SAW sensor has also been built up. According to these models and the ability of SAW array signals to provide the redundant information, the multi-parameter information sensing model and the multi-parameter signal processing model of SAW sensor—the K matrix, have been set up. Thus, the theoretical foundation of SAW sensor systematic analysis and design based on the multi-parameter information sensing and recognition was put up. The key technology of SAW chemical sensor system design under the multi-parameter disturbance condition has been studied in this paper. A SAW sensor system for measuring Sarin gas with the concentration of less than 1ppm at the temperature disturbance has been designed. The performance of the system under the conditions of single-parameter and multi-parameter disturbance has also been tested and analyzed.The main points of this work were set forth as follows:1. The theoretical foundation of SAW sensor multi-parameter information sensing The theory foundation of SAW sensor, including SAW piezoelectric vibration theory, disturbance theory of SAW sensor and analytic theory of SAW device, was analyzed systematically. The idea that the linear superposition of SAW solution on the piezoelectric substrate is the physical basis of multi-parameter sensing of SAW sensor was proposed in this paper. This laid down the theoretical basis for establishing the mathematic analytic model of SAW sensor multi-parameter information sensing system.2. Establishment of the information sensing and signal processing models of SAW sensorThe full physical process of SAW sensor information sensing was classified innovatively as three basic mapping processes. These are:(1) Mapping from the external disturbance I to the physical parameterαon the piezoelectric substrate(2) Mapping from the physical parameterαon the piezoelectric substrate to change of SAW signal parameter(3) Mapping from SAW signal parameter change to electric signal parameter changeIt was found that the first mapping process of these three mapping processes in SAW sensor information sensing, i.e., mapping from the external disturbance I to the physical parameterαon the piezoelectric substrate, was the key link in causing distortion of SAW sensor information sensing. Based on the idea that the piezoelectric basic physical parameter"measures"the disturbance, the mathematic expressions which describe the three mapping processes is given . According to these mathematic expressions, the mathematic analytic model of SAW sensor multi-parameter distortion information sensing could be established, thus laying down a key technology foundation for establishing the signal model of SAW chemical micro-gas sensor system.3. Establishment of the information sensing and signal processing models of SAW multi-parameter sensorAccording to the mapping from SAW signal based on SAW oscillator to electric signal, any disturbanceΔIj loaded on SAW signal through SAW sensing element was mapped to the expression of frequency parameterΔωof electric signal, and then the signal processing mathematic model fromΔIj toΔωwas established. Based on both this model and the model of multi-parameter information sensing of SAW sensor, the multi-parameter signal processing mathematic model of SAW sensor from the disturbance vectorΔI correlated with the time-space to the frequency vectorΔωof the electric signal was established, thus converting effectively the multi-parameter sensing of SAW sensor into the orthogonalization processing of the electric signal and realizing the integrated signal processing of SAW sensor multi-parameter information sensing identification technology. As a result, not only the current SAW sensor multi-parameter information sensing identification technologies could be analyzed and evaluated, but also can point out the way for developing new SAW sensor multi-parameter information sensing identification technology.4. Study on the key technology of SAW chemical micro-gas sensor system and the system designSAW multi-parameter sensor system for measuring the micro-gas of sarin (G) at temperature disturbance was analyzed. The key techniques which may influence the accuracy of system sensing, response speed and information identification ability, including design of SAW sensing device array, design of SAW oscillator, preparation of chemical absorption film material, coating technique of absorption film, the structural design of SAW sensor, signal processing and measurement of SAW sensor etc., were investigated in depth. The basic design requirements and optimal design parameters for reaching the performance goal of this experimental system were obtained, such as the optimal structural design parameters of Saw delay line and the minimum Q value requirement, the optimal operating frequency range of SAW oscillator and the minimum frequency stability, the optimal absorption method of chemical absorption film material and infrared characterization of its property, the optimal coating technique of chemical absorption film material and the minimum rotation speed of spinning coating technique, the optimal signal measurement method of SAW sensor and the structural design of SAW sensor. All of these works have laid down a foundation for designing SAW chemical micro-gas sensor system.5. Realization of SAW chemical micro-gas sensor system design and sensor system experimentSAW chemical micro-gas sensor system was designed based on the information sensing model and signal processing model of SAW multi-parameter sensor. The component performances of SAW chemical micro-gas sensor system, sensing performance of temperature T and chemical gas G as well as the disturbance sensing performance of T and G multi-parameters were tested.6. The performance analysis of SAW chemical micro-gas sensor systemThe test data of the high stable crystal oscillator, the temperature variations of SAW device and SAW oscillator, effect of the chemical absorbing film on SAW device, the temperature (T) sensing and the chemical gas of Sarin (G) sensing, as well as the multi-parameters T and G disturbance sensing have been analyzed quantitatively and qualitatively. Based on these test data, the sensing accuracy and the recognition error of the temperature (T) and Sarin (G) of SAW multi-parameter sensor have been calculated approximately. The results have showed that the SAW sensor system meets the design specifications perfectly. The correctness of the analytical model of SAW multi-parameter sensor system has been demonstrated.From the viewpoint of the information sensing system, SAW sensor system has been studied in this paper. Aiming at the high rate of misrecognition and weak anti-interference, a whole mathematic analytical model of SAW sensor system based on the multi-parameter sensing has been proposed and established innovatively. The theoretic and technology foundations of the design and analysis of SAW multi-parameter sensor system have been built up. To meet the urgent requirements for measuring Sarin (G) gas in real time, SAW chemical micro-gas sensor system at the multi-parameter disturbance of Sarin (G) and temperature (T) has been developed firstly in domestic. This work will propel the development of SAW sensor technology in China forward.
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