Dual Sound Channel Saw Mass Deposition Effect Sensor Research

After mechanisation and informatisation of human activities,the acquisition of the right information has become the largest obstacle to total automation. Therefore,breakthroughs are required in technology,price,size,weight,power consumption and user-friendliness.SAW sensors have the advantages of high sensitivity,low cost when produced in large volume,low power consumption,ruggedness and lightness. They also have the potential of sensing various physical,chemical and biochemical measurands. Because of that,SAW technology,after having received wide use in signal processing applications,has become the focus of considerable research efforts in recent years for sensor applications.In the present thesis,a mass-loading-effect SAW sensor was developed. A square sensing area was formed upon each of the SAW propagation paths using photoresist. When some kind of material deposits on this area,the SAW propagation velocity will decrease due to the mass-loading effect,causing a shift in the device's oscillation frequency,which gives indication of the mass deposited. The dual-path architecture,one for sensing and one for reference,was used to compensate for the disturbance of temperature.The thesis consists of seven chapters. Chapter 1 introduces the principle of SAW devices. The signal processing applications of SAW technology is also briefly reviewed in chapter 1,with the emphasis laid on mobile communications. Chapter 2 summarizes the applications of SAW technology sensors,including their functional mechanisms,their applications reported to date and their special applications. In chapter 3,the design considerations and fabrication process of the SAW sensor chip are given,while the design of the measurement circuit is presented in chapter 4. The measurement results are introduced in chapter 5,including the direct characterization of the sensor chip,the evaluation of the measurement circuit,the effect of the temperature compensation and the sensing characteristic of the whole system. Some suggestions for further investigation and optimization are given in chapter 6 whileChapter 7 is devoted to the summary and conclusion.The temperature coefficient was measured to be 7Hz/C,which was three orders of magnitude lower compared with that of the single path configuration. The reduced sensitivity turned out to be 49ppm cm 2 / g,which lies in reasonable agreement with the theoretical prediction. The linearity is 4%. This sensor system can be adjusted to measure various measurands if proper selective absorption films are utilized.