Theoretical Analysis, Design And Simulation Of SAW Microsensors In TPMS

Tire Pressure Monitoring System (TPMS) is a system alerting the driver when the pressure or temperature of the tire drops to an unsafe level. TPMS will not only help prevent accidents, but save consumption of fuel and vehicle maintenance costs. Two kinds of TPMS products are being developed, referring to indirect TPMS and direct TPMS. Compared with the indirect TPMS, the direct TPMS is much better in performance. As far as the direct TPMS is concerned, there are two types of products, according to the different sensors through which the products work. One type employs the active sensors and the other utilizes the passive sensors. The passive sensor is widely developed in the industry.This thesis aims at optimizing the design of a novel wireless passive SAW sensor, based on the theoretical analysis and the numerical simulation. Overall, the thesis includes the following parts:(1) This paper discusses, both qualitatively and quantitatively, the operation and the design principle of the SAW sensor in which the internal reflection within inter-digital transducers (IDTs) is not negligible. For this purpose, the P-matrix model new expreression is developed utilizing the coupling-of-modes (COM) theory. The applicability and accuracy of theP-matrix expreression in analyzing the unitary symmetry IDT and reflector are validated.(2) The design of a novel wireless passive SAW sensor is optimized. This novel SAW sensor is built with a SAW delay line element connected to an antenna. The SAW delay line element consists of a substrate, an inter- digital transducer (IDT), and a reflector. IDTs employed in this research have bidirectional and symmetric structures. Reflectors are designed as unitary short-circuit gratings.(3) The application of the P-Matrix expreression in designing SAW sensors is discussed, utilizing the analysis of the SAW sensors as an example. First of all, the admittance of the IDT and the reflection coefficient of the reflector in the SAW sensor are analyzed using the P-Matrix. The analysis reveals that the reflection coefficient has proper bandwith. The admittance of IDT can be implemented to design the conductance and the matched susceptance of the antenna, consequently fulfill the impedance matching. Secondly, the stimulation of SAW through IDT is analyzed via the P-Matrix method and the expression of the insert loss (IL) can be obtained. The analysis of the IL of our SAW sensor design reveals that this novel design has excellent performance in the respect of IL.(4) The SAW sensor design is sinulated using commerical software CoventorWare?. The distribution of the electric field on IDT, the surface acoustic wave on one period of IDT, and the bending on delay line section, are simulated and analyzed.