| During the parameter acquisition of rotating components, methods to transmit the collected parameters and process signals from the rotating components to fixed receiver reliably and accurately have always been the key factors that affect the performance of data transmission in rotating environment. Wireless data transmission is an efficient way to resolve data transmission problem of rotating components. In rotating environment, the design of wireless data transmission system is based on EMWP (Electromagnetic wave propagation), which has yet seldom been studied at home and abroad. In this dissertation, EMWP characteristics in rotating environment are fundamentally studied in order to provide a strong theoretical support for developing high-performance rotating component radio monitoring system. Furthermore, the research results are applied in designing TPMS (Tire Pressure Monitoring System). The main contents are as follows: Assuming the rotation-related time and space parameters, EMWP characteristics in rotating environment are studied. In particular, the Doppler frequency shift, the dynamic characteristics of the transmitting antenna and the EMW polarization characteristics in rotating movement are analyzed. The free space path loss model in rotating environment is analyzed. The reflection two-ray propagation model as well as the good conductor reflection two-ray propagation model in rotating environment is studied in detail. The application of radio monitoring in rotating environment is also analyzed. The above research results are applied to the design of TPMS, and the new methods of improving wireless transmission performance are presented and tested as well.Some results are achieved through a lot of theoretical research and many tests.1. The mathematical relationships in rotating environment, i.e. the distance between transmitter and receiver as well as the unobstructed line-of-sight space angle at any time, are derived, which are also related to the parameters of rotation radius, angle, velocity, space wave vector, etc. By using Lorentz transformation, the relationship between the rotation Doppler frequency shift and working frequency, rotation radius, velocity, etc. is established. The results show that the Doppler frequency shift in rotation environment varies periodically like the cosine function curves. The higher the rotating velocity and the rotating radius are, the greater the frequency shift becomes, which can reach up to several KHz, even up to several MHz. Taking TPMS as an example, the dynamic variation characteristics of rotating transmitting antenna are analyzed and compared with single antenna. The impedance variations of transmitting antenna at 12 angle orientations as well as the gains directed towards receiving antenna are given. The results show that the antenna radiation patterns apparently change with tire rotating. In addition, EMW polarization characteristics from rotating transmitter are analyzed. The results show that the rotation changes the transmitting linear polarization wave into circular polarization wave, and polarization mismatch causes excess power losses.2. The general propagation model in rotating environment is established. The results show that the received signal envelope is related not only to path number of incident waves, attenuation coefficient, propagation time-delay,Doppler frequency shift and arrival angle in rotating environment, but also to path loss caused by impedance matching factor, antenna directivity, antenna efficiency and polarization mismatch at the rotating transimitting and fixed receiving ends. The free space path loss model in rotating environment is established. The results show that path losses vary periodically and fluctuate like cosine function curve. At given short distance, the periodicity of path loss change is the same as rotating periodicity. The bigger the velocity is, the faster the path loss changes. Considering the time-delay difference caused by both the direct propagation path and the reflected propagation path between rotating transmitter and fixed receiver, as well as the Doppler frequency shift caused by rotating velocity and incidence wave direction, the two-ray propagation model in rotating environment is established. Because of superposition, only two orthogonal polarizations, i.e. parallel and perpendicular E-field polarizations, need be considered to solve general reflection problems. The simulation results show that the path loss varies rapidly with the rotation angles in a large range. The reflection coefficient, the field strength envelope and the path loss vary with the parameters such as the radius of rotating components, rotation velocity, dielectric constant and working frequency. When the reflection plane is a good conductor surface, the study shows that the path loss fluctuation is more severe than that of ground reflection plane. In order to verify the two-ray propagation model, path loss test is carried out on outdoor ground. The test results show that the presented propagation model in this dissertation is reasonably accurate for predicting signal strength over radio monitoring in rotating environment.3. Based on the EMWP characteristics analysis, the model research and the current technology condition in rotating environment, a TPMS was designed, which includes the overall control scheme, the hardware assembly design and software strategy. The improving methods of wireless data transmission performance were presented, which include: Considering the twelve impedance values reasonably, the impedance value at 240 degrees orientation is used for impedance circuit matching design. Lower working frequency is used as carrier frequency. The length of data frame is optimized and shortened with efficient signal conditioning algorithm and high data rate. The transmitting antenna of metal valve is lengthened and placed as horizontally as possible, which makes the radiation E-field approximately parallel to the reflecting plane. Secondly, a large number of vehicle-carrying tests on various pavements are implemented for both the improved TPMS and the old TPMS. The test results show that wireless transmission power is increased by 20~30dB, and the receiving probabilities of successful data frame transmission are improved greatly. In urban district, mountain area, special high-speed pavement and bumpy pavement, the receiving probabilities are all more than 90 percent over wireless channel. In general high-speed pavement, the receiving probability is even more than 95 percent. Meanwhile, the test results prove that the improving methods are effective. Thirdly, vehicle-carrying function tests in various climates are carried out. The test results show that the TPMS is capable of monitoring rotating tire pressure and temperature reliably and accurately under various environments. Finally, to further improve the performance of wireless data transmission in rotating environment, a quasi-static antenna is presented. The antenna characteristics are analyzed and compared with the existing dynamic antenna. The results show that the gain and resistance of the presented quasi-static antenna is much larger than that of the rotating dynamic antenna, the mainlobe width increases, and that the received power from the quasi-static antenna is further increased by 10~20dB.
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