A mixed pseudo-orthogonal frequency coding (Mixed-POFC) structure is proposed as a new spreadspectrum technique in this paper, which employs frequency and time diversity to enhance tag properties and balances the spectrum utilization and code diversity. The coding method of SAW RFID tags in this paper uses Mixed-POFC with multi-track chip arrangements. The cross-correlation and auto correlation of Mixed-POFC and POFC are calculated to demonstrate the reduced overlap between the adjacent center frequencies with the Mixed-POFC method. The center frequency of the IDT and Bragg reflectors is calculated by a coupling of modes (COM) module. The combination of the calculation results of the Bragg reflectors shows that compared with a 7-chip POFC, the coding number of a 7-chip Mixed-POFC is increased from 120 to 144 with the same fractional bandwidth of 12%. To demonstrate the validity of Mixed-POFC, finite element analysis (FEA) technology is used to analyze the frequency characteristics of Mixed-POFC chips. The maximum error between designed frequencies and simulation frequencies is only 1.7%, which verifies that the Mixed-POFC method is feasible.

The paleo-tectonic stress fieldwas hereby inverted by using the stereographic projection method through field and underground observations of conjugate shear joints. On the basis of analyzing and studying the characteristics of gas occurrence in mining areas, the control effect of paleo-tectonic stress field on gas occurrence was discussed from three aspects of gas generation, preservation environment and gas migration. The results show that: (1) During the Indosinian and early-middle Yanshan period, the coal seam was buried deep, and the temperature and pressure conditions were suitable for massive gas generation, especially during the Indosinian period featuring massive gas generation and weak gas migration; (2) During the late Yanshan period, the metamorphic evolution rate of coal seams accelerated, secondary hydrocarbon generation occurred in the coal seams, and a large amount of gas was generated. Meanwhile, the gas migration was enhanced. The gas generation amount was much larger than the emission amount, therefore, making it still a period of massive gas generation in general; (3) During the Himalayan period, the coal measure stratum was in the uplift stage, and a large number of geological structures were developed in the stratum. The tectonic stress field in this period caused the escape of massive coal seam gas. Multi-stage tectonic stress field acted on coal measures strata in turn, resulting in gas generation in coal seam and gas migration at the same time. Besides, gas occurrence is the superposition effect of gas generation, preservation conditions, and gas migration in coal seam.