Contrasting Figures Figures1616 and and17,17, it is easy to find that the error of the slope in Figure 16 is far less than that in Figure 17. It says that the linearity for stress testing is better than that for temperature testing.4.3. Comparison of Resonant Properties between Stress and TemperatureWhen we put thenthereby the slope curve in Figures Figures1616 and and1717 together, and show them in Figure 18, the similar character between graphite lattice resonant cavity and square lattice resonant cavity can be found. It says that the temperature slope is far bigger than the stress slope; it means that this kind of resonant cavity is more sensitive for temperature, and what is more, the slope for temperature is also descending when the resonant cavity enlarges.

Of course, it means that we can reduce the sensitivity of the resonant cavity for temperature by enlarging the resonant cavity.Figure 18The slopes for the curves which are between resonant frequency and temperature and between resonant frequency and stress respectively.5. ConclusionWe have studied the temperature and stress characteristic of PBGS empty resonant cavities with square lattice and graphite lattice by FDTD method. The results show that the resonant cavities, both square and graphite lattice, have the similar character. Firstly, they have more and more resonant frequency with the cavity enlarging. Secondly, there is better linearity for the curves between the resonant frequency and stress. But when the cavity enlarges enough, the curve between resonant frequency and temperature will become sectionalized line from nonlinear curve.

Obviously, this character is convenient for us to test temperature. At last, the most important character for the resonant cavities is that the slope of the curves between resonant frequency and temperature will be descending as the cavity is enlarging. It means that the temperature sensitivity will be descending as the cavity is enlarging. Nevertheless, once you put some structure in the center of the cavity, this kind of cavity will fast raise the temperature sensitivity. Obviously, this character is convenient for us to design the temperature and stress sensor.AcknowledgmentsThe author would like to acknowledge Dr. QiuMing Luo for helpful discussions and the Super Computing Center, ShenZhen university, for support to their work.

This GSK-3 work was supported by Natural Science Basic Research Plan in Shaanxi Province of China, Grant no. 2010JM8006.
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