A study on raising the fundamental TS-mode resistance by energy trapping for 3rd overtone resonator performance enhancement

AT-cut quartz resonator is used widely as a frequency source in electric devices. The main mode of AT-cut quartz plate is thickness-shear mode, which the frequency is inverse proportion to the plate thickness. Due to the sandwich structure, only odd thickness-shear overtones exist in AT crystal resonators. Normally, the vibration amplitude of fundamental mode is larger than that of all overtones. And that means the effect-series-resistance of the fundamental mode is lowest. In this paper, different energy trapping effects of fundamental and 3^rd overtone are used to control the resistance ratio of these two modes. Two kinds of 5.0*3.2mm size resonators, 50MHz and 54MHz 3^rd overtone (the fundamental mode frequencies are 16.67MHz and 18MHz, respectively), with different beveled chips are made. Comparing to the 3^rd overtone, the fundamental mode has longer wavelength and stronger penetration ability to sink energy through the mounted end. The experiment data show that a proper beveling could cut the energy flux of 3^rd overtone off, but allow some energy flux of fundamental mode propagates outward. And then the resistance ratio of these two modes could be controlled.