FREQUENCY-OUTPUT FORCE SENSOR USING A MULTIMODE DOUBLY ROTATED QUARTZ RESONATOR

This paper discusses the usability of disk-plate resonators operating in thickness-shear modes as force sensors providing frequency output. The main limitation occurring in the case of single-mode operation comes from its thermal sensitivity. Thus, we suggest a drastic reduction of this limitation by simultaneous operation on two vibrating modes. This can be done because both the force and temperature sensitivities of thickness modes can be predicted and are reproducible. Then the frequency variations of both operating modes appear as the right-hand sides of a system of two equations in terms of two unknowns: force and temperature. If both modes are properly chosen, we can expect better results by solving this system than separately measuring temperature and then correcting the output, as would be done in the case of monomode operation. It is shown that simultaneously using so-called anharmonic modes presents significant advantages in the suggested kind of sensors. The discussion includes experimental results obtained from SC-cut contoured resonators, although an actual realization should not necessarily be limited to this cut.