This paper presents models developed through analytical or numerical computation and finite element analysis to improve the resolution of a new kind of vibrating magnetometers. This peculiar magnetometer uses the piezoelectric transduction to actuate a quartz resonator at its resonance frequency taking advantage of the high Q factor of a quartz resonator to achieve high resolution. The magnetic sensitive element is a thin ferromagnetic film of Nickel-Cobalt which is sputtered on the moving beams of the resonator. This magnetic thin film applies a periodic torque on the resonator, shifting its resonance frequency. This torque depends on the magnetic field applied; therefore the value of the magnetic field can be deduced from the frequency shift measurement. The aim of this paper is to develop and improve sensitivity models which will be useful tools in a future work to establish the optimal geometry for a resonator and the best position of the magnetic thin film on it in order to improve the sensitivity and resolution of the global sensor.
This paper investigates the design of a Vibrating Beam Accelerometer (VBA) with a resolution of 50 nano-g combined with an integrated thermal sensor. Despite quartz intrinsic thermal stability, the time delay between vibrating beam's temperature and package's temperature gives way to unwanted transient thermal behavior and thus bias instability. The aim of this study is to include a thermal sensor consisting in a torsional resonator directly at the center of the beam. Previous work demonstrated the feasibility of such integration on a tactical class accelerometer but also highlighted limitations like high motional resistance of the torsional resonator. Benefits of the in-situ temperature sensor are investigated thanks to finite element analysis of the accelerometer transient thermal behavior, which shall be compared to measurements on actual cells.
In [1] we presented a new length extension mode (LEM) piezoelectric micro-resonator. Thanks to a specific design, anchor losses were lowered to maximize the Q.f product and the resonator. Viscous fluid damping is neglected since the resonator is under vacuum and so is the thermoelastic damping for a length extension mode. With a Q predicted over one million the resonator is well suited for MEMS oscillator devices. Nevertheless it appears that one remaining loss source was not evaluated through our previous work: the viscoelastic damping arising from the presence of gold electrodes on the resonator surface. To investigate the influence of the gold thin film on this new resonator, we studied several papers on the quality factor of gold coated resonators and deduced a frequency dependence of the viscoelastic behavior of the gold thin film. This dependence shows that the damping for the LEM resonator won't be as important as firstly predicted and is compliant for time and frequency applications. Furthermore, the damping can be reduced to improve the quality factor with new electrode designs. These designs shall also provide low motional resistances in order not to deteriorate the phase noise far from the carrier. Two different approaches are compared to reduce electrode damping for the LEM resonator: contactless electrodes and partial electrode coating on the resonator surface. It appears that both approaches are interesting regarding the available processing technologies and give promising phase noise predictions.
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