Department Seminar of Omer Halevy - New approaches for sensitivity enhancement in resonant accelerometers

14 June 2023, 14:00 - 15:00 
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Department Seminar of Omer Halevy - New approaches for sensitivity enhancement in resonant accelerometers

 

School of Mechanical Engineering Seminar
Wednesday 19.06.2023 at 14:00

Wolfson Building of Mechanical Engineering, Room 206

New approaches for sensitivity enhancement in resonant accelerometers

Omer Halevy

PhD student under the supervision of Prof. Slava Krylov

School of Mechanical Engineering, Tel Aviv University, Tel Aviv, Israel

 

Resonant inertial micro sensors in general and resonant accelerometers in particular, have gained significant attention of researchers and microelectromechanical systems (MEMS) practitioners.  Compared to their statically operated counterparts, resonant devices demonstrate higher sensitivity, wider dynamic range and better robustness. In micro scale resonant accelerometers, the inertial forces transferred to the vibrating sensing element by the proof mass of realistic dimensions are usually too small to provide sufficient measured frequency shift. To overcome this sensitivity limitation, various force amplification approaches have been suggested, including geometric offsets, mechanical leverages or electrostatic tuning.

In this work we explore two possible approaches for sensitivity enhancement of resonant accelerometers. The first is based on the use of an electrostatically actuated bistable cantilever serving as a sensing element. In the framework of the suggested architecture, the beam and the proof mass are coupled through fringing electrostatic fields. The electrodes configuration is tailored in such a way that small deflection of the proof mass results in perturbation of the electric field and thus of the effective stiffness and frequency of the cantilever. The device’s nonlinear dynamics are described using reduced order Galerkin and numerical finite differences models; a finite elements analysis is used for the evaluation of the electrostatic forces. The architecture of the electrodes allows tuning of the beam behavior in a wide range, starting from linear and up to nonlinear bistable responses. By choosing an appropriate value of the actuating voltage, close to the bistability threshold, the cantilever can be positioned in a configuration where the frequency sensitivity of the device to the electrode’s deflection is enhanced while the frequency itself is higher than in the initial unactuated state. The multilevel sensing element structure was fabricated from a Silicon on insulator wafer using a two-stage critically timed deep reactive ion etching. The device was operated statically and dynamically, and an increase of the resonant frequency induced by an increase in the voltage/deflection was registered. Based on the model and experimental results, by integrating the bistable cantilever with a proof mass, a design of a highly sensitive resonant accelerometer with a state-of-the-art performance is presented.

The second design is a novel architecture of a resonant accelerometer incorporating four proof masses and a compliant parallel motion linkage as a force amplifier. A simple, Manhattan geometry, manufacturable, device is distinguished by low parasitic compliance and purely axial, lacking any bending, loading of the sensing beams. Silicon on insulator devices were fabricated using an external subcontractor services and operated in open loop and in a non-differential mode, the acceleration was emulated by an electrostatic force. Consistently with the model prediction a sensitivity of ≈ 2.3 Hz to voltage square [S1] was experimentally demonstrated in a Silicon device with ≈ 500 μm×480 μm×25 μm proof masses and 250 μm long and ≈ 1.5 μm wide resonant sensing beams. This value was converted to an equivalent scale factor of ≈ 417 Hz/g, through the use of the parallel plate actuator model.

In addition, the nonlinear dynamic behavior of a generic differential vibrating beam accelerometer is studied numerically and analytically with the emphasize on the frequency locking phenomenon. The device incorporates two tuning fork oscillators attached to a proof mass and described as a weakly nonlinear Kirchhoff beam driven through the self-excitation loop. Our numerical results obtained using the reduced order model indicate that the influence of the geometric nonlinearity and inertial coupling on the locking is minor while the role of the structural coupling is dominant. An analytical prediction of the acceleration range where the locking occurs is obtained by considering a two coupled Van der Pol oscillators model and is found to be in a good agreement with the numerical results.

Join Zoom Meeting https://tau-ac-il.zoom.us/j/86497933118

 


 [S1]Why we cannot write the SF here? As in the paper?

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