A simple and low-cost continuous liquid-level sensor based on two parallel plastic optical fibers (POFs) in a helical structure is presented. The change in the liquid level is determined by measuring the side-coupling power in the passive fiber. The side-coupling ratio is increased by just filling the gap between the two POFs with ultraviolet-curable optical cement, making the proposed sensor competitive. The experimental results show that the side-coupling power declines as the liquid level rises. The sensitivity and the measurement range are flexible and affected by the geometric parameters of the helical structure. A higher sensitivity of 0.0208 μW/mm is acquired for a smaller curvature radius of 5 mm, and the measurement range can be expanded to 120 mm by enlarging the screw pitch to 40 mm. In addition, the reversibility and temperature dependence are studied. The proposed sensor is a cost-effective solution offering the advantages of a simple fabrication process, good reversibility, and compensable temperature dependence.
This study presents a microelectromechanical systems S-springs vibration ring gyroscope (MSVRG), which is driven by electrostatic force and detected by capacitance. First, a ring resonator structure with eight S-shaped symmetrical supporting springs is developed, and the capacitor electrodes are designed according to the vibration characteristics of the ring resonator. Then, a precise equivalent stiffness model of MSVRG is established based on the vibration mechanics and the Cassette theorem, which can be employed for any other ring gyroscope with differently shaped springs. Moreover, the mode resonant frequency error of between experiments, finite-element analysis (FEA) and theory calculation, is 10.54% and 3.76%, respectively. After that, the process of MSVRG structure is introduced and the structure is manufactured, and the theory calculation and FEA value with processed parameters have 1.19% and 4.59% difference with resonant frequency tested value, respectively. Finally, the static performance of the fabricated MSVRG is tested, and the bias instability is about 0.0119 deg/s and angle random walk is about 0.0359 deg/s1/2 at room temperature.
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