Sebastian Weidlich

The aviation industry is adopting liquid hydrogen (LH₂) for sustainable flight, requiring robust safety systems. This work is an example of adaptation of a Micro-Electro-Mechanical Systems (MEMS)-based structural health monitoring (SHM) system for LH₂ tanks, developed in the H2ELIOS project. It uses a multisensor approach that combines MEMS sensors to monitor vibration and acceleration, shape memory alloy (SMA) strain sensors for measuring tank expansion, and hydrogen leakage sensors to prevent false alarms. This SHM technology detects cracks and delamination of material and coating, enabling predictive maintenance via digital twins and ensuring structural integrity.

This letter investigates the origin of zero-rate-output (ZRO) anomalies observed in Lissajous frequcy-modulated (LFM) microelectromechanical systems (MEMS) gyroscopes employing electrostatic ring resonators. Although LFM detection offers high scale-factor stability through frequency-based angular-rate encoding, residual bias errors often emerge even under zero angular rate. Experimental measurements reveal the presence of a second-harmonic component in the frequency modulation that cannot be explained by conventional linear cross-axis coupling models. To clarify this behavior, a theoretical model is developed considering the inclination of parallel-plate electrostatic transducers under large-amplitude wineglass-mode vibration. The analysis shows that the electrostatic stiffness becomes quadratically dependent on the vibration amplitude of the orthogonal mode, producing a second-order coupling term proportional to $\cos (2\theta)$. Experimental results obtained using an field-programmable gate array (FPGA)-based dual-axis control system confirm that the amplitude of the second-harmonic component scales with the square of the drive voltage, validating the proposed model. These findings demonstrate that plate-tilt-induced nonlinear coupling is a major source of ZRO fluctuation in LFM gyroscopes.