Qiying Liu

This work presents a theoretical study on the size-dependent free vibration of porous nickel-alumina functionally graded (FGM) microplates. A refined continuum model is established by integrating the modified couple stress theory (MCST) with Kirchhoff plate theory. Unlike traditional models, this framework explicitly incorporates a power-law distribution of the material length scale parameter and corrects for the physical neutral surface shift. The vibration characteristics under four distinct porosity distribution patterns (Even, X, O, and V-types) are systematically evaluated. Significantly, a counter-intuitive ‘frequency reversal phenomenon’ is revealed in the Ni-Al ₂ O ₃ system. It is found that while the uniform (Even) porosity yields higher fundamental frequencies in ceramic-rich regimes, the optimal strategy shifts to uneven distributions (specifically O-type) in metal-rich regimes. This reversal mechanism is attributed to the competition between global mass reduction and local stiffness preservation, driven by the extreme density contrast of the nickel phase. These findings provide new physical insights into the mass-stiffness coupling effect in micro-scale composites, offering theoretical guidance for high-performance MEMS resonator design.

Resonant MEMS sensors operating in harsh fluidic environments demand high sensitivity and structural robustness, which conventional silicon devices often fail to provide. This paper proposes the design and comprehensive multiphysics calibration of a highly sensitive, photothermally actuated MEMS sensor utilizing a porous Cu-Ni functionally graded material (FGM) microcantilever. Rather than traditional power sensing, this study pioneers its application in trace mass sensing, providing a rigorous mass-loading calibration curve ([[EQUATION]]). The device exhibits an exceptional trace mass sensitivity of 25.5 Hz/ng in air and maintains a highly linear responsivity of 8.5 Hz/ng even in heavily damped aqueous environments. Through rigorous topology optimization, a central (O-type) pore distribution is identified as the optimal configuration to capture target molecules near the physical neutral plane, successfully overcoming the traditional mass-stiffness penalty. Furthermore, fluid-structure interaction analyses confirm the sensor's operational integrity in highly viscous fluids (e.g., gasoline and water), retaining significantly higher Q-factors than conventional counterparts. By validating these device-level metrics using the Modified Couple Stress Theory (MCST) and Temperature-Dependent Material Properties (TDMP), the proposed Cu-Ni FGM sensor offers a robust, high-stability paradigm for next-generation in-situ mass detection in harsh environments.

High-performance resonant mass sensors are increasingly demanded for the trace detection of volatile organic compounds (VOCs) and hazardous gases in environmental monitoring. A critical challenge in current gas sensors is the inherent trade-off between increasing the specific surface area for gas molecule adsorption and maintaining the structural stiffness required for high-frequency resonance. This paper proposes a novel high-sensitivity micro-resonant gas sensor based on a porous functionally graded material (FGM) sandwich microplate. To accurately calibrate the sensor's dynamic response at the micro-scale, a refined mathematical model is established using the Modified Couple Stress Theory (MCST) with a position-dependent material length scale parameter. Furthermore, a multi-objective topology optimization framework based on the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is developed. Rather than using pre-defined porous patterns, the algorithm autonomously aligns the mass-removal regions with the physical neutral surface of the microplate. By maximizing mass reduction in this low-stress region while preserving flexural rigidity, the optimized free-topology design achieves a 29.9% increase in the fundamental frequency compared to conventional O-type designs. This frequency boost directly translates to a significantly enhanced mass responsivity, providing a rigorous theoretical and design foundation for next-generation trace gas measurement devices.