Xiaoyi Wang

Handheld Fourier-transform near-infrared (FTNIR) microspectrometers demand MEMS micromirrors capable of generating large piston displacement (LPD) for high spectral resolution, alongside the strict mechanical robustness required for field deployment. However, conventional electrothermal actuators rely on rigid and brittle inorganic dielectrics (e.g., Al-SiO2), which severely suffer from impact-induced fracture and inherently restrict the maximum actuation stroke. Here, we demonstrate a highly robust LPD electrothermal micromirror driven by an aluminum-photosensitive polyimide (Al-PSPI) bimorph actuator. The device features a 1 mm × 1 mm square mirror within a compact 1.85 mm × 1.85 mm footprint. Leveraging the superior mechanical compliance and resilience of PSPI, the actuators can survive drop heights up to 1.9 m, a 25-fold improvement over conventional Al-SiO2 bimorph counterparts. The micromirror achieves a maximum piston displacement exceeding 450 μm at an ultra-low driving voltage of 7.5 V, exhibiting a fundamental resonance frequency of ~588 Hz and a rapid response time of ~30 ms. To validate its practical utility, the micromirror was integrated into a compact, 350-gram handheld FTNIR prototype. The compact FTNIR achieves a spectral resolution of 26.2 cm-1 and covers a wide spectral range from 800 nm to 2500 nm, and it maintains stable operation under rigorous logarithmic sweep vibration testing (1 g, 20–2000 Hz, 12 min). This work establishes a versatile actuator design paradigm that fundamentally resolves the structural fragility of large-stroke MEMS mirrors, paving the way for next-generation portable hyperspectral imaging and highly reliable interferometric systems operating in extreme environments.

Real-time monitoring of bolt preload is vital for the predictive maintenance of critical infrastructures. Conventional approaches often rely on wired or battery-powered sensors, making them unsuitable for large-scale distributed deployments. This paper presents a novel passive wireless bolt preload monitoring system based on the ultrasonic time-of-flight (ToF). The system includes a sensor and a reader coupled through magnetic resonance coils. The sensor, consisting of a piezoelectric transducer and a resonant coil, is installed directly on the bolt head. The reader includes a 4.5 MHz radio frequency (RF) signal transceiver and a ToF measurement circuit. RF energy is wirelessly delivered to the sensor through the resonant coupling network to excite longitudinal ultrasonic waves within the bolt. Echoes from internal interfaces are coupled back through the same path for ToF information extraction. Experimental results show a strong linear correlation (R² > 0.999) between ToF and preload across various bolt sizes (M16, M18, M20), with measurement errors below 2 % compared to commercial sensors. The system demonstrates robustness against spatial misalignment, fixture variability, temperature shifts, and humidity variations. This passive wireless, non-invasive, and high-precision system holds strong potential for long-term structural health monitoring with minimal maintenance requirements.

Piezoelectric MEMS micromirrors for light modulation and optical beam steering have been drawing extensive attention recently, but their applications are still limited due to low fill factor and low resonant frequency, especially when the well-established piezoelectric material–AlN is employed. This study proposes a bow-shaped unimorph piezoelectric actuator that can generate multidegree-of-freedom motion with high fill factor. Particularly, a tip-tilt-piston (TTP) piezoelectric micromirror made of such actuators is designed, fabricated, and characterized. The fill factor is as large as 73% with a mirror plate size of $1.0\times 1.0$ mm. The measured resonant frequencies for the piston, tip, and tilt modes are 0.890, 1.747, and 1.781 kHz, respectively. The measured maximum piston stroke and tip or tilt angle reach $3.3~\mu $ m and 14.4 mrad with high linearity under 24 V_pp. This bow-shaped actuator design provides a new direction for enhancing piezoelectric actuation efficiency and capability.

In this paper, we present a novel specified-time adaptive output-feedback control scheme for microelectromechanical system (MEMS) gyroscopes subjected to sampling constraint. The primary contribution of this study lies in the development of a computationally efficient Unknown System Dynamics Estimator (USDE) based on the invariant manifold principle, which accurately estimates total system uncertainty with minimal computational cost. To overcome the potential corruption of velocity signals due to measurement noise and the inherent resource limitations of MEMS gyroscope platforms, we integrate a variable-threshold event-triggered state observer into the USDE. This innovative architecture replaces actual velocity measurements with their estimated values, ensuring high estimation accuracy while minimizing computational burden. Additionally, to meet the stringent response speed requirements of MEMS gyroscopes in practical applications, we introduce a Specified-Time Funnel Control (STFC) scheme. This control approach guarantees that the displacement error converges to the desired value within a predefined time, simultaneously constraining the error bounds, which results in superior transient and steady-state performance of the system. The novelty of this work lies in the combination of the USDE with the event-triggered observer and STFC, providing a robust solution for MEMS gyroscope control under stringent resource constraints. The effectiveness and superiority of the proposed method are rigorously validated through both theoretical stability analysis using Lyapunov methods and extensive simulation and experimental results, demonstrating its significant improvement over existing approaches.

This paper presents a high-sensitivity CMOS-MEMS thermal-based integrated sensor system for flow rate sensing, which integrates thermopile detectors and a low-noise capacitively-coupled instrumentation amplifier (CCIA) interface circuit. To enhance sensor performance, we propose a custom post-CMOS fabrication process that utilizes the metal-2 layer as a hard mask, enabling self-alignment patterning and suspended film thinning. This fabrication method improves both sensitivity and power efficiency. The thermal detector is designed using high Seebeck-coefficient materials (n+/p+ polysilicon) within the CMOS fabrication process, incorporating a series connection of 32 pairs of thermocouples to further enhance sensitivity. To optimize integration and minimize chip size, a hybrid ASIC amplification circuit is incorporated for system-level analysis. The CCIA circuit employs chopper modulation to effectively suppress DC offset and flicker noise, while a high-gain two-stage operational amplifier (op-amp) ensures precise closed-loop gain control. Experimental results demonstrate that the proposed system achieves an ultra-high sensitivity of 3.42 mV/(m/s)/mW, a detection limit of 2.49 mm/s, a rapid response time of 3 ms. These results highlight the potential of the proposed sensor system for high-precision, portable flow sensing applications.