In this work, a micro heater enabled gas sensor based on a nano crystalline WO3 - TiO2 composite is developed for the selective detection of nitrogen dioxide (NO2) gas. A detailed comprehensive analysis of micro-heater materials was carried out to evaluate their thermal efficiency leading to the selection of tungsten (W) as an optimal material due to its stability and ability to generate high temperatures at low bias voltage. The micro heater plays a crucial role in establishing a uniform and controlled temperature profile, which significantly enhances gas adsorption and minimizes the effects of humidity. Prior to fabrication, the sensor is designed and analyzed using finite element method (FEM) based multiphysics simulations. The optimized micro heater configuration enabled the device to achieve an ideal operating temperature of approximately 453.15 K under low-voltage conditions. The WO3 (95%) - TiO2 (5%) composite sensing layer was synthesized and characterized using scanning electron microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray Diffraction (XRD) confirming its nanocrystalline structure. The presented sensor exhibits a high response of 82% toward NO2 gas, demonstrating the effectiveness of combining an optimized micro-heater design with heterostructured sensing materials for enhanced gas sensing performance.
This paper examines titanium-based phononic crystal reflectors used in a surface acoustic wave resonator to replace a conventional grating reflector. The proposed phononic crystal generates a wide band gap from 960 MHz to 1900 MHz and reflects the escaped acoustic energy back into the resonator body. The phononic crystal periodic structure consists of square titanium pillars repeatedly patterned on a 15 degrees YX LiNO3/SiO2/silicon plate. In addition to bandgap reflection, when designing phononic crystal reflector materials (titanium) that differ from electrode materials (aluminum), acoustic wave reflection increased due to an increase in acoustic impedance (impedance mismatch between the electrode and phononic crystal materials). The study shows that the phononic-crystal bandgap can be tuned by varying the height, width, and material of the periodically arranged square pillars. After applying Square-titanium-based phononic crystal reflectors to the resonator, the stored energy was enhanced, and the loss was reduced compared with the resonator using traditional reflector gratings. The resonator achieves a Bode Q equal to 1800, presenting a 2.76-fold enhancement over a resonator with a conventional reflector. The finite element method (FEM) is employed to analyze the resonance behavior of defect-engineered phononic-crystal structures.
A high-performance DC-DC converter is essential to handle the low output voltage of photovoltaic (PV) cells for the effective usage of solar-powered LED street lighting, which would otherwise result in severe heat dissipation and destroy the internal components. Moreover, the established techniques experience practical issues such as inaccurate tracking across variable environmental conditions, high power loss, and heavy control oscillations that decline the illumination consistency. To fix these challenges, a robust high-performance DC-DC converter topology coupled with a voltage-lift Perturb Observe Maximum Power Point Tracking (MPPT) controller is proposed, which is designed for a 60 W LED street light powered by a 12 V PV array. The proposed PV system successfully reduces the voltage stress on power semiconductor devices, eliminates the control instabilities around the MPP, and safeguards the internal components from thermal wear, enabling a significant improvement in the overall system lifespan. The performance validation via the circuit simulations establishes the high efficacy of the design, while attaining the peak conversion efficiency of 93.25
Structural rigidity, wall proximity, and the difficulty of accessing thin boundary layers at high Reynolds numbers prevent hot wires from directly measuring wall shear stress on airfoil surfaces. To address this issue, a microscale flexible MEMS thermal film is used. The sensor is small and flexible, which allows it to be attached to the airfoil surface and positioned within the boundary layer for direct shear stress measurement. First, the sensor is calibrated on a flat plate under zero-pressure-gradient conditions to establish a baseline relationship between the output voltage and wall shear stress. Second, the linearity and R² value of the sensor are calculated. The transfer of this calibration to a curved NACA 0012 airfoil is quantitatively justified by evaluating the local curvature ratio (r/δ ≈ 120 > 50) and the pressure gradient parameter (|β|<0.1). The shear stress on the airfoil is expressed as a third-order polynomial, derived from the extended King’s law using the implicit function theorem and Taylor expansion. A comprehensive uncertainty analysis encompassing six error sources (sensor positioning in three directions, temperature variation, electrical noise, repeatability, Clauser method, and calibration transfer) yields an expanded relative uncertainty of ± 17.0
This paper presents a piezoresistive three-axis accelerometer featuring a square-ring proof mass suspended from a central anchor. The first three vibration modes of the structure are employed to sense triaxial acceleration, while independent sensitive beams and integrated piezoresistors enable decoupled readout of the three-axis signals. The primary deformation directions of the three sensitive modes are all aligned with the z-axis, allowing for a unified design of damping characteristics and overload protection structures. The central anchor mitigates the influence of packaging stress on sensing performance. The design principles and methods for achieving matched sensitivity across the three axes are discussed. Prototype devices were fabricated with a simplified process. Measurement results show that the sensitivities of the x- and y-axes are approximately 0.74 times that of the z-axis, validating the proposed design approach. A better match may be achieved through the use of thicker wafers. The off-axis sensitivity is less than 2.32
