Selective Ultrasonic Gravimetric Sensors Based on Capacitive Micromachined Ultrasound Transducer Structure-A Review

Excitation of single mode shear horizontal (0,1) guided wave in a narrow plate waveguide using d24 piezoelectric wafers

Piezoelectric ultrasonic transducers are widely used for exciting shear-horizontal (SH) guided waves in narrow plate waveguides (NPW) for high-temperature wall thickness monitoring. The SH(0,1) mode in NPW exhibits nearly nondispersive propagation, making it ideal for monitoring. However, achieving high modal purity and ensuring optimal size matching between the transducer and NPW remain challenging. Existing studies approximate NPW behavior using dispersion curves of plates with infinite width (PIW), leading to inaccuracies in transducer excitation parameter selection. To address this issue, this study develops a dispersion-based excitation parameter selection method for single-mode SH(0,1) wave generation using face-shear (d24) PZT wafers. First, dispersion analysis of SH waves in NPW is conducted using the Floquet periodic boundary conditions method, comparing NPW and PIW dispersion curves to evaluate their differences. Results indicate that in NPW, the cutoff frequency of the SH wave decreases with increasing plate width but remains independent of plate thickness-this contrasts with PIW, where the cutoff frequency varies with plate thickness. Next, based on the dispersion characteristics of SH waves in NPW and SH(0,1) mode shapes, a transducer design optimization approach is proposed. The optimal width and excitation frequency of a symmetrically double-sided d24 PZT wafer transducer are determined. Finite Element simulations and experimental validation are employed to assess the impact of wafer length on excitation performance. Results show that wafers of 6-36 mm length can excite the SH(0,1) mode in a 30 mm wide NPW, with excitation purity and signal-to-noise ratio maximized when the wafer length matches the SH(0,1) mode shape (18-24 mm). A transducer-to-NPW size ratio of 0.6-0.8 enables nearly nondispersive, single-mode SH(0,1) wave excitation. This study provides theoretical guidance for transducer design and has potential implications for broad engineering applications.

A comprehensive review on advancements in sensors for air pollution applications

Air pollution, originating from both natural and human-made sources, presents significant threats to human health and the environment. This review explores the latest technological advancements in air quality sensors focusing on their applications in monitoring a wide range of pollution sources from volcanic eruptions and wildfires to industrial emissions, transportation, agricultural activities and indoor air quality. The review categorizes these sources and examines the operational principles, system architectures, and effectiveness of various air quality monitoring instruments including low-cost sensors, gas analyzers, weather stations, passive sampling devices and remote sensing technologies such as satellite and LiDAR. Key insights include the rapid evolution of sensor technology driven by the need for more accurate, real-time monitoring solutions that are both cost-effective and widely accessible. Despite significant advancements, challenges such as sensor calibration, standardization, and data integration remain critical for ensuring reliable air quality assessments. The manuscript concludes by emphasizing the need for continued innovation and the integration of advanced sensor technologies with regulatory frameworks to enhance environmental management and public health protection.

Black titanium oxide: synthesis, modification, characterization, physiochemical properties, and emerging applications for energy conversion and storage, and environmental sustainability

Since its advent in 2011, black titanium oxide (B-TiOx) has garnered significant attention due to its exceptional optical characteristics, notably its enhanced absorption spectrum ranging from 200 to 2000 nm, in stark contrast to its unmodified counterpart. The escalating urgency to address global climate change has spurred intensified research into this material for sustainable hydrogen production through thermal, photocatalytic, electrocatalytic, or hybrid water-splitting techniques. The rapid advancements in this dynamic field necessitate a comprehensive update. In this review, we endeavor to provide a detailed examination and forward-looking insights into the captivating attributes, synthesis methods, modifications, and characterizations of B-TiOx, as well as a nuanced understanding of its physicochemical properties. We place particular emphasis on the potential integration of B-TiOx into solar and electrochemical energy systems, highlighting its applications in green hydrogen generation, CO2 reduction, and supercapacitor technology, among others. Recent breakthroughs in the structure-property relationship of B-TiOx and its applications, grounded in both theoretical and empirical studies, are underscored. Additionally, we will address the challenges of scaling up B-TiOx production, its long-term stability, and economic viability to align with ambitious future objectives.

Inkjet-Printed Functionalization of CMUT-Based CO2 Sensors

The trade-off between the functionalization shift of the informative parameters and sensitivity of capacitive micromachined ultrasound transducers (CMUT)-based CO₂ sensors is addressed, and the CMUT surface modification process by thin inkjet-printed polyethyleneimine (PEI) films is optimized. It was shown that by the proper preparation of the active CMUT surface and properly diluted PEI solution, it is possible to minimize the functionalization shift of the resonance frequency and the quality of the resonance and preserve the sensitivity potential. So, after optimization, we demonstrated 23.2 kHz frequency shift readings of the sensor with 16 MHz nominal frequency while in the gas chamber and switching between pure N₂ and CO₂. After testing the sensors with different PEI film thickness, it was confirmed that a 200 nm average thickness of a PEI film is an optimum, because this is the practical limit of CO₂ absorption depth at given conditions. Additionally, we note that modification of the hydrophilic/hydrophobic properties of the CMUT surface allows changing the nanoscale surface roughness of the printed PEI film and controlling the area resolution of the inkjet functionalization by reducing the diameter of a single dot down to 150 μm by a commercially available printer cartridge.