The intrinsic stresses introduced during the MEMS multilayer deposition process and the thermal stresses introduced during operation can significantly impact the performance, reliability, and lifetime of the product. The mechanical properties of the MEMS multilayer system are analyzed. An accurate closed-form solution is obtained for the multilayer system, including both intrinsic stresses and thermal stresses, and validated by numerical FEM simulation. Thin films are deposited on silicon substrates, and wafer bending measurements are carried out. Based on this formalism, the residual stresses in various multilayer systems are extracted and analyzed using parameter estimation theory.
The size-of-source effect (SSE) is a major source of uncertainty in radiation thermometers and thermal imaging cameras. This effect is considered a systematic error and is typically evaluated by measuring changes in the detected signal as the size of the radiant source is varied using a set of circular apertures of different diameters. The accurate characterization of the SSE requires measurements over a wide range of object sizes with well-distributed sample points, which is both time-consuming and labor-intensive. This paper proposes a new approach in which the aperture of an iris diaphragm is continuously adjusted to vary the size of the radiant source. An experimental study was conducted to compare the results obtained with individual fixed apertures and to assess whether the camera frame rate and the iris-driving period influence the measured temperature. The proposed approach reproduced the SSE with the same accuracy as measurements made with individual apertures while providing a significantly larger number of measurement points and a notable reduction in the measurement time. Furthermore, the method showed no significant sensitivity to the driving speed of the iris or the camera's frame rate within the investigated range. However, temporal effects arising from the optical components were found to disturb the measurement.
High-precision analysis of the stable isotopic composition of atmospheric methane (CH 4 ) is essential for attributing its sources and sinks and for a more precise understanding of the global methane cycle. Although conventional isotope ratio mass spectrometry (IRMS) provides high accuracy, it lacks in situ capabilities and provides only low data rates. Tunable laser spectrometers offer higher acquisition rates and high sensitivity. In accordance with the Beer–Lambert law, the absorption signal increases proportionally with the optical path length, requiring kilometer-scale paths for atmospheric CH 4 detection and thus the use of optical cavities. Here, we present an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) system for determining the isotopic ratio ( δ 13 C) of the stable isotopologues 12 CH 4 and 13 CH 4 in the mid-infrared range at 3000 cm −1 (3333 nm wavelength). The optical setup comprises a high-finesse V-shaped cavity with highly reflective mirrors ( r =0.999893), resulting in a theoretically effective path length of 22.53 km, which is integrated into an Invar cell with active temperature and pressure stabilization. Allan deviation analysis of the temperature regulation shows a minimum of σ =8.85 µK at an integration time of τ=1.6×104s, and for the gas temperature inside the cell, it gives a minimum of σ =600 µK at τ =6 s, which shows thermal stability that is compatible with an uncertainty in the isotopic ratio of ≤0.1 ‰ (Bergamaschi et al., 1994). Spectral measurements confirm active cavity locking, a symmetric mode structure and frequency calibration using a germanium etalon and a methane reference cell. The spectral resolution of the measurement is given by the free spectral range (FSR) of the cavity with FSR≈84 MHz. The system presented here demonstrates the stability and resolution required for high-precision isotopic methane analysis.
High-precision analysis of the stable isotopic composition of atmospheric methane (CH4) is essential for attributing its sources and sinks and for a more precise understanding of the global methane cycle. Although conventional isotope ratio mass spectrometry (IRMS) provides high accuracy, it lacks in situ capabilities and provides only low data rates. Tunable laser spectrometers offer higher acquisition rates and high sensitivity. In accordance with the Beer–Lambert law, the absorption signal increases proportionally with the optical path length, requiring kilometer-scale paths for atmospheric CH4 detection and thus the use of optical cavities. Here, we present an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) system for determining the isotopic ratio (δ13C) of the stable isotopologues 12CH4 and 13CH4 in the mid-infrared range at 3000 cm−1 (3333 nm wavelength). The optical setup comprises a high-finesse V-shaped cavity with highly reflective mirrors (r=0.999893), resulting in a theoretically effective path length of 22.53 km, which is integrated into an Invar cell with active temperature and pressure stabilization. Allan deviation analysis of the temperature regulation shows a minimum of σ=8.85 µK at an integration time of τ=1.6×104s, and for the gas temperature inside the cell, it gives a minimum of σ=600 µK at τ=6 s, which shows thermal stability that is compatible with an uncertainty in the isotopic ratio of ≤0.1 ‰ (Bergamaschi et al., 1994). Spectral measurements confirm active cavity locking, a symmetric mode structure and frequency calibration using a germanium etalon and a methane reference cell. The spectral resolution of the measurement is given by the free spectral range (FSR) of the cavity with FSR≈84 MHz. The system presented here demonstrates the stability and resolution required for high-precision isotopic methane analysis.
Emission measurement of on-road vehicles in traffic is an important step for air pollution control and, thus, the reduction of negative effects on public health. Remote emission sensing (RES) is a state-of-the-art technology to detect high emitters by monitoring thousands of vehicles in traffic continuously. State-of-the-art (SOTA) RES systems use optical techniques to measure the ratio of specific pollutants to CO2 in vehicle exhaust plumes in order to determine emission factors. Highly accurate SOTA systems use laser absorption spectroscopy for measurement of the pollutant ratio in vehicle exhaust plumes. To obtain the absolute concentration of the single pollutants in the exhaust plume, the absorption path length must be known. In this work we present a 3D gas schlieren imaging sensor (GSIS) system which allows the geometrical reconstruction of 3D density fields of vehicle exhaust plumes in RES applications. Thus, it allows us to obtain the vehicle exhaust plume size and thereby enables estimation of the absorption path length from any direction. Furthermore, it is possible to determine where the laser intersects with the exhaust plume and, thus, to assess if the measurement is valid. The 3D-GSIS system consists of an array of low-cost digital cameras operating in the range of visible light. By means of advanced image processing and tomographic reconstruction techniques, the 3D displacement and density fields of vehicle exhaust plumes can be reconstructed. For validation, we characterized the 3D-GSIS system in the lab using hot air and CO2 plumes. Moreover, the 3D density fields of on-road passing vehicles are estimated and reconstructed using the 3D-GSIS system. The 3D-GSIS system is to be combined with an advanced RES system to measure the direct concentration of pollutants in vehicle exhaust plumes in the future.
