A reference material of pure manganese flake for manganese content calibration in X-ray energy/wavelength dispersive spectrometers (EDS/WDS) was developed. The homogeneity and stability of manganese content in the pure manganese flake were examined using electron probe microanalysis (EPMA). The manganese content (mass fraction, %) of the reference material was determined using inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). The uncertainties of the reference material were evaluated. The results show that the pure manganese flake reference material exhibits good homogeneity and stability in manganese content. The certified value of manganese content in the reference material is 99.48% with an expanded uncertainty of 0.92% (k=2). The developed pure manganese flake reference material for EDS/WDS calibration can meet the calibration requirements of EDS/WDS and provide technical support for manganese element analysis in scientific research and industry in China.
Due to the varying quality of probes produced by different manufacturers, the development of electric field standard devices has become particularly important. To meet the calibration requirements of low-frequency, high-field-strength electric field probes, a low-frequency electric field standard device was developed using the parallel plate method. The device consists of two square aluminum plates with a side length of 1 m and a plate spacing of 0.5 m. The frequency range is DC to 10 kHz, with an electric field strength range of 0 to 3000 V/m. Through theoretical analysis, software simulation, and experimental measurements, the effects of edge effects, plate material, structure shape, operating frequency, and other factors on the standard electric field generated by parallel plates were studied, and an uncertainty evaluation was conducted. A new measurement model was proposed, and uncertainty components caused by seven factors were evaluated separately: plate voltage, plate spacing, field uniformity within the parallel plates, probe fixture, probe alignment, finite size of parallel plates, and probe influence. The resulting expanded uncertainty is U=6.8% (k=2). The results show that the developed electric field standard device can meet the calibration requirements for low-frequency electric field probes.
Methanol gasoline and ethanol gasoline, as two distinct types of clean energy sources, possess unique properties and characteristics. Accurate identification of these alcohol-based gasoline types is crucial for ensuring fuel quality and vehicle safety. Near-Infrared Spectroscopy (NIR) is a pivotal method for identifying alcohol-based gasoline types, and modelling based on NIR's effective characteristic wavelengths can overcome the effects of interfering and noisy spectral segments on model accuracy. This study employed the characteristic spectral bands of methanol and ethanol molecules in NIR spectra to develop a Partial Least Squares Discriminant Analysis (PLS-DA) model for distinguishing between methanol and ethanol gasoline. The success rates of full-wavelength spectral, Variable Importance in Projection (VIP) spectral, and feature spectral band models were compared under identical modelling conditions. Results indicated that the full-wavelength and VIP spectral models showed lower accuracy in identifying low-content alcohol-based gasoline samples, with success rates of 90% and 96.7% respectively. In contrast, the optimal feature spectral band model, constructed using the complete differential spectral information of methanol and ethanol molecules (4500～5200+5600～7200+7900～8800 cm−1), achieved a 100% success rate in identifying alcohol-based gasoline samples with volume fractions of 0.5% to 80%. The study demonstrates that selecting feature spectral bands based on chemical structure is an effective wavelength selection method, enhancing model accuracy significantly. In summary, this research successfully establishes a highly accurate model for the qualitative identification of alcohol-based gasoline types using selected NIR spectral bands based on chemical information, showing potential for application in other fuel type identifications.
This paper investigates a single-loop spiral differential microphone array, engineered based on the Jacobi-Anger expansion. The circular differential microphone array it employs is capable of generating a frequency-invariant beampattern that can be steered in any direction. However, this array faces performance deterioration due to the zero value of the Bessel function at specific frequencies, leading to nulls in white noise gain and directivity factor. The concentric circular microphone array, while addressing these nulls, requires a larger number of microphones and a more extensive array distribution area. We propose a single-loop spiral differential microphone array, structured on the Archimedes spiral. The study compares and analyzes differences in white noise gain, directivity factor, and beam pattern between the proposed array and the conventional circular differential array. The impact of spiral parameters on the array’s performance is also examined. Simulation results demonstrate that the single-loop spiral differential array mitigates the issues of deep nulls in white noise gain and directivity factor at certain frequencies, observed in the circular differential array. This is achieved without increasing the microphone count, showcasing superior performance. Furthermore, as the number of microphones increases, the array’s beamforming performance is progressively enhanced.
For calibrating the emission sound source level of mobile sound sources in open waters, the location of the sound source is usually determined using GPS, ultra-short baseline, or inertial navigation instruments. After calibration experiments, it's essential to calibrate the time axis of both sound source level data and positional measurement data. As sound pressure data and sound source location are often collected on different vessels, a time axis calibration of both sets of data is needed before processing. To simplify this calibration process, a method based on beamforming for precise long-distance measurement of underwater sound sources is proposed. This method uses the geometric relationship between the virtual source created by water surface reflections and the actual sound source position for long-distance precise measurement and derives a formula for distance calculation. The feasibility of the theory was verified through numerical simulations, and the impact of linear array design on this method was discussed. Further validation was conducted during lake tests, analyzing the influence of the experimental sound field on the positioning algorithm. Within 200 meters, the positioning difference between this method and GPS results was less than 1%, demonstrating its feasibility.
