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.
The airborne ultrasonic imaging instrument, utilizing passive sound source localization technology, plays a pivotal role in localizing and imaging ultrasonic sources. This paper reviews the developmental history and future prospects of these instruments, focusing on the evaluation of key metrological parameters critical for their performance. These parameters include positioning error, lateral spatial resolution, and sound pressure level accuracy, among others. The paper presents research methods for evaluating these five key parameters and analyzes factors that influence the assessment process. This comprehensive evaluation ensures the objective assessment of airborne ultrasonic imaging instruments, contributing to the performance enhancement of such devices, particularly those produced domestically.
This paper addresses the limitations of traditional coupler reciprocity methods in calibrating hydrophones, such as size constraints and material restrictions, aiming to enhance calibration accuracy. A transfer coupler reciprocity method is proposed for hydrophone sensitivity calibration, addressing issues like varying coupler volume parameters for different hydrophones. The principles of this method are detailed, and both reference and transfer couplers, including three-transducer and four-transducer types, are developed. Calibration standards based on this method are established, and calibration experiments for standard hydrophones in the 20 Hz to 2 kHz frequency range are conducted using both types of transfer couplers. The results from these two couplers are compared, showing good consistency, and measurement uncertainties are evaluated. To verify the calibration accuracy, results are compared with those from a low-frequency underwater sound primary standard. The deviations are found to be within 0.5 dB, less than the total uncertainty of the comparison devices, validating the accuracy and achieving a measurement uncertainty of 0.4 dB (k=2). By integrating reference and transfer couplers, traditional challenges in coupler reciprocity calibration are overcome, improving accuracy and laying the foundation for higher-level low-frequency underwater acoustic standards.
To better satisfy the measurement needs for sound acquisition directionality in smart audio devices and to enhance the flexibility, efficiency, and cost-effectiveness of measurement setups, this study explores the viability of using virtual sound fields. Virtual sound fields are synthesized via vector synthesis. The study compares virtual and physical sound sources in terms of sound field radiation directivity through sound field simulation experiments. Furthermore, an acoustic camera is used to compare the differences in directivity when capturing and localizing virtual versus real sound sources. The simulation data reveal that smaller loudspeaker angles make it easier for virtual sources to replicate the sound field radiation directivity of real physical sources. Lower frequencies increase the 'sweet spot' range, where the virtual sound field closely approximates the directivity of the real physical sound field. Practical measurement experiments demonstrate that lower frequencies in the virtual sound field align closer to the physical sound field's directivity. Specifically, with a speaker angle of 22.5° and frequencies below 2 kHz, the acoustic camera achieves azimuthal accuracy of less than 3° for virtual sound fields; however, at frequencies above 4 kHz, the camera struggles to accurately capture the azimuth of virtual sound fields. The virtual sound field proves effective for measuring directionality in mid to low-frequency ranges, offering a flexible approach to creating complex virtual acoustic environments for assessing smart audio devices.
Sound intensity, an essential acoustical parameter indicating the direction of sound energy flow, is increasingly significant in acoustics, especially for sound power measurement and noise source identification. The two-microphone method is the prevalent technique for sound intensity measurement. This method, being approximate, inherently contains systematic errors and limits the frequency range for accurate measurement. Additionally, phase mismatch in microphone pairs is a critical factor affecting measurement accuracy. This paper focuses on accurately measuring the phase mismatch between two microphones, a key aspect of microphone pairing. Utilizing the coupler comparison method and electrostatic actuator method, the study achieves normalized and quantitative measurement of microphone phase mismatch. The research contributes to refining microphone pairing accuracy and enhancing sound intensity measurement reliability.
Interferometric fiber optic hydrophones represent a novel class of hydrophones offering numerous benefits over traditional devices. The accuracy in capturing underwater acoustic signals is intricately linked to the employed demodulation algorithms. This paper briefly outlines the construction and operational principles of these hydrophones, with a focus on comparing and analyzing the principles and developments of demodulation algorithms, particularly the Phase Generated Carrier (PGC) and the 3×3 coupler approaches. It delineates the attributes, strengths, and limitations of these primary demodulation algorithms and proposes potential avenues for future research.
The air ultrasonic source imager (beamforming method) is widely utilized in detecting partial discharges and gas leaks. Calibration of its minimum imaging sound pressure level (SPL) is crucial for quantitatively assessing the instrument, directly impacting the detection capabilities for minimal gas leaks, operating distance, and partial discharge detection. With beamforming technology advancements, optimizing array size, number of transducers, and inter-transducer spacing has enhanced source identification and positioning accuracy. As a result, under portable array conditions, the detectable minimum imaging SPL has decreased, posing challenges in obtaining quantitative results, and causing comparison and measurement issues in domestic and international products. This study establishes a calibration system for the minimum imaging SPL of air ultrasonic source imagers using a low-background noise measurement system. Three widely-used air ultrasonic source imagers are selected for experiments, simulating acoustic signals from partial discharges and gas leaks with small-sized sources. Calibration distance and environment are determined, and concentric positioning rings are used to monitor imaging localization errors of small sources. A 12-line high-precision laser leveler aids in minimizing signal alignment impact. This method enables the calibration of minimum imaging SPL. The measurement uncertainty is assessed, showing that within the 20–40 kHz frequency range, the expanded uncertainty of the minimum imaging SPL can reach 3 dB (k=2).
Microphone windscreens, pivotal in acoustic detection systems, serve to mitigate wind noise interference in outdoor testing, ensuring accurate and reliable data. The windproof efficacy of these windscreens is critical to test outcomes. This study focuses on the methodologies for assessing windscreen windproof performance and the factors influencing these results. The windscreen's windproof capability is quantified using the 1/3 octave frequency difference pre- and post-windscreen application at a constant wind speed. The impacts of measuring point position and background noise on windproof performance are explored. Results reveal that the turbulence increase at the flow field edge leads to test results at the wind tunnel inlet's edge being 2.0 to 32.8 dB higher than those in the central region. Thus, it is advisable to avoid the tunnel inlet's edge for test positioning. Additionally, altering the wind tunnel's background noise with sound sources demonstrated that test outcomes remain unaffected by background noise if the 1/3 octave band sound pressure level is at least 7 dB lower than the measurement band's sound pressure level. Consequently, to determine if background noise meets testing standards, the 1/3 octave band sound pressure level should be used, ensuring it is at least 7 dB lower than the measured band's level.
Stable cavitation, characterized by the periodic oscillation of microbubbles in water under low acoustic pressure, contrasts with transient cavitation due to its stable and controllable temperature increase, presenting more promising applications. This paper describes the construction of a monitoring platform for the stable cavitation threshold, employing a passive cavitation detection method. The method monitors stable cavitation activity in focused acoustic fields in water with varying oxygen contents, using the emergence of subharmonics as an indicator of stable cavitation. Combining narrow-band mechanical filtering and multiple averaging techniques, the acoustic signals received by high-sensitivity hydrophones are filtered and noise-reduced. Spectral analysis of these signals explores the relationship between oxygen content and the appearance of subharmonics under ultrasonic influence. The results demonstrate that multiple averaging effectively reduces noise interference and improves signal-to-noise ratio, enhancing the detection of weak signals. Additionally, increasing oxygen content lowers the stable cavitation threshold, aligning with theoretical expectations.
Quantitative analysis of tin content in infant supplementary food rice powder was conducted using external standard and standard addition methods. The study investigated the effects of different acids added during pre-digestion and complex matrices on the tin content results. An accurate method for determining tin content in infant supplementary food rice powder was established using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The study analyzed the sources of uncertainty in the determination process of infant supplementary food rice powder, evaluated each component of uncertainty, and calculated the method's expanded uncertainty. The analysis showed that pre-digestion with nitric acid followed by the addition of hydrochloric acid before microwave digestion, and the standard addition method for tin analysis resulted in a correlation coefficient (r2) above 0.9998. The method detection limit was 0.02 mg/kg, and the measurement deviation for certified reference material was +1.2%. When tin content was measured at 1.31 mg/kg, the expanded uncertainty was 0.04 mg/kg with a coverage factor of k=2. The standard addition method was suitable for determining tin content in infant supplementary food rice powder, proving to be more accurate and reliable.
The indoor architecture and design of sports venues require careful consideration of both the acoustic environment and spatial aesthetics. Given that most venues have large volumes and unique shapes, they are prone to prolonged reverberation, leading to challenges like low speech intelligibility, echoes, and acoustic focusing. Consequently, specific architectural acoustic designs tailored to the venue's needs are essential. This paper outlines the architectural acoustic design process for an indoor gymnasium and swimming pool within a sports center. It begins by establishing a target range for the reverberation time, followed by utilizing sound-absorbing materials and strategic interior layout to reduce reverberation. The design's efficacy was affirmed through theoretical calculations and onsite measurements. Results indicate that the achieved acoustic environment fulfills the design objectives, adequately supporting the sports center's daily operational needs and serving as a valuable reference for future large-scale sports center projects.
The reception sensitivity of hydrophones is a crucial indicator of their acoustic performance. The advent of low-frequency, large-scale vector hydrophones presents new challenges: conventional standing wave tubes cannot calibrate these devices due to size constraints, and anechoic water tanks, with their boundary conditions, fail to separate direct and reflected waves of low-frequency signals using pulse sound technology. Addressing these issues, this paper investigates a method for free field sensitivity measurement of vector hydrophones using transient signals in small water tanks. Based on the analytical solution of surface vibration displacement of a single resonant piezoelectric transmitter under sinusoidal pulse signal excitation, the relationship between transient and steady-state signal amplitudes is analyzed. Finite element software is used for modal, harmonic response, and transient analysis, considering commonly used transmitters in hydroacoustic testing. This simulation studies the choice of sound source and receiver location for vector hydrophone sensitivity testing using transient signals. An experimental setup in a small water tank measures the hydrophone's acoustic pressure sensitivity using a comparison method. This approach overcomes spatial limitations and extends the lower frequency measurement limit for vector hydrophones in confined spaces.
This paper presents the design of a broadband, low-noise underwater acoustic general-purpose measurement amplifier, based on signal conditioning technology. Serving as the primary stage amplifier for hydrophones, it amplifies weak underwater acoustic signals, thereby enhancing the signal-to-noise ratio essential for subsequent filtering and processing stages. The design features twin JFET field-effect transistors in the input stage to optimize impedance conversion and minimize bias noise. The amplifier boasts a high gain capability, with a maximum of 110 dB, a dynamic gain range of −30 to 110 dB, operating bandwidth from 1 Hz to 200 kHz, and equivalent input noise below 5 nV/√Hz. Gain levels can be controlled via an RS232 bus. Key attributes include adjustable gain stages, broad bandwidth, low noise, high linearity, and versatility. Comparative tests with similar foreign amplifiers confirm that this design fulfills technical specifications, delivering performance on par with international counterparts and demonstrating efficacy in practical applications.
This study analyzes factors affecting the measurement accuracy of laser meters, identifying three key factors: the movement speed, the angle of incidence between the measurement line and the measurement surface's normal, and the spacing distance between the laser transmitter and the measurement surface. Employing a controlled variable method, one factor is varied while the others remain constant, and the impact of each factor on measurement accuracy is determined by comparing and analyzing the laser meter's distance measurement indication error. Experimental analysis reveals that the angle of incidence between the measurement line and the normal of the measurement surface is the primary influential factor, followed by the distance between the laser transmitter and the measurement surface, both requiring strict control to maintain error within the instrument's nominal accuracy. The effect of movement speed and state on accuracy is minimal, thus not a primary factor. Consequently, special attention should be given to the placement angle and distance from the measurement surface when using and calibrating the laser meter to achieve high measurement accuracy.
Addressing the challenges in the calibration process of nucleic acid extractors, this study explores the key metrological characteristics and measurement traceability system based on the JJF 1874-2020 standard, "Calibration Specification for (Automatic) Nucleic Acid Extractors." Using common nucleic acid extractors as examples, this paper analyzes the calibration methods and uncertainty assessments for four metrological characteristics: temperature, vibration frequency, and nucleic acid extraction efficiency. The results include temperature indication errors of 0.5 ℃ at 55 ℃ and 0.7 ℃ at 70 ℃, temperature uniformity of 0.3 ℃ at 55 ℃ and 0.5 ℃ at 70 ℃, temperature stability of ±0.1 ℃, vibration frequency stability of ±0.1 Hz, nucleic acid extraction efficiency of 82.9%, efficiency homogeneity of 6.3%, and repeatability of 4.5%. The study evaluates the uncertainty of temperature indication errors and nucleic acid extraction efficiency. Compared to the JJF 1874-2020 standard, additional uncertainty components from the micro spectrophotometer, pipettor, and electronic balance are included. The study summarizes the types and pros and cons of temperature and vibration frequency measuring devices, analyzes factors affecting nucleic acid recovery rate, and highlights the importance of using consistent extraction methods and reagents. It proposes solutions and optimization methods for calibration challenges and discusses the concept and detection methods of cross-contamination rates in nucleic acid extractors, with an experimental finding of 0.0% cross-contamination rate.
This study investigates the sources of uncertainty in determining the lead content in metronidazole pharmaceuticals using inductively coupled plasma mass spectrometry (ICP-MS). Following the 2321 method of the Pharmacopoeia of the People’s Republic of China (2020 edition), lead content was measured using ICP-MS post-microwave digestion. The study analyzed the uncertainty contributed by sample weighing, microwave digestion, preparation of standard working solutions, regression fitting of the standard curve, and repeatability of measurements to establish combined and expanded uncertainties. The findings indicate that the preparation of standard working solutions is the primary contributor to uncertainty, with a relative uncertainty of 1.44%. Other factors such as sample weighing, microwave digestion, and repeatability have a lesser impact on the overall uncertainty. For a sample weight of 0.10 g, the lead content in metronidazole tablets was found to be 0.5063 μg/g, with an expanded uncertainty of 0.01793 μg/g (k = 2).
