计量科学与技术

Design of a Broadband Low-Noise Measurement Amplifier

JIAO Haibo, XIE Pengfei, WANG Jiaheng, HE Rongchang

2023, 67(11): 3-9, 70. doi: 10.12338/j.issn.2096-9015.2023.0298

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Abstract:
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.

The Structure and Performance Study of Single-Loop Spiral Differential Microphone Array

CHEN Weisong, HUANG Zhixun, WANG Xueyan, NIU Feng

2023, 67(11): 10-16. doi: 10.12338/j.issn.2096-9015.2023.0290

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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.

Research Progress on Interferometric Fiber Optic Hydrophone Signal Demodulation Algorithm

LIANG Qiumin, WANG Min, WANG Wenxia, WANG Ke, ZHENG Huifeng

2023, 67(11): 17-23, 78. doi: 10.12338/j.issn.2096-9015.2023.0293

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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.

Exploring Virtual Sound Fields for Directivity Measurement of Smart Audio Devices

SANG Jinqiu, HUANG Bing, QIN Zhaoqi, WANG Xueyan, LU Xikun, NIU Feng

2023, 67(11): 24-32. doi: 10.12338/j.issn.2096-9015.2023.0297

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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.

Performance Evaluation of Key Parameters of Air Ultrasonic Source Imaging Instrument

WANG Xiaobo, ZHANG Ruiwen, XIAO Jian, XU Shengnan, CHEN Jian, GAO Shenping, SHEN Yuhang

2023, 67(11): 33-38. doi: 10.12338/j.issn.2096-9015.2023.0270

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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.

Research on Calibration Method of Vector Hydrophone Sensitivity in Small Water Tank

CHEN Hongjuan, LIU Zemin, ZHANG Jiale

2023, 67(11): 39-52. doi: 10.12338/j.issn.2096-9015.2023.0287

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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.

Assessment of Axial Sound Field in Air-Coupled Ultrasonic Transducers via Laser Tomography

ZHANG Xiaoli, HE Chenghao, FENG Xiujuan, ZHANG Hui, NIU Feng, HE Longbiao

2023, 67(11): 53-61. doi: 10.12338/j.issn.2096-9015.2023.0302

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Air-coupled ultrasonic transducers, renowned for their non-contact, non-invasive, and completely non-destructive properties, have a wide range of applications in non-destructive testing, particularly in aerospace composite materials and porous materials. The study of axial sound field reconstruction in these transducers is critical as parameters such as near-field length and directionality significantly impact resolution, anti-interference capability, and positioning accuracy in non-destructive testing applications. Laser tomography, with its advantages of high spatial resolution, broad frequency range, and non-invasive sound field mapping, presents a promising approach for sound field reconstruction. However, its application has been predominantly focused on radial sound field characterization, with limited and incomplete exploration in the axial sound field domain. This research conducts a comprehensive investigation into the axial sound field distribution of air-coupled ultrasonic transducers from theoretical, simulation, and experimental perspectives using laser tomography. The study reveals a high degree of consistency between experimental results and simulations. Additionally, the research contrasts these findings with axial sound field measurements obtained via traditional microphone methods, validating the efficacy of laser tomography for accurate reconstruction of the axial sound field in air-coupled transducers. These results are invaluable for enhancing the measurement accuracy of the axial sound field in air-coupled transducers and contribute significantly to their design and calibration.

Study on Hydrophone Calibration Using the Transfer Coupler Reciprocity Method

WANG Shiquan, XU Zhuohua, WU Boyue, JIA Guanghui

2023, 67(11): 62-70. doi: 10.12338/j.issn.2096-9015.2023.0292

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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.

Calibration of Minimum Imaging Sound Pressure Level in Air Ultrasonic Source Imagers and Uncertainty Assessment

ZHANG Ruiwen, PANG Xiaofeng, GAO Shenping, SHEN Yuhang

2023, 67(11): 71-78. doi: 10.12338/j.issn.2096-9015.2023.0256

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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).

Study on the Detection Method for Ultrasonic Stable Cavitation Threshold

RUAN Weidi, LU Zhenwei, SHAO Jiacun

2023, 67(11): 79-84, 52. doi: 10.12338/j.issn.2096-9015.2023.0278

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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.

Research on Calibrations of Phase Mismatch in Sound Intensity Microphone Pairs

ZHOU Changhua, LUO Benyi, DAI Bin

2023, 67(11): 85-90. doi: 10.12338/j.issn.2096-9015.2023.0276

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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.

2023 Vol. 67, No. 11

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