An in-situ online calibration method for sound velocity and relative sensitivity of hydrophones in a standing wave sound field

Abstract

This invention discloses an in-situ online calibration method for sound velocity and relative sensitivity of hydrophones in a standing wave sound field, comprising the following steps: 1) calibrating the hydrophone to be installed under normal pressure using a hydrophone calibration method, such as the vibrating liquid column method, and issuing a calibration certificate; 2) sorting the calibration data from step 1) according to consistency, selecting the hydrophones with the highest consistency and embedding them into the wall of the acoustic tube, and numbering them sequentially; 3) injecting distilled water into the acoustic tube, evacuating the vacuum to eliminate air bubbles in the water; 4) controlling the water temperature and static pressure in the acoustic tube to predetermined values ​​as needed, and performing in-situ online calibration of sound velocity, hydrophone position, and relative sensitivity in the water after stabilization. This invention eliminates the need to establish an approximate traveling wave field inside the tube, and can directly achieve calibration of the relative sensitivity, sound velocity, position, etc. of the hydrophone inside the tube through a single signal transmission, which not only provides high calibration accuracy but also saves calibration time.

Description

Technical fields:

[0001] This invention belongs to the field of metrology and testing, and specifically relates to an in-situ online calibration method for sound velocity and relative sensitivity of hydrophones in a standing wave sound field. Background technology:

[0002] With the development of underwater acoustic countermeasures and sonar technology, my country's active sonar for submarine exploration currently operates at frequencies in the kilohertz range, while the low-frequency limit of passive sonar reaches several hundred hertz, with operating depths generally reaching 450 meters. The acoustic performance of the acoustic baffles on sonar equipment directly affects the performance of underwater transducers and arrays, and even the overall technical specifications of the sonar, thus impacting submarine detection capabilities. Meanwhile, the acoustic and vibrational performance of anechoic and acoustically insulating tiles installed on submarines in the high hydrostatic pressure operating frequency band directly relates to the submarine's stealth capabilities. Therefore, during the research and development and production of equipment and models, it is necessary to accurately evaluate and test the acoustic and vibrational characteristics of passive underwater acoustic materials such as acoustic baffles, anechoic tiles, and acoustically insulating tiles at different operating frequencies, in different temperature environments, and under different water pressure environments to ensure the quality of military products.

[0003] The existing standing wave tube calibration devices using a "water-component-air" layered mode and traveling wave tube calibration devices simulating a "water-component-water" working mode are as follows: the standing wave tube acoustic tube structure is as follows: Figure 1 As shown, a standing wave tube calibration device consists of a standing wave tube body, a transmitting transducer, and a set of hydrophones (3-4 hydrophones). With electronic measuring instruments and a matching temperature and pressure control system, it is configured as such. The standing wave tube is placed vertically, with the transmitting transducer at the bottom and the sample of the material to be tested placed at the tube opening. The hydrophones are embedded in the tube wall. A long pulse signal is emitted by the transmitting transducer, forming a planar standing wave sound field inside the tube. A pair of hydrophones is selected according to the test frequency to collect the sound signal. After signal separation, acoustic performance parameters such as the sound pressure reflection coefficient (echo reduction) and sound absorption coefficient of the material component in the "water-component-air" layered pattern can be calculated.

[0004] Traveling wave tube acoustic tube structure as follows Figure 2As shown, a traveling wave tube (TWT) calibration device consists of a TWT tube body, a pair of transmitting transducers, and a set of hydrophones. Equipped with electronic measuring instruments and a supporting temperature and pressure control system, it is configured as a TWT calibration device. The TWT is placed vertically, consisting of an upper and lower section. The transmitting transducer and auxiliary transducer are placed at the bottom and top, respectively, and the sample of the material to be tested is placed in the middle of the tube. The hydrophones are also embedded in the wall of the TWT tube. Four to five hydrophones are embedded in the walls of both the upper and lower sections of the tube. During testing, the hydrophone pair is first selected according to the test frequency. Based on the acquired sound field of the upper tube, active noise cancellation is achieved using the auxiliary transmitter, establishing a traveling wave sound field in the upper tube and a standing wave sound field in the lower tube. Through signal acquisition and separation technology, calibration tests are performed on parameters such as the sound pressure reflection coefficient (echo reduction), sound pressure transmission sound pressure (insertion loss), and sound absorption coefficient of the hydroacoustic material component in a "water-component-water" layered pattern.

[0005] Whether using traveling wave tubes or standing wave tubes to calibrate the acoustic performance of underwater acoustic materials, a planar standing wave sound field is designed to be generated within the sound tube. The incident and reflected sound waves are separated using the multi-hydrophone transfer function method or the transfer matrix method. Taking the testing of standing wave tubes #1 and #2 as examples, the complex sound pressure reflection coefficient can be calculated:

[0006]

[0007] Where k is the wave number, k = 2πf / c, f is the frequency, and c is the sound velocity of the water medium in the pipe under the current water temperature and pressure conditions; x1 and x2 are the positions of hydrophones #1 and #2; l 12 H represents the spacing between hydrophones #1 and #2. 12 Transfer function for hydrophone:

[0008]

[0009] Here, A1 and A2 are the voltage signal amplitudes received by hydrophones #1 and #2, respectively. and M1 and M2 are the phase values ​​of the voltage signal received by the hydrophone, respectively, under the current water temperature and pressure conditions and at the current frequency. θ1 and θ2 are the phase values ​​of the sensitivity of the two hydrophones under the current environmental and frequency conditions.

[0010] The amplitude and phase of the voltage signals from each hydrophone are acquired online by high-precision and high-resolution acquisition equipment, and the measurement error is negligible. The main factors affecting the accuracy of the sound pressure reflection coefficient measurement are the relative sensitivity deviation of the hydrophone pair (including amplitude and phase deviation) and the sound velocity of the water medium in the tube. Although the sound tube is manufactured with high precision and the positioning accuracy of the hydrophone is very high, slight deviations are inevitable during installation, and these deviations also affect the measurement of R.

[0011] According to waveguide theory, the speed of sound in a pipe is generally taken as 0.98 times the speed of sound in distilled water in a free field. The speed of sound in distilled water in a free field is calculated using a theoretical formula, and its relationship with temperature t is: c0 = 1557 - 0.0245 × (74 - t) 2 The calculated sound velocity in the pipe deviates from the actual sound velocity under varying temperature and pressure conditions.

[0012] Furthermore, due to limitations in existing domestic hydrophone calibration technology, standing wave tube and traveling wave tube hydrophones only undergo sensitivity consistency calibration under normal pressure conditions before installation. The hydrophone sensitivity is calibrated using the vibrating liquid column method, with a measurement uncertainty of 0.6 dB (k=2) for sound pressure sensitivity testing and 4° (k=2) for phase testing. These measurement uncertainties are relatively large. After the hydrophone is installed on the sound tube, the ambient temperature and pressure vary depending on the testing conditions, and the hydrophone sensitivity will also change accordingly. Therefore, the sensitivity calibration data under normal pressure is clearly insufficient, and using normal pressure data to replace calibration data under pressure conditions will lead to significant deviations in the measured acoustic performance of the material samples.

[0013] In response, the applicant disclosed an online calibration method for the sensitivity consistency of a traveling wave tube hydrophone, Chinese Patent Publication No. CN110160622A. This method utilizes the characteristics of traveling wave sound fields to simultaneously calibrate multiple hydrophones under specific environmental conditions within a traveling wave tube. However, due to the relative difficulty in constructing a planar traveling wave sound field, this method is only suitable for relative sensitivity phase amplitude calibration of hydrophones within a traveling wave tube, and it does not calibrate the position of the hydrophones when the sound velocity in the water medium is different. Summary of the Invention:

[0014] The technical problem to be solved by the present invention is to provide an in-situ online calibration method for sound velocity and relative sensitivity of hydrophones in a standing wave sound field. This method is for calibrating the relative sensitivity of at least three hydrophones embedded in the sound tube and the sound velocity of the water medium in the sound tube in the device mentioned in the background art, and to compensate for the consistency effects introduced by the sensitivity differences of the hydrophones themselves and installation, water temperature, water pressure, etc.

[0015] The technical solution of this invention is to provide an in-situ online calibration method for sound velocity and relative sensitivity of a hydrophone in a standing wave sound field, comprising the following steps:

[0016] 1) The hydrophone to be installed is calibrated under normal pressure using hydrophone calibration methods, such as the vibrating liquid column method, and a calibration certificate is issued.

[0017] 2) Based on the calibration data from step 1), sort them according to consistency, select the hydrophones with the highest consistency and embed them into the acoustic tube wall, and number them sequentially.

[0018] 3) Inject distilled water into the sound tube, create a vacuum, and eliminate air bubbles in the water;

[0019] 4) As needed, control the water temperature and static pressure in the sound tube to the predetermined values, and after stabilization, perform in-situ online calibration of the sound velocity in the water and the position and relative sensitivity of the hydrophone;

[0020] 5) Transmit a single-frequency long pulse signal or a single-frequency continuous wave signal at the calibration frequency to establish a plane standing wave sound field inside the sound tube. Based on the number of hydrophones being calibrated, list the real and imaginary parts of the equations for the incident sound pressure and reflected sound pressure inside the sound tube. Solve the multivariate nonlinear equation system. Use the sound velocity in the tube calculated by the classical formula, the hydrophone position designed in the sound tube drawing, and the sensitivity phase amplitude characteristics of the hydrophones calibrated offline as preliminary estimates of the unknowns. Alternatively, list the overdetermined equations and use the least squares method to calibrate the unknowns.

[0021] 6) Calculate the amplitude and phase of the sound pressure reflection coefficient of the reflecting object obtained by different hydrophone combinations according to formula (1), compare the deviation of each calculation result before and after calibration, and if the phase amplitude deviation after calibration is much smaller than the phase amplitude deviation before calibration, then the multi-parameter calibration is considered to be effective.

[0022] 7) Based on the calibrated parameters, perform acoustic performance measurements of the acoustic materials at the current frequency and under the current water temperature and pressure.

[0023] 8) Adjust the traveling wave tube water temperature and static water pressure as needed, and repeat steps 5) to 7) until calibration and material acoustic performance measurement are performed under all environmental conditions.

[0024] 9) Release the hydrostatic pressure to normal pressure.

[0025] Preferably, in step 5), in a plane standing wave sound field environment, any two hydrophones form a hydrophone pair. The complex sound pressure reflection coefficients of the reflecting interface measured by the transfer function should be equal. If three hydrophones with the best consistency are selected, a set of multivariate nonlinear equations can be established. If more than three hydrophones with the best consistency are selected, an overdetermined equation is established. The sound velocity in the tube calculated by the classical formula, the hydrophone position designed in the sound tube drawing, and the sensitivity amplitude and sensitivity characteristics of the hydrophones calibrated offline are used as preliminary estimates of unknowns. The least squares method is used to calibrate and obtain the sound velocity of the water medium in the sound tube under the current water temperature and water pressure environment, the position of each calibrated hydrophone, and the relative sensitivity amplitude and phase between hydrophones.

[0026] Preferably, the calibration signal is a continuous sinusoidal signal or a long sinusoidal pulse. By calibrating at frequency points successively under specific water temperature and hydrostatic pressure conditions, the sound velocity in the pipe, hydrophone position, and relative sensitivity phase amplitude characteristics are calibrated in situ online across the entire measurement frequency band, the entire range of working water temperature and hydrostatic pressure.

[0027] Furthermore, conducting in-situ online calibration of multiple parameters before each measurement of the acoustic properties of underwater acoustic materials can reduce the measurement errors caused by the deviation between the calculated and actual sound velocity of the water medium in the pipe, the positioning deviation of the hydrophone, and the inconsistency of the phase amplitude of the hydrophone sensitivity, making the measurement of the acoustic property parameters of the sample more accurate.

[0028] Compared with the prior art, the present invention has the following advantages after adopting the above solution:

[0029] This in-situ online calibration method eliminates the need to establish an approximate traveling wave field inside the tube. It allows for the calibration of the relative sensitivity, sound velocity, and position of the hydrophone within the tube with a single signal transmission, resulting in high calibration accuracy and time savings. Furthermore, the acoustic properties of the material sample within the tube, such as sound pressure reflection coefficient and sound pressure transmission coefficient, can be calculated using the reference data, significantly improving testing efficiency. Attached image description:

[0030] Figure 1 This is a schematic diagram of a standing wave tube acoustic tube structure.

[0031] Figure 2 This is a schematic diagram of a traveling wave tube acoustic tube structure.

[0032] Figure 3 This is a schematic diagram of the standing wave sound field in a standing wave tube.

[0033] Figure 4 This is a schematic diagram showing the results of online calibration of the sensitivity, sound velocity, and position of the hydrophone on the traveling wave tube during testing.

[0034] Figure 5 This is a schematic diagram showing the results of online calibration of the sensitivity, sound velocity, and position of the hydrophone in the traveling wave tube during testing. Detailed implementation method:

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0036] This invention discloses an in-situ online calibration method for sound velocity and relative sensitivity of a hydrophone in a standing wave sound field, characterized by the following steps:

[0037] 1) The hydrophone to be installed is calibrated under normal pressure using hydrophone calibration methods, such as the vibrating liquid column method, and a calibration certificate is issued.

[0038] 2) Based on the calibration data from step 1), sort them according to consistency, select the hydrophones with the highest consistency and embed them into the acoustic tube wall, and number them sequentially.

[0039] 3) Inject distilled water into the sound tube, create a vacuum, and eliminate air bubbles in the water;

[0040] 4) As needed, control the water temperature and static pressure in the sound tube to the predetermined values, and after stabilization, perform in-situ online calibration of the sound velocity in the water and the position and relative sensitivity of the hydrophone;

[0041] 5) Transmit a single-frequency long pulse signal or a single-frequency continuous wave signal at the calibration frequency to establish a plane standing wave sound field in the sound tube, and list the real part and imaginary part of the equations for the incident sound pressure and reflected sound pressure in the sound tube according to the number of hydrophones to be calibrated. The equations for the incident sound pressure and reflected sound pressure in the sound tube can be found in Equations (7) and (8) below. Solve the multivariate nonlinear equation system. Use the sound velocity in the tube calculated by the classical formula, the hydrophone position designed in the sound tube drawing, and the sensitivity phase amplitude characteristics of the hydrophone calibrated offline as the preliminary estimate of the unknowns, or list the overdetermined equations and calibrate the unknowns using the least squares method.

[0042] 6) Calculate the amplitude and phase of the sound pressure reflection coefficient of the reflecting object obtained by different hydrophone combinations according to formula (1), compare the deviation of each calculation result before and after calibration, and if the phase amplitude deviation after calibration is much smaller than the phase amplitude deviation before calibration, then the multi-parameter calibration is considered to be effective.

[0043] 7) Based on the calibrated parameters, perform acoustic performance measurements of the acoustic materials at the current frequency and under the current water temperature and pressure.

[0044] 8) Adjust the traveling wave tube water temperature and static water pressure as needed, and repeat steps 5) to 7) until calibration and material acoustic performance measurement are performed under all environmental conditions.

[0045] 9) Release the hydrostatic pressure to normal pressure.

[0046] When conducting calibration, a stable planar standing wave sound field must first be established within the sound tube. For example... Figure 1 In the standing wave tube shown, a single-frequency long pulse or a single-frequency continuous signal p is emitted by a transmitting transducer at the bottom of the tube. i (The upper frequency limit is determined by the inner diameter of the acoustic tube). After the pulse sound reaches the material sample, part of it is absorbed by the material sample, and the other part is reflected. r The reflected sound and the incident sound form a stable planar standing wave sound field inside the sound tube. Figure 2The traveling wave tube shown can, without a material sample, unidirectionally emit long pulse or continuous sound signals, similar to a standing wave tube, to create a stable planar standing wave sound field within the tube, thereby calibrating the sensitivity of all hydrophones within the tube. Alternatively, after placing a material sample, the sensitivity of the hydrophones in the upper and lower sections of the tube can be calibrated separately. The bottom transmitting transducer emits a signal, while the top auxiliary transducer does not. Part of the sound signal passes through the material sample into the upper tube, serving as the incident signal, while the rest is reflected by the secondary transmitter, thus creating a standing wave sound field within the upper tube. Similarly, a stable standing wave sound field can be created within the lower section of the tube to calibrate the hydrophone group there, with the bottom transmitting transducer remaining silent and the top auxiliary transducer emitting long pulse or continuous signals.

[0047] Taking calibration in a standing wave tube as an example, such as Figure 3 As shown. Incident sound p in and reflected sound p reflected by the material sample re A stable standing wave sound field is formed by superposition. A coordinate system is given, with the bottom surface of the material sample at x=0. The position coordinates of each hydrophone, its distance from the bottom surface of the material sample, and the spacing between hydrophones are given. The sound pressure signal U received at the locations of hydrophones m and n are also given. m and U n It can be expressed using incident sound pressure and reflected sound pressure. That is, the sound pressure signal U received at the locations of hydrophones m and n. m and U n The incident sound pressure p can be used in and reflected sound pressure p re Represented as:

[0048]

[0049] Sound pressure signals can also be received by a hydrophone as voltage signals (amplitude V, phase). The sensitivity values ​​(amplitude M, phase θ) are expressed as follows:

[0050]

[0051] Then the incident sound pressure p in and reflected sound pressure p re It can be expressed by the following formula:

[0052]

[0053] Figure 1The standing wave tube shown contains four hydrophones (1#, 2#, 3#, and 4#), resulting in six hydrophone combinations: (1#, 2#), (1#, 3#), (1#, 4#), (2#, 3#), (2#, 4#), and (3#, 4#). These combinations allow for the calculation of incident and reflected sound pressure within the tube. If the sound velocity in the tube, the hydrophone sensitivity amplitude and phase, and the hydrophone positions are accurately calibrated, then under the same sound field environment, any combination of hydrophones should yield the same calculated incident and reflected sound pressure within the tube. If two hydrophone pairs (1#, 2#) and (2#, 3#) are selected, the following equation applies:

[0054]

[0055] If hydrophones #1, #2, and #3 are paired up, and hydrophone #3 is used as the reference, relative sensitivity calibration is performed. The calibration parameters include the speed of sound in water (c) and the relative sensitivity amplitude (M) of hydrophones #1 and #2 relative to hydrophone #3. 13 M 23 Phase θ 13 θ 23 The distances D1, D2, and D3 of the three hydrophones from the bottom surface of the material sample are considered as eight parameters. The equation they satisfy is:

[0056]

[0057] Among them, M 13 =M1 / M3, M 23 =M2 / M3, θ 13 =θ1-θ3, θ 23 =θ2-θ3. This can be broken down into four equations, each of which contains a real part equation and an imaginary part equation, resulting in eight equations and eight unknowns used for calibration.

[0058] Preliminary estimates of unknowns: The speed of sound was calculated using classical formulas as the initial value; the positions of the three hydrophones were determined from the acoustic tube design drawings; and the sensitivity amplitude and phase of the hydrophones were obtained from data calibrated offline at ambient temperature and pressure. The eight unknowns were calibrated by solving a system of multivariate nonlinear equations.

[0059] If there are more than 3 hydrophones in the acoustic tube, such as 4 hydrophones paired together, 20 equations can be formed with a total of 11 unknowns. If 5 hydrophones are paired together, 36 equations can be formed with a total of 14 unknowns, forming an overdetermined equation. The unknowns can be calibrated using the least squares method.

[0060] Figure 4 and Figure 5These are the results of online calibration of the sensitivity, sound velocity, and position of each hydrophone in the upper and lower tubes of a traveling wave tube during one test. The surface reflection coefficient of the transmitter, calculated before and after calibration, is compared and analyzed. It is evident that after calibration, under different hydrophone combinations, whether in the upper or lower tube, the sound pressure reflection coefficient R0 = p re / p in The amplitude and phase consistency are excellent, whereas before calibration, the deviation was large, especially in the phase angle.

[0061] This invention applies to calibration devices for underwater acoustic materials such as standing wave tubes and traveling wave tubes, significantly improving the measurement accuracy of sample acoustic characteristic parameters. It represents a novel hydrophone calibration technology and application. Compared to traditional offline measurement methods, this invention solves the problems of difficult online on-site calibration and calibration under specific application conditions, thus improving calibration accuracy. Compared to online calibration methods for the sensitivity consistency of traveling wave tube hydrophones, this invention overcomes the difficulties in constructing planar traveling wave sound fields and the incompleteness of calibration parameters, demonstrating greater applicability and reliability.

[0062] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. Any equivalent structural or procedural modifications made using this specification are included within the patent protection scope of the present invention.

Claims

1. A method for in-situ, on-line calibration of sound speed and hydrophone relative sensitivity in a standing acoustic wave field, characterized by: It comprises the following steps, 1) issuing a calibration certificate by means of a hydrophone calibration method; 2) according to the calibration data of step 1), sorting by consistency, and selecting a plurality of hydrophones with high consistency to be embedded on the wall of the sound tube and numbered in sequence; 3) injecting distilled water into the sound tube, vacuumizing, and eliminating bubbles in the water; 4) controlling the water temperature and hydrostatic pressure of the sound tube to a predetermined value, and after stabilization, carrying out in-situ online calibration of the sound speed in water and the position and relative sensitivity of the hydrophone; 5) transmitting a single-frequency long pulse signal or a single-frequency continuous wave signal of a calibration frequency to establish a plane standing wave field in the sound tube, and listing the real part and imaginary part equations of the incident sound pressure and reflected sound pressure equations in the sound tube according to the number of the hydrophones to be calibrated, solving the multivariate nonlinear equation set, taking the sound speed in the tube calculated by the classical formula, the position of the hydrophone designed on the sound tube drawing, and the sensitivity phase amplitude characteristic of the hydrophone calibrated offline as the preliminary estimated value of the unknown quantity, or listing the overdetermined equation, and calibrating the unknown quantity by the least square method; 6) calculating the amplitude and phase of the sound pressure reflection coefficient of the reflection object calculated by different hydrophone combinations, comparing the deviation of each calculation result before and after calibration, and if the phase amplitude deviation after calibration is much smaller than that before calibration, it is considered that the multi-parameter calibration is effective; 7) according to the calibrated parameters, carrying out the acoustic material performance measurement of the current water temperature and water pressure under the current frequency; 8) adjusting the water temperature and hydrostatic pressure of the traveling wave tube as needed, repeating steps 5) to 7), until the calibration and material acoustic performance measurement under all environmental conditions are completed; 9) releasing the hydrostatic pressure to normal pressure.

2. The method for in-situ, on-line calibration of sound speed and hydrophone relative sensitivity in a standing acoustic wave field according to claim 1, wherein: In step 5), in the plane standing wave field environment, any two hydrophones form a hydrophone pair, and the complex sound pressure reflection coefficient of the reflection interface measured by the transfer function should be equal, if three hydrophones with high consistency are selected, a multivariate nonlinear equation set can be established, if the number of hydrophones with high consistency exceeds three, an overdetermined equation is established, the sound speed in the tube calculated by the classical formula, the position of the hydrophone designed on the sound tube drawing, and the sensitivity phase amplitude characteristic of the hydrophone calibrated offline are taken as the preliminary estimated value of the unknown quantity, and the least square method is used to calibrate the sound speed in the water medium in the sound tube, the position of each calibration hydrophone, and the relative sensitivity amplitude and phase between the hydrophones under the current water temperature and water pressure environment.

3. The method for in-situ, on-line calibration of acoustic velocity and hydrophone relative sensitivity in a standing acoustic wave field of claim 1, wherein: The calibration signal is a sine continuous signal or a sine long pulse, and the sound speed in the tube, the position of the hydrophone, and the relative sensitivity phase amplitude characteristic in the whole measurement frequency range, all working water temperature and hydrostatic pressure range are calibrated in-situ online under the condition of set water temperature and hydrostatic pressure by frequency point calibration in sequence.

4. The method for in-situ, on-line calibration of sound speed and hydrophone relative sensitivity in a standing acoustic wave field of claim 1, wherein: Before each measurement of the acoustic characteristics of the underwater acoustic material, the in-situ online calibration of the multi-parameters is carried out.

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