Standard hydrophone free field sensitivity phase response determination method

Abstract

The invention relates to a standard hydrophone free field sensitivity phase response determination method, which comprises the following steps: step 1, determining the amplitude sensitivity of a hydrophone, during measurement, placing a light-reflecting sound-transmitting diaphragm at a point in a far field of an auxiliary emitter, measuring by using a laser interference method to obtain the displacement at the point in a sound field, further obtaining a sound pressure value, and determining the amplitude sensitivity of the hydrophone; the standard hydrophone is placed at the same position in the sound field, the emission state is kept unchanged, the open-circuit voltage response of the standard hydrophone is measured, and the amplitude sensitivity of the standard hydrophone can be measured through a replacement comparison method. According to the method, the phase response can be accurately determined, the influence of many factors on the phase response in a reciprocity method calibration process is solved, and the method has the characteristics of simplicity, convenience and accuracy.

Description

Technical Field:

[0001] The present invention belongs to the technical field of underwater acoustic engineering, and particularly relates to a method for determining the phase response of the free-field sensitivity of a standard hydrophone based on laser interferometry. Background Art:

[0002] In the field of underwater acoustic engineering, the reproduction and transfer of underwater acoustic pressure values are usually carried out through standard hydrophones. The calibration of the sensitivity of standard hydrophones is achieved by using primary calibration methods such as the three-transducer free-field reciprocity method and the laser interferometry method, so as to realize the reproduction and transfer of acoustic pressure values. Usually, the sensitivity of the hydrophone obtained by calibration is the amplitude sensitivity of the hydrophone, that is, the response of the hydrophone to the acoustic pressure amplitude at different frequencies. With the development of underwater acoustic technology and its underwater acoustic detection equipment, higher requirements are put forward for the traceability of underwater acoustic pressure. Not only the amplitude sensitivity of the hydrophone is concerned, but also its phase sensitivity. In a series of international standards such as IEC 60565-1:2020 and IEC 60565-2:2019 issued by the International Electrotechnical Commission (IEC), the definition of the complex sensitivity of the hydrophone is also proposed. The calibration of the complex sensitivity of the standard hydrophone is of great significance for the measurement and engineering application of underwater acoustic complex pressure.

[0003] Currently, the calibration methods for the free-field sensitivity of standard hydrophones mainly include primary calibration methods such as the three-transducer spherical wave reciprocity method and the laser interferometry method. The three-transducer spherical wave reciprocity method is the most commonly used primary calibration method for the free-field sensitivity of hydrophones. When calibrating the sensitivity of a standard hydrophone using the three-transducer spherical wave reciprocity method, it is necessary to measure the transfer impedances of the three sets of transducer pair combinations of the transmitting transducer - standard hydrophone, transmitting transducer - reciprocity transducer, and reciprocity transducer - standard hydrophone, and at the same time, it is necessary to determine the distances between the acoustic centers of the three sets of transducer pairs. The free-field sensitivity of the standard device, that is, the sensitivity amplitude frequency response, can be determined by measuring the transfer impedance and the distance parameters. In order to determine the phase response of the standard hydrophone, it is necessary to accurately measure the distances between the acoustic centers of the three sets of transducer pairs. Due to the existence of influencing factors such as the installation of the three sets of transducer pairs, the alignment of the acoustic axes, and the measurement accuracy of the distances between the acoustic centers during the calibration process, a large error is directly generated in the determination of the phase response of the hydrophone.

[0004] With the development of laser vibration measurement technology, the measurement of vibration by laser interferometry is increasingly widely used in engineering applications. Laser interferometry is a non-contact and non-intrusive measurement method. By using the interference effect of coherent laser beams, the vibration values of the object surface, such as vibration velocity, displacement, acceleration and other parameters, can be measured. When measuring, there is no need to affect the measured object by adding additional mass, so the measurement results are accurate. At the same time, the laser can be focused to the micron scale, with high spatial resolution. With the in-depth application, the measurement of vibration by laser interferometry is applied to the measurement of sound field parameters. By accurately measuring parameters such as the particle vibration velocity and displacement in the sound field, the accurate sound pressure value can be reproduced, which is used for the mapping and reconstruction of the sound field, as well as the transmission and traceability of the sound pressure value, etc. It has a high accuracy in reproducing the sound pressure value. At present, the national sound pressure standard has been established based on laser interferometry, which plays an important role in the metrology and engineering measurement of sound pressure. However, at present, the method for determining the phase response of the free-field sensitivity of a standard hydrophone based on laser interferometry is easily affected by many factors on the phase response, the accuracy needs to be improved, and the determination method is relatively complex. Summary of the Invention:

[0005] The technical problem to be solved by the present invention is to provide a method for determining the phase response of the free-field sensitivity of a standard hydrophone, which can accurately determine its phase response, solves the influence of many factors on the phase response in the reciprocity calibration process, and has the characteristics of simplicity and accuracy.

[0006] The technical solution of the present invention is to provide a method for determining the phase response of the free-field sensitivity of a standard hydrophone, including the following steps:

[0007] Step 1: Determination of the amplitude sensitivity of the hydrophone

[0008] Use the laser interferometry hydrophone sensitivity measurement system to measure the amplitude sensitivity of the standard hydrophone. The main components of this system include: function generator, power amplifier, auxiliary emitter, measurement pool, reflective sound-transmitting diaphragm, laser vibrometer, filter, digital oscilloscope, control computer and other devices. During the measurement, place the reflective sound-transmitting diaphragm at a point in the far field of the auxiliary emitter, use laser interferometry to measure the displacement at this point in the sound field, and then obtain the sound pressure value. Then place the standard hydrophone at the same position in the sound field, keep the emission state unchanged, measure its open-circuit voltage response, and the amplitude sensitivity of the standard hydrophone can be measured by the substitution comparison method:

[0009]

[0010] In the formula, M(f) is the amplitude sensitivity of the standard hydrophone; e oc(f) is the open-circuit voltage of the standard hydrophone; ξ(f) is the displacement in the sound field measured by the laser vibrometer; ω = 2πf is the angular frequency, and f is the signal frequency; ρ is the medium density; c is the sound speed in the medium; n* is the equivalent refractive index of the medium;

[0011] Step 2. Processing the amplitude-frequency response of the hydrophone,

[0012] For the amplitude-frequency response result of the hydrophone sensitivity obtained in Step 1, use the multi-spline interpolation method for interpolation and smoothing processing to obtain the hydrophone sensitivity and its frequency response M at more frequency points within the frequency range of 0 to 1.2f2 I (f), M I (f) should satisfy the mathematical condition of being continuously differentiable. Take the natural logarithm ln[M I (f)] of its frequency response, where f2 is the upper limit frequency;

[0013] Step 3. Pass the obtained signal through an all-pass filter,

[0014] Take the natural logarithm of the interpolated sensitivity frequency response obtained in Step 2 and pass it through a pre-designed all-pass filter to obtain the output signal

[0015] Step 4. Determine the equivalent acoustic center and radius of the standard hydrophone,

[0016] Arrange an auxiliary transmitter and the standard hydrophone to be measured in the sound field. The distance between the auxiliary transmitter and the standard hydrophone satisfies the acoustic far-field condition. Adjust the surface distance between the auxiliary transmitter and the standard hydrophone to be x1. When the auxiliary transmitter emits, measure the open-circuit voltage of the standard hydrophone as e x1 , Move the standard hydrophone away from the auxiliary transmitter along the direction of the geometric center connection line between the auxiliary transmitter and the standard hydrophone to position x2, keep the transmitted signal unchanged, and measure the open-circuit voltage of the standard hydrophone as e x2 , Then the acoustic center radius r0(f) of the standard hydrophone at different frequencies can be expressed as:

[0017]

[0018] Step 5. Calculate and correct the phase response of the hydrophone,

[0019] Calculate the imaginary part of the output signal of the all-pass filter, and use the acoustic center radius of the standard hydrophone determined in Step 4 for phase compensation to determine the phase response of the standard hydrophone

[0020]

[0021] In the formula, k is the wave number, k = 2πf / c, and Im(·) is the operation of finding the imaginary part of a complex number.

[0022] In the present invention, the free-field sensitivity of a standard hydrophone is calibrated by using the laser interference method within a certain frequency range to obtain the amplitude response of its free-field sensitivity within this frequency range. By selecting calibration frequency points or interpolating and smoothing its frequency response, the amplitude response of the sensitivity is made to satisfy the mathematical condition of being continuously differentiable, and the mathematical interpolation method is used to interpolate the low-frequency part of the amplitude sensitivity frequency response to 0 Hz and the high-frequency part to 1.2 times the highest frequency. After taking the natural logarithm of the sensitivity amplitude response, it passes through a pre-designed all-pass phase shifter (all-pass filter). By using the present invention, the distance from the acoustic center of the standard hydrophone to its working surface is determined to perform phase compensation on the data passing through the all-pass phase shifter, thereby obtaining the phase response of the standard hydrophone.

[0023] Preferably, in step 1, n* is a constant, usually taken as 1.01.

[0024] Preferably, in step 2, the interpolation and smoothing process refers to interpolating and smoothing the hydrophone amplitude sensitivity frequency response data obtained from experimental measurements by using the mathematical interpolation method.

[0025] Preferably, in step 3, the designed all-pass filter does not change the amplitude of the input signal, but only performs a 90° phase shift on the phase of the input signal. Its amplitude-frequency response is a constant 1, and the phase-frequency response is -π / 2 in the negative half-axis region and π / 2 in the positive half-axis region.

[0026] Preferably, in step 4, the acoustic axes of the auxiliary transmitter and the standard hydrophone are on the same straight line, and the calibration direction of the standard hydrophone is consistent with the acoustic axis.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] Since calibrating the hydrophone sensitivity by the laser interference method is a direct measurement method, when calibrating the present invention, only the sound pressure at a specific position and the open-circuit receiving voltage of the hydrophone at this point need to be measured to determine the sensitivity of the hydrophone, which has the characteristics of simplicity and high efficiency. At the same time, the influence of factors such as the determination of the acoustic center of the transmitting transducer, the reciprocal transducer, and the reciprocity of the transducer on the calibration result is eliminated, and the calibration result is more accurate. Description of the drawings:

[0029] Figure 1 It is a schematic diagram of the hardware device composition scheme for measuring a hydrophone by the laser interference method of the present invention.

[0030] Figure 2 It is the amplitude-frequency response and phase-frequency response of the all-pass filter of the present invention.

[0031] Figure 3Schematic diagram of determining the sound center radius of a standard hydrophone according to the present invention. Specific implementation method:

[0032] The present invention will be further described below with reference to the accompanying drawings:

[0033] According to Figure 1 The system block diagram shown in the figure is used to construct a laser interferometry hydrophone sensitivity measurement system. The hydrophone to be measured is a spherical hydrophone with a diameter of about 6 mm. The specific implementation process and steps for determining its phase response are as follows:

[0034] Step 1: Determination of hydrophone amplitude sensitivity;

[0035] The amplitude sensitivity of the standard hydrophone is measured using the laser interferometer hydrophone sensitivity measurement system. The measurement is performed using the substitution comparison method. The function generator generates a measurement signal that is amplified by the power amplifier and then stimulates the auxiliary transmitter to radiate sound waves into the water medium to generate the sound field required for measurement. The reflective sound-transmitting diaphragm is placed in the far field of the auxiliary transmitter, and the laser beam incident on the reflective sound-transmitting diaphragm is measured. The particle velocity in the sound field is obtained by measuring the vibration of the reflective sound-transmitting diaphragm, and the water sound pressure value at this position is obtained by the relationship between the sound pressure and the particle velocity under plane wave conditions. The measured hydrophone is placed in the sound field so that its calibration direction is aligned with the acoustic axis of the auxiliary transmitter, and the working surface of the hydrophone coincides with the reflective diaphragm. Keeping the emission state unchanged, the open-circuit voltage output of the standard hydrophone is measured, and the amplitude sensitivity of the measured standard hydrophone can be calculated using formula (1). By changing the frequency f, the amplitude sensitivity frequency response M(f) of the hydrophone in the measurement frequency range of f1 to f2 is obtained.

[0036] Step 2: Processing of the amplitude-frequency response of the hydrophone;

[0037] The amplitude frequency response result of the hydrophone sensitivity obtained in step 1 is interpolated and smoothed using the cubic spline interpolation method to obtain the amplitude response M of the hydrophone sensitivity in the frequency range from 0 Hz to 1.2 times the upper limit frequency of the measurement. I (f), take the natural logarithm of its frequency response ln[M I (f)].

[0038] Step 3, passing the obtained signal through an all-pass phase shift filter;

[0039] Take the natural logarithm of the interpolated sensitivity frequency response obtained in step 2 and pass it through a pre-designed all-pass filter. In this embodiment, the all-pass filter does not change the amplitude of the input signal, but only shifts the phase of the input signal by 90°. Its amplitude-frequency response and phase-frequency response are as follows: Figure 2 As shown, its amplitude frequency response is a constant of 1, and the phase frequency response is -π / 2 in the negative half axis region and π / 2 in the positive half axis region. The output signal is

[0040]

[0041] Wherein, M I (Ω) is the Fourier transform of ln[M I (f)], denotes the inverse Fourier transform.

[0042] Step 4. Determine the equivalent acoustic center and radius of the standard hydrophone;

[0043] According to the scheme as Figure 3 shown, arrange an auxiliary transmitter and the standard hydrophone to be measured in the sound field. The distance between the auxiliary transmitter and the standard hydrophone satisfies the acoustic far-field condition, the acoustic axes of the two are on the same straight line, and the calibration direction of the standard hydrophone is consistent with the acoustic axis. Adjust the surface distance between the auxiliary transmitter and the standard hydrophone to be x1. When the auxiliary transmitter emits, measure the open-circuit voltage of the standard hydrophone as e x1 , move the standard hydrophone away from the auxiliary transmitter along the connecting line between the geometric centers of the auxiliary transmitter and the standard hydrophone to the position x2, keep the transmitted signal unchanged, and measure the open-circuit voltage of the standard hydrophone as e x2 , and calculate the acoustic center radius r0 of the standard hydrophone by using formula (2).

[0044] Step 5. Calculate and correct the phase response of the hydrophone;

[0045] For the output signal obtained in step 3, perform complex operations, and the phase response of the hydrophone can be obtained by using formula (3).

[0046] The present invention discloses a method for determining the phase response of a standard hydrophone based on the laser interferometry method, and further obtaining the complex sensitivity of the standard hydrophone. This method calibrates the free-field sensitivity of the standard hydrophone by using the laser interferometry method within a certain frequency range to obtain the amplitude response of its free-field sensitivity within this frequency range. Regarding the standard hydrophone as a minimum-phase response system, by selecting the calibration frequency points or interpolating and smoothing its frequency response, making its sensitivity amplitude response satisfy the mathematical conditions of continuity and differentiability, and using the mathematical interpolation method to obtain its amplitude response within the range from 0 Hz to 1.2 times the highest measurement frequency. Take the natural logarithm of the amplitude response and then pass it through an all-pass phase shifter. And determine the distance from the acoustic center of the standard hydrophone to its working surface according to the method proposed by the present invention, and perform phase compensation on the data passed through the all-pass phase shifter, then the phase response of the standard hydrophone can be obtained.

[0047] The above is only an illustration of the preferred embodiments of the present invention, but it should not be construed as a limitation of the claims. All equivalent process transformations made using the specification of the present invention are included within the scope of the patent protection of the present invention.

Claims

1. A method for determining the phase response of the free-field sensitivity of a standard hydrophone, characterized in that: including the following steps, Step 1, determination of the amplitude sensitivity of the hydrophone, Measure the amplitude sensitivity of the standard hydrophone using the laser interferometry hydrophone sensitivity measurement system. During the measurement, place the reflective sound-transmitting diaphragm at a point in the far field of the auxiliary transmitter. Use laser interferometry to measure the displacement at this point in the sound field, and then obtain the sound pressure value. Then place the standard hydrophone at the same position in the sound field, keep the emission state unchanged, and measure its open-circuit voltage response. The amplitude sensitivity of the standard hydrophone can be measured through the substitution comparison method: where M(f) is the amplitude sensitivity of the standard hydrophone; e oc (f) is the open-circuit voltage of the standard hydrophone; ξ(f) is the displacement in the sound field measured by the laser vibrometer; ω = 2πf is the angular frequency, f is the signal frequency; ρ is the medium density; c is the sound speed in the medium; n* is the equivalent refractive index of the medium; Step 2, processing of the amplitude-frequency response of the hydrophone, For the amplitude-frequency response results of the hydrophone sensitivity obtained in Step 1, the multi-spline interpolation method is used for interpolation and smoothing to obtain the hydrophone sensitivity and its frequency response M at more frequency points within the frequency range of 0 to 1.2f2. I (f), take the natural logarithm ln[M I (f)] of its frequency response, where f2 is the upper limit frequency. Step 3, pass the obtained signal through an all-pass filter, Take the natural logarithm of the interpolated sensitivity frequency response obtained in step 2 and pass it through a pre-designed all-pass filter to obtain the output signal where M I (Ω) is the Fourier transform of ln[M I (f)], denotes the inverse Fourier transform; Step 4, determine the equivalent acoustic center and radius of the standard hydrophone, Arrange an auxiliary transmitter and a standard hydrophone under test in the sound field. The distance between the auxiliary transmitter and the standard hydrophone satisfies the acoustic far-field condition. Adjust the surface distance between the auxiliary transmitter and the standard hydrophone to be x1. When the auxiliary transmitter emits, measure the open-circuit voltage of the standard hydrophone as e x1 , move the standard hydrophone away from the auxiliary transmitter along the direction of the geometric center connection line between the auxiliary transmitter and the standard hydrophone to the position x2. Keep the transmitted signal unchanged and measure the open-circuit voltage of the standard hydrophone as e x2 , then the acoustic center radius r0(f) of the standard hydrophone at different frequencies can be expressed as: Step 5, calculate and correct the phase response of the hydrophone, Calculate the imaginary part of the output signal of the all-pass filter, and perform phase compensation using the acoustic center radius of the standard hydrophone determined in step 4, then the phase response of the standard hydrophone can be determined to determine the phase response of the standard hydrophone In the formula, k is the wave number, k = 2πf / c, and Im(·) is the operation of finding the imaginary part of a complex number.

2. The method for determining the phase response of the free-field sensitivity of a standard hydrophone according to claim 1, wherein: In Step 1, n* is a constant, taking 1.

01.

3. The method for determining the phase response of the free-field sensitivity of a standard hydrophone according to claim 1, characterized in that: In Step 2, interpolation and smoothing processing refers to using mathematical interpolation methods to interpolate and smooth the hydrophone amplitude sensitivity frequency response data obtained from experimental measurements.

4. The method for determining the phase response of the free-field sensitivity of a standard hydrophone according to claim 1, wherein: In Step 3, the all-pass filter does not change the amplitude of the input signal, but only translates the phase of the input signal by 90°. Its amplitude-frequency response is a constant 1, and the phase-frequency response is -π / 2 in the negative half-axis region and π / 2 in the positive half-axis region.

5. The method for determining the phase response of the free-field sensitivity of a standard hydrophone according to claim 1, characterized in that: In Step 4, the acoustic axes of the auxiliary transmitter and the standard hydrophone are on the same straight line, and the calibration direction of the standard hydrophone is consistent with the acoustic axis.

6. The method for determining the phase response of the free-field sensitivity of a standard hydrophone according to claim 1, characterized in that: In Step 2, the cubic spline interpolation method is used for interpolation and smoothing processing.

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