CN112146744B - Method for accurately measuring reciprocal constant of reverberation pool - Google Patents
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Abstract
The invention discloses a method for accurately measuring a reciprocal constant of a reverberation pool, which mainly comprises a hydrophone and a reciprocal transducer, wherein the hydrophone and the reciprocal transducer move on two sides of the reverberation pool respectively, collect sound field information of the reverberation pool, and calculate the reciprocal constant of the reverberation pool by combining the reciprocity of the reciprocal transducer with the collected sound field information. The invention has more used spatial information, lower requirements on the sound source level of the transmitting transducer and higher precision of the test result; the method is used for measuring the reciprocal constant of the reverberation water pool in the research subject, the measurement result is basically consistent with the result of the reverberation time method, the effectiveness of the method is proved, and the method can be gradually applied to the parameter calibration of each reverberation field.
Description
Technical Field
The invention relates to the field of acoustic metering test technology, in particular to an accurate measurement method for a reciprocal constant of a reverberation water pool.
Background
The underwater acoustic measurement and test usually adopts free field condition, i.e. the condition of isotropy and no interface reflection, and usually needs to combine with impulse sound technology to reach the ideal free field. Therefore, a large anechoic pool needs to be built for free field calibration at lower frequencies. The method has higher accuracy, but has high engineering cost and low-frequency test lower limit. The reverberant sound field is relatively easy to obtain, and the lower limit of the test frequency is far lower than that of the free field method.
The reverberation sound field is also called diffuse reflection sound field, diffusion sound field or dispersion sound field, and the sound field is characterized in that the sound energy density is uniform, the incident sound energy in all directions is uniform, and the sound waves transmitted to a certain point in all directions are irregularly distributed. In 1961, the method for calibrating the acoustic sensor in the reverberant field was proposed by h.g. diesel, and then applied to absolute (reciprocal) calibration of the hydrophone by domestic wuweinshoo, shenpaul, etc., with good results. In the reciprocal calibration of reverberant fields, it is most important to measure the reciprocal constant of the sound field. Common methods are reverberation time method and reverberation radius method. The reverberation time method is a method for obtaining a reciprocal constant of a reverberation pool by measuring the reverberation time of the reverberation pool and calculating by using a formula, and is the most commonly used method at present. However, the measurement of the reverberation time has a spatial error and a repetitive error, so that a method of averaging the measurements of multiple sampling points in the space needs to be adopted, and a stable result can be obtained by averaging the measurements of more than 7 sampling points for multiple times. The reciprocal constant of the reverberation pool is obtained by dividing twice of the reverberation radius by the density of water and the transmission frequency. The reverberation radius is the distance between the direct sound and the reflected sound, so the reverberation radius can be obtained by respectively measuring the direct wave sound pressure and the reverberation field sound pressure generated by the same sound source in the anechoic water pool and the reverberation water pool, but the anechoic effect of the anechoic water pool at low frequency is poor, so the method has great limitation, and is not common.
In summary, both methods need to go through multiple measurement tests, and the accuracy of the measurement result is proportional to the measurement times, and a large number of repeated tests at different positions are needed to realize the accurate measurement of the reciprocity constant.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for accurately measuring the reciprocal constant of a reverberation water pool.
The purpose of the invention is achieved by the following technical scheme: the method for accurately measuring the reciprocity constant of the reverberation water pool mainly comprises the following steps:
1) The reciprocal transducer randomly moves in a region which is more than half wavelength away from each pool surface and water surface at one side of the reverberation pool and transmits a broadband continuous signal T;
2) The hydrophones are arranged on the other side of the reverberation pool and also randomly move in a region which is more than a half wavelength away from each pool surface and the water surface;
3) The signal-to-noise ratio of an open-circuit voltage signal E1 at the output end of the hydrophone is not lower than 30dB, A/D sampling is carried out on the open-circuit voltage signal at the output end of the hydrophone and a transmitting current signal E2 of the reciprocal transducer, and the signal acquisition length is 2 minutes;
4) Processing signals of E1 and E2 to obtain power P at the frequency point of interest U And P I Calculating to obtain reverberationThe reciprocal constant J of the pool is calculated by the formula:
in the formula, M J Sensitivity of the hydrophone; m H Is the sensitivity of the reciprocal transducer.
The reciprocal transducer is a broadband transducer, the working bandwidth of the wideband transducer is larger than the bandwidth B of a broadband continuous signal T, the voltage response sent in the bandwidth is not lower than 160dB, the reciprocity deviation is lower than 0.3dB, and the sensitivity of the reciprocal transducer needs to be known.
The hydrophone has a sensitivity deviation within the bandwidth B of the band continuous signal T of better than +/-0.5 dB.
The broadband continuous signal T has a power spectrum curve similar to the transmission response curve of the reciprocal transducer.
The broadband continuous signal T adopts a signal with the power spectral density being approximately constant.
The E1 and E2 signal processing mode mainly comprises the following steps:
1) Divide E1 and E2 into 120 segments, denoted as U s1 ，U s2 ，…，U S120 And I s1 ，I s2 ，…，I S120 Adding Hanning window with same time length to each segment of signal, and estimating power spectrum with the calculation formula of 1s
In the formula (I), the compound is shown in the specification,
represents U si Is used to generate a power spectrum function of (c),
is represented by si PT represents the power spectrum transformation of the signal, L represents the length of the window signal, hann tableShowing a Hanning window;
2) For the frequency point of interest f 0 The power of the point is averaged to obtain P U And P I The calculation method is as follows
The invention has the beneficial effects that: the invention breaks through the original measuring method of the reciprocal constant of the reverberation pool, the hydrophone and the reciprocal transducer respectively move at two sides of the pool, the sound field information of the reverberation pool is collected, the reciprocity of the reciprocal transducer is utilized to combine the collected sound field information to calculate the reciprocal constant of the reverberation pool, which is equivalent to that the hydrophone collects numerous spatial point positions in a reverberation control area, the used spatial information is more, the requirement on the sound source level of the transmitting transducer is lower, and the test result has higher precision; the method is used for measuring the reciprocal constant of a reverberation water pool in a research subject, the measurement result is basically consistent with the result of a reverberation time method, the validity of the method is proved, and the method can be gradually applied to parameter calibration of each reverberation field.
Drawings
Fig. 1 is a schematic view of the sound field arrangement of the present invention.
FIG. 2 is a graph comparing the reciprocal constants measured by the reverberation time method according to the present invention.
Description of reference numerals: a reverberation pool 1, a space region 2, a reciprocal transducer 3, a space region 4 and a hydrophone 5.
Detailed Description
The invention will be described in detail below with reference to the following drawings:
example 1: as shown in the attached drawing, the method for accurately measuring the reciprocal constant of the reverberation water pool mainly comprises the following steps:
1) The reciprocal transducer 3 moves randomly in a region which is more than a half wavelength away from each pool surface and water surface at one side of the reverberation pool 1 and transmits a broadband continuous signal T;
2) The hydrophones 5 are arranged on the other side of the reverberation pool 1 and also move randomly in a region which is more than a half wavelength away from each pool surface and water surface;
3) The signal-to-noise ratio of the open-circuit voltage signal E1 at the output end of the hydrophone 5 is not lower than 30dB, A/D sampling is carried out on the open-circuit voltage signal at the output end of the hydrophone 5 and the emission current signal E2 of the reciprocal transducer 3, and the signal acquisition length is 2 minutes;
4) Processing signals of E1 and E2 to obtain power P at the frequency point of interest U And P I And calculating to obtain a reciprocity constant J of the reverberation pool 1, wherein the calculation formula is as follows:
in the formula, M J The sensitivity of the hydrophone 5; m H The sensitivity of the reciprocal transducer 3.
The reciprocal transducer 3 is a broadband transducer, the working bandwidth of which is larger than the bandwidth B of the broadband continuous signal T, the sending voltage response in the bandwidth is not lower than 160dB, the reciprocity deviation is lower than 0.3dB, and the sensitivity of the reciprocal transducer 3 needs to be known. The hydrophone 5 has a sensitivity deviation of better than + -0.5 dB within the bandwidth B of the band continuous signal T. The broadband continuous signal T has a power spectrum curve similar to the transmit response curve of the reciprocal transducer 3. The broadband continuous signal T adopts a signal with approximately constant power spectral density, such as a chirp signal, white noise and the like.
The E1 and E2 signal processing method mainly comprises the following steps:
1) Divide E1 and E2 into 120 segments, denoted as U s1 ，U s2 ，…，U S120 And I s1 ，I s2 ，…，I S120 Each segment is 1s in length, a Hanning window with the same time length is added to each segment of signal, and then power spectrum estimation is carried out on the Hanning window, wherein the calculation formula is
In the formula (I), the compound is shown in the specification,
represents U si As a function of the power spectrum of (a),
is represented by I si PT denotes power spectrum transformation of a signal, [ ], [ [ indicates a point product ] ], [ [ L ] denotes a length of a window signal, ] hann denotes a hanning window;
2) For the frequency point of interest f 0 The power of the position is averaged to obtain P U And P I The calculation method is as follows
Example 2: this example measured the reciprocity factor in the frequency range of 2kHz to 10kHz in a 15 m.times.9 m.times.6 m reverberant pool 1. The measuring system comprises a reciprocal transducer 3, a hydrophone 5, a signal source, a current sampler, a power amplifier, a digital oscilloscope and the like.
A reciprocal transducer 3 and a hydrophone 5 are placed in the reverberant pool 1, the reciprocal transducer 3 being located in the spatial region 2 and the hydrophone 5 being located in the spatial region 4. The space areas 2 and 4 are respectively 1m away from the pool wall, the pool bottom and the water surface, and are 2.5m away from the center line, namely the space areas 2 and 4 are symmetrical about the center line of the reverberation pool 1. The reciprocal transducer 3 is excited to generate a noise signal with a bandwidth of 1.6kHz to 12.5kHz, and the reciprocal transducer 3 is moved slowly and at a uniform speed in the spatial region 2, while the hydrophone 5 is moved slowly and at a uniform speed in the spatial region 4. The sampling rate of the digital oscilloscope is set to 50kHz, and an open-circuit voltage signal E1 at the output end of the hydrophone 5 and a transmitting current signal E2 of the reciprocal transducer 3 are respectively acquired. After 2 minutes, the reciprocal transducer 3 and hydrophone 5 were stopped from moving and the acquisition of E1 and E2 was stopped. Signals E1 and E2 are equally divided into 120 segments, denoted as U s1 ，U s2 ，…，U S120 And I s1 ，I s2 ，…，I S120 Adding Hanning window with same time length to each signal segment, and estimating power spectrum with the formula
In the formula (I), the compound is shown in the specification,
represents U si A power spectrum function of;
is represented by si A power spectrum function of; PT represents the power spectrum transformation of the signal; an indication of a dot product; l represents the length of the window signal; hann denotes a hanning window. Finally, averaging the power of the 1/3 octave center frequency in the frequency band of 2 kHz-10 kHz to obtain P U And P I The calculation method is as follows
And then calculating a reciprocity constant J of the reverberation pool, wherein the calculation formula is as follows:
fig. 2 is a comparison of the reciprocity constants measured by the reverberation time method and the present invention. As can be seen, the reciprocity constants measured by the two methods are substantially the same. The reverberation time method is to obtain the reciprocity constant of the reverberation pool 1 by measuring the reverberation time of 7 space points, and theoretically, the precision of the reciprocity constant can be effectively improved by increasing the number of the measurement points. However, the invention adopts dynamic acquisition, the whole acquisition process contains the reverberation sound field information of an infinite number of space points, and compared with a reverberation time method, the method has higher precision.
It should be understood that equivalent substitutions and changes to the technical solution and the inventive concept of the present invention should be made by those skilled in the art to the protection scope of the appended claims.
Claims (5)
1. A method for accurately measuring a reciprocal constant of a reverberation pool is characterized by comprising the following steps: the method comprises the following steps:
1) The reciprocal transducer (3) moves randomly in a region which is on one side of the reverberation water pool (1) and is more than half wavelength away from each pool surface and water surface, and emits a broadband continuous signal T;
2) The hydrophones (5) are arranged on the other side of the reverberation pool (1) and also randomly move in a region which is more than a half wavelength away from each pool surface and water surface;
3) The signal-to-noise ratio of an open-circuit voltage signal E1 at the output end of the hydrophone (5) is not lower than 30dB, A/D sampling is carried out on the open-circuit voltage signal at the output end of the hydrophone (5) and a transmitting current signal E2 of the reciprocal transducer (3), and the signal acquisition length is 2 minutes;
4) Processing signals of E1 and E2 to obtain power P at the concerned frequency point U And P I And calculating to obtain a reciprocity constant J of the reverberation pool (1), wherein the calculation formula is as follows:
in the formula, M J Is the sensitivity of the hydrophone (5); m H Is the sensitivity of the reciprocal transducer (3);
the E1 and E2 signal processing mode comprises the following steps:
4.1 E1 and E2 are divided into 120 segments, denoted as U s1 ，U s2 ，…，U S120 And I s1 ，I s2 ，…，I S120 Each segment is 1s in length, a Hanning window with the same time length is added to each segment of signal, and then power spectrum estimation is carried out on the Hanning window, wherein the calculation formula is
In the formula (I), the compound is shown in the specification,
represents U si As a function of the power spectrum of (a),
is represented by si PT represents the power spectrum transformation of the signal, L represents the length of the window signal, and hann represents the hanning window;
4.2 For a frequency point of interest f) 0 The power of the point is averaged to obtain P U And P I The calculation method is as follows
2. The method for accurately measuring the reciprocal constant of the reverberation pool of claim 1, wherein: the reciprocal transducer (3) is a broadband transducer, the working bandwidth of the transducer is larger than the bandwidth B of the broadband continuous signal T, the voltage response sent in the bandwidth is not lower than 160dB, and the reciprocity deviation is lower than 0.3dB.
3. The method for accurately measuring the reciprocal constant of the reverberation pool of claim 1, wherein: the sensitivity deviation of the hydrophone (5) within the bandwidth B of the broadband continuous signal T is better than +/-0.5 dB.
4. The method for accurately measuring the reciprocal constant of the reverberation pool of claim 1, wherein: the broadband continuous signal T has a power spectrum curve similar to the transmission response curve of the reciprocal transducer (3).
5. The method for accurately measuring the reciprocal constant of the reverberation pool of claim 1, wherein: the broadband continuous signal T adopts a signal with the power spectral density being approximately constant.
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| US4434648A (en) * | 1981-02-26 | 1984-03-06 | Cornell Research Foundation, Inc. | Electroacoustic transducer calibration method and apparatus |
| CN104501939A (en) * | 2014-11-19 | 2015-04-08 | 哈尔滨工程大学 | Inversion method utilizing single hydrophone to measure reverberation time of non-anechoic pool |
| CN106501795A (en) * | 2016-11-09 | 2017-03-15 | 哈尔滨工程大学 | A kind of method that utilization reverberation tank carries out underwater acoustic transducer reciprocity calbration |
| CN108037496A (en) * | 2017-10-11 | 2018-05-15 | 中国船舶重工集团公司第七〇五研究所 | A kind of free field hydrophone plural number sensitivity accurate measurement method |
| CN109302667A (en) * | 2018-09-01 | 2019-02-01 | 哈尔滨工程大学 | A fast measurement method and device for broadband transmission response of underwater acoustic emission transducer |
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| US4453238A (en) * | 1982-04-15 | 1984-06-05 | The United States Of America As Represented By The Secretary Of The Navy | Apparatus and method for determining the phase sensitivity of hydrophones |
| US9835764B2 (en) * | 2014-09-25 | 2017-12-05 | The United States Of America As Represented By The Secretary Of The Navy | System and method for the calibration of a hydrophone line array |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US4434648A (en) * | 1981-02-26 | 1984-03-06 | Cornell Research Foundation, Inc. | Electroacoustic transducer calibration method and apparatus |
| CN104501939A (en) * | 2014-11-19 | 2015-04-08 | 哈尔滨工程大学 | Inversion method utilizing single hydrophone to measure reverberation time of non-anechoic pool |
| CN106501795A (en) * | 2016-11-09 | 2017-03-15 | 哈尔滨工程大学 | A kind of method that utilization reverberation tank carries out underwater acoustic transducer reciprocity calbration |
| CN108037496A (en) * | 2017-10-11 | 2018-05-15 | 中国船舶重工集团公司第七〇五研究所 | A kind of free field hydrophone plural number sensitivity accurate measurement method |
| CN109302667A (en) * | 2018-09-01 | 2019-02-01 | 哈尔滨工程大学 | A fast measurement method and device for broadband transmission response of underwater acoustic emission transducer |
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