CN108037496B - Method for accurately measuring complex sensitivity of free-field hydrophone - Google Patents
Method for accurately measuring complex sensitivity of free-field hydrophone Download PDFInfo
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- CN108037496B CN108037496B CN201710941363.9A CN201710941363A CN108037496B CN 108037496 B CN108037496 B CN 108037496B CN 201710941363 A CN201710941363 A CN 201710941363A CN 108037496 B CN108037496 B CN 108037496B
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Abstract
The invention discloses a method for accurately measuring the complex sensitivity of a free-field hydrophone, which relates to the field of free-field underwater acoustic measurement and is mainly used for free-field reciprocity calibration of the hydrophone. The method comprises the steps of firstly measuring the distances between a transmitting transducer and a hydrophone, between a reciprocal transducer and the hydrophone and between the transmitting transducer and the reciprocal transducer by adopting a plurality of high-frequency pulses, correcting the acoustic center of the hydrophone, and eliminating the influence of the acoustic center offset of the hydrophone on the measurement. Meanwhile, the complex signal is adopted to measure the complex sensitivity of the hydrophone, and the signal is transformed from a time domain to a frequency domain through Fourier transform to form a linear frequency response system, so that the complex sensitivity calibration in the real sense is realized. The invention can improve the measurement precision of the sensitivity phase of the hydrophone and make up the defects of the current single-frequency pulse measurement method.
Description
Technical Field
The invention relates to the field of underwater acoustic measurement, belongs to the technology of free field hydrophone sensitivity calibration, and mainly relates to a method for accurately measuring the complex sensitivity of a free field hydrophone.
Background
With the development of underwater sound technology, underwater sound measurement plays an important role in guaranteeing performance indexes and normal use of underwater sound equipment. The free field reciprocity calibration is a classical hydrophone sensitivity absolute calibration method, and the method can carry out absolute calibration on the amplitude and the phase of the sensitivity of a hydrophone under the condition of not introducing a standard hydrophone by utilizing the electro-acoustic reciprocity principle, thereby greatly reducing the measurement uncertainty of the sensitivity of the hydrophone. In order to ensure the measurement accuracy of the sensitivity amplitude and phase of the hydrophone, a calibration system proposed by Luker-van Buren is generally adopted at present, namely, a transmitting transducer, a measured hydrophone and a reciprocal transducer are sequentially arranged in a straight line under water in the measurement process, the transfer impedance of each group of transducer pairs is respectively measured by adopting a pulse acoustic technology, and finally the sensitivity amplitude and phase of the hydrophone are obtained. In the system, because the distance relation among the transmitting transducer, the tested hydrophone and the reciprocal transducer is known, the influence of the distance on the measurement of the sensitivity phase of the hydrophone can be eliminated, and therefore, the method can reduce the measurement uncertainty of the calibration of the sensitivity phase, particularly the high-frequency sensitivity phase. However, this method can eliminate the influence of distance on the phase on the premise that the acoustic center and the geometric center of the measured hydrophone are at the same point. In the actual measurement process, the geometric center and the acoustic center of the hydrophone tend to have a certain deviation, and the suspension system and the support system also generally cause the actual acoustic center of the tested hydrophone to have an offset, so that the calibration of the sensitivity of the hydrophone, particularly the calibration of the sensitivity phase, has a certain error, and the phase error increases with the increase of the frequency.
At present, the pulse acoustic technology is generally adopted in a free field to measure the amplitude and the phase of the sensitivity of a hydrophone, and the amplitude and the phase are obtained by performing FFT analysis on a pulse signal. The method can only measure the sensitivity of the set frequency in a time domain range, and the measuring steps are relatively complex. In this regard, a complex calibration of the hydrophone sensitivity needs to be performed by constructing a complex pulse to measure the offset between the acoustic and geometric centers of the hydrophone. The time domain signal is transformed to the frequency domain through the Fourier transform of the complex signal, so that not only can the complex calibration in the real sense be realized, but also the single-frequency calibration and the broadband calibration can be realized. The method can improve the measurement precision and make up for the defects of the traditional single-frequency pulse measurement.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method for accurately measuring the complex sensitivity of a free-field hydrophone. The method is mainly applied to the precise measurement of the amplitude and the phase of the sensitivity of the hydrophone by a free field reciprocity method.
The object of the present invention is achieved by the following technical means. In free-field reciprocity calibration, the inconsistency between the acoustic center and the geometric center of the hydrophone has an effect on the measurement of the amplitude and phase of the hydrophone sensitivity, and particularly has a greater effect on the measurement of the sensitivity phase, and the phase error increases with increasing frequency. The method for accurately measuring the complex sensitivity of the free-field hydrophone comprises the steps of firstly measuring the distances between a transmitting transducer and the hydrophone, between a reciprocal transducer and the hydrophone and between the transmitting transducer and the reciprocal transducer by adopting a plurality of high-frequency pulses, correcting the acoustic center of the hydrophone, eliminating the influence of the acoustic center offset of the hydrophone on measurement, simultaneously measuring the complex sensitivity of the hydrophone by adopting a plurality of signals, converting the signals from a time domain to a frequency domain by Fourier transform to form a linear frequency response system, and realizing the calibration of the complex sensitivity in the true sense. Compare in ordinary single-frequency pulse calibration, the conversion of time domain to frequency domain is realized to complex signal accessible Fourier transform, becomes the frequency response of time domain signal system, not only can realize single-frequency calibration, can realize broadband signal calibration simultaneously, improves the efficiency of underwater acoustic measurement, compensaties current single-frequency pulse measuring not enough.
Furthermore, the method specifically comprises the following steps:
(1) the method for measuring the acoustic center deviation of the hydrophone comprises the following steps:
1) the signal source transmits high-frequency ranging pulse y0(t) the data acquisition card adopts an external trigger mode to synchronously acquire the pulse signal y sent by the signal source0' (t) transmitting pulse signal y with transmitting transducer0'(t-τ)；
2) The signal source transmits orthogonal signals y with the same frequency as the step 1)1(t) synchronously acquiring the pulse signal y emitted by the signal source in the same way1' (t) transmitting pulse signal y with transmitting transducer1(t-τ)；
3) And constructing a plurality of signals as shown in formula (1):
4) obtaining the delay time of the signal through the step response of the complex signal, and obtaining the distance d between the transmitting transducer and the acoustic center of the hydrophoneFJDistance d between the reciprocal transducer and the hydrophoneHJAnd the distance d between the transmitting transducers and the reciprocal transducerFHAnd calculating the sound center deviation according to the formula (2)
Δd＝dFH-dFJ-dHJ (2)
(2) The free field hydrophone complex sensitivity calibration method comprises the following steps:
1) the transmitting transducer (reciprocal transducer) needs to transmit two groups of orthogonal pulse signals or broadband signals respectively, form complex voltage and current signals, align the complex current and voltage signals in a time domain and obtain complex transfer impedance as shown in the formula (3);
2) fourier transformation is carried out on the complex transfer impedance, as shown in formula (4), at the moment, time domain signals are converted into frequency domain response functions, a group of linear response systems of the signals are formed, the linear systems are frequency and phase responses, and at the moment, the transfer impedance is as shown in formula (5);
3) the phase position of the sensitivity of the hydrophone to be measured can be calibrated by free field reciprocity according to the measurement result of the acoustic center deviation of the hydrophone to be measured
The invention has the beneficial effects that:
a) by the aid of the acoustic center offset measurement, influences on hydrophone sensitivity phase measurement under the conditions of hydrophone suspension offset, misalignment of the acoustic center and the geometric center of the hydrophone and the like can be eliminated, and uncertainty of the sensitivity phase measurement is reduced.
b) By constructing the complex signal, a true calibration of the complex sensitivity is achieved.
c) By constructing the complex signal and performing Fourier transform on the complex signal, the time domain signal is transformed into the frequency response of a frequency domain linear system, so that single-frequency and broadband signal calibration can be realized, and the defect of current single-frequency measurement is overcome.
Drawings
FIG. 1 is a schematic diagram of acoustic center deviation of a hydrophone.
FIG. 2 is a diagram of HF pulse ranging.
FIG. 3 is a schematic diagram of hydrophone acoustic center offset and distance measurements.
Detailed Description
The invention will be described in detail below with reference to the following drawings:
aiming at the defects of the existing hydrophone reciprocity calibration, the invention adopts a complex calibration technology to solve the problem of accurate measurement of the sensitivity amplitude and the phase of the hydrophone. By analyzing the acoustic center offset of the hydrophone, the influence of the acoustic center offset on the sensitivity measurement of the hydrophone is eliminated; by constructing the complex signals and performing Fourier transform on the complex signals, real complex sensitivity calibration is realized, and the sensitivity and the phase of the hydrophone can be measured in a frequency domain range.
According to the free-field electro-acoustic reciprocity principle, the free-field reciprocity method calibration must employ three transducers: a transmitting transducer F for transmitting sound waves only, a hydrophone J for receiving sound waves only, and a reciprocal transducer H for both transmitting and receiving and satisfying linear, passive, and reciprocal conditions. Respectively measuring the complex transfer impedance Z of the transmitting transducer and the measured hydrophone in the measuring processFJ(f) Complex transfer impedance Z of transmitting transducer and reciprocal transducerFH(f) And complex transfer impedance Z of the reciprocal transducer and the hydrophone under testHJ(f) The three transfer impedances are all response functions of frequency change, and the calculation formula of the transfer impedance is as follows:
wherein, UFJ(f)、UFH(f)、UHJ(f) Respectively a transmitting transducer-a tested hydrophone, a transmitting transducer-a reciprocal transducer and a reciprocal transducer-a tested hydrophoneA plurality of open circuit voltages of the group transducer pairs;
IFJ(f)、IFH(f)、IHJ(f) respectively transmitting a plurality of current signals of three transducer pairs of a transmitting transducer-a tested hydrophone, a transmitting transducer-a reciprocal transducer and a reciprocal transducer-a tested hydrophone;
θFJ(f)、θFH(f)、θHJ(f) three groups of transducers, namely a transmitting transducer-the tested hydrophone, a transmitting transducer-a reciprocal transducer and a reciprocal transducer-the tested hydrophone, respectively, respond to the frequency of the transferred impedance phase;
the calculation formula of the sensitivity and the phase of the hydrophone can be obtained according to the relation between the transfer impedance and the distance as follows:
in the formula, JsIs a reciprocal constant in a spherical wave
Meanwhile, the phase of the sensitivity is related to the response of the transmitting transducer, the reciprocal transducer and the hydrophone and the measuring distance, and the influence of the measuring distance on the phase of the sensitivity is increased along with the increase of the frequency. The Luker-van Buren system theoretically has dFH＝dFJ+dHJThe effect of the distance on the phase measurement can now be eliminated. However, in actual measurement, the geometric center and the acoustic center of the hydrophone are usually not at the same point, as shown in fig. 1. When the transfer impedance of the transmitting transducer and the tested hydrophone and the transfer impedance of the reciprocal transducer and the tested hydrophone are respectively measured, the direction of the hydrophone needs to be respectively aligned to the transmitting transducer and the reciprocal transducer, a distance deviation delta d can be generated in the rotating process, and the distance relation can be expressed as
dFH＝dFJ+dHJ+Δd (4)
The influence of the distance in equation (3) on the sensitivity phase cannot be eliminated, and the influence of the distance error on the sensitivity phase increases with the increase of the frequency, and the influence of the error needs to be eliminated in the measurement process.
High frequency pulses are used here to measure the distance between the transmitting transducer and the hydrophone. For a common single-frequency pulse signal, because a phase difference exists between a signal received by a hydrophone and a signal transmitted by the hydrophone, the initial position of the signal cannot be accurately judged, and an error is generated in the measurement of the distance. In order to accurately obtain the distance between the transmitting transducer and the hydrophone, orthogonal pulse signals are respectively transmitted, and a time domain waveform diagram of a transmitting signal and a receiving signal of the hydrophone is obtained in a time domain, as shown in fig. 2 a). Since the signals are orthogonal, a complex signal is constructed as shown in equation (5) and its amplitude is calculated as a time-dependent curve, as shown in fig. 2 b).
In fig. 2, the delay time of the transmission signal and the reception signal becomes a time difference between the complex amplitudes thereof regardless of the phases and phase offsets of the transmission signal and the reception signal.
The sensitivity of a hydrophone is a complex number of amplitude and phase. In the measuring process, the method is adopted to realize the complex number, and Fourier transform calculation is carried out on the complex signals to obtain a function of the amplitude and the phase of the transfer impedance in the free field along with the change of the frequency, so that the frequency response of the system is formed. The amplitude and phase of the sensitivity of the hydrophone can be measured in the frequency domain by analyzing the linear response of the frequency domain.
The method adopts a free field reciprocity method to accurately measure the sensitivity amplitude and phase of the hydrophone. Firstly, a sound field is arranged under the condition of a free field as shown in figure 3, and a transmitting transducer, a tested hydrophone and a reciprocal transducer are sequentially arranged under water to form a straight lineLines and are in the same horizontal plane. In order to ensure the measurement accuracy, the distances among the acoustic centers of the transmitting transducer, the reciprocal transducer and the measured hydrophone are required to be measured. The measured direction of the hydrophone is firstly aligned to the transmitting transducer, and the distance d between the transmitting transducer and the acoustic center of the measured hydrophone is measured by adopting a plurality of high-frequency pulsesFJ(ii) a Rotating the hydrophone by 180 degrees to ensure that the measured direction is aligned to the reciprocal transducer, and measuring the distance d between the transmitting transducer and the acoustic center of the measured hydrophoneHJ(ii) a The tested hydrophone is moved away, and the distance d between the transmitting transducer and the acoustic center of the reciprocal transducer is measuredHJ. And the deviation Δ d is calculated as shown in equation (4). Where Δ d is 2 Δ x, and Δ x is the deviation of the hydrophone acoustic center from the geometric center.
To achieve true hydrophone complex measurements, complex signals need to be constructed at both the transmit and receive ends. The transmitting transducer (reciprocal transducer) needs to transmit two groups of orthogonal pulse signals or broadband signals respectively and form a complex signal. Since there is a certain time delay between the transmitted current signal and the open-circuit voltage signal, it is necessary to align the signals according to the previously measured distance parameters, and finally obtain the complex transfer impedance as shown in equation (6)
Fourier transforming the complex transferred impedance to a frequency response function as shown in equation (7)
Equation (7) is the frequency response function of the transferred impedance, which converts the time domain signal into the frequency response function, and the transmission current, the transferred impedance and the hydrophone open-circuit voltage are connected by a set of linear response system, and the relationship among them constitutes the frequency response function of the linear response system. In the frequency response function, if a narrowband signal (single-frequency signal) is used, f ═ f0At this time, a single frequency response of the complex transfer impedance is obtainedThe preparation method comprises the following steps of; if a broadband signal is used, the broadband response of the corresponding complex transfer impedance needs to be obtained according to the frequency response and the frequency relationship of the broadband signal.
Since the transmitting transducer has a difference in acoustic path length from the hydrophone under test, the method in equation (7) is described herein
Instead of the phase of the real transfer impedance, the phase due to the path difference needs to be subtracted, which can be expressed as transfer impedance when combining fig. 2 and 3 and equation (4)
The method is adopted to obtain the complex transfer impedance Z of the transmitting transducer and the tested hydrophoneFJ(f) Complex transfer impedance Z of reciprocal transducer and receiving hydrophoneHJ(f) And the complex transfer impedance Z of the transmitting transducer and the reciprocal transducerFH(f)。
The distance between the acoustic centers of the transducers and the transfer impedance of the transducers are obtained, and the amplitude of the measuring sensitivity according to the formula (2) can be accurately measured (the phase deviation is within the allowable range of the measuring error and can be ignored). Due to the existence of acoustic center deviation, the phase of the sensitivity of the tested hydrophone can be obtained from the formula (3)
The distance between the transmitting transducer and the acoustic center can be accurately measured by adopting a complex measuring method, and the phase sensitivity of the measured hydrophone can be accurately measured; meanwhile, a complex measurement method is adopted to transform the time domain signal into a frequency response function through Fourier transform, so that the measurement of single frequency and broadband sensitivity can be realized.
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 (1)
1. A method for accurately measuring the complex sensitivity of a free-field hydrophone is characterized by comprising the following steps: firstly, measuring the distances between a transmitting transducer and a hydrophone, between a reciprocal transducer and the hydrophone, and between the transmitting transducer and the reciprocal transducer by adopting a plurality of high-frequency pulses, correcting the acoustic center of the hydrophone, eliminating the influence of the acoustic center offset of the hydrophone on the measurement, simultaneously measuring the complex sensitivity of the hydrophone by adopting a plurality of signals, transforming the signals from a time domain to a frequency domain by Fourier transformation to form a linear frequency response system, and realizing the calibration of the complex sensitivity in the real sense; the method specifically comprises the following steps:
(1) the method for measuring the acoustic center deviation of the hydrophone comprises the following steps:
1) the signal source transmits high-frequency ranging pulse y0(t) the data acquisition card adopts an external trigger mode to synchronously acquire the pulse signal y sent by the signal source0' (t) transmitting pulse signal y with transmitting transducer0'(t-τ)；
2) The signal source transmits orthogonal signals y with the same frequency as the step 1)1(t) synchronously acquiring the pulse signal y emitted by the signal source in the same way1' (t) transmitting pulse signal y with transmitting transducer1(t-τ)；
3) And constructing a plurality of signals as shown in formula (1):
4) obtaining the delay time of the signal through the step response of the complex signal, and obtaining the distance d between the transmitting transducer and the acoustic center of the hydrophoneFJDistance d between the reciprocal transducer and the hydrophoneHJAnd the distance d between the transmitting transducers and the reciprocal transducerFHAnd calculating the sound center deviation according to the formula (2)
Δd＝dFH-dFJ-dHJ (2)
(2) The free field hydrophone complex sensitivity calibration method comprises the following steps:
1) the transmitting transducer and the reciprocal transducer need to transmit two groups of orthogonal pulse signals or broadband signals respectively, form complex voltage and current signals, align the complex current and voltage signals in a time domain and obtain complex transfer impedance as shown in the formula (3);
2) fourier transformation is carried out on the complex transfer impedance, as shown in formula (4), at the moment, time domain signals are converted into frequency domain response functions, a group of linear response systems of the signals are formed, the linear systems are frequency and phase responses, and at the moment, the transfer impedance is as shown in formula (5);
3) the phase position of the sensitivity of the hydrophone to be measured can be calibrated by free field reciprocity according to the measurement result of the acoustic center deviation of the hydrophone to be measured
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| CN108709634A (en) * | 2018-07-20 | 2018-10-26 | 中国科学院声学研究所 | A kind of acoustic wave transducer sensitivity measuring apparatus and its method |
| CN109443514B (en) * | 2018-09-13 | 2020-12-22 | 中国船舶重工集团公司第七一五研究所 | Sound pressure sensitivity calibration cavity and test method thereof |
| CN109443515B (en) * | 2018-09-13 | 2021-05-14 | 中国船舶重工集团公司第七一五研究所 | System and method for testing sensitivity of small-size hydrophone in air |
| CN110186546B (en) * | 2019-05-08 | 2020-04-14 | 浙江大学 | Hydrophone sensitivity free field broadband calibration method based on pink noise |
| CN110208778B (en) * | 2019-05-10 | 2021-04-13 | 中国船舶重工集团公司第七一五研究所 | Transducer broadband complex response measuring device and method based on logarithm variable window function |
| CN110207809B (en) * | 2019-05-31 | 2020-04-14 | 浙江大学 | Transducer transfer impedance calibration device based on spatial frequency domain smoothing technology |
| CN110988850B (en) * | 2019-11-05 | 2023-08-15 | 中国船舶重工集团公司第七一五研究所 | Target scattering-based transducer directivity measurement method and device |
| CN111586546B (en) * | 2020-03-26 | 2021-08-17 | 中国船舶重工集团公司第七一五研究所 | Method and system for measuring resonance point transmission response of low-frequency transducer |
| CN112146744B (en) * | 2020-09-09 | 2022-10-21 | 中国船舶重工集团公司第七一五研究所 | Method for accurately measuring reciprocal constant of reverberation pool |
| CN112964350B (en) * | 2020-12-03 | 2023-06-09 | 中国船舶重工集团公司第七一五研究所 | Method and system for absolute calibration of complex sensitivity of rotary hydrophone based on circular guide rail |
| CN112964349A (en) * | 2020-12-03 | 2021-06-15 | 中国船舶重工集团公司第七一五研究所 | Noise measurement hydrophone sensitivity absolute calibration device and method |
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| CN101915901A (en) * | 2010-08-17 | 2010-12-15 | 中国科学院深圳先进技术研究院 | Magnetic resonance imaging method and device |
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