CN109991590B - System and method for testing low-frequency emission characteristic of transducer in pressure tank in limited space - Google Patents

System and method for testing low-frequency emission characteristic of transducer in pressure tank in limited space Download PDF

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CN109991590B
CN109991590B CN201910129514.XA CN201910129514A CN109991590B CN 109991590 B CN109991590 B CN 109991590B CN 201910129514 A CN201910129514 A CN 201910129514A CN 109991590 B CN109991590 B CN 109991590B
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平自红
赵涵
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715th Research Institute of CSIC
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    • G01—MEASURING; TESTING
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Abstract

The invention belongs to the technical field of underwater acoustic sensor parameter testing, and mainly relates to a system and a method for testing the low-frequency emission characteristic of a transducer in a pressure tank in a limited space. A signal source generates a complex linear frequency sweeping signal, a low-frequency transducer is excited by a power amplifier to generate sound waves, and the sound waves are transmitted through different paths and received by a standard hydrophone. And (4) carrying out conjugate multiplication on the obtained receiving signal and the transmitting signal to obtain a complex transmission function of the system, and carrying out filtering on the complex transmission function. The measured frequency is used as the central frequency of the filter, the frequency deviation generated by the direct sound and the reflected sound is used as the bandwidth of the filter, the influence of the reflected wave is eliminated through multiple times of filtering, the direct wave signal corresponding to the required test frequency is obtained, and finally the sending response and the sound source level of the low-frequency transmitting transducer are obtained.

Description

System and method for testing low-frequency emission characteristic of transducer in pressure tank in limited space
Technical Field
The invention relates to the technical field of underwater acoustic sensor parameter testing, in particular to a system and a method for testing the low-frequency emission characteristic of a transducer in a pressure tank in a limited space.
Background
In the research of underwater sound technology, underwater sound pressure is the most important acoustic quantity, and the main electroacoustic parameters of various sonar equipment are based on the underwater sound pressure and must be detected and calculated. Calibration tests of underwater acoustic pressure are usually performed in a free field, and the reflection influence in the acoustic field must be overcome to perform free field calibration of the transducer and the sonar in a limited water area, wherein the most common method is a pulsed acoustic signal technology which uses a time domain method to realize the separation of a direct signal and an echo signal. However, the transient processing in the narrow band channel of this method can cause distortion of the pulse signal, and as the frequency is reduced, the effect is reduced, which causes the limit of the lower frequency limit in the free field calibration. With the development of ocean exploration technology, the application of deep water transducers in the commercial and military fields is more and more extensive, and the labor of the deep water transducers cannot be saved in the exploration fields. For the purpose of detection farther and deeper, active sonar is developed towards a low frequency. The deep water performance of transducers is typically achieved under laboratory conditions using a pressure vessel of limited size to simulate high hydrostatic pressures. However, because the pressure vessel has a limited size, the low-frequency performance of the pressure vessel is limited due to the influence of internal reflection of the tank body, and the pressure vessel is difficult to realize. Take a conventional pressure tank of 4.0m × 12m phi as an example. The lower limit of the measured frequency was 3kHz using the conventional acoustic pulse method. Therefore, the existing free field calibration method is difficult to meet the low-frequency test requirement of the actual deep water sonar equipment.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, provides a system and a method for testing the low-frequency emission characteristic of a transducer in a pressure tank in a limited space, provides a method for reducing the test frequency in the limited space, realizes the test of the low-frequency characteristic of the transducer, establishes a test system for the emission characteristic of the transducer in the pressure tank, and realizes the test of the low-frequency characteristic of the transducer under high hydrostatic pressure.
The object of the present invention is achieved by the following technical means. A system for testing the low-frequency emission characteristic of a transducer in a pressure tank of a limited space is characterized in that the whole testing system is arranged in the pressure tank of the limited space and mainly comprises a low-frequency emission excitation system, a tested emission transducer, a data acquisition system and a testing control analysis platform; the low-frequency emission excitation system is used for generating a complex linear frequency sweep signal required by a test, the complex linear frequency sweep signal is used for exciting a tested emission transducer, the distance between the tested emission transducer and a hydrophone is set to be d, the hydrophone receives the signal after sound propagation in a pressure tank, a data acquisition system synchronously acquires an emission signal and a receiving signal, then a test control analysis platform processes the acquired signal, and a variable resolution time delay spectroscopy method is used for analyzing the target characteristic of the whole system, so that the characteristic parameter of the emission transducer is obtained.
The invention has disclosed a method for testing the low-frequency emission characteristic of the transducer in the pressure tank of limited space at the same time, this method regards transmitting system, aqueous medium and hydrophone in the pressure tank of limited space as a whole, the low-frequency launches the excitation system and is used for producing the complex number linear sweep frequency signal that the test needs, utilize the complex number linear sweep frequency signal to stimulate the transmitting transducer to be measured, after the sound propagation through the pressure tank, receive the signal by the hydrophone, utilize variable resolution time delay spectroscopy to analyze the target characteristic of the whole system, only carry on the variable resolution time delay spectroscopy analysis process to the transmission function of the system, thus obtain the emission characteristic of the transmitting transducer; after a data acquisition system synchronously acquires transmitting signals and receiving signals, conjugate multiplication is carried out on the transmitting signals and the receiving signals of a synthesized complex number to obtain a transmission function of the whole transmitting and receiving system in the pressure tank, a required measurement frequency is used as a central frequency of a filter, when the transmission function of the whole pressure tank system is subjected to filtering processing, a central frequency filter with variable resolution is adopted, the bandwidth of the filter is used as the bandwidth of the filter by frequency deviation caused by delay of direct sound and multiple reflected sound, and the obtained system transmission function is subjected to fractional filtering analysis through the determined frequency shift of different reflected waves.
The method comprises the following specific steps:
(1) a signal source is controlled by a computer to generate a sine linear sweep frequency signal, a transmitting transducer is excited by a power amplifier, the transmitting transducer works to transmit sound waves into water in a pressure tank, and the sound waves are received by a hydrophone after passing through a propagation distance d;
(2) after passing through the signal conditioning system, the signals received by the hydrophones and the transmitting signals of the signal source are synchronously acquired by the data acquisition system;
(3) changing the sine linear frequency sweep signal of the step (1) into a cosine linear frequency sweep signal, and repeating the steps (1) and (2) to obtain a new receiving signal of the hydrophone;
(4) respectively combining the transmitting signals and the receiving signals obtained in the steps (2) and (3) into complex signals according to the form of cos theta + jsin theta;
(5) dividing the received signal and the transmitted signal to obtain a transmission function of the whole system, filtering the obtained transmission function, wherein the center frequency of a filter is the frequency of a linear sweep frequency signal, the bandwidth of the filter is set according to a formula (7), and the center frequency filtering with different resolutions is realized by changing the frequency deviation corresponding to different propagation distances, so that a direct wave signal is obtained;
the deviation Δ f of the instantaneous frequency of the signal received by the hydrophone is:
Figure GDA0002669428270000021
wherein, Δ riThe propagation distance of reflected waves between the transmitting transducer and the receiving hydrophone through different propagation paths, c is the speed of sound waves in water, fstartIs the starting frequency, fstopTo terminate the frequency, tsIs the signal frequency from fstartChange to fstopThe sweep frequency time of (2);
(6) the sending response and the sound source level of the transmitting transducer can be obtained through formulas (10-12);
the transmit voltage response level is calculated according to equation (10):
SV＝20lg UFP-M0+20lg d-20lg UF (10)
the transmit current response level is calculated according to equation (11):
SI＝20lg UFP-M0+20lg d-20lg IF (11)
exciting the transmitting transducer to transmit, and measuring the open-circuit voltage U of the standard hydrophoneFPCalculating the sound pressure level of the sound source according to the formula (12) as follows:
LSP＝20lg UFP-M0+20lg d (12)
wherein M is0The free field voltage sensitivity of a standard hydrophone, in units of V/Pa;
d is the distance between the transmitting transducer to be measured and the sound center of the standard hydrophone, and the unit is m;
excitation voltage amplitude UFAmplitude of excitation current IFOpen circuit voltage U of standard hydrophoneFP。
The invention has the beneficial effects that: by using the method and the test system, the transmission characteristics of the transmitting transducer with lower frequency can be tested in the pressure tank with limited size, and the problems of the method and the system needed by laboratory test and solution of the low-frequency transmission performance of the deep water transducer are solved. The whole design is simple and easy to use, and a technical approach is provided for measuring the low-frequency performance of the transmitting transducer in the existing pressure tank.
Drawings
FIG. 1 is a schematic block diagram of a variable resolution time delay spectroscopy test system within a pressure tank;
FIG. 2 is a schematic diagram of a transmitting-water-receiving system in a pressure tank;
FIG. 3 is a schematic diagram of a variable resolution time-lapse spectroscopy analysis process;
fig. 4 is a schematic diagram of an emission characteristic test.
Detailed Description
The invention will be described in detail below with reference to the following drawings:
as shown in figure 1, the invention discloses a system for testing the low-frequency emission characteristic of a transducer in a pressure tank of a limited space, wherein the whole testing system is arranged in the pressure tank of the limited space and mainly comprises a low-frequency emission excitation system, a tested emission transducer, a data acquisition system and a testing control analysis platform; the low-frequency transmitting and exciting system is used for generating a complex linear frequency sweeping signal required by testing, the tested transmitting transducer is excited by the complex linear frequency sweeping signal, the distance between the tested transmitting transducer and a hydrophone is set to be d, a computer controls a signal source to transmit the frequency sweeping signal, a power amplifier excites the transmitting transducer, the hydrophone receives the signal after sound propagation in a pressure tank, a data acquisition system synchronously acquires the transmitting signal and the receiving signal, a test control analysis platform processes the acquired signal, and the target characteristic of the whole system is analyzed by a variable resolution time delay spectroscopy method, so that the characteristic parameter of the transmitting transducer is obtained.
The invention can be applied to a pressure container in a limited space, can be used for solving the problem of low-frequency test under high hydrostatic pressure, and particularly can meet the requirement of low-frequency excitation by an excitation system and generate a complex linear frequency sweeping signal required by the test.
The invention provides the following technical approaches to realize the test of the low-frequency characteristic of the transmitting transducer in the existing pressure tank: by referring to the traditional Time Delay Spectroscopy (TDS) method, we propose a variable-resolution time delay spectroscopy. Starting from the signal form and the processing object, the applicability and the pertinence of the TDS method are improved. It is characterized in that: (1) different from the traditional TDS method that the object of analysis is the received time domain signal, the method takes a transducer transmitting system, a sound field in a tank body and a receiving hydrophone as a system to be considered, analyzes the target characteristics of the system and analyzes the transmission function characteristics of the transmission and the reception of the system; (2) unlike TDS method, which uses simple linear sweep signal as the generating signal, it uses complex linear sweep signal as the generating signal of the test system, and uses the conjugate characteristic of complex signal to eliminate the influence of generating signal. (3) Different from the TDS method which utilizes a narrow-band central frequency filter to carry out mobile filtering on a received signal, the center frequency bandwidth of the TDS method is fixed, and the center frequency filter with variable bandwidth is adopted to carry out filtering processing on target characteristic parameters (system transfer functions) so as to obtain a direct sound signal with required measuring frequency. In this way, we can effectively lower the lower frequency limit of the transmitting transducer in a space of limited size.
In the whole test system, linear sweep frequency signals (sine signals and cosine signals) are sequentially generated by a signal source, a tested transmitting transducer is excited by a low-frequency power amplifier, a standard hydrophone receives signals, a data acquisition system synchronously acquires transmitting signals and receiving signals, and then conjugate multiplication is carried out on the transmitting signals and the receiving signals which are synthesized into a plurality of numbers to obtain a transmission function of the whole transmitting and receiving system in the pressure tank. With the desired measurement frequency as the center frequency of the filter, the bandwidth of the filter can be the bandwidth as the frequency offset caused by the delay of the direct sound and reflected sound. And performing fractional filtering analysis on the obtained system transfer function through the determined frequency shifts of different reflected waves. According to theoretical calculation, in a general closed space, 3-5 times of reflected waves can eliminate most reflection influences, so that a relatively ideal direct wave signal is obtained.
In order to obtain accurate arrival time of the reflected wave, after the positions of the transmitting transducer and the receiving hydrophone are determined in the pressure tank, the arrival time of the direct sound and the reflected sound is determined by adopting a higher-frequency sound pulse method. Because at high frequencies, the ping method can achieve higher frequency resolution.
The measurement principle is as follows: consider the transmitting transducer, pressure tank basin, and receiving hydrophone as an overall system (as shown in FIG. 2) that includes three sequential linear elements: a transmitting transducer, a water pool and a receiving hydrophone. Analysis of its target characteristics and estimates of the transmission impedance of the free-field transmitting transducer and the receiving hydrophone are analyzed. By the variable resolution time delay spectroscopy, the influence of multiple reflected waves in the pressure tank at low frequency can be effectively eliminated, and a relatively ideal direct wave signal is obtained.
Transmission impedance of transmitting transducer and receiving hydrophone in pressure tank
Figure GDA0002669428270000041
Figure GDA0002669428270000042
In the formula (I), the compound is shown in the specification,
Figure GDA0002669428270000043
is the open circuit voltage received by the hydrophone,
Figure GDA0002669428270000044
is a transmitting transducerThe excitation current of the terminal.
Transmission impedance of transmitting transducer and receiving hydrophone in free field
Figure GDA0002669428270000045
Figure GDA0002669428270000046
In the formula (I), the compound is shown in the specification,
Figure GDA0002669428270000051
is the free-field sensitivity of the hydrophone,
Figure GDA0002669428270000052
is the transmit transducer transmit voltage response.
Assuming transfer function of pressure tank pool
Figure GDA0002669428270000053
The transmission impedance of the transmitting transducer to the receiving hydrophone in the pressure tank can be expressed as:
Figure GDA0002669428270000054
since the free-field calibration process is based on calibration of the hydrophone and receiver hydrophone transmission impedances under direct wave propagation conditions, this means that there is a unique transfer function
Figure GDA0002669428270000055
Each element of the system may be represented by its transfer function. Considering the reflection, the pool transfer function can be defined as the ratio of the total sound pressure at the receiving point to the direct wave sound pressure; meanwhile, it is assumed that the receiving sound pressure of the hydrophone is under the condition of limited reflected wave
Figure GDA0002669428270000056
Can be used forSound pressure of direct wave
Figure GDA0002669428270000057
And the sound pressure of the reflected wave
Figure GDA0002669428270000058
Is expressed as shown in equation (4).
Figure GDA0002669428270000059
Sound pressure of reflected wave
Figure GDA00026694282700000510
Can pass through direct wave sound pressure
Figure GDA00026694282700000511
Sum difference Deltar between direct wave and reflected waveiThe introduced phase delay.
Let Δ r1<Δr2<…<ΔrnThe reflection factor is independent of frequency and the sound pressure amplitude of the reflected wave is independent of the path difference, the reflected wave can be expressed as equation (5).
Figure GDA00026694282700000512
Wherein k is the wave velocity.
Transfer function of pool
Figure GDA00026694282700000513
It can also be expressed in the form of reflected wave and direct wave, as shown in equation (6).
Figure GDA00026694282700000514
Wherein the frequency deviation Δ fi＝c/ΔriAnd using it as the bandwidth of the center frequency filter for the entire pressure tank launch system-waterAnd filtering the transmission function signal of the pool-receiving system, eliminating the influence of multiple reflections on the direct sound, and obtaining the direct signal with the required frequency.
Time-delay spectroscopy principle with variable resolution
The finite travel time of the acoustic wave in the medium is exploited to ensure free field conditions in the calibration. For all applications, it has several key features: (1) using a complex linear sweep frequency signal as a measuring signal; (2) the measurements were performed in a reflective environment. (3) Adopting a central frequency filter with variable resolution; the principle of the method is as shown in fig. 1, exciting a transmitting transducer to generate a linear frequency sweep signal, receiving a propagation signal by a hydrophone, generating a frequency deviation between the transmitted signal and the received signal within a certain propagation distance due to the influence of reflection in a finite pressure tank, and selecting the length of a propagation path of the received signal by using a central frequency following filter, wherein the frequency deviation is a constant which is in a proportional relation with the propagation time of a sound wave in a medium. Propagation time: t is ti＝ΔriC, wherein Δ r0D is the distance traveled by the direct wave between the transmitting transducer and the receiving hydrophone, Δ riThe propagation distance of reflected waves passing through different propagation paths between the transmitting transducer and the receiving hydrophone is c, and the velocity of sound waves in water is c. Frequency sweeping speed:
Figure GDA0002669428270000061
wherein f isstartIs the starting frequency, fstopTo terminate the frequency, tsIs the signal frequency from fstartChange to fstopTime of the sweep. As a result of the detuning, only signals of a certain propagation time can be received. While the reflected wave requires a longer travel time than the direct sound, its frequency is also lower. For a fixed sweep speed, the acoustic wave emitted by the transmitting transducer needs some time to reach the hydrophone, and the deviation Δ f of the instantaneous frequency of the signal received by the hydrophone is:
Figure GDA0002669428270000062
when filtering the received signal, the frequency deviation is chosen to be equal to Δ f, i.e. the direct sound signal between the transmitting transducer and the receiving hydrophone is chosen, thereby filtering out the influence of reverberation in the measurement field.
The spatial resolution Δ x of the signal is determined by the bandwidth B of the follower filter: Δ x is c · B/s and the bandwidth B of the filter depends on the setting of the sweep speed s, for a given sweep speed the transient response of the filter is measured in terms of a frequency response that should not interfere with the measured object. In selecting the bandwidth of the filter, the following conditions should also be satisfied: b is2≤s。
Transmission characteristic calibration principle:
the transmitting transducer (F) to be measured and the standard hydrophone (P) are placed in a free sound field, as shown in figure 4, and the excitation voltage amplitude U of the transducer is measuredFAnd excitation current amplitude IF. Measuring open circuit voltage U of standard hydrophoneFPThe transmission voltage response S is calculated from equations (8) and (9), respectivelyVAnd sending a current response SI：
Figure GDA0002669428270000063
Figure GDA0002669428270000064
In the formula:
M0the free field voltage sensitivity of a standard hydrophone, in units of V/Pa;
d is the distance between the transmitting transducer to be measured and the sound center of the standard hydrophone, and the unit is m.
For convenience of use, the transmit response measurement of the transmitting transducer is often expressed in terms of "level", and the transmit voltage response level (dB, reference value of 1uPa · m/V) is calculated according to equation (10):
SV＝20lg UFP-M0+20lg d-20lg UF (10)
the transmission current response level (dB, reference value of 1 μ Pa · m/A) is calculated according to equation (11):
SI＝20lg UFP-M0+20lg d-20lg IF (11)
as shown in figure 4, the transmitting transducer is excited to transmit, and the open-circuit voltage U of the standard hydrophone is measuredFPCalculating the sound pressure level (dB, the reference value is 1uPa · m) of the sound source according to the formula (12) as
LSP＝20lg UFP-M0+20lg d (12)
By the method, the lower limit of the measuring frequency can be realized in a limited pressure tank container compared with the lower limit of the measuring frequency of a conventional sound pulse method, the correct evaluation of the low-frequency acoustic characteristics of the deep water transmitting transducer is realized, and the problems of a method and a test system required by the low-frequency test of the deep water transmitting transducer under laboratory conditions are solved. Provides test means and technical support for the development of the deep water transducer.
The invention has disclosed a method for testing the low-frequency emission characteristic of the transducer in the pressure tank of limited space at the same time, this method regards transmitting system, aqueous medium and hydrophone in the pressure tank of limited space as a whole, the low-frequency launches the excitation system and is used for producing the complex number linear sweep frequency signal that the test needs, utilize the complex number linear sweep frequency signal to stimulate the transmitting transducer to be measured, after the sound propagation through the pressure tank, receive the signal by the hydrophone, utilize variable resolution time delay spectroscopy to analyze the target characteristic of the whole system, only carry on the variable resolution time delay spectroscopy analysis process to the transmission function of the system, thus obtain the emission characteristic of the transmitting transducer; after a data acquisition system synchronously acquires transmitting signals and receiving signals, conjugate multiplication is carried out on the transmitting signals and the receiving signals of a synthesized complex number to obtain a transmission function of the whole transmitting and receiving system in the pressure tank, a required measurement frequency is used as a central frequency of a filter, when the transmission function of the whole pressure tank system is subjected to filtering processing, a central frequency filter with variable resolution is adopted, the bandwidth of the filter is used as the bandwidth of the filter by frequency deviation caused by delay of direct sound and multiple reflected sound, and the obtained system transmission function is subjected to fractional filtering analysis through the determined frequency shift of different reflected waves.
It should be noted that: when the whole system is analyzed by using the time delay spectroscopy with variable resolution, the center frequency following filter adopted in the analysis is variable in bandwidth, namely variable in resolution, different from the traditional time delay spectroscopy. When the transmission function of the whole pressure tank system is filtered, a central frequency filter with variable resolution is adopted, which is different from a traditional time delay spectroscopy method which utilizes a central frequency following filter with fixed bandwidth; the bandwidth of the filter is determined by the frequency deviation caused by the delay of the direct sound and the multiple reflected sound.
The method comprises the following specific steps:
(1) a signal source is controlled by a computer to generate a sine linear sweep frequency signal, a transmitting transducer is excited by a power amplifier, the transmitting transducer works to transmit sound waves into water in a pressure tank, and the sound waves are received by a hydrophone after passing through a propagation distance d;
(2) after passing through the signal conditioning system, the signals received by the hydrophones and the transmitting signals of the signal source are synchronously acquired by the data acquisition system;
(3) changing the sine linear frequency sweep signal of the step (1) into a cosine linear frequency sweep signal, and repeating the steps (1) and (2) to obtain a new receiving signal of the hydrophone;
(4) respectively combining the transmitting signals and the receiving signals obtained in the steps (2) and (3) into complex signals according to a cos theta + j sin theta form;
(5) as shown in fig. 3, the received signal and the transmitted signal are divided to obtain a transmission function of the whole system, the obtained transmission function is filtered, the center frequency of the filter is the frequency of the linear sweep signal, the bandwidth of the filter is set according to the formula (7), and the center frequency filtering with different resolutions is realized by changing the frequency deviation corresponding to different propagation distances, so as to obtain a direct wave signal;
the deviation Δ f of the instantaneous frequency of the signal received by the hydrophone is:
Figure GDA0002669428270000081
wherein, Δ riThe propagation distance of reflected waves between the transmitting transducer and the receiving hydrophone through different propagation paths, c is the speed of sound waves in water, fstartIs the starting frequency, fstopTo terminate the frequency, tsIs the signal frequency from fstartChange to fstopThe sweep frequency time of (2);
(6) the sending response and the sound source level of the transmitting transducer can be obtained through formulas (10-12);
the transmit voltage response level is calculated according to equation (10):
SV＝20lg UFP-M0+20lg d-20lg UF (10)
the transmit current response level is calculated according to equation (11):
SI＝20lg UFP-M0+20lg d-20lg IF (11)
exciting the transmitting transducer to transmit, and measuring the open-circuit voltage U of the standard hydrophoneFPCalculating the sound pressure level of the sound source according to the formula (12) as follows:
LSP＝20lg UFP-M0+20lg d (12)
wherein M is0The free field voltage sensitivity of a standard hydrophone, in units of V/Pa;
d is the distance between the transmitting transducer to be measured and the sound center of the standard hydrophone, and the unit is m;
excitation voltage amplitude UFAmplitude of excitation current IFOpen circuit voltage U of standard hydrophoneFP。
The invention meets the requirement of testing the low-frequency characteristic of the transmitting transducer in the pressure tank in the limited space, solves the problems of the method and the system for testing the low-frequency characteristic of the transmitting transducer, and expands the low-frequency testing capability of the existing pressure tank for reducing the lower limit of the testing frequency. In order to meet the requirement of testing the low-frequency characteristic of an energy converter in a pressure tank body with a limited size, the invention provides a variable-resolution time-delay spectrum testing method, which can expand the lower limit of the frequency test of the existing high-pressure water tank from 3kHz to 500 Hz. Different from the traditional Time Delay Spectroscopy (TDS), the method is based on the characteristic analysis of targets (a transmitter, a water pool and a receiver) and the estimation of the transmission impedance of a free field transmitter and the receiver, can effectively reduce the lower frequency limit of the test in the existing pressure tank, and meets the test requirement of sonar equipment on low-frequency performance.
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 (3)

1. A system for testing the low frequency emission characteristics of a transducer in a confined space pressure tank, comprising: the whole test system is arranged in a pressure tank in a limited space and mainly comprises a low-frequency transmitting and exciting system, a to-be-tested transmitting transducer, a data acquisition system and a test control analysis platform; the low-frequency transmitting and exciting system is used for generating a complex linear frequency sweeping signal required by testing, the tested transmitting transducer is excited by the complex linear frequency sweeping signal, the distance between the tested transmitting transducer and a hydrophone is set to be d, the hydrophone receives the signal after sound propagation in a pressure tank, a data acquisition system synchronously acquires a transmitting signal and a receiving signal, a test control analysis platform processes the acquired signal, a central frequency filter with variable bandwidth is used for filtering characteristic parameters of a target, the spatial resolution of the signal is determined by the bandwidth of a following filter, and the target characteristic of the whole system is analyzed by a variable resolution time delay spectroscopy method, so that the characteristic parameters of the transmitting transducer are obtained.
2. A method of using the system for testing the low frequency emission characteristics of a transducer in a confined space pressure tank of claim 1, wherein: the method considers an energy converter transmitting system, a water medium in a finite space pressure tank body and a hydrophone as a whole, a low-frequency transmitting and exciting system is used for generating a complex linear sweep frequency signal required by testing, the transmitting energy converter to be tested is excited by the complex linear sweep frequency signal, the hydrophone receives the signal after sound propagation in the pressure tank, the target characteristic of the whole system is analyzed by a variable resolution time delay spectroscopy, and only the transmission function of the system is analyzed and processed by the variable resolution time delay spectroscopy, so that the transmitting characteristic of the transmitting energy converter is obtained; after a data acquisition system synchronously acquires transmitting signals and receiving signals, conjugate multiplication is carried out on the transmitting signals and the receiving signals of a synthesized complex number to obtain a transmission function of the whole transmitting and receiving system in the pressure tank, a required measurement frequency is used as a central frequency of a filter, when the transmission function of the whole pressure tank system is subjected to filtering processing, a central frequency filter with variable resolution is adopted, the bandwidth of the filter is used as the bandwidth of the filter by frequency deviation caused by delay of direct sound and multiple reflected sound, and the obtained system transmission function is subjected to fractional filtering analysis through the determined frequency shift of different reflected waves.
3. The method for testing the low frequency emission characteristics of a transducer in a confined space pressure tank of claim 2 wherein: the method comprises the following specific steps:
(1) a signal source is controlled by a computer to generate a sine linear sweep frequency signal, a transmitting transducer is excited by a power amplifier, the transmitting transducer works to transmit sound waves into water in a pressure tank, and the sound waves are received by a hydrophone after passing through a propagation distance d;
(2) after passing through the signal conditioning system, the signals received by the hydrophones and the transmitting signals of the signal source are synchronously acquired by the data acquisition system;
(3) changing the sine linear frequency sweep signal of the step (1) into a cosine linear frequency sweep signal, and repeating the steps (1) and (2) to obtain a new receiving signal of the hydrophone;
(4) respectively combining the transmitting signals and the receiving signals obtained in the steps (2) and (3) into complex signals according to the form of cos theta + jsin theta;
(5) dividing the received signal and the transmitted signal to obtain a transmission function of the whole system, filtering the obtained transmission function, wherein the center frequency of a filter is the frequency of a linear sweep frequency signal, the bandwidth of the filter is set according to a formula (7), and the center frequency filtering with different resolutions is realized by changing the frequency deviation corresponding to different propagation distances, so that a direct wave signal is obtained;
the deviation Δ f of the instantaneous frequency of the signal received by the hydrophone is:
Figure FDA0002717391950000021
wherein, Δ riThe propagation distance of reflected waves between the transmitting transducer and the receiving hydrophone through different propagation paths, c is the speed of sound waves in water, fstartIs the starting frequency, fstopTo terminate the frequency, tsIs the signal frequency from fstartChange to fstopThe sweep frequency time of (2);
(6) the sending response and the sound source level of the transmitting transducer can be obtained through formulas (10-12);
the transmit voltage response level is calculated according to equation (10):
SV＝20lg UFP-M0+20lg d-20lg UF (10)
the transmit current response level is calculated according to equation (11):
SI＝20lgUFP-M0+20lg d-20lg IF (11)
exciting the transmitting transducer to transmit, and measuring the open-circuit voltage U of the standard hydrophoneFPCalculating the sound pressure level of the sound source according to the formula (12) as follows:
LSP＝20lgUFP-M0+20lg d (12)
wherein M is0The free field voltage sensitivity of a standard hydrophone, in units of V/Pa;
d is the distance between the transmitting transducer to be measured and the sound center of the standard hydrophone, and the unit is m;
excitation voltage amplitude UFAmplitude of excitation current IFOpen circuit voltage U of standard hydrophoneFP。
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