Online calibration method for sending response of low-frequency sound tube transducer

Abstract

The invention relates to the technical field of metering testing, in particular to a low-frequency sound tube transducer sending response online calibration method, which comprises the following steps of: establishing an underwater acoustic material decoupling characteristic parameter low-frequency sound tube calibration system, calculating the radiation sound pressure of a transducer by utilizing the sound pressure measured by a hydrophone group in a standing wave field, and obtaining the radiation sound pressure of a transmitting transducer in a low-frequency sound tube; and finally, calculating to obtain the sending response of the transmitting transducer. The low-frequency transmitting transducer calibration method solves the calibration problem of the low-frequency transmitting transducer under the high hydrostatic pressure.

Description

Technical Field

[0001] The invention relates to the field of measurement and testing technology, and specifically relates to an online calibration method for a low-frequency acoustic tube transducer transmission response. Background Art

[0002] Hydroacoustic materials are used in hydroacoustic engineering. According to their main functions, they can be divided into anechoic materials and decoupling materials, which are used to absorb the detection sound waves of active sonar and shield the vibration noise of the shell from radiating to the external water area. In theory, it is generally assumed that the hydroacoustic material layer and the shell application model are planar multilayer structures, simulating the double-layer shell (double-layer steel plate with ribs in the middle, with a water layer in the middle) and single-layer shell (water layer-steel plate-air) structures. Since the hydroacoustic material layer is mostly made of rubber material and has a cavity structure inside, when the equipment shell reaches a certain sea depth, the hydroacoustic material layer is squeezed by the seawater pressure, the shape changes, and its acoustic performance also changes accordingly, especially the compression of the internal cavity structure has a greater impact on the low-frequency acoustic vibration performance under a certain pressure. Therefore, the study of the low-frequency sound tube calibration method of the acoustic and decoupling characteristic parameters of hydroacoustic materials under a certain hydrostatic pressure is crucial for practical applications.

[0003] At present, it is still difficult to measure the acoustic performance of hydroacoustic material samples in the frequency band below 1kHz in a free field under certain water temperature and water pressure conditions. Because the wavelength in water is much larger than the size of the material sample, the edge diffraction and diffraction interference of the sample are serious. A relatively ideal plane wave sound field can be generated in the hydroacoustic low-frequency sound tube. The required sample size is small, the boundary conditions are simple, and it is easy to compare with the theoretical calculation results. Low-frequency sound tubes can be divided into traveling wave tubes and standing wave tubes. When the traveling wave tube measurement device measures the reflection and transmission coefficients of the sample, the front and rear boundaries of the sample are both water media, which is suitable for evaluating the acoustic performance of the sample itself and can simulate the working conditions of the double-hull submarine anechoic tile. The standing wave tube equipment can simulate the stratification of the single-hull submarine of "water medium-hydroacoustic material layer-hull-air", and the double hydrophone transfer function method is used to measure the sound absorption coefficient and vibration velocity transfer coefficient of the sample under air backing. In theory, its lowest operating frequency is not limited by the length of the sound tube. As long as there is enough low-frequency signal-to-noise ratio in the tube, the measurement requirements can be met.

[0004] However, the key technology of the above-mentioned low-frequency sound tube is the low-frequency transmitting transducer which is limited by the inner diameter of the sound tube. Whether the sound source can establish the sound field required by the low-frequency sound tube under the drive of the power amplifier and achieve the signal-to-noise ratio required for the measurement, it is necessary to calibrate the transmission response of the low-frequency transmitting transducer under a certain hydrostatic pressure, and compensate according to the transmission response when designing the driving signal. At present, the electroacoustic parameter calibration of the low-frequency transmitting transducer under high hydrostatic pressure can generally only be carried out using a high-pressure anechoic water tank device. Due to the limitation of the water tank size, the lowest measurement frequency is generally in the kilohertz range, which cannot meet the measurement frequency requirements of the low-frequency sound tube transmitting transducer. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an online calibration method for the sending response of a low-frequency sound tube transducer. The method utilizes a hydrophone group on the wall of the low-frequency sound tube to perform online calibration on the sending response of a transmitting transducer installed at the bottom of the sound tube. This method can not only avoid disassembling the bulky low-frequency transmitting transducer for inspection, but also realize calibration under high hydrostatic pressure conditions.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for online calibration of a low-frequency acoustic tube transducer transmission response, the steps of which are:

[0007] (1) The low-frequency sound tube is placed vertically, and a transmitting transducer is set at the bottom. A group of offline calibrated measuring hydrophones are embedded on the tube wall at a certain distance. The tube is filled with degassed water medium. The water surface reaches a preset height. There is a cavity between the water surface and the upper cover of the low-frequency sound tube. The sound pressure reflection coefficient of the water-air interface is set to -1.

[0008] (2) When calibration is required under a certain hydrostatic pressure, the nitrogen pressurization control system provides high-precision pressure through the high-pressure air pipe and high-pressure valve on the upper cover; when measurement is required under certain water temperature conditions, the water temperature inside the low-frequency sound tube is accurately adjusted through the low-frequency sound tube outer water jacket temperature control system;

[0009] (3) Under certain water temperature and hydrostatic pressure conditions, the transmitting transducer at the bottom of the low-frequency sound tube transmits a sinusoidal continuous signal at each frequency point, and the measuring hydrophone group embedded in the tube wall measures the sound pressure signal of the standing wave field at the hydrophone position in the tube. The calibration system collects and processes the sound source driving voltage at the working frequency and the open-circuit voltage signal of the hydrophone group;

[0010] (4) Using the sound pressure measured by the hydrophone group in the standing wave field, the transducer radiation sound pressure is calculated, and the radiation sound pressure of the transmitting transducer in the low-frequency sound tube is obtained. Finally, the transmission response of the transmitting transducer is calculated.

[0011] In some embodiments, when the low-frequency sound tube performs online calibration of the transmitting transducer, a stable plane wave standing wave sound field is first established in the tube.

[0012] The transmitting transducer is installed at the bottom of the low-frequency sound tube and emits a sinusoidal continuous sound wave. Assume that the radiated sound pressure is p s , incident vertically on the water surface, assuming the sound pressure is p in Due to the total reflection of the water-air interface, the sound pressure reflection coefficient is -1, and the reflected sound pressure is p re , a standing wave field is formed in the water medium, and the sound pressures received by the measuring hydrophone 1 and the measuring hydrophone 2 on the pipe wall are p1 and p2 respectively;

[0013] The emitting transducer at the bottom of the low-frequency sound tube emits a sinusoidal continuous wave with a frequency of f and an amplitude of A, forming a plane standing wave sound field in the waveguide in the tube. The radiated sound pressure on the radiating surface of the emitting transducer is:

[0014] p s (x) = P0·exp(jωt) (1)

[0015] Then the incident wave sound pressure in water medium is:

[0016] p in (x) = P0 exp[j(ωt-kx)] (2)

[0017] Assume r is the water surface sound pressure reflection coefficient, the reflected wave sound pressure is:

[0018] p re (x)=r·P0·exp[j(ωt+kx)] (3)

[0019] The sound pressure at the measured hydrophone 1 can be written as:

[0020] p1=P0·exp(jkd1)+r·exp[-jkd1] (4)

[0021] The sound pressure at the measured hydrophone 2 can be written as:

[0022] p2=P0·exp[-jk(d1+d 12 )]+r·P0·exp[jk(d1+d 12 )] (5)

[0023] In the formula, the term exp(jωt) is abbreviated, k = ω / c, ω = 2πf, c is the sound speed of the water medium, f is the calibration frequency, d1 is the distance from the radiating surface of the transmitting transducer to the hydrophone 1, and d 12 is the distance between hydrophones 1 and 2, l is the distance from hydrophone 2 to the water surface;

[0024] The radiated sound pressure P0 of the transmitting transducer is measured by equations (4) and (5):

[0025]

[0026] The open circuit voltages of hydrophones 1 and 2 are measured as u1 and u2, and the receiving sensitivities are M1 and M2 respectively. The above formula contains:

[0027]

[0028] The measured driving voltage of the transmitting transducer is U F , and finally the transducer’s transmitting voltage response is calculated:

[0029]

[0030] Compared with the prior art, the beneficial effects of the present invention are: firstly, the sound pressure is measured by the dual hydrophones in the standing wave field, the transducer radiation sound pressure is separated, and then compared with the driving voltage of the transducer, and the transmission voltage response is calculated. This patent is applied to the subordinate project, and the online transmission characteristic parameters of the transmitting transducer are obtained. When measuring the acoustic vibration parameters of samples such as submarine acoustic covering layers, the low-frequency response of the transducer can be compensated, the low-frequency signal-to-noise ratio of the sound field is improved, and the measurement accuracy of the low-frequency sound tube calibration system is improved.

[0031] Details of one or more embodiments of the present application are presented in the following drawings and descriptions to make other features, purposes and advantages of the present application more concise and easy to understand. The present application is fully described and understood through the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A block diagram of an online calibration system for sending responses of a low-frequency acoustic tube transducer of the present invention;

[0033] Figure 2 This is a principle block diagram of the low-frequency acoustic tube transducer sending response online calibration system of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The present invention provides a technical solution: an online calibration method for a low-frequency acoustic tube transducer transmission response, the steps of which are:

[0036] (1) The low-frequency sound tube is placed vertically, and a transmitting transducer is set at the bottom. A group of offline calibrated measuring hydrophones are embedded on the tube wall at a certain distance. The tube is filled with degassed water medium. The water surface reaches a preset height. There is a cavity between the water surface and the upper cover of the low-frequency sound tube. The sound pressure reflection coefficient of the water-air interface is set to -1.

[0037] (2) When calibration is required under a certain hydrostatic pressure, the nitrogen pressurization control system provides high-precision pressure through the high-pressure air pipe and high-pressure valve on the upper cover; when measurement is required under certain water temperature conditions, the water temperature inside the low-frequency sound tube is accurately adjusted through the low-frequency sound tube outer water jacket temperature control system;

[0038] (3) Under certain water temperature and hydrostatic pressure conditions, the transmitting transducer at the bottom of the low-frequency sound tube transmits a sinusoidal continuous signal at each frequency point, and the measuring hydrophone group embedded in the tube wall measures the sound pressure signal of the standing wave field at the hydrophone position in the tube. The calibration system collects and processes the sound source driving voltage at the working frequency and the open-circuit voltage signal of the hydrophone group;

[0039] (4) Using the sound pressure measured by the hydrophone group in the standing wave field, the transducer radiation sound pressure is calculated, and the radiation sound pressure of the transmitting transducer in the low-frequency sound tube is obtained. Finally, the transmission response of the transmitting transducer is calculated.

[0040] The method of using the hydrophone group on the wall of the low-frequency sound tube to perform online calibration on the sending response of the transmitting transducer installed at the bottom of the sound tube can not only avoid disassembling the bulky low-frequency transmitting transducer for inspection, but also realize calibration under high static water pressure conditions.

[0041] This patent was applied to the subordinate project, and the emission characteristic parameters of the transmitting transducer were obtained. When measuring the acoustic vibration parameters of the sample, the low-frequency response of the transducer can be compensated, the low-frequency signal-to-noise ratio of the sound field can be improved, and the measurement accuracy of the low-frequency sound tube calibration system can be improved. This is a brand-new method and application for calibrating the transmitting transducer under high hydrostatic pressure. Compared with the traditional offline calibration method, this method solves the problem of difficult on-site calibration and low-frequency calibration under high hydrostatic pressure conditions.

[0042] This method has not been reported in domestic or foreign journals.

[0043] The technical problems to be solved by the present invention include:

[0044] 1) Establish a low-frequency sound tube calibration system for the decoupling characteristic parameters of underwater acoustic materials, and configure the low-frequency sound tube with a sound wave transmitting system and receiving system, a signal acquisition and analysis system, and a sound tube variable temperature and voltage control system.

[0045] 2) Compile the system calibration software of the above step 1), including the transducer transmission response calibration module, to realize the collection and analysis of the sound pressure signal of the standing wave field in the tube and the transducer driving voltage signal, and calculate the transmission response of the transmitting transducer.

[0046] The online calibration method for sending response of a low-frequency acoustic tube transducer described in the present invention is implemented as follows:

[0047] The low-frequency sound tube calibration system implementing the patented measurement method is shown in the attached Figure 1 As shown in the figure (the low-frequency sound tube is placed vertically, the transmitting transducer is installed at the bottom of the sound tube, the lower sound tube is filled with degassed water to a certain height, the upper part is a cavity, the measuring hydrophone group is embedded and installed in the wall of the low-frequency sound tube, and the system also includes electronic instruments and temperature and voltage control auxiliary equipment), it can be divided into the following three parts:

[0048] (1) Low-frequency sound tube. The inner diameter is Φ300mm / outer diameter is 600mm, and the length is 3m. It consists of two sections with lengths of 2m and 1m. It is placed vertically and opened and closed by mechanical control. The transmitting transducer is installed at the bottom of the sound tube, and a vibration isolation and decoupling design is adopted between the transducer and the flange. The 2m section of the lower sound tube is filled with pure water. When the water surface reaches a certain height, the hydrophone group is embedded in the tube wall. The sensitive element at the end of the hydrophone can measure the sound pressure in the tube. The upper sound tube above the sample is a cavity, which can be injected with pressurized nitrogen.

[0049] (2) Electronic measuring instruments. The signal transmission system includes a signal generator and a power amplifier; the receiving system includes a multi-channel preamplifier and a filter, corresponding to the low-frequency acoustic tube measurement hydrophone group, to condition the weak current signal output by the measurement hydrophone group; the signal processing part includes a multi-channel signal acquisition analyzer, which synchronously collects and processes the multi-channel hydrophone reception signals; the computer and peripherals are used to install the measurement software, perform electronic instrument control and acoustic calculations, and output the measurement results.

[0050] (3) Computer and calibration software. Used for electronic measuring instrument control, voltage signal acquisition and analysis, acoustic calculation, and result output.

[0051] When the low-frequency sound tube is conducting online calibration of the transmitting transducer, a stable plane wave standing wave sound field must first be established in the tube, such as Figure 2 As shown (the radiating surface of the transmitting transducer is at x=0, and the position coordinates of the measuring hydrophone group, the hydrophone spacing, the height of the water surface, and the schematic diagram of the incident and reflected sound waves are given respectively), the position and coordinates of the acoustic tube measuring hydrophone, the transmitting transducer, and the water surface are given;

[0052] The transmitting transducer is installed at the bottom of the low-frequency sound tube and emits a sinusoidal continuous sound wave. Assume that the radiated sound pressure is p s , incident vertically on the water surface, assuming the sound pressure is p in Due to the total reflection of the water-air interface, the sound pressure reflection coefficient is -1, and the reflected sound pressure is p re , a standing wave field is formed in the water medium, and the sound pressures received by the measuring hydrophone 1 and the measuring hydrophone 2 on the pipe wall are p1 and p2 respectively;

[0053] The emitting transducer at the bottom of the low-frequency sound tube emits a sinusoidal continuous wave with a frequency of f and an amplitude of A, forming a plane standing wave sound field in the waveguide in the tube. The radiated sound pressure on the radiating surface of the emitting transducer is:

[0054] p s (x) = P0·exp(jωt) (1)

[0055] Then the incident wave sound pressure in water medium is:

[0056] p in(x) = P0 exp[j(ωt-kx)] (2)

[0057] Assume r is the water surface sound pressure reflection coefficient, the reflected wave sound pressure is:

[0058] p re (x)=r·P0·exp[j(ωt+kx)] (3)

[0059] The sound pressure at the measured hydrophone 1 can be written as:

[0060] p1=P0·exp(jkd1)+r·exp[-jkd1] (4)

[0061] The sound pressure at the measured hydrophone 2 can be written as:

[0062] p2=P0·exp[-jk(d1+d 12 )]+r·P0·exp[jk(d1+d 12 )] (5)

[0063] In the formula, the term exp(jωt) is abbreviated, k = ω / c, ω = 2πf, c is the sound speed of the water medium, f is the calibration frequency, d1 is the distance from the radiating surface of the transmitting transducer to the hydrophone 1, and d 12 is the distance between hydrophones 1 and 2, l is the distance from hydrophone 2 to the water surface;

[0064] The radiated sound pressure P0 of the transmitting transducer is measured by equations (4) and (5):

[0065]

[0066] The open circuit voltages of hydrophones 1 and 2 are measured as u1 and u2, and the receiving sensitivities are M1 and M2 respectively. The above formula contains:

[0067]

[0068] The measured driving voltage of the transmitting transducer is U F , and finally the transducer’s transmitting voltage response is calculated:

[0069]

[0070] Through this technical solution, the calibration work is carried out in the attached Figure 1 The system shown is carried out in a low-frequency sound tube that meets the standing wave field condition, and the specific implementation method is as follows:

[0071] 1) Open the bottom flange of the low-frequency sound tube and install the calibrated transmitting transducer at the bottom of the sound tube to ensure flatness and sealing;

[0072] 2) Install the offline calibrated measurement hydrophone group in the wall of the acoustic tube and record the hydrophone number;

[0073] 3) Start the pressure control system connected to the low-frequency sound tube, turn on the vacuum device to form a negative pressure in the low-frequency sound tube, use the external atmospheric pressure to inject pure water into the low-frequency sound tube to a certain height, and record the height of the water surface;

[0074] 4) Turn on the measurement system, run the measurement software on the computer, select the required measurement frequency point, set the signal source output amplitude on the measurement software interface, and adjust the power amplifier gain and impedance so that a standing wave field is formed between the transmitting transducer and the water surface;

[0075] 5) The measurement software controls the instrument to work automatically, collects and processes the two-way hydrophone signals and the power amplifier driving voltage signal, and calculates the transmission voltage response within the measurement frequency range;

[0076] 6) Adjust different hydrostatic pressures or water temperatures and repeat step 5);

[0077] 7) After the measurement is completed, open the pressure relief valve to release the pressure in the low-frequency tube.

[0078] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

[0079] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for online calibration of a low-frequency acoustic tube transducer transmission response, characterized in that: The steps are: (1) The low-frequency sound tube is placed vertically, and a transmitting transducer is set at the bottom. A group of offline calibrated measuring hydrophones are embedded on the tube wall at a certain distance. The tube is filled with degassed water medium. The water surface reaches a preset height. There is a cavity between the water surface and the upper cover of the low-frequency sound tube. The sound pressure reflection coefficient of the water-air interface is set to -1. (2) When calibration is required under a certain hydrostatic pressure, the nitrogen pressurization control system provides high-precision pressure through the high-pressure air pipe and high-pressure valve on the upper cover; when measurement is required under certain water temperature conditions, the water temperature inside the low-frequency sound tube is accurately adjusted through the low-frequency sound tube outer water jacket temperature control system; (3) Under certain water temperature and hydrostatic pressure conditions, the transmitting transducer at the bottom of the low-frequency sound tube transmits a sinusoidal continuous signal at each frequency point, and the measuring hydrophone group embedded in the tube wall measures the sound pressure signal of the standing wave field at the hydrophone position in the tube. The calibration system collects and processes the sound source driving voltage at the working frequency and the open-circuit voltage signal of the hydrophone group; (4) Using the sound pressure measured by the hydrophone group in the standing wave field, the transducer radiation sound pressure is calculated, and the radiation sound pressure of the transmitting transducer in the low-frequency sound tube is obtained. Finally, the transmission response of the transmitting transducer is calculated.

2. The online calibration method for transmitting response of a low-frequency acoustic tube transducer according to claim 1, characterized in that: When the low-frequency sound tube is conducting online calibration of the transmitting transducer, a stable plane wave standing wave sound field is first established in the tube. The transmitting transducer is installed at the bottom of the low-frequency sound tube and emits a sinusoidal continuous sound wave. Assume that the radiated sound pressure is p s , incident vertically on the water surface, assuming the sound pressure is p in Due to the total reflection of the water-air interface, the sound pressure reflection coefficient is -1, and the reflected sound pressure is p re , a standing wave field is formed in the water medium, and the sound pressures received by the measuring hydrophone 1 and the measuring hydrophone 2 on the pipe wall are p1 and p2 respectively; The emitting transducer at the bottom of the low-frequency sound tube emits a sinusoidal continuous wave with a frequency of f and an amplitude of A, forming a plane standing wave sound field in the waveguide in the tube. The radiated sound pressure on the radiating surface of the emitting transducer is: p s (x)=P0·exp(jωt) (1) Then the incident wave sound pressure in water medium is: p in (x)=P0·exp[j(ωt-kx)] (2) Assume r is the water surface sound pressure reflection coefficient, the reflected wave sound pressure is: p re (x)=r·P0·exp[j(ωt+kx)] (3) The sound pressure at the measured hydrophone 1 can be written as: p1=P0·exp(jkd1)+r·exp[-jkd1] (4) The sound pressure at the measured hydrophone 2 can be written as: p2=P0·exp[-jk(d1+d 12 )]+r·P0·exp[jk(d1+d 12 )] (5) In the formula, the term exp(jωt) is abbreviated, k = ω / c, ω = 2πf, c is the sound speed of the water medium, f is the calibration frequency, d1 is the distance from the radiating surface of the transmitting transducer to the hydrophone 1, and d 12 is the distance between hydrophones 1 and 2, l is the distance from hydrophone 2 to the water surface; The radiated sound pressure P0 of the transmitting transducer is measured by equations (4) and (5): The open circuit voltages of hydrophones 1 and 2 are measured as u1 and u2, and the receiving sensitivities are M1 and M2 respectively. The above formula contains: The measured driving voltage of the transmitting transducer is U F , and finally the transducer’s transmitting voltage response is calculated:

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