A calibration device and calibration method for acoustic measurement of surface pulsating pressure

Abstract

The present invention discloses a calibration device and a calibration method for acoustic measurement of surface pulsating pressure. The calibration device includes a signal generator for generating noise and a plane wave generator disposed in an anechoic chamber. The plane wave generator can convert the noise signal generated by the signal generator into a plane wave. A microphone interface for connecting a monitoring microphone is provided on the plane wave generator, so that the monitoring microphone can monitor the plane wave in the plane wave generator. The plane wave generator further includes an output port for outputting the plane wave, and a reference microphone and a measurement microphone of the surface pulsating pressure acoustic measurement device to be calibrated can monitor the plane wave in the plane wave generator through the output port. It further includes a data acquisition module for acquiring data of the monitoring microphone, the reference microphone, and the measurement microphone. The present invention can calibrate the surface pulsating pressure acoustic measurement device, thereby improving the measurement accuracy of the acoustic measurement device.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerodynamic testing, and particularly relates to a calibration device and a calibration method for acoustic measurement of surface pulsating pressure. Background Art

[0002] Low-altitude economy is a comprehensive economic form that drives the development of related industries with low-altitude flight activities as the core, covering many fields such as aircraft R & D and manufacturing, operation services, and comprehensive support. The altitude of the low-altitude economy airspace is usually below 1000 meters, with civil manned and unmanned aircraft as carriers, and the application scenarios mainly include urban air traffic, logistics, fire rescue, emergency medical treatment, etc. In order to reduce pollutant emissions and requirements for runways, low-altitude economy aircraft are mainly electric vertical takeoff and landing (EVTOL) multi-rotor drones. Due to the low flight altitude, the noise generated by aircraft such as multi-rotor drones will have a serious impact on the production and life of urban residents. According to the theory of aeroacoustics, the noise generated by the rotor will increase with the increase of load and flight speed. Therefore, the noise problem needs to be focused on and solved during the aircraft design and R & D process.

[0003] During the movement of the aircraft, when the airflow flows through the surface of the airframe or rotor blades, complex flow phenomena such as flow separation and vortex shedding will occur, thereby inducing surface pulsating pressure. Surface pulsating pressure is the main source of aircraft structural vibration and aeroacoustic noise. Due to the great difficulties in numerical calculation and prediction of turbulence, accurately measuring the surface pulsating pressure through wind tunnel tests is the main means to deeply understand the generation mechanism of aircraft aeroacoustic noise and study and solve the noise problem.

[0004] The conventional wind tunnel measurement methods for aircraft surface pulsating pressure mainly include: pulsating pressure sensors, pressure-sensitive paint, pressure film tapes, etc. These measurement methods have disadvantages such as "high price, difficult installation, inconvenient use and calibration". The acoustic measurement method for aircraft surface pulsating pressure mainly uses the sound pressure measured by a microphone to inversely deduce the surface pulsating pressure. At present, the microphone, which is the core component of the measurement system, has been fully realized in mass production in China. Arranging the microphone at a distance can improve the spatial resolution of the measurement points and is not limited by the special shape of the object. Therefore, the acoustic method for measuring surface pulsating pressure has advantages such as "low cost, high sensitivity, and convenient installation".

[0005] Due to the existence of viscous heat dissipation in the acoustic measurement waveguide of surface pulsating pressure, signal phase distortion and amplitude distortion will occur. In order to obtain accurate results, the measurement system needs to be calibrated. However, there is no equipment in the prior art for calibrating the acoustic measurement device of surface pulsating pressure. Summary of the Invention

[0006] The object of the present invention is to provide a calibration device and a calibration method for surface pulsating pressure acoustic measurement, which can partially solve or alleviate the above deficiencies in the prior art and can calibrate a surface pulsating pressure acoustic measurement device.

[0007] In order to solve the above-mentioned technical problems, the present invention specifically adopts the following technical solutions:

[0008] In a first aspect of the present invention, there is provided a calibration device for surface pulsating pressure acoustic measurement, including a signal generator for generating noise and a plane wave generator disposed in an anechoic chamber. The plane wave generator can convert the noise signal generated by the signal generator into a plane wave. A microphone interface for connecting a monitoring microphone is provided on the plane wave generator, so that the monitoring microphone can monitor the plane wave in the plane wave generator. The plane wave generator further includes an output port for outputting the plane wave, and a reference microphone and a measurement microphone of the surface pulsating pressure acoustic measurement device to be calibrated can monitor the plane wave in the plane wave generator through the output port. It also includes a data acquisition module for acquiring data of the monitoring microphone, the reference microphone, and the measurement microphone.

[0009] As an improvement, a plurality of input interfaces and output interfaces are provided on the anechoic chamber. The plane wave generator is connected to the input interface for receiving signals from the signal generator. The monitoring microphone, the reference microphone, and the measurement microphone are connected to the output interface for the data acquisition module to acquire data of the monitoring microphone, the reference microphone, and the measurement microphone.

[0010] As an improvement, a temperature, humidity, and pressure sensor disposed in the anechoic chamber is further included, and the temperature, humidity, and pressure sensor can output an analog voltage signal.

[0011] As an improvement, the anechoic chamber is of a flip type, including a box body and a cover plate. A sealing rubber strip is provided at the edge where the box body and the cover plate are buckled together. The box body is filled with sound insulation material, and vibration isolation pads are provided at the bottom of the box body.

[0012] As an improvement, a power amplifier is provided between the signal generator and the plane wave generator.

[0013] The present invention also provides a calibration method for surface pulsating pressure acoustic measurement, which is calibrated by using the above-mentioned calibration device for surface pulsating pressure acoustic measurement, including:

[0014] S1 Select a reference microphone and install the reference microphone on the object to be measured;

[0015] The plane wave generator in S2 generates a plane wave, which is monitored by the monitored microphone and the reference microphone to obtain the sound pressure signal. The transfer function between the monitored microphone and the reference microphone, namely transfer function I, is constructed using the sound pressure signal output by the monitored microphone and the sound pressure signal output by the reference microphone.

[0016] In S3, the measuring microphone of the surface pulsation pressure acoustic measurement device to be calibrated is installed on the object to be measured.

[0017] The plane wave generator in S6 generates a plane wave, which is monitored by the monitored microphone and the measuring microphone to obtain the sound pressure signal. The transfer function between the monitored microphone and the measuring microphone, namely transfer function II, is constructed using the sound pressure signal output by the monitored microphone and the sound pressure signal output by the measuring microphone.

[0018] In S9, the transfer function between the measuring microphone and the reference microphone, namely transfer function III, is obtained using the transfer function I and transfer function II.

[0019] Repeat steps S1 to S5 to obtain several transfer functions III, and use the several transfer functions III to construct the calibration transfer function.

[0020] As an improvement, the transfer function I is:

[0021] ;

[0022] where TF1 is the transfer parameter I, is the frequency-domain sound pressure signal of the monitored microphone, is the frequency-domain sound pressure signal of the reference microphone.

[0023] As an improvement, the transfer function II is:

[0024] ；

[0025] where TF2 is the transfer parameter II, is the frequency-domain sound pressure signal of the monitored microphone, is the frequency-domain sound pressure signal of the measuring microphone.

[0026] As an improvement, the transfer function III is:

[0027] ;

[0028] where TF is the transfer parameter III, TF1 is the transfer parameter I, TF2 is the transfer parameter II, is the frequency-domain sound pressure signal of the monitored microphone, is the frequency-domain sound pressure signal of the reference microphone, To measure the frequency-domain sound pressure signal of a microphone.

[0029] As an improvement, the calibration transfer function is:

[0030] ;

[0031] where, TF Cal is the calibration transfer parameter, N is the number of transfer functions III, is the transfer function III with sequence number i, and i is the serial number of the transfer function.

[0032] Beneficial effects: In the present invention, the Helmholtz resonator of the plane wave generator is designed according to the acoustic resonance peak frequency of the equal cross-section inner tube, and its geometric parameters are determined by accurately calculating the acoustic capacitance and the acoustic mass of the cavity opening. It can accurately process sound waves of specific frequencies. When sound waves of this specific frequency appear in the plane wave tube, the Helmholtz resonator resonates, consumes the energy of the sound waves, effectively eliminates the resonance peak, makes the sound wave propagation in the tube more stable, and avoids the interference of resonance on the measurement calibration signal.

[0033] The special design of the continuously variable cross-section tube changes the propagation characteristics of sound waves in the tube. Its exponential smooth curve structure from the large end to the small end suppresses the higher-order acoustic modes, reduces the reflection and scattering of sound waves, and makes the sound waves propagate closer to the ideal state of plane waves. This propagation method reduces the interaction with background noise, reduces the influence of background noise on the measurement signal, and thus improves the signal-to-noise ratio.

[0034] In the calibration device of the present invention, an anechoic chamber is provided to isolate external interference. During the acoustic measurement calibration process, external noise will interfere with the accuracy of the measurement results. The anechoic chamber not only blocks the noise but also prevents the rapid exchange of air inside and outside the chamber, reduces the small air pressure changes and temperature fluctuations caused by air flow, maintains the stability of the acoustic environment inside the chamber, helps to improve the reliability of the measurement, and solves the problem of difficult isolation of low-frequency background noise.

[0035] In addition, in the calibration method provided by the present invention, the sound pressure signals output by the monitoring microphone and the reference microphone are collected through the data acquisition module. However, this signal is a time-domain signal. Therefore, methods such as Fourier transform are usually used to convert the time-domain signal into a frequency-domain signal to obtain the frequency-domain sound pressure signal of the monitoring microphone and the frequency-domain sound pressure signal of the reference microphone. The transfer function I between the monitoring microphone and the reference microphone is calculated according to the frequency-domain sound pressure signals of the monitoring microphone and the reference microphone. This transfer function reflects the conversion relationship of the sound pressure signals between the two at different frequencies.

[0036] Then the data acquisition module collects the sound pressure signals output by the monitoring microphone and the measuring microphone, and calculates the transfer function II between the monitoring microphone and the reference microphone according to the frequency domain sound pressure signal of the monitoring microphone and the frequency domain sound pressure signal of the measuring microphone.

[0037] Transfer function I describes the sound pressure signal transfer relationship between the monitoring microphone and the reference microphone, and transfer function II describes the sound pressure signal transfer relationship between the monitoring microphone and the measuring microphone. Since the monitoring microphone exists in both transfer relationships, the transfer function III between the measuring microphone and the reference microphone can be derived by mathematical operations using these two known transfer functions.

[0038] Transfer function III defines the transfer relationship between the measurement microphone and the reference microphone, whose performance is known and accurate. Through transfer function III, the measurement results of the measurement microphone can be compared with the reference microphone to determine the performance deviation of the measurement microphone. Based on this deviation, the measurement microphone can be calibrated to make its measurement results more accurate and reliable, thereby improving the accuracy of surface pressure pulsation acoustic measurements.

[0039] Finally, by taking multiple measurements and constructing a calibration transfer function, the impact of random errors on the measurement results can be effectively reduced. Random errors show a certain degree of randomness in multiple measurements. Some measurement results may be too large, while others may be too small. By averaging, these errors can be offset, thus obtaining a more accurate transfer function. Using this calibration transfer function to calibrate the measurement microphone can improve the accuracy of the calibration and make the measurement results of the measurement microphone closer to the true value.

[0040] In addition, the transfer function III obtained from a single measurement may have abnormal values. When constructing the verification transfer function, the influence of abnormal values ​​on the final result can be reduced by averaging multiple transfer functions III. The verification transfer function obtained in this way can better reflect the true relationship between the measurement microphone and the reference microphone, and enhance the reliability of the entire calibration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without paying creative labor.

[0042] Figure 1Schematic diagram of the calibration device in Embodiment 1 of the present invention;

[0043] Figure 2 Schematic cross-sectional view of the plane wave generator in Embodiment 2 of the present invention;

[0044] Figure 3 Schematic perspective view of the plane wave generator in Embodiment 2 of the present invention;

[0045] Figure 4 Schematic diagram of the Helmholtz resonator;

[0046] Figure 5 Schematic diagram of the mounting base;

[0047] Figure 6 Flowchart of Embodiment 3 of the present invention.

[0048] Summary of reference signs identification:

[0049] 1 is a loudspeaker; 2 is an outer cylinder; 3 is a continuously variable cross-section inner tube; 4 is an equal cross-section inner tube; 5 is an equal cross-section branch pipe; 6 is a mounting base; 7 is a microphone adapter; 8 is a Helmholtz resonator; 9 is an annular cover plate. 61 is a mounting cavity; 62 is a sound guiding hole; 81 is an opening; 82 is a cavity.

[0050] 101 is a signal generator; 102 is a power amplifier; 103 is a plane wave generator; 104 is a monitoring microphone; 105 is a reference microphone; 106 is a temperature, humidity and pressure sensor; 107 is an anechoic chamber; 108 is an electrical interface. Detailed implementation manners

[0051] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] In this article, suffixes such as "module", "component" or "unit" used to represent elements are only for the convenience of describing the present invention, and they have no specific meaning in themselves. Therefore, "module", "component" or "unit" can be used interchangeably.

[0053] In this text, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", "front", "rear", "one end", "the other end", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0054] In this text, unless otherwise clearly specified and defined, terms such as "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] In this text, "and / or" includes any and all combinations of one or more of the listed related items.

[0056] In this text, "a plurality of" means two or more, that is, it includes two, three, four, five, etc.

[0057] Embodiment 1: As Figure 1 shown, the present invention provides a calibration device for surface pulsating pressure acoustic measurement, including an anechoic chamber 107, a signal generator 101 for generating a noise signal, and a plane wave generator 103 arranged in the anechoic chamber 107. The plane wave generator 103 can convert the noise signal generated by the signal generator 101 into a plane wave; a microphone interface for connecting a monitoring microphone 104 is arranged on the plane wave generator 103, so that the monitoring microphone 104 can monitor the plane wave inside the plane wave generator 103; the plane wave generator 103 further includes an output port for outputting the plane wave, and a reference microphone 105 and a measurement microphone (not shown in the figure) of the surface pulsating pressure acoustic measurement device to be calibrated can monitor the plane wave inside the plane wave generator 103 through the output port; it further includes a data acquisition module for acquiring the data of the monitoring microphone 104, the reference microphone 105, and the measurement microphone.

[0058] Among them, the signal generator 101 generates a noise signal and transmits it to the plane wave generator 103. The plane wave generator 103 converts the noise signal into a plane wave. The reference microphone 105 and the measurement microphone are respectively installed on the object to be measured (not shown in the figure), and the plane wave is monitored through the output port of the plane wave generator 103. While the reference microphone 105 and the measurement microphone are monitoring the plane wave, the monitoring microphone 104 also participates in the monitoring, and the monitoring microphone 104 is used as an intermediate quantity bridging the reference microphone 105 and the measurement microphone, so as to obtain the calibration transfer function of the measurement system to calibrate the system output.

[0059] Specifically, the signal generator 101 in this embodiment can generate white noise, pink noise and sine wave noise signals, convert the audio signal through the speaker on the plane wave generator 103, and convert it into a plane wave by the plane wave generator 103 to cope with different types of calibration scenarios.

[0060] The plane wave generator 103 in this embodiment is used to convert the noise signal generated by the signal generator 101 into a pure plane wave as the physical reference quantity for calibration to calibrate the measurement system.

[0061] The plane wave generator 103 includes a speaker for generating sound and a sound tube for "purifying" sound waves. The sound tube has an output port for outputting a plane wave, and the reference microphone 105 and the measurement microphone of the measurement system to be calibrated both monitor the plane wave through the output port. In addition, a microphone interface is provided on the sound tube for connecting the monitoring microphone 104. The specific structure of the plane wave generator 103 is specifically introduced in Embodiment 2 and will not be elaborated here.

[0062] The anechoic chamber 107 is used to isolate external interference, and the entire calibration process is carried out inside the anechoic chamber. In order to accommodate the calibration equipment, its external dimensions can be more than 500mm×500mm×500mm. In this embodiment, the anechoic chamber 107 is of a flip type and includes a box body and a cover plate; a sealing strip is provided at the edge where the box body and the cover plate are buckled together; sound insulation materials are filled in the box body, and in order to ensure the sound insulation effect, the thickness of the sound insulation materials can be more than 100mm. In addition, vibration isolation pads are provided at the bottom of the box body.

[0063] The flip type design makes the installation, debugging and maintenance of the internal equipment of the anechoic chamber 107 more convenient. When installing, replacing or checking equipment such as the plane wave generator and the microphone, there is no need for a complex disassembly process, and the cover plate can be opened to directly operate, improving work efficiency.

[0064] The sealing strip can effectively fill the gap between the box body and the cover plate, preventing external noise from entering the muffler. During the acoustic measurement calibration process, external noise will interfere with the accuracy of the measurement results. The presence of the sealing strip can greatly reduce the impact of external noise on the measurement and ensure a quiet environment inside the muffler. In addition to blocking noise, the sealing strip can also prevent the rapid exchange of air inside and outside the box, reduce the minute air pressure changes and temperature fluctuations caused by air flow, maintain the stability of the acoustic environment inside the box, and contribute to improving the reliability of the measurement.

[0065] When a plane wave propagates inside the muffler 107, it will encounter the box wall and be reflected. The sound-absorbing material can absorb these reflected sound waves, reducing the multiple reflections and reverberation phenomena of sound waves inside the box. This makes the sound waves received by the microphone purer and closer to the original characteristics of the plane wave, which is beneficial to improving the measurement accuracy.

[0066] External vibrations (such as vibrations generated by the operation of laboratory equipment, vibrations transmitted from the ground, etc.) will be transmitted to the inside through the bottom of the muffler, affecting the measurement accuracy of the microphone. Vibration isolation pads, such as rubber vibration isolation pads, can effectively isolate these vibrations, reduce the interference of vibrations on the measurement system, and ensure the stability of the measurement results.

[0067] For the convenience of connecting with other devices, a number of electrical interfaces 108 are provided on the muffler 107, including input interfaces and output interfaces; the plane wave generator 103 is connected to the input interface for receiving signals from the signal generator; the monitoring microphone 104, reference microphone 105, and measurement microphone are connected to the output interface, facilitating the data acquisition module to collect data from the monitoring microphone 104, reference microphone 105, and measurement microphone.

[0068] In some embodiments, the input interfaces and output interfaces on the muffler 107 are preselected as BNC (Bayonet Neill–Concelman connector) interfaces to achieve stable signal transmission between devices, ensure the quality of signals during the calibration process, and ensure the accuracy of surface pulsation pressure acoustic measurement calibration.

[0069] More specifically, the input interfaces and output interfaces are arranged on the back of the muffler and are sealed. While facilitating the connection with other devices, on the one hand, it avoids generating noise pollution to the surrounding environment, and on the other hand, it prevents the leakage of internal sound waves from affecting the stability of the acoustic environment inside the box. In addition, the sealing treatment can also play a certain protective role, preventing dust, water vapor, etc. from entering the muffler, avoiding damage to internal devices, extending the service life of the devices, and ensuring the long-term stable operation of the calibration device.

[0070] In addition, in some embodiments, it further includes a temperature, humidity, and pressure sensor 106 disposed in the muffler 107, and the temperature, humidity, and pressure sensor 106 can output an analog voltage signal. The propagation characteristics of sound in air are affected by temperature, humidity, and air pressure. Changes in temperature will change the thermal motion state of air molecules and affect the speed of sound; changes in humidity will affect the density and viscosity of air, thereby affecting the propagation loss of sound waves; changes in air pressure will also act on the speed of sound and sound propagation characteristics. The temperature, humidity, and pressure sensor monitors these environmental parameters in the muffler in real time and outputs the measurement results as an analog voltage signal. By obtaining this environmental data, the sound pressure signal collected by the microphone can be corrected to compensate for the measurement error caused by environmental factors, thereby improving the accuracy of the surface pulsation pressure acoustic measurement calibration.

[0071] In some embodiments, a power amplifier 102 is disposed between the signal generator 101 and the plane wave generator 103. The signal generated by the signal generator 101 usually has a low power, while the plane wave generator 103 requires sufficient power to drive its operation to generate a plane wave that meets the requirements. The power amplifier 102 can amplify the low-power signal output by the signal generator, increase the power and amplitude of the signal, so that it has sufficient energy to drive the plane wave generator, ensuring that the plane wave generator can generate a plane wave with a certain intensity and amplitude, so as to provide a stable and measurable sound source in the acoustic measurement calibration.

[0072] In addition, the calibration device in this embodiment further includes a data acquisition module for collecting and storing the data of the monitoring microphone 104, the reference microphone 105, the measurement microphone, and the temperature, humidity, and pressure sensor 106. This is convenient for subsequent accurate comparison and analysis of the data of different microphones, so as to accurately measure and evaluate the acoustic parameters.

[0073] In this embodiment, the signal generator 101 uses a Protek DG1022Z. This signal generator 101 has built-in signals such as sine waves and white noise, and has working modes such as continuous and scanning. The signal output interface is a BNC interface. The power amplifier 102 uses a HiVi HIFI260. Its output power is not less than 30W, and the gain is adjustable. The adjustment range is preferably 0dB - 40dB. The signal generator and the power amplifier are connected by a 4m long 50-ohm coaxial cable, and both ends are BNC interfaces. The impedance of the coaxial cable is 50Ω or 75Ω, preferably 50Ω. The output of the power amplifier is a XLR interface, which is connected to the input interface of the muffler 107 through an audio cable, and the input interface of the muffler is connected to the full-frequency speaker 1 in the plane wave generator 103.

[0074] The frequency range of the full-frequency speaker 1 used in the plane wave generator 103 is 10 Hz - 16000 Hz, the diameter is 90 mm, the diameter of its cylindrical outer cylinder is 100 mm, and the height is 80 mm. The microphone interface on the side of the plane wave generator 103 is made by 3D printing, preferably resin material. The inner diameter of the mounting seat cavity is 12.7 mm. After installing a 1 / 4-inch adapter in the cavity, it supports a 1 / 4-inch microphone.

[0075] The outer shell of the anechoic box 107 is made of hardwood, and there are 8 BNC interfaces on the front as output interfaces and input interfaces. The external dimensions are 500 mm × 500 mm × 500 mm. The inside of the anechoic box is pasted with sound-absorbing cotton with a thickness of 100 mm. The anechoic box includes an upper cover and a cavity, and a rubber sealing ring is installed around the edges of the upper cover and the cavity. Four rubber feet with a height of 10 mm are installed at the bottom of the anechoic box.

[0076] The monitoring microphone 104, the reference microphone 105 and the measuring microphone all adopt MA411A pre-polarized pressure field microphones (1 / 4 inch). The power supply and signal measurement of the microphones are provided by a data acquisition device, and the data acquisition device adopts the XCQ108 expandable multi-channel data acquisition system. The temperature, humidity and pressure sensor 106 adopts the MS8607 integrated sensor.

[0077] Embodiment 2: As Figure 2 shown, this embodiment provides a plane wave generator 103 for surface pulsating pressure measurement calibration, including a speaker 1 and a sound tube connected to the speaker 1; the sound tube includes a funnel-shaped continuously variable cross-section inner tube 3, the large end of the continuously variable cross-section inner tube 3 is connected to the sound-emitting end of the speaker 1, and the small end is connected to an equal cross-section inner tube 4; the inner diameter of the equal cross-section inner tube 4 is the same as the inner diameter of the opening at the small end of the continuously variable cross-section inner tube 3, and the speaker 1, the continuously variable cross-section inner tube 3 and the equal cross-section inner tube 4 are coaxially installed.

[0078] It also includes an outer tube 2 sleeved outside the continuously variable cross-section inner tube 3 and the equal cross-section inner tube 4, and the outer tube 2 and the variable cross-section inner tube 3 and the equal cross-section inner tube 4 enclose a cavity; at least two Helmholtz resonators 8 are arranged along the axial direction of the inner wall of the equal cross-section inner tube 4.

[0079] An equal cross-section branch pipe 5 is installed between the outer tube 2 and the equal cross-section inner tube 4. One end of the equal cross-section branch pipe 5 leads to the inside of the equal cross-section inner tube 4, and the other end extends to the outer tube 2; and a microphone interface for connecting to a microphone is installed at the end of the cross-section branch pipe 5 extending to the outer tube 2.

[0080] The loudspeaker 1 serves as the sound source of the entire plane wave generator and can generate acoustic wave signals with a wide frequency band. During the calibration of surface pulsation pressure measurement, it provides the initial acoustic energy for the system, simulating acoustic waves of various frequencies that may be encountered in actual measurement scenarios, and is the basis for the entire measurement and calibration work to be carried out.

[0081] The sound tube is the core functional module of the plane wave generator 103. Through structural optimization and resonance control, it provides a stable and wide-frequency plane wave calibration signal for surface pulsation pressure measurement, solving the problems of signal distortion and noise interference in traditional acoustic measurements.

[0082] Among them, the continuously variable cross-section inner tube 3 is funnel-shaped, including a large end and a small end. The large end is connected to the sound-emitting end of the loudspeaker 2, and the small end is connected to the constant cross-section inner tube 4. When the acoustic wave propagates from the large end to the small end, due to the gradually decreasing pipe diameter, the generation of high-order acoustic wave modes can be suppressed. In a traditional straight pipe, high-order modes may make the propagation characteristics of the acoustic wave become complex and affect the measurement accuracy. The design of the continuously variable cross-section inner tube enables the acoustic wave to propagate closer to the form of a plane wave, reducing the interference of high-order modes on the measurement results.

[0083] More specifically, the curve between the large-end opening and the small-end opening of the continuously variable cross-section inner tube 3 is an exponential smooth curve, that is, the cross-sectional area changes gradually according to an exponential function. The advantages of such a setting are as follows: First, it can reduce the reflection and diffraction of acoustic waves in the tube, suppress the generation of high-order modes (such as radial modes), make the acoustic wave propagate closer to the form of a plane wave, and thus improve the purity of the calibration signal. Second, the mathematical continuity of the exponential gradient curve reduces the phase distortion and amplitude attenuation of the acoustic wave during propagation, ensuring the accuracy of the calibration signal. Third, the exponential gradient curve enables a smooth transition at the connection between the continuously variable cross-section inner tube and the constant cross-section inner tube, reducing the risk of local turbulence and resonance. Fourth, the exponential curve avoids sharp corners, reduces the generation of air flow separation and turbulent noise, and improves the signal-to-noise ratio.

[0084] In this embodiment, the area of any cross-section in the cavity of the continuously variable cross-section inner tube 3 is calculated using the formula:

[0085] where S(x) is the cross-sectional area at a distance x from the large end, x is the distance from the large end; S0 is the area of the large-end opening of the continuously variable cross-section inner tube, and δ is the winding index of the continuously variable cross-section inner tube;

[0086] using the formula:

[0087]

[0088] Calculate the winding index of the continuously variable cross-section inner tube 3; where δ is the winding index of the continuously variable cross-section inner tube 3, L is the length of the continuously variable cross-section inner tube, d0 is the inner diameter of the large-end opening of the continuously variable cross-section inner tube, and d1 is the inner diameter of the small-end opening of the continuously variable cross-section inner tube;

[0089] Using the formula:

[0090]

[0091] Calculate the length of the continuously variable cross-section inner tube 3; where L is the length of the continuously variable cross-section inner tube 3, d0 is the inner diameter of the large-end opening of the continuously variable cross-section inner tube 3, and d1 is the inner diameter of the small-end opening of the continuously variable cross-section inner tube 3, f low Is the lower limit frequency of the surface pulsation pressure measurement system, and c0 is the speed of sound in air.

[0092] In addition, it can be foreseen that the large-end opening area of the continuously variable cross-section inner tube 3 can be calculated using the formula:

[0093] S0 = π d 0 2 / 4 to calculate; where S0 is the large-end opening area of the continuously variable cross-section inner tube 3, and d0 is the inner diameter of the large-end opening of the continuously variable cross-section inner tube 3.

[0094] In this embodiment, the inner diameter of the equal cross-section inner tube 4 is the same as the inner diameter of the small-end opening of the continuously variable cross-section inner tube 3, and they are coaxially installed with the speaker 1 and the continuously variable cross-section inner tube 3. Its function is to provide a stable propagation channel for the sound wave processed by the continuously variable cross-section inner tube 3, ensure that the sound wave continues to propagate in a relatively stable state therein, reduce the scattering and reflection of the sound wave, and enable the sound wave to maintain good consistency and stability. The equal cross-section inner tube also provides space for the installation of the Helmholtz resonator, facilitating the processing of sound waves of specific frequencies through the resonator. In addition, the outlet end of the equal cross-section inner tube 4 also serves as the output port of the plane wave. During calibration, the reference microphone and the measurement microphone of the measurement system to be calibrated both monitor the plane wave through the output port.

[0095] More specifically, the inner diameter of the equal cross-section inner tube 4 is calculated using the formula:

[0096]

[0097] Calculate; where d2 is the inner diameter of the equal cross-section inner tube 4, c0 is the speed of sound in air, and generally c0 = 343 m / s, f up The upper limit of the frequency range of the speaker. Since the inner diameter of the equal cross-section inner tube 4 is the same as the inner diameter of the small-end opening of the continuously variable cross-section inner tube 3, in this embodiment, the inner diameter of the equal cross-section inner tube 4 can be determined first and then the inner diameter of the small-end opening of the continuously variable cross-section inner tube 3 can be determined.

[0098] The outer cylinder 2 is sleeved outside the continuously variable cross-section inner tube 3 and the constant cross-section inner tube 4, and encloses a cavity with the continuously variable cross-section inner tube 3 and the constant cross-section inner tube 4. In some embodiments, the shape of the outer cylinder 2 is preferably cylindrical. The purpose of setting the outer cylinder 2 is to provide physical protection for the internal continuously variable cross-section inner tube 3 and constant cross-section inner tube 4, prevent damage to the acoustic tube caused by external collisions, extrusion and other factors, and ensure the integrity and stability of the acoustic tube structure. In addition, the cavity can play a certain sound insulation role, reduce the interference of external environmental noise on the sound wave propagation in the tube. At the same time, it can also buffer the external vibration to a certain extent and reduce the impact of vibration on the measurement results.

[0099] In addition, in this embodiment, three Helmholtz resonators 8 are arranged at equal intervals along the axial direction of the constant cross-section inner tube 4.

[0100] The Helmholtz resonator 8 is an acoustic element that selectively absorbs the sound wave energy of a specific frequency by matching the acoustic capacitance and acoustic mass, thereby eliminating the resonance phenomenon. In the present invention, it is integrated on the inner wall of the constant cross-section inner tube of the plane wave generator and is used to calibrate the surface pulsation pressure measurement system.

[0101] When there is a sound wave in the constant cross-section inner tube 4 with the same resonance frequency as the resonator, the resonator will resonate with the sound wave and absorb the energy of the sound wave of this frequency, thereby eliminating or greatly weakening the resonance phenomenon of this frequency. Resonance may cause standing waves to form in the tube, affecting the measurement accuracy. The Helmholtz resonator can effectively avoid this situation. By eliminating the resonance of a specific frequency, the frequency characteristics of the sound wave in the tube become smoother, improving the frequency response performance of the entire plane wave generator system, and thus enhancing the measurement calibration accuracy.

[0102] Specifically, the Helmholtz resonator 4 includes a cavity 82 embedded in the inner wall of the constant cross-section inner tube 4. The opening 81 of the cavity 82 faces the inner side of the inner wall of the constant cross-section inner tube 3, and the width of the opening 81 of the cavity 82 is smaller than the width of the cavity 82.

[0103] In this embodiment, the cavity 82 of the Helmholtz resonator 8 is a cube; the acoustic capacitance of the cavity 82 of the Helmholtz resonator 8 and the acoustic mass of the opening 81 are obtained according to the acoustic cavity resonance frequency of the constant cross-section inner tube 4; and the depth of the cavity 82 of the Helmholtz resonator 8 is obtained according to the acoustic capacitance of the cavity 82, and the length and diameter of the opening 81 are obtained according to the acoustic mass of the cavity opening 81. Specifically:

[0104] The acoustic cavity resonance frequency of the constant cross-section inner tube 4 is calculated using the formula:

[0105]

[0106] Calculate; where, f ris the acoustic cavity resonance frequency, c0 is the speed of sound in air, and d2 is the inner diameter of the equal - cross - section inner tube 4;

[0107] The relationship between the acoustic capacitance of the cavity 82 of the Helmholtz resonator 8 and the acoustic mass of the opening 81 of the cavity 82 and the acoustic cavity resonance frequency of the equal - cross - section inner tube 4 is:

[0108] ;

[0109] Among them, M b is the acoustic mass, C b is the cavity acoustic capacitance, f r is the acoustic cavity resonance frequency;

[0110] The cavity acoustic capacitance is calculated using the formula:

[0111]

[0112] Calculated; where C b is the cavity acoustic capacitance, H is the depth of the cavity of the Helmholtz resonator 8, ρ0 is the density of air, and c0 is the speed of sound in air;

[0113] The acoustic mass of the opening 81 of the Helmholtz resonator 8 is calculated using the formula:

[0114]

[0115] Calculated; where M b is the acoustic mass, l is the length of the opening, d is the diameter of the opening, and ρ0 is the density of air.

[0116] In this embodiment, an equal - cross - section branch pipe 5 is further provided on the sound tube, which is used to guide the sound wave propagating in the equal - cross - section inner tube 4 to the outside, facilitating docking with the microphone to realize the acquisition of the sound wave signal.

[0117] In addition, in this embodiment, one Helmholtz resonator 8 that is farthest from the continuously variable cross - section inner tube 3 is aligned with the equal - cross - section branch pipe 5. The aligned layout can reduce the interference of the sound wave during propagation. If the position of the Helmholtz resonator and the equal - cross - section branch pipe is improper, it may cause additional reflection or interference phenomena when the sound wave propagates to the branch pipe.

[0118] For the convenience of installing the microphone, a microphone interface for connecting with the microphone is installed at one end of the equal - cross - section branch pipe 5 extending to the outer cylinder 2. Specifically, the microphone interface includes a mounting seat 6 connected to the equal - cross - section branch pipe 5, and a sound - guiding hole 62 communicating with the equal - cross - section branch pipe 5 is opened on the mounting seat 6; a microphone adapter 7 is arranged in the mounting seat 6.

[0119] The sound guiding hole 62 on the mounting base 6 provides a direct channel for the propagation of sound waves. Its aperture is 1 mm - 3 mm, preferably 2 mm, ensuring that the sound waves in the equal cross-section branch pipe 5 can smoothly enter the inside of the microphone interface without obstruction. In actual measurement, the sizes and interface types of microphones may vary. The microphone adapter 7 can be designed specifically according to the specifications of the microphone. For example, in this embodiment, the microphone adapter 7 has two sizes, 1 / 2 inch and 1 / 4 inch, enabling the plane wave generator to be compatible with a variety of different specifications of microphones, improving the versatility and applicability of the plane wave generator, and meeting the connection requirements of different measurement scenarios and microphones.

[0120] More specifically, the mounting base 6 is preferably made of resin material through 3D printing, and a rubber ring mounting groove is reserved in the center inside.

[0121] In this embodiment, the loudspeaker 1 is a HiVi M3N full-range loudspeaker. The rated power of the loudspeaker is 15 W. The frequency response curve is flat in the range of 100 Hz - 10,000 Hz. The panel diameter is 90 mm, the opening size is 75 mm, the depth is 53 mm, and the total thickness of the loudspeaker is 57.4 mm.

[0122] The cylindrical outer cylinder 2 is made of 304 stainless steel material, with an outer diameter of 100 mm, an inner diameter of 90 mm, and a thickness of 5 mm. Four M3×6 mm threaded holes are opened at the top of the outer cylinder 2. The loudspeaker 1 is connected to the outer cylinder 2 by screws, and a rubber ring gasket is used to seal between the opening edge of the loudspeaker 1 and the outer cylinder 2. A groove with a width of 30 mm, a height of 20 mm, and a depth of 20 mm is opened on the side of the outer cylinder 2 for accommodating the microphone interface, making the microphone interface flush with the outer surface of the outer cylinder 2, as Figure 3 shown.

[0123] The continuously variable cross-section inner tube 3 is made of 304 stainless steel material, with a wall thickness of 2 mm, an inner diameter of the large end opening of 86 mm, an inner diameter of the small end opening of 12 mm. Between the large end and the small end openings is an exponential smooth curve S(x) = S0*exp(-50*x), where x is the distance from the large end, and the winding index δ = 50. Two M1.5×3 mm positioning holes are opened at the small end of the continuously variable cross-section inner tube, and a flange is provided at the large end. Four threaded holes with the same positions as the threaded holes on the outer cylinder are circumferentially opened on the flange

[0124] The equal cross-section inner tube 4 is made of 304 stainless steel material, with a wall thickness of 2 mm and a length of 80 mm. Two M1.5×3 mm positioning holes are opened at the same position at the top of the equal cross-section inner tube 4 and the bottom of the continuously variable cross-section inner tube 3. They are connected by a pin, and the contact surface is welded by argon arc welding.

[0125] To achieve the closure of the bottom of the outer cylinder 2 and the equal - cross - section inner tube 4, an annular cover plate 9 can be provided at their bottoms. Of course, the annular cover plate 9 can also be integrally formed with the outer cylinder.

[0126] As Figure 4 shown, a 2 - mm single - side through - hole is opened 30 mm from the bottom of the equal - cross - section inner tube 4. A 2 - mm through - hole is opened opposite to this through - hole. A cavity 82 with an inner side length of 5 mm and a thickness of 2 mm is welded outside the through - hole, thus forming a Helmholtz resonator 8. There are 3 Helmholtz resonators 8 distributed along the height direction of the equal - cross - section inner tube, with a spacing of 10 mm.

[0127] As Figure 5 shown, the microphone mounting seat 6 is made of resin material through 3D printing. Its external dimensions are 30 mm (width) × 20 mm (height) × 30 mm (depth). There is a microphone mounting cavity 61 with a diameter of 12.7 mm inside. A rubber ring is provided at the center of the mounting cavity 61. The depth of the mounting cavity 61 is 20 mm. A sound - guiding hole 62 with a diameter of 2 mm and a depth of 10 mm is opened at the center of the bottom of the mounting cavity 61. The equal - cross - section inner tube 4 and the mounting seat 6 are connected by a stainless - steel tube, namely the equal - cross - section branch pipe 5, with a length of 20 mm, an outer diameter of 2 mm, and an inner diameter of 1.6 mm. The microphone adapter 7 is made of resin material through 3D printing. Its shape is a cylinder, with an outer diameter of 12.7 mm and an inner diameter of 6.35 mm.

[0128] Embodiment 3: As Figure 6 shown, the present invention also provides a calibration method for surface pulsating pressure acoustic measurement, which is calibrated using the above - mentioned surface pulsating pressure acoustic measurement calibration device.

[0129] Before the calibration starts, the signal generator 101, power amplifier 102, anechoic chamber 107, plane - wave generator 103 and data acquisition module are connected in sequence through a special cable. A 50 - ohm coaxial cable with a length of 4 m is used to connect the signal generator 101 and the power amplifier 102. The power amplifier 102 and the anechoic chamber 107 are connected through an audio cable. The input interface of the anechoic chamber 107 is connected to the full - frequency speaker 1 in the plane - wave generator 103. The monitoring microphone 4 is installed on the plane - wave generator 103 from the microphone interface of the plane - wave generator 103. The monitoring microphone 4 is connected to the output interface of the anechoic chamber 107, and the temperature - humidity - pressure sensor 106 is connected to the other three output interfaces of the anechoic chamber 107. There is another output interface on the anechoic chamber 107 connected to a reference microphone or a surface pulsating pressure sensor. Before calibrating the measurement system, it is also necessary to calibrate the sensitivities of the monitoring microphone 104, reference microphone 105 and surface pulsating pressure measurement microphone using a piston calibrator.

[0130] The calibration steps for the surface pulsating pressure acoustic measurement device include:

[0131] S1 Select a reference microphone and install the reference microphone on the object to be measured.

[0132] The object to be measured is provided with a prefabricated mounting hole, which can install the reference microphone 105 or the measurement microphone of the surface pulsating pressure acoustic measurement device to be calibrated. The prefabricated mounting hole not only provides a standardized interface for the installation of the reference microphone and the measurement microphone, but also can conveniently install the reference microphone or the measurement microphone on the object to be measured. When it is necessary to replace the microphone, the operation can be completed quickly and accurately, improving the work efficiency.

[0133] In this step, the reference microphone 105 is installed using the prefabricated mounting hole, and the top of the reference microphone 105 should be flush with the object surface. When the top of the microphone is flush with the object surface, the microphone can directly sense the acoustic environment on the object surface, and the measured sound pressure signal can more truly reflect the pulsating pressure situation on the object surface, thus providing a reliable basis for calibration.

[0134] In addition, a high-precision microphone should be selected as the reference microphone, such as the MA411A pre-polarized pressure field microphone. The reference microphone plays a benchmark role throughout the calibration process. It has known, relatively accurate and stable acoustic performance, and its measurement results are used as the reference standard for calibrating the measurement microphone. By comparing the measurement results of the measurement microphone with the reference microphone, the performance deviation of the measurement microphone can be determined, and then the measurement microphone can be calibrated to improve the accuracy and reliability of the entire measurement system.

[0135] S2 The plane wave generator 103 generates a plane wave, which is monitored by the monitoring microphone 104 and the reference microphone 105 to obtain sound pressure signals; the transfer function between the monitoring microphone 104 and the reference microphone 105, that is, transfer function I, is constructed using the sound pressure signal output by the monitoring microphone 104 and the sound pressure signal output by the reference microphone 105; specifically, the transfer function I is:

[0136] ;

[0137] where TF1 is the transfer parameter I, is the frequency-domain sound pressure signal of the monitoring microphone 104, is the frequency-domain sound pressure signal of the reference microphone 105.

[0138] Turn on the data acquisition module, power amplifier 102, and signal generator 101 in sequence; set the sampling rate of the data acquisition module to 51.2 kHz and the acquisition time to 10 s; the signal generator 101 outputs a white noise signal; obtain the sound pressure signals measured by the monitoring microphone 104 and the reference microphone 105 through the host computer. It should be noted that when collecting, the plane wave generator 103 needs to be placed directly above the reference microphone 105 so that the reference microphone 105 is within the range of the sound tube output port. At the same time, apply pressure to the full-frequency speaker to make the plane wave generator 103 closely adhere to and seal the object surface.

[0139] After receiving the signal transmitted by the signal generator 101 through the power amplifier 102, the plane wave generator 103 generates a plane wave. The monitoring microphone 104 listens to the plane wave through the microphone interface on the plane wave generator 101, and the reference microphone 105 listens to the plane wave through the output port of the plane wave generator 104. The two microphones simultaneously acquire the sound pressure signal of the plane wave and convert it into an electrical signal for output.

[0140] The data acquisition module acquires the sound pressure signals output by the monitoring microphone 104 and the reference microphone 105. However, this signal is a time-domain signal. Therefore, methods such as Fourier transform are usually used to convert the time-domain signal into a frequency-domain signal to obtain the frequency-domain sound pressure signal of the monitoring microphone and the frequency-domain sound pressure signal of the reference microphone. Calculate the transfer function I between the monitoring microphone 104 and the reference microphone 105 based on the frequency-domain sound pressure signal of the monitoring microphone and the frequency-domain sound pressure signal of the reference microphone. This transfer function reflects the conversion relationship of the sound pressure signals between the two at different frequencies.

[0141] S3 Install the measurement microphone of the surface pulsating pressure acoustic measurement device to be calibrated on the object to be measured.

[0142] After the transfer function I is constructed, replace the reference microphone 105 with the measurement microphone of the surface pulsating pressure acoustic measurement device to be calibrated. The installation method on the object to be measured is the same as that of the reference microphone 105, which will not be elaborated here.

[0143] S4 The plane wave generated by the plane wave generator 103 is listened to by the monitoring microphone 104 and the measurement microphone to obtain the sound pressure signal; construct the transfer function between the monitoring microphone 104 and the measurement microphone, that is, the transfer function II, using the sound pressure signal output by the monitoring microphone 104 and the sound pressure signal output by the measurement microphone; the transfer function II is:

[0144] ；

[0145] Among them, TF2 is the transfer parameter II, is the frequency-domain sound pressure signal of the monitoring microphone 104, To measure the frequency-domain sound pressure signal of the microphone.

[0146] Similar to step S2, the data acquisition module collects the sound pressure signals output by the monitoring microphone 104 and the measurement microphone, and uses methods such as Fourier transform to convert the time-domain signal into a frequency-domain signal, obtaining the frequency-domain sound pressure signal of the monitoring microphone 104 and the frequency-domain sound pressure signal of the measurement microphone. According to the frequency-domain sound pressure signals of the monitoring microphone 104 and the measurement microphone, the transfer function II between the monitoring microphone 104 and the reference microphone is calculated. This transfer function reflects the conversion relationship of the sound pressure signals between the two at different frequencies.

[0147] S5 Obtain the transfer function between the measurement microphone and the reference microphone 105, that is, transfer function III, using the transfer function I and transfer function II; the transfer function III is:

[0148] ;

[0149] where TF is the transfer parameter III, TF1 is the transfer parameter I, and TF2 is the transfer parameter II. is the frequency-domain sound pressure signal of the monitoring microphone 104. is the frequency-domain sound pressure signal of the reference microphone 105. is the frequency-domain sound pressure signal of the measurement microphone.

[0150] The transfer function I describes the transfer relationship of the sound pressure signal between the monitoring microphone 104 and the reference microphone 105, and the transfer function II describes the transfer relationship of the sound pressure signal between the monitoring microphone 104 and the measurement microphone. Since the monitoring microphone 104 exists in both transfer relationships, the transfer function III between the measurement microphone and the reference microphone 105 can be derived through mathematical operations using these two known transfer functions.

[0151] The transfer function III clarifies the transfer relationship between the measurement microphone and the reference microphone 105, and the performance of the reference microphone is known and accurate. Through the transfer function III, the measurement result of the measurement microphone can be compared with the reference microphone 105 to determine the performance deviation of the measurement microphone. According to this deviation, the measurement microphone can be calibrated to make its measurement result more accurate and reliable, improving the accuracy of the acoustic measurement of the surface pulsation pressure.

[0152] S6 Repeat steps S1 - S5 to obtain several transfer functions III, and use the several transfer functions III to construct a calibration transfer function. The calibration transfer function is:

[0153] ;

[0154] where TFCal To verify the transfer parameters, N is the number of transfer functions III, is the transfer function III with sequence i, where i is the sequence number of the transfer function.

[0155] In the actual measurement and calibration process, due to the influence of various factors (such as fluctuations in environmental noise, slight differences in equipment, random errors in the measurement process, etc.), the transfer function III obtained by a single measurement may have certain errors and uncertainties. By repeating steps S1 to S5, multiple transfer functions III can be obtained, and these transfer functions III reflect the transfer relationship between the measurement microphone and the reference microphone 105 under different measurement conditions. Using these multiple transfer functions III to construct a verification transfer function is based on the principle of statistics. By averaging multiple measurement results, the influence of random errors is reduced to obtain a verification transfer function that can more accurately reflect the true transfer relationship between the measurement microphone and the reference microphone 105.

[0156] By taking multiple measurements and constructing a calibration transfer function, the impact of random errors on the measurement results can be effectively reduced. Random errors show a certain degree of randomness in multiple measurements. Some measurement results may be too large, while others may be too small. By averaging, these errors can be offset, thus obtaining a more accurate transfer function. Using this calibration transfer function to calibrate the measurement microphone can improve the accuracy of the calibration and make the measurement results of the measurement microphone closer to the true value.

[0157] In addition, the transfer function III obtained from a single measurement may have abnormal values. When constructing the verification transfer function, the influence of abnormal values ​​on the final result can be reduced by averaging multiple transfer functions III. The verification transfer function obtained in this way can better reflect the true relationship between the measurement microphone and the reference microphone, and enhance the reliability of the entire calibration process.

[0158] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0159] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit of the present invention and the scope protected by the claims. All of these fall within the protection scope of the present invention.

Claims

1. A calibration device for acoustic measurement of surface pulsating pressure, characterized in that: It includes a signal generator for generating a noise signal and a plane wave generator disposed inside an anechoic chamber. The plane wave generator can convert the noise signal generated by the signal generator into a plane wave. A microphone interface for connecting a monitoring microphone is provided on the plane wave generator, so that the monitoring microphone can monitor the plane wave inside the plane wave generator. The plane wave generator further includes an output port for outputting the plane wave, and a reference microphone and a measurement microphone of the surface pulsation pressure acoustic measurement device to be calibrated can monitor the plane wave inside the plane wave generator through the output port. It also includes a data acquisition module for collecting data of the monitoring microphone, the reference microphone, and the measurement microphone. Among them, the plane wave generator includes a loudspeaker and a sound tube connected to the loudspeaker. The sound tube includes a funnel-shaped continuously variable cross-section inner tube. The large end of the continuously variable cross-section inner tube is connected to the sound-emitting end of the loudspeaker, and the small end is connected to an equal cross-section inner tube. The inner diameter of the equal cross-section inner tube is the same as the inner diameter of the opening at the small end of the continuously variable cross-section inner tube, and the loudspeaker, the continuously variable cross-section inner tube, and the equal cross-section inner tube are coaxially installed. It further includes an outer cylinder sleeved outside the continuously variable cross-section inner tube and the equal cross-section inner tube. The outer cylinder and the variable cross-section inner tube and the equal cross-section inner tube enclose a cavity. At least two Helmholtz resonators are arranged along the axial direction of the inner wall of the equal cross-section inner tube. An equal cross-section branch pipe is installed between the outer cylinder and the equal cross-section inner tube. One end of the equal cross-section branch pipe leads to the inside of the equal cross-section inner tube, and the other end extends to the outer cylinder. And a microphone interface for connecting to a microphone is installed at the end of the cross-section branch pipe extending to the outer cylinder. The Helmholtz resonator includes a cavity embedded in the inner wall of the equal cross-section inner tube. The opening of the cavity faces the inner side of the inner wall of the equal cross-section inner tube, and the opening width of the cavity is smaller than the width of the cavity.

2. The calibration device for surface pulsating pressure acoustic measurement according to claim 1, characterized in that: A plurality of input interfaces and output interfaces are provided on the anechoic chamber. The plane wave generator is connected to the input interface for receiving signals from the signal generator. The monitoring microphone, the reference microphone, and the measurement microphone are connected to the output interface, facilitating the data acquisition module to collect data of the monitoring microphone, the reference microphone, and the measurement microphone.

3. The calibration device for surface pulsating pressure acoustic measurement according to claim 1, characterized in that: It also includes a temperature, humidity, and pressure sensor disposed inside the anechoic chamber. The temperature, humidity, and pressure sensor can output an analog voltage signal.

4. A calibration device for surface pulsating pressure acoustic measurement according to claim 1, characterized in that: The anechoic chamber is of a flip type and includes a box body and a cover plate. Sealing rubber strips are provided at the edges where the box body and the cover plate are buckled together. Sound insulation materials are filled inside the box body, and vibration isolation pads are provided at the bottom outside the box body.

5. The calibration device for surface pulsating pressure acoustic measurement according to claim 1, characterized in that: A power amplifier is provided between the signal generator and the plane wave generator.

6. A calibration method for surface pulsating pressure acoustic measurement, which is calibrated by using the calibration device for surface pulsating pressure acoustic measurement according to any one of claims 1 to 5, characterized in that It includes: S1 Select a reference microphone and install the reference microphone on the object to be measured. S2 The plane wave generator generates a plane wave that is monitored by the monitoring microphone and the reference microphone to obtain a sound pressure signal. Construct a transfer function between the monitoring microphone and the reference microphone, namely transfer function I, using the sound pressure signal output by the monitoring microphone and the sound pressure signal output by the reference microphone. S3 Install the measurement microphone of the surface pulsation pressure acoustic measurement device to be calibrated on the object to be measured. The plane wave generated by the S4 plane wave generator is monitored by the monitored microphone and the measurement microphone, and the sound pressure signal is obtained; the transfer function between the monitored microphone and the measurement microphone, that is, the transfer function II, is constructed by using the sound pressure signal output by the monitored microphone and the sound pressure signal output by the measurement microphone. S5 Use the transfer function I and the transfer function II to obtain the transfer function between the measurement microphone and the reference microphone, that is, the transfer function III. S6 Repeat steps S1 to S5, obtain a number of transfer functions III, and construct a calibration transfer function by using the number of transfer functions III.

7. A calibration method for surface pulsating pressure acoustic measurement according to claim 6, characterized in that The transfer function I is: ； Among them, TF1 is the transfer parameter I, is the frequency-domain sound pressure signal of the monitoring microphone, is the frequency-domain sound pressure signal of the reference microphone.

8. A calibration method for surface pulsating pressure acoustic measurement according to claim 6, characterized in that The transfer function II is: ； wherein, TF2 is the transfer parameter II, is the frequency-domain sound pressure signal of the monitoring microphone, is the frequency-domain sound pressure signal of the measurement microphone.

9. A calibration method for surface pulsating pressure acoustic measurement according to claim 6, characterized in that The transfer function III is: ； Among them, TF is transfer parameter III, TF1 is transfer parameter I, and TF2 is transfer parameter II. is the frequency-domain sound pressure signal of the monitoring microphone, is the frequency-domain sound pressure signal of the reference microphone, is the frequency-domain sound pressure signal of the measurement microphone.

10. A calibration method for surface pulsating pressure acoustic measurement according to claim 6, characterized in that The calibration transfer function is: ； Among them, TF Cal is the verification transfer parameter, N is the number of transfer functions III, is the transfer function III with sequence number i, and i is the serial number of the transfer function.

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