Radiated noise calculation method for MEMS vector hydrophone

Abstract

The present invention provides a method for calculating the radiated noise of a MEMS vector hydrophone. In order to solve the problem that the traditional sound pressure array measurement system is too large, a single vector hydrophone is used to receive the broadband noise signal radiated by the sound source to be measured. By processing the sound pressure and vibration velocity, the active sound intensity can be calculated, and the signal-to-noise ratio can be improved by using the mutual cancellation of isotropic noise. The power spectrum of the received signal at different times is calculated, the center frequency is set, and a 1 / 3 octave bandpass filter is used to estimate the sound source level of the target. The present invention performs a series of quantitative analyses on the target radiated noise collected by the noise collection system, mainly including the calculation of parameters such as the line spectrum signal radiated by the target and the sound source level of the broadband signal. The single vector hydrophone measurement system is compact and flexible, and is easy to use in engineering practice. It not only has a considerable gain, but also can measure the radiated noise of underwater vehicles in the far field.

Description

Technical Field

[0001] The invention relates to an underwater acoustic signal processing technology, and in particular to a radiation noise calculation method for a MEMS vector hydrophone. Background Art

[0002] Traditional sound pressure array measurement technology is widely used in the field of underwater radiated noise measurement, but when measuring far-field targets, a larger array is often required to achieve the far-field signal-to-noise ratio required for the test. The single-vector hydrophone underwater noise source sound source level measurement system has the advantages of low cost, simple system, and convenient deployment and recovery. In addition, the single-vector hydrophone measurement system can simultaneously measure the sound pressure information and vibration velocity information at the receiving point. By processing the sound pressure and vibration velocity, the active sound intensity can be calculated, and the signal-to-noise ratio can be improved by using the mutual cancellation of isotropic noise. The single-vector hydrophone measurement system is easy to use in practical engineering. It not only has considerable gain, but also can measure the radiated noise of underwater vehicles in the far field. In order to accurately calculate the radiated noise, the selected noise signal is played back and analyzed with an FFT spectrum analyzer. According to the provisions and requirements of the national military standard, the line spectrum analysis adopts a linear average method and selects a suitable analysis frequency band and frequency resolution. The signal corresponding to the 1 / 3oct spectrum analysis is selected for line spectrum analysis to calculate the spectrum line frequency and its amplitude. Noise measurement and analysis software is designed using MATLAB to achieve efficient analysis of the time and frequency domain characteristics of radiated noise, as well as calculation of radiation target parameters such as sound pressure level and sound source level of line spectrum and broadband signals. Summary of the invention

[0003] Purpose of the invention: The present invention provides a method for calculating the radiated noise of a MEMS vector hydrophone, which has low requirements on the sound source depth and the number of array elements and has high sound source level measurement accuracy.

[0004] Technical solution: To solve the above technical problems, the present invention provides a method for calculating the radiation noise of a MEMS vector hydrophone, comprising the following steps:

[0005] Step 1, obtaining the radiation noise of the underwater target;

[0006] Step 2, calculating the power spectrum at different times according to the radiation noise signal obtained in step 1;

[0007] Step 3, intercepting the effective data segment of the radiation noise signal obtained in step 1;

[0008] Step 4, setting the center frequency of the 1 / 3 octave bandpass filter according to the sound source spectrum information obtained in step 2;

[0009] Step 5, transform the effective radiation noise signal intercepted in step 3 into the frequency domain, and filter it using the 1 / 3 octave bandpass filter set in step 4;

[0010] Step 6, performing an inverse frequency domain transform on the result of step 5 to calculate the effective value of the signal;

[0011] Step 7, using the result of step 6 to calculate the 1 / 3 octave band sound pressure level by compensating the sensitivity;

[0012] Step 8, calculate the 1 / 3 octave band sound source level.

[0013] Preferably, in step 1, a single composite MEMS vector hydrophone is used to receive the noise signal of the underwater target.

[0014] Preferably, the 1 / 3 octave sound pressure level L in step 7 is p (i) is the frequency band sound pressure level at a distance d from the equivalent center in the direction of the sound axis of the output of the i-th filter.

[0015] When used, in step 7, for the broadband noise signal, its broadband sound pressure level L p It can be calculated by converting the output of the broadband filter:

[0016]

[0017] Where L p (i) is the 1 / 3 octave band sound pressure level.

[0018] The 1 / 3 octave band sound source level L in step 8 p0 (i) is:

[0019] L p0 (i) = L p (i)+20log(d / d0)

[0020] Where L p (i) is the 1 / 3 octave band sound pressure level, d is the distance between the hydrophone and the equivalent center; d0 is the reference distance, which is 1 m.

[0021] Beneficial effects: The present invention uses a single vector hydrophone to receive the broadband noise signal radiated by the sound source to be measured, calculates the active sound intensity by processing the sound pressure and vibration velocity, and uses the isotropic noise to cancel each other out to improve the signal-to-noise ratio. The power spectrum of the received signal at different times is calculated, the center frequency is set, and a 1 / 3 octave bandpass filter is used to estimate the sound source level of the target. A series of quantitative analyses are performed on the target radiation noise, mainly including the calculation of parameters such as the line spectrum signal radiated by the target and the sound source level of the broadband signal. The measurement system is compact and flexible, and has considerable gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flow chart of the sound source level calculation method in the present invention;

[0023] Figure 2 is the 1 / 3 octave band sound source level calculated by the present invention;

[0024] Figure 3 It is a schematic diagram of the overall structure of the coaxial packaged attitude self-calibration MEMS vector hydrophone; DETAILED DESCRIPTION

[0025] Example:

[0026] The radiation noise calculation method for the coaxial packaged attitude self-calibration MEMS vector hydrophone of the present invention uses a single vector hydrophone to receive the broadband noise signal radiated by the measured sound source, and can calculate the active sound intensity by processing the sound pressure and vibration velocity, and improve the signal-to-noise ratio by using the mutual cancellation of isotropic noise. The power spectrum of the received signal at different times is calculated, the center frequency is set, and the sound source level of the target is estimated by using a 1 / 3 octave bandpass filter. The present invention performs a series of quantitative analyses on the target radiation noise collected by the noise collection system, mainly including the calculation of parameters such as the line spectrum signal radiated by the target and the sound source level of the broadband signal. The hydrophone used in the test adopts coaxial packaging technology, and the high-precision electronic compass and the MEMS vector hydrophone are integrated and packaged, and the X-axis direction of the MEMS vector hydrophone is coincident with the north direction, and the data obtained by the dynamic calibration test are used to compensate and correct the vector direction-finding error. The single vector hydrophone measurement system is small and flexible, and is easy to use in engineering practice. It not only has a considerable gain, but also can measure the radiation noise of underwater vehicles in the far field.

[0027] Taking the underwater sound source level calculation of a group of target noise sources to be measured as an example, the specific implementation process of the method described in the present invention is as follows:

[0028] Step 1, obtain the noise signal radiated by the underwater sound source: use a single MEMS vector hydrophone to receive the noise signal radiated by the underwater target sound source, the frequency band is 20Hz-2000Hz, the sampling frequency is 40kHz, the lake depth is 40 meters; the sound source depth is 15 meters, the receiving sensor depth is 15 meters, and the distance between the sound source and the receiving sensor is 15 meters. The line spectrum signal-to-noise ratio is 10dB. The observation data is 200s long. Step 2, calculate the power spectrum of the radiated noise signal at different times;

[0029] Step 3, intercepting the radiation noise signal data segment to be analyzed according to the acquisition time;

[0030] Step 4: Obtain the sound source spectrum information based on the power spectrum analysis result of the noise signal, with the upper and lower limits of the noise power spectrum frequency (20Hz-2000Hz) as the 1 / 3 octave center frequency;

[0031] Step 5, transform the intercepted radiation noise signal segment into the frequency domain, and filter it using a 1 / 3 octave bandpass filter with set parameters;

[0032] Step 6, perform inverse frequency domain transformation on the output result of the 1 / 3 octave bandpass filter to calculate the effective value of the signal;

[0033] Step 7, using the effective value of the noise signal and the sensitivity of the hydrophone to calculate the 1 / 3 octave band sound pressure level;

[0034] 1 / 3 octave sound pressure level L p (i) is the radiated noise signal measured in the far field converted to the frequency band sound pressure level at 1 meter from the equivalent sound center within the specified bandwidth. The converted reference sound pressure is 1 micropascal and the 1 / 3 octave sound pressure level L p (i) is the frequency band sound pressure level at the distance d from the equivalent center of the sound source to the hydrophone in the direction of the acoustic axis of the output of the ith filter of the 1 / 3 octave bandpass filter, in dB;

[0035] Its broadband sound pressure level L p It can be calculated from the output of the broadband filter: broadband sound pressure level L p for:

[0036]

[0037] Among them, L p (i) is the 1 / 3 octave band sound pressure level.

[0038] Calculate the 1 / 3 octave band sound source level, the 1 / 3 octave band sound source level L of the noise source p0 (i) is:

[0039] L p0 (i) = L p (i)+20log(d / d0)

[0040] Among them, L p (i) is the 1 / 3 octave band sound pressure level, d is the distance between the hydrophone and the equivalent center of the sound source, and d0 is the reference distance. Using an equal response broadband filter to measure, the broadband sound source level L p0 It can be calculated from the broadband sound pressure level:

[0041] L p0 =L p +20log(d / d0)

[0042] Among them, L p is the broadband sound pressure level at a distance d from the equivalent center in the direction of the acoustic axis, dB, d is the distance from the hydrophone to the acoustic equivalent center, m; d0 is the reference distance, d0 = 1m.

[0043] like Figure 1-2As shown, Figure 1 This is a flow chart of the broadband sound source level calculation program, which illustrates the application process of the method. Figure 2 It is the 1 / 3 octave sound source level calculated by the present invention according to the sound source signal. It can be seen that the average error between the 1 / 3 octave sound source level calculated by the method of the present invention and the 1 / 3 octave sound source level of the actual sound source signal is less than 2dB, which effectively reduces the volume of the measurement system while ensuring the measurement accuracy.

[0044] Coaxial packaged attitude self-calibration MEMS vector hydrophone Figure 3 As shown, it includes a support platform 2, a compass bearing compartment cap 3, a compass bearing compartment 4, a tube body 5, a cable interface 6, and a locking buckle 7. The MEMS vector hydroacoustic sensor is placed on the support platform 2 and the sensor is sealed and fixed with A and B glue in a 1:1 ratio; the piezoelectric ceramic tube is sleeved on the round tube of the support platform and fixed between the support platform and the compass bearing compartment cap with A and B glue in a 1:1 ratio; the compass is placed in the compass bearing compartment 4, and the wires of the MEMS vector hydroacoustic sensor, the piezoelectric ceramic tube, and the compass are led out from the lead holes of the compass bearing compartment 4, connected to the weak signal conditioning circuit in the cavity of the tube body 5, and then connected to the cable at the cable interface 6 through the through hole at the bottom of the tube body 5; the locking buckle 7 is used to ensure that the cable will not slip.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for calculating the radiation noise of a MEMS vector hydrophone, characterized in that The following steps are involved: Step 1, obtaining the radiation noise of the underwater target; Step 2, calculating the power spectrum at different times according to the radiation noise signal obtained in step 1; Step 3, intercepting the effective data segment of the radiation noise signal obtained in step 1; Step 4, setting the center frequency of the 1 / 3 octave bandpass filter according to the sound source spectrum information obtained in step 2; Step 5, transform the effective radiation noise signal intercepted in step 3 into the frequency domain, and filter it using the 1 / 3 octave bandpass filter set in step 4; Step 6, performing an inverse frequency domain transform on the result of step 5 to calculate the effective value of the signal; Step 7, using the result of step 6 to calculate the 1 / 3 octave band sound pressure level by compensating the sensitivity; Step 8, calculate the 1 / 3 octave band sound source level.

2. The method for calculating the radiation noise of the MEMS vector hydrophone according to claim 1, characterized in that: In the step 1, a single composite MEMS vector hydrophone is used to receive the noise signal of the underwater target.

3. The method for calculating the radiation noise of the MEMS vector hydrophone according to claim 1, characterized in that: The 1 / 3 octave band sound pressure level L in step 7 p (i) is the frequency band sound pressure level at a distance d from the equivalent center in the direction of the sound axis of the output of the i-th filter.

4. The method for calculating the radiation noise of the MEMS vector hydrophone according to claim 3, characterized in that: In step 7, for the broadband noise signal, its broadband sound pressure level L p It can be calculated from the output of the broadband filter: Where L p (i) is the 1 / 3 octave band sound pressure level.

5. The method for calculating the radiation noise of the MEMS vector hydrophone according to claim 1, characterized in that: The 1 / 3 octave band sound source level L in step 8 p0 (i) is: L p0 (i)=L p (i)+20log(d / d0) Where L p (i) is the 1 / 3 octave band sound pressure level, d is the distance between the hydrophone and the equivalent center, and d0 is the reference distance.

6. The method for calculating radiation noise of a MEMS vector hydrophone according to claim 5, characterized in that: The reference distance d0 in step 8 is 1m.

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