This standard specifies two methods for measuring the insertion loss and echo reduction of hydroacoustic material samples: the pulse tube method and the free field method. The measurement results can be used for the design basis and performance evaluation of sonar domes, sound-transmitting windows, reflective shield baffles and anechoic covering layers. This standard is applicable to uniform and layered uniform hydroacoustic material samples. GB/T 14369-1993 Acoustics Method for measuring insertion loss and echo reduction of hydroacoustic material samples GB/T14369-1993 Standard download decompression password: www.bzxz.net
This standard specifies two methods for measuring insertion loss and echo reduction of hydroacoustic material samples: the pulse tube method and the free field method. The measurement results can be used for the design basis and performance evaluation of sonar domes, sound-transmitting windows, reflective shield baffles and anechoic covering layers. This standard is applicable to uniform and layered uniform hydroacoustic material samples.

National Standard of the People's Republic of China
Acoustics--Measurement method of Insertion lossand echo reduction for the underwateracouatical material sumple
1 Subject content and scope of application
GB/T 14369-93
This standard specifies two measurement methods for insertion loss and echo reduction of underwateracouatical material samples: pulse tube method and free field method. The measurement results can be used for the design basis and performance evaluation of sonar domes, sound-transmitting windows, reflective dome baffles and anechoic covering layers. This standard is applicable to uniform and stratified underwater acoustic material samples. 2 Cited standards
GB 3947
Terms of acoustics
GB5266 Measurement of longitudinal wave velocity and attenuation of hydroacoustic materials-Pulse tube method GB3223 Free-field calibration method of hydroacoustic transducer 3 Terminology
3.1 Insertion loss
In the plane wave acoustic field, a hydroacoustic material sample is inserted vertically in the direction of propagation. The logarithm of the ratio of the sound power at the rear of the sample to that at the front of the hydroacoustic material sample multiplied by 10, unit, dB (decibel). Its relationship with the sound pressure transmission factor is
I = 201g(1/r,)
3.2 Echo reduction E, echo reduction (1)
In the plane wave sound field, the hydroacoustic material sample is inserted vertically in the direction of sound propagation, and the logarithm to the base 10 of the ratio of the sound power of the incident wave and the reflected wave caused is multiplied by 10, unit, dB (decibel). It is related to the sound pressure reflection factor r, by
E, = 20lg(1/r)
4 Water-filled tube method
4.1 Measuring device
The measuring device of the sample in the sound tube is shown in Figure 1. The requirements for the water-filled sound tube, transducer and measuring instrument shall comply with the provisions of Chapter 3 of (B5266 China National Technical Supervision Bureau 1993-03-17 approved 1993-12-01 implementation
:com).
4.2 Measuring conditions
See GB 5266 Sections 1.2 and 1.3.
4.3 Sample requirements
CB/T 14369-93
4.3.1 The sample should be made into a round plate shape with a flat surface and uniform thickness. There should be a gap between the sound tube and the width should be less than 0.3mm. 4.3.2 The surface of the sample should be wiped clean and soaked in water (at least for days) to make the surface fully wetted. During the test, there should be no bubbles on the surface of the sample to ensure the reliability of the test. 4.4 Measurement method
4.4.1 Measurement signal
Sensor
Valve indicator
Figure 1 Sound tube measurement device
Measurement is carried out using a pulse modulated sinusoidal signal. 4.4.2 Frequency limit
The test frequency of this method should meet the following requirements: faf(u+ar*)/x
- the distance between the transmitter and the hydrophone, m! Where: d-
the maximum geometrical dimension of the transmitter and the hydrophone, m; 41+4
man- the wavelength in water corresponding to the highest test frequency, m. 5.2.2 According to the requirements of the steady-state conditions of the pulse measurement technology, the acoustic pulse should include at least two steady-state wave frequencies. (9)
5.2.3. If the acoustic properties of the material are related to environmental conditions such as temperature and static pressure, the test environmental conditions should be indicated in the measurement results. 5.3 Sample requirementsWww.bzxZ.net
5.3.1 In order to reduce the influence of the radiation, the sample should be in the shape of a rectangular flat plate with a flat surface and uniform thickness, and the length of each side should be greater than 5 times the wavelength in water of the test frequency.
5.3.2 The surface of the sample should be wiped clean. Soak it in water to make its surface fully wetted and the temperature reach equilibrium before measurement. 5.4 Measurement method
5.4.1 Test signal, impulse modulated sinusoidal signal is used for measurement. 5.4.2 Measurement
5.4.2.1 Measurement of insertion loss
The transducer and sample are arranged according to Figure 3. The hydrophone and sample should be placed in the far field of the transmitter. In order to minimize the influence of diffracted waves, the distance d between the hydrophone and the sample should be close, but not less than A/4. The measurement device is shown in Figure 2.
GB/T 14369-93
Transmitter
Figure 3 Insertion loss measurement layout diagram
Measure the attenuator readings % and corresponding to the amplitudes of the transmitted pulse and the direct pulse when the sample is placed. The attenuation is measured by comparing the electric pulse E after the standard resistor voltage division, after attenuation by the standard attenuator αd, with the pulse voltage shown by the hydrophone and making them equal (α=2Q lg). E
Thus, the insertion loss is:
I, = αe — αa
5.4.2.2 Measurement of echo reduction
The transducer and the sample are arranged as shown in Figure 4. The hydrophone and the sample should be placed in the far field of the transmitter. The distance between the hydrophone and the sample should be as small as possible, and the waveforms of the reflected pulse and the direct pulse should be separated. The measurement device is shown in Figure 2.
Hydrophone
Figure 4 Schematic diagram of echo reduction measurement
Measure the attenuator readings a, and corresponding to the amplitudes of the reflected pulse and the direct pulse, and the distances 4, and d. Then the echo reduction E, is;
E. = α, — ad — 20 lgl
Note: In the measurement of, and, the placement of the sample is required to be asymmetric with respect to the transducer to minimize the influence of the diffracted wave. 5.5 Measurement uncertainty
The system uncertainty (determined by the accuracy of the test equipment such as the attenuator and standard resistor, the influence of the test environment, and the degree of satisfaction of the required conditions during the test) is 1d3.
The random uncertainty (caused by the accidental factors of the amplitude measurement) is 0.6dB, then 1 and E, the total uncertainty of the measurement will be less than 1.2 dB.
GE/T 14369--93
Appendix A
Measurement of insertion loss and echo reduction under oblique incidence (reference part)
In many underwater acoustic engineering works, it is necessary to measure the response of the mother material sample with the change of the incident angle A1 insertion loss
The transducer and the sample are arranged as shown in Figure 3, and the measurement device is shown in Figure 2. During the measurement, the sample between the transmitter and the hydrophone is rotated in its original position, and the attenuator reading corresponding to the amplitude of the transmitted pulse is measured at different incident angles. The sample is taken out, and the attenuator reading aa corresponding to the direct pulse is measured, and the response of the insertion loss with the change of the incident angle can be obtained.
When the incident angle gradually increases, the effective sensitivity of the sample will gradually decrease, so the measurement error will increase, so it is best to use a directional transmitting transducer, and the more directional, the better.
A2 Echo reduction
Arrange the transducer and sample according to Figure A. The measurement equipment is shown in Figure 2 and the water break plate
transmitter is according to
Figure A1 Schematic diagram of echo reduction measurement layout
Figure A1:—
-Incident angle:
Where: 00
The direct wave sound path between the transmitter and the water device, m; The sound path emitted to the sample plate and then reaching the hydrophone through reflection, I1. d - AB - VAO + BO + 2 A.BO - cS28d = AO + O
AO -rDse
BO· cosg
00 + 0
（A3)
GB/T 14369—93
The measurement method is to calculate the values ​​of AO1 and O according to the required incident angle, move the transmitting transducer and hydrophone to point A and point B, and measure the attenuator readings a, and E corresponding to the amplitudes of the reflected pulse and the direct pulse: = a - a - 20 e
+++**+.( A4 )
If you want to measure the response of the reflection factor changing with the incident angle, you can make scales on the hanging rod according to the calculated values ​​in advance, and pre-calibrate the positions of the transmitter and hydrophone. During the measurement process, corresponding to different incident angles, you only need to keep moving the corresponding hanging points of the hanging transmitter and hydrophone. When measuring with the pulse method, in order to separate the reflected pulse and the direct pulse waveform, the distance C01 and 0) from the hanging rod to the plate to be measured should meet r<(一d,)/, and should also meet the free field far field conditions. The characteristic of this measurement method is that under various incident angles, the reflection point 0 is always located at the same position of the plate to be measured, and it is also relatively simple and convenient.
Note, (I; and E, the measurement of oblique radiation response is carried out in free field using the pulse method, and its requirements are given in the text. ② It is best to use a finger transmitter when measuring.
Additional remarks:
This standard is reviewed and approved by the National Technical Committee for Acoustics Standardization. This standard is proposed by the Ultrasonic and Underwater Acoustics Technical Committee. This standard is compiled by the Institute of Acoustics of the Chinese Academy of Sciences, the 715th Institute and the 721st Factory of China State Shipbuilding Corporation, and other units. The main drafters of this standard are Wang Rongjin and Miao Rongxing.
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