Some standard content:
National Standard of the People's Republic of China
Acoustics-Callbration of high frequency hydrophone
Acoustics-Callbration of high frequency hydrophoneGB/T 15611—1995
This standard refers to IEC866:1987 "Characteristics and calibration methods of hydrophones working in the frequency range of 0.5~15MHz". 1 Content and scope of application
This standard specifies the method of calibrating piezoelectric high frequency hydrophones using the transducer reciprocity method. The applicable frequency range of this standard is 0.5~10MHz. The calibration of high frequency hydrophones in the frequency range of 0.1～0.5MHz uses GB/T 3223.
2 Calibration
2.1 Calibration principle
First, use the self-reciprocity method to calibrate the apparent transmission current response of the auxiliary transducer, and then calibrate the free field sensitivity of the hydrophone in the known sound field generated by the auxiliary transducer.
2.1.1 Calibrate the sending current response of the auxiliary transducer by the self-commutation method. Use a planar reciprocal transducer as an auxiliary transducer and calibrate it by the self-commutation method (see Appendix A). Figure 1 shows an experimental setup for high-frequency hydrophone calibration. Under ideal free-field plane wave conditions, its apparent sending current response is si =
, 1/2
Jp= 24
Where: P, — the voltage emitted by the auxiliary transducer 1 in the form of a plane wave, Pa; I1\ — the excitation current of the auxiliary transducer, AU. — the voltage of the first echo signal received by the auxiliary transducer from the self-reflector R, V:_ plane wave reciprocity constant, /Pa\,
Af — the effective auxiliary radiation area of the auxiliary transducer, m2; p — the density of water, kg/m
C — the speed of sound propagation in water, m/s.
2.1-2 Measure the free field sensitivity of the hydrophone by substitution method (1)||tt| |Remove the reflector R, place the hydrophone calibrated in the known sound field generated by the auxiliary transducer 1, and its open-circuit output voltage is U. Then, assuming the ideal free-field plane wave condition, the apparent free-field sensitivity M of the hydrophone is M*=
2.1.3 Correction for non-rigid conditions
Considering that the actual measured sound field is a non-ideal free-field plane wave, due to the diffraction of the transducer and the propagation attenuation of the sound wave in water, the influence of the sound pressure reflection factor of the reflector, etc., only after the calibration result is corrected (see Appendix C), the free-field sensitivity M of the hydrophone is
where: -
Correction factor
2.2 Measurement conditions
2.2. 1 Overall measurement arrangement
Figures 1 and 2 show two experimental setups for hydrophone calibration. First, the auxiliary transducer 1 emits a burst of sound of 10 to 20 cycles, and the sound pulse is reflected by the stainless steel reflector in the water tank. In the self-calibration of the auxiliary transducer, the position of the transducer is adjusted so that the acoustic axis of the transmitter is perpendicular to the reflector surface. In the second step of hydrophone calibration, the reflector is removed, the position and direction of the hydrophone are adjusted so that the main axis of the transmitter is aligned with the most sensitive direction of the hydrophone,
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releases the value generator
the frequency signal is displayed in a slow "increment"
||Release supply
Sofa amplifier
2.2.2 Measuring instruments
4 Distribution network
Filter
Preamplifier
Auxiliary transducer
Experimental device for calibration of two transducers by reciprocity method 1 Distribution network
Open A
Switch A
Terminal
Current control
Figure 2 Experimental device for calibration of two transducers by reciprocity method I Reflection
Demonstration
Hydrophone
: Burst sound generator
Working frequency
0. 5-~10 MHz
Pulse repetition frequency 50 Hz~1.3kHz
Pulse width
b.Frequency meter
1 μs20 ps
Frequency range>20MHz
Accuracy better than +10-8
Stability better than ±10-5
cMatching network (adjustable inductance)
1~1 000 μH
Preamplifier and filter
CB/T 15611—1995
Continuously adjustable
Continuously adjustable
For hydrophone impedance conversion and signal amplification, digital memory should be calibrated in advance. Oscilloscope
Frequency response range>20 MHz
Input impedance 1Mn/30pF
A/D conversion ≥8 hit
f, current transformer
accuracy better than +1%
standard non-inductive resistor R
accuracy better than ±1%
precision attenuator
range α～60 dB
accuracy better than main.1 dB
2.2.3 Auxiliary transducer
The auxiliary transducer should be a circular plane piston transducer with a diameter greater than 10 times the wavelength in water, and the ratio of its diameter to the diameter of the hydrophone should be greater than 5. The effective radius a of the auxiliary transducer is the radius of the equivalent piston sound source. The spatial distribution of the sound pressure amplitude in the far field is very close to the sound field generated by the active sound source with a radius of α. The value of the effective radius 4; should not be greater than 10.2% to 15% of the radius of the sensitive element (see Appendix B for the method of determining the effective radius).
The auxiliary transducers should be reciprocal. This can be checked as follows: Check the transducers in pairs, one for transmitting and the other for receiving. Slightly change the position of one transducer, interchange the functions of transmitting and receiving, and compare the transfer impedance. The difference between the values should not be greater than 10%. If it is greater than 10%, at least one of the transducers is unqualified. Testing with a third transducer can reveal which one is unsuitable. If the two transducers are of the same structure, they may be linear or nonlinear to the same extent. Therefore, several types of transducers should be used for inspection. 2. 2. 4 Reflection Group
The reflector should be composed of a stainless steel disk. The disk should have a diameter large enough to reflect all the sound waves from the auxiliary transducer. The thickness of the reflector should be such that the first reflection from the rear surface will not interfere with the burst sound directly reflected from the front surface at the lowest frequency. The flatness of the reflector should be better than ±10 μm and the surface finish should be better than ±5 μm. 2.2.5 Sound path
During the calibration process, it is recommended that the total length of the sound path (2d for the self-commutation method, d + d for the reciprocal method of two transducers, usually d - d, see Figure 1) should be between 1.5 and 3 times the near-field distance. 2.2.6 Test water tank
The water model should be sufficiently filled to ensure that the distance between the auxiliary transducer and the hydrophone is at least 1.5 times the near-field distance of the auxiliary transducer. The four walls and the water surface of the water tank should be sufficiently far away from the transducer and the hydrophone to ensure that the wall reflection signal is separated from the direct sound. Moreover, if possible, these surfaces should be covered with sound absorbing materials. The water tank is filled with fresh distilled water or degassed water, preferably replaced every 181 or the air pool in the water is removed by reducing the pressure to GB/T 15611-1995
2000Pa or heating to 80℃ for 1h. 2.2.7 Adjustment
The transducer, hydrophone and reflector should be mounted on a stable and rigid support and can be properly adjusted. In order to ensure the accuracy of the measurement, the directional adjustment accuracy of the sound center is required to be better than ±0.05°, and the adjustment accuracy of the transducer position is required to be better than ±0.1mm. 2.3 Calibration Procedure
For the calibration device of Figure 1, the high-frequency calibration of the hydrophone is performed using the digital storage oscilloscope method, as shown in Figure 1. Adjust the reflector: make its surface perpendicular to the incident sound wave and satisfy 1.5<(2dA/a)<3. Measure the I, and U, values.
b. Remove the reflector and adjust the hydrophone to be tested so that the axis of the incident sound wave passes through the sound center of the hydrophone to be tested and d is equal to d, and the U value is measured.
2,b Step can be performed by observing the oscilloscope, adjusting the reflector or hydrophone, or adjusting the auxiliary transducer to maximize the received signal voltage. After measuring the I, U, and U values, the apparent free-field sensitivity of the hydrophone can be obtained according to formula (2). For the calibration device of Figure 2, the high-frequency calibration of the hydrophone is performed using the precision attenuator method. The calibration procedure is as follows: a. Adjust the distance 4 between the auxiliary transducer T and the reflector R to satisfy 1, 5 < 2da/a3; b. Link switch A to the 1est position, switch B to U,Position, switch C is placed in position u, adjust the position of T to maximize the first echo from the reflector, and by changing the position of linkage switch A, the reference voltages U and U at both ends of R are alternately displayed on the oscilloscope, and the attenuation of the precision attenuator is adjusted to make the two equal. From the attenuator reading, the ratio is obtained. = U,/0. - 10-0.054
C. Switch C is in the position of I, and by changing the linkage switch A, the signals of I, and the current Irar=er/R flowing through R are alternately displayed on the oscilloscope. Adjust the attenuation base of the precision attenuator to make them equal. From the attenuator reading α2, we can get the ratio αn = I,/Imf = 10-6. 5k,
d. Remove the reflector and adjust the distance between the auxiliary transducer T and the hydrophone H to (d,+d)=2d to satisfy 1.5(d,+d)A/ai3:
e. Set the linkage switch to 1 test position, switch H to U position, switch C to U position, repeatedly adjust the lateral position and orientation of T and H to make them in an acoustic coaxial state. At this time, the output U of the hydrophone reaches the maximum value. Change the position of the linkage switch A so that the U signal and the signal are displayed alternately on the oscilloscope. Adjust the precision attenuator to make the two equal. From the attenuator reading α, we can get the ratio ay - U/Urer - 10-ho,
The apparent self-sensitivity of the hydrophone is
[ Rrande/2
an! am
2.4 Calculation of results
When calculating the calibration results, it is necessary to correct the apparent voltage sensitivity. The correction factor is, then the white field voltage sensitivity of the hydrophone
M = M\k
is charged to:
h = (RuiG(rp)1/2
-（4)
Where: When the auxiliary transducer is used as a receiving transducer, if the electrical load conditions (such as the output impedance of the sound signal generator) do not change during the transmission and reception process, and the transmitting circuit is not disconnected during the reception process, the signal voltage multiplied by this factor is equivalent to the open circuit voltage. The value can be obtained by measuring the current I passing through the circuit when the transducer is replaced by a short-circuit ring;
CB/T 15611—1995
The voltage generated by the hydrophone must be multiplied by this factor to obtain the equivalent open-circuit voltage. Generally speaking, the input impedance of the preamplifier is much larger than the impedance of the output relay of the hydrophone, so there is no need to correct the open-circuit voltage: the correction made in the self-calibration of the auxiliary transducer to take into account the change of the sound wave from transmission to reception; G-correction made to take into account the corresponding change when the hydrophone is calibrated in the known sound field of the auxiliary transducer. Sound pressure reflection factor, for stainless steel and water, rp-0.937; r
-attenuation coefficient of ultrasonic wave in pure and degassed water, a = 2. 2×10-\f\Hz-\m-1, f=23℃. The calculation of the correction factor k is shown in Appendix I)
This standard recommends that when the ratio of the diameter of the auxiliary transducer to the diameter of the hydrophone is greater than 5. a.
The total sound path during calibration is 1.5 to 3.0 times the near-field distance of the auxiliary transducer, that is, b,
The correction factor is:
where Gr: is a function of the normalized distance S, as shown in Figure 3. 1.u
Gc value as a function of the normalized distance S
Figure 3Gc value as a function of the normalized distance Figure 2.5 Uncertainty of calibration
Normalized distance
The recommended calibration procedure and simplified correction factor provide a method for calibrating the free-field voltage sensitivity of the hydrophone in the U.5 to 10 MHz frequency band. The total system uncertainty of this method is less than -1. 5 dB, and the statistical uncertainty of the measurement is less than 1. 5 dB. GB/T 15611
Appendix A
Plane wave reciprocity calibration
(Supplement)
A reciprocal transducer is a transducer type that satisfies the following electromechanical reciprocity conditions: V—the uniform vibration velocity of the radiating surface of the transducer when transmitting; {--the input current of the transducer when transmitting: U--the open circuit voltage generated by the force F acting on the acoustically rigid transducer when receiving. The definition of the current response sent by the transmitting transducer and the white field sensitivity of the receiving transducer: S=
Where: Pu-
the sound pressure adjacent to the surface of the transmitting transducer when the transmitting transducer input current is 1 without interference; -(Al)
the undisturbed plane wave sound field sound pressure at the acoustic center of the original receiving transducer if the receiving transducer is removed. Under the action of this sound pressure, the transducer generates an output open circuit voltage. For plane waves, the relationship between the sound pressure and the surface vibration velocity V in front of the transmitting transducer is: P. = pCV
Where: 0—density of water
——speed of sound propagation in water.
（A3）
Assuming that the sound wave propagates without loss and diffraction between the transmitting and receiving transducers, the infinite plane wave propagates in a non-lossy medium like:
Pu= Pr p
The force acting on the surface area A of the receiving transducer is: F—2AF
Therefore, under the assumed flat wave conditions, the ratio MUI-24
（A4）
...(A5)
is only determined by the area A of the transducer, and this ratio is defined as the plane wave constant r. J is known, and P can be directly determined by measuring U and, thus, M and S can also be determined accordingly.
Note: If the real transducer input current and receiving pressure of a burst sound (pulse reflected by the reflector) are transmitted and received, M_UL
M, S, are the apparent values of the free field sensitivity and the transducer sending current response assuming ideal plane wave test conditions, so from (A2) and (A7) it can be obtained
GB/T 15611-1995
In any actual test within the frequency range specified in this standard, true plane wave conditions cannot be achieved, so the difference between P, and the average sound pressure P. on the surface of the sensitive element of the receiving transducer must be corrected. Appendix B
Calculation of the effective radius of the auxiliary transducer
(Supplement)
The effective radius α of the auxiliary transducer can be determined by the curve of the change of the sound pressure vibration along the acoustic axis with the distance. This sound field distribution can be obtained by using a hydrophone to measure the sound field generated by the auxiliary transducer. Here, the diameter of the hydrophone sensitive element should be equal to or less than one tenth of the diameter of the auxiliary transducer sensitive element, and the sound emission should be long enough to achieve the state test condition. Comparing the experimentally determined sound field distribution with the expected sound field distribution of the ideal live sound source, by adjusting the radius α of the ideal piston sound source, the ideal sound field distribution can be made to best match the experimental data. The theoretical distribution of the sound field of the piston sound source is as follows: [(21 +)2 -2e*
P/P = 2sin -
Where: P\-the sound pressure amplitude at a distance Z from the transducer surface along the sound axis, Pa; P-plane wave sound pressure amplitude P.=pC·V,Pa; a——sound source radius, m;
z—axial distance: m
-amplitude attenuation coefficient
, a method to obtain this kiss (used by British NPL. months ago) is as follows: If Y,(Z.)=20 lo81nV.,V, the signal voltage amplitude Y,(Z,) generated by the water dew is defined as follows:
20log2sin [(+)18-Z,e2
Let x,-Y(z.)-y(z.)
parameters?
x minimizes with respect to α.
This degree of fit is only used for 1.5Z.Repeatedly adjust the lateral position and orientation of T and H to make them in acoustic coaxial state. At this time, the output U of the hydrophone reaches the maximum value. Change the position of the linkage switch A to make the U signal and the signal alternately displayed on the oscilloscope. Adjust the precision attenuator to make the two equal. The ratio ay - U/Urer - 10-ho can be obtained from the attenuator reading α. The apparent voltage sensitivity of the hydrophone is
[ Rrande/2
an! am
2.4 Result calculation
When calculating the calibration result, the apparent voltage sensitivity needs to be corrected. The correction factor is, then the white field voltage sensitivity of the hydrophone
M = M\k
is:
h = (RuiG(rp)1/2
-（4)
Where: When the auxiliary transducer is used as a receiving transducer, if the electrical load conditions (such as the output impedance of the sound signal generator) do not change during the transmission and reception process, and the transmitting circuit is not disconnected during the reception process, the signal voltage multiplied by this factor is equivalent to the open circuit voltage. The value can be obtained by measuring the current I passing through the circuit when the transducer is replaced by a short-circuit ring;
CB/T 15611—1995
The voltage generated by the hydrophone must be multiplied by this factor to obtain the equivalent open-circuit voltage. Generally speaking, the input impedance of the preamplifier is much larger than the impedance of the output relay of the hydrophone, so there is no need to correct the open-circuit voltage: the correction made in the self-calibration of the auxiliary transducer to take into account the change of the sound wave from transmission to reception; G-correction made to take into account the corresponding change when the hydrophone is calibrated in the known sound field of the auxiliary transducer. Sound pressure reflection factor, for stainless steel and water, rp-0.937; r
-attenuation coefficient of ultrasonic wave in pure and degassed water, a = 2. 2×10-\f\Hz-\m-1, f=23℃. The calculation of the correction factor k is shown in Appendix I)
This standard recommends that when the ratio of the diameter of the auxiliary transducer to the diameter of the hydrophone is greater than 5. a.
The total sound path during calibration is 1.5 to 3.0 times the near-field distance of the auxiliary transducer, that is, b,
The correction factor is:
where Gr: is a function of the normalized distance S, as shown in Figure 3. 1.u
Gc value as a function of the normalized distance S
Figure 3Gc value as a function of the normalized distance Figure 2.5 Uncertainty of calibration
Normalized distance
The recommended calibration procedure and simplified correction factor provide a method for calibrating the free-field voltage sensitivity of the hydrophone in the U.5 to 10 MHz frequency band. The total system uncertainty of this method is less than -1. 5 dB, and the statistical uncertainty of the measurement is less than 1. 5 dB. GB/T 15611
Appendix A
Plane wave reciprocity calibration
(Supplement)
A reciprocal transducer is a transducer type that satisfies the following electromechanical reciprocity conditions: V—the uniform vibration velocity of the radiating surface of the transducer when transmitting; {--the input current of the transducer when transmitting: U--the open circuit voltage generated by the force F acting on the acoustically rigid transducer when receiving. The definition of the current response sent by the transmitting transducer and the white field sensitivity of the receiving transducer: S=
Where: Pu-
the sound pressure adjacent to the surface of the transmitting transducer when the transmitting transducer input current is 1 without interference; -(Al)
the undisturbed plane wave sound field sound pressure at the acoustic center of the original receiving transducer if the receiving transducer is removed. Under the action of this sound pressure, the transducer generates an output open circuit voltage. For plane waves, the relationship between the sound pressure and the surface vibration velocity V in front of the transmitting transducer is: P. = pCV
Where: 0—density of water
——speed of sound propagation in water.
（A3）
Assuming that the sound wave propagates without loss and diffraction between the transmitting and receiving transducers, the infinite plane wave propagates in a non-lossy medium like:
Pu= Pr p
The force acting on the surface area A of the receiving transducer is: F—2AF
Therefore, under the assumed flat wave conditions, the ratio MUI-24
（A4）
...(A5)
is only determined by the area A of the transducer, and this ratio is defined as the plane wave constant r. J is known, and P can be directly determined by measuring U and, thus, M and S can also be determined accordingly.
Note: If the real transducer input current and receiving pressure of a burst sound (pulse reflected by the reflector) are transmitted and received, M_UL
M, S, are the apparent values of the free field sensitivity and the transducer sending current response assuming ideal plane wave test conditions, so from (A2) and (A7) it can be obtained
GB/T 15611-1995
In any actual test within the frequency range specified in this standard, true plane wave conditions cannot be achieved, so the difference between P, and the average sound pressure P. on the surface of the sensitive element of the receiving transducer must be corrected. Appendix B
Calculation of the effective radius of the auxiliary transducer
(Supplement)
The effective radius α of the auxiliary transducer can be determined by the curve of the change of the sound pressure vibration along the acoustic axis with the distance. This sound field distribution can be obtained by using a hydrophone to measure the sound field generated by the auxiliary transducer. Here, the diameter of the hydrophone sensitive element should be equal to or less than one tenth of the diameter of the auxiliary transducer sensitive element, and the sound emission should be long enough to achieve the state test condition. Comparing the experimentally determined sound field distribution with the expected sound field distribution of the ideal live sound source, by adjusting the radius α of the ideal piston sound source, the ideal sound field distribution can be made to best match the experimental data. The theoretical distribution of the sound field of the piston sound source is as follows: [(21 +)2 -2e*
P/P = 2sin -
Where: P\-the sound pressure amplitude at a distance Z from the transducer surface along the sound axis, Pa; P-plane wave sound pressure amplitude P.=pC·V,Pa; a——sound source radius, m;
z—axial distance: m
-amplitude attenuation coefficient
, a method to obtain this kiss (used by British NPL. months ago) is as follows: If Y,(Z.)=20 lo81nV.,V, the signal voltage amplitude Y,(Z,) generated by the water dew is defined as follows:
20log2sin [(+)18-Z,e2
Let x,-Y(z.)-y(z.)
parameters?
x minimizes with respect to α.
This degree of fit is only used for 1.5Z.Repeatedly adjust the lateral position and orientation of T and H to make them in acoustic coaxial state. At this time, the output U of the hydrophone reaches the maximum value. Change the position of the linkage switch A to make the U signal and the signal alternately displayed on the oscilloscope. Adjust the precision attenuator to make the two equal. The ratio ay - U/Urer - 10-ho can be obtained from the attenuator reading α. The apparent voltage sensitivity of the hydrophone is
[ Rrande/2
an! am
2.4 Result calculation
When calculating the calibration result, the apparent voltage sensitivity needs to be corrected. The correction factor is, then the white field voltage sensitivity of the hydrophone
M = M\k
is:
h = (RuiG(rp)1/2
-（4)
Where: When the auxiliary transducer is used as a receiving transducer, if the electrical load conditions (such as the output impedance of the sound signal generator) do not change during the transmission and reception process, and the transmitting circuit is not disconnected during the reception process, the signal voltage multiplied by this factor is equivalent to the open circuit voltage. The value can be obtained by measuring the current I passing through the circuit when the transducer is replaced by a short-circuit ring;
CB/T 15611—1995
The voltage generated by the hydrophone must be multiplied by this factor to obtain the equivalent open-circuit voltage. Generally speaking, the input impedance of the preamplifier is much larger than the impedance of the output relay of the hydrophone, so there is no need to correct the open-circuit voltage: the correction made in the self-calibration of the auxiliary transducer to take into account the change of the sound wave from transmission to reception; G-correction made to take into account the corresponding change when the hydrophone is calibrated in the known sound field of the auxiliary transducer. Sound pressure reflection factor, for stainless steel and water, rp-0.937; r
-attenuation coefficient of ultrasonic wave in pure and degassed water, a = 2. 2×10-\f\Hz-\m-1, f=23℃. The calculation of the correction factor k is shown in Appendix I)
This standard recommends that when the ratio of the diameter of the auxiliary transducer to the diameter of the hydrophone is greater than 5. a.
The total sound path during calibration is 1.5 to 3.0 times the near-field distance of the auxiliary transducer, that is, b,
The correction factor is:
where Gr: is a function of the normalized distance S, as shown in Figure 3. 1.u
Gc value as a function of the normalized distance S
Figure 3Gc value as a function of the normalized distance Figure 2.5 Uncertainty of calibration
Normalized distance
The recommended calibration procedure and simplified correction factor provide a method for calibrating the free-field voltage sensitivity of the hydrophone in the U.5 to 10 MHz frequency band. The total system uncertainty of this method is less than -1. 5 dB, and the statistical uncertainty of the measurement is less than 1. 5 dB. GB/T 15611
Appendix A
Plane wave reciprocity calibration
(Supplement)
A reciprocal transducer is a transducer type that satisfies the following electromechanical reciprocity conditions: V—the uniform vibration velocity of the radiating surface of the transducer when transmitting; {--the input current of the transducer when transmitting: U--the open circuit voltage generated by the force F acting on the acoustically rigid transducer when receiving. The definition of the current response sent by the transmitting transducer and the white field sensitivity of the receiving transducer: S=
Where: Pu-
the sound pressure adjacent to the surface of the transmitting transducer when the transmitting transducer input current is 1 without interference; -(Al)
the undisturbed plane wave sound field sound pressure at the acoustic center of the original receiving transducer if the receiving transducer is removed. Under the action of this sound pressure, the transducer generates an output open circuit voltage. For plane waves, the relationship between the sound pressure and the surface vibration velocity V in front of the transmitting transducer is: P. = pCV
Where: 0—density of water
——speed of sound propagation in water.
（A3）
Assuming that the sound wave propagates without loss and diffraction between the transmitting and receiving transducers, the infinite plane wave propagates in a non-lossy medium like:
Pu= Pr p
The force acting on the surface area A of the receiving transducer is: F—2AF
Therefore, under the assumed flat wave conditions, the ratio MUI-24
（A4）
...(A5)
is only determined by the area A of the transducer, and this ratio is defined as the plane wave constant r. J is known, and P can be directly determined by measuring U and, thus, M and S can also be determined accordingly.
Note: If the real transducer input current and receiving pressure of a burst sound (pulse reflected by the reflector) are transmitted and received, M_UL
M, S, are the apparent values of the free field sensitivity and the transducer sending current response assuming ideal plane wave test conditions, so from (A2) and (A7) it can be obtained
GB/T 15611-1995
In any actual test within the frequency range specified in this standard, true plane wave conditions cannot be achieved, so the difference between P, and the average sound pressure P. on the surface of the sensitive element of the receiving transducer must be corrected. Appendix B
Calculation of the effective radius of the auxiliary transducer
(Supplement)
The effective radius α of the auxiliary transducer can be determined by the curve of the change of the sound pressure vibration along the acoustic axis with the distance. This sound field distribution can be obtained by using a hydrophone to measure the sound field generated by the auxiliary transducer. Here, the diameter of the hydrophone sensitive element should be equal to or less than one tenth of the diameter of the auxiliary transducer sensitive element, and the sound emission should be long enough to achieve the state test condition. Comparing the experimentally determined sound field distribution with the expected sound field distribution of the ideal live sound source, by adjusting the radius α of the ideal piston sound source, the ideal sound field distribution can be made to best match the experimental data. The theoretical distribution of the sound field of the piston sound source is as follows: [(21 +)2 -2e*
P/P = 2sin -
Where: P\-the sound pressure amplitude at a distance Z from the transducer surface along the sound axis, Pa; P-plane wave sound pressure amplitude P.=pC·V,Pa; a——sound source radius, m;
z—axial distance: m
-amplitude attenuation coefficient
, a method to obtain this kiss (used by British NPL. months ago) is as follows: If Y,(Z.)=20 lo81nV.,V, the signal voltage amplitude Y,(Z,) generated by the water dew is defined as follows:
20log2sin [(+)18-Z,e2
Let x,-Y(z.)-y(z.)
parameters?
x minimizes with respect to α.
This degree of fit is only used for 1.5Z.The instrument is a function of the normalized distance S, as shown in Figure 3. 1.u
Gc value as a function of the normalized distance S
Figure 3Gc value as a function of the normalized distance Figure 2.5 Calibration uncertainty
Normalized distance S
The recommended calibration procedure and simplified correction factor provide a method for calibrating the free-field voltage sensitivity of hydrophones in the U.5-10 MHz frequency band. The total system uncertainty of this method is less than -1.5 dB, and the statistical uncertainty of the measurement is less than 1.5 dB. GB/T 15611
Appendix A
Plane wave reciprocity calibration
(Supplement)
A reciprocal transducer is a transducer type that satisfies the following electromechanical reciprocity conditions: V—the uniform vibration velocity of the radiating surface of the transducer when transmitting; {--the input current of the transducer when transmitting: U--the open circuit voltage generated by the force F acting on the acoustically rigid transducer when receiving. The definition of the current response sent by the transmitting transducer and the white field sensitivity of the receiving transducer: S=
Where: Pu-
the sound pressure adjacent to the surface of the transmitting transducer when the transmitting transducer input current is 1 without interference; -(Al)
the undisturbed plane wave sound field sound pressure at the acoustic center of the original receiving transducer if the receiving transducer is removed. Under the action of this sound pressure, the transducer generates an output open circuit voltage. For plane waves, the relationship between the sound pressure and the surface vibration velocity V in front of the transmitting transducer is: P. = pCV
Where: 0—density of water
——speed of sound propagation in water.
（A3）
Assuming that the sound wave propagates without loss and diffraction between the transmitting and receiving transducers, the infinite plane wave propagates in a non-lossy medium like:
Pu= Pr p
The force acting on the surface area A of the receiving transducer is: F—2AF
Therefore, under the assumed flat wave conditions, the ratio MUI-24
（A4）
...(A5)
is only determined by the area A of the transducer, and this ratio is defined as the plane wave constant r. J is known, and P can be directly determined by measuring U and, thus, M and S can also be determined accordingly.
Note: If the real transducer input current and receiving pressure of a burst sound (pulse reflected by the reflector) are transmitted and received, M_UL
M, S, are the apparent values of the free field sensitivity and the transducer sending current response assuming ideal plane wave test conditions, so from (A2) and (A7) it can be obtained
GB/T 15611-1995
In any actual test within the frequency range specified in this standard, true plane wave conditions cannot be achieved, so the difference between P, and the average sound pressure P. on the surface of the sensitive element of the receiving transducer must be corrected. Appendix B
Calculation of the effective radius of the auxiliary transducer
(Supplement)
The effective radius α of the auxiliary transducer can be determined by the curve of the change of the sound pressure vibration along the acoustic axis with the distance. This sound field distribution can be obtained by using a hydrophone to measure the sound field generated by the auxiliary transducer. Here, the diameter of the hydrophone sensitive element should be equal to or less than one tenth of the diameter of the auxiliary transducer sensitive element, and the sound emission should be long enough to achieve the state test condition. Comparing the experimentally determined sound field distribution with the expected sound field distribution of the ideal live sound source, by adjusting the radius α of the ideal piston sound source, the ideal sound field distribution can be made to best match the experimental data. The theoretical distribution of the sound field of the piston sound source is as follows: [(21 +)2 -2e*
P/P = 2sin -
Where: P\-the sound pressure amplitude at a distance Z from the transducer surface along the sound axis, Pa; P-plane wave sound pressure amplitude P.=pC·V,Pa; a——sound source radius, m;
z—axial distance: m
-amplitude attenuation coefficient
, a method to obtain this kiss (used by British NPL. months ago) is as follows: If Y,(Z.)=20 lo81nV.,V, the signal voltage amplitude Y,(Z,) generated by the water dew is defined as follows:
20log2sin [(+)18-Z,e2
Let x,-Y(z.)-y(z.)
parameters?
x minimizes with respect to α.
This degree of fit is only used for 1.5Z.The instrument is a function of the normalized distance S, as shown in Figure 3. 1.u
Gc value as a function of the normalized distance S
Figure 3Gc value as a function of the normalized distance Figure 2.5 Calibration uncertainty
Normalized distance S
The recommended calibration procedure and simplified correction factor provide a method for calibrating the free-field voltage sensitivity of hydrophones in the U.5-10 MHz frequency band. The total system uncertainty of this method is less than -1.5 dB, and the statistical uncertainty of the measurement is less than 1.5 dB. GB/T 15611
Appendix A
Plane wave reciprocity calibration
(Supplement)
A reciprocal transducer is a transducer type that satisfies the following electromechanical reciprocity conditions: V—the uniform vibration velocity of the radiating surface of the transducer when transmitting; {--the input current of the transducer when transmitting: U--the open circuit voltage generated by the force F acting on the acoustically rigid transducer when receiving. The definition of the current response sent by the transmitting transducer and the white field sensitivity of the receiving transducer: S=
Where: Pu-
the sound pressure adjacent to the surface of the transmitting transducer when the transmitting transducer input current is 1 without interference; -(Al)
the undisturbed plane wave sound field sound pressure at the acoustic center of the original receiving transducer if the receiving transducer is removed. Under the action of this sound pressure, the transducer generates an output open circuit voltage. For plane waves, the relationship between the sound pressure and the surface vibration velocity V in front of the transmitting transducer is: P. = pCV
Where: 0—density of water
——speed of sound propagation in water.
（A3）
Assuming that the sound wave propagates without loss and diffraction between the transmitting and receiving transducers, the infinite plane wave propagates in a non-lossy medium like:
Pu= Pr p
The force acting on the surface area A of the receiving transducer is: F—2AF
Therefore, under the assumed flat wave conditions, the ratio MUI-24
（A4）
...(A5)
is only determined by the area A of the transducer, and this ratio is defined as the plane wave constant r. J is known, and P can be directly determined by measuring U and, thus, M and S can also be determined accordingly.
Note: If the real transducer input current and receiving pressure of a burst sound (pulse reflected by the reflector) are transmitted and received, M_UL
M, S, are the apparent values of the free field sensitivity and the transducer sending current response assuming ideal plane wave test conditions, so from (A2) and (A7) it can be obtained
GB/T 15611-1995
In any actual test within the frequency range specified in this standard, true plane wave conditions cannot be achieved, so the difference between P, and the average sound pressure P. on the surface of the sensitive element of the receiving transducer must be corrected. Appendix B
Calculation of the effective radius of the auxiliary transducer
(Supplement)
The effective radius α of the auxiliary transducer can be determined by the curve of the change of the sound pressure vibration along the acoustic axis with the distance. This sound field distribution can be obtained by using a hydrophone to measure the sound field generated by the auxiliary transducer. Here, the diameter of the hydrophone sensitive element should be equal to or less than one tenth of the diameter of the auxiliary transducer sensitive element, and the sound emission should be long enough to achieve the state test condition. Comparing the experimentally determined sound field distribution with the expected sound field distribution of the ideal live sound source, by adjusting the radius α of the ideal piston sound source, the ideal sound field distribution can be made to best match the experimental data. The theoretical distribution of the sound field of the piston sound source is as follows: [(21 +)2 -2e*
P/P = 2sin -
Where: P\-the sound pressure amplitude at a distance Z from the transducer surface along the sound axis, Pa; P-plane wave sound pressure amplitude P.=pC·V,Pa; a——sound source radius, m;
z—axial distance: m
-amplitude attenuation coefficient
, a method to obtain this kiss (used by British NPL. months ago) is as follows: If Y,(Z.)=20 lo81nV.,V, the signal voltage amplitude Y,(Z,) generated by the water dew is defined as follows:
20log2sin [(+)18-Z,e2
Let x,-Y(z.)-y(z.)
parameters?
x minimizes with respect to α.
This degree of fit is only used for 1.5Z.The value of is used to check whether the theoretical model introduced as a substitute for the real sound field is successful. If the value of X(2.) is less than 0.5 dB, it means that the introduced model is successful. Appendix C
Calculation of the correction factor
(Supplement)
A more common correction factor is
h= (knGrp)v
Where: (--Correction made to take into account the change of sound waves from transmission to reception during the calibration of the auxiliary transducer: G:--Correction made to take into account the corresponding change when the hydrophone is calibrated in the sound field of the auxiliary transducer; c)
GB/T15611—1995
The following is a logarithmic graph of the normalized distance and IP/P ratio for various ratios of receiving and transmitting diameters derived from an ideal piston sound source. The value of G corresponds to the case where the auxiliary transducer is both transmitting and receiving, and can be obtained from the curve corresponding to the diameter ratio of 1 in the figure. G, the value corresponds to the situation of auxiliary transducer transmission and hydrophone reception, which can be obtained from the curve of appropriate diameter ratio. This standard recommends that this ratio should be less than 0.2.
-Sound pressure reflection factor, for the interface between water and stainless steel, rp=0.937. d
Normalized distance
Figure C1 Relationship between normalized distance and average sound pressure of transducers of different sizes (the parameter in the figure is the ratio of the diameter of the receiving transducer to the diameter of the transmitting transducer) Additional notes:
This standard is proposed by the National Technical Committee for Acoustic Standardization. This standard was drafted by the Institute of Acoustics of the Chinese Academy of Sciences, the 715th Institute of China Shipbuilding Industry Corporation, Shanghai Jiaotong University, and the 721 Factory of China Shipbuilding Industry Corporation.
The main drafters of this standard are Zhu Hou, Wang Yueqi, Shou Wende, Ai Wenjun, and Zheng Jinhong.
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