Acoustics--Free-field calibration method of underwater sound transducers
Some standard content:
National Standard of the People's Republic of China
Acoustics-Free-field calibration method of underwater sound transducers1 Subject content and scope of application
GB/T 3223-94
Replaces GB322382
This standard specifies the calibration method of underwater acoustic transducers under white-field spherical wave conditions: reciprocity method and comparison method. The reciprocity method of this standard is applicable to the calibration of standard hydrophones and standard sound sources, and the comparison method is applicable to the calibration of measurement hydrophones and underwater acoustic transmitters. The frequency range is from hundreds of Hz to megahertz.
All measurements in this standard are carried out under steady-state conditions. When the performance of the calibrated underwater acoustic transducer is related to environmental conditions (such as temperature, static pressure, etc.), these environmental conditions should be stated in the calibration results.
2 Reference standards
GB3947 Acoustic terms
GB3102.7 Acoustic quantities and units
GB3238 Levels of acoustic quantities and their reference values
GB3240 Common frequencies in acoustic measurementsbzxz.net
3 Terms
3.1 Geometric acoustic center The geometric acoustic center is the center of geometric symmetry of the transducer structure or radiating surface, such as the center of a spherical transducer. Note: At low frequencies, the effective acoustic center is consistent with the geometric acoustic center. 3.2 Reference acoustic center The reference acoustic center is a specified point on the transducer, used as the coordinate origin when describing its characteristics. This point is optional and is generally the geometric acoustic center. 3.3 Open circuit voltage of hydraphone The instantaneous voltage at the output end of the hydraphone when no current flows out. The unit is volt, V. 3.4 Electrical transfer impedance Zr of transducer pair The electrical transfer impedance of a transducer pair consisting of a transmitter (F) and a hydrophone (J>) at the base frequency is the complex ratio of the open circuit voltage of the hydrophone to the current of the input transmitter when the transducer pair is placed in the sound field and its main axis is located on a straight line relative to the pointing device. The unit is ohm. When expressed in mathematical form: Zmi = uy/ir, its modulus and amplitude are: Z = [u| = U/r, = argZe = —
Approved by the State Administration of Technical Supervision on December 27, 1994 (1) +***( 2) Implemented on August 1, 1995 GB/T 322394
Where, U, is the effective value of the open-circuit voltage of the hydrophone, V; Ir is the effective value of the input transmitter current, A; the phase of the open-circuit voltage of the hydrophone, rad; and the phase of the input transmitter current, ad. Note: (1) When the electrical transfer impedance is related to the acoustic field, electrical load, environment, etc. of the transducer pair, these conditions should be indicated at the same time. When the transducer pair is in the free field far field condition, its electrical transfer impedance modulus is inversely proportional to the distance between the acoustic centers of the transducer pair. That is, [Z] + d = constant
3.5 Free-field [voltage] sensitivity M. free-field [voltage] sensitivity 33
The complex ratio of the open-circuit voltage at the output of the hydrophone to the instantaneous voltage P at the acoustic center before the hydrophone is introduced into the free acoustic field. The unit is volt per Pascal, V/Pa. When expressed in mathematical form:
Mr=u/pe
The value and phase are:
Mr- [n/pl -U/pu=
（4）
.（5)
Note: ① The free-field sensitivity is the direction of the plane wave propagation. It is generally the direction of maximum sensitivity relative to the specified direction of plane wave propagation, and the acoustic center is generally the reference acoustic center. They should be clearly marked on the hydrophone. Its output terminal and power should also be specified when giving the sensitivity. ② The complex value and effective value of the free-field sensitivity use the same symbol Mi. If not specified, they generally refer to the value. The instantaneous value and effective value of the free-field sound pressure in formula (4) also use the same symbol. The phase of the free-field sensitivity is the phase difference between the hydrophone opening voltage μ and the instantaneous sound pressure of the free-field. 3.6 Free-field [voltage] sensitivity [level] M, free-field [voltage] sensitivity level The logarithm of the ratio of the value of the free field sensitivity M to the reference sensitivity M. to the base 10 multiplied by 20. The unit is decibel, dB, and it is expressed in mathematical form as:
M: -: 20lg(M/M,)
Note: The reference value of the free field sensitivity M, is 1 ViμPa. 3-7 Transmitting current response S, transtmitting current response.(6)
The instantaneous sound pressure at a reference distance from the acoustic center of the transmitter at a certain rate and a specified direction. The complex ratio of the product of the reference distance and the current input to its terminal, the reference distance is 1m. The unit is meter per ampere, Pa·m/A. When expressed in mathematical form:
S, ode/i
The value and phase are:
S, - Ipod,/il = podell, ps, - d-,(7)
Note: (D) The specified direction of the transmitter is generally the earth axis direction; the acoustic center is generally the reference acoustic center, and they should be clearly marked on the transmitter. The input frequency (optional) should also be specified when giving the transmitting current response. The complex value and value of the transmitting current response use the same symbol 51. If not specified, it generally refers to its value. The instantaneous value and effective value of the sound pressure in formula (8) also use the same symbol.
@The phase difference between the instantaneous sound pressure and the current at the transmitting current response. 3. 8 Transmitting current response [level] S, transmitting cutrent response levelThe logarithm to the base 10 of the ratio of the value S of the transmitting current response to its reference value S multiplied by 20. The unit is paging, dB. When expressed in mathematical form:
GB/T 3223--94
St = 20lg(S,/St,)
Note: The reference value of the transmitting current response is 1 μPa m/A. 3.9 Transmitting voltage response Sytransmittingyoltageresponse(9)
At a certain frequency or specified direction, the complex ratio of the product of the instantaneous sound pressure at a reference distance d from the transmitter's acoustic center and the reference distance to the voltage u applied to the input terminal. The reference distance is 1m. The unit is Pascal meter per ount, Pa, m/V. When expressed in mathematical form:
Sy = pado/u
The magnitude and phase are:
Su lpoda/ul - pud,/U, Py = Fr, - Note: Same as note 3.7.
3.10 Transmitting voltage response [level] Sy transmittingoltageresponselevel(10)
The logarithm of the ratio of the value S of the transmitting voltage response to its reference value Su multiplied by 20. The unit is decibel, dB. When expressed in mathematical form:
Sy -20lg(Su/Sw.)
Note: The standard value of the transmitted voltage response is 1Ma·m/V. 3.11 Electroacoustic reciprocity principle (12)
The principle that the ratio of the receiving sensitivity of a linear, passive, reversible electroacoustic transducer when used as a hydrophone and the corresponding transmitting response when used as a transmitter is independent of the structure of the transducer itself. Note: The above ratio is a constant, called the reciprocity constant. This constant is related to the properties of the acoustic field in which the transducer is located. Under free-field spherical wave conditions, there are: J, -- MI/S,
---- , - j,β --
Wherein, J.——free-field spherical wave reciprocity constant, m·#/kg; Mfi——free field sensitivity, V/n
, ---transmitted current response, Pa m/A ;
u-----density of medium-kz/m,
f----frequency, Hzr
...·complex angle wave number, m-
d.-—test distance (1m), m
propagation coefficient,m-1,
. Attenuation coefficient, dB/mt
.-Phase coefficient, rad/m
——Angular wave number, m-,
Angular condensation rate, rad/s:
Acoustic transmission, m/s.
4 Reciprocity calibration
4.1 Principle
..-([4
GB/T 3223 -- 94
The reciprocity calibration method is an absolute calibration method based on the electroacoustic principle followed by the reciprocal transducer. This method requires three transducers, of which at least one is a reciprocal transducer (H), the other is a transmitter (F) and a hydrophone (J). These transducers are only required to meet the linear condition. In the free field far field, three measurements are made according to the combination shown in Figure 1. The sum of the current of each transducer to the input transmitter, the open circuit voltage u of the hydrophone, or its electrical transfer impedance Z are measured respectively. The free field sensitivity of the hydrophone and the reciprocal transducer and the transmission current response of the reciprocal transducer and the transmitter can be obtained.
In the first set of measurements, the transmitter The far-field sound pressure of the transmitter (F) at the acoustic center of the hydrophone (J) at the calibration distance from its acoustic center, ignoring the time factor e\, is:
where: Pa\
padndg-e)
igSm.ed-dn
sound pressure at the reference distance d. from the acoustic center of the transmitter F), Pa; reference distance (lm), m
ip-input current of the transmitter (F), A;
SE—transmitting current response of the transmitter (F).Pa·m/A; -complex angle wave number.m-
Then its electrical transfer impedance Zn is:
Zu = y/ir = Uj/pa.e ·pdfjlie =where: WF·-open circuit voltage of the hydrophone (J), V; Mu——self-field sensitivity of the hydrophone (J), V/Pn. rS
Similarly for the first group of measurements, the electrical transfer impedance 2m when the transmitting group (F) sends and the reciprocal transducer (H) receives is: ZEH-UFH/'P-MSNIdH)-ed\m)
Where: FH\\-H is the open circuit voltage of the reciprocal transducer (H), V; ----the input current of the transmitter (F), A: iL
the white field sensitivity of the reciprocal transducer (H), V/Pa; - the distance between the transmitter (F) and the acoustic center of the reciprocal transducer (H), Ⅱ. For the third set of measurements, the electrical transfer impedance Z when the reciprocal transducer (H) transmits and the hydrophone (J) receives is: ZH=H/in=(MnSn/du)+c'tda-m
Where: u}-F: the open circuit voltage of the hydrophone (J) when the reciprocal transducer (H) transmits, V: the input current of the reciprocal transducer (I).A; -(. 15)
GB/T 3223-94
- the transmitting current response of the reciprocal transducer (H), Pa*m/A; Sr
d: the distance between the acoustic centers of the reciprocal transducer (H) and the hydrophone (J), m. From equations (16) and (17), we can obtain:
Z/Zpi = (Mdm/Melt +dim)+ew
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