GB 3223-1982 Free-field calibration method for underwater acoustic transducers
Some standard content:
1 Introduction
National Standard of the People's Republic of China
Free-field calibration method of underwater sound transducers
GB3229—82
1.1 This standard specifies the calibration methods of underwater sound transducers under free-field spherical wave conditions: reciprocity method and comparison method. The reciprocity method is used to calibrate standard hydrophones and standard sound sources. The comparison method is used to calibrate hydrophones and underwater acoustic transmitters. The applicable frequency range of this standard is 1001 MHz to 1 MHz. 1.2 All measurements in this standard are carried out under steady-state conditions. When the performance of the transducer is related to environmental conditions (such as temperature, static electricity, etc.), these environmental conditions shall be mentioned in the calibration results. 1.3 This standard was prepared with reference to the international standard IFC565 (1977) "Calibration of hydrophones". The names of the terms, quantities and units used in this standard. The symbols and other information refer to the provisions of the relevant standards GB 3102.7-82 "Quantities and Units of Acoustics", GB 3238-82 "Levels and Reference Values of Acoustic Quantities" and GB 3240-82 "Common Frequencies in Acoustic Measurements". 2 Terms and Terms
2.1 Free Field bZxz.net
A sound field in a uniform and isotropic medium where the boundary effects can be ignored. 2.2 Far Field
A sound field in which the instantaneous sound pressure and instantaneous particle velocity are in phase at a distance from the sound source. Note that the pressure in this field is inversely proportional to the source velocity, that is, the pressure generated by the sound source at a certain point is inversely proportional to the distance from the point to the source. 2.3 The effective center of the hydrophone is a point on or near the transmitter, and when observed from a distance, the sound waves appear to radiate from this point. Note: The acoustic center of the hydrophone when used as a hydrophone is the same as the acoustic center of the transmitter. 2.4: A hydrophone is a transducer that converts underwater acoustic signals into electrical signals. 2.5 A hydrophone is a transducer that converts electrical signals into underwater acoustic signals. 2.6 A reversible transducer is a transducer whose energy conversion loss is independent of the transmission direction. A reversible transducer can be used as both a transmitter and a hydrophone. 2.7 A reciprocal transducer is a transducer that is linear, reciprocal, and satisfies the reciprocity principle. 2.8 The open-circuit voltage of a hydrophone (i
) is the voltage present at the output end of the hydrophone when no current flows out. In this standard, all voltages, currents, and sounds are effective values unless otherwise specified. The output terminal of a hydrophone can be the output of a hydrophone head, a power supply, or a preamplifier. 2.9 The electrical impedance of a transducer The electrical impedance at a certain frequency is the complex ratio of the instantaneous voltage applied to the electrical terminal of the transducer to the instantaneous current induced. Unit, issued by the National Bureau of Standards on October 12, 1982, implemented in 1983-01, GB 3223--82
.
Note: This impedance is related to the acoustic field, environment (static pressure, temperature) and electrical load (connected cable length) of the transducer. Therefore, when giving the impedance value of the transducer, these conditions of the transducer should be specified at the same time. 2.10 Transfer impedance of transducer pair [model] "Z" The transfer impedance model of the transducer pair composed of a transmitter (F) and a hydrophone (J) at a certain frequency is the ratio of the open circuit voltage of the hydrophone to the current flowing into the transmitter. Unit: Ohm. Mathematically expressed:
Izf/=U/Ir
Note: 0) The transfer impedance is related to the direction of the transducer, the acoustic field, environment and electrical load. Therefore, when giving the transfer impedance value, these conditions of the transducer pair should be specified at the same time.
If the transducer pair is in the free field far field conditions specified in this standard, its transfer impedance is inversely proportional to the distance d between the transmitter and the acoustic center of the hydrophone, that is,
2.1F free field [voltage] sensitivity M
IZel·d=constant
is the ratio of the open circuit voltage U at the output of the hydrophone to the free field sound pressure pj at the acoustic center of the hydrophone before the hydrophone is introduced into the sound field. Unit: volt per Pascal, V/Pa. Mathematically expressed as:
M-Uf/p, ...
Note that the free field sensitivity is for a plane traveling wave. The direction, output terminal and frequency of the hydrophone relative to the propagation of the half-surface wave should be indicated at the same time. 2.12 Free field [voltage] sensitivity i level] M is the logarithm of the ratio of the free field sensitivity M to its reference value M, multiplied by 20 with a base of 10. Unit: decibel, dB. Expressed in mathematical formula:
M=20lg(M/M,)
Note: The reference value of free field sensitivity level 2 is 1 V/μPa. (3
2.13 Transmitting current response S
The transmitting current response SI of a transmitter at a certain frequency is the ratio of the sound pressure p in the far field at a certain reference distance d from its acoustic center in a specified direction, and the product of the reference distance and the current I applied to the input terminal. Unit: meter per ampere, Pa·m/A. Mathematical expression:
Sr=p-djI.
Note: The specified direction and input terminal of the transmitter can be arbitrarily selected, and the acoustic center is determined by experiment according to the definition. When giving the transmitting current response, the specified direction, the input terminal and the acoustic center position should be indicated. 2.14 Transmitting current response level S,
is the logarithm of the ratio of the transmitting current response S to its reference value St with the base 10 multiplied by 20. Unit, decibel, dB. Mathematical expression:
S) =20ig(S/S)
Note: The reference value Sr of the transmission current response level is 1uPa·m/A. (6)
2.15 Transmission voltage response S
The transmission voltage response S of the transmitter at a certain frequency is the ratio of the product of the voltage P in the far field at a certain reference distance d from its acoustic center in the specified direction and the reference distance to the voltage applied to the input terminal. Unit: Pa·m/V. Mathematically expressed as:
Sr= Pa'd/ti
Note: The specified direction and the integrated terminal of the transmitter can be selected arbitrarily, and the center is determined by the definition experiment. When giving the transmission voltage response, its specified direction, input terminal and the position of the acoustic center should also be indicated. 2.16 Transmit voltage response secondary value Sv
GB3223-82
is the ratio of the transmit voltage response S to its reference value S+, multiplied by 20 with the logarithm of 10. Unit: decibel, dB. Mathematical expression:
Sp--20lgtS./Sur)
Note: The reference value of the transmit voltage response secondary value is SxlPa+m/V2.17 Electroacoustic reciprocity principle
The ratio of the free field sensitivity of a linear, reversible, electroacoustic transducer when used as a hydrophone to the transmit current response SI when used as a transmitter is related to the structure of the transducer itself. Note: The above ratio is a five-dimensional efficiency, and this constant is related to the product properties. The reciprocity constant in this standard is the reciprocity constant of spherical waves in the free field, which is: Js=M/S,=2/0f
density of the medium, kg/,
f-frequency, s-!
3 Reciprocity calibration
Reciprocity calibration is an absolute calibration method for calibrating transducers in the free field using the principle of electrical reciprocity. This method uses a calibration standard hydrophone and a standard source.
3.1 Original Class
Reciprocity calibration requires three transducers, one of which is the reciprocal transducer (H), and the other two transducers are the transmitter (F) and the hydrophone (J). These two transducers are only required to meet the linear condition. In the free field, the above transducers are arranged as shown in Figure 1, and three measurements are made to measure their transfer impedances Z respectively. According to the electroacoustic reciprocity principle, from these three transfer impedance values, the free field sensitivity of the reciprocal transducer and the hydrophone, and the sending current response of the reciprocal transducer and the transmitter can be calculated. The three measurements are as follows:
(1) When the transmitter (F) sends and the reciprocal transducer (H) receives (see Figure 1), the transfer impedance Z is: Urn_Uen Pa.enden
i Z 1--
In the formula, [-
The open circuit voltage generated by the reciprocal transducer (H) placed in the sound field of the transmitter (F), V; The current applied to the input end of the transmitter (F), A:-(10)
—The distance between the transmitter (F) and the acoustic center of the reciprocal transducer (I1), \,
The sound pressure generated by the transmitter (F) at the center of the reciprocal transducer (H) at a distance d from the center of H, PaPt,FH
The free field sensitivity of the reciprocal transducer (H), V/Pa, Si——The sending current response of the transmitter (I), Pa·m/A.0
GB 8223—B2
（2）When the transmitter (F) transmits and the hydrophone (J) receives [Figure 1 (b), its transfer impedance "ZF" is Zt[=U/'=M,SF/d
-the distance between the acoustic centers of the transmitter (F) and the hydrophone (J), III where: d
（11）
the self-field sensitivity of the hydrophone (J), /Pa. (3)When the reciprocal transducer (H) transmits and the hydrophone (J) receives LFigure 1 (c), its transfer impedance |Hr" is: [Z[-(u/Ih=M.Sa/dm
the distance between the acoustic centers of the reciprocal transducer (H) and the hydrophone (J), ㎡, d
SrH—The sending current response of a reciprocal transducer (HI), Pa·m/A. From equations (10) and (11), we can get:
[Zru,/|Zm|=MHdp/M;deH
According to the electroacoustic universal principle, the universal transducer (11) should have: Mμ/Srh=2/pf =Js
From equations (12) and (14), we can get:
[Zui =MMu/sd
（12)
+（15)
So from equations (13) and (15), we can get the self-field sensitivity of the point-to-point transducer (It) and the hydrophone (J), respectively: Mu=[(] Z [- Zuli! Zt b(dr-du/dr).JJ?M,-[(|Zm 1: 12h. 1/ 12ph -)-
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