This standard specifies the definition of various acoustic parameters of the ultrasonic field in water and other liquids within the frequency range of 0.5 to 15 MHz, as well as the conditions and methods for measuring the ultrasonic field parameters generated by medical ultrasonic equipment in water using calibrated piezoelectric hydrophones. GB/T 16540-1996 Acoustics Ultrasonic field characteristics in the frequency range of 0.5 to 15 MHz and its measurement hydrophone method GB/T16540-1996 Standard download decompression password: www.bzxz.net
This standard specifies the definition of various acoustic parameters of the ultrasonic field in water and other liquids within the frequency range of 0.5 to 15 MHz, as well as the conditions and methods for measuring the ultrasonic field parameters generated by medical ultrasonic equipment in water using calibrated piezoelectric hydrophones.

GB/T 16540-1996
This standard is compiled based on the international standard IEC1102:1991 "Ultrasonic field characteristics and their measurement in the frequency range of 05-15MHz using hydrophones" and the amendment document 1102Amend.1cIEC:1993 of the standard. It is equivalent to the international standard in terms of technical content and consistent with it in terms of writing rules.
This standard has made appropriate modifications and deletions to a small amount of content such as the scope, referenced standards, definitions, measurement requirements and drawings of IEC1102:1991 to make the content more correct and concise.
This standard specifies the performance requirements of high-frequency ultrasonic hydrophones not specified in GB4128-1995. Appendix A, Appendix B, Appendix C and Appendix D of this standard are all suggestive appendices. This standard is proposed and managed by the National Technical Committee for Acoustic Standardization. The drafting units of this standard are: Shanghai Jiaotong University, Institute of Acoustics, Chinese Academy of Sciences, China Institute of Metrology, and Shanghai Madison Medical Equipment Co., Ltd.
The main drafters of this standard are Shou Wende, Jiang Yiping, Zhu Houqing, Xiong Dalian, and the following. This standard is entrusted to the Ultrasonic and Underwater Acoustic Subcommittee of the National Acoustic Standardization Technical Committee for interpretation. 556
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IEC Foreword
1) The technical preparations made by the International Electrotechnical Commission and the formal decisions and agreements made represent the opinions of all national committees with special interests. This decision expresses the international consensus on the subject of the discussion as effectively as possible. 2) For international use, they adopt the form of recommendations, and they are accepted by national committees with that point of view. 3) In order to promote international unification, the International Electrotechnical Commission has expressed the hope that all national committees will try their best to adopt the texts recommended by the International Electrotechnical Commission in national regulations as long as national conditions permit. This international standard was proposed by the International Electrotechnical Commission Technical Committee 87 (Ultrasonics). The text of this International Standard is based on the following documents: Six-month method
87(CO)6
Voting report
87(CO)8
Full information on the voting for the approval of this standard can be found in the voting report shown in the table above. This International Standard describes the performance requirements for ultrasonic hydrophones in addition to those given in IEC866. All annexes are informative. In this standard, the following typography is used: - Requirements and definitions: Roman,
- Notes: Small Roman;
Follow; Small italics;
Terms used in this standard and specified in clause 3: Small Roman bold. 557
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IEC Introduction
The main purpose of this International Standard is to define various acoustic parameters. These parameters are used to specify and describe the characteristics of ultrasonic fields propagating in liquids, and in particular in water, with the help of hydrophones. The measurement methods used to determine these parameters are briefly described. This International Standard has many similarities with the American Institute of Ultrasound in Medicine/National Electrical Manufacturers Association (AIUM/NEMA) safety standard. Although every effort has been made to keep the two consistent, there are still some basic differences in the methods of the former and the latter. The basic principle of this International Standard is to specify the sound field in terms of sound pressure parameters. When hydrophones are used to describe the sound field characteristics, sound pressure is the basic measured quantity. Of course, if other measurement devices are used in the future, a new International Standard with additional definitions and methods will be needed. Examples of such devices are thermistors or thermocouples. This International Standard also specifies sound intensity parameters similar to those given in the AIUM/ENMA safety standard, but these parameters are considered derived quantities and are only meaningful if certain assumptions are made about the ultrasonic field being measured. When accuracy requirements are not high, some alternative simplified methods can be used. These methods will be given in the IEC Guidance Document (in preparation). This standard specifies the definitions of various acoustic parameters of ultrasonic fields in water and other liquids in the frequency range 0.5 to 15 MHz, as well as the conditions and methods for measuring the parameters of the ultrasonic field generated by medical ultrasonic equipment in water using calibrated piezoelectric hydrophones. Note: This standard uses SI units. In the description of some parameters, such as beam area parameters and sound intensity parameters, it may be more convenient to use other units. For example, beam area can be expressed in cm, and sound intensity can be expressed in W/cm2 or mW/cm2. 2 Referenced Standards
The following standards contain provisions that constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T3947—1996 Acoustic terminology
GB/T4128—1995 Standard hydrophone (neqIEC500:1974;IEC866:1987) GB/T15611—1995 Calibration of high-frequency hydrophone IEC50 (801) International Electrotechnical Vocabulary (IEV), Chapter 801: Acoustics and electroacoustics (1984) IEC469-1:1987 Pulse technology and instrumentation, Part 1: Pulse terms and definitions IEC854:1986 Performance measurement methods for ultrasonic pulse echo diagnostic equipment 3 Definitions
This standard adopts the following definitions.
3.1 Acoustic pulse crest factoracoustic pulse crest factor The ratio of the spatial peak time peak sound pressure in the sound field to the root mean square sound pressure calculated during its pulse peak period. 3.2 Acoustic pulse waveformacoustic pulse waveform The time waveform of the instantaneous sound pressure at a specified position in the sound field. The time for displaying the waveform should be long enough to include a waveform of all meaningful acoustic information in a single pulse or burst of pure tone, or in a single or multiple cycles of a continuous wave. 3.3 Acoustic repetition period The pulse repetition period of a non-automatic scanning system or the scanning repetition period of an automatic scanning system. For a continuous wave system, it is the time interval between two consecutive weeks.
3.4 ​​Acoustic-working frequency (f.wr) Acoustic-working frequency Approved by the State Administration of Technical Supervision on September 13, 1996 and implemented on March 1, 1997
GB/T16540-1996
The hydrophone is placed in the sound field at a position corresponding to the spatial peak time peak sound pressure, and its output signal is analyzed using the zero-crossing frequency technique or the spectrum analysis method (see Figure 1) to obtain the working frequency. The unit is Hertz, Hz. There are several types of acoustic working frequencies: 3.4.1 Zero-crossing acoustic working frequency The acoustic working frequency determined by the average interval between the zero sound pressure points in the sound pressure waveform. 3.4.2 Arithmetic mean acoustic working frequency The arithmetic mean of f and f2. fi, f, are the frequencies corresponding to a 3dB drop in amplitude from the highest point in the sound pressure spectrum. 3.4.3 Geometric mean acoustic working frequency The geometric mean of fi and f.
3.4.4 Modal acoustic working frequency The frequency corresponding to the peak in the sound pressure spectrum.
Note: This standard uses the arithmetic mean acoustic working frequency. See Appendix D. 3.5 Bandwidth The difference between frequency f and f2. f1 and f2 are the frequencies corresponding to a 3dB drop in amplitude from the highest point in the sound pressure spectrum. 3.6 Beam alignment axis A straight line connecting the spatial peak and temporal peak sound pressure points on two hemispheres is used only for alignment. The center of the hemisphere is roughly consistent with the geometric center of the ultrasonic transducer or ultrasonic transducer array element. The radius of the first hemisphere is Ag/(λ), where Ag is the geometric area of ​​the ultrasonic transducer or ultrasonic transducer array element, and λ is the wavelength of the ultrasonic wave at the nominal frequency. The radius of the second hemisphere is 2Ag/(λ) or Ag/(3λ), whichever is appropriate. For alignment, this line can be projected onto the surface of the ultrasonic transducer or ultrasonic transducer array element. In most practical applications, two planes perpendicular to the direction of ultrasonic propagation are usually used. In the case where the single peak is not on the hemisphere, another hemisphere with a different radius is selected to produce a single peak (see Figure 2). 3.7 Beam area (Ab) beam-area
The area of ​​a specified surface consisting of all points with the following properties. At these points, the square integral of the pulse sound pressure is greater than a specified percentage of the maximum value of the square integral of the pulse sound pressure on the surface. The unit is square meter, m2. For ultrasonic transducers with cylindrical active elements, this specified surface is cylindrical; for ultrasonic transducers with spherical active elements, this specified surface is spherical and has a certain radius. For -6 dB and -20 dB beam areas, the specified values ​​are 25% and 1% respectively. Note: The beam area can be composed of several parts. 3.8 Beam-average pulse acoustic pressure (pbap) beam-average pulse acoustic pressure The pulse sound pressure generated by an ultrasonic transducer or an ultrasonic transducer array element is averaged within a 6 dB beam area on a specified surface or on a surface containing the spatial peak time peak sound pressure points. The unit is Pascal, Pa. Note: A 6 dB beam area is generally used, but other beam areas can also be used. 3.9 Beam-average pulse-average acoustic intensity (Ibapa)bean-average pulse-average acoustic intensity The pulse-average acoustic intensity generated by an ultrasonic transducer or an ultrasonic transducer array element is averaged within a 6dB acoustic beam area on a specified surface or a surface containing a spatial peak temporal peak acoustic pressure point. The unit is watt per square meter, W/m. Note: A 6dB acoustic beam area is generally used, but other acoustic beam areas can also be used. 3.10 Beam-average root mean square acoustic pressure (pbar)beam-average rm,s acoustic pressure The root mean square acoustic pressure generated by an ultrasonic transducer or an ultrasonic transducer array element is averaged within a 6dB acoustic beam area on a specified surface or a surface containing a spatial peak temporal peak acoustic pressure point. The unit is Pascal, Pa. Note: A 6dB acoustic beam area is generally used, but other acoustic beam areas can also be used. 3.11 Beam-average temporal-averge acoustic intensity The temporal-average acoustic intensity produced by an ultrasonic transducer or an array of ultrasonic transducers is averaged over a 6 dB beam area on a specified surface or on a surface containing the spatial peak temporal peak sound pressure point. The unit is watt per square meter, W/m2. Note: A 6 dB beam area is generally used, but other beam areas may also be used. 3.12 Central scam line The ultrasonic scan line closest to the symmetry axis of the scanning plane in an automatic scanning system560
GB/T16540-1996
In an automatic scanning system, 3.13 Effective area of ​​an ultrasonic transducer (ADeffective area of ​​an ultrasonic transducer) is the area of ​​an ideal piston ultrasonic transducer that is approximately equivalent to the axial sound pressure distribution observed in the auxiliary direction of the actual ultrasonic transducer at a finite interaxial distance. The unit is square meters, m°. 3.14 Effective radius of a hydrophone active element (a, aa, agJeffective radius of a hydrophone active element is the radius of an ideal rigid disc receiver hydrophone whose beamwidth of the directivity function is predicted to be equal to the beamwidth of the actual hydrophone. The beamwidth is determined by a specified value at the maximum value of the directivity response. For specified 3dB and 6dB levels, the radius is represented by a: and as respectively. The unit is meter,.
3.15 End of-cable loaded sensitivity of hydrophone cable (M.) When a hydrophone is connected to a load of specified electrical input impedance, the ratio of the output voltage at the end of its cable or connector to the instantaneous sound pressure of the undisturbed plane wave free field at the acoustic center of the hydrophone when the hydrophone is removed. The unit is volt per Pascal, V/Pa. 3.16 End-of-cable open-circuit sensitivity of a hydrophone The ratio of the open-circuit voltage at the end of the cable or connector of a hydrophone to the instantaneous sound pressure of the undisturbed plane wave free field at the acoustic center of the hydrophone when the hydrophone is removed. The unit is volt per, V/Pa. 3.17 Mean-peak-cycle acoustic pressure (pm) The arithmetic mean of the absolute values ​​of the maximum positive and maximum negative values ​​of the instantaneous pressure in a pulse peak cycle. The unit is Pa, Pa, 3.18 Nominal frequency nominal frequency is the working frequency of the ultrasonic transducer or transducer array provided by the designer or manufacturer. 3.19 Nonlinear propagation parameter (om) nonlinearpropagationparameter is an index that can be used to predict the nonlinear distortion of ultrasound for a specified ultrasonic transducer, expressed as: pe pm (F-yvaln(Fg 1) + F)
where: B is the nonlinear parameter (β1+B/2A=3.5 in 20C pure water) t is the angular frequency (u=2 element fawfwt is the acoustic frequency): 1 is the distance from the ultrasonic transducer surface to the plane containing the spatial peak time peak sound pressure; F is 0.69 times the ratio of the ultrasonic transducer geometric area to the 6dB beam area; Ps is the average peak period sound pressure at the point in the sound field corresponding to the spatial peak time peak sound pressure. Note: The above formula is applicable to the ultrasonic field of F2.1, and the indicators within the range of F≤2.1 are under consideration. (1)
3.20 Peak-negative acoustic pressure (p- or p.) peak -negative acoustic pressure; peak -rarefactional acoustic pressure The maximum absolute value of the negative instantaneous acoustic pressure in a sound field or on a specified surface during the sound repetition period. Peak negative acoustic pressure is represented by a positive number. The unit is Pa. (See Figure 5).
3.21 Peak-positive acoustic pressure (p+ or p.) peak -positive acoustic pressure, peak-compressional acoustic pressure The maximum value of the positive instantaneous acoustic pressure in a sound field or on a specified surface during the sound repetition period. The unit is Pa. See Figure 5. 3.22 Pulse acoustic pressure (p.) pulse acoustic pressure The square root of the ratio of the square integral of the pulse acoustic pressure at a specific point in the sound field to the pulse duration. The unit is Pa. See Figure 7. 3.23 Pulse-average intensity pulse-average intensity The ratio of the integral of the pulse acoustic intensity at a specific point in the sound field to the pulse duration. The unit is watt per square meter, W/m3.24 Pulse beam width (Wpbg, Wpbzo) pulse beam-width is the distance between two points in the specified direction of the maximum point of the square integral of the pulse sound pressure on a specified surface. The square integral of the pulse sound pressure at these two points should be a certain percentage of the maximum value of the square integral of the pulse sound pressure on the surface. These two points are on both sides of the maximum point of the square integral of the pulse pressure and are the farthest apart. If a specified surface is provided, the surface should pass through the spatial peak and temporal peak points of the entire sound field. For -6dB and -20dB pulse beam gamuts, the specified values ​​are 25% and 1% respectively. The unit is meter, m. Note: The specified surface is usually a plane perpendicular to the collimation axis of the sound beam. For ultrasonic transducers with cylindrical active elements, it may be a cylindrical surface, and for ultrasonic transducers with spherical active elements, it may be a spherical surface.
GB/T 16540—1996
3.25 Pulse beam radius (Wprs,Wpr2o)pulse beam-radiiThe two distances between the point of maximum value of the square integral of the pulse sound pressure and the point specified by the pulse sound beam width on the specified surface. The unit is meter, m.
3.26Pulse duration (ta)pulse duration1.25 times the time interval between the time when the integral value of the square of the instantaneous sound pressure reaches 10% of the final value and the time when it reaches 90% of the final value. The final value of the time integral of the square of the instantaneous sound pressure is the square integral of the pulse sound pressure. The unit is second, S, (see Figure 3). 3.27Pulse sound intensity integral (I)pulse-intensity integralThe time integral of the instantaneous sound intensity at a specific point in the sound field within the entire sound pulse waveform. The unit is joule per square meter, J/m2. Note: For many measurements covered by this standard, the pulse sound intensity integral is proportional to the pulse sound pressure square integral. 3.28Pulse peak cyclepulse-peak cycleA single cycle between two zero instantaneous sound pressure points in the sound pulse waveform signal. The single signal cycle should consist of the half cycle containing the time peak sound pressure and one of the two adjacent half cycles. The adjacent half cycle should contain the larger absolute value of the instantaneous sound pressure peak (see Figure 5). 3.29 Pulse sound pressure square integral (pi) pulse -pressure -squared integral The time integral of the square of the instantaneous sound pressure at a specific point in the sound field within the entire sound pulse waveform. The unit is Pa squared·second, Pa·s, (see Figure 3).
3.30 Root mean square sound pressure (prms) RMSacoustic pressure The root mean square of the instantaneous sound pressure at a specific point in the sound field. Unless otherwise specified, the root mean square should be obtained in integer multiples of the sound repetition period. The unit is Pa, Pa, (see Figure 7).
3.31 Scan area (A.) scan -area
For an automatic scanning system, it is an area on the surface under investigation. It consists of all points in the sound beam area of ​​any sound beam passing through the surface within the scanning repetition period. The unit is square meter, m. 3.32 Scanning plane scan -plane
For automatic scanning system, the plane containing all ultrasonic scanning lines. 3.33 Spatial -average pulse acoustic pressure (peap) For non-automatic scanning system, it is the beam average pulse acoustic pressure. The unit is Pa. Note: For automatic scanning system, spatial -average pulse acoustic pressure cannot be used, only beam average pulse acoustic pressure can be used. 3.34 Spatial -average pulse -average intensity For non-automatic scanning system, it is the beam average pulse average intensity. The unit is Watt per square meter, W/m2. Note: For automatic scanning system, spatial -average pulse -average intensity cannot be used, only beam average pulse intensity can be used. 3.35 Spatial -average rms acoustic pressure (par) For non-automatic scanning system, it is the beam average rms acoustic pressure; for automatic scanning system, it is equal to the average of rms acoustic pressure over the scanning area. The root mean square sound pressure is obtained during the entire scanning repetition cycle. The unit is Pa. 3.36 Spatial-average temporal-average intensity (Isata) For non-automatic scanning systems, it is the average temporal-average intensity of the sound beam; for automatic scanning systems, it is the average of the temporal-average intensity over the scanning area. The temporal-average intensity is obtained during the entire scanning repetition cycle. The unit is watt per square meter, W/m2. 3.37 Spatial-peak pulse average intensity (Ispa) The maximum value of the pulse-peak intensity in the sound field or on a specified surface. The unit is watt per square meter, W/m2. 3.38 Spatial-peak pulse-intensity integral (Isp) The maximum value of the integral of the pulse-intensity in the sound field or on a specified surface. The unit is joule per square meter, J/m\. 3.39 Spatial-peak pulse acoustic pressure (pap)spatial-peak pulse acoustic pressureThe maximum value of the pulse acoustic pressure in the sound field or on a specified surface. The unit is Pascal, Pa. 3.40 Spatial-peak root mean square acoustic pressure (pspr)spatial-peak rms acoustic pressure562
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The maximum value of the root mean square acoustic pressure in the sound field or on a specified surface. The unit is Pascal, Pa. 3.41 Spatial-peak time-average sound intensity (Ispta)spatial-peak temporal-average intensityThe maximum value of the time-average sound intensity in the sound field or on a specified surface. The unit is Watt per square meter, W/m. 3.42 Spatial-peak temporal-peak acoustic pressure (Psptp)spatial-peak temporal-peak acoustic pressure: peak sound pressureuer
The larger of the positive peak sound pressure or the negative peak sound pressure. The unit is Pascal, Pa. 3.43 Spatial-peak temporal-peak intensity (Isptp) spatial-peak temporal-peak intensity The maximum value of the temporal peak sound intensity in the sound field or on a specified surface. The unit is watts per square meter, W/m. 3.44 Symmetry axis of the scan plane The virtual line on the scan plane that has an equal number of scan lines on both sides. 3.45 Time-average sound intensity termporal-average intensity The time average of the instantaneous sound intensity at a specific point in the sound field. Unless otherwise specified, the time average is obtained in integer multiples of the sound repetition period. The unit is watts per square meter, W/m.
3.46 Temporal-peak acoustic intensity The maximum value of the absolute value of the instantaneous sound pressure at a specific point in the sound field. The unit is Pascal, Pa. 3.47 Temporal-peak intensity temporal-peak intensity The maximum value of the instantaneous sound intensity at a specific point in the sound field. The unit is watt per square meter, W/m2. 3.48 Ultrasonic scan line ultrasonic scan line For automatic scanning systems, it is the collimation axis of the sound beam of a specific ultrasonic transducer array element group, or the collimation axis of the sound beam of a specific excited ultrasonic transducer or ultrasonic transducer array element group.
3.49 Ultrasonic scan line separation (S.) ultrasonic scan lines separation For automatic scanning systems, it is the distance between two consecutive ultrasonic scan lines of the same type and two intersection points of a specified surface. The unit is meter, m.
3.50 Ultrasonic transducer element group ultrasonic transducer element group A group of ultrasonic transducer elements that are excited together to produce a single sound pulse. 4 Symbols
Effective radius of the hydrophone sensitive optical element
Geometric radius of the hydrophone sensitive element
Effective radius of the ultrasonic transducer
Effective radius of the hydrophone determined by directivity response measurements at 3 dB and 6 dB Maximum effective radius for a given hydrophone application Effective area of ​​the ultrasonic transducer
Acoustic area
Geometric area of ​​the ultrasonic transducer
Scanning area
Sound speed in liquid (usually water)
Capacitance at the end of the hydrophone cable
Parallel input capacitance of the electrical load
Acoustic operating frequency
Pulse repetition frequency
0.69XA/6dB sound east area)
=2 yuan/in
p+(pe)
Instantaneous sound intensity
GB/T 16540--1996
Beam average pulse average sound intensity
Beam average time average sound intensity
Pulse sound intensity integral
Space average pulse average sound intensity
Space average time average sound intensity
Space peak pulse average sound intensity
Space peak pulse sound intensity integral
Space peak time average sound intensity
Space peak time peak sound intensity
Angular wave number
Distance between hydrophone and ultrasonic transducer||tt ||Distance between the ultrasonic transducer surface and the plane containing the spatial peak time peak sound pressureOpen circuit sensitivity at the end of the hydrophone cable
Loaded sensitivity at the end of the hydrophone cable
Instantaneous sound pressure
Beam average root mean square sound pressure
Beam average pulse sound pressure
Square integral of pulse sound pressure
Peak period average sound pressure
Time peak sound pressure
Spatial average pulse sound pressure
Spatial average root mean square sound pressure
Spatial peak pulse sound pressure||tt ||Spatial peak RMS sound pressure
Spatial peak temporal peak sound pressure
Pulse sound pressure
RMS sound pressure
Positive peak sound pressure
Negative peak sound pressure
Parallel input resistance of the electric load
Ultrasonic scanning line spacing in the plane under investigationPulse duration
Voltage at the end of the hydrophone cable
Instantaneous velocity of medium particles
Complex impedance of hydrophone
Complex input impedance of the electric loadbzxz.net
Nonlinear parameters||t t||—3dB and -6dB half-beamwidth
Wavelength of sound waves in liquid
Density of liquid (usually water)
Non-linear propagation parameter
w=2 yuanf
5 Measurement requirements
Angular frequency
5.1 Requirements for hydrophones and amplifiers
GB/T16540--1996
In addition to complying with the requirements of GB4128 for high-frequency hydrophones, the requirements of this standard for hydrophone performance shall also meet the technical requirements stated in this article.
5.1.1 Instantaneous sound pressure
The instantaneous sound pressure at a point in the sound field measured by the hydrophone (t) is calculated using the formula (2) p(t) = ur(t)/Mu
where: ut(t) - voltage at the end of the hydrophone cable, V: ML - load sensitivity at the end of the hydrophone cable, V/Pa. 5.1.2 Hydrophone sensitivity
The load sensitivity at the end of the hydrophone cable should be measured under the conditions of the specified electrical load. Assuming that the open-circuit sensitivity of the hydrophone cable end is known, the load sensitivity at the end of the cable can be determined according to the method described in A1.1 of Appendix A. 5.1.3 Directional response of a hydrophone
The directional response of a hydrophone is determined for two purposes: first, as part of the method of characterizing the acoustic field described in clauses 7 and 8, in which case the directional response shall be determined at an appropriate acoustic operating frequency; and second, to derive the effective radius of the hydrophone sensitive element, in which case it shall be measured at the frequency given below: 3/agMHz and 10MHz, whichever is smaller,
where a is the geometric radius of the sensitive element in mrn. Note: This frequency is chosen to ensure that the directivity function consists of a single principal bee. The symmetry of the directional response shall comply with the requirements of GB4128. The directional response of a hydrophone shall be determined according to the following steps: The hydrophone is mounted on a bracket located in the far field of a unit circular ultrasonic transducer as described in 7.1.2. The transducer is operated in burst mode at the appropriate frequency for which the directional response is required. Keep the normal of the hydrophone sensitive element approximately parallel to the collimation axis of the sound beam, translate the hydrophone in the direction perpendicular to the collimation axis of the sound beam, and rotate the hydrophone around the two axes passing through the plane of the hydrophone sensitive element to maximize the received signal. The measurement of the signal received by the hydrophone is achieved using any of the two rotation axes through the plane of the sensitive element. The signal is the number of times the hydrophone is rotated at an angle of 0. The directional response is determined by dividing the signal received at a certain angle by the maximum received signal.
5.1.4 Effective radius of the hydrophone sensitive element The effective radius of the hydrophone sensitive element shall be determined by the following method: At the rate determined by the criteria given in 5.1.3, the directional response shall be determined according to the method briefly described in 5.1.3. Assuming that the sensitive element of the hydrophone is circular, its directivity function is roughly similar to that of the rigid disk receiver, which is: 2J(ka sino)
ka sing
Wu Zhong: J.--——Order-like Bessel function-Radius of the disk,
Angular wave number, rad.
At the maximum value of 3dB and 6dB, the values ​​of kasino are 1.62 and 2.22 respectively. The half-beam width of the measured directivity function is 9% and %, and the effective radius a3 and α can be determined by equations (4) and (5): 1.62
（4）
GB/T16540—1996
a ksing.
The effective radius of the hydrophone sensitive element is the arithmetic mean of α3 and α. (5)
For hydrophones with non-circular sensing elements, the above method can still be used to determine the approximate effective size in any specified direction. In this case, the axis of rotation used to measure the directional response is perpendicular to the specified direction. Strictly speaking, the above directivity function only applies to circular rigid elements, but it can also be applied to elements of other shapes with an error of less than 20%. 5.1.5 Selection of hydrophone sensing element size The selection of the effective radius of the hydrophone sensing element is determined by the following considerations: a) The effective radius of the sensing element should theoretically be less than 1/4 wavelength, so that changes in phase and amplitude have no significant effect on the measurement uncertainty.
Due to the wide variety of ultrasonic transducer types, it is impossible to establish a simple relationship between the optimal effective element size of the hydrophone and parameters such as the size of the ultrasonic transducer, the sound wavelength and the distance from the ultrasonic transducer. However, it is reasonable to relax the above requirements in the far field. For example, for circular ultrasonic transducers, the following criteria can be used to guide the determination of the maximum effective radius amax of the hydrophone sensing element. If the distance between the hydrophone and the ultrasonic transducer surface is l, then amax is: a
-(12 + ai)1/2
amax = 8ar
where: a1 is the effective radius of the ultrasonic transducer, m; the wavelength of the input sound wave, m.
(6)
For ultrasonic transducers with non-circular elements, a1 in the above formula is half of the maximum size of the ultrasonic transducer or ultrasonic transducer array element. b) Practical requirements for signal-to-noise ratio or other considerations may lead to the use of hydrophone elements larger than the above recommended sizes. In this case, the measurement results can be interpreted as the integral of the sound pressure on the sensitive element surface of the piezoelectric hydrophone. A deconvolution algorithm can be used to correct the spatial average, but the reliability of this approximation should be evaluated based on the change of the received signal with the position of the hydrophone. The following criterion should be used: when the hydrophone is translated from the position of maximum received signal in any direction perpendicular to the collimation axis of the sound beam by an amount equal to the radius of the sensitive element, the signal reduction should be less than 1 dB. Under these conditions, the spatial average correction is sufficiently accurate for most applications. Further correction may be achieved by using diffraction correction.
5.1.6 Bandwidth
When the nonlinear propagation parameter value exceeds 0.5 (see 8.1.9), the upper limit of the bandwidth shall be taken as the smaller of the frequency 3 octaves above the acoustic operating frequency or 40 MHz, within which the variation of the cable end sensitivity of the hydrophone or hydrophone-amplifier combination shall be less than ±6 dB.
5.1.7 Linearity
The upper limit of the linear dynamic range of the hydrophone shall be at least 1 MPa. 5.1.8 Hydrophone Amplifier
Hydrophone amplifiers shall meet the following performance requirements: For all amplifiers:
The variation of the gain of the hydrophone amplifier combination shall be less than ±6 dB within the range of 1 octave below to 3 octaves above the operating frequency.
The overall sensitivity of the hydrophone and amplifier combination shall vary by less than ±0.5 dB (Class A) and less than ±1 dB (Class B) at any 100kHz frequency increment within the bandwidth. The linearity of the amplifier shall be ±0.3 dB for a 50dB input signal dynamic range. The resistive input impedance shall introduce less than 0.3 dB correction to the hydrophone sensitivity in the range of 1 octave below the acoustic operating frequency to 3 octaves above the acoustic operating frequency (see A.1. of Appendix A).1). The correction introduced by the capacitive input impedance to the hydrophone sensitivity should be less than 2 dB in the range of 1 octave below the acoustic operating frequency to 3 octaves above the acoustic operating frequency.
The output impedance should be suitable for driving coaxial cable. GB/T 16540—1996
The noise measured when connected to the hydrophone should be low enough to enable measurements to be carried out with an appropriate signal-to-noise ratio at any frequency within the bandwidth considered.
Additional requirements for differential amplifiers:
In addition to the impedance measured between the two active inputs, the impedance requirements given above should apply. The common mode rejection ratio should be at least 40 dB in the frequency range of 1 octave below the acoustic operating frequency to 2 octaves above the acoustic operating frequency.
5.2 Requirements for positioning systems and water tanks
There are various possible systems for mounting ultrasonic transducers and hydrophones, such as the device shown in Appendix C. The general performance requirements for such a system are briefly described here and are considered to be optimal for the purposes of this standard. Other positioning systems may be used provided they are equivalent to the requirements described in this section. Figure 4 shows the configuration of the water tank, transducer and hydrophone and is intended to illustrate only the coordinate axes and degrees of freedom involved in this document. 5.2.1 Positioning system
5.2.1.1 Transducer positioning system
The ultrasonic transducer is mounted in the coordinate positioning system so that the axis of symmetry of its active element is parallel to the y-axis or z-axis of the hydrophone positioning system. The axis of symmetry for ultrasonic transducers with cylindrical active elements shall be the axis of the cylinder. For spherical ultrasonic transducers consisting of parts of a sphere, the axis of symmetry shall pass through the center of the sphere and the center of the dividing surface. For some spherical transducers consisting of a whole (or nearly whole) sphere and supported by small components such as tubes and rods, the axis of symmetry shall pass through the center of the sphere and the center of the supporting surface. The ultrasonic transducer shall be mounted in a manner that allows 360° rotation about the axis of symmetry. 5.2.1.2 Hydrophone Positioning System
The hydrophone shall be mounted on a micro-positioning system with the following degrees of freedom: Translation along three rectangular coordinate axes (αyz in Figure 4) One of the axes (designated as α axis) is perpendicular to the sensitive element. Note 1: After adjustment, the axis shall be parallel to the beam collimation axis. When describing the characteristics of the automatic scanning system, one of the other two translation axes of the hydrophone (designated as axis) shall be perpendicular to the scanning plane and the third axis shall be designated as axis.
There shall also be two rotational degrees of freedom, both of which shall be perpendicular to the direction of maximum sensitivity of the hydrophone, preferably through the sensitive element. One rotational axis shall be parallel to axis and the other to axis. All translational and rotational systems shall have position indicators. In the high frequency range of ultrasonic transducers, the most important thing is the repeatability of positioning. For most applications, a repeatability of ±0.01 mm at 15 MHz is suitable.
Note 2: Although the hydrophone is used as the element for scanning the whole sound field; in certain types of measurement situations with unit ultrasonic transducers, it is also possible to move or rotate the ultrasonic transducer instead of the hydrophone. 5.2.2 Water Tank
The dimensions of the water tank shall meet the requirements of relative movement between the ultrasonic transducer and the hydrophone with a sufficiently large margin, and during movement, the hydrophone sensitive element shall be able to be positioned at any position in the sound field required for measurement. For non-automatic scanning systems, the distance between the water tank wall and the ultrasonic transducer in the direction parallel to the collimation axis of the sound beam, or in the direction of the symmetry axis of the scanning plane for automatic scanning systems, shall be significantly greater than the maximum distance between the ultrasonic transducer and the hydrophone (e.g. 30% to 100%). For non-automatic scanning systems, the distance between the water tank wall and the ultrasonic transducer in the direction perpendicular to the collimation axis of the sound beam or in the direction perpendicular to the symmetry axis of the scanning plane for automatic scanning systems should be significantly greater than the maximum distance from the collimation axis of the sound beam of the non-automatic scanning system or from the outermost scanning line of the automatic scanning system to the hydrophone (e.g. 30% to 100%). The size of the hydrophone must also be considered. For diaphragm hydrophones, additional width must be required in the direction perpendicular to the collimation axis of the sound beam. Note: The above principles for selecting the size of the water tank apply to pulse durations less than 10us. For longer pulse durations, it must be ensured that the reflected waves at the boundaries do not affect the measurement of the direct waves.
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