Acoustics--Methods for measuring the longitudinal sound speed and attenuation coefficient of rubbers and plastics in the frequency range 1 MHz to 10 MHz
Some standard content:
GB/T 18022—2000
Rubber, plastics and composite materials based on them are commonly used materials in acoustic engineering and are also important research objects in the field of acoustics. Their acoustic property data are valuable basic data. This standard is specially formulated to make the measurement data comparable for communication and use.
Appendix A of this standard is the appendix of the standard.
Appendix B of this standard is the appendix of the suggestion and is for reference only. This standard is proposed by the Chinese Academy of Sciences.
This standard is under the jurisdiction of the National Technical Committee for Acoustics Standardization. The drafting unit of this standard: Institute of Acoustics, Chinese Academy of Sciences. Main drafters of this standard: Niu Fengqi, Zhu Chenggang, Cheng Yang
National Standard of the People's Republic of China
Acoustics--Methods for measuring the longitudinal sound speedand attenuation coefficient of rubbers and plastics in thefrequency range 1 MHz to 10 MHz1 Scope
GB/T18022--2000
This standard specifies the measurement methods for the longitudinal sound speed and attenuation coefficient of rubbers and plastics and composite materials based on them. The applicable frequency range of this standard is 1 to 10 MHz. 2 Referenced standards
The provisions contained in the following standards 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. GB3102.7--1993 Acoustic quantities and units GB/T3947-1996 Acoustic terminology
GB/T.4472--1984 General rules for determination of density and relative density of chemical products 3 Measurement principle
3.1 In this standard, the sound velocity and sound attenuation coefficient are measured using the insertion substitution method. In the test water tank, the sample of the material to be tested is inserted into the plane wave sound beam path between the transmitting transducer and the receiving transducer, and it is made to replace the same length of water. The sound velocity and sound attenuation coefficient of the material are measured by means of the changes in the propagation time and amplitude of the sound pulse signal before and after the sample is inserted, as shown in Figure 1. Cheek pulse
Generator
Deaerated distilled water
Transmitting transducer
Oscilloscope
Receiving transducer
Figure 1 Block diagram of the measurement principle of the insertion substitution method
Approved by the State Administration of Quality and Technical Supervision on March 16, 2000 and implemented on December 1, 2000
3.2 Sound velocity measurement
GB/T 18022—2000
Measured by the insertion substitution method. The constant temperature water tank is filled with deaerated distilled water. The distance between the transmitting and receiving transducers is not greater than the near field length of the transmitting transducer to ensure that the sample under test is in the plane beam acoustic field of the transmitting transducer. The RF pulse generator excites the transmitting transducer with an electric pulse to generate an acoustic pulse that radiates into the water, which is received by the receiving transducer and sent to the oscilloscope for display. If the sample to be tested is inserted between the transmitting and receiving transducers, the propagation time of the acoustic pulse will change, from which the sound velocity in the sample material can be obtained: dcw
Where: c-—sound velocity in the sample material, m/s; d——sample thickness, m;
t——change in the propagation time of the acoustic pulse caused by the insertion of the sample (a negative value is taken when the time is shortened, i.e. the pulse waveform moves forward, and a positive value is taken when the time is extended, i.e. the pulse waveform moves backward), s;
Cu--sound velocity in water, m/s.
3.3 Measurement of acoustic attenuation coefficient
Measurement is carried out by the insertion substitution method, as shown in Figure 1. When a sample is inserted into the plane wave acoustic beam path between the transmitting and receiving transducers, the amplitude of the acoustic pulse displayed by the oscilloscope will change, from which the acoustic attenuation coefficient of the sample material can be obtained. The measurement can be carried out by the single sample method or the double sample method.
3.3.1 Single sample method
Using a sample of a certain thickness, when no standing wave appears in the sample and the influence of acoustic attenuation and beam expansion in water can be ignored, the calculation formula for the acoustic attenuation coefficient of the sample material is:
201og A
Where: α—acoustic attenuation coefficient of the sample material, dB/m; d-sample thickness, m;
A. ——received pulse amplitude before inserting the sample, V; A—received pulse amplitude after inserting the sample, V; 0
—sample material density, kg/m,
-sound velocity in the sample material, m/s;
P-water density, kg/m,
sound velocity in water, m/s.
3.3.2 Double sample method
(pc + Pwcu)
4pcpwca
·（2)
Two samples of different thicknesses are inserted successively in the plane wave acoustic beam path between the transmitting and receiving transducers. When no standing wave appears in the sample and the influence of acoustic attenuation and acoustic beam expansion in water can be ignored, the calculation formula for the acoustic attenuation coefficient of the sample material is: 20
d, -- d,
Where: α is the acoustic attenuation coefficient of the sample material, dB/m; di is the thickness of the thick sample, m;
dz is the thickness of the thin sample, m,bzxz.net
A is the amplitude of the received pulse when the thick sample is inserted, V; A2 is the amplitude of the received pulse when the thin sample is inserted, V. 4 Requirements for measuring equipment and samples
4.1 Instruments and equipment
4.1.1 Vernier caliper: The minimum scale should not exceed 0.02mm. 424
(3)
GB/T 18022—2000
4.1.2 Micrometer: The minimum scale should not exceed 0.002mm. 4.1.3 Thermometer: The resolution should reach 0.1℃. 4.1.4 Balance: The sensitivity should not exceed 0.001g. 4.7.5 RF pulse generator:
Frequency range: 1~10MHz;
Pulse width: 1~30us;
Repetition frequency: 50~200Hz;
Pulse amplitude (peak-to-peak): Continuously adjustable, the maximum value is not less than 100V; Amplitude variation: ±0.05dB.
4.1.6 Oscilloscope
Bandwidth: 0~40MHz;
Sensitivity: better than 5mV/div;
Time axis error: ±3%;
Amplitude axis error: ±3%.
4.1.7 Transducer: Generally, a piezoelectric ceramic transducer with a flat circular radiation surface is used. The diameter of the piezoelectric ceramic disc should be much larger than its thickness (generally not less than 10 times) to meet the requirement that the radiation surface is piston vibration. The operating frequency is in the range of 1~10MHz, which can be met by multiple pairs of transducers.
4.1.8 Water tank: The size of the water tank should be large enough to ensure that the reflected wave does not affect the measurement of the direct pulse. 4.2 Sample: The lateral size should be greater than twice the effective diameter of the transducer, the thickness should be greater than 10 wavelengths, and the non-parallelism of the two surfaces should not exceed 0.02 mm.
5 Measurement steps
5.1 Sound velocity measurement
5.1.1 Place the sample in a test water tank filled with degassed distilled water, keep the temperature fluctuation within ±0.1℃, keep the predetermined temperature constant for more than 1h, make the sample surface fully wetted and free of bubbles, and measure the water temperature with a precision thermometer. 5.1.2 Adjust the output of the RF pulse generator to an appropriate amplitude, observe the waveform of the oscilloscope, adjust the clamping system of the transducer, make the amplitude of the first received signal maximum, ensure that the radiation surfaces of the transmitting and receiving transducers are parallel, and the acoustic axis is aligned. 5.1.3 Take a narrow pulse and make it have an obvious maximum value at the center, and measure its frequency with an oscilloscope. 5.1.4. Insert the sample between the two transducers, adjust the scanning range and delay trigger of the oscilloscope, so that the time resolution of the received signal waveform before and after the sample is inserted is large enough.
5.1.5 Select the peak of the maximum value or the zero crossing point in the received pulse as the mark position, and use the electronic cursor of the oscilloscope to measure the time difference t before and after the sample is inserted.
5.1.6 Use a vernier caliper or micrometer to measure the sample thickness d under water temperature conditions. 5.1.7 Obtain the sound velocity cw in distilled water at the measurement temperature from Appendix A. 5.1.8 Substitute the relevant values into formula (1) to obtain the sound velocity c in the sample material. 5.2 Measurement of acoustic attenuation coefficient
5.2.1 The measurement preparation work is the same as 5.1.1 and 5.1.2. 5.2.2 Adjust the output of the RF pulse generator so that the received signal contains 15~~18 sine waves, and use a digital oscilloscope to measure its frequency. 5.2.3 Measure using the single sample method
5.2.3.1 Adjust the output of the RF pulse generator so that the transmission signal amplitude is appropriate when the sample is inserted. Use the electronic cursor of the oscilloscope to measure the amplitude A of the first received pulse before and after the sample with a thickness of d is inserted. and A. 5.2.3.2 Use a vernier caliper or a dry ruler to measure the sample thickness d under water temperature conditions. 5.2.3.3 From Appendix A, find the density P of water and the sound velocity cwc425
GB/T 18022—2000
5.2.3.4 Use the method in GB/T4472 to measure the density p of the sample material. 5.2.3.5 Substitute the relevant values into formula (2) to obtain the acoustic attenuation coefficient α of the sample material. 5.2.4 Measurement using the double sample method
5.2.4.1 Adjust the output of the RF pulse generator so that the transmission signal amplitude is appropriate when inserting a thicker sample. Use the electronic cursor of the oscilloscope to measure the first received pulse amplitude Ai and A2 when inserting a sample with a thickness of d, and d2. 5.2.4.2 Use a vernier caliper or micrometer to measure the sample thickness, and d2 at water temperature. 5.2.4.3 Substitute the relevant values into formula (3) to calculate the acoustic attenuation coefficient α of the sample material. 6 Measurement error
6.1 Sound velocity measurement
6.1.1 Measure in accordance with the requirements specified in this standard. For the same material, the error in sound velocity measurement decreases monotonically with the increase of sample thickness. 6.1.2 Measure in accordance with the requirements specified in this standard. For samples of the same thickness, the closer the sound velocity of the material is to the sound velocity in water, the smaller the error in sound velocity measurement.
6.2 Measurement of sound attenuation coefficient
6.2.1 The measurement is carried out in accordance with the requirements specified in this standard. For the same material, the error of the sound attenuation coefficient measurement decreases monotonically with the increase of the sample thickness (single sample method) or the thickness difference (double sample method). 6.2.2 The measurement is carried out in accordance with the requirements specified in this standard. When the sample thickness (single sample method) or the thickness difference (double sample method) is the same, the error of the sound attenuation coefficient measurement decreases monotonically with the increase of the material sound attenuation coefficient. 6.3 The formula for calculating the error is shown in Appendix B.
Temperature T
GB/T18022--2000
Appendix A
(Appendix to the standard)
Density and sound velocity of degassed distilled water in the temperature range of 0 to 100℃Table Al
Density and sound velocity of degassed distilled water in the temperature range of 0 to 100℃Density.
Temperature T
Density.
Sound velocity.
GB/T 18022—2000
Appendix B
(Suggested Appendix)
Calculation formula for sound velocity and attenuation coefficient measurement error 1, a2,…,α,…,, are directly measured quantities, y is the derived quantity, and B1
y= f(αi+a,,αi,,α.)
The formula for its relative error is:
Based on this, the expression for the relative error of sound velocity measurement in this standard can be derived: (Ax)
/cu-c)r/△d)2
The expression for the relative error of sound attenuation coefficient measurement by single sample method: (At)
[会\+(会)
《()+[()】
The expression for the uncertainty of sound attenuation coefficient measurement by double sample method: Aa
f(Ad,)2 +(△d2)2
(d, -d,)2
【+（会】）
α(d, - d,)\Ll A,
Table B1 and B2 are examples of systematic errors in the measurement of sound velocity and attenuation coefficient. B2
Table B1 Systematic Error in Sound Velocity Measurement
Sample Name
Organic Glass
Polyurethane Rubber
Note: The sample thickness error △d is taken from the minimum scale of the vernier caliper, and the propagation time difference △t/t is based on the instruction manual of the digital oscilloscope. Table B2
Sample name
Organic glass
Polyurethane rubber
Systematic error in attenuation coefficient measurement
·(B1)
·(B3)
··（B4）
（B5）
1The sample thickness error Ad is taken from the minimum scale of the vernier caliper, and the propagation time difference and amplitude error At/t and AA:/A.△A2/A2 are based on the instruction manual of the digital oscilloscope.
2When calculating the α measurement error, the dB in this unit must be converted to NP. 428
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