A method for measuring acoustic nonlinear coefficient of materials using phase diagram

Abstract

The present invention discloses a method for measuring the acoustic nonlinear coefficient of a material using a phase diagram, which is to use finite amplitude ultrasound to perform nondestructive testing on materials with mechanical nonlinearity, use the displacement signal and sound pressure signal or the displacement signal and particle vibration velocity signal obtained by the detection to form a phase diagram, and then measure the acoustic nonlinear coefficient according to the characteristics of the phase diagram. The method of the present invention is simpler and can expand experimental conditions. The nonlinear coefficient can still be measured under conditions of a longer distance, stronger excitation, and a larger nonlinear coefficient, and the test result is more accurate; the applicable conditions of the present invention can be close to the location where the shock wave is generated.

Description

Technical Field

[0001] The invention relates to a method for measuring the acoustic nonlinear coefficient of a material, in particular to a method for measuring the acoustic nonlinear coefficient of a material by utilizing a phase diagram. Background Art

[0002] Compared with the second-order linear elastic parameters, the acoustic nonlinear coefficient is related to the higher-order elastic parameters of the material, and is more suitable for reflecting and evaluating the stress concentration, micro-damage, fatigue degree, etc. inside the material. It can also be used to detect the slight changes in mechanical properties caused by lesions in biological tissues. Imaging using the harmonics caused by this nonlinearity can not only improve the distinction between micro-damage or lesion tissues, but also improve the resolution of the image.

[0003] Generally, when limited amplitude ultrasound propagates in a material, it will excite high-order harmonics, and the received signal is a distorted nonlinear ultrasonic signal. Sometimes, two ultrasonic signals of different frequencies are used for simultaneous excitation, which will generate high-order harmonics and sum and difference frequency waves at the same time. The acoustic nonlinear coefficient of a material is often measured experimentally based on the amplitude formula of the second harmonic, and the amplitude of the second harmonic is compared with the amplitude of the fundamental frequency signal to obtain the acoustic nonlinear coefficient. However, since the amplitude formula of the second harmonic is obtained by solving the second-order perturbation expansion equation of the nonlinear acoustic wave equation, the expansion equations of the third order and above are ignored, which makes the amplitude formula of the second harmonic not accurate enough, so that this equation can only be relatively reliable under experimental conditions of small amplitude excitation and short-distance propagation. Under experimental conditions of high excitation amplitude, large nonlinear coefficient and long propagation distance, the use of this formula will cause large errors. Other related methods for measuring the acoustic nonlinear coefficient of materials are rarely reported. Sometimes, the KZK equation, Westervelt equation and Blackstock equation are used for experimental qualitative verification, but they are rarely used for quantitative measurement of nonlinear coefficients.

[0004] The acoustic nonlinear coefficient of a material is not necessarily important in itself. In nondestructive testing of materials and medical applications, the change in the relative nonlinear coefficient is what people are concerned about. The nonlinear coefficient obtained by the perturbation method is β = 8A2 / (A1 2 k 2 x), usually β'=A2 / A1 2 To replace the nonlinear coefficient, but because the displacement amplitude of the excitation signal is difficult to measure, it can be replaced by the voltage of the signal, which requires the sensitivity of the sensor to be close to the amplitude of the two frequencies. Summary of the invention

[0005] The purpose of the present invention is to provide a method for measuring the acoustic nonlinear coefficient of a material using a phase diagram. The method of the present invention is simpler and can expand the experimental conditions. The nonlinear coefficient can still be measured under the conditions of a longer distance, a stronger excitation, and a larger nonlinear coefficient, and the test result is more accurate; the applicable conditions of the present invention can be close to the location where the shock wave is generated.

[0006] The technical solution of the present invention is a method for measuring the acoustic nonlinear coefficient of a material using a phase diagram, which uses finite amplitude ultrasound to perform nondestructive testing on materials with mechanical nonlinearity, forms a phase diagram based on the displacement signal and sound pressure signal or the displacement signal and particle vibration velocity signal obtained by the detection, and then measures the acoustic nonlinear coefficient based on the characteristics of the phase diagram.

[0007] The aforementioned method for measuring the acoustic nonlinear coefficient of a material using a phase diagram comprises the following steps:

[0008] 1) A finite amplitude ultrasonic signal is excited at one end of the material and propagates in the material, then is received by a signal receiver at the other end of the material and transmitted to a signal recorder for recording;

[0009] 2) obtaining and converting a displacement signal and an acoustic pressure signal or a displacement signal and a particle vibration velocity signal according to the signal recorded in step 1), and then drawing a phase diagram using the displacement signal and the acoustic pressure signal or the displacement signal and the particle vibration velocity signal;

[0010] 3) The acoustic nonlinear coefficient of the material is calculated by the formula β = 4.7㏑(S1 / S2) / xP, where: β is the acoustic nonlinear coefficient, S1 / S2 is the ratio of the upper and lower phase diagram areas divided by the X axis or the ratio of the right and left phase diagram areas divided by the Y axis in the phase diagram, x is the ultrasonic propagation distance or the thickness of the material, and P is the sound pressure value.

[0011] In the aforementioned method of measuring the acoustic nonlinear coefficient of a material using a phase diagram, the finite amplitude ultrasonic signal in step 1) is a sinusoidal signal of at least 20 cycles.

[0012] In the aforementioned method of measuring the acoustic nonlinear coefficient of a material using a phase diagram, the finite amplitude ultrasonic signal in step 1) is generated by transmitting the electrical signal generated by a signal generator to a power amplifier, amplifying it, and then applying it to an ultrasonic sensor.

[0013] The aforementioned method of measuring the acoustic nonlinear coefficient of a material using a phase diagram, step 1) the material is a fluid, the signal receiver is a sound pressure receiver, the received signal is a sound pressure signal P, and then the particle vibration velocity signal v is converted by the formula P=zv, where: z is the acoustic impedance of the material; the displacement signal is obtained by numerically integrating the particle vibration velocity signal v with respect to time.

[0014] In the aforementioned method of measuring the acoustic nonlinear coefficient of a material using a phase diagram, step 1) the material is solid, the signal receiver is an ultrasonic sensor, the received signal is a displacement signal, and the particle vibration velocity signal is obtained by numerically derivatizing the displacement signal with respect to time.

[0015] In the aforementioned method of measuring the acoustic nonlinear coefficient of a material using a phase diagram, the signal recorder in step 1) is an oscilloscope or a computer.

[0016] Beneficial effects of the present invention

[0017] The present invention processes the nonlinear ultrasonic signal obtained by detecting the nonlinear dielectric material to obtain a nonlinear phase diagram of displacement and sound pressure or displacement and particle vibration velocity. When the signal is strengthened from linear to nonlinear, such as the nonlinear coefficient increases, the excitation signal increases, the propagation distance becomes larger, etc., the phase diagram will evolve from an ellipse to an irregular ellipse or egg shape, and become more and more irregular. That is, the area ratio of the right and left sides of the ellipse gradually changes from 1, and the change trend is related to the nonlinear coefficient. The acoustic nonlinear coefficient of the material can be obtained by calculation through a fitting formula.

[0018] Compared with the traditional method of characterizing the nonlinear coefficient using the relative amplitude of the second harmonic, the technical solution of the present invention is simpler and can expand the experimental conditions. The acoustic nonlinear coefficient can still be measured under conditions of greater distance, stronger excitation, and larger nonlinear coefficient, and the test results are more accurate. The applicable conditions of the present invention can be close to the location where the shock wave is generated.

[0019] Combining the advantages of high accuracy and non-destructive measurement of the present invention, in terms of non-destructive testing and evaluation, micro-damage inside the material can be detected, and even phases in the material, such as segregation, can be evaluated. In medicine, local biological tissue lesions can be detected, and the changes in the acoustic nonlinear coefficient caused by the changes in mechanical properties caused by the changes can be used to detect the lesions and their locations early by measuring the acoustic nonlinear coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attached Figure 1 The phase diagram of changing the excitation amplitude in Example 1, wherein the fourth line from the inside to the outside has exceeded the position where the shock wave is generated, the solid line is the theoretical result, and the scattered points are the experimental results;

[0021] Attached Figure 2 It is a phase diagram of changing the propagation distance in Example 1. The line from left to right is the case where the propagation distance increases. The solid line is the theoretical result, and the scattered points are the experimental results. All measurements do not exceed the shock wave generation position.

[0022] Attached Figure 3 This is a framework diagram of the measurement method described in Example 1. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0024] Embodiments of the present invention

[0025] Embodiment 1:

[0026] A method for measuring the acoustic nonlinear coefficient of a material using a phase diagram, wherein the measured material is water, and the steps are as follows:

[0027] 1) Input the 20-cycle sinusoidal signal generated by the signal generator with an amplitude of 5.0Vpp (which can be adjusted as needed) and a main frequency of 2.25MHz (related to the main frequency of the ultrasonic sensor) into the power amplifier (gain: 50dB), and output it to the ultrasonic sensor with a main frequency of 2.25MHz placed in the water. After the ultrasonic sensor generates an ultrasonic signal, it propagates in the water and is received by the hydrophone placed in the water and controlled by the 3D position controller, and then transmitted to the oscilloscope or computer for recording; the device framework diagram is shown in Figure 3. At the same time, the experimental device can be a commercial experimental system that includes a signal generator, an amplifier, a filter, etc.

[0028] 2) The signal received by the hydrophone in step 1) is a voltage signal, which is converted into a sound pressure signal P through the sensitivity of the hydrophone, and then converted into a particle vibration velocity signal v through P=zv, where: z is the acoustic impedance of water.

[0029] 3) After numerically integrating the particle vibration velocity signal v obtained in step 2) with respect to time, a displacement signal is obtained, and the displacement signal and the particle vibration velocity signal v are plotted into a phase diagram, where the horizontal axis is the displacement and the vertical axis is the sound pressure or particle vibration velocity.

[0030] 4) Calculate the numerical area of ​​the right and left sides or the upper and lower sides of the phase diagram drawn in step 3), and calculate the ratio S1 / S2 of the right and left or upper and lower areas.

[0031] 5) Change the propagation distance, repeat steps 1)-4), and measure the area ratio S1 / S2 of the phase diagram multiple times.

[0032] 6) Change the excitation amplitude, repeat steps 1)-4), and measure the area ratio S1 / S2 of the phase diagram multiple times.

[0033] 7) The acoustic nonlinear coefficient β of the material is obtained using the formula β = 4.7㏑(S1 / S2) / xP, where x is the propagation distance or sample thickness (in m), and P is the excitation sound pressure value (in bar, or 10 5 Pa). In order to obtain the nonlinear coefficient more accurately, the results of multiple measurements can be used to make small corrections to the constant coefficients in the formula to minimize the relative error between them, and then the nonlinear coefficient can be calculated more accurately.

[0034] The nonlinear coefficient of water measured in this experimental example is 3.46, which is very close to 3.5 in the literature, and the propagation distance is also close to the location where the shock wave is generated.

[0035] Embodiment 2:

[0036] A method for measuring the acoustic nonlinear coefficient of a material using a phase diagram, wherein the material is solid metal aluminum, comprising the following steps:

[0037] 1) Input the 20-cycle sinusoidal signal generated by the signal generator with an amplitude of 5.0Vpp (which can be adjusted as needed) and a main frequency of 2MHz (related to the main frequency of the ultrasonic sensor) into the power amplifier (gain: 50dB), and output the ultrasonic sensor with a main frequency of 2MHz on one side of the flat aluminum block. After the sensor generates an ultrasonic signal, it propagates in the aluminum block and is received by the broadband ultrasonic sensor placed on the other side of the aluminum block and transmitted to an oscilloscope or computer for recording. The broadband ultrasonic sensor frequency can at least cover the fundamental frequency and the second harmonic frequency. At the same time, the experimental device can be a commercial experimental system that includes a signal generator, an amplifier, a filter, etc.

[0038] 2) The signal measured in step 1) is a displacement signal. The displacement is numerically differentiated with respect to time to obtain a particle vibration velocity signal v, which is converted into an acoustic pressure signal P through P=zv, where: z is the acoustic impedance of aluminum. The measured displacement and the derivative particle vibration velocity are plotted into a phase diagram, with the horizontal axis being the displacement signal and the vertical axis being the particle vibration velocity signal.

[0039] 3) Calculate the numerical area of ​​the right and left sides or the upper and lower sides of the phase diagram drawn in step 2), and calculate the ratio S1 / S2 of the right and left or upper and lower areas.

[0040] 4) Change the excitation amplitude, repeat steps 1)-3), and measure the ratio S1 / S2 of the right-left or top-bottom area of ​​the phase diagram multiple times.

[0041] 5) The nonlinear coefficient β of the material is calculated using the formula β = 4.7㏑(S1 / S2) / xP, and a small correction of the coefficient 4.7 is made to make the results of multiple measurements closest, so that the acoustic nonlinear coefficient is calculated to be stable, where x is the thickness of the aluminum block and P is the converted excitation sound pressure in step 2).

[0042] The nonlinear coefficient of aluminum measured in this embodiment is 6.92, which is very close to 7.0 in the literature.

[0043] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for measuring the acoustic nonlinear coefficient of a material using a phase diagram, characterized in that: The method comprises the following steps: 1) A finite amplitude ultrasonic signal is excited at one end of the material and propagates in the material, then is received by a signal receiver at the other end of the material and transmitted to a signal recorder for recording; 2) obtaining and converting a displacement signal and an acoustic pressure signal or a displacement signal and a particle vibration velocity signal according to the signal recorded in step 1), and then drawing a phase diagram using the displacement signal and the acoustic pressure signal or the displacement signal and the particle vibration velocity signal; 3) The acoustic nonlinear coefficient of the material is calculated by the formula β = 4.7㏑(S1 / S2) / xP, where: β is the acoustic nonlinear coefficient, S1 / S2 is the ratio of the upper and lower phase diagram areas divided by the X axis or the ratio of the right and left phase diagram areas divided by the Y axis in the phase diagram, x is the ultrasonic propagation distance or the thickness of the material, and P is the sound pressure value.

2. The method for measuring the acoustic nonlinear coefficient of a material using a phase diagram according to claim 1, characterized in that: In step 1), the finite amplitude ultrasonic signal is a sinusoidal signal of at least 20 cycles.

3. The method for measuring the acoustic nonlinear coefficient of a material using a phase diagram according to claim 1, characterized in that: In step 1), the limited amplitude ultrasonic signal is generated by transmitting the electrical signal generated by the signal generator to the power amplifier, amplifying it and then applying it to the ultrasonic sensor.

4. The method for measuring the acoustic nonlinear coefficient of a material using a phase diagram according to claim 1, characterized in that: Step 1) The material is a fluid, the signal receiver is a sound pressure receiver, the received signal is a sound pressure signal P, and then the particle vibration velocity signal v is converted by the formula P=zv, where: z is the acoustic impedance of the material; the displacement signal is obtained by numerically integrating the particle vibration velocity signal v with respect to time.

5. The method for measuring the acoustic nonlinear coefficient of a material using a phase diagram according to claim 1, characterized in that: Step 1) The material is solid, the signal receiver is an ultrasonic sensor, the received signal is a displacement signal, and the particle vibration velocity signal is obtained by numerically derivatizing the displacement signal with respect to time.

6. The method for measuring the acoustic nonlinear coefficient of a material using a phase diagram according to claim 1, characterized in that: Step 1) The signal recorder is an oscilloscope or a computer.

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