A method for measuring the acoustic nonlinear coefficient of a material using phase relationships

Abstract

The present invention discloses a method for measuring the acoustic nonlinear coefficient of a material by using the phase relationship. It uses finite-amplitude ultrasound to perform non-destructive testing on a material with mechanical nonlinearity, performs Hilbert transform processing on the detected and / or calculated displacement signal or particle vibration velocity signal to obtain the phase of the nonlinear signal, and then obtains the normalized angular frequency through numerical calculation, so as to measure the acoustic nonlinear coefficient according to the maximum value of the normalized angular frequency. The method of the present invention is simpler, and can expand the experimental conditions. The nonlinear coefficient can still be measured under conditions of longer distance, stronger excitation, and larger nonlinear coefficient, and the test results are more accurate; the applicable conditions of the present invention can approach the generation position of the shock wave.

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 relationship. 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 finite 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 frequencies at the same time. The experimental measurement of the nonlinear coefficient of a material is often 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 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 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 object of the present invention is to provide a method for measuring the acoustic nonlinear coefficient of a material using the phase relationship. 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 longer 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 generation position of the shock wave.

[0006] The technical solution of the present invention: A method for measuring the acoustic nonlinear coefficient of a material using the phase relationship is to perform non-destructive testing on a material with mechanical nonlinearity using finite-amplitude ultrasound, perform Hilbert transform processing on the detected and / or calculated displacement signal or particle vibration velocity signal to obtain the phase of the nonlinear signal, and then obtain the normalized angular frequency through numerical calculation, so as to measure the acoustic nonlinear coefficient of the material according to the maximum value of the normalized angular frequency.

[0007] The method for measuring the acoustic nonlinear coefficient of a material using the phase relationship described above includes the following steps:

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

[0009] 2) Obtain or calculate the displacement signal, sound pressure or particle vibration velocity signal according to the signal recorded in step 1), then perform Hilbert transform on the displacement signal or particle vibration velocity signal, and then obtain the normalized angular frequency of the nonlinear signal through numerical calculation. Take the maximum value among them to obtain the maximum value N of the normalized angular frequency of the nonlinear signal max ;

[0010] 3) Use the normalized angular frequency of the displacement signal and according to the formula β = 4.7ln(1 + 25lg(N max )) / xP, or use the normalized angular frequency of the particle vibration velocity and according to the formula β = 1.4ln(1 + 15lg(N max )) / xP to obtain the acoustic nonlinear coefficient β of the material; where: x is the ultrasonic propagation distance or the thickness of the material, and P is the sound pressure value.

[0011] In the method for measuring the acoustic nonlinear coefficient of a material using the phase relationship described above, the finite-amplitude ultrasonic signal in step 1) is at least a 20-cycle sine signal.

[0012] In the method for measuring the acoustic nonlinear coefficient of a material using the phase relationship described above, 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 the voltage and then applying it to an ultrasonic sensor.

[0013] In the above method for measuring the acoustic nonlinear coefficient of a material using the phase relationship, in step 1), the material is a fluid, the signal receiver is an acoustic pressure receiver, the received signal is an acoustic pressure signal P, and then the particle vibration velocity signal v is converted through 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 above method for measuring the acoustic nonlinear coefficient of a material using the phase relationship, in step 1), the material is a solid, the signal receiver is an ultrasonic sensor, the received signal is a displacement signal, the particle vibration velocity signal v is obtained by numerically differentiating the displacement signal with respect to time, and the acoustic pressure signal P is obtained by conversion through the formula P = zv, where z is the acoustic impedance of the material.

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

[0016] In the above method for measuring the acoustic nonlinear coefficient of a material using the phase relationship, in step 2), the maximum value N of the normalized angular frequency max is obtained as follows: First, perform a Hilbert transform on the displacement signal or the particle vibration velocity signal to obtain a phase from -π to π; then perform unwrapping on the phase and numerically differentiate with respect to time. The numerical differentiation with respect to time is to divide the differentiated unwrapped signal by the time step, and finally divide by the angular frequency of the excitation signal to obtain the normalized angular frequency, and take the maximum value among them to obtain the maximum value N of the normalized angular frequency. max .

[0017] Advantages of the present invention

[0018] The present invention performs Hilbert transform processing on the nonlinear ultrasonic signal obtained by detecting the nonlinear medium material to obtain the phase of displacement or particle vibration velocity. When the signal strengthens from linear to nonlinear, such as when the nonlinear coefficient increases, the excitation signal increases, and the propagation distance is suitable, etc., the normalized angular frequency in the phase relationship will evolve from a completely straight line to a non-uniform signal with periodic changes, and the nonlinear phenomenon tends to be more obvious, and the greater the maximum value of the normalized angular frequency. The nonlinear coefficient can be calculated based on this change trend, and thus the acoustic nonlinear coefficient of the material can be obtained by calculating relevant parameters through a fitting formula. The solution of the present invention is simpler, and the experimental conditions can be extended. The acoustic nonlinear coefficient of the material can still be measured under conditions of longer 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 generation position of the shock wave.

[0019] Combined with the advantages of high precision and non-destructive measurement of the present invention, in non-destructive testing and evaluation, micro-damage inside materials can be detected, and even phases in materials, such as segregation, can be evaluated. In medicine, local biological tissue lesions can be detected. By using the change in the acoustic non-linear coefficient caused by the change in mechanical properties caused by the lesions, through the measurement of the non-linear coefficient, the lesions and their locations can be detected early. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attached Figure 1 is the normalized angular frequency at different excitation amplitudes calculated using the displacement signal, indicating that as the excitation amplitude increases, the non-linearity becomes more obvious and the maximum value of the normalized angular frequency also increases; the lines of three colors represent three excitation amplitudes respectively, the solid line is the simulation calculation result, and the scatter points are the experimental results.

[0021] Attached Figure 2 is the framework diagram of the measurement method described in Embodiment 1. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be further described below in conjunction with embodiments, but it is not used as a basis for limiting the present invention.

[0023] Embodiments of the present invention

[0024] Embodiment 1:

[0025] A method for measuring the acoustic non-linear coefficient of a material using the phase relationship, wherein the material is liquid water, and the measurement steps are as follows:

[0026] 1) Input the 20-cycle sine electrical signal 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) generated by the signal generator into the power amplifier (gain: 50dB), and output it to the ultrasonic sensor with a main frequency of 2.25MHz placed in water. After the sensor generates an ultrasonic signal, it propagates in water and is received by the hydrophone whose position is controlled by the 3D position controller and transmitted to the oscilloscope or computer for recording; the framework diagram of the device is as Figure 2 shown. At the same time, the experimental device can be a commercial experimental system including a signal generator, an amplifier, a filter, etc.

[0027] 2) The voltage signal received by the hydrophone in step 1) 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 the propagation medium. After the particle vibration velocity signal v is numerically integrated with respect to time, a displacement signal is obtained.

[0028] 3) Perform a Hilbert transform on the displacement signal (or the particle vibration velocity signal) to obtain the phase of the non-linear signal, perform unwrapping, and then divide by the time step and the angular frequency of the excitation signal to obtain the normalized angular frequency, and obtain the maximum value N of the normalized angular frequency. max 。

[0029] 4) Change the measurement position and repeat steps 1)-3) to measure the maximum value N of the normalized angular frequency multiple times. max 。

[0030] 5) Change the excitation amplitude and repeat steps 1)-3) to measure the maximum value N of the normalized angular frequency multiple times. max 。

[0031] 6) Use the maximum value N of the normalized angular frequency of the particle vibration velocity signal max and calculate according to β = 1.4ln(1 + 15lg(N max ) ) / xP, where x is the ultrasonic propagation distance or the thickness of the material (unit: m), P is the excitation sound pressure value (unit: bar, or 10 5 Pa), and the obtained acoustic non-linear coefficient is 3.48. To obtain the acoustic non-linear coefficient more accurately, the constant coefficient in the formula can be slightly corrected using the results of multiple measurements to minimize the relative error, and then the non-linear coefficient is calculated more accurately.

[0032] Example 2:

[0033] A method for measuring the acoustic non-linear coefficient of a material using the phase relationship, the material being solid aluminum, the steps being as follows:

[0034] 1) Input the electrical signal of a 20-cycle sine signal with a main frequency of 2 MHz (related to the main frequency of the ultrasonic sensor) and an amplitude of 5.0 Vpp generated by a signal generator into a power amplifier (gain: 50 dB), and output it to an ultrasonic sensor with a main frequency of 2 MHz on one side of a flat aluminum block. After the sensor generates an ultrasonic signal, it propagates in the aluminum block and is received by a broadband ultrasonic sensor placed on the other side of the aluminum block and transmitted to an oscilloscope or a computer for recording. The broadband ultrasonic sensor needs to cover at least the fundamental frequency and the second harmonic frequency.

[0035] 2) The ultrasonic sensor in step 1) receives a displacement signal, and numerically differentiates the time to obtain the particle vibration velocity signal v.

[0036] 3) Perform a Hilbert transform on the displacement signal (or the particle vibration velocity signal) to obtain the phase of the non-linear signal, perform unwrapping, and then divide by the time step and the angular frequency to obtain the normalized angular frequency, and obtain the maximum value N of the normalized angular frequency. max 。

[0037] 4) Change the excitation amplitude and repeat steps 1)-3) to measure the maximum value N of the normalized angular frequency multiple times. max .

[0038] 5) Use the maximum value of the normalized angular frequency signal of the displacement signal and obtain the material nonlinear coefficient according to β = 4.7ln(1 + 25lg(N max )) / xP, where: x is the ultrasonic propagation distance or the thickness of the material, P is the converted excitation sound pressure value, where P is converted through P = zv, v is the particle vibration velocity signal, and z is the acoustic impedance of the propagation medium. To obtain the nonlinear coefficient more accurately, the constant coefficient in the formula can be slightly corrected using the results of multiple measurements to minimize the relative error between them, and then the nonlinear coefficient can be calculated more accurately.

[0039] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A method for measuring the acoustic nonlinear coefficient of a material using phase relationships, characterized in that, The method includes the following steps: 1) Use finite-amplitude ultrasound to perform non-destructive testing on materials with mechanical non-linearity. Excite a finite-amplitude ultrasound signal at one end of the material, and let it propagate in the material, and then be received by a signal receiver set at the other end of the material and transmitted to a signal recorder for recording; 2) Obtain or calculate the displacement signal, sound pressure or particle vibration velocity signal based on the signal recorded in step 1), then perform Hilbert transform on the displacement signal or particle vibration velocity signal, and then obtain the normalized angular frequency of the non-linear signal through numerical calculation, and take the maximum value among them to obtain the maximum value of the normalized angular frequency of the non-linear signal N max ; Among them, the process of obtaining the maximum value of the normalized angular frequency N max is as follows: First, perform Hilbert transform on the displacement signal or particle vibration velocity signal to obtain the phase from -π to π; then perform unwrapping on the phase and then take the derivative with respect to the time value. Taking the derivative with respect to the time value is to divide the differentiated signal after unwrapping by the time step, and finally divide by the angular frequency of the excitation signal to obtain the normalized angular frequency, and take the maximum value among them as the maximum value of the normalized angular frequency N max ; 3) Using the normalized angular frequency of the displacement signal and according to the formula , or using the normalized angular frequency of the particle vibration velocity and according to the formula to obtain the acoustic nonlinear coefficient β of the material; where: x is the ultrasonic propagation distance or the thickness of the material, P is the sound pressure signal.

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

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

4. The method for measuring the acoustic nonlinear coefficient of a material using the phase relationship according to claim 1, characterized in that: Step 1) The material is a fluid, and the signal receiver is usually a sound pressure receiver, and the received signal is a sound pressure signal P , and then through the formula P = zv to convert the particle vibration velocity signal v, 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 relationship according to claim 1, characterized in that: Step 1) The material is solid, and the signal receiver is an ultrasonic sensor. If the received signal is a displacement signal, the particle vibration velocity signal v is obtained by numerically differentiating the displacement signal with respect to time, and the sound pressure signal P is obtained through the formula P = zv, where z is the acoustic impedance of the material.

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

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