Harmonic imaging and impedance matching echo-PIV measurement method and system

Abstract

The invention provides an echo-PIV measurement method and system for harmonic imaging and impedance matching, and belongs to the fluid mechanics and acoustic measurement technology. According to the method, suspension liquid with acoustic impedance matching is configured, an ultrasonic microbubble contrast agent is added into the suspension liquid, an ultrasonic probe is used for emitting adjacent pulses with the phase difference of 180 degrees, double-frequency signals are reserved through a high-pass filter, low-intensity signals are removed through threshold value filtering processing, and finally instantaneous photos of adjacent flow fields are processed through a cross-correlation algorithm. And instantaneous velocity field information of the suspension flow field is obtained. According to the echo-PIV measuring method and system for harmonic imaging and impedance matching, the measurable volume fraction of the suspension liquid is improved, and the method can be applied to measurement of industrial suspension liquid.

Description

Technical Field

[0001] The present invention relates to the technical field of fluid mechanics and acoustic measurement, and in particular to an echo-PIV measurement method and system for harmonic imaging and impedance matching. Background Art

[0002] Since the suspended particles are opaque themselves, the light transmittance of the suspension decreases rapidly with the increase of the volume fraction. The traditional optical PIV method can only be used to measure the internal flow field of suspensions with a volume fraction less than 0.1%. The key parameters for suspension measurement include volume fraction, particle size ratio, and density ratio. An increase in the volume fraction means a decrease in the particle spacing, and a decrease in the particle size ratio means that more particle-liquid interfaces need to be penetrated. The number of penetrated particle-liquid interface layers is approximately equal to twice the measurement penetration depth divided by the particle spacing. Therefore, the core problem in the development of suspension measurement technology is how to increase the number of penetrable particle-liquid interface layers while ensuring the signal-to-noise ratio.

[0003] Currently, the main measurement methods for the flow field of solid-liquid two-phase flow suspensions are the optical PIV method and the ultrasonic echo-PIV method. The optical PIV measurement method is to configure a solid-liquid two-phase suspension with refractive index matching, and use a high-speed camera to continuously capture the flow field area illuminated by a plane laser. The optical tracer added to the suspension will reflect the laser to the camera, and the algorithm is used to perform cross-correlation processing on the photos taken by the high-speed camera, so as to obtain the motion characteristics of the flow field of the suspension illuminated by the plane laser at different times. The traditional echo-PIV measurement method is to use fundamental frequency ultrasonic waves for imaging, collect ultrasonic images of the flow field area at a certain speed, and perform image cross-correlation processing on two adjacent ultrasonic images, so as to obtain the motion characteristics of the flow field in the measurement area at a certain moment, such as velocity distribution or vorticity distribution.

[0004] Due to the very short wavelength of light, the optical PIV measurement method has poor penetration ability. A slight refractive index mismatch between the solid phase and the liquid phase of the suspension will cause a sharp drop in the light penetration in the suspension, and the image contrast and signal-to-noise ratio will decrease. Therefore, using the optical PIV method to measure the flow field of suspensions has very strict requirements for the experimental conditions.

[0005] The traditional echo-PIV ultrasonic imaging method for measuring suspensions is to use fundamental frequency imaging. Ultrasonic waves have a much longer wavelength than light, which also means that ultrasonic waves have stronger penetration ability than light. However, the resolution and contrast of the traditional fundamental frequency ultrasonic measurement method are lower than those of the optical measurement method. And as the volume fraction of the suspension increases, the images of the solid-phase particles in the suspension interfere with each other, artifacts appear in the ultrasonic images, the images of different particles overlap, the image quality decreases, and the algorithm cannot be used to obtain an accurate velocity field, which limits the measurable volume fraction of the suspension and results in the inability to be applied to the measurement of industrial suspensions with high volume fractions and small particle size ratios. Summary of the Invention

[0006] The object of the present invention is to provide a harmonic imaging and impedance matching echo-PIV measurement method and system, which improves the measurable volume fraction of the suspension, and this method can be applied to the measurement of industrial suspensions.

[0007] To achieve the above object, the present invention provides a harmonic imaging and impedance matching echo-PIV measurement method, including the following steps: Configure a suspension with acoustic impedance matching; Add an ultrasonic microbubble contrast agent to the suspension; Use an ultrasonic probe to emit adjacent pulses; Retain the double-frequency signal in the original ultrasonic reflection signal through a high-pass filter; Remove the harmonic image signal of the solid-phase particles in the suspension through threshold filtering; Process two adjacent instantaneous flow field photos through a cross-correlation algorithm to obtain the displacement of the tracer particles and calculate the instantaneous velocity field of the flow field.

[0008] Preferably, the suspension is composed of low-density polyethylene particles and water mixed in a volume fraction of 8%.

[0009] Preferably, the ratio of the ultrasonic microbubble contrast agent to the suspension is 1:5000 - 1:20000.

[0010] Preferably, the microbubble contrast agent is composed of bubbles wrapped with a protein film, and its diameter is in the range of 1 - 10 microns.

[0011] Preferably, the phase difference between adjacent pulses is 180 degrees.

[0012] The present invention also provides a harmonic imaging and impedance matching echo-PIV measurement system, including: An ultrasonic probe for emitting and receiving ultrasonic signals; A pulse inversion module for controlling the ultrasonic probe to emit adjacent pulses with a phase difference of 180 degrees; A high-pass filter for retaining harmonic signals; A threshold filtering module for removing the harmonic image signal of the solid-phase particles in the suspension; An image processing module for processing images through a cross-correlation algorithm to obtain the velocity field information of the suspension flow field.

[0013] Preferably, the ultrasonic probe is a linear probe.

[0014] Preferably, the image processing module includes a cross-correlation algorithm unit for processing two adjacent instantaneous flow field photos to obtain the displacement of the tracer particles.

[0015] Therefore, the present invention adopts the above-mentioned echo-PIV measurement method and system for harmonic imaging and impedance matching, and the beneficial technical effects are as follows: The present invention is used for measuring the flow field of a solid-liquid two-phase flow suspension. Compared with the optical PIV measurement method, it can effectively improve the measurement depth and can measure suspensions with a larger volume fraction. Compared with the traditional echo-PIV ultrasonic measurement technology, the ultrasonic images obtained by the present invention have a higher signal-to-noise ratio and contrast. Using the images obtained by the present invention for algorithm processing can obtain more accurate suspension flow field information. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a flowchart of an echo-PIV measurement method for harmonic imaging and impedance matching according to the present invention; Figure 2 is a comparison between the fundamental frequency imaging and pulse inversion harmonic imaging of the suspension; among them, Figure 2 in (a) is the fundamental frequency imaging of the untreated suspension; Figure 2 in (b) is the pulse inversion harmonic imaging; Figure 3 is the pulse inversion principle and signal processing; among them, Figure 3 in (a) is the principle of pulse inversion; Figure 3 in (b) is the principle of processing ultrasonic image signals based on pulse inversion; Figure 4 is the contrast of the fundamental wave and harmonic images under suspensions with different volume fractions. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The technical solutions of the present invention will be further described below with reference to the drawings and embodiments.

[0018] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0019] Embodiment 1 The echo-PIV measurement method for harmonic imaging and impedance matching proposed by the present invention is used for measuring the flow field of a solid-liquid two-phase flow suspension. This method significantly improves the measurement accuracy and applicable range of the suspension flow field by optimizing the acoustic impedance matching of the suspension, introducing ultrasonic microbubble contrast agents, and combining pulse inversion technology and high-pass filtering processing.

[0020] 1. Preparation of the suspension and addition of the contrast agent.

[0021] Mix low-density polyethylene particles with water in a volume fraction ratio of 8% to form a solid-liquid two-phase suspension with acoustic impedance matching. The acoustic impedance of low-density polyethylene particles is similar to that of water, so it can effectively reduce the scattering and reflection of sound waves in the suspension and improve the penetration ability of measurement. Add ultrasonic microbubble contrast agent to the suspension, and the ratio is 1:5000 - 1:20000. The microbubble contrast agent consists of bubbles wrapped by a protein film, with a diameter in the range of 1 - 10 microns, and can be evenly distributed in the suspension and serve as tracer particles.

[0022] 2. Fundamental frequency imaging.

[0023] Under fundamental frequency imaging, the ultrasonic image of the suspension is as shown in (a) of Figure 2 . Due to the interference of the signals of the solid-phase particles in the suspension, obvious artifacts appear in the image, and as the volume fraction of the suspension increases, the image quality deteriorates further. The resolution and contrast of fundamental frequency imaging are relatively low, and it is unable to effectively distinguish the solid-phase particles and the liquid-phase background in the suspension, which limits its application in high-volume-fraction suspensions.

[0024] 3. Pulse inversion and harmonic imaging.

[0025] To solve the limitations of fundamental frequency imaging, this embodiment adopts pulse inversion technology and high-pass filtering processing. The specific steps are as follows: 3.1 Pulse inversion: Use an ultrasonic probe to emit two adjacent pulses with a phase difference of 180 degrees. Through pulse inversion technology, the fundamental frequency signal (f0 frequency band) is weakened, while the second harmonic frequency signal (2f0 frequency band) is enhanced.

[0026] 3.2 High-pass filtering: Use a high-pass filter to retain the second harmonic frequency signal and eliminate the fundamental frequency signal in the low-frequency band.

[0027] 3.3 Threshold filtering: Further remove the harmonic image signals of the low-intensity solid-phase particles in the suspension and retain the strong signals of the ultrasonic microbubble contrast agent.

[0028] After the above processing, the harmonic image of the suspension is as shown in (b) of Figure 2 . Harmonic imaging significantly improves the signal-to-noise ratio and contrast of the image, and the artifact problem is effectively solved.

[0029] 4. The principle and advantages of harmonic imaging.

[0030] The principle of harmonic imaging is as shown in Figure 3 . Figure 3 In (a) of Figure 3Among them, (b) shows the principle of processing ultrasonic image signals based on pulse inversion. The fundamental frequency signal is removed by a high-pass filter, and the harmonic signal is retained. Since the signal intensity of ultrasonic microbubble contrast agents in the double-frequency band is much higher than that of solid-phase particles in the suspension, artifacts can be significantly reduced and the image quality can be improved.

[0031] 5. Comparative experiments at different volume fractions.

[0032] Figure 4 Shows the contrast between the fundamental wave and harmonic images of suspensions with different volume fractions. The experimental results show that as the volume fraction of the suspension increases, the image quality of fundamental frequency imaging deteriorates rapidly, while harmonic imaging can still maintain good signal-to-noise ratio and contrast at high volume fractions. This indicates that the proposed method is suitable for measuring industrial suspensions with high volume fractions and small particle size ratios.

[0033] Embodiment 2 A harmonic imaging and impedance matching echo-PIV measurement system, comprising: An ultrasonic probe for transmitting and receiving ultrasonic signals.

[0034] The ultrasonic probe is a linear probe.

[0035] A pulse inversion module for controlling the ultrasonic probe to transmit adjacent pulses with a phase difference of 180 degrees; A high-pass filter for retaining harmonic signals; A threshold filtering module for removing the harmonic image signals of solid-phase particles in the suspension; An image processing module for processing the image through a cross-correlation algorithm to obtain the velocity field information of the suspension flow field.

[0036] The image processing module includes a cross-correlation algorithm unit for processing two adjacent instantaneous photos of the flow field to obtain the displacement of the tracer particles.

[0037] It should be noted that the content not elaborated in detail in the present invention is all prior art and is well known to those skilled in the art.

[0038] Therefore, the present invention adopts the above-mentioned harmonic imaging and impedance matching echo-PIV measurement method and system, which improves the measurable volume fraction of the suspension, and this method can be applied to the measurement of industrial suspensions.

[0039] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for echo-PIV measurement with harmonic imaging and impedance matching, characterized in that, Comprising the following steps: Configure a suspension with acoustic impedance matching; Add an ultrasonic microbubble contrast agent to the suspension; Use an ultrasonic probe to emit adjacent pulses; Retain the double-frequency signal in the original ultrasonic reflection signal through a high-pass filter; Remove the harmonic image signal of the solid-phase particles in the suspension through threshold filtering; Process two adjacent instantaneous photographs of the flow field through the cross-correlation algorithm to obtain the displacement of the tracer particles and calculate the instantaneous velocity field of the flow field.

2. The echo-PIV measurement method for harmonic imaging and impedance matching according to claim 1, wherein The suspension is composed of low-density polyethylene particles and water mixed in a volume fraction of 8%; 3. A method for echo-PIV measurement with harmonic imaging and impedance matching according to claim 1, characterized in that, The ratio of the ultrasonic microbubble contrast agent to the suspension is 1:5000 - 1:20000; 4. A method for echo-PIV measurement of harmonic imaging and impedance matching according to claim 1, wherein The microbubble contrast agent consists of bubbles wrapped in a protein film, and its diameter ranges from 1 to 10 microns; 5. A method for echo-PIV measurement of harmonic imaging and impedance matching according to claim 1, characterized in that, The phase difference between adjacent pulses is 180 degrees; 6. A harmonic imaging and impedance matching echo-PIV measurement system, characterized in that, Including: An ultrasonic probe for emitting and receiving ultrasonic signals; A pulse inversion module for controlling the ultrasonic probe to emit adjacent pulses with a phase difference of 180 degrees; A high-pass filter for retaining the harmonic signal; A threshold filtering module for removing the harmonic image signal of the solid-phase particles in the suspension; An image processing module for processing images through the cross-correlation algorithm to obtain the velocity field information of the suspension flow field; 7. A harmonic imaging and impedance matching echo-PIV measurement system according to claim 6, wherein The ultrasonic probe is a linear probe; 8. A harmonic imaging and impedance matching echo-PIV measurement system according to claim 6, wherein The image processing module includes a cross-correlation algorithm unit for processing two adjacent instantaneous photographs of the flow field to obtain the displacement of the tracer particles.

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