Measurement method of spatial distribution and intensity of ultrasonic cavitation

Abstract

The present application proposes a method for measuring the spatial distribution and intensity of ultrasonic cavitation, which includes: establishing a measurement area; classifying each measurement point in the cavitation space; calling the series of selected points with sound pressure values ​​greater than a a point set Ma; arranging the point set Ma in a manner similar to an elliptical path; connecting the origin with each selected point in the point set Ma in the surface to form a set of vectors S1; using the set of vectors S1 to calculate the isointensity lines of the surface; connecting the isointensity lines in each surface through a smooth surface to obtain a shuttle-shaped isointensity surface; each determined numerical value a corresponds to an isointensity surface, and the distribution and intensity of the entire cavitation space are represented by the isointensity surfaces of each layer; the cavitation space distribution and intensity when the device output power is greater than 600W are obtained by fitting the cavitation space distribution and intensity when the device output power is less than or equal to 600W through an intensity function.

Description

Technical Field

[0001] The present application relates to ultrasonic cavitation technology, and in particular to a method for measuring the distribution and intensity of ultrasonic cavitation space. Background Art

[0002] At low ultrasonic focusing intensities, thermal effects are the primary interaction, but higher focusing intensities may introduce other effects, such as ultrasonic cavitation. Ultrasonic cavitation refers to a series of dynamic processes, including oscillation, compression, expansion, collapse, and closure, caused by the excitation of tiny bubble nuclei in a liquid by ultrasonic waves. It is further divided into steady-state cavitation and transient cavitation. When sound waves pass through a liquid, the cavitation nuclei in the liquid oscillate periodically at the frequency of the sound waves. At low ultrasonic intensities, the radial oscillation of the bubbles is controlled by the sound pressure, with the volume being compressed and reduced during the positive pressure phase. During the negative pressure phase, the microbubbles are stretched and expanded, meaning they oscillate left and right along the equilibrium radius, a phenomenon known as steady-state cavitation. As the ultrasonic intensity increases, the vibration amplitude of the bubbles increases, and the bubble vibration is then controlled by the inertia of the surrounding medium. The cavitation nuclei rapidly expand during the negative pressure phase of the ultrasonic field and rapidly collapse during the subsequent positive pressure phase. This phenomenon is known as transient cavitation. Transient cavitation generates a huge pressure shock wave of gigapascal-level due to the collapse of microbubbles. The shock wave decays within 100 microns, allowing it to precisely damage the target at the subcellular level.

[0003] The creation and control of cavitation clouds are still relatively difficult. In order to understand and control them, a method to characterize their intensity and spatial distribution is needed. Summary of the Invention

[0004] Due to the destructive and random nature of cavitation clouds, it is difficult to observe them using conventional measurement methods. If direct measurement methods are used to measure iso-intensity surfaces, the randomness not only causes large fluctuations in the measured values ​​at the same point, but also requires extremely fast responses to find the same point. Therefore, a method for measuring the spatial distribution and intensity of ultrasonic cavitation is proposed here, which uses a fixed measurement point and uses a low-power output state to fit the high-power output.

[0005] This application proposes a method for measuring the spatial distribution and intensity of ultrasonic cavitation, which includes:

[0006] Establish a measurement area; the measurement area is a large cubic space enclosing the cavitation cloud, with the length of its long side being 50% longer than the longest diameter of the cavitation cloud, and the width and height being 0.8-1 times the length of the long side; the space is evenly divided into small cubes with a length, width and height that are 0.01-0.1 times the length, width and height of the large cubic space, and the small cubes will be evenly filled in the large cube, with a number of 1,000-1,000,000; each vertex of the small cube is set as a measurement point; a three-degree-of-freedom platform is used to measure the sound pressure at each measurement point, with the measurement device being allowed to stay at each measurement point for a period of time and the readings during this period being averaged to obtain a set of measurement points arranged within the large cubic measurement area, and the sound pressure values ​​corresponding to each measurement point;

[0007] By classifying each measurement point in the cavitation space into a set of parallel planes, a gridded point matrix can be obtained;

[0008] For each measurement point in the plane, the point with the maximum sound pressure value is taken as the origin, and the two-dimensional coordinates of each measurement point can be established; set a sound pressure value a, find a point A in the plane with a sound pressure value closest to the value a and larger than a as the selection point, and then find a point with a sound pressure value smaller than a and a point with a sound pressure value larger than a among the 8 measurement points adjacent to point A; select point B with a sound pressure value closest to a as the selection point among the points with a sound pressure value larger than a; find a point with a sound pressure value smaller than a and a measurement point with a sound pressure value larger than a from the 8 measurement points adjacent to point B; repeat this process until the selected point is the same as point A; this series of selection points with sound pressure values ​​greater than a is called a point set Ma; the point set Ma is arranged in a path similar to an ellipse; in the plane, the origin is connected to each selection point in the point set Ma to form a set of vectors S1; the set of vectors S1 is used to calculate the isointensity lines of the plane;

[0009] Connect the isointensity lines in each surface through a smooth surface to obtain a spindle-shaped isointensity surface;

[0010] Each value a of a certain value corresponds to an iso-intensity surface, and the iso-intensity surfaces of each layer represent the distribution and intensity of the entire cavitation space;

[0011] The cavitation spatial distribution and intensity when the device output power is greater than 600W are obtained by fitting the cavitation spatial distribution and intensity when the device output power is less than or equal to 600W through the intensity function.

[0012] Preferably, the isointensities are obtained by a two-dimensional geometric method:

[0013] After extension, each vector in the set of vectors S1 will pass through another measurement point, the sound pressure of which is less than the sound pressure of the measurement point in the S1 vector, and the calculated position point sa of the value a is obtained in proportion to the measurement point; all the position points sa calculated by all the vectors in the set of vectors S1 are distributed in the four quadrants of the corresponding surface, and the position points sa in each quadrant are connected into a curve, and the curves of the four quadrants will form elliptical isointensity lines.

[0014] Preferably, the isointensities are obtained by a three-dimensional geometric method:

[0015] A three-dimensional vector is formed using the position coordinates and sound pressure values ​​of each selected point in the point set Ma and the measurement points with sound intensity less than a among the 8 measurement points around each selected point. The first component of the three-dimensional vector is the X-axis coordinate, the second component is the Y-axis coordinate, and the third component is the Z-axis coordinate. The X-axis coordinate and the Y-axis coordinate correspond to the position of the point on its corresponding surface. The Z-axis coordinate corresponds to the sound pressure value. A plane PZ is generated by the vector generated by each selected point in the point set Ma and the measurement points with sound intensity less than a among the 8 points around each selected point. A plane Za is made perpendicular to the Z axis on the Z axis. The plane passes through the point with value a on the Z axis. The plane PZ intersects with the plane Za at a point. The three-dimensional coordinates of the intersection are (x, y, a), which is the approximate point on the surface at the position (x, y) with sound pressure value a. All the approximate points are grouped in the four quadrants of the surface and connected with a fifth-order polynomial curve to obtain elliptical isointensity lines.

[0016] The method for measuring the spatial distribution and intensity of ultrasonic cavitation in the present application divides the cavitation space into small cubes to fix the measurement points and uses a low-power output state to fit the spatial distribution and intensity of ultrasonic cavitation with high-power output, which can more accurately determine the spatial distribution and intensity of acoustic cavitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Measuring spatial cube distribution

[0018] Figure 2 Proportional calculation of vectors and their directions in two-dimensional calculations

[0019] Figure 3 Selecting points and their vector directions for 3D calculations

[0020] Figure 4 Three-dimensional normal vector generation space plane and solution

[0021] Figure 5 Fusiform isostrong surface

[0022] Figure 6 Multi-layer equal intensity distribution spatial map

[0023] Figure 7Non-convergence model diagram when the sound pressure is selected outside the range

[0024] Figure 8 Isosurface generated isosurface map DETAILED DESCRIPTION

[0025] Establish a measurement area, which is a cubic space enclosing the cavitation cloud. The length of its long side is 50% longer than the longest diameter of the cavitation cloud, and the width and height are 0.8-1 times the length of the long side. The space is evenly divided into small cubes with a length, width and height of 0.01-0.1 times the length, width and height of the large cubic space. The small cubes will be evenly filled in the large cube. Figure 1 , and the number is 1000-1000000, each vertex is set as a measurement point, and the sound pressure of each vertex of the small cube is measured using a three-degree-of-freedom platform. The measuring equipment is made to stay at each measurement point for a period of time and the readings during this period are averaged to obtain a set of points arranged in the measurement area of ​​the large cube and the sound pressure of each point.

[0026] By classifying the points in the cavitation space into a set of parallel planes, a gridded point matrix can be obtained.

[0027] For each measurement point in the surface, the point with the largest sound pressure value is taken as the origin, and the two-dimensional coordinates of each point can be established; set a sound pressure value a, find a point A in the space whose sound pressure is closest to the value a and is larger than a, and then find points A1, A2, A3, etc. with smaller sound pressure values ​​than a among the 8 adjacent points. There are still several points with sound pressure values ​​larger than a among the 8 points adjacent to A. Select point B with the sound pressure closest to a from these points, and find points B1, B2, B3, etc. with sound pressure values ​​smaller than a from the 8 points adjacent to point B. Repeat the above process until the coordinates of the selected point are the same as those of point A. This series of selected points with sound pressure values ​​greater than a is called point set Ma. A, B, C, this series of point sets Ma with sound pressure values ​​larger than a will mostly be arranged in an elliptical path.

[0028] The point with the maximum sound pressure in the plane is used as the origin, and a set of vectors S1 is obtained by connecting the points just selected. This set of vectors is used to calculate the equipotential lines of each split plane. We use two-dimensional and three-dimensional geometric solutions to approximate the equipotential lines.

[0029] When a two-dimensional geometric solution is used, each vector in S1 will pass through another measurement point after extension. The sound pressure of this measurement point will be less than the sound pressure of the measurement point in the S1 vector. The calculation position point sa of the value a is obtained proportionally with this measurement point. The point set sa is divided into four quadrants. The point set in each quadrant is connected into a curve using a 5th-order polynomial solution. The curves of the four quadrants will form an isointensity line similar to an ellipse, as shown in the following figure: Figure 2, which is suitable for fast solutions when the sound field varies uniformly. Connecting each set of parallel isointensity lines with a smooth surface creates an isointensity surface of sound pressure value A, similar to a shuttle. The smooth surface is generated using interpolation.

[0030] When a three-dimensional geometric solution is selected, Figure 3 , transform the coordinates and sound pressure of each point in Ma into a three-dimensional vector, such as

[0031] A(xa,ya,za),A1(xa1,ba2,za2),A2(xa2,ya2,za2)

[0032] B(xb,yb,zb),B1(xb1,yb1,zb1),B2(xb2,yb2,zb2)

[0033] x, y are its coordinates in the measurement plane, z is its sound pressure value, convert the point in Ma and its corresponding point into a three-dimensional vector in the xyz coordinate system, the vector generated by it and its corresponding point will generate a plane PZ, make a plane Za perpendicular to the Z axis on the Z axis, the plane passes through the point with value a on the Z axis, the plane PZ must intersect with the plane Za at a point, the coordinates of the point are (x, y, a), as shown Figure 4 Substituting its x and y back into the original plane gives the approximate point of the sound pressure value a. The fitting result is consistent with the measurement result in the case of uneven sound pressure. The reason is not clear at present. The approximate points of each sound pressure value a, Sa1, Sa2, Sa3, Sb1, Sb2, Sb3, Sb4, etc., are grouped into quadrants and connected with a fifth-order polynomial curve. The four quadrants will finally be combined into an ellipse-like isointensity line, as shown in the figure. Figure 3 .

[0034] If we place this set of parallel planes in three-dimensional space according to coordinates and connect them with smooth surfaces, we will get a spindle-shaped isotropic surface, such as Figure 5 .

[0035] By combining multiple groups of equal strength surfaces, we can obtain a multi-layered spindle-shaped body, such as Figure 6 , to determine the working intensity of cavitation in space. The value of the sound pressure intensity a is an interval. When it is too small, its point-finding mechanism cannot converge it into a spindle shape, and can only map it into a peak shape such as Figure 7 The range of the sound pressure intensity a depends on experimental testing, and is preferably confirmed with the assistance of ultrasonic images in degassed water.

[0036] The current mainstream isosurface equipotential surface generation method mostly generates it as an infinitely expanding cone. Figure 8This is because they mostly use triangulation to generate equipotential surfaces. Based on experimental observations, we have specialized the shape of the phenomenon, and the generated isopotential bodies are more conducive to the determination of the working range.

[0037] The low power (≤600W) sound pressure and the sound pressure range of the same interval are fitted to determine the working conditions at high power (>600W) to reduce the loss of the measurement equipment.

[0038] Unless otherwise defined, all technical and / or scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which the invention relates. The materials, methods, and examples mentioned in this application are illustrative only and not restrictive.

[0039] Although the present invention has been described in conjunction with specific embodiments, those skilled in the art may make appropriate substitutions, modifications and changes within the scope of the invention of this application, and such substitutions, modifications and changes shall still fall within the scope of protection of this application.

Claims

1. A method for measuring the spatial distribution and intensity of ultrasonic cavitation, comprising: Establish a measurement area; the measurement area is a large cubic space enclosing the cavitation cloud, with the length of its long side 50% longer than the longest diameter of the cavitation cloud, and the width and height being 0.8-1 times the length of the long side; the space is evenly divided into small cubes with a length, width and height of 0.01-0.1 times the length, width and height of the large cubic space, and the small cubes will be evenly filled in the large cube, and the number of small cubes will be 1,000-1,000,000; each vertex of the small cube is set as a measurement point; use a three-degree-of-freedom platform to measure the sound pressure at each measurement point, so that the measuring equipment stays at each measurement point for a period of time and the readings during this period are averaged to obtain a set of measurement points arranged in the large cubic measurement area, and the sound pressure value corresponding to each measurement point; By classifying each measurement point in the cavitation space into a set of parallel planes, a gridded point matrix can be obtained; For each measurement point in the plane, the two-dimensional coordinates of each measurement point can be established by taking the point with the maximum sound pressure value as the origin. Set a sound pressure value a, find a point A in the plane with a sound pressure value closest to a and larger than a as the selection point, then find points with a smaller sound pressure value than a and points with a larger sound pressure value than a among the eight measurement points adjacent to point A. Among the points with a sound pressure value larger than a, select point B with a sound pressure value closest to a as the selection point. Find points with sound pressure values ​​smaller than a and points with sound pressure values ​​larger than a from the eight measurement points adjacent to point B; repeat this process until the selected point overlaps with point A; a series of selected points with sound pressure values ​​greater than a is called a point set Ma; the point set Ma is arranged in an elliptical path; in the surface, the origin is connected to each selected point in the point set Ma to form a set of vectors S1; the set of vectors S1 is used to calculate the isointensity lines of the surface; Connect the isointensity lines in each surface through a smooth surface to obtain a spindle-shaped isointensity surface; Each value a of a certain value corresponds to an iso-intensity surface, and the iso-intensity surfaces of each layer represent the distribution and intensity of the entire cavitation space; The cavitation spatial distribution and intensity when the device output power is greater than 600W are obtained by fitting the cavitation spatial distribution and intensity when the device output power is less than or equal to 600W through the intensity function.

2. The method for measuring the spatial distribution and intensity of ultrasonic cavitation according to claim 1, characterized in that: The isointensities are obtained by two-dimensional geometric methods: After extension, each vector in the set of vectors S1 will pass through another measurement point, the sound pressure of which is less than the sound pressure of the measurement point in the S1 vector, and the calculated position point sa of the value a is obtained in proportion to the measurement point; all the position points sa calculated by all the vectors in the set of vectors S1 are distributed in the four quadrants of the corresponding surface, and the position points sa in each quadrant are connected into a curve, and the curves of the four quadrants will form elliptical isointensity lines.

3. The method for measuring the spatial distribution and intensity of ultrasonic cavitation according to claim 1, characterized in that: The isointensities are obtained by three-dimensional geometric methods: A three-dimensional vector is formed using the position coordinates and sound pressure values ​​of each selected point in the point set Ma and the measurement points with sound pressure less than a among the eight measurement points around each selected point. The first component of the three-dimensional vector is the X-axis coordinate, the second component is the Y-axis coordinate, and the third component is the Z-axis coordinate. The X-axis coordinate and the Y-axis coordinate correspond to the position of the point on its corresponding surface. The Z-axis coordinate corresponds to the sound pressure value. A plane PZ is generated by the vector generated by each selected point in the point set Ma and the measurement points with sound pressure less than a among the eight points around each selected point. A plane Za is made perpendicular to the Z axis on the Z axis. The plane passes through the point with value a on the Z axis. Plane PZ intersects plane Za at a point with three-dimensional coordinates (x, y, a), which is the approximate point on the surface at position (x, y) with sound pressure value a. All approximate points are grouped in the four quadrants of the surface and connected with a fifth-order polynomial curve to obtain elliptical isointensity lines.

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