Method and device for measuring morphological oscillation eigenfrequency of electrostatic suspension metal liquid drops
By acquiring and analyzing multi-frame oscillation images of electrostatically suspended metal droplets, plotting amplitude-frequency curves and taking the average value, the problems of reliance on subjective judgment and hysteresis effects in existing technologies are solved, and high-precision intrinsic frequency determination is achieved.
Patent Information
- Application Number
- CN202511079779.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-01
- Publication Date
- 2025-11-11
AI Technical Summary
In the existing technology, the method for determining the intrinsic frequency of electrostatically suspended metal droplet morphology oscillation relies on the operator's subjective perception and does not consider the hysteresis effect, resulting in low measurement accuracy.
By acquiring multiple frames of oscillation images under dynamically changing excitation frequencies, boundary extraction and Fourier transform are performed to plot amplitude-frequency curves. The mean of the forward and reverse oscillation frequencies is taken as the intrinsic frequency, taking into account the hysteresis effect.
This method enables high-precision determination of the intrinsic frequency of metal droplet morphological oscillation, reduces the influence of hysteresis, and improves the accuracy and precision of the measurement.
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Figure CN120927518A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of measuring the thermophysical parameters of liquid metals, and in particular to a method and apparatus for measuring the intrinsic frequency of oscillations in the shape of electrostatically suspended metal droplets. Background Technology
[0002] Droplet oscillation is an important method for determining the surface tension, viscosity, and other thermophysical properties of liquid metals. Accurately determining the intrinsic frequency of the oscillation of the metal droplet shape is crucial for measuring these properties using this method. Electrostatic levitation technology, with its high vacuum and containerless characteristics, is particularly suitable for determining the liquid properties of high-temperature, highly reactive metal materials. Under electrostatic levitation conditions, active electric field modulation is used as the external excitation, and the morphological oscillation of suspended metal droplets can be excited through forced vibration.
[0003] According to the principle of forced vibration, when the external excitation frequency equals the intrinsic frequency of the metal droplet's morphological oscillation, the droplet is in a resonant state, at which point the oscillation amplitude is at its maximum. Related techniques determine whether a resonant state has been reached by directly observing the magnitude of the metal droplet's oscillation amplitude; however, this method relies too heavily on the operator's subjective perception. Furthermore, these techniques do not consider the potential hysteresis effect between the droplet's response and the external excitation, further reducing the accuracy of measuring the intrinsic frequency of the metal droplet's morphological oscillation. Summary of the Invention
[0004] The purpose of this application is to provide a method and apparatus for measuring the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation, which digitizes the process of electrostatically suspended metal droplet morphological oscillation and considers the hysteresis effect to improve the accuracy and precision of measuring the intrinsic frequency of metal droplet morphological oscillation.
[0005] To achieve the above objectives, this application provides the following solution:
[0006] In a first aspect, this application provides a method for determining the intrinsic frequency of oscillations in the shape of electrostatically suspended metal droplets, comprising:
[0007] Based on the applied dynamically changing excitation frequency, multiple frames of oscillation images of electrostatically suspended metal droplets are acquired at each excitation frequency; wherein, the dynamic change process of the excitation frequency is that the initial excitation frequency gradually increases to the final excitation frequency, and the final excitation frequency gradually decreases to the initial excitation frequency.
[0008] Perform the following steps for each oscillation image at each excitation frequency:
[0009] Boundary extraction is performed on the oscillating image to obtain a set of boundary points;
[0010] The instantaneous amplitude is determined based on the boundary point set and the metal droplet profile expression.
[0011] Fourier transform and fitting are performed on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency.
[0012] Based on the morphological oscillation frequency and amplitude at each excitation frequency, plot the positive and negative morphological oscillation amplitude-frequency curves;
[0013] The average of the forward and reverse oscillation frequencies at the point of maximum amplitude in the curve is taken as the intrinsic frequency of the metal droplet morphological oscillation.
[0014] Secondly, this application provides a device for measuring the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation, comprising: an image acquisition module, an instantaneous amplitude determination module, a frequency amplitude acquisition module, a curve plotting module, and an intrinsic frequency determination module.
[0015] The image acquisition module is used to acquire multiple frames of oscillation images of electrostatically suspended metal droplets at each excitation frequency according to the applied dynamically changing excitation frequency; wherein, the dynamic change process of the excitation frequency is that the initial excitation frequency gradually increases to the final excitation frequency, and the final excitation frequency gradually decreases to the initial excitation frequency;
[0016] The instantaneous amplitude determination module is used to perform the following steps for each oscillation image at each excitation frequency: extract the boundary of the oscillation image to obtain a set of boundary points; and determine the instantaneous amplitude based on the set of boundary points and the profile expression of the metal droplet.
[0017] The frequency and amplitude acquisition module is used to perform Fourier transform and fitting on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency.
[0018] The curve plotting module is used to plot positive and negative morphological oscillation amplitude-frequency curves based on the morphological oscillation frequency and amplitude at each excitation frequency.
[0019] The intrinsic frequency determination module is used to take the average of the forward oscillation frequency and the reverse oscillation frequency at the point of maximum amplitude in the curve, and use it as the intrinsic frequency of the metal droplet morphological oscillation.
[0020] According to the specific embodiments provided in this application, the following technical effects are disclosed:
[0021] This application provides a method and apparatus for determining the intrinsic frequency of morphological oscillation in electrostatically suspended metal droplets. By applying a dynamically changing excitation frequency, multiple frames of oscillation images are acquired at each excitation frequency, fully considering the influence of hysteresis to achieve initial image acquisition. Boundary extraction is performed on each oscillation image at each excitation frequency, and the instantaneous amplitude is determined based on the boundary point set and the metal droplet contour expression. This transforms the oscillation image into metal droplet contour information, enabling the acquisition of the instantaneous amplitude during the morphological oscillation of electrostatically suspended metal droplets. This facilitates subsequent determination of the morphological oscillation frequency and amplitude within the instantaneous amplitude. The method involves obtaining the morphological oscillation frequency and amplitude at the current excitation frequency by performing Fourier transform and fitting on the instantaneous amplitude of each oscillation image. Based on the morphological oscillation frequency and amplitude at each excitation frequency, positive and negative morphological oscillation amplitude-frequency curves are plotted to comprehensively analyze the morphological changes of the metal droplet. The morphological oscillation process is digitized, avoiding the problem of inaccurate resonance judgment by visually observing the metal droplet. The average of the positive and negative oscillation frequencies is used as the intrinsic frequency of the metal droplet morphological oscillation, fully considering the hysteresis effect and achieving high-precision intrinsic frequency determination. Attached Figure Description
[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0023] Figure 1 A flowchart illustrating a method for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillations, provided in an embodiment of this application;
[0024] Figure 2 Here is a schematic diagram of the second-order oscillation image of a Zr droplet; where (a) is the droplet image at 0 ms, (b) is the droplet image at 1.8 ms, (c) is the droplet image at 3.6 ms, (d) is the droplet image at 5.6 ms, (e) is the droplet image at 7.6 ms, and (f) is the droplet image at 9.6 ms.
[0025] Figure 3 The image shows the result of boundary extraction and fitting of the second-order oscillation image of a Zr metal droplet. The solid circles represent the extracted edge point set, and the solid line represents the fitting result of the metal droplet contour. Among them, (a) is the droplet boundary at 0 ms, (b) is the droplet boundary at 1.8 ms, (c) is the droplet boundary at 3.6 ms, (d) is the droplet boundary at 5.6 ms, (e) is the droplet boundary at 7.6 ms, and (f) is the droplet boundary at 9.6 ms.
[0026] Figure 4 The spectrum is obtained by performing a Fourier transform on the instantaneous amplitude of the second-order oscillation image of a Zr droplet.
[0027] Figure 5 The graph shows the continuous instantaneous amplitude curve, which is fitted to the instantaneous amplitude of the second-order oscillation image of the Zr droplet over time. The solid dots represent the instantaneous amplitude of the second-order oscillation image of the Zr droplet, and the solid line represents the fitting result of the continuous instantaneous amplitude.
[0028] Figure 6 The morphological oscillation amplitude-frequency curve of a 1.39 mm radius Zr droplet at 1923 K is shown.
[0029] Figure 7 This is a schematic diagram of the functional modules of a device for measuring the intrinsic frequency of electrostatically suspended metal droplet morphology oscillation, provided in an embodiment of this application. Detailed Implementation
[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0031] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0032] In one exemplary embodiment, such as Figure 1 As shown, a method for determining the intrinsic frequency of oscillation in the shape of electrostatically suspended metal droplets is provided, comprising the following steps 100 to 500. Wherein:
[0033] Step 100: Based on the applied dynamically changing excitation frequency, acquire multiple frames of oscillation images of the electrostatically suspended metal droplet at each excitation frequency; wherein, the dynamic change process of the excitation frequency is that the initial excitation frequency gradually increases to the final excitation frequency, and the final excitation frequency gradually decreases to the initial excitation frequency.
[0034] Optionally, use the same frequency interval ΔF MThis process involves gradually increasing the initial excitation frequency in step 100 to the final excitation frequency, and then gradually decreasing the final excitation frequency back to the initial excitation frequency. This application employs equally spaced frequency changes to comprehensively cover all possible frequency points from the initial excitation frequency to the final excitation frequency, avoiding the omission of any important frequency information, and comprehensively evaluating the oscillation characteristics of the metal droplet at different excitation frequencies, thus achieving uniform sampling.
[0035] Step 200: For each oscillation image at each excitation frequency, perform the following steps: extract the boundary of the oscillation image to obtain a set of boundary points; determine the instantaneous amplitude based on the set of boundary points and the profile expression of the metal droplet.
[0036] Step 300: Perform Fourier transform and fitting on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency.
[0037] Step 400: Based on the morphological oscillation frequency and amplitude at each excitation frequency, plot the positive and negative morphological oscillation amplitude-frequency curves.
[0038] Step 500: Take the average of the forward oscillation frequency and the reverse oscillation frequency at the point of maximum amplitude in the curve as the intrinsic frequency of the metal droplet morphological oscillation.
[0039] By implementing steps 100 to 500 above, this application acquires multiple frames of oscillation images at each excitation frequency by applying a dynamically changing excitation frequency, fully considering the influence of hysteresis, and achieving preliminary image acquisition; it extracts the boundaries of each oscillation image at each excitation frequency, and determines the instantaneous amplitude based on the boundary point set and the metal droplet contour expression, converting the oscillation image into metal droplet contour information, thus realizing the acquisition of the instantaneous amplitude during the morphological oscillation of electrostatically suspended metal droplets, which is beneficial for further acquisition of the morphological oscillation frequency and amplitude in the subsequent instantaneous amplitude; through Fourier transform and fitting are performed on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude at the current excitation frequency. Based on the morphological oscillation frequency and amplitude at each excitation frequency, forward and reverse morphological oscillation amplitude-frequency curves are plotted to comprehensively analyze the morphological changes of the metal droplet. The morphological oscillation process is digitized to avoid the problem of inaccurate resonance judgment by visual observation of the metal droplet. The mean of the forward and reverse oscillation frequencies is used as the intrinsic frequency of the metal droplet morphological oscillation, fully considering the hysteresis effect, and realizing high-precision intrinsic frequency determination.
[0040] In another exemplary embodiment of this application, in order to obtain electrostatically suspended metal droplets, the above steps are replaced by the following steps 110 to 120:
[0041] Step 110: Place the metal to be tested into an electrostatic levitation device for levitation and melting.
[0042] Step 120: The stably suspended metal droplet is kept at a set temperature T to obtain an electrostatically suspended metal droplet, wherein the radius of the electrostatically suspended metal droplet before the applied excitation frequency is:
[0043]
[0044] Where r0 is the radius of the metal droplet, m is the mass of the metal droplet, and ρ is the density of the metal droplet at temperature T.
[0045] Optionally, the set temperature T of the stably suspended metal droplet can be adjusted by controlling the laser heating power to obtain the intrinsic frequency of the metal droplet's morphological oscillation under different temperature conditions.
[0046] This application uses electrostatic levitation technology to suspend and melt the metal to be tested (high-temperature metal material) in step 110. The stably suspended metal droplets are kept at a set temperature T to obtain electrostatically suspended metal droplets, which are used as the object for applying excitation frequency and image acquisition.
[0047] The acquisition of multiple frames of oscillation images of electrostatically suspended metal droplets at each excitation frequency specifically includes: applying periodic amplitude modulation to the suspension voltage as an excitation signal; when the excitation frequency is close to the intrinsic frequency of the morphological oscillation of the metal droplet, it will cause the metal droplet to resonate and excite the morphological oscillation of the metal droplet; according to the set sampling rate (e.g., 1000fps to 2000fps), a high-speed camera is used to continuously shoot the metal droplet at the excitation frequency to acquire multiple frames of oscillation images.
[0048] In another exemplary embodiment of this application, in order to provide basic data for subsequent morphological oscillation analysis, boundary extraction is performed on the oscillation image to obtain a boundary point set. Optionally, subpixel edge detection is used to extract the boundary of the oscillation image to obtain the boundary point set. The subpixel edge detection used in this application can achieve high-precision boundary positioning, more accurately reflect the true shape of the metal droplet, enhance image details, and improve data quality.
[0049] In order to transform the boundary point set into the profile information of the metal droplet and obtain the instantaneous amplitude, the above steps are replaced by the following steps 201 to 203:
[0050] Step 201: Convert the edge point set from rectangular coordinates with the center of the metal droplet as the origin to polar coordinates. The conversion formula is:
[0051]
[0052] Where r is the polar radius of the edge point relative to the center of the metal droplet. The angle between the edge point and the center of the metal droplet.
[0053] Step 202: Based on the polar radius and angle, construct the profile expression of the metal droplet. The profile expression of the metal droplet is as follows:
[0054]
[0055] in, To describe the profile of a liquid metal droplet at different angles The function of the polar radius at different times t, where l is the order of the metal droplet morphological oscillation, determined by the acquired oscillation images; r0 is the radius of the metal droplet before the initial excitation frequency is applied. ε represents the effect of morphological oscillations on the edge profile of a metal droplet. l (t) represents the instantaneous amplitude of the metal droplet. Reflects the spatial orientation of metal droplet oscillation;
[0056] Step 203: Determine the instantaneous amplitude based on the metal droplet profile expression fitted to the edge point set in polar coordinates. Optionally, the least squares method can be used to fit the metal droplet profile expression to the edge point set in polar coordinates.
[0057] This application enables accurate location of the edge position of a metal droplet through boundary extraction of multiple oscillation images, thereby obtaining an edge point set. This provides basic data for subsequent analysis of the droplet's shape and oscillation characteristics, making the edge features of the metal droplet clearer. Converting the rectangular coordinates of the edge point set to polar coordinates more intuitively represents the radius and angle changes of the metal droplet, which helps in subsequent fitting of the metal droplet profile expression. The least squares method is used to fit the metal droplet profile expression of the edge point set in polar coordinates to obtain the instantaneous amplitude. This facilitates an intuitive understanding of the instantaneous amplitude change of the metal droplet in each oscillation image, and helps to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency, thereby realizing the determination of the intrinsic frequency.
[0058] In another exemplary embodiment of this application, in order to obtain the morphological oscillation frequency and morphological oscillation amplitude, step 300 is replaced by steps 301 to 304:
[0059] Step 301: Perform a Fourier transform on the instantaneous amplitude of each oscillation image to obtain a spectrum. Optionally, use data processing software (such as Origin software) to perform a Fourier transform on the discrete instantaneous amplitude.
[0060] Step 302: Determine the frequency of maximum intensity in the spectrum as the morphological oscillation frequency of the metal droplet at the current excitation frequency.
[0061] Step 303: Construct a continuous instantaneous amplitude expression with time as the independent variable. The continuous instantaneous amplitude expression is as follows:
[0062]
[0063] Where ε0 and denoted as amplitude and initial phase of the morphological oscillation, respectively, and f is the frequency of the morphological oscillation.
[0064] Step 304: Based on the continuous instantaneous amplitude expression fitted from the instantaneous amplitude of each oscillation image, obtain the morphological oscillation amplitude of the metal droplet at the current excitation frequency.
[0065] This application uses Fourier transform to convert the instantaneous amplitude in the time domain into a spectrum in the frequency domain. By analyzing the spectrum, the frequency with the maximum intensity is extracted and identified, which is used as the morphological oscillation frequency of the metal droplet. This helps in the subsequent analysis of the morphological oscillation amplitude of the metal droplet. Based on the continuous instantaneous amplitude expression fitted from the instantaneous amplitude of each oscillation image, the morphological oscillation amplitude of the metal droplet is obtained, providing important basic data for subsequent morphological oscillation amplitude-frequency curve plotting, intrinsic frequency calculation, etc.
[0066] The average of the forward and reverse oscillation frequencies at the points of maximum amplitude in the curve is taken as the intrinsic frequency of the metal droplet morphological oscillation. Specifically, this involves: determining the forward oscillation frequency f1 and the reverse oscillation frequency f2 corresponding to the points of maximum amplitude in the forward and reverse morphological oscillation amplitude-frequency curves; and averaging the forward oscillation frequency f1 and the reverse oscillation frequency f2 to obtain the intrinsic frequency F of the metal droplet morphological oscillation. T Among them, the eigenfrequency F of the metal droplet morphology oscillation T The calculation formula is:
[0067]
[0068] Among them, the morphological oscillation amplitude-frequency curve is the curve of the morphological oscillation amplitude of the metal droplet changing with the morphological oscillation frequency.
[0069] This application obtains a continuous instantaneous amplitude expression (or continuous instantaneous amplitude curve) that varies with time by performing a Fourier transform and fitting on the discrete instantaneous amplitude. It then obtains the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency. Based on the morphological oscillation frequency and amplitude at each excitation frequency, it plots the morphological oscillation amplitude-frequency curve, determines the forward and reverse oscillation frequencies corresponding to the maximum amplitude, i.e., the oscillation frequencies in the resonance state, and takes the average of the forward and reverse oscillation frequencies as the intrinsic frequency of the metal droplet's morphological oscillation. This reduces the influence of hysteresis on the measurement results and improves the accuracy and precision of the intrinsic frequency measurement.
[0070] The following example illustrates this application using the determination of the oscillation frequency of electrostatically suspended Zr droplets.
[0071] Step 1: Place 73 mg of pure zirconium solid into an electrostatic levitation device and stabilize it. Adjust the laser heating power to reach a temperature of 1923 K. Before applying the excitation, the radius of the Zr droplet is 1.39 mm.
[0072] Step 2: Apply a sinusoidal excitation frequency to the stably suspended Zr metal droplet to induce a second-order axisymmetric oscillation. The amplitude of the excitation signal is 2000V, and the frequency is F. M To adjust the parameters.
[0073] Step 3: Within the range of 50Hz to 200Hz, gradually increase or decrease the excitation frequency F in 1Hz intervals. M Since the droplet oscillation frequency in the experiment did not exceed 500Hz, based on the Nyquist bandwidth, the sampling rate of the high-speed CCD (Charge Coupled Device) camera was set to 1000Hz to acquire 1000 frames of oscillation images of the Zr droplet at each excitation frequency. The acquired oscillation images are shown below. Figure 2 As shown in the image, the oscillation order l of the metal droplet shape can be determined to be 2.
[0074] Step 4: Perform the following steps for each oscillation image at each excitation frequency:
[0075] (1) Subpixel edge detection is used to extract the boundary of the oscillating image. Figure 3 The solid circles represent the extracted set of edge points.
[0076] (2) Convert the edge point set from rectangular coordinates (x, y) with the center of the metal Zr droplet as the origin to polar coordinates. The conversion formula is:
[0077]
[0078] Where r is the polar radius of the edge point relative to the center of the metal droplet. The angle between the edge point and the center of the metal droplet.
[0079] Based on the polar radius r and angle Construct a profile expression for the metal droplet, wherein the metal droplet profile expression is:
[0080]
[0081] in, To describe the profile of a liquid metal droplet at different angles The function of the polar radius at different times t, where l is the order of the metal droplet morphological oscillation, determined by the acquired oscillation images; r0 is the radius of the metal droplet before the initial excitation frequency is applied. ε represents the effect of morphological oscillations on the edge profile of a metal droplet. l (t) represents the instantaneous amplitude of the metal droplet. Reflects the spatial orientation of metal droplet oscillation;
[0082] The instantaneous amplitude is determined based on the profile expression of the metal droplet fitted by the edge point set in polar coordinates.
[0083] Figure 3 The solid line represents the fitted profile of the metal droplet. Figure 5 The solid dot represents the instantaneous amplitude ε2(t) of the second-order oscillation image of the Zr droplet (where ε... l The order l in (t) is 2).
[0084] Step 5: Use Origin software to perform Fourier transform on the instantaneous amplitude of each oscillation image to obtain the spectrum, as shown below. Figure 4 As shown.
[0085] The maximum intensity frequency of 132 Hz in the spectrum is determined as the actual morphological oscillation frequency f of the metal Zr droplet at the current excitation frequency.
[0086] Using time as the independent variable, a continuous instantaneous amplitude expression is constructed, which is:
[0087]
[0088] Where ε0 and denoted as amplitude and initial phase of the morphological oscillation, respectively, and f is the frequency of the morphological oscillation.
[0089] Based on the continuous instantaneous amplitude expression fitted from the instantaneous amplitude of each oscillation image, the morphological oscillation amplitude of the metal droplet at the current excitation frequency is obtained.
[0090] The fitting results of continuous instantaneous amplitude are in Figure 5 The equation is given by a solid line and is as follows:
[0091] ε2(t)=0.11×sin(264πt+0.78).
[0092] Therefore, the morphological oscillation amplitude of the Zr droplet was determined to be 0.11 mm.
[0093] Step 6: Within the range of 50Hz to 200Hz, gradually increase or decrease the excitation frequency F in 1Hz intervals. MBased on the morphological oscillation frequency and amplitude at each excitation frequency, plot the forward and reverse morphological oscillation amplitude-frequency curves, as follows: Figure 6 As shown in the amplitude-frequency curve of the morphological oscillation, a hysteresis phenomenon appears during the increase and decrease of the excitation frequency.
[0094] Step 7: Take the average of the forward oscillation frequency of 142Hz and the reverse oscillation frequency of 132Hz at the point of maximum amplitude in the curve, and use it as the intrinsic frequency of the oscillation of the Zr droplet with a radius of 1.39mm at 1923K (i.e., 137Hz).
[0095] Based on the same inventive concept, this application also provides an apparatus for measuring the intrinsic frequency of electrostatic suspended metal droplet oscillation, used to implement the method for measuring the intrinsic frequency of electrostatic suspended metal droplet oscillation as described above. The solution provided by this apparatus is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the apparatus for measuring the intrinsic frequency of electrostatic suspended metal droplet oscillation provided below can be found in the limitations of the method for measuring the intrinsic frequency of electrostatic suspended metal droplet oscillation described above, and will not be repeated here.
[0096] In one exemplary embodiment, such as Figure 7 As shown, a device for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation is provided, comprising: an image acquisition module 1, an instantaneous amplitude determination module 2, a frequency amplitude acquisition module 3, a curve plotting module 4, and an intrinsic frequency determination module 5.
[0097] The image acquisition module 1 is used to acquire multiple frames of oscillation images of electrostatically suspended metal droplets at each excitation frequency according to the applied dynamically changing excitation frequency; wherein, the dynamic change process of the excitation frequency is that the initial excitation frequency gradually increases to the final excitation frequency, and the final excitation frequency gradually decreases to the initial excitation frequency.
[0098] The instantaneous amplitude determination module 2 is used to perform the following steps for each oscillation image at each excitation frequency: extract the boundary of the oscillation image to obtain a set of boundary points; and determine the instantaneous amplitude based on the set of boundary points and the profile expression of the metal droplet.
[0099] The frequency amplitude acquisition module 3 is used to perform Fourier transform and fitting on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and morphological oscillation amplitude of the metal droplet at the current excitation frequency.
[0100] The curve plotting module 4 is used to plot the positive and negative morphological oscillation amplitude-frequency curves based on the morphological oscillation frequency and amplitude at each excitation frequency.
[0101] The intrinsic frequency determination module 5 is used to take the average of the forward oscillation frequency and the reverse oscillation frequency at the maximum amplitude point in the curve as the intrinsic frequency of the metal droplet morphological oscillation.
[0102] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0103] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A method for determining the intrinsic frequency of oscillation in the shape of electrostatically suspended metal droplets, characterized in that, include: Based on the applied dynamically changing excitation frequency, multiple frames of oscillation images of electrostatically suspended metal droplets are acquired at each excitation frequency; wherein, the dynamic change process of the excitation frequency is that the initial excitation frequency gradually increases to the final excitation frequency, and the final excitation frequency gradually decreases to the initial excitation frequency. Perform the following steps for each oscillation image at each excitation frequency: Boundary extraction is performed on the oscillating image to obtain a set of boundary points; The instantaneous amplitude is determined based on the boundary point set and the metal droplet profile expression. Fourier transform and fitting are performed on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency. Based on the morphological oscillation frequency and amplitude at each excitation frequency, plot the positive and negative morphological oscillation amplitude-frequency curves; The average of the forward and reverse oscillation frequencies at the point of maximum amplitude in the curve is taken as the intrinsic frequency of the metal droplet morphological oscillation.
2. The method for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation according to claim 1, characterized in that, Based on the boundary point set and the metal droplet profile expression, the instantaneous amplitude is determined, specifically including: The edge point set is converted from rectangular coordinates (originating at the center of the metal droplet) to polar coordinates using the following formula: Where r is the polar radius of the edge point relative to the center of the metal droplet. The angle between the edge point and the center of the metal droplet; Based on the polar radius and angle, a profile expression for the metal droplet is constructed, which is: in, The function describes the polar radius of the metal droplet profile at different angles φ and different times t, where l is the order of the metal droplet morphological oscillation; and r0 is the radius of the metal droplet before the initial excitation frequency is applied. ε represents the effect of morphological oscillations on the edge profile of a metal droplet. l (t) represents the instantaneous amplitude of the metal droplet. Reflects the spatial orientation of metal droplet oscillation; The instantaneous amplitude is determined based on the profile expression of the metal droplet fitted by the edge point set in polar coordinates.
3. The method for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation according to claim 1, characterized in that, Fourier transform and fitting are performed on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency, specifically including: Perform a Fourier transform on the instantaneous amplitude of each oscillation image to obtain the spectrum. The frequency of maximum intensity in the spectrum is determined as the morphological oscillation frequency of the metal droplet at the current excitation frequency. Using time as the independent variable, a continuous instantaneous amplitude expression is constructed, which is: Where ε0 and These are the amplitude and initial phase of the morphological oscillation, respectively, and f is the frequency of the morphological oscillation. Based on the continuous instantaneous amplitude expression fitted from the instantaneous amplitude of each oscillation image, the morphological oscillation amplitude of the metal droplet at the current excitation frequency is obtained.
4. The method for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation according to claim 1, characterized in that, Subpixel edge detection is used to extract the boundary of the oscillating image, resulting in a set of boundary points.
5. The method for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation according to claim 1, characterized in that, Using the same frequency interval ΔF M This causes the initial excitation frequency to gradually increase to the final excitation frequency, and the final excitation frequency to gradually decrease to the initial excitation frequency.
6. The method for determining the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation according to any one of claims 1-5, characterized in that, The method for obtaining electrostatically suspended metal droplets is as follows: The metal to be tested is placed in an electrostatic levitation device for levitation and melting; A stably suspended metal droplet is held at a set temperature T to obtain an electrostatically suspended metal droplet. The radius of the electrostatically suspended metal droplet before the applied excitation frequency is: Where r0 is the radius of the metal droplet, m is the mass of the metal droplet, and ρ is the density of the metal droplet at temperature T.
7. A device for measuring the intrinsic frequency of electrostatically suspended metal droplet morphological oscillation, characterized in that, include: The image acquisition module is used to acquire multiple frames of oscillation images of electrostatically suspended metal droplets at each excitation frequency according to the applied dynamically changing excitation frequency; wherein, the dynamic change process of the excitation frequency is that the initial excitation frequency gradually increases to the final excitation frequency, and the final excitation frequency gradually decreases to the initial excitation frequency. The instantaneous amplitude determination module is used to perform the following steps for each oscillation image at each excitation frequency: extract the boundary of the oscillation image to obtain a set of boundary points; and determine the instantaneous amplitude based on the set of boundary points and the profile expression of the metal droplet. The frequency and amplitude acquisition module is used to perform Fourier transform and fitting on the instantaneous amplitude of each oscillation image to obtain the morphological oscillation frequency and amplitude of the metal droplet at the current excitation frequency. The curve plotting module is used to plot positive and negative morphological oscillation amplitude-frequency curves based on the morphological oscillation frequency and amplitude at each excitation frequency. The intrinsic frequency determination module is used to take the average of the forward oscillation frequency and the reverse oscillation frequency at the point of maximum amplitude in the curve as the intrinsic frequency of the metal droplet morphological oscillation.