CN113466333B - Experimental system and detection method for researching focused ultrasound excited liquid drop ejection characteristics - Google Patents
Experimental system and detection method for researching focused ultrasound excited liquid drop ejection characteristics Download PDFInfo
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Abstract
The invention provides an experimental system and a detection method for researching the spray characteristics of focused ultrasound excited liquid drops, wherein a self-focusing ultrasonic transducer is used in combination with a source fluid pool array, the liquid drop formation, separation and flight characteristic observation of various reagents under different ultrasonic driving parameters in the ultrasonic liquid transfer process are utilized to predict the liquid characteristics, a data set is established, and a design scheme of excitation power can be directly given according to the requirement on the flight speed of liquid drops during the coalescence of the liquid drops when an unknown reagent is excited, so that the time is saved, high-flux reagent distribution can be realized, and a key technical scheme is provided for the construction of a miniaturized and micro reagent transfer device.
Description
Technical Field
The invention relates to the technical field of focusing acoustic energy to realize high-flux reagent transfer, in particular to an experimental system and a detection method for researching the spray characteristics of focused ultrasound-excited liquid drops.
Background
With the continuous shrinking of reaction systems in biochemical analysis, there is an urgent need for nano-liter scale micro-droplet transfer techniques, such as inkjet printing (based on thermal, piezoelectric, and electrokinetic fluid droplet generation mechanisms), pressure-driven techniques, laser-assisted bio-printing, stereolithography, and Acoustic Droplet Ejection (ADE). Wherein inkjet printing and pressure driven techniques require nozzles or orifices to produce droplets, which can impart significant shear stress to the fluid during droplet formation, leading to high cell death rates if used to transfer cells, and the nozzles or orifices are also highly susceptible to clogging, affecting overall system performance; laser-assisted bioprinting is susceptible to metal contamination; stereolithography is difficult to spread in the biological field because of the residue of a photo-curing agent that affects the activity of DNA. ADE as a non-contact micro-droplet transfer technology can avoid cross contamination, can realize high-flux fluid transmission, and has high fluid transmission precision without being limited by a nozzle. The ADE system has been widely used as a powerful micro-droplet transfer tool for the distribution and transfer of proteins, nucleic acids, and living cells.
The ADE system consists essentially of three parts, including an ultrasound transducer (e.g., a piezoelectric transducer), a source fluid cell, and a target substrate. When the system works, the source fluid pool is fixed, and the target substrate is positioned right above the source fluid pool and moves simultaneously with the ultrasonic transducer below the source fluid pool. To maximize the efficiency of the droplet ejection, the distance between the ultrasonic transducer and the source fluid cell is adjusted according to the depth of the liquid in the source fluid cell so that the ultrasonic transducer focus point is always at the liquid surface in the source fluid cell. When using a single ultrasound transducer, the positioner should allow the ultrasound transducer to move rapidly from one source fluid pool to another, thereby enabling droplet transfer of different reagents. Because the different reagents have different fluidic characteristics, resulting in different power requirements for the ultrasound transducers to excite the droplets, when a single ultrasound transducer is used for droplet excitation of different reagents, the excitation power of the reagents in the respective source fluid cells needs to be evaluated to ensure successful ejection of the reagent droplets. Coalescence of upwardly flying droplets on a target substrate is affected by the Weber number We (We = ρ U) 2 D/σ, where ρ is the density of the liquid, U is the velocity of the drop, D is the drop diameter, and σ is the liquid surface tension), there is an optimal range of weber numbers for drop coalescence during drop transfer, for example, when the drop flight velocity is too low, it will not coalesce efficiently on the target substrate, and when the velocity is too high, it will cause the drop to splash. From the calculation formula of the Weber number, the velocity sum when a specific reagent is sprayedThe change in volume is the primary controllable factor affecting droplet coalescence. The volume of the droplets depends on the wavelength and focal length of the ultrasound transducer, which is fixed for an ADE system based on a single focused ultrasound transducer, and the change in droplet volume is not as significant for coalescence as the velocity, so adjusting the droplet flight velocity by controlling the ultrasound power is a more desirable approach. The complex physical properties of the fluids, particularly differences in surface tension and viscosity, result in different ultrasonic drive powers being required for different fluids to achieve a particular drop flight speed and coalescence effect.
There are two methods of evaluating the drive power required to eject a drop. The first method increases the acoustic power delivered to the fluid surface in 0.1dB increments until the acoustic intensity is sufficient to produce a single drop of the desired velocity. Currently, most ADE systems use this method, which is easy to implement, but the step of increasing the acoustic power in increments is repeated when each reagent is ejected, and the specific number of increases cannot be determined, and the procedure is extremely complicated when the number of ejected samples is large. The second method is Dynamic Fluid Analysis (DFA), which uses interferometric perturbation measurements to characterize the dynamic response of a fluid surface to acoustic energy in real time. By this measurement, the jetting threshold of the droplet, i.e. the ultrasonic drive power of the "zero velocity" droplet, can be determined quickly. However, there is no description in the literature of how to determine the optimum acoustic power to obtain the desired drop velocity.
Currently, these two power control schemes have been applied in studies of ADE. In particular, dynamic fluid analysis is combined with an audit measurement of the acoustic impedance of each source fluid pool so that the ADE can be extended to a variety of fluids. They all suffer from the same problem, however, that when thousands of fluid transfer operations are involved, a significant amount of time will be wasted in repeating the power evaluation and determination process. The conventional surface tension measurement methods are as follows: the pendant drop method, the maximum bubble pressure method, the capillary height method, the donuo ring method and the like, and the viscosity measurement method comprises the following steps: the falling ball method, the damped vibration method, the rotating barrel method, the capillary method and the like all have the defect that the falling ball method, the damped vibration method, the rotating barrel method, the capillary method and the like have to be in contact with a test sample, and the equipment is extremely troublesome to clean when the number of samples is large, so that the method is obviously not suitable for measuring the physical characteristics of the fluid in the ADE system. Therefore, a device and a method for rapidly determining the fluid characteristics of a plurality of reagents in a source fluid pool array are urgently needed, and a foundation is laid for realizing convenient and accurate regulation and control of excitation power in the ultrasonic pipetting process.
Disclosure of Invention
The invention aims to provide an experimental system for researching the spraying characteristics of focused ultrasound excited liquid drops.
Another technical problem to be solved by the present invention is to provide a detection method for studying the ejection characteristics of focused ultrasound-excited droplets.
In order to solve the technical problems, the technical scheme of the invention is as follows:
an experimental system for researching the spray characteristics of a focused ultrasound excited liquid drop comprises a self-focusing ultrasonic transducer, a signal generator, an oscilloscope, a pulse transceiver, a source fluid pool array, a liquid drop observation device, a power amplifier, a coupling medium and a three-dimensional displacement platform, wherein the coupling medium is arranged between the self-focusing ultrasonic transducer and the source fluid pool array, the three-dimensional displacement platform is used for controlling the self-focusing ultrasonic transducer and the source fluid pool array, the liquid drop observation device is formed by connecting a high-speed camera and an upper computer through a line, the signal generator is respectively connected with the power amplifier and the high-speed camera through a line, the pulse transceiver is connected with the oscilloscope through a line, the power amplifier and the pulse transceiver are respectively connected with the self-focusing ultrasonic transducer through a line, the self-focusing ultrasonic transducer is fixed on the left side of one three-dimensional displacement platform by using a clamp, the source fluid pool array is fixed above the other three-dimensional displacement platform, the two three-dimensional displacement platforms can move in the X, Y and Z directions, the ultrasonic transducer can move to enable the ultrasonic transducer to move to be capable of moving right below each source fluid pool in the source fluid pool, the interface of the source fluid and the air, the coupling medium is connected with the self-focusing ultrasonic transducer through the coupling medium, and the concave fluid pool, and the coupling medium, and the source fluid pool array, and the concave fluid pool are filled in the concave fluid pool.
Preferably, in the experimental system for studying the droplet ejection characteristics excited by the focused ultrasound, the coupling medium is a fluid medium having an acoustic impedance substantially equal to an acoustic impedance of the source fluid pool.
A detection method for researching the spray characteristics of focused ultrasound excited liquid drops comprises the following steps:
(1) The pulse transceiver obtains echoes generated when ultrasonic waves pass through different acoustic impedance interfaces through the self-focusing ultrasonic transducer, and completes measurement of sound velocity of different reagents and measurement of liquid level height of the reagents in the source fluid pool according to difference values of receiving time of echo signals;
(2) The dynamic process of exciting a reagent to generate liquid drops in each source fluid pool unit by a self-focusing ultrasonic transducer is tracked and observed in real time, the capillary wave height at the threshold energy position and the characteristic parameters of the liquid drop speed in the exciting process are recorded, and the surface tension and the viscosity of the reagent are measured according to the characteristic parameters and the corresponding ultrasonic driving power.
In the detection method, echoes generated by ultrasonic passing through interfaces with different acoustic impedances comprise an initial pulse echo signal, a coupling medium/source fluid pool bottom interface echo signal, a source fluid pool top bottom/reagent interface echo signal and a reagent/air interface echo signal. The threshold energy refers to the ultrasonic energy used to break the droplet off the surface of the reagent at a velocity of 0. The capillary wave refers to a liquid level bulge caused after ultrasonic focusing on the surface of a reagent.
Preferably, the detection method for studying the droplet ejection characteristics excited by focused ultrasound measures the sound velocity by the time difference between the initial pulse echo signal received by the pulse transceiver and the oscilloscope and the echo signal of the bottom interface of the coupling medium/source fluid pool; and the reagent liquid level height is measured by the time difference between the echo signal of the upper bottom/reagent interface of the source fluid pool and the echo signal of the reagent/air interface received by the pulse transceiver and the oscilloscope.
Preferably, the detection method for studying the focused ultrasound-excited droplet ejection characteristics synchronously controls the power amplifier and the droplet observation device in real time, and realizes the single excitation of the droplet and the recording of the capillary height and the excitation power of the single droplet in the excitation process, and the detection method comprises the following specific steps:
(1) The signal generator outputs two paths of signals, the first signal is a sine pulse and drives the self-focusing ultrasonic transducer after passing through the power amplifier, and the second signal is a TTL signal and drives the high-speed camera;
(2) The first signal is set to be in an external trigger mode, and the whole system carries out liquid drop excitation once when a signal generator trigger key is clicked once and records related data.
Preferably, the detection method for studying the droplet ejection characteristics excited by the focused ultrasound includes the following steps of adjusting the positions of the self-focusing ultrasound transducer and the source fluid cell array, so that the focal point of the self-focusing ultrasound transducer is located at the reagent surface, and gradually reducing the ultrasound energy until a threshold energy point appears:
(1) The liquid level height is measured through a pulse transceiver and an oscilloscope;
(2) Finely adjusting the position of the self-focusing ultrasonic transducer in the Z direction to enable the amplitude of an echo signal of a reagent/air interface to be maximum, wherein the focus of the self-focusing ultrasonic transducer is positioned on the surface of the reagent;
(3) And gradually reducing the ultrasonic energy to the threshold point, recording the used ultrasonic driving power P, and performing image processing on the capillary wave excited by the threshold energy to obtain the capillary wave height h.
Preferably, in the detection method for studying the droplet ejection characteristics excited by the focused ultrasound, the capillary height of the droplet is measured by extracting the edge of the capillary image by using an image edge recognition algorithm and intercepting a required part as the height of the capillary, and the capillary height h is obtained by calculating the number of pixel points in the vertical direction.
Preferably, in the detection method for studying the droplet ejection characteristics excited by the focused ultrasound, the lowest point of the intercepted required part is a position where the liquid level at the bottom of the capillary wave starts to rise, and the highest point is a finest position where the neck is formed by the boundary between the capillary wave and the droplet, namely, a top point of the capillary wave at the moment when the droplet is separated from the droplet.
Preferably, the detection method for studying the ejection characteristics of the focused ultrasound-excited liquid droplets uses a reagent with a known surface tension to predict the surface tension of an unknown reagent according to the capillary height at the threshold and the ultrasonic driving power, and comprises the following specific steps: using the ultrasonic drive power P and the measured density ρ, sound velocity c, and capillary height h, the surface tension of the agent is obtained according to the following equation:
wherein sigma 1 、ρ 1 、c 1 、h 1 、P 1 Knowing the surface tension, density, speed of sound, capillary height and ultrasonic drive power at threshold, σ, of the first reagent 2 、ρ 2 、c 2 、h 2 、P 2 The surface tension, density, speed of sound, capillary height and ultrasonic drive power at the threshold of the second reagent are unknown. c. The h value can be measured by the method.
The detection method for researching the ejection characteristics of the focused ultrasound excited liquid drops realizes the viscosity prediction of unknown reagents based on a separation speed-ultrasonic driving power data set and a separation speed-capillary height data set of various known viscosity reagents. The drop separation speed is the initial speed of the upward flight of the drop separation moment, the speed is in direct proportion to the ultrasonic driving power, the capillary wave height of the drop separation moment is in direct proportion to the drop separation speed, under the condition that the drop separation speeds are the same, the required ultrasonic driving power is increased in proportion along with the increase of the viscosity of the reagent, and meanwhile, the corresponding capillary wave height is also increased in proportion, so that the standard for predicting the viscosity of unknown reagents can be used after a database of relevant characteristic parameters of various reagents is established.
The viscosity value interval of the various agents with known viscosity comprises the viscosity variation range of the agents commonly used in practical application.
The measurement of the droplet speed uses a standard centroid algorithm to extract coordinates of centroids of the same droplet at different moments in the flying process, droplet centroid coordinates of any two time points and a time point at which the droplet is about to break away are selected, and the speed of the droplet in breaking away is calculated under the condition of only considering the gravitational acceleration.
Has the advantages that:
the experimental system and the detection method for researching the focused ultrasound excited droplet ejection characteristics use the self-focusing ultrasonic transducer in combination with a source fluid pool array, realize the prediction of liquid characteristics by utilizing the observation of droplet formation, separation and flight characteristics of various reagents under different ultrasonic driving parameters in the ultrasonic pipetting process, establish a data set, directly provide a design scheme of excitation power according to the requirement on the droplet flight speed during droplet coalescence when exciting unknown reagents, not only save time, but also realize high-flux reagent distribution, and provide a key technical scheme for the construction of a miniaturized and micro-reagent transfer device. Wherein, the first and the second end of the pipe are connected with each other,
the self-focusing ultrasonic transducer can directly drive energy to a required position, and the displacement platform can move in the X direction and the Y direction, so that each fluid pool unit in the source fluid pool array can be conveniently operated.
Based on the observation of the formation, separation and flight characteristics of liquid drops of various reagents in the source fluid pool array under different ultrasonic driving parameters, the surface tension and viscosity of the various reagents are measured.
A relational data set of reagent properties and ultrasonic driving energy is established through multiple experiments and can be used as a database all the time, so that reagents with different properties can be sprayed according to requirements more directly and accurately.
Drawings
FIG. 1 is a simplified diagram of an experimental system for studying the droplet ejection characteristics of focused ultrasound excitation;
FIG. 2 is a schematic diagram of droplet excitation by a self-focusing ultrasonic transducer;
FIG. 3 is a schematic diagram of echo signals generated after ultrasound passes through interfaces with different acoustic impedances;
FIG. 4 is an experimental plot of a drop about to break off and its capillary wave;
FIG. 5 is a GUI interface for calculating capillary height using MATLAB;
FIG. 6 is a GUI interface for calculating drop break-off velocity using MATLAB;
FIG. 7 is a graph showing drop break-off speed versus ultrasonic drive power for different viscosities;
FIG. 8 is a graph showing the relationship between capillary height and drop release velocity for different viscosities;
in the figure:
1: droplet, 2: capillary wave, 3: first source fluid pool, 4: second source fluid pool
5: first reagent, 6: second reagent, 7: coupling medium, 8: self-focusing ultrasonic transducer
9: drop to be released, 10: highest point of capillary, 11: lowest point of capillary wave
12: signal generator, 13: oscilloscope, 14: pulse transceiver, 15: power amplifier
16: high-speed camera, 17: upper computer
Detailed Description
Example 1
The specific information of each component in the following embodiments is as follows: self-focusing ultrasonic transducers were purchased from OLYMPUS V309, USA AFG3000, oscilloscope TDS 2024, inc. TDS 2024, pulsed transceiver from OLYMPUS Model 5073PR, USA 384-well microplates or other products with the same function as the source fluid cell array, high-speed cameras from Photoron FASTCAM SA5, power amplifiers from Amplifier Research 125A250, and three-dimensional displacement platform from Tokyo Han, china.
As shown in fig. 1-2, the experimental system for studying the droplet ejection characteristics excited by focused ultrasound includes a self-focusing ultrasonic transducer 8, a signal generator 12, an oscilloscope 13, a pulse transceiver 14, a source fluid pool array, a droplet observation device, a power amplifier 15, a coupling medium 7 interposed between the self-focusing ultrasonic transducer and the source fluid pool array, and a three-dimensional displacement platform (not shown) for controlling the self-focusing ultrasonic transducer and the source fluid pool array, wherein the coupling medium is a fluid medium having acoustic impedance, the source has substantially the same acoustic impedance as the source fluid pool, the droplet observation device is composed of a high-speed camera 16 and an upper computer 17, the signal generator is respectively connected with the power amplifier and the high-speed camera, the pulse transceiver is connected with an oscilloscope, the power amplifier and the pulse transceiver are respectively connected with the self-focusing ultrasonic transducer, the self-focusing ultrasonic transducer is fixed on the left side of one three-dimensional displacement platform by using a clamp, the source fluid pool array is fixed above the other three-dimensional displacement platform, the two three-dimensional displacement platforms can move in three directions of X, Y and Z, the movement in the direction of the ultrasonic transducer enables the source fluid array to move to contact with the air of the source fluid pool in the positive source fluid pool, and the concave fluid pool, the air of the ultrasonic transducer is connected with the ultrasonic transducer, and the concave displacement platform, the ultrasonic transducer is connected with the ultrasonic transducer, and the ultrasonic transducer. The source fluid cell array comprises at least two source fluid cells: a first source fluid cell 3 and a second source fluid cell 4, wherein the first source fluid cell 3 contains a first reagent 5 and the second source fluid cell 4 contains a second reagent 6.
The source fluid cell structure may be a material having a planar structure, such as a glass slide (glass or polystyrene microscope slide) or the like, as well as single well and multiwell plates for molecular biology applications, capillaries (e.g., capillary arrays), and the like.
The coupling medium refers to a fluid medium having an acoustic impedance substantially the same as that of the source fluid cell, and is in contact with and connected to the self-focusing ultrasonic transducer and the source fluid cell, respectively, to allow efficient energy transfer from the ultrasonic transducer to the source fluid cell. For example, when the source cell is polystyrene with an acoustic impedance of about 2.3MRayl and water with an acoustic impedance of about 1.7MRayl, water may be selected as the coupling medium, or a better match may be achieved by adding other fluids to the water, and used in the practice of the invention.
As shown in fig. 2, the self-focusing ultrasonic transducer 8 emits ultrasonic waves through the coupling medium 7, the source fluid pool to the reagent surface to form capillary waves 2 and excite droplets 1. Reflected waves as shown in fig. 3 are formed when the ultrasound passes through various regions with different acoustic impedances, and the reflected waves include an initial pulse echo signal, a coupling medium/source fluid pool bottom interface echo signal, a source fluid pool top/reagent interface echo signal, and a reagent/air interface echo signal. The four signals are available to the pulse transceiver and displayed on an oscilloscope.
If the distance from the lowest point of the concave mask of the self-focusing ultrasonic transducer 8 to the lower bottom of the source fluid pool is fixed to be L, different reagents are filled between the self-focusing ultrasonic transducer and the source fluid pool to be used as coupling media, a pulse transceiver is used for obtaining an initial pulse signal and a coupling medium/source fluid pool lower bottom interface echo signal and displaying the initial pulse signal and the coupling medium/source fluid pool lower bottom interface echo signal on an oscilloscope, and a time difference t between the two echo signals is obtained c The sound velocity in the reagent can be obtained as follows:
obtaining the time difference th between echo signals of the upper bottom/reagent interface and the reagent/air interface of the source fluid pool through an oscilloscope, wherein if the sound velocity in the reagent is c, the liquid level height in the source fluid pool is
At the moment, the three-dimensional displacement platform of the ultrasonic transducer is adjusted and controlled to enable the focus of the three-dimensional displacement platform to be positioned on the surface of the reagent, and then liquid drop excitation can be carried out.
The power amplifier and the liquid drop observation system are synchronously controlled as shown in fig. 1, so that the single excitation of the liquid drop and the recording of the capillary wave height and the excitation power of the single liquid drop in the excitation process are realized. The signal generator outputs two paths of signals, the first signal is a sine pulse and drives the self-focusing ultrasonic transducer after passing through the power amplifier, and the second signal is a TTL signal and drives the high-speed camera; the first signal is set to be in an external trigger mode, and the whole system carries out liquid drop excitation once when a signal generator trigger key is clicked once and records related data.
And processing an image shot by a high-speed camera after the liquid drop is excited, converting the image into a binary image, and writing an MATLAB program for capillary height calculation and speed calculation respectively. The identification of the capillary wave profile is realized by using a bounding function, the height interception is realized by selecting a capillary wave fixed characteristic, as shown in fig. 4, the lowest point 11 of the capillary wave is the initial uplift position of the liquid level at the bottom of the capillary wave, the highest point 10 of the capillary wave is the thinnest position of the neck formed by the junction of the capillary wave and the liquid drop, after the program processing, a capillary wave height map as shown in fig. 5 is formed, and the capillary wave height can be obtained by calculating the number of pixel points in the vertical direction in the rightmost map of fig. 5; calculating the drop separation speed, firstly, using a hole filling function imfill to a binary image to enable the drop image to only leave a circular area, then, writing a program to identify the centroid of the drop according to a distance centroid algorithm principle, as shown in fig. 6, arbitrarily selecting the coordinates of the drop centroid of two time points and the time point at which the drop is about to separate, calculating the speed of the drop 9 at which the drop is about to separate under the condition of only considering the gravitational acceleration, wherein z1 in fig. 6 is the frame rate of the difference between the left drop image and the right drop image, z2 is the frame rate of the difference between the left shorter drop image and the separated drop image, the frame rate used by a high-speed camera is 20000fps, and the size of each pixel point in a shot image is 5 μm, and the specific steps are as follows:
1) Taking any two time points t in the flight process of the same liquid drop 1 、t 2 The resulting centroid coordinate x 1 、x 2 And the point of time t when the droplet is detached 0 ；
2) The drop break-off speed was:
wherein h is x ＝x 2 -x 1 ，Δt 1 ＝t 2 -t 1 ，Δt 2 ＝t 1 -t 0 G is the gravity acceleration of 9.8m/s 2 。
The drop firing was gradually reduced in firing power and the drop break-off speed recorded at a series of power values until a threshold occurred and the capillary height recorded at that time.
The prediction of the surface tension of an unknown agent with an agent of known surface tension is achieved from the capillary height at the threshold and the ultrasonic drive power as follows:
using the ultrasonic drive power P and the measured density ρ, sound velocity c, and capillary height h, the surface tension of the agent is obtained according to the following equation:
wherein sigma 1 、ρ 1 、c 1 、h 1 、P 1 Knowing the surface tension, density, speed of sound, capillary height and ultrasonic drive power at threshold, σ, of the first reagent 2 、ρ 2 、c 2 、h 2 、P 2 The surface tension, density, speed of sound, capillary height and ultrasonic drive power at the threshold of the second reagent are unknown.
Prediction of unknown agent viscosity is accomplished by establishing a pull-off velocity-ultrasonic drive power dataset and a pull-off velocity-capillary height dataset for a variety of known viscosity agents. The drop separation speed is the initial speed of upward flight at the drop separation moment, the speed is proportional to the ultrasonic driving power, the capillary wave height at the drop separation moment is proportional to the drop separation speed, under the condition that the drop separation speed is the same, the required ultrasonic driving power is increased in proportion along with the increase of the viscosity of the reagent, and the corresponding capillary wave height is also increased in proportion, as shown in figures 7 and 8, so that the method can be used as a standard for predicting the viscosity of unknown reagents after a database of relevant characteristic parameters of various reagents is established. When the method is used for prediction, the capillary wave height and the ultrasonic driving power at any speed point are obtained, and the viscosity information is obtained by comparing the capillary wave height and the ultrasonic driving power with a known database.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.
Claims (6)
1. A detection method for researching the liquid drop spraying characteristic excited by focused ultrasound is characterized in that an experimental system comprises a self-focusing ultrasonic transducer, a signal generator, an oscilloscope, a pulse transceiver, a source fluid pool array, a liquid drop observation device, a power amplifier, a coupling medium between the self-focusing ultrasonic transducer and the source fluid pool array and a three-dimensional displacement platform for controlling the self-focusing ultrasonic transducer and the source fluid pool array, wherein the liquid drop observation device is formed by connecting a high-speed camera and an upper computer through a circuit, the signal generator is respectively connected with the power amplifier and the high-speed camera through a circuit, the pulse transceiver is connected with the oscilloscope through a circuit, the power amplifier and the pulse transceiver are respectively connected with the self-focusing ultrasonic transducer through a circuit, the self-focusing ultrasonic transducer is fixed on the left side of one three-dimensional displacement platform by using a clamp, the source fluid pool array is fixed above the other three-dimensional displacement platform, the two three-dimensional displacement platforms can move in the X, Y and Z directions, and a filling coupling medium is dripped between a concave mask of the self-focusing ultrasonic transducer and the source fluid pool to enable the coupling medium to be in contact with the source fluid pool array, and is characterized in that: the method comprises the following steps:
(1) The pulse transceiver obtains echoes generated when ultrasonic waves pass through different acoustic impedance interfaces through the self-focusing ultrasonic transducer, and completes measurement of sound velocity of different reagents and measurement of liquid level height of the reagents in the source fluid pool according to difference values of receiving time of echo signals;
(2) The dynamic process of exciting a reagent to generate liquid drops in each source fluid pool unit by a self-focusing ultrasonic transducer is tracked and observed in real time, the capillary wave height at the threshold energy position and the characteristic parameters of the liquid drop speed in the exciting process are recorded, and the measurement of the surface tension and the viscosity of the reagent is realized according to the characteristic parameters and the corresponding ultrasonic driving power: using the ultrasonic drive power P and the measured density ρ, sound velocity c, and capillary height h, the surface tension of the agent is obtained according to the following equation:
wherein σ 1 、ρ 1 、c 1 、h 1 、P 1 The surface tension and density of the first reagent are knownSpeed of sound, capillary height and ultrasonic drive power at threshold, σ 2 、ρ 2 、c 2 、h 2 、P 2 The values of c and h can be measured by the method for unknown surface tension, density, sound velocity, capillary height and ultrasonic driving power at the threshold value of the second reagent.
2. The detection method for researching the ejection characteristics of the focused ultrasound-excited liquid drops according to claim 1, characterized in that: measuring the sound velocity through the time difference between the initial pulse echo signal received by the pulse transceiver and the oscilloscope and the echo signal of the bottom interface of the coupling medium/source fluid pool; and the reagent liquid level height is measured by the time difference between the echo signal of the upper bottom/reagent interface of the source fluid pool and the echo signal of the reagent/air interface received by the pulse transceiver and the oscilloscope.
3. The detection method for researching the ejection characteristics of the focused ultrasound-excited liquid drops as claimed in claim 2, wherein: the method is characterized in that a power amplifier and a liquid drop observation device are synchronously controlled in real time, so that single excitation of liquid drops and recording of capillary wave height and excitation power of the single liquid drops in the excitation process are realized, and the method comprises the following specific steps:
(1) The signal generator outputs two paths of signals, the first signal is a sine pulse and drives the self-focusing ultrasonic transducer after passing through the power amplifier, and the second signal is a TTL signal and drives the high-speed camera;
(2) The first signal is set to be in an external trigger mode, and the whole system carries out liquid drop excitation once and records related data when the signal generator trigger key is clicked once.
4. The detection method for researching the ejection characteristics of the focused ultrasound-excited liquid drops according to claim 1, is characterized in that: adjusting the positions of a self-focusing ultrasonic transducer and a source fluid pool array to enable the focal point of the self-focusing ultrasonic transducer to be positioned at the surface of the reagent, and gradually reducing ultrasonic energy until a threshold energy point appears, wherein the method comprises the following specific steps:
(1) The liquid level height is measured through a pulse transceiver and an oscilloscope;
(2) Finely adjusting the position of the self-focusing ultrasonic transducer in the Z direction to enable the amplitude of an echo signal of a reagent/air interface to be maximum, wherein the focus of the self-focusing ultrasonic transducer is positioned on the surface of the reagent;
(3) And gradually reducing the ultrasonic energy to the threshold point, recording the used ultrasonic driving power P, and performing image processing on the capillary wave excited by the threshold energy to obtain the capillary wave height h.
5. The detection method for researching the ejection characteristics of the focused ultrasound-excited liquid drops according to claim 1, characterized in that: the liquid drop capillary wave height measurement uses an image edge recognition algorithm to extract the edge of a capillary wave image and intercept a required part as the capillary wave height, and the capillary wave height h is obtained by calculating the number of pixel points in the vertical direction.
6. The detection method for researching the ejection characteristics of the focused ultrasound-excited liquid drops as claimed in claim 5, wherein: the lowest point of the part required for intercepting is the position where the liquid level at the bottom of the capillary wave begins to rise, and the highest point is the thinnest position where the neck is formed by the junction of the capillary wave and the liquid drop, namely the top point of the capillary wave at the moment the liquid drop breaks away from.
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