CN112495675B

CN112495675B - High flux micro-droplet generating device based on multi-source excitation

Info

Publication number: CN112495675B
Application number: CN202011163897.1A
Authority: CN
Inventors: 胡亮; 佘垒; 付新
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-10-27
Filing date: 2020-10-27
Publication date: 2022-04-01
Anticipated expiration: 2040-10-27
Also published as: CN112495675A

Abstract

The invention provides a high-flux micro-droplet generating device based on multi-source excitation, which utilizes a plurality of acoustic vibration sources to generate converged and superposed acoustic signals to act near a micron-sized small hole, so that liquid jet ejected through the small hole is disturbed, the liquid jet breaks to form small droplets due to Rayleigh instability, and satellite droplets in a droplet queue can be eliminated. An acoustic lens structure is arranged, so that acoustic signals generated by an acoustic vibration source can be converged and superposed more intensively; the acoustic lens isolates the liquid in the pressure liquid containing cavity from the vibration excitation element of the acoustic vibration source, so that the vibration excitation element can be prevented from being damaged; the pressure liquid cavity and the surface of the acoustic lens, which is in contact with the liquid, adopt materials generating few pollutants to adapt to high-cleanliness occasions; meanwhile, the liquid drop generating device provided by the invention is utilized to respectively provide sine waveform excitation signals with different frequencies for a plurality of sound vibration sources, and the sound wave signals generated by the sound vibration sources are also sine waveforms, so that waveform parameters can be modified conveniently to obtain better control effect on the liquid drop shapes.

Description

High flux micro-droplet generating device based on multi-source excitation

Technical Field

The invention relates to the technical field of liquid drop generating devices, in particular to a high-flux micro-liquid drop generating device based on multi-source excitation.

Background

Rayleigh instability of a jet is an interfacial fluid mechanics principle, which means that the jet can automatically break into liquid drops consistent with a given frequency under the vibration disturbance of the given frequency. The micro-droplet generating device based on jet Rayleigh instability can generate micron-sized droplets with adjustable frequency, size and droplet spacing, is particularly suitable for occasions with high-flux droplet requirements such as flux exceeding 10000 droplets/second, and has wide application in industries such as inkjet printing, bio-pharmaceuticals, additive manufacturing, EUV lithography machine light source target droplet generation and the like.

The existing micro-droplet generating device mostly adopts a built-in single excitation source, namely, a disturbance rod is used for guiding disturbance generated by piezoelectric ceramics to a position close to a nozzle in a cavity, so as to provide sound pressure disturbance for triggering Rayleigh instability for jet flow, and the disturbance rod is designed into a variable amplitude rod structure, so that the amplitude of the disturbance is improved. However, the design can only be used under a specific frequency, and if the frequency of the liquid drops is adjusted and the excellent performance of the liquid drops is ensured, the structural design of the amplitude transformer needs to be replaced, so that the operation and the use are inconvenient. In addition, because the frequency response of a single excitation source is fixed, the excited disturbance waveform is difficult to control, and the regulation and control effect of liquid drops is limited; for example, a satellite droplet is formed between main droplets after the jet flow is broken by single sine wave disturbance, and the satellite droplet can be given a relative speed relative to the main droplets by reasonably adjusting the waveform of the disturbance, so that the satellite droplet and the main droplets are quickly fused, and the occurrence of the satellite droplet is restrained.

In patent CN 103064260 a (a tin droplet target generating device for an extreme ultraviolet lithography machine light source), a single excitation source amplitude transformer structure is adopted to provide disturbance for a droplet generator, the use frequency is limited, and the disturbance waveform is inconvenient to regulate; patent CN 101879493 a (ultrasonic focused liquid atomizer) adopts acoustic focusing as a disturbance source for atomization, and a single excitation source has a single disturbance mode, belongs to an atomizer, does not belong to a rayleigh type droplet generator, and cannot generate single-row uniformly-distributed droplets; the patent CN 107051805 a (a droplet generator device with multi-excitation vibration) adopts multi-excitation disturbance, the excitation component is an electrically excited vibration plate, the vibration plate directly contacts with jet flow, and is not suitable for complex environments with high temperature and high viscosity, and the superposition mode of disturbance is unpredictable; patent CN 108295915 a (a method and apparatus for controlling jet break-off and droplet generation) adopts modulated wave to control the fusion of main droplet and satellite droplet, the excitation method is electric field non-contact disturbance, and its applicability is limited by the fluid electrical characteristics.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a high-flux micro-droplet generating device based on multi-source non-contact excitation, which can generate high-flux micro-droplets in a wider frequency range, can conveniently regulate and control the shapes of the droplets by regulating the waveform of disturbance, and is suitable for various complex environments and fluids. To achieve this, the disturbance propagation and amplification assembly of the present invention utilizes non-contact acoustic focusing techniques, employs a plano-concave acoustic lens structure, and is provided with multiple excitation sources. The power-receiving excitation unit (here, piezoelectric ceramic) is in non-contact with the jet flow fluid, and disturbance is transmitted to the nozzle in a spherical sound wave form, so that the applicability of a complex environment is improved. The nozzle is positioned at the acoustic focus of the acoustic lens, and the focusing action of the acoustic lens focuses and amplifies the disturbance generated by the piezoelectric ceramic, so that the disturbance with larger amplitude can be generated in a wider frequency range, and the frequency adjusting range of the liquid drop generator is enlarged. The disturbance of the multiple excitation sources is superposed at the focus, and the superposed disturbance waveform can be conveniently adjusted by adjusting the parameters of each excitation source, so that the form of the generated liquid drop can be conveniently adjusted and controlled, for example, the occurrence of satellite liquid drops is inhibited.

The invention comprises a liquid supply component, a pressure liquid cavity, a spray head and an excitation component; the liquid supply assembly is used for supplementing liquid to the pressure liquid cavity and maintaining the positive pressure of the liquid relative to the environment outside the cavity; the spray head is arranged on the wall surface of the pressure liquid cavity and is provided with a small hole with the diameter of 1-1000 microns; the excitation assembly comprises two or more than two sound vibration sources, each sound vibration source comprises an excitation element and a sound lens, and the sound lens is of a concave structure; the sound focuses of the sound lenses are all positioned at the small holes of the spray head.

Furthermore, the concave surfaces of the two or more than two acoustic lenses are coplanar on the same spherical surface.

Furthermore, the nozzle comprises a pore plate, a small hole is formed in the pore plate, a sealing ring is arranged between the pore plate and the pressure liquid containing cavity, and the pore plate and the sealing ring are tightly pressed on the wall surface of the pressure liquid containing cavity by using a pressing end cover.

Preferably, the inner wall surface of the pressure liquid container is made of high-cleanliness stainless steel or a fluorine-containing resin material.

Preferably, the acoustic lens is made of quartz glass.

Preferably, the excitation element of the acoustic vibration source is a piezoelectric ceramic stack.

Further, the liquid pressure monitoring device also comprises a pressure sensor for monitoring the liquid pressure in the pressure liquid cavity; the liquid temperature monitoring device further comprises a temperature sensor for monitoring the liquid temperature in the pressure liquid cavity.

Preferably, the pores have a diameter of between 10 and 100 microns.

Further, the plurality of sound vibration sources respectively receive sine wave-shaped excitation signals with different frequencies.

The invention provides a high-flux micro-droplet generating device based on multi-source excitation, which utilizes a plurality of acoustic vibration sources to generate converged and superposed acoustic signals to act near a micron-sized small hole, so that liquid jet ejected through the small hole is disturbed and is broken to form small droplets due to Rayleigh instability; the sound wave is used as a disturbance signal to be applied to liquid flow to generate liquid drops, so that the liquid drop generator is suitable for wide application occasions including high-temperature, high-viscosity or insulating liquid and the like; the plurality of sound vibration sources can generate sound waves with different frequencies and other characteristics, and the sound waves are superposed and then act on the small holes, so that satellite droplets generated by jet flow fracture can be eliminated, and the size and the number of the droplets generated by the device can be more accurately controlled; an acoustic lens structure is arranged, so that acoustic signals generated by an acoustic vibration source can be converged and superposed more intensively; the acoustic lens isolates the liquid in the pressure liquid containing cavity from the vibration excitation element of the acoustic vibration source, so that the vibration excitation element can be prevented from being damaged; the pressure liquid cavity and the surface of the acoustic lens, which is in contact with the liquid, adopt materials generating few pollutants to adapt to high-cleanliness occasions; a hold-down structure is provided to fix the orifice plate so as to facilitate replacement of orifice plates of different sizes.

The liquid drop generating device provided by the invention is utilized to respectively provide sine waveform excitation signals with different frequencies for a plurality of sound vibration sources, and the sound wave signals generated by the sound vibration sources are also sine waveforms, so that waveform parameters can be modified conveniently to obtain better control effect on the liquid drop shapes.

Drawings

FIG. 1 is a schematic structural diagram of a micro-droplet generator;

FIG. 2 is a schematic illustration of acoustic wave disturbance propagation;

FIG. 3 is a schematic diagram of acoustic path focusing for a single excitation source;

FIG. 4 is a schematic illustration of a jet breaking into droplets under a single sinusoidal excitation;

FIG. 5 is a schematic of jet break-up into droplets under multi-source harmonic excitation.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

As shown in fig. 1 and fig. 2, the high-flux micro-droplet generating device based on multi-source excitation according to the present invention includes a liquid supply assembly LS, a pressure liquid chamber CH, a nozzle SP, and an excitation assembly ST. The liquid supply assembly LS includes a low pulsation advection pump 1 and a high precision pressure control valve 2. The low-pulsation advection pump 1 supplies liquid to the cavity, and the high-precision pressure control valve 2 adjusts the liquid pressure of the cavity, so that the jet speed can be adjusted, and the size and the distance of liquid drops can be controlled. The pressure liquid cavity CH comprises an upper cover plate 3, a cavity 4 and a lower cover plate 5, the upper cover plate, the lower cover plate and the cavity are connected through bolts and sealed through sealing gaskets, the upper cover plate, the lower cover plate and the cavity are used for storing liquid and providing an installation structure for other components, and the inner wall surface of the pressure liquid cavity is made of materials with low pollutant generation, such as high-cleanliness stainless steel or fluorine-containing resin. The spray head SP adopts a pore plate type nozzle structure and comprises a pressing end cover 6, a pore plate 7 and a sealing ring 8, wherein the pressing end cover 6 presses the pore plate 7 on the lower cover plate 5 and provides pretightening force for the sealing ring 8, the pore plate 7 is made of a hard thin plate material, a micron-sized (1-1000 microns) through pore 9 is processed by femtosecond laser and other processes, liquid in a cavity is ejected out through the pore 9 of the pore plate to generate jet flow with the diameter of the micron-sized diameter, the diameter of the jet flow is consistent with that of the pore, the structure is convenient to disassemble, the pore plates 7 with different sizes can be conveniently replaced, and the diameter of the jet flow is adjusted, so that the size of liquid drops is controlled; the oversized holes 9 need to fit with high power and large volume sound vibration source 20, the undersized holes 9 are inconvenient to process, and preferably, the diameter of the holes 9 is between 10 microns and 100 microns. The excitation assembly ST comprises a signal generator 10, a power amplifier 11 and a plurality of acoustic vibration sources 20, each acoustic vibration source 20 comprising an excitation element such as a piezo-ceramic stack 12, a backing 13 and an acoustic lens 15; the signal generator 10 generates a sine wave signal with a set frequency, the sine wave signal is amplified by the power amplifier 11 and then is connected to the piezoelectric ceramic stack 12, the piezoelectric ceramic stack 12 converts the electric signal into a vibration signal, and the backing 13 is used for reducing energy dissipation; the acoustic lens 15 is a concave structure for amplifying the acoustic wave 14, and is made of quartz glass to avoid generating pollutants, and the acoustic lens 15 separates the piezoelectric ceramic stack 12 from the liquid in the chamber to avoid the piezoelectric ceramic stack 12 from being damaged by high-temperature liquid tin in a light source droplet generating device of an EUV lithography machine; the vibration signal in the form of a plane wave generated by the piezoelectric ceramic stack 12 is converted into a sound wave 14 in the form of a spherical wave and converged at the acoustic focus of the acoustic lens 15, and the sound pressure at the acoustic focus is highest; the concave surfaces of the acoustic lenses 15 are coplanar with the same spherical surface, so that the distances between the acoustic lenses 15 and the small holes 9 are equal, and the phase calculation when the acoustic wave signals are superposed is convenient to calculate; the aperture 9 of the aperture plate 7 is arranged at the acoustic focus of the acoustic lens 15; each source 20 is controlled individually using a different channel of signal generator 10 and power amplifier 11; the acoustic waves 14 generated by the plurality of acoustic vibration sources 20 are superimposed at the aperture plate 7, and the acoustic focuses of the plurality of acoustic lenses 15 overlap at the aperture 9. The sensor 16 is arranged to monitor the pressure or temperature inside the pressure liquid cavity CH, monitor the pressure inside the pressure liquid cavity CH and perform feedback control to adjust the jet flow rate ejected from the small hole 9 and the amount of liquid generated subsequently, monitor the temperature inside the pressure liquid cavity CH and perform feedback control to be suitable for the EUV lithography light source target drop generating device, and the device needs to be heated to melt tin into liquid.

As shown in fig. 3, 4 and 5, when the device of the present invention is used, the liquid supply assembly LS is operated to stabilize the liquid pressure in the pressure liquid chamber CH, and at this time, the small holes 9 of the orifice plate 7 eject the jet flow with the consistent diameter and aperture; starting a signal generator 10 and a power amplifier 11, and inputting a sine wave-shaped excitation signal with a single frequency f to a sound vibration source 20A; the piezoelectric ceramic stack 12 of the acoustic vibration source 20A vibrates to generate acoustic waves 14, and the acoustic waves are focused and transmitted to the small holes 9 through the acoustic lens 15; the jet flow is excited by the sound wave 14 to generate a Rayleigh instability phenomenon and is broken into liquid drops 17, and the frequency of the generated liquid drops is f. Fig. 4 shows a waveform of the acoustic wave 14 and a schematic of the jet breaking into droplets 17; under a single sinusoidal excitation signal, undesirable satellite droplets 19 often exist between the main droplets 18, and when the excitation frequency is low, the distance between the main droplets 18 is large, and two satellite droplets 19 may appear between the main droplets 18; the frequency of the exciting signal input to the sound vibration source 20A is adjusted to control the frequency of the liquid drops, but the signal frequency f should avoid the characteristic frequency of the structure, so that the liquid drops are prevented from becoming a power ultrasonic component to cause jet atomization, and the size, the number and the motion track of the liquid drops generated after the jet atomization cannot be controlled; as shown in fig. 5, a sine-wave-shaped excitation signal of a single frequency 2f is input to the acoustic vibration source 20B, and the acoustic vibration source 20B generates an acoustic wave signal and is superimposed with the acoustic wave signal generated by the acoustic vibration source 20A at the small hole 9; adjusting the amplitude A of the excitation signal of the

acoustic vibration sources

20A and 20B₁,A₂The sum phase difference phi can be adjusted to superimpose the waveform of the harmonic excitation signal 21To cause satellite droplets 19 to move 20 towards The main droplet 18, The principle of this phenomenon can be found in references "The Nonlinear Capillary nature of a Liquid Jet, k.c. chaudhary and t.maxworth, j.fluid Mech. (1980)"; further, a sinusoidal excitation signal of a single frequency 3f may be input to the acoustic vibration source 20C, and the acoustic vibration source 20C generates an acoustic signal and is superimposed with the acoustic signals generated by the

acoustic vibration sources

20A and 20B at the aperture 9, thereby achieving finer and wider-application satellite droplet behavior control, for example, when the droplet pitch is larger and the frequency f is smaller. The sine wave forms of the excitation signals of the

sound vibration sources

20A, 20B and 20C and the frequencies f, 2f and 3f thereof in the above operation are only given as an example, and it is not intended to limit the relative magnitude or the multiple relationship of the wave forms of the excitation signals of the sound vibration sources 20 or the frequencies thereof to be set as such.

In the positional relationship description of the present invention, the appearance of terms such as "inner", "outer", "upper", "lower", "left", "right", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings is merely for convenience of describing the embodiments and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation and operation, and thus, is not to be construed as limiting the present invention.

The foregoing summary and structure are provided to explain the principles, general features, and advantages of the product and to enable others skilled in the art to understand the invention. The foregoing examples and description have been presented to illustrate the principles of the invention and are intended to provide various changes and modifications within the spirit and scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The high-flux micro-droplet generating device based on multi-source excitation is characterized in that: the device comprises a liquid supply assembly, a pressure liquid cavity, a spray head and an excitation assembly; the liquid supply assembly is used for supplementing liquid to the pressure liquid cavity and maintaining the positive pressure of the liquid relative to the environment outside the cavity; the spray head is arranged on the wall surface of the pressure liquid cavity and is provided with a small hole with the diameter of 1-1000 microns; the excitation assembly comprises more than two acoustic vibration sources, each acoustic vibration source comprises an excitation element and an acoustic lens, and the acoustic lens is of a concave structure; the sound focuses of the sound lenses are all positioned at the small holes of the spray head; the sound waves of the sound vibration sources are superposed to form disturbance, and the disturbance acts near the small hole of the spray head.

2. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the concave surfaces of the more than two acoustic lenses are coplanar on the same spherical surface.

3. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the sprayer comprises a pore plate, a small hole is formed in the pore plate, a sealing ring is arranged between the pore plate and the pressure liquid containing cavity, and the pore plate and the sealing ring are pressed on the wall surface of the pressure liquid containing cavity through a pressing end cover.

4. The multi-source excitation-based high-flux micro-droplet generation device as claimed in claim 1 or 3, wherein: the inner wall surface of the pressure liquid containing cavity is made of high-cleanliness stainless steel or fluorine-containing resin materials.

5. The multi-source excitation-based high-flux micro-droplet generation device as claimed in claim 1 or 2, wherein: the acoustic lens is made of quartz glass material.

6. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the excitation element of the acoustic vibration source is a piezoelectric ceramic stack.

7. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the pressure sensor is further included to monitor the liquid pressure inside the pressure liquid cavity.

8. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the liquid temperature monitoring device further comprises a temperature sensor for monitoring the liquid temperature in the pressure liquid cavity.

9. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the pores have a diameter of between 10 and 100 microns.

10. The multi-source excitation-based high-flux micro-droplet generation device of claim 1, wherein: the plurality of acoustic vibration sources respectively receive sine wave-shaped excitation signals with different frequencies.