A microfluidic device for particle sorting based on phononic crystal structure

Abstract

The present invention discloses a microfluidic device for particle sorting based on a phononic crystal structure, which includes a piezoelectric interdigital transducer structure, a phononic crystal structure bonded to the upper layer of the piezoelectric interdigital transducer structure using ultrasonic coupling glue, a bulk acoustic wave reflection area surrounded by the phononic crystal structure, a microfluidic structure within the bulk acoustic wave reflection area, a packaging layer above the microfluidic structure, and a microfluidic inlet and three microfluidic outlets within the packaging layer. The present invention discloses a microfluidic device for particle sorting based on a phononic crystal structure, which has the characteristics of high throughput and low shear force, and does not damage the biological activity of the microparticles in the sorted sample while performing large-scale sorting. In the present invention, particle sorting is achieved using only a single sound wave excitation device, namely a piezoelectric interdigital transducer structure, and then the upper phononic crystal structure is bonded to the piezoelectric interdigital transducer using ultrasonic coupling glue, effectively controlling the sound wave while reducing the number of interdigital transducers.

Description

Technical Field

[0001] The present invention relates to the field of biomedicine, and in particular to a microfluidic device for particle sorting based on a phononic crystal structure. Background Art

[0002] The separation of heterogeneous particle and cell mixtures is an important task for various applications in chemical science, biology, and medicine. In particular, for cell-based therapy and medical research, separating different cells and removing unwanted particles such as bacteria and debris from cell solutions are crucial for diagnosing and treating related diseases. Researchers have developed a variety of different microfluidic sorting devices by using external fields such as electric fields, magnetic fields, and acoustic fields, or by utilizing special microstructures and the microfluidic effects they induce. Among them, active sorting technology using bulk acoustic waves to generate acoustic fields has attracted widespread attention due to its advantages of rapid response, high throughput, and low shear force.

[0003] When liquid is stored in a rectangular microchannel made of a solid substrate, if bulk acoustic waves (BAWs) are traveling within both the bottom and sidewalls of the microchannel, the sound velocities of the solid substrate and the liquid are mismatched, causing the BAWs to be coupled from the solid substrate into the liquid via refraction. This is known as leaky waves within the liquid. When two BAWs with opposite directions exist within the solid substrate, they are coupled into the liquid and then into the liquid, producing two leaky waves with opposite directions. These two waves produce a coherent effect, generating acoustic forces that balance in fixed regions known as pressure nodes and pressure antinodes. As long as the diameter of particles suspended in the microchannel liquid is significantly smaller than half the wavelength of the leaky waves, these acoustic forces can drive particle motion. Particles of different densities will move toward the pressure nodes or antinodes, with larger diameter particles moving faster. This principle enables particle sorting.

[0004] In recent decades, phononic crystal devices have been successfully applied in fields such as radio frequency communications, acousto-optic modulation, and micromechanical vibration reduction. The application of phononic crystals in microfluidics has become a new research direction in recent years. By leveraging the characteristic of phononic crystals that they reflect sound waves with frequencies within their bandgap, the direction of sound wave propagation can be effectively controlled, thereby controlling the direction of the acoustic force generated by the sound waves refracting into the microfluidics, thereby realizing complex microfluidic functions. Furthermore, because phononic crystals are fabricated using a planar photolithography process, the devices can be manufactured at low cost and in large quantities, making them a promising candidate for application in microfluidics.

[0005] Currently, the most common microfluidic particle sorting devices using acoustic methods generally employ multiple sets of interdigital electrodes fabricated on a piezoelectric device. The orientation of the interdigital electrodes, which generate acoustic waves, is used to control the direction of the acoustic wave transmission. However, this method suffers from high material and processing costs, and the device is not easily assembled, making it unsuitable for mass production. To address these issues, the following solution is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a microfluidic device for particle sorting based on a phononic crystal structure, which can reduce the cost of traditional devices while applying phononic crystals to the new function of particle acoustic sorting.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] In the present application, the piezoelectric acoustic wave excitation device, ultrasonic coupling material, acoustic wave control area, microchannel structure, and rectangular packaging structure are arranged in sequence from bottom to top.

[0009] In this application, the piezoelectric acoustic wave excitation device is a metal interdigitated electrode made on a 128°YX lithium niobate piezoelectric material. When an alternating current is passed through it, a periodic electric field is generated. By utilizing the inverse piezoelectric effect of the piezoelectric material, an acoustic surface wave is generated on the surface of the piezoelectric material with a propagation direction perpendicular to the metal interdigitated electrode and having the same frequency as the periodic electric field.

[0010] In this application, the ultrasonic coupling material is mainly composed of a water-soluble colloidal material, which is used to transfer the surface acoustic waves generated by the piezoelectric acoustic wave excitation device to the acoustic wave control area of the upper layer, generate bulk acoustic waves in the upper layer and enable the bulk acoustic waves to operate within the acoustic wave control area.

[0011] In the present application, the acoustic wave control region includes at least: a phononic crystal and a bulk acoustic wave reflection region. The phononic crystal is a Bragg scattering phononic crystal obtained by deep reactive ion etching on a substrate. The substrate is a single-crystal silicon material with a (100) crystal orientation. The scatterer is in the shape of a cylindrical through hole, and the planar shape of the lattice unit is a square. The bulk acoustic wave reflection region is a rectangular region surrounded by periodically distributed phononic crystal units on a silicon substrate serving as a bulk acoustic wave propagation medium, and is used to control the transmission and distribution of bulk acoustic waves within the silicon substrate.

[0012] In the present application, the rectangular packaging structure is made of polydimethylsiloxane (PDMS), and includes a rectangular parallelepiped slightly wider than the microchannel structure, and a through hole penetrating the rectangular parallelepiped.

[0013] The rectangular packaging structure is used to seal the microchannel structure at the lower layer, providing a microfluid inlet and outlet for the microchannel while reducing the volatilization of the microfluid during the flow in the microchannel.

[0014] There are four cylindrical through-holes running through the rectangular parallelepiped. These holes are divided into one microfluidic inlet hole and three microfluidic outlet holes. The diameter of the inlet hole is consistent with the width of the underlying microfluidic channel. However, at the outlet, the diameter of the outlet hole is designed to be larger than the width of the microfluidic channel's collection port, as the collection port of the underlying microfluidic channel is narrow, hindering external access to the sorted microfluid.

[0015] In this application, the microfluidic structure is a key component for sorting mixed particles. It is contained within the bulk acoustic wave reflection region and covered by the rectangular encapsulation structure. The microfluidic structure includes a microchannel and three particle collection ports. During operation, sound waves are refracted from the bulk acoustic wave reflection region into the liquid within the microchannel.

[0016] In this application, when the device is operating, a microfluidic sample containing two mixed suspended particles of different diameters flows from an external sample storage device through a plastic pipe to the inlet of the rectangular packaging structure, then enters the microfluidic channel from the inlet of the packaging structure. After passing through the microfluidic channel, the mixed suspended particles in the liquid are separated according to their different diameters. The different suspended particles enter different particle collection ports within the microfluidic channel, then flow from the collection ports into the outlet of the rectangular packaging structure, out through the outlet, and are collected outside the device.

[0017] As described above, the present application's microfluidic device for particle sorting based on a phononic crystal structure has the following advantages: the present application only requires the production of a single set of metal interdigital electrodes on a piezoelectric material, and the generated surface acoustic waves are coupled to the acoustic wave control area on the silicon substrate through ultrasonic coupling glue, thereby allowing the acoustic waves controlled by the phononic crystal to refract into the liquid in the microchannel, and the mixed suspended particles in the microchannel liquid can be sorted according to different diameters. While traditional acoustic sorting devices require the production of multiple sets of metal interdigital electrodes to generate acoustic waves in different directions, the number of metal interdigital electrodes is reduced, thereby lowering the production cost; the present application produces a microchannel structure on a silicon wafer, thereby reducing the production cost and material cost of the microchannel, and since the device is assembled by bonding with ultrasonic coupling glue, the device is detachable, and the piezoelectric acoustic wave excitation device with a higher cost at the bottom layer can be reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an overall appearance diagram of a microfluidic device for particle sorting based on a phononic crystal structure according to an embodiment, in which the encapsulation layer and the microchannel structure covered by the encapsulation layer are magnified;

[0019] Figure 2 Schematic diagram of the assembly structure of a microfluidic device for particle sorting based on a phononic crystal structure according to an embodiment;

[0020] Figure 3 1. The structure of the acoustic wave excitation device in the microfluidic device for particle sorting based on the phononic crystal structure in the embodiment, i.e., a schematic diagram of the structure of the interdigital transducer;

[0021] Figure 4 Schematic diagram of the shape of the ultrasonic coupling glue, which is the connecting layer between the acoustic wave excitation device and the acoustic wave control layer of the microfluidic device of the embodiment;

[0022] Figure 5 Schematic diagram of the structure of the acoustic wave control layer in the microfluidic device of the embodiment;

[0023] Figure 6A Detailed schematic diagram of the phononic crystal of the acoustic wave control layer in the microfluidic device of the embodiment, including a silicon substrate and a scatterer in the shape of a through hole;

[0024] Figure 6B Schematic diagram of the microfluidic structure details of the acoustic wave control layer in the microfluidic device of the embodiment, including a main channel and three collection ports at the tail end;

[0025] Figure 6C Schematic diagram of the details of the phononic crystal unit structure in the microfluidic device of the embodiment;

[0026] Figure 7A The embodiment of the microfluidic device is a process in which a bulk acoustic wave is refracted from a bulk acoustic wave reflection region into a liquid in a microchannel;

[0027] Figure 7B In the embodiment of the microfluidic device, the acoustic force generated by the refraction of the bulk acoustic wave into the liquid in the microchannel, and the pressure node and pressure anti-node regions formed thereby;

[0028] Figure 8A Schematic diagram of the propagation directions of incident and reflected waves on a phononic crystal substrate in a microfluidic device according to an embodiment;

[0029] Figure 8B Schematic diagram of the pressure node formed by coupling of incident wave and reflected wave into the microchannel in the microfluidic device of the embodiment;

[0030] Figure 8C Schematic diagram of the process from mixing to separation of suspended particles of different diameters in a microchannel in a microfluidic device according to an embodiment;

[0031] Figure 9A 1 is a schematic diagram of the overall structure of the encapsulation layer of the microfluidic channel in the microfluidic device of the embodiment, wherein the encapsulation layer is located above the microfluidic channel;

[0032] Figure 9B Schematic diagram of the alignment between the microchannel encapsulation layer and the underlying microchannel in the microfluidic device of the embodiment.

[0033] Figure numerals: 1. piezoelectric material substrate; 2. metal interdigital electrode; 3. ultrasonic coupling adhesive layer; 4. single crystal silicon material substrate; 5. phononic crystal structure; 6. bulk acoustic wave reflection area; 7. microchannel structure; 8. packaging layer; 9. small diameter particle collecting port of microchannel; 10. large diameter particle collecting port of microchannel; 11. silicon substrate of silicon-air structure phononic crystal; 12. cylindrical through hole of silicon-air structure phononic crystal, with air inside; 13. particle inlet through hole passing through the packaging layer; 14. small diameter particle outlet through hole passing through the packaging layer; 15. large diameter particle outlet through hole passing through the packaging layer. DETAILED DESCRIPTION

[0034] The following description is only a preferred embodiment of the present invention, and the protection scope is not limited to this embodiment. All technical solutions under the concept of the present invention should fall within the protection scope of the present invention.

[0035] See Figure 1 , the embodiment of the present invention relates to a microfluidic device for particle sorting based on a phononic crystal structure. Figure 1 and Figure 2 As shown, the microfluidic device includes: a piezoelectric material substrate 1, a metal interdigital electrode 2, an ultrasonic coupling adhesive layer 3, a single crystal silicon substrate 4, a phononic crystal structure 5, a bulk acoustic wave reflection area 6, a microchannel structure 7, and a microchannel packaging layer 8. The piezoelectric material substrate 1 and the metal interdigital electrode 2 are combined to form an interdigital transducer for generating sound waves; an ultrasonic coupling adhesive layer 3 is coated between the single crystal silicon substrate 4 and the piezoelectric material substrate 1 to transfer the sound waves generated on the piezoelectric material 1 to the single crystal silicon substrate 4; a phononic crystal structure 5 is made on the single crystal silicon substrate 4, and a bulk acoustic wave reflection area 6 is reserved for controlling the propagation direction of the sound waves; a microchannel structure 7 is made by making the bulk acoustic wave reflection area 6 on the single crystal silicon substrate to provide a sorting channel for microfluid samples mixed with suspended particles, while utilizing the limiting effect of the bulk acoustic wave reflection area 6 on the sound waves to generate a specific acoustic force acting on the suspended particles to achieve sorting; an encapsulation layer 8 is made above the microchannel structure 7 to provide a closed top cover for the microchannel while also providing an inlet and outlet for the microchannel to exchange samples with the outside world.

[0036] The piezoelectric substrate 1 exhibits the inverse piezoelectric effect. When a periodic electric field is applied to its surface, it generates surface acoustic waves (SAWs) of the same frequency as the periodic electric field. Typical piezoelectric materials include lithium niobate (LiNbO3), zinc oxide (ZnO), and aluminum nitride (AlN). In this embodiment, the piezoelectric substrate is lithium niobate propagating in the X direction at a 128° Y-tangential angle. The material's sound velocity is approximately c = 3992 m / s.

[0037] Metal interdigitated electrodes 2 can be made on the surface of the piezoelectric substrate material to generate a periodic electric field, and the propagation direction of the generated surface acoustic wave is as follows: Figure 3 As shown, the metal interdigital electrodes 2 are perpendicular to each other. In this embodiment of the present invention, to generate surface acoustic waves of sufficient intensity, the metal interdigital electrodes 2 are formed using a deposition process on a piezoelectric substrate, comprising a 20nm-thick titanium adhesion layer and a 200nm-thick gold conductive layer. To enable the piezoelectric substrate to generate surface acoustic waves of frequency f, the width w and spacing d of the metal electrodes are designed according to the following formula: w = d = c / (4f).

[0038] like Figure 4 Figure 3 shows an ultrasonic coupling adhesive layer 3, which is used to couple surface acoustic waves generated on the piezoelectric substrate to the upper single-crystal silicon substrate. Ultrasonic coupling adhesives are typically made of water-soluble molecular materials. The ultrasonic coupling adhesive used in this embodiment of the present invention primarily contains trichlorohydroxydiphenyl ether. During use, a thickness of approximately 300-500 μm is evenly applied to the piezoelectric material in the area where surface acoustic waves propagate.

[0039] The ultrasonic coupling adhesive layer 3 can transfer the surface acoustic wave generated by the surface of the piezoelectric material to the single crystal silicon substrate 4, and the transmission mode of the acoustic wave in the single crystal silicon substrate is bulk acoustic wave.

[0040] like Figure 5 As shown, a periodic phononic crystal structure 5, a bulk acoustic wave reflection region 6 and a microchannel structure 7 are fabricated on a single crystal silicon substrate 4. The details of the periodic phononic crystal structure are shown in FIG. Figure 6A As shown in FIG, in the designed area on the single crystal silicon substrate, periodic cylindrical through holes are etched as scatterers of each phononic crystal unit, and the spacing between each cylindrical through hole is the same, so each cylindrical through hole 12 and the single crystal silicon material 11 around it form a, as shown in FIG. Figure 6C The square lattice phononic crystal unit is shown. The details of the microfluidic structure 7 are shown in Figure 6B As shown, it includes a main channel and three collecting ports.

[0041] The most important physical property of a phononic crystal unit is its bandgap characteristic, which is its ability to block and reflect incident sound waves with frequencies within its bandgap frequency range.

[0042] In previous studies on microfluidic acoustic sorting, it was found that acoustic coherent waves can be used to generate pressure nodes in the microchannel, thereby capturing suspended particles in the microchannel to the pressure nodes. Figure 7A The figure shows a cross section of a rectangular microchannel. When the traveling bulk acoustic wave contacts the liquid at the bottom of the microchannel, the viscosity of the liquid relative to the substrate increases, causing part of the acoustic wave to be refracted into the liquid at an angle of ,in and The speed of the sound wave in the liquid of the microfluidic channel and the speed of the sound wave in the solid substrate of the microfluidic channel are respectively. When the traveling sound wave contacts the liquid at the side wall of the microfluidic channel, the sound wave will be refracted into the liquid in the same direction, and the refraction angle is 0.

[0043] In the embodiment of the present invention, phononic crystals are used to generate two sets of bulk acoustic waves with opposite directions and fixed phase difference, such as Figure 7B As shown, after these two waves are refracted into the liquid, they will superimpose on each other in the liquid to produce an acoustic coherent wave field. This will generate the following acoustic forces: acoustic radiation force Viscous drag induced by acoustic flow , acting on the suspended particles in the liquid. In addition, the suspended particles are also affected by their own gravity G and buoyancy F f The role of Figure 7B shown.

[0044] Acoustic radiation force: ,

[0045] Viscous drag:

[0046] in is the sound pressure in the liquid, is the volume of suspended particles, is the compressibility of the liquid, and k are the wavelength and wave vector of the sound wave refracted into the liquid, is the vertical distance between the particle and the pressure node area, and are the density of the liquid and the density of the particles suspended in the liquid, is the dynamic viscosity of the liquid, is the diameter of the suspended particles, and are the flow rate of the liquid and the movement speed of the particles suspended in the liquid, respectively. It is called the acoustic contrast coefficient. When and Under the combined action of When , the suspended particles move toward the pressure antinode. The acceleration of the spherical particles driven by the acoustic force is: , it can be seen that the diameter of particles with the same density The larger the acceleration In the present invention, two spherical particles with different diameters and the same density are selected and mixed in a liquid as samples to be sorted. The density of the particles and the density of the liquid are selected so that , so particles move toward the pressure node when subjected to acoustic forces. Particles of different diameters experience different accelerations toward the pressure node during flow, and therefore move at different speeds toward the pressure node. Larger diameter particles experience greater acceleration and move faster, while smaller diameter particles move slower toward the pressure node. Based on this principle, particles of different diameters can be separated and collected separately at the outlet of the microchannel.

[0047] In the example of the present invention, the phononic crystal has its own unique bandgap characteristics. A piezoelectric substrate is used to generate sound waves with a frequency within the bandgap of the phononic crystal. After passing through the ultrasonic coupling glue and entering the silicon substrate, a bulk acoustic wave is formed. After the bulk acoustic wave enters the bulk acoustic wave reflection area, it encounters the boundary of the phononic crystal and forms a reflection. Then, the reflected sound wave interferes with the incident sound wave and refracts into the microchannel 7 to form a pressure node. Therefore, a bulk acoustic wave reflection area 6 is designed in the area surrounded by the periodic phononic crystal structure to input sound waves and receive reflected sound waves. The reflection area is a rectangular area surrounded by the phononic crystal structure 5 in the plane 4. The incident and reflection paths of the sound wave on the single crystal silicon substrate are as follows: Figure 8A As shown in , both the incident wave and the reflected wave enter the liquid in the microchannel through fluid-solid coupling and form an interference effect, as shown in Figure 8B As shown, the pressure nodes are approximately distributed on a line near the central axis of the microchannel.

[0048] In the present invention, the Figure 8C As shown, it is finally possible to separate the white particles from the black and white mixed particles. In the process of a liquid mixed with two suspended particles of different diameters flowing from the starting end of the microchannel to the collection port at a suitable speed, the suspended particles will be affected by the acoustic force and move toward the pressure node in the middle of the microchannel. The diameter of the black spherical particles is larger, and the acceleration of their movement driven by the acoustic force is also larger. Conversely, the acceleration of the movement of the white spherical particles with a smaller diameter is smaller, so the speed of the black particles moving toward the pressure node is faster and they can move to the pressure node earlier. Finally, the following can be formed. Figure 8C As shown in the results, smaller white particles move to the two side collection ports 9, while larger black particles and a small number of white particles move to the central collection port 10. This method allows for the rapid extraction of high-purity small-diameter white particles. Subsequently, by subjecting the sample obtained from collection port 10 to multiple sorting steps, larger-diameter black particles of relatively high purity can also be extracted.

[0049] The above operations describe the movement of liquid within the microchannel. The complete particle sorting process involves powering the device, delivering samples from the outside into the microchannel, and simultaneously collecting the sorted samples from the microchannel back to the outside. However, because the collection port of a microchannel is generally narrow and cannot be directly connected to the outside world using a pipe, a cover plate with a microchannel structure, as shown in Figure 9, is designed in this embodiment of the present invention. This serves as an encapsulation layer for the microchannel and also provides a larger inlet and outlet for connecting the microchannel to the outside world.

[0050] like Figure 9A As shown, in the structure of the encapsulation layer 8, the through hole 13 is used to transport the liquid carrying mixed particles from the outside into the microchannel below, and the through holes 14 and 15 are used to collect particles in the particle collecting ports 9 and 10 of the microchannel below, respectively.

[0051] The method of fixing the encapsulation layer 8 to the underlying single crystal silicon substrate is to use plasma to treat the surface of the single crystal silicon substrate so that it has a layer of chemical bonds on the surface, and then align the inlet and outlet of the encapsulation layer with the microchannel on the single crystal silicon substrate for bonding. The alignment of the encapsulation layer and the microchannel is as follows: Figure 9B As shown, the bottom surface of through-hole 13 is aligned with the starting end of the underlying microfluidic channel, while the bottom surfaces of through-holes 14 and 15 are aligned with the collection ports 9 and 10 of the underlying microfluidic channel, respectively. Encapsulation layer 8 is made of polydimethylsiloxane (PDMS). Four through-holes of appropriate diameter are formed at designated locations on a rectangular parallelepiped of PDMS to form encapsulation layer 8.

[0052] In summary, the present invention introduces a microchannel structure in the bulk acoustic wave reflection area surrounded by periodically distributed square lattice phononic crystals, and successfully applies phononic crystals to the acoustic sorting function in the field of microfluidics. In the present invention, metal interdigitated electrodes 2 are used to generate a periodic electric field on the upper surface of the piezoelectric material substrate, and then the inverse piezoelectric effect of the piezoelectric material is used to generate surface acoustic waves. Subsequently, the surface acoustic waves only need to be transferred to the upper single crystal silicon substrate. Traditional acoustic standing wave particle sorting devices require the production of multiple sets of metal interdigitated electrodes 2 in opposite directions to generate surface acoustic waves in opposite directions. The present invention successfully reduces the number of metal interdigitated electrodes 2; the key part of the microfluidics in the present invention is produced on a single crystal silicon substrate, and the processing cost and material cost are relatively low. Therefore, the present invention successfully reduces the production cost on the basis of traditional acoustic sorting devices and has a high industrial utilization value.

[0053] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A microfluidic device for particle sorting based on a phononic crystal structure, comprising a piezoelectric acoustic wave excitation device, an ultrasonic coupling adhesive layer (3), a phononic crystal structure (5) and an encapsulation layer (8), characterized in that: The phononic crystal structure (5) is located above one side of the piezoelectric acoustic wave excitation device, and the phononic crystal structure (5) is connected to the piezoelectric acoustic wave excitation device via an ultrasonic coupling adhesive layer (3); a bulk acoustic wave reflection region (6) is provided on the surface of the phononic crystal structure (5); a particle sorting microchannel is provided on the bulk acoustic wave reflection region (6); and an encapsulation layer (8) is provided on the particle sorting microchannel; The piezoelectric acoustic wave excitation device comprises a piezoelectric material substrate (1), and a metal interdigital electrode (2) is provided on the surface of the piezoelectric material substrate (1); The ultrasonic coupling adhesive layer (3) is provided with ultrasonic coupling adhesive, the ultrasonic coupling adhesive is a water-soluble molecular material, and the ultrasonic coupling adhesive is located between the bulk acoustic wave reflection area (6) and the piezoelectric acoustic wave excitation device; The phononic crystal structure (5) is a square lattice silicon-air phononic crystal, comprising a solid substrate and an acoustic wave scattering structure arranged on the solid substrate, wherein the solid substrate is a silicon substrate, the acoustic wave scattering structure is a cylindrical through hole, and the acoustic wave scattering structure is distributed on the silicon substrate according to a square lattice structure.

2. A microfluidic device for particle sorting based on a phononic crystal structure according to claim 1, characterized in that: The bulk acoustic wave reflection region (6) comprises a bulk acoustic wave propagation medium and a phononic crystal structure arranged around the bulk acoustic wave propagation medium, wherein the bulk acoustic wave propagation medium is a rectangular plate-shaped silicon material, and the phononic crystal is a square lattice silicon-air phononic crystal. The bulk acoustic wave reflection region (6) is used to reflect the bulk acoustic wave entering the region through the bulk acoustic wave propagation medium, so that the reflected wave is superimposed on the incident wave, thereby forming a coherent wave in the reflection region.

3. The microfluidic device for particle sorting based on phononic crystal structure according to claim 1, characterized in that: The particle sorting microchannel comprises a microchannel structure (7) and three collecting ports. The particle sorting microchannel is located in a bulk acoustic wave reflection region (6). The three collecting ports are all arranged at one end of the microchannel structure (7). The three collecting ports are used to collect particles of different diameters after sorting.

4. The microfluidic device for particle sorting based on phononic crystal structure according to claim 1, characterized in that: The encapsulation layer (8) includes a rectangular solid cover plate, a microfluidic inlet and three microfluidic outlets, wherein the microfluidic inlet is located at one end of the solid cover plate, and the three microfluidic outlets are all located at the other end of the solid cover plate. The rectangular solid cover plate is a polydimethylsiloxane-based plate, and the encapsulation layer (8) of the particle sorting microfluidic channel is located above the particle sorting microfluidic channel.

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