Microfluidic mixing device based on stepped interdigital structure and method of using the same

Abstract

The present application relates to the technical field of microfluidic mixing, and particularly relates to a microfluidic mixing device based on a ladder-shaped interdigital structure and a use method thereof, and mainly solves the technical problem of poor mixing effect of the existing microfluidic mixing device based on an interdigital transducer. The device comprises a piezoelectric substrate, a flexible substrate and a ladder-shaped interdigital transducer, the lower surface of the flexible substrate is provided with a microchannel, and the ladder-shaped interdigital transducer comprises a first bus bar, a second bus bar, a first interdigital electrode, a second interdigital electrode, a drainage bar and an electrical connection part. The length of the second interdigital electrode of the ladder-shaped interdigital transducer of the device increases with the flow direction of the fluid, a gradient acoustic field can be formed, thereby improving the energy utilization rate, and the ladder-shaped interdigital transducer is directly located below the microchannel, so that the acoustic field energy can directly act on the fluid, the energy attenuation rate is small, and thus the device can greatly improve the mixing effect, thereby meeting the actual mixing demand.

Description

Technical Field

[0001] This invention relates to the field of microfluidic mixing technology, and in particular to a microfluidic mixing device based on a stepped interdigital structure and its usage method. Background Technology

[0002] Microfluidic mixing technology is a core supporting technology in fields such as biochemical analysis, drug development, materials synthesis, and environmental monitoring. Its mixing efficiency and control precision directly determine the detection accuracy, reaction rate, and product quality. In microscale environments, fluid flow is mostly laminar, and the mixing process completed solely by molecular diffusion is extremely slow. Therefore, it is necessary to enhance the mixing effect through external energy inputs such as heat, magnetism, electricity, and sound. Among these, acoustic fluid control-based mixing technology has become a research hotspot in the field of microfluidic mixing due to its advantages such as rapid response, precise control, and minimal damage to the medium.

[0003] Interdigital transducers are a common structure used to achieve acoustic-fluidic mixing. They generate surface acoustic waves (SAWs) by fabricating periodically interlaced metal electrodes on a piezoelectric substrate and exciting them with an applied electrical signal. The interaction between the SAWs and the fluid within the microchannel induces acoustic-fluid effects and radiation forces, thereby achieving fluid mixing. Existing interdigital transducers all employ an equal-length interdigital structure (i.e., adjacent interdigitates are of the same length). By applying a fixed-frequency electrical signal to a parallel interdigital array, traveling-wave SAWs are generated to drive fluid vortex motion. While microfluidic mixing devices based on this interdigital transducer can achieve fluid mixing within a certain range, the uniform distribution of the traveling-wave SAWs generated by the equal-length interdigitates within the microchannel prevents the formation of localized strong disturbance regions. This results in low-intensity vortex motion of the fluid, slow expansion rate of the interface liquid surface, and the separate arrangement of the interdigital transducers and microchannels, leading to a long energy transfer path and a large energy attenuation rate. All these factors combined result in poor mixing performance, failing to meet practical mixing requirements.

[0004] Therefore, there is an urgent need for a microfluidic mixing device with better mixing effect. Summary of the Invention

[0005] To overcome the technical shortcomings of existing microfluidic mixing devices based on interdigital transducers, which have poor mixing effects, this invention provides a microfluidic mixing device based on a stepped interdigital structure and its usage method.

[0006] The microfluidic mixing device based on a stepped interdigitated structure provided by the present invention includes:

[0007] piezoelectric substrate;

[0008] A flexible substrate is attached to the upper surface of the piezoelectric substrate. The lower surface of the flexible substrate has microchannels. The microchannels are Y-shaped grooves formed by the intersection of a main channel and two branch channels. The main channel is arranged in the left-right direction and its free end extends upward through the flexible substrate to form a liquid outlet. The free ends of the two branch channels both extend upward through the flexible substrate to form liquid inlets.

[0009] A stepped interdigital transducer is fixed between the piezoelectric substrate and the flexible substrate and arranged corresponding to the main channel. The stepped interdigital transducer includes a first busbar and a second busbar. The first busbar and the second busbar are arranged left and right and respectively adjacent to the front and rear sides of the main channel. The first busbar and the second busbar extend to the outside of the flexible substrate through a guide bar to form an electrical connection. The first busbar extends vertically into the main channel with a plurality of first interdigital electrodes, which are spaced apart in the left and right direction. The second busbar extends vertically into the main channel with a plurality of second interdigital electrodes, which are spaced apart in the left and right direction. The plurality of first interdigital electrodes and second interdigital electrodes are staggered in the left and right direction. The lengths of the plurality of first interdigital electrodes are all equal, and the lengths of the plurality of second interdigital electrodes increase with the direction of fluid flow.

[0010] Optionally, the piezoelectric substrate is lithium niobate with a 128° Y-cut, and the X-axis direction of the lithium niobate is consistent with the left-right direction.

[0011] Optionally, the free ends of the main channel and the free ends of the branch channels are enlarged to form ends, and the ends penetrate the flexible substrate through the liquid channel to form a liquid inlet or liquid outlet.

[0012] Optionally, the liquid channel is connected to a needle for injecting or aspirating liquid.

[0013] Optionally, the lengths of the multiple second interdigital electrodes increase linearly with the direction of fluid flow.

[0014] Optionally, a glass slide is fixed below the piezoelectric substrate.

[0015] Optionally, the electrical connection is sequentially connected to a power attenuator, a power amplifier, and a signal generator, the frequency of which is adjustable.

[0016] The method of using the aforementioned microfluidic mixing device based on a stepped interdigitated structure provided by the present invention includes the following steps:

[0017] S1. Determine the target frequency through experiments:

[0018] S11. After differentiating the two liquids to be mixed by color, continuously inject them into the microchannel through two liquid inlets;

[0019] S12. Activate the stepped interdigital transducer to excite surface acoustic waves to act on the liquid;

[0020] S13. Adjust the frequency of the signal generator while monitoring the displacement of the interface liquid surface, and determine the target frequency according to the required mixing degree;

[0021] S2. Microfluidic mixing:

[0022] S21. The two liquids to be mixed are continuously injected into the microchannel through two liquid inlets respectively;

[0023] S22. Activate the stepped interdigital transducer to excite surface acoustic waves to act on the liquid;

[0024] S23. Adjust the frequency of the signal generator to the target frequency and perform microfluidic mixing.

[0025] Optionally, a denser liquid to be mixed can be injected through a liquid inlet located on the side where the second interdigital electrode is located.

[0026] Optionally, when sufficient mixing is required, the target frequency can be controlled between 1MHz and 50MHz; when the mixing effect needs to be controlled, the target frequency can be controlled between 50MHz and 100MHz.

[0027] The technical solution provided by this invention has the following advantages compared with the prior art:

[0028] The microfluidic mixing device based on a stepped interdigital structure provided by this invention employs a stepped interdigital transducer. The length of the second interdigital electrode of the stepped interdigital transducer increases with the direction of fluid flow, which can form a gradient sound field, thereby improving energy utilization. On the other hand, the stepped interdigital transducer is located directly below the microchannel, allowing the sound field energy to act directly on the fluid with a small energy attenuation rate. Combining these two aspects, the device can significantly improve the mixing effect, thereby meeting practical mixing requirements.

[0029] The present invention provides a method for using a microfluidic mixing device based on a stepped interdigitated structure. Taking into account the influence of frequency on the mixing effect, the method first determines the target frequency according to the required degree of mixing, and then mixes the microfluidic fluid at the target frequency. This can adapt to the mixing requirements of different microfluidics, and in particular improves the adaptability to mixing complex samples. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the microfluidic mixing device in an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the flexible substrate in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the stepped interdigital transducer in an embodiment of the present invention;

[0035] Figure 4 This diagram shows a comparison of the mixing effects of stepped interdigital transducers and equal-length interdigital transducers as frequency varies in embodiments of the present invention.

[0036] Figure 5 This diagram illustrates the mixing effect when the input frequency is 1MHz in an embodiment of the present invention.

[0037] Figure 6 This diagram illustrates the mixing effect when the input frequency is 42MHz in an embodiment of the present invention.

[0038] Figure 7 This diagram illustrates the mixing effect when the input frequency is 75MHz in an embodiment of the present invention.

[0039] In the picture:

[0040] 1. Piezoelectric substrate; 2. Flexible substrate; 21. Main channel; 22. Branch channel; 23. Liquid inlet; 24. Liquid outlet; 25. End; 26. Needle; 27. Clearance groove; 3. Stepped interdigital transducer; 31. First busbar; 32. Second busbar; 33. Drainage bar; 34. First interdigital electrode; 35. Second interdigital electrode; 36. Electrical connection. Detailed Implementation

[0041] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0042] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0044] The following is combined with Figures 1 to 7 Specific embodiments of the present invention will be described in detail below.

[0045] This embodiment provides a microfluidic mixing device based on a stepped interdigital structure, including a piezoelectric substrate 1, a flexible substrate 2, and a stepped interdigital transducer 3.

[0046] Among them, the piezoelectric substrate 1 serves as the core functional carrier and has two main functions: first, to provide physical support for the flexible substrate 2 and the stepped interdigital transducer 3; second, to generate surface acoustic waves: when an alternating voltage is applied to the stepped interdigital transducer 3, the alternating voltage will form a periodic electric field inside the piezoelectric substrate 1. Under the action of the electric field, the crystal lattice of the piezoelectric substrate 1 will generate periodic mechanical vibrations. These mechanical vibrations propagate along the surface of the piezoelectric substrate 1, thereby forming surface acoustic waves.

[0047] Specifically, in this embodiment, the piezoelectric substrate 1 is a 128° Y-cut lithium niobate, and the X-axis direction of the lithium niobate is consistent with the left-right direction. A 128° Y-cut means that the initial cutting surface of the lithium niobate is rotated 128° clockwise around its Y-axis before cutting. The left-right direction is defined for ease of describing the relative positions of the components; the flow direction after fluid convergence is the left-right direction. Since the X-axis direction is consistent with the left-right direction, and the propagation direction of surface acoustic waves in this structure is also the left-right direction, this ensures that the surface acoustic waves can propagate along the X-axis direction of the lithium niobate. The lithium niobate with this cutting and arrangement method has good surface acoustic wave conduction performance, and the energy loss is low when the surface acoustic waves propagate along its X-axis direction, enabling efficient coupling of the acoustic energy excited by the stepped interdigital transducer 3 into the fluid. Simultaneously, the lithium niobate exhibits high mechanical stability and a high degree of matching with the thermal expansion coefficient of the flexible substrate 2, maintaining a firm connection with the flexible substrate 2 even after long-term use, avoiding structural loosening due to temperature changes. In other embodiments, the piezoelectric substrate 1 may also be made of other piezoelectric materials such as quartz or sodium potassium niobate.

[0048] Specifically, the shape of the piezoelectric substrate 1 is not limited. For example, in this embodiment, the piezoelectric substrate 1 is rectangular, and the length of the rectangle is arranged along the left-right direction, and the width is arranged along the front-back direction.

[0049] As a further improvement to the piezoelectric substrate 1, a glass slide is fixed underneath the piezoelectric substrate 1. The glass slide mainly serves as a testing platform and provides fixed support for the piezoelectric substrate 1.

[0050] The shape, material, and size of the glass slide are not limited. For example, in this embodiment, the glass slide is rectangular, made of glass, and 1 mm thick. The glass slide and the piezoelectric substrate 1 are bonded and fixed together with polyvinyl chloride adhesive.

[0051] The flexible substrate 2 is attached and fixed to the upper surface of the piezoelectric substrate 1. The lower surface of the flexible substrate 2 is provided with microchannels. The microchannels are Y-shaped grooves formed by the intersection of a main channel 21 and two branch channels 22. The main channel 21 is arranged in the left and right directions and its free end extends upward through the flexible substrate 2 to form a liquid outlet 24. The free ends of the two branch channels 22 both extend upward through the flexible substrate 2 to form a liquid inlet 23.

[0052] Specifically, the flexible substrate 2 can be fixed on the piezoelectric substrate 1 using methods commonly used in the art. For example, in this embodiment, the flexible substrate 2 is fixed on the piezoelectric substrate 1 by bonding, which is achieved by photoresist bonding or oxygen plasma treatment.

[0053] Specifically, the material of the flexible substrate 2 is not limited. For example, in this embodiment, the flexible substrate 2 is made of polydimethylsiloxane (PDMS). Polydimethylsiloxane is hydrophobic and suitable for hydrophobic liquids; when the fluid is a non-hydrophobic liquid, the inner wall of the microchannel needs to be hydrophilicized.

[0054] It is easy to understand that, since the flexible substrate 2 is bonded and fixed to the upper surface of the piezoelectric substrate 1, and the stepped interdigital transducer 3 is located between the piezoelectric substrate 1 and the flexible substrate 2, a clearance groove 27 should be provided in the area of ​​the flexible substrate 2 corresponding to the stepped interdigital transducer 3 to simultaneously meet these two positional requirements. Of course, if the thickness of the stepped interdigital transducer 3 is very thin and does not affect the bonding between the flexible substrate 2 and the piezoelectric substrate 1, the clearance groove may not be provided.

[0055] Specifically, in this embodiment, the free ends of the main channel 21 and the branch channel 22 are both enlarged to form end caps 25. These end caps 25 penetrate the flexible substrate 2 through a liquid channel to form a liquid inlet 23 or a liquid outlet 24. The diameter of the liquid channel is smaller than that of the end caps 25, thus forming a relatively large liquid storage cavity and a relatively small liquid inlet 23 or liquid outlet 24, which facilitates continuous liquid supply and injection / extraction. In other embodiments, the free ends of the main channel 21 and the branch channel 22 can also directly penetrate the flexible substrate 2 to form a liquid inlet 23 or a liquid outlet 24.

[0056] As a further improvement to the liquid channel, a needle 26 for injecting or aspirating liquid is connected to the liquid channel. Injection or aspiration is performed through this needle 26, which better meets the needs of microfluidic mixing in small spaces.

[0057] The stepped interdigital transducer 3 is fixed between the piezoelectric substrate 1 and the flexible substrate 2 and is arranged corresponding to the main channel 21. The stepped interdigital transducer 3 includes a first busbar 31 and a second busbar 32. The first busbar 31 and the second busbar 32 are arranged left and right and are respectively adjacent to the front and rear sides of the main channel 21. The first busbar 31 and the second busbar 32 extend to the outside of the flexible substrate 2 through the guide bar 33 to form an electrical connection part 36. The first busbar 31 extends vertically into the main channel 21 with a plurality of first interdigital electrodes 34 and the plurality of first interdigital electrodes 34 are spaced apart in the left and right direction. The second busbar 32 extends vertically into the main channel 21 with a plurality of second interdigital electrodes 35 and the plurality of second interdigital electrodes 35 are spaced apart in the left and right direction. The plurality of first interdigital electrodes 34 and second interdigital electrodes 35 are staggered in the left and right direction. The lengths of the plurality of first interdigital electrodes 34 are all equal, and the lengths of the plurality of second interdigital electrodes 35 increase with the direction of fluid flow.

[0058] Specifically, the stepped interdigital transducer 3 can be fixed on the piezoelectric substrate 1 using methods commonly used in the art. For example, in this embodiment, the stepped interdigital transducer 3 is fixed on the piezoelectric substrate 1 by bonding, which is achieved by photoresist bonding or oxygen plasma treatment.

[0059] It should be noted that the main purpose of arranging the stepped interdigital transducers 3 corresponding to the main channel 21 is to allow the generated acoustic field energy to directly act on the fluid, shortening the energy transfer path and thus reducing the energy attenuation rate. Specifically, in this embodiment, the lengths of the multiple second interdigital electrodes 35 increase linearly with the fluid flow direction. If the length of the first second interdigital electrode 35 in the fluid flow direction is... L 0 Then the first i The length of the second interdigital electrode 35 is L i = L 0 + k ×( i -1), where, L 0 The value range is 500-900μm, for example, in this embodiment... L 0 =500μm, k The linear growth coefficient is... k The value range is 12.5-80, for example, in this embodiment... k =46.6, i It is a positive integer, for example, in this embodiment i =10, with the longest second interdigital electrode 35 having a length of 900 μm. In other embodiments, the lengths of the plurality of second interdigital electrodes 35 may also increase non-linearly with the direction of fluid flow.

[0060] It is important to note that Figure 1 and Figure 3 The diagram shows five second interdigital electrodes 35, primarily used to illustrate the structure; however... Figures 4 to 7 The number of second interdigital electrodes 35 used in the experiment was 10.

[0061] Specifically, the size of the stepped interdigital transducer 3 is not limited. For example, in this embodiment, the width of the first interdigital electrode 34 and the second interdigital electrode 35 is 25 μm, the interdigital distance between the first interdigital electrode 34 and the second interdigital electrode 35 is 25 μm, the length of the first busbar 31 and the length of the second busbar 32 are both 530 μm and the width is 100 μm, and the width of the main channel 21 of the microchannel is 1000 μm and the height is 75 μm.

[0062] Specifically, the stepped interdigital transducer 3 can be manufactured using common processes in the field. For example, in this embodiment, the stepped interdigital transducer 3 is fabricated by magnetron sputtering and ion beam etching after the pattern is prepared by photolithography.

[0063] Specifically, the structure of the electrical connection part 36 is not limited, as long as it can meet the function of electrical signal transmission. For example, in this embodiment, the electrical connection part 36 is a solder pad, which is gold-plated to achieve a stable circuit connection. During connection, one end of the solder wire is soldered to the solder pad and the other end is connected to the signal interface of the test platform through a clamp. Compared with the traditional wire connection, this connection method reduces the contact resistance to below 5Ω and reduces the signal transmission loss by more than 30%. Moreover, the clamp connection allows for quick disassembly, which is more suitable for the needs of modular testing and batch verification in the modern equipment manufacturing field.

[0064] Specifically, in this embodiment, the electrical connection portion 36 is sequentially connected to a power attenuator, a power amplifier, and a signal generator, the frequency of which is adjustable. The signal generator outputs signals of different frequencies, the power amplifier amplifies the signal power, and the power attenuator attenuates the signal power to achieve signal stability. By providing different frequencies for microfluidic fusion through the signal generator, the influence of frequency on the mixing effect can be considered, thus adapting to the mixing requirements of different microfluidics.

[0065] The fabrication process of the microfluidic mixing device based on the stepped interdigital structure in this embodiment is as follows:

[0066] 1) Clean the piezoelectric substrate 1 made of lithium niobate in deionized water by ultrasonic cleaning for 5 minutes, take it out and let it dry; then place the piezoelectric substrate 1 in the vacuum chamber of a vacuum magnetron sputtering instrument, first sputter a 20nm chromium bonding layer on its surface, and then sputter a 100nm gold electrode layer on the chromium bonding layer.

[0067] 2) Select AZ-6130 photoresist, apply the photoresist evenly on the piezoelectric substrate 1, place it on a heating plate, and heat it at 100°C for 1 minute; align the mask with the stepped interdigitated pattern with the piezoelectric substrate 1 and expose it under ultraviolet light for 5 seconds; immerse the exposed piezoelectric substrate 1 in the prepared developing solution for 15 seconds, remove it, and then remove the excess chromium bonding layer and gold electrode layer by ion beam etching, finally forming a stepped interdigitated transducer 3 with a first busbar 31, a second busbar 32, a guide bar 33, a first interdigitated electrode 34, a second interdigitated electrode 35, and two electrical connection parts 36 on the piezoelectric substrate 1;

[0068] 3) Mix the PDMS prepolymer and curing agent at a mass ratio of 10:1 and stir evenly. Pour the mixture into a silicone mold, degas it, and cure it in an oven at 80°C for 2 hours. After removing it, you will get a flexible substrate 2 with microchannels.

[0069] 4) Align the microchannel of the flexible substrate 2 with the stepped interdigital transducer 3 on the piezoelectric substrate 1, bond them after oxygen plasma treatment, and then install the needle 26.

[0070] 5) Fix the piezoelectric substrate 1 to the glass slide with polyvinyl chloride tape to complete the device fabrication.

[0071] The method of using the microfluidic mixing device based on the stepped interdigitated structure in this embodiment includes the following steps:

[0072] S1. Determine the target frequency through experiments:

[0073] S11. After differentiating the two liquids to be mixed by color, they are continuously injected into the microchannel through two liquid inlets 23;

[0074] If the two liquids to be mixed are color-differentiated, no additional operation is required. However, if the two liquids to be mixed are the same color, a fluorescent agent or other substance that can distinguish the colors and has no effect on the test needs to be added to one of the liquids to facilitate subsequent monitoring of the interface.

[0075] S12. Activate the stepped interdigital transducer 3 to excite surface acoustic waves to act on the liquid;

[0076] S13. Adjust the frequency of the signal generator while monitoring the displacement of the interface liquid surface, and determine the target frequency according to the required mixing degree;

[0077] It should be noted that microfluidic flow is mostly in a laminar state. When mixing, the interface between the two liquids to be mixed will be displaced. The greater the displacement, the stronger the acoustic disturbance and the better the mixing effect. The required degree of mixing is determined according to the actual situation. Generally, full mixing is required, but there are special cases where the degree of mixing needs to be controlled.

[0078] Experiments revealed that the displacement of the interface liquid surface generally decreased with increasing frequency, but two fluctuations were observed: First, in the frequency range of 22MHz-42MHz, the displacement of the interface liquid surface increased with increasing frequency. This is related to the stepped interdigital transducer 3 and the piezoelectric substrate 1. This frequency range is close to the resonant coupling frequency between the stepped interdigital transducer 3 and the surface acoustic wave (SAW). At this frequency, the energy transfer efficiency of the SAW in the stepped interdigital transducer 3 is locally improved, and the disturbance intensity of the sound field on the liquid is temporarily enhanced. However, this peak value is still lower than the effect at 1MHz. Figure 5 and Figure 6As shown, because the wavelength of a 1MHz low-frequency sound wave is much larger than the microchannel size, the sound wave can penetrate the entire microchannel cross-section, and the vibration period is relatively long, giving the fluid enough time to form a stable vortex. While the sound wave in this frequency band enhances local energy due to resonance, its rapid attenuation limits its overall effective range. Secondly, in the frequency range of 60MHz-75MHz, the displacement of the interface liquid surface remains essentially unchanged with increasing frequency, and bubbles can be observed forming in the liquid, such as... Figure 7 As shown, this is because the high-frequency sound waves in this band create violent pressure vibrations in the liquid, triggering the acoustic cavitation effect to generate bubbles. When the bubbles collapse, the instantaneous impact released forces the two liquids to mix, and the overall attenuation results in the displacement of the interface liquid surface remaining unchanged.

[0079] Experiments show that when thorough mixing is required, the target frequency should be controlled in the low-frequency band of 1MHz to 50MHz. At this frequency, the surface acoustic wave energy loss excited by the stepped interdigital transducer 3 is low, the sound field has a large disturbance intensity on the fluid, the fluid is disturbed step by step along the length of the interdigital fingers, and the liquid level rises as the length of the interdigital fingers of the stepped interdigital transducer 3 increases, achieving thorough mixing at the longest interdigital finger. When the degree of mixing needs to be controlled, the target frequency should be controlled in the range of 50MHz to 100MHz. At this frequency, the surface acoustic wave has a large attenuation coefficient in the fluid, the disturbance intensity is weak, and the mixing uniformity decreases synchronously, achieving controllable attenuation of the mixing effect.

[0080] During the experiment, the displacement of the interface liquid surface can be monitored in real time using a high-speed camera. If there is a deviation between the actual mixing effect and the target mixing effect, the frequency can be finely adjusted to correct the deviation until the expected mixing degree is met.

[0081] S2. Microfluidic mixing:

[0082] S21. The two liquids to be mixed are continuously injected into the microchannel through two liquid inlets 23 respectively;

[0083] Specifically, a denser liquid to be mixed is injected through a liquid inlet 23 located on the side of the second interdigital electrode 35. The denser liquid to be mixed has a higher acoustic impedance. The surface acoustic waves excited by the stepped interdigital transducer 3 generate an acoustic impedance difference at the interface liquid surface, forming a directional force from the liquid with high acoustic impedance to the liquid with low acoustic impedance. This force works in conjunction with the acoustic field gradient of the second interdigital electrode 35 to further enhance the mixing disturbance effect, especially to reduce the problem of unevenness caused by gravity settling of high-density liquid.

[0084] It should be noted that the two liquid inlets 23 are connected in parallel and the liquid inlet volume is controlled by a micro-injection pump. In this embodiment, the liquid inlet rate of both liquid inlets 23 is set to 20 μl / min to ensure that the two liquids to be mixed enter the main channel 21 in an equal and synchronous manner.

[0085] S22. Activate the stepped interdigital transducer 3 to excite surface acoustic waves to act on the liquid;

[0086] S23. Adjust the frequency of the signal generator to the target frequency and perform microfluidic mixing.

[0087] To verify the advantages of the stepped interdigital transducer 3 proposed in this application over the medium-length interdigital transducers in the prior art, microfluidic mixing experiments were conducted at different frequencies using both the stepped interdigital transducer 3 and the equal-length interdigital transducer. The experimental results are as follows: Figure 4 As shown:

[0088] When the input frequency is 1MHz, the displacement of the interface liquid surface of the stepped interdigital transducer 3 reaches more than 500μm, proving that the mixing effect is good. When the input frequency is 100MHz, the displacement of the interface liquid surface can still be maintained at about 200μm, proving that the mixing effect is still above 40%. The maximum displacement of the interface liquid surface of the equal-length interdigital transducer is even less than the minimum displacement of the interface liquid surface of the stepped interdigital transducer 3. It can be seen that the stepped interdigital transducer 3 proposed in this application is significantly better than the equal-length interdigital transducer in the prior art in terms of mixing effect. Furthermore, the stepped interdigital transducer 3 has a greater response to frequency changes than the equal-length interdigital transducer, especially at low frequencies, which is more obvious and can greatly improve the mixing effect at low frequencies.

[0089] The above are merely specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A microfluidic mixing device based on a stepped interdigitated structure, characterized in that, include: Piezoelectric substrate (1); A flexible substrate (2) is attached to the upper surface of the piezoelectric substrate (1). A microchannel is provided on the lower surface of the flexible substrate (2). The microchannel is a Y-shaped groove formed by the intersection of a main channel (21) and two branch channels (22). The main channel (21) is arranged in the left and right direction and its free end extends upward through the flexible substrate (2) to form a liquid outlet (24). The free ends of the two branch channels (22) extend upward through the flexible substrate (2) to form a liquid inlet (23). A stepped interdigital transducer (3) is fixed between the piezoelectric substrate (1) and the flexible substrate (2) and arranged corresponding to the main channel (21). The stepped interdigital transducer (3) includes a first busbar (31) and a second busbar (32). The first busbar (31) and the second busbar (32) are arranged left and right and respectively adjacent to the front and rear sides of the main channel (21). The first busbar (31) and the second busbar (32) extend to the outside of the flexible substrate (2) through a guide bar (33) to form an electrical connection (36). The first interdigitated electrode (34) extends vertically into the main channel (21) and is distributed at intervals in the left and right directions. The second busbar (32) extends vertically into the main channel (21) and is distributed at intervals in the left and right directions. The first interdigitated electrode (34) and the second interdigitated electrode (35) are staggered in the left and right directions. The lengths of the first interdigitated electrode (34) are all equal, and the lengths of the second interdigitated electrode (35) increase with the direction of fluid flow.

2. The microfluidic mixing device based on a stepped interdigitated structure according to claim 1, characterized in that, The piezoelectric substrate (1) is lithium niobate with a 128° Y-cut, and the X-axis direction of the lithium niobate is consistent with the left and right directions.

3. The microfluidic mixing device based on a stepped interdigitated structure according to claim 1, characterized in that, The free ends of the main channel (21) and the free ends of the branch channel (22) are both enlarged to form end heads (25), and the end heads (25) pass through the flexible substrate (2) through the liquid channel to form a liquid inlet (23) or a liquid outlet (24).

4. The microfluidic mixing device based on a stepped interdigitated structure according to claim 3, characterized in that, The liquid channel is connected to a needle (26) for injecting or aspirating liquid.

5. The microfluidic mixing device based on a stepped interdigitated structure according to claim 1, characterized in that, The lengths of the multiple second interdigital electrodes (35) increase linearly with the direction of fluid flow.

6. The microfluidic mixing device based on a stepped interdigitated structure according to claim 1, characterized in that, A glass slide is fixed below the piezoelectric substrate (1).

7. The microfluidic mixing device based on a stepped interdigitated structure according to any one of claims 1 to 6, characterized in that, The electrical connection part (36) is connected in sequence to a power attenuator, a power amplifier and a signal generator, and the frequency of the signal generator can be adjusted.

8. A method of using the microfluidic mixing device based on a stepped interdigitated structure as described in claim 7, characterized in that, Includes the following steps: S1. Determine the target frequency through experiments: S11. After differentiating the two liquids to be mixed by color, they are continuously injected into the microchannel through two liquid inlets (23); S12. Activate the stepped interdigital transducer (3) to excite surface acoustic waves to act on the liquid; S13. Adjust the frequency of the signal generator while monitoring the displacement of the interface liquid surface, and determine the target frequency according to the required mixing degree; S2. Microfluidic mixing: S21. The two liquids to be mixed are continuously injected into the microchannel through two liquid inlets (23); S22. Activate the stepped interdigital transducer (3) to excite surface acoustic waves to act on the liquid; S23. Adjust the frequency of the signal generator to the target frequency and perform microfluidic mixing.

9. The method of using the microfluidic mixing device based on a stepped interdigitated structure according to claim 8, characterized in that, The denser liquid to be mixed is injected through the liquid inlet (23) located on the side of the second interdigital electrode (35).

10. The method of using the microfluidic mixing device based on a stepped interdigitated structure according to claim 8, characterized in that, When sufficient mixing is required, the target frequency should be controlled between 1MHz and 50MHz; when the mixing effect needs to be controlled, the target frequency should be controlled between 50MHz and 100MHz.

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