A piezoelectric ultrasonic self-cleaning microfluidic chip

Abstract

A piezoelectric ultrasonic self-cleaning microfluidic chip belongs to the field of microfluidic technology. The present invention includes a piezoelectric ultrasonic generator, a microfluidic chip and a cleaning liquid. The microfluidic chip is fixedly mounted on the piezoelectric ultrasonic generator. A microchannel is provided inside the microfluidic chip, or a microstructure provided at the bottom of the microfluidic chip and the piezoelectric ultrasonic generator are irreversibly sealed to form a microchannel. The upper surface of the microfluidic chip is provided with at least one liquid inlet and liquid outlet connected to the microchannel. The cleaning liquid enters the microchannel through the liquid inlet, flows along the microchannel, and is discharged through the liquid outlet. The present invention generates high-frequency ultrasonic surface waves through a piezoelectric ultrasonic generator, couples them into the microchannel of the microfluidic chip, and forms an acoustic flow effect inside the cleaning liquid. This can effectively remove residues inside the microfluidic chip, especially in the corner area, thereby improving the cleaning efficiency and controllability of the microfluidic chip.

Description

Technical Field

[0001] The invention belongs to the field of microfluidic technology, and in particular relates to a piezoelectric ultrasonic self-cleaning microfluidic chip. Background Art

[0002] Based on the manipulation of trace amounts of liquid at the microscale (usually <1mm), microfluidic chips are widely used in biochemical analysis, medical diagnosis, food testing, and aerospace fields. They have the advantages of small size, low energy consumption, high throughput, and high integration. Most microfluidic chips contain corner structures to change the flow direction of the transmission medium. However, the fluid flow in these corners is relatively complex, often accompanied by strong secondary flows, which can easily lead to channel blockage and affect chip performance. Therefore, improving the self-cleaning ability of chips and enhancing the reliability of microfluidic transmission remain important issues in microfluidic technology.

[0003] At present, the main cleaning methods adopted are positive pressure cleaning liquid cleaning and negative pressure suction. These methods can easily cause microfluidic chip seal rupture and reagent contamination. Some studies have also reduced liquid retention at corners by improving corner geometry (such as specially designed arc structures). However, the actual processing of such microfluidic chips is difficult, and these traditional cleaning processes have poor controllability and poor cleaning effects. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of microfluidic chips being easily clogged, chips being easily broken by traditional cleaning methods, poor controllability of the cleaning process and poor cleaning effect, and difficulty in processing and manufacturing due to changing the corner geometry to reduce liquid retention at the corners. A piezoelectric ultrasonic self-cleaning microfluidic chip is provided.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A piezoelectric ultrasonic self-cleaning microfluidic chip comprises a piezoelectric ultrasonic generator, a microfluidic chip and a cleaning liquid. The microfluidic chip is fixedly mounted on the piezoelectric ultrasonic generator, a microchannel is provided inside the microfluidic chip, or a microstructure provided at the bottom of the microfluidic chip and the piezoelectric ultrasonic generator are irreversibly sealed to form a closed microchannel; at least one liquid inlet and liquid outlet connected to the microchannel are provided on the upper surface of the microfluidic chip, the cleaning liquid enters the microchannel through the liquid inlet, flows along the microchannel, and is discharged through the liquid outlet.

[0007] Furthermore, the piezoelectric ultrasonic generating device includes a piezoelectric substrate, an electrode, a sound absorbing block and an AC excitation module; the electrode is located at one end of the upper surface of the piezoelectric substrate and the two are made into one body, and the sound absorbing block is fixed on the upper surface of the piezoelectric substrate; the AC excitation module is connected to the positive and negative poles of the electrode through leads; the microfluidic chip is fixed on the upper surface of the piezoelectric substrate, and the microstructure at the bottom of the microfluidic chip and the upper surface of the piezoelectric substrate are irreversibly sealed to form the closed microchannel.

[0008] Furthermore, the piezoelectric ultrasonic generating device includes a piezoelectric ceramic sheet, a brass base, a sound absorbing block and an AC excitation module; the piezoelectric ceramic sheet and the sound absorbing block are both fixed on the upper surface of the brass base, and the AC excitation module is connected to the piezoelectric ceramic sheet and the brass base respectively through the positive and negative poles of the excitation signal leads; the microfluidic chip is fixed on the upper surface of the brass base, and the microstructure at the bottom of the microfluidic chip and the upper surface of the brass base are irreversibly sealed to form the closed microchannel.

[0009] Furthermore, the electrode is formed on one end of the upper surface of the piezoelectric substrate by magnetron sputtering and ion beam etching processes.

[0010] Furthermore, the piezoelectric substrate is a Y-128° tangential lithium niobate, piezoelectric ceramic or piezoelectric polymer material, or a composite substrate consisting of a glass, metal or plastic non-piezoelectric material and a piezoelectric film with a thickness of 0.2mm to 1mm deposited on its surface.

[0011] Furthermore, the electrodes are rectangular interdigital electrodes or arc-shaped interdigital electrodes, and the electrode material is one or a combination of gold, platinum, aluminum, silver, FTO conductive glass, titanium, chromium, and carbon.

[0012] Furthermore, the shape of the microchannel is one or a combination of straight line, broken line, and arc; the overall depth of the microchannel remains consistent, and the overall width of the microchannel is the same or different.

[0013] Furthermore, at least two of the microchannels are arranged in parallel along the length direction or the width direction of the microfluidic chip.

[0014] Furthermore, the cleaning liquid is deionized water, methanol, ethanol, isopropanol or acetone solution.

[0015] Furthermore, the sound absorbing block is made of rubber, sound absorbing foam or glass fiber.

[0016] The beneficial effects of the present invention compared to the prior art are as follows: the piezoelectric ultrasonic self-cleaning microfluidic chip provided by the present invention forms ultrasonic surface waves on the surface of the substrate through an AC excitation module, thereby realizing the self-cleaning function of the microfluidic chip. The piezoelectric ultrasonic generator does not require mechanical drive, has a simple structure, a small size, high acoustic-to-electric conversion efficiency, low power consumption, and is easy to integrate with other systems; the rapid adjustment of the piezoelectric ultrasonic wave can be achieved by changing the amplitude and frequency of the excitation signal, with higher controllability and faster response speed; the acoustic flow effect generated inside the cleaning liquid is used to form an acoustic flow vortex to remove the retained matter inside the microchannel, especially in the corner area, with higher cleaning efficiency and without causing damage to the microfluidic chip; the cleaning liquid can be selected from deionized water or other liquids (methanol, ethanol, isopropanol or acetone solution), which is not easy to cause reagent contamination and affect use; this cleaning method does not require special design of the microchannel structure, and the production cost of the microfluidic chip is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The main view of the piezoelectric ultrasonic self-cleaning microfluidic chip of the present invention Figure 1 , the microchannel is set inside the microfluidic chip;

[0018] Figure 2 A top view of the piezoelectric ultrasonic self-cleaning microfluidic chip of the present invention Figure 1 ;

[0019] Figure 3 1 is a top view of the arc-shaped interdigitated electrode structure 1;

[0020] Figure 4 is a top view of the second arc-shaped interdigitated electrode structure;

[0021] Figure 5 is a top view of a piezoelectric ceramic transducer;

[0022] Figure 6 The main view of the piezoelectric ultrasonic self-cleaning microfluidic chip of the present invention Figure 2 , a front view of a closed microchannel formed by irreversible sealing between the microstructure at the bottom of the microfluidic chip and the upper surface of the piezoelectric substrate;

[0023] Figure 7 It is a top view of the 'Y'-shaped microchannel;

[0024] Figure 8 It is a top view of the broken line microchannel;

[0025] Figure 9 A top view of a microchannel formed by the intersection of a 'T'-shaped microchannel and an annular microchannel;

[0026] Figure 10 This is a top view of the microfluidic chip;

[0027] Figure 11 The main view of the piezoelectric ultrasonic self-cleaning microfluidic chip of the present invention Figure 3 , the microchannel is set inside the microfluidic chip;

[0028] Figure 12 A top view of the piezoelectric ultrasonic self-cleaning microfluidic chip of the present invention Figure 3 ;

[0029] Figure 13 The main view of the piezoelectric ultrasonic self-cleaning microfluidic chip of the present invention Figure 4 ,The microstructure at the bottom of the microfluidic chip and the upper surface of the brass substrate are irreversibly sealed to form a closed microchannel;

[0030] The names and reference numerals of the components involved in the above drawings are as follows:

[0031] Piezoelectric substrate 1, electrode 2, microfluidic chip 3, liquid inlet 3-1, microchannel 3-2, liquid outlet 3-3, cleaning liquid 4, sound absorbing block 5, AC excitation module 6, piezoelectric ceramic 7, brass substrate 8. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions of the present invention in conjunction with the accompanying drawings of the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention and are not limited thereto. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0033] Specific implementation method 1: Figure 1-Figure 4 、 Figure 6 As shown, this embodiment discloses a piezoelectric ultrasonic self-cleaning microfluidic chip, including a piezoelectric ultrasonic generator, a microfluidic chip 3 and a cleaning liquid 4, wherein the microfluidic chip 3 is fixedly mounted on the piezoelectric ultrasonic generator, and a microchannel 3-2 is provided inside the microfluidic chip 3, or a microstructure provided at the bottom of the microfluidic chip 3 and the piezoelectric ultrasonic generator are irreversibly sealed to form a closed microchannel 3-2, thereby achieving bonding of the contact surface to ensure that the cleaning liquid 4 in the microfluidic chip 3 does not leak; at least one liquid inlet 3-1 and a liquid outlet 3-3 connected to the microchannel 3-2 are vertically opened on the upper surface of the microfluidic chip 3 (the liquid inlet 3-1 and the liquid outlet 3-3 are formed by punching holes at both ends of the microchannel 3-2 with a chip puncher), the cleaning liquid 4 enters the microchannel 3-2 through the liquid inlet 3-1, flows along the microchannel 3-2, and is discharged through the liquid outlet 3-3 under the action of the acoustic flow pressure; the electrode 2 is a rectangular interdigital electrode or an arc-shaped interdigital electrode (which is the existing technology).

[0034] The piezoelectric ultrasonic generator includes a piezoelectric substrate 1, an electrode 2, a sound absorbing block 5 and an AC excitation module 6; the electrode 2 is located at one end of the upper surface of the piezoelectric substrate 1 and the two are made into one body, the sound absorbing block 5 is fixed on the upper surface of the piezoelectric substrate 1 (the sound absorbing block 5 is fixed to the upper surface of the piezoelectric substrate 1 by epoxy resin glue, and the number of sound absorbing blocks 5 is preferably two, and the two sound absorbing blocks 5 are arranged at both ends of the upper surface of the piezoelectric substrate 1 to absorb ultrasonic waves), the AC excitation module 6 is connected to the positive and negative poles of the electrode 2 through a lead to provide an excitation signal for the piezoelectric ultrasonic generator; the microfluidic chip 3 is fixed on the upper surface of the piezoelectric substrate 1, and the microstructure at the bottom of the microfluidic chip 3 is irreversibly sealed with the upper surface of the piezoelectric substrate 1 to form the closed microchannel 3-2.

[0035] like Figure 1 As shown, a microchannel 3 - 2 is provided inside the microfluidic chip 3 , and the cleaning fluid 4 does not directly contact the piezoelectric substrate 1 when flowing through the microchannel 3 - 2 .

[0036] like Figure 6 As shown, a microstructure is provided at the bottom of the microfluidic chip 3 , and the microstructure and the upper surface of the piezoelectric substrate 1 are irreversibly sealed to form the closed microchannel 3 - 2 , and the cleaning liquid 4 in the microchannel 3 - 2 is in direct contact with the piezoelectric substrate 1 .

[0037] like Figure 2 As shown, the electrode 2 is formed on one end of the upper surface of the piezoelectric substrate 1 by magnetron sputtering and ion beam etching processes.

[0038] The piezoelectric substrate 1 is a Y-128° tangential lithium niobate (LiNbO3), piezoelectric ceramics or piezoelectric polymer material, or a composite substrate consisting of glass, metal or plastic non-piezoelectric material and a piezoelectric film with a thickness of 0.2mm to 1mm deposited on its surface.

[0039] like Figure 2 As shown; the interdigital width of the rectangular interdigital electrode is 3μm to 10μm, the gap between two adjacent interdigital fingers is 5μm to 15μm, the interdigital thickness is 0.01μm to 0.05μm, and the number of interdigital pairs is 30 to 90 pairs; the material of the electrode 2 is one or a combination of gold, platinum, aluminum, silver, FTO conductive glass, titanium, chromium, and carbon.

[0040] The material of the microfluidic chip 3 is one or a combination of polydimethylsiloxane, polymethyl methacrylate, glass and polymer resin.

[0041] like Figure 7-Figure 9As shown, the shape of the microchannel 3-2 is one or a combination of straight line, broken line, and arc shape, such as a 'Y'-shaped microchannel (a combination of broken line and straight line microchannels), a broken line microchannel, an arc-shaped microchannel, a 'T'-shaped microchannel and a circular microchannel (a combination of straight line and arc-shaped microchannels). Figure 10 Schematic diagram of four microchannel shapes integrated on the same microfluidic chip 3 , the four microchannel shapes are: a 'Y'-shaped microchannel, a curved microchannel, a broken-line microchannel, and a combination of a straight-line and curved microchannel.

[0042] The overall depth of the microchannel 3-2 remains consistent; the width of the microchannel 3-2 is 0.1mm to 1mm, the depth of the microchannel 3-2 is 0.1mm to 0.5mm, and the overall width of the microchannel 3-2 is the same or different.

[0043] At least two microchannels 3 - 2 are arranged in parallel along the length direction or the width direction of the microfluidic chip 3 .

[0044] The cleaning solution 4 is deionized water, methanol, ethanol, isopropanol or acetone solution.

[0045] like Figure 1 、 Figure 2 As shown, the material of the sound absorbing block 5 is rubber, sound absorbing foam or glass fiber, which can allow ultrasonic waves to enter the sound absorbing material without reflection and be mostly absorbed, thereby reducing the interference of reflected waves.

[0046] like Figure 2 As shown, the AC excitation module 6 is composed of an AC signal generator and a power amplifier (which is the existing technology), and provides an excitation signal with a frequency between 10 MHz and 300 MHz and an output power between 400 mW and 3 W.

[0047] The working principle of the specific embodiment 1 is as follows: the AC excitation module 6 applies an AC excitation signal between the positive and negative electrodes of the rectangular interdigital electrode or the arc-shaped interdigital electrode. Under the action of the alternating electric field, due to the inverse piezoelectric effect, the piezoelectric substrate 1 will cause mechanical distortion inside the lattice due to the offset of the charge center, converting the high-frequency electrical signal into mechanical vibration of its own frequency, and exciting an ultrasonic surface wave propagating in a direction perpendicular to the electrode on the surface of the piezoelectric substrate 1. The ultrasonic surface wave enters the microchannel 3-2 through the interface between the microfluidic chip 3 and the piezoelectric substrate 1, which is preliminarily filled with liquid. Port 3-1 fills microchannel 3-2 with cleaning liquid 4. High-frequency vibrations cause the cleaning liquid 4 to form discrete droplets. Ultrasonic surface waves couple into the droplets, generating an acoustic streaming effect. The energy carried by the acoustic waves also couples to the droplets at a certain angle, converting them into kinetic energy, driving the cleaning liquid 4 along microchannel 3-2. Substances trapped within microchannel 3-2, especially at corners, are drawn into the cleaning liquid 4 by the acoustic streaming and discharged from microfluidic chip 3 through liquid outlet 3-3, effectively cleaning the chip 3. Changing the amplitude and frequency of the AC excitation signal can quickly adjust the amplitude and frequency of the ultrasonic surface waves, thereby varying the cleaning intensity and efficiency.

[0048] Specific implementation method 2: Figure 5 、 Figure 11-13 As shown, this embodiment discloses a piezoelectric ultrasonic self-cleaning microfluidic chip, including a piezoelectric ultrasonic generator, a microfluidic chip 3 and a cleaning liquid 4, wherein the microfluidic chip 3 is fixedly mounted on the piezoelectric ultrasonic generator, and a microchannel 3-2 is provided inside the microfluidic chip 3, or a microstructure provided at the bottom of the microfluidic chip 3 and the piezoelectric ultrasonic generator are irreversibly sealed to form a closed microchannel 3-2, thereby achieving bonding of the contact surface and ensuring that the cleaning liquid 4 in the microfluidic chip 3 is leak-free; at least one liquid inlet 3-1 and a liquid outlet 3-3 connected to the microchannel 3-2 are vertically opened on the upper surface of the microfluidic chip 3, and the cleaning liquid 4 enters the microchannel 3-2 through the liquid inlet 3-1, flows along the microchannel 3-2, and is discharged through the liquid outlet 3-3.

[0049] The piezoelectric ultrasonic generating device includes a piezoelectric ceramic sheet 7, a brass base 8 (a piezoelectric ceramic transducer is formed by combining the piezoelectric ceramic sheet 7 and the brass base 8), a sound absorbing block 5 and an AC excitation module 6; the piezoelectric ceramic sheet 7 and the sound absorbing block 5 are both fixed on the upper surface of the brass base 8 (the sound absorbing block 5 is fixed on the upper surface of the brass base 8 by epoxy resin glue, and the number of sound absorbing blocks 5 is preferably two, and the two sound absorbing blocks 5 are arranged at both ends of the upper surface of the brass base 8 to absorb ultrasonic waves), and the AC excitation module 6 is connected to the piezoelectric ceramic sheet 7 and the brass base 8 respectively through the positive and negative poles of the excitation signal lead; the microfluidic chip 3 is fixed on the upper surface of the brass base 8, and the microstructure at the bottom of the microfluidic chip 3 is irreversibly sealed with the upper surface of the brass base 8 to form the closed microchannel 3-2.

[0050] In this embodiment, the piezoelectric ultrasonic generator uses a piezoelectric ceramic sheet 7 and a brass substrate 8 instead of the electrode 2 and the piezoelectric substrate 1 .

[0051] like Figure 11 As shown, a microchannel 3 - 2 is provided inside the microfluidic chip 3 , and the cleaning liquid 4 does not directly contact the brass substrate 8 when flowing through the microchannel 3 - 2 .

[0052] like Figure 13 As shown, a microstructure is provided at the bottom of the microfluidic chip 3 , and the microstructure and the upper surface of the brass substrate 8 are irreversibly sealed to form the closed microchannel 3 - 2 , and the cleaning liquid 4 in the microchannel 3 - 2 is in direct contact with the brass substrate 8 .

[0053] like Figure 11-13 As shown, the material of the microfluidic chip 3 is one or a combination of polydimethylsiloxane, polymethyl methacrylate, glass and polymer resin.

[0054] like Figure 7-Figure 9 As shown, the shape of the microchannel 3-2 is one or a combination of straight line, broken line, and arc shape, such as a 'Y'-shaped microchannel (a combination of broken line and straight line microchannels), a broken line microchannel, an arc-shaped microchannel, a 'T'-shaped microchannel and a circular microchannel (a combination of straight line and arc-shaped microchannels). Figure 10 Schematic diagram of four microchannel shapes integrated on the same microfluidic chip 3 , the four microchannel shapes are: a 'Y'-shaped microchannel, a curved microchannel, a broken-line microchannel, and a combination of a straight-line and curved microchannel.

[0055] The overall depth of the microchannel 3-2 remains consistent; the width of the microchannel 3-2 is 0.1mm to 1mm, the depth of the microchannel 3-2 is 0.1mm to 0.5mm, and the overall width of the microchannel 3-2 is the same or different.

[0056] At least two microchannels 3 - 2 are arranged in parallel along the length direction or the width direction of the microfluidic chip 3 .

[0057] The cleaning solution 4 is deionized water, methanol, ethanol, isopropanol or acetone solution.

[0058] like Figure 11-13 As shown, the material of the sound absorbing block 5 is rubber, sound absorbing foam or glass fiber, which can allow ultrasonic waves to enter the sound absorbing material without reflection and be mostly absorbed, thereby reducing the interference of reflected waves.

[0059] like Figure 11-13 As shown, the AC excitation module 6 is composed of an AC signal generator and a power amplifier (which is the existing technology), and provides an excitation signal with a frequency between 10 MHz and 300 MHz and an output power between 400 mW and 3 W.

[0060] The working principle of the second embodiment refers to the working principle of the first embodiment.

Claims

1. A piezoelectric ultrasonic self-cleaning microfluidic chip, characterized by: The invention comprises a piezoelectric ultrasonic wave generator, a microfluidic chip (3) and a cleaning liquid (4); the microfluidic chip (3) is fixedly mounted on the piezoelectric ultrasonic wave generator; a microchannel (3-2) is provided inside the microfluidic chip (3); or a microstructure provided at the bottom of the microfluidic chip (3) and the piezoelectric ultrasonic wave generator are irreversibly sealed to form a closed microchannel (3-2); and the upper surface of the microfluidic chip (3) is provided with at least one liquid inlet (3-1) and a liquid outlet (3-3) connected to the microchannel (3-2); the cleaning liquid (4) enters the microchannel (3-2) through the liquid inlet (3-1), flows along the microchannel (3-2), and is discharged through the liquid outlet (3-3).

2. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 1, characterized in that: The piezoelectric ultrasonic generating device comprises a piezoelectric substrate (1), an electrode (2), a sound absorbing block (5), and an AC excitation module (6); the electrode (2) is located at one end of the upper surface of the piezoelectric substrate (1) and the two are made into one body, and the sound absorbing block (5) is fixed on the upper surface of the piezoelectric substrate (1); the AC excitation module (6) is connected to the positive and negative poles of the electrode (2) through a lead; the microfluidic chip (3) is fixed on the upper surface of the piezoelectric substrate (1), and the microstructure provided at the bottom of the microfluidic chip (3) and the upper surface of the piezoelectric substrate (1) are irreversibly sealed to form the closed microchannel (3-2).

3. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 1, characterized in that: The piezoelectric ultrasonic generating device comprises a piezoelectric ceramic sheet (7), a brass base (8), a sound absorbing block (5) and an AC excitation module (6); the piezoelectric ceramic sheet (7) and the sound absorbing block (5) are both fixed on the upper surface of the brass base (8); the AC excitation module (6) is connected to the piezoelectric ceramic sheet (7) and the brass base (8) via the positive and negative poles of the excitation signal leads; the microfluidic chip (3) is fixed on the upper surface of the brass base (8); the microstructure provided on the bottom of the microfluidic chip (3) and the upper surface of the brass base (8) are irreversibly sealed to form the closed microchannel (3-2).

4. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 2, characterized in that: The electrode (2) is formed on one end of the upper surface of the piezoelectric substrate (1) by magnetron sputtering and ion beam etching processes.

5. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 2, characterized in that: The piezoelectric substrate (1) is a Y-128° tangential lithium niobate, piezoelectric ceramics or piezoelectric polymer material, or a composite substrate consisting of glass, metal or plastic non-piezoelectric material and a piezoelectric film with a thickness of 0.2mm to 1mm deposited on its surface.

6. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 2, characterized in that: The electrode (2) is a rectangular interdigital electrode or an arc-shaped interdigital electrode, and the material of the electrode (2) is one or a combination of gold, platinum, aluminum, silver, FTO conductive glass, titanium, chromium, and carbon.

7. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 1, characterized in that: The shape of the microchannel (3-2) is one of a straight line, a broken line, and an arc, or a combination thereof; the overall depth of the microchannel (3-2) remains consistent, and the overall width of the microchannel (3-2) is the same or different.

8. A piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 1 or 7, characterized in that: At least two microchannels (3-2) are arranged in parallel along the length direction or the width direction of the microfluidic chip (3).

9. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 1, characterized in that: The cleaning liquid (4) is deionized water, methanol, ethanol, isopropanol or acetone solution.

10. The piezoelectric ultrasonic self-cleaning microfluidic chip according to claim 2 or 3, characterized in that: The material of the sound absorbing block (5) is rubber, sound absorbing foam or glass fiber.

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