P-type narrow cavity retardation low-frequency sound absorption metamaterial

Abstract

The invention provides a P-type narrow cavity retardation low-frequency sound absorption metamaterial, and belongs to the technical field of sound absorption materials. The central honeycomb unit and the three P-type sound absorption units form a triangular assembly which is used as a basic structure of the sound absorption metamaterial; the P-type sound absorption unit comprises a P-type cavity defined by a top plate, a back plate and side walls, and the P-type cavity comprises an open cavity and a narrow cavity; the P-type sound absorption unit and the central honeycomb unit are made of hard materials, the cavity wall of the P-type cavity is coated with a flexible coating, and the interior of the central honeycomb unit is filled with a porous sound absorption material; the cross section of the narrow cavity of the P-type cavity in the direction from the top plate to the back plate is in a V shape, and a V-shaped slit is formed. Micropores are formed in a top plate of the P-type sound absorption unit, are distributed in the open cavity or the narrow cavity and are at least tightly attached to the side wall of one face of the P-type cavity. According to the invention, two sound absorption behaviors of prolonging a sound propagation path and geometric resonance by clinging the micropores to the cavity wall are simultaneously realized within a limited material thickness range.

Description

Technical Field

[0001] This invention provides a P-type cavity-blocking low-frequency sound-absorbing metamaterial, belonging to the field of sound-absorbing material technology. Background Technology

[0002] Improving passenger comfort and reducing noise pollution are important themes in high-speed train design. Special sound-absorbing materials are usually installed inside and outside the carriages of high-speed trains to dissipate noise energy into other forms of energy as much as possible during train operation, thereby protecting passengers' hearing health and overall riding experience.

[0003] Currently, among the various forms of sound-absorbing materials, the most common are those using porous foams, fiber materials, or Helmholtz resonators. These materials dissipate sound energy through friction, viscosity, and resonance within the material. Under certain porosity and thickness requirements, these materials exhibit progressive energy attenuation when excited by sound waves, resulting in progressively decreasing sound pressure levels. Depending on the material specifications and pore distribution, this attenuation may be broadband or targeted to specific frequency bands. Regardless, each sound wave-material interaction typically involves two mechanisms: viscous dissipation and thermal conversion, corresponding to frictional sound absorption and thermal energy dissipation. Correspondingly, on the sound absorption coefficient-frequency curve, these traditional sound-absorbing materials exhibit a peak segment and a plateau segment containing multiple small fluctuations, and are considered to possess relatively ideal broadband sound absorption capabilities.

[0004] However, with the continuous increase in the speed of high-speed trains, the problem of low- and mid-frequency noise has become increasingly prominent. On the one hand, the increase in train speed leads to a significant increase in the low-frequency components of aerodynamic noise, wheel-rail vibration noise, and locomotive traction noise. These low-frequency noises have high energy density and long propagation distances, causing continuous interference to passengers and potentially even health problems. On the other hand, the wavelengths of low-frequency noise are relatively long, making it difficult to effectively eliminate them using traditional sound-absorbing materials. This is because traditional materials have low absorption efficiency for low frequencies, requiring a significant increase in material thickness or volume to match the wavelength. This not only occupies valuable carriage space but may also disrupt the overall uniformity of the material. At the same time, with the increase in material geometry, the mass of sound-absorbing devices also increases, which runs counter to the lightweight requirements of high-speed trains. Furthermore, once designed and manufactured, the sound absorption performance of sound-absorbing materials based on traditional porous or resonant structures, especially their targeting of low frequencies, is fixed. It is difficult to adjust the absorption frequency band or efficiency through simple means, making it difficult to meet the goal of today's high-speed trains to precisely control sound absorption performance according to different noise spectra. Summary of the Invention

[0005] This invention, based on traditional sound-absorbing materials and grounded in experimental, finite element simulation, and theoretical analysis, fully considers the propagation characteristics of low-frequency sound waves. It cleverly combines the close contact between micropores and cavity walls with optimized cavity geometry in a composite design. This provides a composite acoustic metamaterial that simultaneously achieves two sound absorption behaviors—extending the sound propagation path through close contact between micropores and cavity walls and geometric resonance—without significantly impacting the processing technology, material cost, installation space, or lightweighting of the sound-absorbing material. This composite structure utilizes the close contact between micropores and cavity walls to enhance dissipation, cleverly designing a P-shaped sound-absorbing material. Leveraging the geometric diversity of the P-shaped cavity, it achieves efficient low-frequency sound absorption, stable sound absorption, a high absorption coefficient, and adjustable and controllable absorption frequency bands. Furthermore, its ingenious design, simple structure, low cost, and convenient installation make it a promising candidate for noise control in high-speed trains.

[0006] The specific technical solution is as follows:

[0007] A P-type cavity blocking low-frequency sound-absorbing metamaterial includes a central honeycomb unit with a hexagonal honeycomb structure, and three P-type sound-absorbing units arranged sequentially around the central honeycomb unit. The central honeycomb unit and the three P-type sound-absorbing units form a triangular assembly as the basic structure of the sound-absorbing metamaterial.

[0008] The P-type sound-absorbing unit includes a P-type cavity formed by a top plate, a back plate, and side walls. The P-type cavity includes an open cavity and a narrow cavity.

[0009] Both the P-type sound-absorbing unit and the central honeycomb unit are made of rigid materials. The walls of the P-type chamber are coated with a flexible coating, and the interior of the central honeycomb unit is filled with porous sound-absorbing material.

[0010] The cross-section of the narrow cavity of the P-type chamber from the top plate to the back plate is V-shaped, forming a V-shaped slit;

[0011] The top plate of the P-type sound-absorbing unit has micropores, which are distributed in the open cavity or the narrow cavity, and are at least in close contact with one side wall of the P-type cavity.

[0012] Furthermore, there are three P-type sound-absorbing units: three chamber walls tightly attached to the P-type sound-absorbing unit, two chamber walls tightly attached to the P-type sound-absorbing unit, and one chamber wall tightly attached to the P-type sound-absorbing unit.

[0013] The micropores of the three-chamber wall, which are closely attached to the P-type sound-absorbing unit, are opened at the end of the narrow cavity and are close to the three side walls of the end of the narrow cavity; the diameter of the pores is 0.5-2mm; the opening angle of the upper part of the V-shaped slit of the three-chamber wall, which is closely attached to the P-type sound-absorbing unit, is 30-60°, and the depth of the V-shaped slit is 0.5-0.8 times the height of the P-type cavity; the axis of the micropore is located on the center line of the V-shaped slit.

[0014] The micropores of the double-cavity wall, closely attached to the P-type sound-absorbing unit, are located in the center of the narrow cavity, adhering to both side walls of the cavity. The aperture ranges from 0.5 to 2 mm, adjusted according to specific impedance matching. The upper opening angle of the V-shaped slit, also closely attached to the double-cavity wall of the P-type sound-absorbing unit, is 45-75°, and the depth of the V-shaped slit is 0.6-0.9 times the height of the P-type cavity. The axis of the micropores is located on the center line of the V-shaped slit.

[0015] The micropores of the single-cavity wall closely adhering to the P-type sound-absorbing unit are opened in the open cavity, closely adhering to one side wall of the open cavity; the pore diameter is 1-3mm;

[0016] The depth of the V-shaped slit is greater than the diameter of the micropore.

[0017] The distance between the micropore and the sidewall of the P-shaped chamber is less than wavelength λ / 10. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the P-type cavity-blocking low-frequency sound-absorbing metamaterial structure of the present invention;

[0019] Figure 2 This is an exploded view of the P-type cavity-blocking low-frequency sound-absorbing metamaterial assembly of the present invention;

[0020] Figure 3 This is a structural diagram of the three-cavity wall tightly attached P-type sound-absorbing unit of the present invention;

[0021] Figure 4 This is a structural diagram of the double-cavity wall tightly attached P-type sound-absorbing unit of the present invention;

[0022] Figure 5 This is a structural diagram of the single-cavity wall tightly attached P-type sound-absorbing unit of the present invention;

[0023] Figure 6 This is a schematic diagram illustrating the principle of the P-type cavity-blocking low-frequency sound-absorbing metamaterial of the present invention;

[0024] Figure 7 This is a comparison chart of the sound absorption coefficient of the present invention and that of a conventional absorption unit;

[0025] Figure 8 This is a comparison diagram of the viscous dissipation of the present invention and the viscous dissipation of a conventional absorption unit. Detailed Implementation

[0026] This embodiment provides a P-type cavity-blocking low-frequency sound-absorbing metamaterial, which is a constructed P-type cavity-encircling honeycomb cavity-blocking low-frequency sound-absorbing metamaterial, such as... Figure 1 As shown, it includes three P-type sound-absorbing units: a three-chamber wall-adhered P-type sound-absorbing unit 1, a double-chamber wall-adhered P-type sound-absorbing unit 2, and a single-chamber wall-adhered P-type sound-absorbing unit 3, as well as a central honeycomb unit 4, as shown. Figure 2 As shown.

[0027] Three chamber walls tightly attached to P-type sound-absorbing unit 1, two chamber walls tightly attached to P-type sound-absorbing unit 2, and one chamber wall tightly attached to P-type sound-absorbing unit 3 surround and wrap around the central honeycomb unit 4, together forming a triangular component. By arranging the components densely, an acoustic metamaterial with low-frequency sound absorption capability is formed.

[0028] The three-chamber wall-adhered P-type sound-absorbing unit 1, the double-chamber wall-adhered P-type sound-absorbing unit 2, the single-chamber wall-adhered P-type sound-absorbing unit 3, and the central honeycomb unit 4 are all made of high-quality rigid metal shells or high-rigidity resin. For the three-chamber wall-adhered P-type sound-absorbing unit 1, the double-chamber wall-adhered P-type sound-absorbing unit 2, and the single-chamber wall-adhered P-type sound-absorbing unit 3, the interior of the chamber walls is coated with flexible coatings, such as polyvinyl alcohol, polyester, and polyimide, to enhance viscous dissipation during sound wave propagation. The central honeycomb unit 4 has a standard hexagonal honeycomb structure, which can be filled with porous sound-absorbing materials, such as glass fiber or foam, to assist in mid-to-high frequency sound absorption. It also incorporates several weight-reduction designs (such as ultra-thin chamber walls and hollow chamber walls) to achieve lightweighting while ensuring structural strength.

[0029] The three-chamber wall-fitted P-type sound-absorbing unit 1 includes a first P-type chamber 11, a first top plate 12, a rigid first back plate 13, a designed first micropore 14 that fits tightly against the three side chamber walls, and a first V-shaped slit 15 located in the narrow cavity of the first P-type chamber 11. Figure 3 As shown. From a top view, the first P-shaped chamber 11, with its three walls tightly attached to the P-shaped sound-absorbing unit 1, is shaped like the letter P. The first top plate 12 is made of thin-walled metal or resin board, and the aperture of the first micro-hole 14 is 0.5-2mm to control the incident impedance of sound waves. The first back plate 13 is a sealed structure to ensure that sound waves do not leak inside the chamber. The first micro-hole 14 is arranged close to the three side walls of the narrow cavity tail, and there is one of them, to guide the sound waves to propagate along the inner wall of the first V-shaped slit 15. The opening angle of the first V-shaped slit 15 is 30-60°, and the depth of the first V-shaped slit 15 is 0.5-0.8 times the height of the chamber, which is used to enhance the viscous resistance of airflow when the micro-holes are tightly attached to the cavity walls. When a sound wave is incident, it enters the cavity through the first micro-hole 14. Unlike traditional micro-porous plate-type sound-absorbing materials, due to the special shape and structure of the P-shaped cavity, the micro-hole and the cavity wall are tightly attached. The sound wave cannot diffuse freely after it is incident, but diffuses along the narrow cavity. At this time, the first V-shaped slit 15 will enhance the viscous dissipation of the sound wave and the cavity wall, thus strengthening the sound dissipation.

[0030] The double-cavity wall-fitted P-type sound-absorbing unit 2 includes a second P-type cavity 21, a second top plate 22, a rigid second back plate 23, second micropores 24 designed to fit tightly against the side walls on both sides of the center of the cavity, and a designed second V-shaped slit, such as... Figure 4As shown. However, at this point, the second micro-hole 24 is located in the center of the cavity, and the second micro-hole 24 is in close contact with the side walls on both sides, allowing the sound wave to diffuse along both sides of the cavity wall. The second backplate 23 has a sealing design; there is one second micro-hole 24, with a diameter of 0.5-2mm. Its position is centered to balance the propagation path; the opening angle of the second V-shaped slit is 45-75°, and its depth is 0.6-0.9 times the height of the cavity. When the sound wave enters the cavity through the second micro-hole 24, the sound wave is restricted by the cavity and diffuses along both sides of the cavity wall. At this time, the micro-hole is in close contact with the cavity wall, extending the sound wave path. Combined with the adhesive effect of the flexible coating, this enhances the dissipation of mid-to-low frequencies.

[0031] The single-cavity wall-adhered P-type sound-absorbing unit 3 includes a third P-type chamber 31, a third top plate 32, a rigid third back plate 33 at the bottom, and a third micropore 34 designed to adhere tightly to one side wall of the open cavity, such as... Figure 5 As shown. The third micropore 34 in the P-type sound-absorbing unit 3 is located in the open cavity of the third P-type cavity 31 and is in close contact with one side wall of the open cavity; the diameter of the third micropore 34 is 1-3mm; the third back plate 33 is sealed; the third micropore 34 is in close contact with the single side cavity wall, and there is one of them. When the sound wave is incident, the sound wave diffuses along the single side cavity wall.

[0032] The working principle of this P-type cavity-blocking low-frequency sound-absorbing metamaterial is as follows: The composite sound-absorbing metamaterial of this invention is typically installed on the inner wall of a high-speed train carriage or near a noise source. When low-frequency noise is incident, this sound-absorbing material simultaneously performs two functions: the tight adhesion between the narrow cavity micropores and the cavity wall, and honeycomb resonance, dissipating a large amount of sound energy. For example... Figure 6 As shown, the outermost P-type sound-absorbing unit not only has the ability to resonate and dissipate sound waves, but also generates more viscous dissipation through the narrow cavity. The central honeycomb unit 4 plays an auxiliary role in resonant dissipation, working in conjunction with the three P-type units to expand the sound absorption frequency band. The three types of P-type units surround the honeycomb unit to form a triangular assembly, and the close-packed arrangement between the assemblies ensures the uniformity and lightweight of the material. The cavity length of the P-type chamber is directly related to the sound absorption path length, and the cavity's obstruction of sound waves significantly enhances the viscous dissipation of the cavity.

[0033] Specifically, the P-type cavity micropores are arranged close to the cavity wall. Although the honeycomb unit has standard resonance, the narrow cavity of the P-type unit is coaxial with the micropores and closely attached to the wall. When sound waves are incident, for traditional micro-perforated plate sound absorbers, the sound waves will undergo Helmholtz resonance after entering the cavity through the micropores, mainly relying on the inertia of the micropores and the capacitance of the cavity to match the impedance. However, this invention introduces a P-type cavity structure on the basis of ordinary honeycomb sound absorbers, causing the sound waves to adhere to the cavity wall and propagate, with a longer path than that of traditional cavity absorbers, resulting in a shift of the resonance frequency to lower frequencies. The P-type cavity will successively undergo three stages: viscous hindrance, heat dissipation, and resonance attenuation. The integral of the absorption coefficient-frequency curve, i.e., the area enclosed by the horizontal axis of the coordinate axis, corresponds to the total sound absorption, such as... Figure 7 and Figure 8As shown. Since the frequency band corresponding to the high-frequency attenuation stage is relatively narrow and its contribution to the integral of the curve is small, the low-frequency absorption coefficient α of the P-type cavity can be obtained by simplifying the acoustic series impedance as shown in Equation 1:

[0034]

[0035] In the formula, z represents the normalized surface impedance. Without changing the material thickness or porosity, the sound absorption performance is directly related to the slit impedance of the P-type cavity. Therefore, to improve low-frequency sound absorption, a larger slit length and a greater number of close-fitting walls are often desired for the P-type cavity to increase viscous resistance and inertial impedance. However, on the other hand, too many close-fitting walls or excessively long slits may cause excessively high impedance, resulting in an overly negative Im(z) and reduced broadband performance. Therefore, this invention designs three types of gradient units—three-walled, two-walled, and single-walled—surrounding the central honeycomb to balance low-frequency shift and broadband coverage. Figure 1 As shown.

[0036] Furthermore, the depth of the V-shaped slits inside the P-shaped cavity is greater than the diameter of the micropore, and their entrances both face the direction of sound wave incidence. The V-shaped slits further impede the sound wave after it enters the micropore. This invention fully utilizes this cavity and further introduces a flexible coating, such as... Figure 3 As shown. Specifically, the contact distance between the micropore and the sidewall is less than wavelength λ / 10, forcing the sound wave to adhere to the wall and flow, thus generating additional sound energy dissipation. Although the sound wave can diffuse along the cavity wall without free attenuation during propagation, it will generate intense viscous friction with the wall surface, dissipating a large amount of sound energy. This achieves the design goal of simultaneously increasing low-frequency sound absorption performance by a factor of two through a series impedance mode (micropore + slit + cavity) with limited material thickness. Specifically, the total impedance theory is extended to Equation 2:

[0037] Z tot =Z h +Z slit +Z cav +R exp (2)

[0038] Z h For the micropore impedance, Z slit Z is the slit impedance. cav For cavity capacitance, R exp The introduction of the P-type cavity significantly increases the total acoustic impedance Re(z) because the close-fitting design of the narrow cavity enhances the effect of the viscous boundary layer thickness, resulting in a viscous acoustic impedance much higher than that of a conventional cavity. This improves impedance matching at low frequencies and achieves more efficient energy dissipation.

[0039] The wall-attached dissipation is similar to that of the cellular resonance dissipation and is also directly related to the slit length L of the P-type cavity. Therefore, the design of the P-type cavity in this invention improves low-frequency offset and increases slit impedance Z.slit While increasing wall-attached dissipation, this also has a reaction effect on the cavity resonance itself, increasing the amount of resonance dissipation. On the other hand, it also indicates that the slit width of the P-type cavity should not be too small while satisfying the condition of being equal to a certain value, thus ensuring the lightweight of the structure.

[0040] Furthermore, the overall sound absorption performance of the sound-absorbing material is directly related to the thickness of the boundary layer and the slit parameters of the micropores. In the actual design process, according to the noise spectrum requirements of high-speed trains, the acoustic impedance can be easily controlled by controlling the micropore diameter, slit length, or coating thickness, thereby further controlling the overall sound absorption performance of the entire sound-absorbing metamaterial. This makes it very important to achieve the design goal of low-frequency adjustable and controllable sound-absorbing material.

[0041] This P-shaped cavity surround-type honeycomb slit-cavity blocking low-frequency sound-absorbing metamaterial ingeniously combines the dissipation enhancement effect of micropores and cavity walls with the honeycomb resonance principle. Based on the traditional micro-perforated plate theory, it expands the series slit impedance, achieving composite sound absorption with a higher and more stable low-frequency sound absorption coefficient while having almost no adverse impact on the processing technology, material cost, installation space, or lightweighting of traditional sound-absorbing materials. The invention has a simple structure, is easy to install, and is inexpensive, and can be installed on the inner wall of high-speed train carriages for noise control. Furthermore, this P-shaped cavity surround-type honeycomb slit-cavity blocking low-frequency sound-absorbing metamaterial can also be applied to areas requiring improved low-frequency sound absorption, such as aircraft cabins, automotive interiors, and building sound insulation. It is also suitable for noise reduction in industrial equipment, acoustic laboratories, and other applications with high sound absorption requirements, demonstrating its broad engineering application value.

Claims

1. A P-type cavity-blocking low-frequency sound-absorbing metamaterial, characterized in that, It includes a central honeycomb unit with a hexagonal honeycomb structure, and three P-type sound-absorbing units that are connected end to end around the central honeycomb unit. The central honeycomb unit and the three P-type sound-absorbing units form a triangular assembly, which serves as the basic structure of the sound-absorbing metamaterial. The P-type sound-absorbing unit includes a P-type cavity formed by a top plate, a back plate, and side walls. The P-type cavity includes an open cavity and a narrow cavity. Both the P-type sound-absorbing unit and the central honeycomb unit are made of rigid materials. The walls of the P-type chamber are coated with a flexible coating, and the interior of the central honeycomb unit is filled with porous sound-absorbing material. The cross-section of the narrow cavity of the P-type chamber from the top plate to the back plate is V-shaped, forming a V-shaped slit; The top plate of the P-type sound-absorbing unit has micropores, which are distributed in the open cavity or the narrow cavity, and are at least in close contact with one side wall of the P-type cavity.

2. The P-type cavity-blocking low-frequency sound-absorbing metamaterial according to claim 1, characterized in that, The depth of the V-shaped slit is greater than the diameter of the micropore.

3. The P-type cavity-blocking low-frequency sound-absorbing metamaterial according to claim 1, characterized in that, The distance between the micropore and the sidewall of the P-shaped chamber is less than wavelength λ / 10.

4. The P-type cavity-blocking low-frequency sound-absorbing metamaterial according to claim 1, characterized in that, The three P-type sound-absorbing units are respectively a three-chamber wall tightly attached P-type sound-absorbing unit, a double-chamber wall tightly attached P-type sound-absorbing unit, and a single-chamber wall tightly attached P-type sound-absorbing unit; The micropores of the three-chamber wall are closely attached to the end of the narrow cavity, and are close to the three side walls of the end of the narrow cavity. The micropores of the double-cavity wall closely adhering to the P-type sound-absorbing unit are opened in the middle of the narrow cavity, closely adhering to the two side walls of the middle of the narrow cavity; The micropores of the single-cavity wall, which are closely attached to the P-type sound-absorbing unit, are opened in the open cavity and are closely attached to one side wall of the open cavity.

5. The P-type cavity-blocking low-frequency sound-absorbing metamaterial according to claim 4, characterized in that, The micropores in the three-chamber wall that are tightly attached to the P-type sound-absorbing unit have a diameter of 0.5-2mm; the opening angle of the upper part of the V-shaped slit in the three-chamber wall that is tightly attached to the P-type sound-absorbing unit is 30-60°, and the depth of the V-shaped slit is 0.5-0.8 times the height of the P-type chamber; the axis of the micropore is located on the center line of the V-shaped slit.

6. The P-type cavity-blocking low-frequency sound-absorbing metamaterial according to claim 4, characterized in that, The micropores of the double-cavity wall tightly attached to the P-type sound-absorbing unit have a diameter of 0.5-2mm; the upper opening angle of the V-shaped slit of the double-cavity wall tightly attached to the P-type sound-absorbing unit is 45-75°, and the depth of the V-shaped slit is 0.6-0.9 times the height of the P-type cavity; the axis of the micropore is located on the center line of the V-shaped slit.

7. The P-type cavity-blocking low-frequency sound-absorbing metamaterial according to claim 4, characterized in that, The micropores in the single-cavity wall that are tightly attached to the P-type sound-absorbing unit have a diameter of 1-3 mm.

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