CN109192190B - Thin-layer metamaterial sound absorption structure - Google Patents
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- CN109192190B CN109192190B CN201811091121.6A CN201811091121A CN109192190B CN 109192190 B CN109192190 B CN 109192190B CN 201811091121 A CN201811091121 A CN 201811091121A CN 109192190 B CN109192190 B CN 109192190B
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- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
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Abstract
A thin-layer metamaterial sound absorption structure is characterized in that the thin-layer metamaterial sound absorption structure is formed by a plurality of sound absorption structure units which are arranged in parallel and periodically, and the units are bonded or welded together through glue; the sound absorption structure unit consists of a rectangular box, an L-shaped plate, a first medium, a second medium, a third medium, a fourth medium and a cover plate; the L-shaped plate, the first medium, the second medium, the third medium and the fourth medium are positioned in the rectangular box, and the cover plate is bonded on the rectangular box; the rectangular box, the L-shaped plate and the cover plate are made of the same material; the 4 dielectric materials are the same and are rectangular; the L-shaped plate is formed by vertically connecting a first side surface and a second side surface into an L shape, the second side surface of the L-shaped plate is vertically erected on the lower bottom surface of the rectangular box, and the first side surface is parallel to the lower bottom surface of the rectangular box. Compared with polyurethane foam or fiber with the same length, width and thickness, the polyurethane foam or fiber provided by the invention can absorb middle and low frequency noise more efficiently, and has a larger average sound absorption coefficient.
Description
Technical Field
The invention relates to the field of vibration and noise control, in particular to a thin-layer metamaterial sound absorption structure.
Background
Along with the development of equipment in the fields of aerospace, naval vessels, railway transportation, vehicle engineering and the like to operation environments such as high speed, large scale, heavy load and the like, the problem of noise caused by the equipment is increasingly prominent. The low noise quality of these equipment compartments is an important goal of modern equipment development, which is critical to the overall quality of the equipment, the comfort and health of the occupants. The sound absorption material is laid in the cabin, which is one of the important technical approaches for solving the high noise of the cabin.
At present, the traditional porous materials mainly comprise various foams and fibers, and are characterized in that a large number of mutually communicated micropores which are opened outwards are formed inside the materials, namely the materials have certain air permeability. The sound absorption coefficient of the porous material in a high-frequency area is larger, if the low-frequency sound absorption performance is required to be increased, the thickness needs to be increased, and the maximum absorption frequency is shifted to a low frequency by about one octave every time the thickness is increased by 1 time. The material height should be greater than 1/4 optimum for the operating wavelength, which results in a larger height for low frequency noise, which is detrimental to practical space utilization. For example, cabin noise of transport vehicles such as high-speed rails, ships, airplanes and the like is mainly low-frequency broadband noise below 3000Hz, and the required sound absorption material is as less than 30mm as possible. The thickness of the sound absorption material laid in the cabin by the existing transport tools such as high-speed rails, ships, airplanes and the like is usually more than 50mm, and if the sound absorption material with smaller thickness can be laid to absorb the noise in the cabin more efficiently, the utilization rate of the space in the cabin can be increased, and a spacious and comfortable environment is provided for passengers. Therefore, designing a thin-layer metamaterial sound absorption structure capable of meeting the low-frequency noise reduction requirement is one of the problems of great concern to the skilled person.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a thin-layer metamaterial sound absorption structure, which can absorb low-frequency broadband noise, has small overall thickness and can meet the requirement of a small-thickness structure on low-frequency noise absorption.
The thin-layer metamaterial sound absorption structure is formed by arranging m multiplied by n sound absorption structure units in parallel and periodically, and all the units can be bonded by glue or welded. m is greater than or equal to 1, and n is greater than or equal to 1. The sound absorption structure unit consists of a rectangular box, an L-shaped plate, a first medium, a second medium, a third medium, a fourth medium and a cover plate. The L-shaped plate, the first medium, the second medium, the third medium and the fourth medium are all located in the rectangular box, and the cover plate is bonded on the first side face of the rectangular box. The rectangular box, the L-shaped plate and the cover plate are made of the same material; the first medium, the second medium, the third medium and the fourth medium are made of the same material.
The rectangular box material can be alloy steel, cast iron, aluminum, carbon steel and other metals, and the selected materials meet the requirements that the elastic modulus E is within the range of 70GPa to 220GPa, the Poisson ratio η is within the range of 0.2 to η to 0.4, and the density rho meets 2500kg/m3≤ρ≤8500kg/m3. The rectangular box has a length of a1, a width of d1, a height of h1, a wall thickness of delta, a1, d1,h1 and delta respectively satisfy a1 is more than or equal to 10mm and less than or equal to 100mm, d1 is more than or equal to 10mm and less than or equal to 100mm, h1 is more than or equal to 20mm and less than or equal to 30mm, and delta is more than or equal to 0.5mm and less than or equal to 2 mm. The second to fourth sides of the rectangular box are closed and the first side is completely open. The rectangular box has an opening on the upper bottom surface, the opening has the length of a3 and the width of d3, and a3 satisfies the condition
d3 satisfies d3 ═ d1- δ.
The first profile and the second profile are vertically connected to form an L shape, the thickness of the first profile and the second profile is d2, or a flat plate with the thickness of d2 is bent into the L shape, and d2 satisfies that d2 is more than or equal to 0.5 and less than or equal to 2 mm. The first profile length of the L-shaped plate is a2, the second profile length is h2, a2 satisfies d2< a2< a1-2 delta-a 3, and h2 satisfies d2< h2< h1-2 delta. The width of the first profile and the second profile of the L-shaped plate is equal to the width of the opening of the upper bottom surface of the rectangular box, which is d 3. The second profile of the L-shaped plate is vertically erected on the lower bottom surface of the rectangular box, the first profile of the L-shaped plate is parallel to the lower bottom surface of the rectangular box and is h2-d2 away from the lower bottom surface of the rectangular box, the distance from the first profile of the L-shaped plate to the inner wall surface of the upper bottom surface of the rectangular box is h4, and h4 meets the condition that h4 is h1-h2-2 delta. The distance from the second profile of the L-shaped panel to the inner wall surface of the second side of the rectangular box is a3, which is equal to the length of the opening in the top bottom surface 111 of the rectangular box.
The first medium material can be selected from polyurethane foam, glass wool, fibers and the like, and the physical parameters of the selected materials meet the following requirements: flow resistivity sigma range 2000N s/m4≤σ≤25000N·s/m4Porosity of
Range of
The tortuosity tau is within a range of 1.02-1.45, the viscosity characteristic length Lambda is within a range of 50 um-300 um, and the thermal characteristic length Lambda is within a range of 80 um-700 um. The first medium is rectangular in shape, has a length and width equal to those of the opening on the upper bottom surface of the rectangular box, respectively, and has a length equal to a3 and a width equal to d 3. First mediumH3, h3 satisfies h3 ═ h1- δ. The first medium is put into the rectangular box from the opening of the upper bottom surface of the rectangular box along the inner wall surface of the second side surface of the rectangular box.
The second medium is rectangular in shape. The length of the second media is equal to the length of the first profile of the L-shaped plate, equal to a 2. The width of the second medium is equal to the width of the first medium, equal to d 3. The height of the second medium is equal to h 4. The second medium is placed into the rectangular box from the first side surface of the rectangular box along the inner wall surface of the upper bottom surface of the rectangular box and the first molded surface of the L-shaped plate 2.
The third medium is rectangular in shape. The third medium has a length of a4, and a4 satisfies a4 ═ a1-a2-a3-2 δ. The width of the third medium is equal to the width of both the first and second media, and is equal to d 3. The third medium height is h5, and h5 satisfies h5 ═ h1-2 δ. The third medium is put into the rectangular box from the first side surface of the rectangular box along the inner wall surface of the upper bottom surface of the rectangular box.
The fourth medium is rectangular in shape. The third medium has a length of a5, and a5 satisfies a5 ═ a2-d 2. The width of the fourth medium is equal to the width of the first, second and third media, and is equal to d 3. The third medium height is h6, and h6 satisfies h6 ═ h2-d 2. The fourth medium is put into the rectangular box from the first side surface of the rectangular box along the inner wall surface of the first molded surface of the L-shaped plate.
The cover plate is rectangular in shape. The length and height of the cover plate are respectively equal to those of the rectangular box, and the length of the cover plate is a1, and the height of the cover plate is h 1. The width of the cover plate is b4, and b4 satisfies that b4 is more than or equal to 0.5mm and less than or equal to 2 mm. The cover plate is tightly attached to the first side face of the rectangular box in a glue bonding or welding mode.
Compared with the prior art, the invention can achieve the following technical effects:
compared with polyurethane foam or fiber with the same length, width and thickness, the thin-layer metamaterial sound absorption structure can absorb middle and low frequency noise more efficiently, and has a larger average sound absorption coefficient. Polyurethane foams or fibers of equal length and width, to achieve the same average sound absorption coefficient as the present invention, require a greater thickness than the thin layer metamaterial sound absorbing structure of the present invention.
Drawings
The invention is described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic view of a thin-layer metamaterial sound absorbing structure according to the present invention;
fig. 2 is a schematic view of a sound-absorbing structural unit 1 according to the present invention, wherein fig. 2(a) is a schematic view of the sound-absorbing structural unit 1 with a cover plate 17 attached thereto, and fig. 2(b) is a schematic view of the internal structure of the sound-absorbing structural unit 1 with the cover plate 17 removed;
FIG. 3 is a schematic view of a rectangular box 11 according to the present invention;
FIG. 4 is a schematic structural view of an L-shaped plate 12 of the present invention;
FIG. 5 is a bar graph comparing the average sound absorption coefficients of the rectangular polyurethane foam with a thickness of 20mm and the rectangular polyurethane foam with a thickness of 34.6mm in the frequency range of 0 to 3000Hz in example 1 of the present invention. The rectangular polyurethane foams of 20mm thickness and 34.6mm thickness were each equal in length and width to those of inventive example 1.
FIG. 6 is a histogram comparing the average sound absorption coefficient of rectangular fibers 23mm thick and rectangular fibers 41.2mm thick at 0-3000 Hz in the example 2 of the present invention. The length and width of the rectangular fibers 23mm thick and 41.2mm thick were equal to those of example 2 of the present invention.
FIG. 7 is a histogram comparing the average sound absorption coefficient of the frequency ranges of 0 to 3000Hz in examples 3, 4 and 5 of the present invention.
FIG. 8 is a histogram comparing the average sound absorption coefficient of 25mm, 27mm and 30mm thick fibers at 0-3000 Hz. The length, width and height of rectangular fibers 25mm, 27mm and 30mm thick were equal to those of examples 3, 4 and 5 of the present invention, respectively.
Detailed Description
In order to make the present invention clearer, the following description will be made with reference to the accompanying drawings.
FIG. 1 is a schematic view of a thin-layer metamaterial sound absorbing structure according to the present invention. The thin-layer metamaterial sound absorption structure is formed by arranging m multiplied by n sound absorption structure units 1 in a parallel periodic mode, and all the units can be bonded through glue or welded. m is greater than or equal to 1, and n is greater than or equal to 1. The sound absorption structure unit 1 is composed of a rectangular box 11, an L-shaped plate 12, a first medium 13, a second medium 14, a third medium 15, a fourth medium 16 and a cover plate 17. The L-shaped plate 12, the first medium 13, the second medium 14, the third medium 15, and the fourth medium 16 are all located within the rectangular box 11, and the cover plate 17 is adhered to the first side 112 of the rectangular box 11.
Fig. 2 is a schematic view of a sound-absorbing structural unit 1 according to the present invention, wherein fig. 2(a) is a schematic view of the sound-absorbing structural unit 1 with a cover plate 17 attached thereto, and fig. 2(b) is a schematic view of the internal structure of the sound-absorbing structural unit 1 with the cover plate 17 removed; FIG. 3 is a schematic view of a rectangular box 11 according to the present invention;
as shown in FIG. 2(a) and FIG. 2(b) in combination with FIG. 3, the rectangular box 11 has a length of a1, a width of d1, a height of h1, and a wall thickness of δ, and a1, d1, h1 and δ respectively satisfy the conditions of 10mm ≦ a1 ≦ 100mm, 10mm ≦ d1 ≦ 100mm, 20mm ≦ h1 ≦ 30mm, and 0.5mm ≦ δ ≦ 2 mm. The second to fourth sides of the rectangular box 11 are closed and the first side 112 is completely open. Rectangular box 11 has an upper bottom 111 open with a length of a3 and a width of d3, a3
d3 satisfies d3 ═ d1- δ.
As shown in FIG. 4, the L-shaped plate 12 is formed by vertically connecting a first profile 121 and a second profile 122 into an L shape, the thickness of the first profile 121 and the second profile 122 is d2, or a flat plate with the thickness of d2 can be bent into an L shape, and d2 satisfies the condition that d2 is more than or equal to 0.5 and less than or equal to 2 mm. The length of the first molded surface 121 of the L-shaped plate 12 is a2, the length of the second molded surface 122 is h2, a2 satisfies d2< a2< a1-2 delta-a 3, and h2 satisfies d2< h2< h1-2 delta. The first profile 121 and the second profile 122 of the L-shaped plate 12 each have a width equal to the width of the opening of the upper bottom 111 of the rectangular box 11, which is d 3. The second profile 122 of the L-shaped plate 12 stands vertically on the lower bottom surface of the rectangular box 11, the first profile 121 of the L-shaped plate 12 is parallel to the lower bottom surface of the rectangular box 11 and is at a distance h2-d2 from the lower bottom surface of the rectangular box 11, and the distance from the first profile 121 of the L-shaped plate 12 to the inner wall surface of the upper bottom surface 111 of the rectangular box 11 is h4, and h4 satisfies h 4-h 1-h2-2 δ. The distance from the second profile 122 of the L-shaped plate 12 to the inner wall surface of the second side 113 of the rectangular box 11 is a3, which is equal to the length of the opening in the upper bottom 111 of the rectangular box 11.
As shown in fig. 2(a) and 2(b), the first medium 13 has a rectangular shape, the length and width of the first medium 13 are equal to those of the opening on the upper bottom surface 111 of the rectangular box 11, respectively, the length of the first medium 13 is equal to a3, and the width of the first medium 13 is equal to d 3. The height of the first medium 13 is h3, and h3 satisfies h 3-h 1- δ. The first medium 13 is put into the rectangular box 11 from the opening of the upper bottom surface 111 of the rectangular box 11 along the inner wall surface of the second side surface 113 of the rectangular box 11.
The second medium 14 is rectangular in shape. The length of the second media 14 is equal to the length of the first profile 121 of the L-shaped plate 12, equal to a 2. The width of the second medium 14 is equal to the width of the first medium 13, equal to d 3. The height of the second medium 14 is equal to h 4. The second medium 14 is placed into the rectangular box from the first side 112 of the rectangular box 11 along the inner wall surface of the upper bottom surface 111 of the rectangular box and the first profile 121 of the L-shaped plate 12.
The third medium 15 is rectangular in shape. The length of the third medium 15 is a4, and a4 satisfies a4 ═ a1-a2-a3-2 δ. The width of the third medium 15 is equal to the width of both the first medium 13 and the second medium 14, and is equal to d 3. The height of the third medium 15 is h5, and h5 satisfies h5 ═ h1-2 δ. The third medium 15 is put into the rectangular box 11 from the first side surface 112 of the rectangular box 11 along the inner wall surface of the upper bottom surface 111 of the rectangular box 11.
The fourth medium 16 is rectangular in shape. The third medium 16 has a length of a5, and a5 satisfies a 5-a 2-d 2. The width of the fourth medium 16 is equal to the width of the first medium 13, the second medium 14, the third medium 15, and is equal to d 3. The third medium 15 has a height h6, and h6 satisfies h6 ═ h2-d 2. The fourth medium 16 is inserted into the rectangular box 11 from the first side 112 of the rectangular box along the inner wall surface of the first profile 121 of the L-shaped plate.
The cover 17 is rectangular in shape. The length and height of the cover 17 are equal to those of the rectangular box 11, respectively, and the cover 17 has a length a1 and a height h 1. The width of the cover plate 17 is b4, and b4 satisfies that b4 is more than or equal to 0.5mm and less than or equal to 2 mm. The cover 17 is adhered or welded to the first side 112 of the rectangular box 11.
Example 1: rectangular box 11, L-shaped plate 12 and cover of sound absorption structure unit 1The plates 17 are made of aluminium sheet and have a material parameter of 2700kg/m3Young's modulus 70GPa and Poisson's ratio 0.33. The rectangular box 11 of the sound-absorbing construction unit 1 has a length a1 of 50mm, a width d1 of 50mm, a height h1 of 20mm and a wall thickness δ of 1 mm. The opening of the first bottom 111 of the rectangular box 11 has a length a 3mm and a width d 3mm 49 mm. The L-shaped plate 12 has a wall thickness d2 of 1mm and a width d3 of 49 mm. The L-shaped plate 12 has a first profile 121 with a length a2 of 19.5mm and a second profile 122 with a length h2 of 9.5 mm. The cover 17 has a length a1 of 50mm, a width d4 of 1mm, and a height h1 of 20 mm. The materials of the first medium 13 to the fourth medium 16 are all polyurethane foam, and the physical parameter is the flow resistivity of 4200 N.s/m4Porosity 0.98, tortuosity 1.03, viscous characteristic length 120um, thermal characteristic length 240 um. The first medium 13 to the fourth medium 16 are each 49m wide as d 3. The first medium 13 has a length a 3-20 mm and a height h 3-19 mm. The second medium 14 has a length a 2-19.5 mm and a height h 4-8.5 mm. The third medium 15 has a length a 4-8.5 mm and a height h 5-18 mm. The fourth medium 16 has a length a 5-18.5 mm and a height h 6-8.5 mm. Example 1 uses a4 × 5 periodic arrangement, i.e., m is 4 and n is 5.
Example 2: the rectangular box 11, the L-shaped plate 12 and the cover plate 17 of the sound absorption structure unit 1 are made of nodular cast iron, and the material parameter is 7300kg/m3Young's modulus 170GPa and Poisson's ratio of 0.3. The rectangular box 11 of the sound-absorbing construction unit 1 has a length a1 of 50mm, a width d1 of 30mm, a height h1 of 23mm and a wall thickness δ of 1 mm. The opening of the first bottom 111 of the rectangular box 11 has a length a 3mm and a width d 3mm 29 mm. The L-shaped plate 12 has a wall thickness d2 of 1mm and a width d3 of 29 mm. The first profile 121 a2 and the second profile 122 h2 of the L-shaped plate 12 are 18mm and 11mm, respectively. The cover 17 has a length a1 of 50mm, a width d4 of 1mm, and a height h1 of 23 mm. The first medium 13 to the fourth medium 16 are made of fibers, and the physical parameter is the flow resistivity of 3600 N.s/m4Porosity 0.97, tortuosity 1.07, viscous characteristic length 273um, thermal characteristic length 672 um. The width of the first medium 13 to the fourth medium 16 is 29 mm. The first medium 13 has a length a 3-20 mm and a height h 3-22 mm. The second medium 14 has a length a 2-18 mm and a height h 4-10 mm. The third medium 15 has a length a 4-10 mm and a height h 5-21 mm. The length a5 of the fourth medium 16 is 17mm and the height h6 is 10 mm. Example 2 uses a3 × 3 periodic arrangement, i.e., m is 3 and n is 3.
Example 3: rectangular box of sound absorption structure unit 111. The materials of the L-shaped plate 12 and the cover plate 17 are alloy steel, and the material parameter is density 7100kg/m3Young's modulus 206GPa and Poisson's ratio 0.27. Rectangular box 11 has a length a1 of 50mm, a width d1 of 40mm, a height h1 of 25mm, and a wall thickness δ of 1 mm. The opening of the first bottom 111 of the rectangular box 11 has a length a 3mm and a width d 3mm 39 mm. The L-shaped plate 12 has a wall thickness d2 of 1mm and a width d3 of 39 mm. The first profile 121 a2 and the second profile 122 h2 of the L-shaped plate 12 are 17mm and 12mm, respectively. The cover 17 has a length a1 of 50mm, a width d4 of 1mm, and a height h1 of 25 mm. The first medium 13 to the fourth medium 16 are made of the same material as in embodiment 2. The first medium 13 to the fourth medium 16 are the same in width, and d3 is 39 mm. The first medium 13 has a length a 3-20 mm and a height h 3-24 mm. The second medium 14 has a length a 2-17 mm and a height h 4-11 mm. The third medium 15 has a length a 4-11 mm and a height h 5-22 mm. The fourth medium 16 has a length a 5-16 mm and a height h 6-11 mm. Example 3 uses a 6 × 5 periodic arrangement, i.e., m is 6 and n is 5.
Example 4: the rectangular box 11, the L-shaped plate 12 and the cover plate 17 of the sound absorption structure unit 1 are made of white cast iron, and the material parameter is 7500kg/m3Young's modulus 133GPa, Poisson's ratio 0.25. Rectangular box 11 has a length a1 of 50mm, a width d1 of 50mm, a height h1 of 27mm and a wall thickness δ of 1 mm. The opening of the first bottom 111 of the rectangular box 11 has a length a 3mm and a width d 3mm 49 mm. The L-shaped plate 12 has a wall thickness d2 of 1mm and a width d3 of 49 mm. The L-shaped plate 12 has a first profile 121 a2 of 16mm and a second profile 122 h2 of 13 mm. The cover 17 has a length a1 of 50mm, a width d4 of 1mm, and a height h1 of 27 mm. The first medium 13 to the fourth medium 16 are the same material as in embodiment 3. The first medium 13 to the fourth medium 16 are the same in width, and d3 is 49 mm. The first medium 13 has a length a 3-20 mm and a height h 3-26 mm. The second medium 14 has a length a 2-16 mm and a height h 4-12 mm. The third medium 15 has a length a 4-25 mm and a height h 5-12 mm. The length a5 of the fourth medium 16 is 15mm, and the height h6 is 12 mm. Example 4 employs a4 × 4 periodic arrangement, i.e., m-n-4.
Example 5: the rectangular box 11, the L-shaped plate 12 and the cover plate 17 of the sound absorption structure unit 1 are made of carbon steel, and the material parameter is 6500kg/m3Young's modulus 200GPa and Poisson's ratio 0.27. Rectangular box 11 has a length a1 of 50mm, a width d1 of 45mm, a height h1 of 30mm and a wall thickness δ of 1 mm. The opening on the first bottom 111 of the rectangular box 11 has a length a 3-20 mm and a width d 3-44 mmmm. The L-shaped plate 12 has a wall thickness d2 of 1mm and a width d3 of 44 mm. The L-shaped plate 12 has a first profile 121 with a length a2 of 14.5mm and a second profile 122 with a length h2 of 14.5 mm. The cover 17 has a length a1 of 50mm, a width d4 of 1mm, and a height h1 of 30 mm. The first medium 13 to the fourth medium 16 are the same material as in embodiment 3. The first medium 13 to the fourth medium 16 are the same in width, and d3 is 44 mm. The first medium 13 has a length a 3-20 mm and a height h 3-29 mm. The second medium 14 has a length a 2-14.5 mm and a height h 4-13.5 mm. The third medium 15 has a length a 4-13.5 mm and a height h 5-28 mm. The length a5 of the fourth medium 16 is 13.5mm, and the height h6 is 13.5 mm. Example 5 employs a2 × 3 periodic arrangement, i.e., m is 2 and n is 3.
On the basis of meeting the conditions, a pressure acoustic module in finite element software COMSOL is used for simulating, the obtained sound absorption coefficient is led into software MATLAB, and the average sound absorption coefficient is calculated.
FIG. 5 is a bar chart showing the average sound absorption coefficient in the 0 to 3000Hz band of the polyurethane foam of example 1, which is equal to example 1 in length, width and height (i.e., height h1 is 20mm), and the polyurethane foam of example 1 in length, width and thickness of 34.6 mm. It can be seen that the average sound absorption coefficient of the polyurethane foam of example 1 of the present invention in the frequency band of 0 to 3000Hz reaches 0.5931, while the average sound absorption coefficient of the polyurethane foam of the same length, width, height and thickness of 20mm in example 1 in the frequency band of 0 to 3000Hz is only 0.3185. Meanwhile, if the average sound absorption coefficient in the frequency band of 0-3000 Hz reaches 0.59, the required polyurethane foam needs to be 34.6mm thick.
FIG. 6 is a bar chart comparing the average sound absorption coefficient of the fibers of example 2, which have the same length, width and height of 23mm (i.e. height h1 is 23mm) as those of example 2, and the fibers of 41.2mm, which have the same length, width and thickness as those of example 2, in the frequency range of 0-3000 Hz. It can be seen that the average sound absorption coefficient of the fiber of example 2 of the present invention in the frequency band of 0 to 3000Hz reaches 0.6697, while the average sound absorption coefficient of the fiber of the same length, width and height as those of example 2 in the thickness of 23mm in the frequency band of 0 to 3000Hz is only 0.3860. Meanwhile, if the average sound absorption coefficient of the fiber reaches 0.6697 in the frequency band of 0-3000 Hz, the fiber needs to be 41.2mm thick.
Figure 7 shows a bar chart comparing the average sound absorption coefficient of example 3, example 4 and example 5. It can be seen that the average sound absorption coefficients of the embodiments 3, 4 and 5 of the invention in the frequency band of 0 to 3000Hz are respectively 0.7, 0.725 and 0.736, which are all greater than 0.7. Along with the increase of the thickness of the embodiment, the average sound absorption coefficient is gradually increased in the frequency range of 0-3000 Hz. And the material of the cover plate and the rectangular box, the width of the sound-absorbing structural unit 1, and the arrangement of the material have almost no influence on the average sound absorption coefficient.
In order to further highlight the advantages of the present invention, fig. 8 shows a bar chart of the sound absorption coefficient of the fiber with the same length, width and height as those of the fiber of example 3, example 4 and example 5 in the frequency band of 0 to 3000 Hz. It can be seen that when the material thickness (i.e., height h1) is 25mm, 27mm and 30mm, respectively, the average sound absorption coefficient reaches 0.429, 0.47 and 0.526, respectively, which are all less than 0.55, and which are less than the average sound absorption coefficient of the inventive example at the same height, length, width and height. This is because, compared with polyurethane foam or fiber with the same length, width and thickness, the thin-layer metamaterial sound absorption structure of the present invention can absorb middle and low frequency noise more efficiently and has a larger average sound absorption coefficient under the same thickness condition. The reason is that due to the existence of the L-shaped plate 12 in the rectangular box 11, the sound wave propagation route is curled, the propagation distance of the sound wave in the rectangular box 11 is increased, and the equivalent sound velocity of the sound wave in the structure is reduced, so that better sound absorption performance can be obtained at low frequency under the condition of the same overall thickness. Polyurethane foams or fibers of equal length and width, to achieve the same average sound absorption coefficient as the present invention, require a greater thickness than the thin layer metamaterial sound absorbing structure of the present invention.
Claims (9)
1. A thin-layer metamaterial sound absorption structure is characterized in that the thin-layer metamaterial sound absorption structure is formed by arranging m multiplied by n sound absorption structure units (1) in parallel and periodically; m is greater than or equal to 1, n is greater than or equal to 1; the sound absorption structure unit (1) consists of a rectangular box (11), an L-shaped plate (12), a first medium (13), a second medium (14), a third medium (15), a fourth medium (16) and a cover plate (17); the L-shaped plate (12), the first medium (13), the second medium (14), the third medium (15) and the fourth medium (16) are all positioned in the rectangular box (11), and the cover plate (17) is adhered to the first side surface (112) of the rectangular box (11); the rectangular box (11), the L-shaped plate (12) and the cover plate (17) are made of the same material; the first medium (13), the second medium (14), the third medium (15) and the fourth medium (16) are made of the same material;
the rectangular box (11) is made of a material with the elastic modulus E ranging from 70GPa to less than or equal to E220 GPa, the Poisson ratio η ranging from 0.2 to η to less than or equal to 0.4, and the density rho of 2500kg/m3≤ρ≤8500kg/m3(ii) a The rectangular box (11) has the length of a1, the width of d1, the height of h1 and the wall thickness of delta, and the a1, the d1 and the h1 respectively meet the conditions that the a1 is more than or equal to 10mm and less than or equal to 100mm, the d1 is more than or equal to 10mm and less than or equal to 100mm, and the h1 is more than or equal to 20mm and less than or equal to 30 mm; the second to fourth sides of the rectangular box (11) are closed, and the first side (112) is completely open; the upper bottom surface (111) of the rectangular box (11) is open, the length of the opening is a3, the width of the opening is d3,
d3＝d1-δ；
the L-shaped plate (12) is formed by vertically connecting a first profile (121) and a second profile (122) into an L shape, and the thickness of the first profile (121) and the second profile (122) is d 2; the length of the first molded surface (121) of the L-shaped plate (12) is a2, the length of the second molded surface (122) is h2, a2 meets d2< a2< a1-2 delta-a 3, and h2 meets d2< h2< h1-2 delta; the widths of the first profile (121) and the second profile (122) of the L-shaped plate (12) are both equal to d3, the second profile (122) of the L-shaped plate (12) is vertically arranged on the lower bottom surface of the rectangular box (11), the first profile (121) of the L-shaped plate (12) is parallel to the lower bottom surface of the rectangular box (11) and is separated from the lower bottom surface of the rectangular box (11) by h2-d2, the distance from the first profile (121) of the L-shaped plate (12) to the inner wall surface of the upper bottom surface (111) of the rectangular box (11) is h4, and h4 satisfies h 4-h 1-h2-2 delta; the distance from the second molded surface (122) of the L-shaped plate (12) to the inner wall surface of the second side surface (113) of the rectangular box (11) is a3 and is equal to the length of the opening on the upper bottom surface (111) of the rectangular box (11);
the physical parameter range of the first medium (13) material satisfies: flow resistivity sigma range 2000N s/m4≤σ≤25000N·s/m4The porosity theta is more than or equal to 0.9 and less than or equal to 0.98, the tortuosity tau is more than or equal to 1.02 and less than or equal to 1.45, the viscous characteristic length Lambda is more than or equal to 50um and less than or equal to 300um, and the thermal characteristic length psi is more than or equal to 80um and less than or equal to 700 um; the first medium (13) is rectangular, the length and width of the first medium (13) are respectively equal to the length and width of the opening on the upper bottom surface (111) of the rectangular box (11), and the length of the first medium (13)Degree equal to a3, width of the first medium (13) equal to d 3; the height of the first medium (13) is h3, h3 satisfies h3 ═ h1- δ; the first medium (13) is put into the rectangular box (11) from the opening of the upper bottom surface (111) of the rectangular box (11) along the inner wall surface of the second side surface (113) of the rectangular box (11);
the second medium (14) is rectangular in shape, the length of the second medium (14) is equal to the length of the first profile (121) of the L-shaped plate (12), equal to a 2; the width of the second medium (14) is equal to the width of the first medium (13), equal to d 3; the height of the second medium (14) is equal to h 4; the second medium (14) is placed into the rectangular box from the first side surface (112) of the rectangular box (11) along the inner wall surface of the upper bottom surface (111) of the rectangular box and the first molded surface (121) of the L-shaped plate (12);
the third medium (15) is rectangular in shape; the length of the third medium (15) is a4, and a4 satisfies a4 ═ a1-a2-a3-2 δ; the width of the third medium (15) is equal to d 3; the height of the third medium (15) is h5, and h5 satisfies h 5-h 1-2 delta; the third medium (15) is put into the rectangular box (11) from the first side surface (112) of the rectangular box (11) along the inner wall surface of the upper bottom surface (111) of the rectangular box (11);
the shape of the fourth medium (16) is rectangular; the third medium 16 has a length of a5, a5 satisfies a5 ═ a2-d 2; the width of the fourth medium (16) is equal to the width of the first medium (13), the second medium (14) and the third medium (15) and is equal to d 3; the height of the third medium (15) is h6, and h6 satisfies h 6-h 2-d 2; a fourth medium (16) is put into the rectangular box (11) from the first side surface (112) of the rectangular box along the inner wall surface of the first molded surface (121) of the L-shaped plate;
the cover plate (17) is rectangular; the length and the height of the cover plate (17) are respectively equal to those of the rectangular box (11), and the length and the height of the cover plate (17) are a1 and h 1; the width of the cover plate (17) is b4, and b4 satisfies that b4 is more than or equal to 0.5mm and less than or equal to 2 mm; the cover plate (17) is closely attached to the first side surface (112) of the rectangular box (11).
2. A sound-absorbing structure in thin-layer metamaterial as claimed in claim 1, characterized in that the rectangular box (11) is made of any one of alloy steel, cast iron, aluminum, carbon steel.
3. A sound-absorbing structure in thin-layer metamaterial as claimed in claim 1, characterized in that the L-shaped panel (12) is bent in an L-shape from a flat plate.
4. A thin layer metamaterial sound absorbing structure as in claim 1 wherein the first medium (13), second medium (14), third medium (15) and fourth medium (16) are made of any one of polyurethane foam, glass wool, fiber.
5. A thin layer metamaterial sound absorbing structure as in claim 1 wherein the sound absorbing structure units (1) are glued or welded together.
6. A thin-layer metamaterial sound absorbing structure as in claim 1 wherein the wall thickness δ of the rectangular box (11) satisfies 0.5mm δ 2 mm.
7. A sound-absorbing structure as defined in claim 1, characterised in that the thickness d2 of the first (121) and second (122) profiles of the L-shaped panel (12) satisfies 0.5 ≤ d2 ≤ 2 mm.
8. A sound-absorbing structure in thin-layer metamaterial as claimed in claim 1, characterized in that the L-shaped panel (12) is bent in an L-shape from a flat plate.
9. A thin layer metamaterial sound absorbing structure as in claim 1 wherein the cover plate (17) is glued or welded to the first side (112) of the rectangular box (11).
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