The present invention relates to a sound absorbing device including a plurality of sound absorbing cells.
A device that efficiently reduces surrounding noise is an important consideration in daily life or industrial sites. A sound absorbing method used in a lot of industrial sites in order to reduce noise generated in various machinery facilities may be representatively divided into porous, resonance, and plate type sound absorbing methods according to a principle thereof.
The porous sound absorbing method is a method that adopts an appropriate material with high sound absorbing performance to enhance sound absorption coefficient at a specific frequency and a wideband frequency, and the resonance and plate type sound absorbing methods are methods that modify an internal structure of a sound absorbing material to partially enhance the sound absorption coefficient at the specific frequency.
Existing sound absorbing techniques have a clear limit that high sound absorption coefficient cannot be expected at a low frequency only with a small thickness of the sound absorbing material, and cannot show a wideband high sound absorbing effect in a low-frequency band.
Therefore, a sound absorbing technique suitable for low-frequency wideband sound absorption is required.
An aspect of the present invention has been made in an effort to provide a sound absorbing device showing a high sound absorbing effect in a low-frequency band.
An exemplary embodiment of the present invention provides a sound absorbing device comprising a plurality of sound absorbing cells arranged adjacent to each other on a plane, wherein each of the plurality of sound absorbing cells includes: a chamber having a volume therein, and in which a plurality of micro holes is perforated on a front surface in which a sound wave is incident; and a neck part introduced and extended to a rear on the front surface and penetrated by a through hole for communicating the outside and the chamber.
A rear end of the neck part may be located in the chamber.
The neck part may be extended in a direction vertical to the front surface, and may have a cylinder shape in which the through hole penetrates a center.
When the sound wave passes through the neck part and the plurality of micro holes, a phase change occurs due to a visco-thermal effect, so a sound wave radiated through the neck part and a sound wave radiated through the plurality of micro holes at a target frequency may have opposite phases.
The chamber may have a pillar shape having the front surface as one bottom.
A thickness of the chamber which becomes a height of the pillar shape may be smaller than a wavelength of the sound wave.
The chamber may have a square pillar shape.
The front surfaces of the plurality of sound absorbing cells may be arranged vertical to a direction in which the sound wave is incident.
All of the plurality of sound absorbing cells may have the same size, and the front surfaces of the plurality of sound absorbing cells may form a plane.
Each of the plurality of sound absorbing cells may have the same volume of the chamber and the same extension length of the neck part.
Each of the plurality of sound absorbing cells may have a different size of the through hole from a sound absorbing cell at least adjacent to one side thereof.
Each of the plurality of sound absorbing cells may have a different number of micro holes from a sound absorbing cell at least adjacent to one side thereof.
The plurality of sound absorbing cells may include a first sound absorbing cell and a second sound absorbing cell different from the first sound absorbing cell in terms of the size of the through hole and the number of micro holes, and the first sound absorbing cell and the second sound absorbing cell may be alternately arranged.
Four sound absorbing cells are adjacent to each other and arranged in a grid form to form one sound absorbing unit, and a plurality of sound absorbing units may be arranged adjacent to each other on the plane.
Four sound absorbing cells may have a square pillar form having the same size, and have a different size of the through hole and a different number of micro holes between sound absorbing cells of which surfaces are in contact with each other.
The sound absorbing unit constituted by four sound absorbing cells may have two or more sound target frequencies.
Four sound absorbing cells may have a different size of the through hole and a different number of micro holes.
The sound absorbing unit constituted by four sound absorbing cells may have four or more sound target frequencies.
A diameter of the through hole and a diameter of each of the micro holes may be 1/90 times less than the wavelength of the incident sound wave.
The number of micro holes may be 4 to 100.
On the front surface, a ratio of an area of one micro hole among the plurality of micro holes and an area of the through hole may be in the range of 1:1 to 1:36.
According to an exemplary embodiment of the present invention, through a structure in which a HelmHoltz resonator and a micro perforated plate are combined, high sound absorption coefficient can be achieved in a low-frequency band.
Further, high sound absorption coefficient can be achieved for a plurality of frequencies in a low-frequency band, and a sound absorbing effect can be shown in a wideband.
Hereinafter, an exemplary embodiment of the present invention will be described in detail so as to be easily implemented by those skilled in the art, with reference to the accompanying drawings. However, the present invention can be realized in various different forms, and is not limited to the exemplary embodiments described below. In addition, in the present specification and drawings, the same component is denoted by the same reference numeral.
The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.
In addition, each configuration illustrated in the drawings is arbitrarily shown for understanding and ease of description, but the present invention is not limited thereto.
Throughout this specification and the claims that follow, when it is described that an element is “coupled” to another element. In addition, unless explicitly described to the contrary, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.
Referring to
The plurality of sound absorbing cells 120 may be arranged in the form of a grid. For example, the plurality of sound absorbing cells 120 may be arranged in the form of the grid on the plane vertical to an incident sound wave S and a through hole 125 (see
In
The sound absorbing cell 120 constituting the sound absorbing device 100 may have a smaller scale (a subwavelength scale) than a wavelength of the sound wave S. That is, a length of one side of the sound absorbing cell 120, e.g., a thickness (a z-axis direction length, H, see
All of the plurality of sound absorbing cells 120 constituting the sound absorbing device 100 may have the same size. In this case, front surfaces 130 of the plurality of sound absorbing cells 120 may be arranged vertical to the direction in which the sound wave is incident, and may form the plane.
In the present specification, ‘front’ means a front direction (a direction close to a sound source generating the sound wave) based on an incident direction of the sound wave, and ‘rear’ means a rear direction (a direction moving away from the sound source generating the sound wave) based on the incident direction of the sound wave.
Hereinafter, the structure of the sound absorbing cell 120 constituting the sound absorbing device 100 according to the exemplary embodiment of the present invention will be described in detail.
According to the exemplary embodiment of the present invention, the sound absorbing cell 120 may have a pillar shape having a front surface 130 in which the sound wave S is incident as one bottom. For example, the sound absorbing cell 120 may have a square pillar shape or a cuboid shape. As a result, as illustrated in
However, a form of the sound absorbing cell 120 is not limited to the cuboid shape, and may be an oblique pillar form.
The structure of the cuboid-shaped sound absorbing cell 120 is illustratively described with reference to
The sound absorbing cell 120 includes a chamber 110 having a volume (space E) therein and a neck part 127 having a predetermined length Ln, which is penetrated by a through hole 125 which makes the chamber be in communication with the outside.
The chamber 110 may have a form in which a plurality of micro holes 126 is perforated on the front surface 130 in which the sound wave is incident. For example, a plate in which the plurality of micro holes 126 having the same size is perforated seals an opened front of a box type structure of which front is opened to form the chamber 110. In this case, the plate (a plate constituting the front surface of the chamber) in which the plurality of micro holes 126 is perforated may have a thickness of 0.1 mm or more. The reason is that when the perforated plate has a thickness smaller than 0.1 mm, propagation of the sound wave is influenced by vibration of the plate itself. According to the exemplary embodiment of the present invention, the plate (the plate constituting the front surface of the chamber) in which the plurality of micro holes 126 is perforated may have a thickness of 2 mm. Since the thickness is a length of the micro hole 126 is extended in a progress direction of the sound wave, the thickness becomes a length of a path of sound wave through the micro hole. Hereinafter, the plate (the plate constituting the front surface of the chamber) in which the plurality of micro holes 126 is perforated has the thickness of 2 mm in
The size of the micro hole 126 may be equal to or less than the size of the through hole 125. According to an exemplary embodiment, a ratio of an area of the micro hole 126 on the front surface 130 of the chamber 110 and an area of the through hole 125 may have a range of 1:1 to 1:36. For example, in order to show the high sound absorbing effect, when the through hole 125 has a diameter of 0.5 to 3 mm, the micro hole 126 may have a diameter of 0.5 mm. Meanwhile, the ratio of the area of the micro hole 126 and the through hole 125 may vary depending on the thickness of the plate (the plate constituting the front surface of the chamber) in which the plurality of micro holes 126 is perforated, and as the thickness of the plate (the plate constituting the front surface of the chamber) decreases, the ratio of the area of the micro hole 126 and the area of the through hole 125 may decrease. That is, as the thickness of the plate (the plate constituting the front surface of the chamber) decreases, a difference between the area of the micro hole 126 and the area of the through hole 125 may increase.
Further, the number of micro holes 126 may be a range of 4 to 100. As an experiment result, since an arrangement position or a spacing interval of the micro hole 126 on the front surface 130 of the chamber 110 does not affect the performance of the sound absorbing device of the present invention, a predetermined number of micro holes 126 may be arranged freely in a region so as not to encroach a central through hole 125 area on the front surface 130.
The neck part 127 may have a form of being introduced and extended toward the internal space E (i.e., to the rear of the front surface 130). As a result, the neck part 127 may have a form of being embedded toward the internal space E on the front surface 130 of the chamber 110. That is, the through hole 125 may penetrate along the neck part 127 on the front surface 130 of the chamber 110. For example, a cross section of the through hole 125 vertical to a penetration direction may be a circular form, and may have a diameter in the range of 0.5 to 3 mm.
The neck part 127 may have a circular cross section having a predetermined size, elongate so as to connect the outside and the internal space E of the sound absorbing cell 120, and have a predetermined diameter 2rn. That is, the neck part 127 may be connected to the rear of the front surface 130 so that the outside and the space E in which the sound wave is generated are in communication with each other through the through hole 125. The neck part 127 may be extended in a direction vertical to the front surface 130, and an end may be located in the chamber. That is, an extension length Ln of the neck part 127 may be smaller than the length (z axis direction) of the internal space E of the chamber 110. For example, the neck part 127 may be extended in the direction vertical to the front surface 130 of the chamber 110, and have a cylinder shape in which the through hole 125 penetrates the center.
Since the chamber 110 may be constituted by an external wall having a predetermined thickness, the space E may have the cuboid shape to correspond to the shape of the chamber 110. For example, referring to
According to the exemplary embodiment, in the sound absorbing cell 120, a cross section in a direction which is in line with the plane on which the plurality of sound absorbing cells is arranged may be a square. That is, the sound absorbing cell 120 may have a square pillar shape. For example, referring to
In the case of describing a sound absorbing process in the sound absorbing cell 120, when the sound wave S which is incident toward the sound absorbing cell 120 is incident on the front surface 130 of the chamber 110, the sound wave S is propagated to the inside of the chamber through the neck part 127 and the micro holes 126. The sound wave S is propagated to the inside of the chamber, and then reflected on the wall surface forming the internal space E of the chamber, and radiated through the neck part 127 and the micro holes 126. In this case, since the diameters of the through hole 125 and the micro holes 126 of the neck part 127 are much smaller than the wavelength of the incident sound wave, a phase change occurs due to a very high visco-thermal dissipation when the sound wave passes through the neck part 127 and the micro hole 126. In this case, the sound absorbing cell 120 is configured so that a phase of the sound wave radiated through the neck part 127 and the phase of the sound wave radiated through the micro holes 126 are opposite at a target frequency. According to the exemplary embodiment of the present invention, the diameter of the through hole 125 and the diameter of the micro hole 126 may be 1/90 times less than the wavelength of the incident sound wave in order to show the very high visco-thermal dissipation so that the phase of the sound wave radiated through the neck part 127 and the phase of the sound wave radiated through the micro holes 126 are opposite. That is, in the sound absorbing device 100 according to the exemplary embodiment of the present invention, sound absorbing cells 120 in which the size (diameter) of the through hole 125 and the number of micro holes 126 are optimally determined (i.e., the phase of the sound wave radiated through the neck part 127 and the phase of the sound wave radiated through the micro holes 126 are made to be opposite at the target frequency) are arranged, and as a result, the sound wave radiated through the neck part 127 and the sound wave radiated through the micro holes 126 in each of the sound absorbing cells 120 are made to be trapped in the near-field region from the front surface of the sound absorbing cells 120 and simultaneously to induce destructive interference in the far-field region from the front surface of the sound absorbing cells 120 to achieve perfect sound absorption in which a reflective wave is 0.
In
As for describing the optimization algorithm to determine the radius of the through hole 125 and the number of micro holes 126, a sequential quadratic programming (SQP) scheme is used so that a difference between effective acoustic impedance of the sound absorbing cell 120 at the front surface 130 calculated for the target frequency and acoustic impedance of external air is minimized, and an object function is set so that a reflection coefficient of the sound absorbing cell 120 is minimized.
Referring to
Meanwhile, the structure of the sound absorbing device 100 is modified to show high sound absorption coefficient for one or more specific frequencies and wideband frequencies, and hereinafter, a sound absorbing device according to a modified exemplary embodiment will be described. In the exemplary embodiment below, duplicated contents with the first exemplary embodiment are omitted and a difference is primarily described.
Referring to
In this case, four sound absorbing cells 220 and 320 constituting the sound absorbing units C2 and C3 may be arrayed in the grid form, and may absorb a plurality of frequencies.
Referring to
The sound absorbing device 200 in which the sound absorbing unit C2 constituted by two types of sound absorbing cells 220 is arrayed may absorb two frequencies.
For reference, in the case of the first exemplary embodiment described above, referring to
In
Referring to
Further, when
Referring to
The sound absorbing device 200 in which the sound absorbing unit C3 constituted by four types of sound absorbing cells 320 is arrayed may absorb four frequencies.
In
Referring to
Further, when
As such, according to the exemplary embodiment of the present invention, through the sound absorbing cell having a structure in which the plate in which the micro hole is perforated coupled to the Helmholtz resonator form in which the through holes is formed in the chamber, high sound absorption coefficient may be provided in a low frequency band.
Further, at least one of the size of the through hole and the number of micro holes in the plurality of sound absorbing cells constituting the sound absorbing device is differently arrayed, and as a result, high sound absorption coefficient may be provided for a plurality of frequencies in the low frequency band, and the sound absorbing effect may be shown in the wideband.
Although the preferred exemplary embodiment of the present invention is described through the above description, but the present invention is not limited thereto and various modifications can be made within the claims and the range of the detailed description and the accompanying drawings of the invention, and this also belongs to the scope of the present invention, of course.
100, 200, 300 Sound absorbing device
110 Chamber
125, 225, 325 Through hole
126, 226, 326 Micro hole
127 Neck part
120, 220, 320 Sound absorbing cell
Number | Date | Country | Kind |
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10-2020-0121367 | Sep 2020 | KR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/KR2021/012882 | 9/17/2021 | WO |