TWI850021B - Acoustic metasurface structure - Google Patents

Abstract

An acoustic metasurface structure is configured to absorb sounds. The acoustic metasurface structure comprises a main body, an externally-connecting configuration and an inner configuration. The externally-connecting configuration and the inner configuration are respectively formed inside the main body. An externally-connecting tube of the externally-connecting configuration is in fluid communication with an external environment and an externally-connecting cavity of the externally-connecting configuration. An inner tube of the inner configuration is in fluid communication with the externally-connecting cavity and an inner cavity of the inner configuration. By the externally-connecting configuration and the inner configuration forming a series-type structure in the main body, the acoustic metasurface structure increases an acoustic impedance. Therefore, under circumstances of the main body having a limited volume, frequencies, which absorption coefficient peaks of the acoustic metasurface structure land on, are lowered, and an absorption coefficient of the acoustic metasurface structure toward low-frequency sounds is increased.

Description

Sound absorbing structure

The present invention is a sound absorbing structure, in particular a sound absorbing structure capable of absorbing low frequency sounds, in particular an ultra-low frequency sound absorbing sheet.

In daily life, many activities will generate noise, such as people and cars passing by, playing music and mechanical operation. In order to reduce the interference caused by noise, there are many sound-absorbing structures used to absorb sound, such as sound-absorbing panels, sound-absorbing structures with porous/micro-slit thin plates and resonant back cavities, active noise absorbers and silencers made using the Holmholtz resonance principle.

Among them, the material of the sound-absorbing board is a porous material made of foam or fiber. Due to the material properties, the sound-absorbing board is more capable of absorbing high-frequency sounds, but it is more difficult to absorb low-frequency sounds. The sound-absorbing structure with porous/micro-seam thin plates and a resonant back cavity is also limited by space, so the volume of the resonant back cavity is limited, so it is not easy to apply to low-frequency noise absorption. Active noise absorbers require complex circuit design, so they are difficult to manufacture and have higher costs.

In addition, silencers made using the Holmholtz resonance principle are widely used for noise absorption in narrow frequency sections of pipes, wherein the silencer includes a hollow cavity and a neck connected to the cavity, and the neck has an opening connected to the external environment. The Holmholtz resonator is a passive silencer and can be regarded as a spring-mass system, where the cavity is the spring and the air in the neck is the mass. The Holmholtz resonator can usually trap and consume noise. The mechanism is that when the noise frequency reaches the structural resonance frequency, the air in the neck vibrates and rubs violently, consuming sound energy. It has been widely used in the engineering field. From the Holmholtz resonance principle, it can be known that by controlling the opening size of the neck, the length of the neck and the volume inside the cavity, a preset frequency section of the muffler can be controlled. The muffler has a good effective absorption rate in the preset frequency section, and has almost no sound absorption effect outside the preset frequency section.

When it is desired to absorb lower frequency sounds by means of the muffler made using the Holmholtz resonance principle, the preset frequency of the muffler should be set to a lower frequency. However, since the preset frequency of the muffler is inversely proportional to the volume inside the cavity, that is, the cavity requires a larger volume to set a lower preset frequency, the muffler occupies a larger space. Therefore, due to space limitations, the muffler is difficult to use to absorb lower frequency sounds.

In summary, current sound-absorbing structures are difficult to absorb low-frequency sounds within a limited volume, or require complex circuit design, so there is still room for improvement.

The main purpose of the present invention is to provide a sound absorbing structure, hoping to improve the problem that the current sound absorbing structure is difficult to achieve the effect of absorbing low-frequency sound under the condition of limited volume, or requires complex circuit design.

To achieve the above-mentioned purpose, the sound-absorbing structure of the present invention comprises: A body, a sound-absorbing hole is formed on the surface of the body, wherein the ratio of the diameter of the body to the diameter of the sound-absorbing hole is between 9.8:1 and 12.35:1, including end values; An external structure formed inside the body, the external structure has an external cavity and an external tube, both ends of the external tube pass through and are located in the external cavity, one end of the external tube is connected to the sound-absorbing hole to connect to the external environment, and the other end of the external tube is connected to the external cavity; and An inner structure is formed inside the body, the inner structure has an inner chamber and an inner connecting tube, the two ends of the inner connecting tube are connected and located in the inner chamber, and the inner connecting tube and the outer connecting tube are arranged at intervals, one end of the inner connecting tube is connected to the outer chamber of the outer connecting structure, and the inner chamber is connected to the outer chamber through the inner connecting tube.

The sound-absorbing structure of the present invention is designed based on the Holmholtz resonance principle and adopts a planarization and extended neck design. The external structure uses the external tube to connect the external chamber and the external environment, and the internal structure uses the internal connecting tube to connect the internal chamber and the external chamber of the external structure. A series structure can be formed inside the main body to increase the acoustic impedance of the sound-absorbing structure, thereby reducing the frequency at which the absorption efficiency peak of the sound-absorbing structure is located. In this way, the absorption efficiency of the sound-absorbing structure for low-frequency sound is improved under the condition that the volume of the main body is limited. The sound-absorbing structure is simple in structure. Sound can be absorbed by simply pointing the sound-absorbing hole of the main body toward the sound source. There is no need for complex circuit design or power connection, and the application range of the sound-absorbing structure can be increased, thereby improving the convenience of use.

Please refer to FIG. 1 to FIG. 4 , which are a first preferred embodiment of the present invention, which includes a body 10a, an outer structure 20 and an inner structure 30.

As shown in FIGS. 1 to 3 , a sound absorbing hole 11 is formed on the surface of the body 10a-10d, and the sound absorbing hole 11 is connected to the external environment, wherein the ratio of the diameter of the body 10a-10d to the sound absorbing hole 11 is between 9.8:1 and 12.35:1, including the end value. Through the design of the diameter ratio of the body 10a-10d to the sound absorbing hole 11, the frequency at which the absorption efficiency peak of the sound absorbing structure is located below the frequency of low-frequency sound, preferably, the ratio of the diameter of the body 10a-10d to the sound absorbing hole 11 is between 10:1 and 10.87:1, including the end value, thereby enabling the frequency at which the absorption efficiency peak of the sound absorbing structure is located below 200 Hz, thereby further reducing the absorption efficiency peak of the sound absorbing structure.

As shown in FIGS. 2 to 5 , the external connection structure 20 is formed inside the body 10a~10d, and the external connection structure 20 has an external connection chamber 21 and an external connection tube 22. The external connection tube 22 is located in the external connection chamber 21, and both ends of the external connection tube 22 are connected. One end of the external connection tube 22 is connected to the sound absorbing hole 11 to connect to the external environment, and the other end of the external connection tube 22 is connected to the external connection chamber 21, so that the external connection chamber 21 is connected to the external environment, wherein one end of the external connection tube 22 is located at the sound absorbing hole 11 and is defined as an external connection end 221, and one end of the external connection tube 22 connected to the external connection chamber 21 is defined as an external opening end 222.

As shown in Figures 2 to 4, the inner structure 30 is formed inside the main body 10a~10d, and the inner structure 30 has an inner chamber 31 and an inner connecting tube 32. The inner connecting tube 32 is located in the inner chamber 31, and the two ends of the inner connecting tube 32 are connected, and the inner connecting tube 32 and the outer tube 22 are arranged at intervals. One end of the inner connecting tube 32 is connected to the outer chamber 21 of the outer structure 20, and the inner chamber 31 is connected to the outer chamber 21 through the inner connecting tube 32, wherein one end of the inner connecting tube 32 connected to the outer chamber 21 is defined as an inner connecting end 321, and one end of the inner connecting tube 32 connected to the inner chamber 31 is defined as an inner opening end 322.

In addition, the outer connecting tube 22 and the inner connecting tube 32 are preferably curved, respectively, so as to increase the length of the outer connecting tube 22 and the inner connecting tube 32 in a limited space. In addition, the cross-section of the outer connecting tube 22 and the inner connecting tube 32 can be circular, square or polygonal, etc., all of which can enable the sound absorbing structure to achieve a sound absorbing effect.

In addition, the main body 10a~10d has a sound absorbing surface 12 and a partition wall 13. The sound absorbing surface 12 is formed on the outer side of the main body 10a~10d, and the sound absorbing hole 11 is located on the sound absorbing surface 12. The partition wall 13 is located inside the main body 10a~10d and separates the external chamber 21 and the internal chamber 31. One end of the internal connecting pipe 32 is set on the partition wall 13 and connected to the external chamber 21.

Furthermore, as shown in FIGS. 4 to 6 , the external chamber 21 and the internal chamber 31 are adjacent to each other on a horizontal reference plane, the external tube 22 is connected to the external environment along a Z direction, and the internal connecting tube 32 is connected to the external chamber 21 along an X direction, the Z direction is perpendicular to the horizontal reference plane, and the X direction is parallel to the horizontal reference plane. In addition, the external connecting tube 22 includes an external connecting section 223 and an extension section 224 connected to each other, the external connecting section 223 extends along the Z direction, and the extension section 224 is extended on the horizontal reference plane. The external connecting chamber 21 and the inner chamber 31 are adjacent to each other on the horizontal reference plane, and the external connecting tube 22 is located in the external connecting chamber 21, and the inner connecting tube 32 is located in the inner chamber 31, so that the sound absorbing structure presents a planar structure, so it can be easily installed on the wall, and because the structure is flat, it occupies a smaller volume and is easier to stack, thereby improving the convenience of construction.

Preferably, the body 10a-10d is in the shape of a disk, the diameter D of the body 10a-10d is located on the horizontal reference plane, the outer chamber 21 and the inner chamber 31 each have a chamber height h in the Z direction, and the chamber heights of the outer chamber 21 and the inner chamber 31 are equal. The body 10a-10d is in the shape of a disk for the convenience of experiments and theoretical calculations. The body 10a-10d can be square or polygonal, etc., and is not limited to the preferred embodiment of the present invention, wherein The body 10a~10d includes an upper cover 14, a lower cover 15 and an annular outer wall 16, the upper cover 14 and the lower cover 15 are respectively combined with the upper and lower sides of the outer wall 16, the partition wall 13 is arranged in the outer wall 16, so that the space surrounded by the upper cover 14, the lower cover 15 and the outer wall 16 is divided into the external chamber 21 and the internal chamber 31, one end of the external tube 22 is embedded in the upper cover 14, and one end of the internal connecting tube 32 is embedded in the partition wall 13.

The sound absorbing structure of the present invention is designed based on the Holmholtz resonance principle. The external structure 20 is connected to the external environment and the external chamber 21 through the external tube 22, so that the external structure 20 forms a resonator that conforms to the Holmholtz resonance principle, and the internal structure 30 is connected to the external chamber 21 and the internal chamber 31 through the internal connecting tube 32, thus forming another resonator that conforms to the Holmholtz resonance principle, and the two resonators are connected in series through the internal connecting tube 32, so that the interior of the body 10a~10d forms a series structure.

In detail, since acoustic impedance can be equivalent to current impedance and the series-parallel formula of current impedance can be applied, the sound-absorbing structure uses a series structure to increase the acoustic impedance, thereby reducing the preset frequency of the sound-absorbing structure. In this way, the sound-absorbing structure can improve the efficiency of absorbing low-frequency sounds when the volume of the main body 10a~10d is limited. In addition, the sound-absorbing structure has a simple structure. Sound can be absorbed by simply pointing the sound-absorbing holes 11 of the main body 10a~10d toward the sound source. There is no need for complex circuit design or power connection, which can increase the scope of application of the sound-absorbing structure and improve convenience of use.

Furthermore, by controlling the volumes of the external chamber 21 and the internal chamber 31, the length and diameter of the external tube 22, and the length and diameter of the internal connecting tube 32, the overall acoustic impedance of the sound absorbing structure can be adjusted, thereby controlling a preset frequency range of the sound absorbing structure.

The control principle of the overall acoustic impedance of the sound absorbing structure will be further described below. Please refer to FIG. 5 to FIG. 7 , where: t is the thickness of the upper cover 14, the lower cover 15 and the outer wall 16 of the main body 10a; D is the diameter of the main body 10a; is the inner diameter of the connecting outer tube 22, and the inner diameter of the connecting outer tube 22 is equal to the diameter of the sound absorbing hole 11; is the inner diameter of the inner connecting tube 32; is the length of the connecting outer tube 22; is the length of the inner connecting tube 32.

Since the outer tube 22 and the inner connecting tube 32 have a relatively long length and a relatively small diameter, a narrow channel is formed inside, so the thermoviscous loss in the tube body (i.e., the outer tube 22 and the inner connecting tube 32) should be considered. Referring to "Acoustic perfect absorbers via Helmholtz resonators with embedded apertures" (Sibo Huang; Xinsheng Fang; Xu Wang; Badreddine Assouar; Qian Cheng; Yong Li, J Acoust Soc Am 145, 254–262 (2019)) and "Acoustic perfect absorbers via spiral metasurfaces with embedded apertures" (Sibo Huang; Xinsheng Fang; Xu Wang; Badreddine Assouar; Qian Cheng; Yong Li, Appl. Phys. Lett. 113, 233501 (2018)), it can be obtained that the acoustic impedance of the tube body is It can be expressed by the following equation: above middle, is the acoustic impedance of the tube; is the air density; is the speed of sound; is the wave number; is the length of the tube; is the specific heat ratio; where is the thermal field function, is the hysteresis field function, which can be expressed by the following equations: in, is the second-order Bezo function of the first kind; is the Bezo function of the first kind of zero order; is the thermal wave number; is the viscous wave number; is the inner diameter of the tube.

In addition, referring to "Perforated panel absorbers with viscous energy dissipation enhanced by orifice design" (Randeberg RT, PhD thesis submitted to NTNU, 2000, Trondheim), when considering the sound radiation from the tube into the open space, the effective length of the tube will increase, so the open end of the tube (i.e., the outer open end 222 of the connecting tube 22 and the inner open end 322 of the inner connecting tube 32) needs to be adjusted to: above middle, is a further correction term for the pipe length; is the ratio of the inner diameter of the tube to the radius of the semicircular chamber. In the preferred embodiment of the present invention, the body 10a-10d is circular, the outer chamber 21 and the inner chamber 31 are semicircular, and the ratio of the inner diameter of the tube to the radius of the semicircular chamber is It can be expressed by the following equation: above middle, is the initial correction for the pipe length. The sound quality is affected by the air entering and exiting the hole to the open space, which can be expressed by the following equation:

When the open end of the tube is corrected, the acoustic impedance provided by the tube and the open end of the tube is It can be expressed by the following equation: in, is the angular frequency of the sound, which can be expressed by the following equation: in, is the frequency of the sound.

Furthermore, the acoustic impedance provided by the chamber It can be expressed by the following equation: in, is the sound pressure; is the air particle velocity; is the volume flow rate of air flowing through the chamber; is the cross-sectional area of the tube; is the volume of the chamber. In the figure, the cross-sectional area of the tube is It can be expressed by the following equation:

Next, referring to "Theory and design of microperforated panel sound-absorbing constructions" (Dah-You Maa, Sci. Sin. 18, 55–71 (1975)) and "On the theory and design of acoustic resonators" (Uno Ingard, J. Acoust. Soc. Am. 25, 1037–61 (1953)), taking into account the friction loss at the boundary of the connecting end of the tube body, the connecting end of the tube body (i.e., the outer connecting end 221 of the connecting outer tube 22 and the inner connecting end 321 of the connecting inner tube 32) corrects the acoustic impedance provided. It can be expressed by the following equation: in, is the dynamic viscosity coefficient.

As mentioned above, the acoustic impedance can be equivalent to the current impedance and the series-parallel formula of the current impedance can be applied. The first preferred embodiment of the sound-absorbing structure is formed by connecting the external structure 20 and the internal structure 30 in series. As shown in FIG8 , it is an equivalent circuit diagram of the acoustic impedance of this embodiment. Therefore, the overall acoustic impedance of the sound-absorbing structure is It can be expressed by the following equation: above middle, is the ratio of the area of the sound absorbing surface 12 of the body 10a-10d to the area of the sound absorbing hole 11, which can be expressed by the following equation: Wherein, A is the area of the sound absorbing surface 12 of the body 10a-10d, which can be expressed by the following equation:

In addition, the sound absorption efficiency It can be expressed by the following equation:

In the first preferred embodiment of the present invention, Substituting into represents that the external structure 20 (including the external tube 22 and the external chamber 21) will Substituting into represents the inner structure 30 (including the inner connecting tube 32 and the inner chamber 31), when and Substituting into equation (3), equation (4) and equation (5), we can obtain , and then Substituting into equation (6), we can get the overall acoustic impedance of the sound absorbing structure: and the frequency of the sound The overall acoustic impedance of the sound absorbing structure The efficiency of sound absorption can be obtained , and due to the overall acoustic impedance of the sound absorbing structure The thickness t of the upper cover 14, the lower cover 15 and the outer wall 16 of the body 10a, the diameter D of the body 10a, the inner diameter of the connecting outer tube 22 , the inner diameter of the inner connecting tube 32 , the length of the outer tube 22 and the length of the inner connecting tube 32 Therefore, by adjusting the structural dimensions of the sound absorbing structure, the sound absorbing structure can have both the corresponding frequency and a higher absorption efficiency.

Please refer to FIG. 5 to FIG. 7. Taking the first preferred embodiment of the present invention as an example, the structural dimensions of the sound absorbing structure are set as follows: the diameter D of the body 10a is 100 mm; the inner diameter of the connecting outer tube 22 is is 10 mm; the inner diameter of the inner connecting tube 32 The length of the outer tube 22 is 10 mm. is 61.2 mm; the length of the inner connecting tube 32 is 61.2 mm; the thickness t of the partition wall 13, the upper cover 14, the lower cover 15 and the outer wall 16 of the main body 10a is 1.5 mm; the chamber height h of the connecting outer chamber 21 and the inner chamber 31 is 14 mm. Please refer to FIG. 9, which is a relationship diagram between frequency (horizontal axis) and absorption efficiency (vertical axis) obtained by experiment and numerical simulation after the sound absorbing structure is set according to the aforementioned structural dimensions. The green line is the experimental result obtained by experimenting with the sound absorbing structure using an impedance tube (SW422, BSWA Technology); the blue line is the theoretical result calculated using the aforementioned equation; and the red line is obtained by finite element method analysis. As shown in the figure, the peak absorption efficiency of the present embodiment is located at 173.2 Hz, and has an absorption efficiency of 0.99, which shows that the present invention can indeed effectively absorb lower frequency sounds, and the frequency band width with an absorption efficiency higher than 0.5 is 13 Hz.

As shown in FIGS. 10 to 12 , in the second preferred embodiment of the present invention, the two sound absorbing structures are arranged side by side, and the sound absorbing holes 11 of the two sound absorbing structures face the same side. The two sound absorbing structures are respectively defined as a first structure 1 and a second structure 2. The outer chamber 21 of the first structure 1 is defined as a first outer chamber 21a, the inner chamber 31 of the first structure 1 is defined as a first inner chamber 31a, and the outer tube 21 of the first structure 1 is defined as a first inner chamber 31a. 2 is defined as a first external tube 22a, and the internal connecting tube 32 of the first structure 1 is defined as a first internal connecting tube 32a; the external chamber 21 of the second structure 2 is defined as a second external chamber 21b, the internal chamber 31 of the second structure 2 is defined as a second internal chamber 31b, the external tube 22 of the second structure 2 is defined as a second external tube 22b, and the internal connecting tube 32 of the second structure 2 is defined as a second internal connecting tube 32b.

The second preferred embodiment of the present invention can be regarded as a parallel structure formed by the first structure 1 and the second structure 2 arranged side by side, so it can be equivalent to a parallel circuit formula. Therefore, the overall acoustic impedance of this embodiment is It can be expressed by the following equation:

In the second preferred embodiment of the present invention, Indicates the first external tube 22a and the first external chamber 21a; Indicates the first inner connecting tube 32a and the first inner chamber 31a; Indicates the second external tube 22b and the second external chamber 21b; Indicates that the second inner connecting tube 32b and the second inner chamber 31b are Substituting into equations (3), (4) and (5) respectively, and then into equation (8), the overall acoustic impedance of the second preferred embodiment of the present invention can be obtained: and sound frequency The overall acoustic impedance Substitution The absorption efficiency of this embodiment can be obtained. .

Taking the second preferred embodiment of the present invention as an example, the structural dimensions of the sound absorbing structure are set as follows: the diameter D of the body 10b is 100 mm; the inner diameter of the first connecting outer tube 22a is , the inner diameter of the first inner connecting tube 32a The inner diameter of the second connecting outer tube 22b and the inner diameter of the second inner connecting tube 32b The length of the first connecting outer tube 22a is 10 mm. and the length of the first inner connecting tube 32a are both 42.3 mm; the length of the second outer tube 22b and the length of the second inner connecting tube 32b are all 33 mm; the thickness t of the partition wall 13, the upper cover 14, the lower cover 15 and the outer wall 16 of the main body 10b is 1.5 mm; the chamber height h connecting the outer chamber 21 and the inner chamber 31 is 14 mm. Please refer to FIG. 13 , which is a relationship diagram between frequency (horizontal axis) and absorption efficiency (vertical axis) obtained through experiments and numerical simulations after the sound absorbing structure is set according to the aforementioned structural dimensions. The green line is the experimental result obtained by experimenting with the sound absorbing structure using an impedance tube (SW422, BSWA Technology); the blue line is the theoretical result calculated using the aforementioned equation; and the red line is obtained by finite element method analysis. As shown in the figure, the present embodiment has two absorption efficiency peaks, one peak is located at 306 Hz and has an absorption efficiency of 0.93; the other peak is located at 326 Hz and has an absorption efficiency of 0.99, and the frequency band width where the absorption efficiency is higher than 0.5 is 45 Hz.

Among them, due to the length of the first connecting outer tube 22a of the first structure 1 and the length of the first inner connecting tube 32a The length of the second outer tube 22b of the second structure 2 is and the length of the second inner connecting tube 32b , so that the absorption efficiency peak of the first structure 1 is at a relatively low frequency, and the absorption efficiency peak of the second structure 2 is at a relatively high frequency, and the frequencies where the absorption efficiency peaks of the two sound-absorbing structures are located are staggered, thereby increasing the frequency segment width of the absorption efficiency of this embodiment being higher than 0.5. In addition, if a plurality of the first preferred embodiments of the present invention are arranged side by side, and the connecting outer tubes 22 and the connecting inner tubes 32 of the plurality of sound-absorbing structures are respectively set to different lengths, the absorption efficiency peaks of the plurality of sound-absorbing structures will be located at different frequencies, respectively, and the frequency segment width of the absorption efficiency being higher than 0.5 can also be increased.

As shown in FIG. 14 and FIG. 15 , in the third preferred embodiment of the present invention, the inner diameter of the outer connecting tube 22 gradually changes from the outer connecting end 221 to the outer opening end 222 , and the inner diameter of the inner connecting tube 32 gradually changes from the inner connecting end 321 to the inner opening end.

In this embodiment, referring to "Perfect acoustic absorption of Helmholtz resonators via tapered necks" (Song C; Huang S; Zhou Z; Zhang J; Jia B; Zhou C; Li Y; Pan Y, Appl Phys Express 2022; 15: 084006), the acoustic impedance of the tube is It can be expressed by the following equation: Among them, Substituting into represents that the external structure 20 (including the external tube 22 and the external chamber 21) will Substituting into represents the inner structure 30 (including the inner connecting tube 32 and the inner chamber 31); The connecting end of the pipe body. is the opening end of the tube; A is the total cross-sectional area of the body 10c; is the length of the tube; b is the thickness of the upper cover 14; is the volume of the tube; and Resistance end correction for the connection and opening ends of the pipe body; and Reactance end correction for the connection and opening ends of the pipe body; is the porosity, i.e., the ratio of the variable cross-sectional area of the tube to the total cross-sectional area of the body 10c; is the perforation constant; is the Bezo function of the first kind of zero order; is the first-order Bezo function; x represents the length of the tube from the opening along the tube. The acoustic impedance correction of the connecting end and the opening end of the tube is and It can be expressed by the following equation: in, is the diameter of the connecting end of the tube. is the diameter of the open end of the tube; In addition, Then replace Replace with To further illustrate, in an embodiment of the present invention, as shown in FIG. 15 , the outer tube 22 is represent , represent The internal connection tube 32 represent , represent In addition, the acoustic impedance correction of the open end and the connection end of the pipe It can be expressed by the following equation: in addition, Then replace Replace with Furthermore, the porosity It can be expressed by the following equation: In addition, the aperture coefficient It can be expressed by the following equation:

Furthermore, the acoustic impedance of the cavity It can be expressed by the following equation: in, is the average cross-sectional area of the connecting end and the open end of the pipe; is the volume of the chamber.

The third preferred embodiment of the present invention is still a series structure, so the overall acoustic impedance of this embodiment is It can be expressed by the following equation:

In the third preferred embodiment of the present invention, p=1 is substituted to represent the external structure 20 (including the external connecting tube 22 and the external connecting chamber 21), and p=2 is substituted to represent the internal structure 30 (including the internal connecting tube 32 and the internal chamber 31); and Then substitute the solution into The overall acoustic impedance of the third preferred embodiment of the present invention can be obtained. and sound frequency The overall acoustic impedance Substitution The absorption efficiency of this embodiment can be obtained. .

Taking the third preferred embodiment of the present invention as an example, the structural dimensions of the sound absorbing structure are set as follows: the diameter D of the body 10c is 100 mm; the thickness t of the partition wall 13, the upper cover 14, the lower cover 15 and the outer wall 16 of the body 10c is 1 mm; the chamber height h of the connecting outer chamber 21 and the inner chamber 31 is 16 mm; the length of the connecting outer tube 22 is 10 mm; is 74.4 mm; the length of the inner connecting tube 32 is 67.4 mm; the inner diameter of the outer connecting end 221 of the outer tube 22 is is 9.2 mm; the inner diameter of the outer open end 222 of the outer tube 22 is 8.8 mm; the inner diameter of the inner connecting end 321 of the inner connecting tube 32 is 13.6 mm; the inner diameter of the inner opening end 322 Please refer to FIG16, which is a relationship diagram between the frequency (horizontal axis) and the absorption efficiency (vertical axis) obtained by numerical simulation after the sound absorbing structure is set according to the aforementioned structural dimensions. The green line is the experimental result obtained by experimenting with the sound absorbing structure using an impedance tube (SW422, BSWA Technology); the blue line is the theoretical result calculated using the aforementioned equation; the red line is obtained by finite element method analysis. As shown in the figure, according to the experimental results, the absorption efficiency peak of this embodiment is approximately at 116 Hz, with an absorption efficiency of 0.75; according to the theoretical and finite element method analysis results, the absorption efficiency peak of this embodiment is approximately at 126 Hz, with an absorption efficiency of 0.95. The third preferred embodiment of the sound absorbing structure is designed with a gradual change in the inner diameter of the outer connecting tube 22 and the inner connecting tube 32. Compared with the first preferred embodiment, when the diameter D of the main body 10c is the same, the absorption efficiency peak of the third preferred embodiment of the sound absorbing structure is at a relatively low frequency. Therefore, the frequency at which the absorption efficiency peak is located can be further reduced through the design of the gradual change in the inner diameter. Regardless of whether the inner diameter of the tube body gradually increases or decreases from the connecting end to the opening end, the effect of reducing the frequency at which the absorption efficiency peak is located can be achieved.

Please refer to Figures 17 to 20, which are the fourth preferred embodiment of the present invention. The sound absorbing structure includes a plurality of extension structures 40, which are connected in sequence and formed inside the main body 10d. The plurality of extension structures 40 respectively have an extension chamber 41 and an extension tube 42. The extension chambers 41 of the plurality of extension structures 40 are connected in sequence. The extension tube 42 of one of the extension structures 40 is connected to the inner chamber 31 of the inner structure 30 through an extension connection hole 43 formed on the main body 10d, and the extension tubes 42 of the remaining extension structures 40 in the plurality of extension structures 40 are connected to the extension chamber 41 of another extension structure 40.

The external structure 20, the internal structure 30 and the plurality of extension structures 40 are connected in sequence, so that the fourth preferred embodiment of the present invention forms a continuous series structure, that is, a series design in which four chambers are connected in sequence formed by the external structure 20, the internal structure 30 and the two extension structures 40 connected in sequence, and a series equivalent circuit can be applied, so the overall acoustic impedance of the sound-absorbing structure of this embodiment is It can be expressed by the following equation:

As shown in FIG. 19 and FIG. 20, taking the fourth preferred embodiment of the present invention as an example, it is a double-layer series structure formed by connecting two first preferred embodiments of the present invention in series, the diameter D of the body 10d is 100 mm; the inner diameter of the connecting outer tube 22 is , the inner diameter of the inner connecting tube 32 and the inner diameter of the plurality of extension tubes 42 The length of the outer tube 22 is 10 mm respectively; , the length of the inner connecting tube 32 and the length of the plurality of extension tubes 42 They are 61.2 mm respectively; the thickness t of the partition wall 13, the upper cover 14, the lower cover 15 and the outer wall 16 of the main body 10d is 1.5 mm; the chamber height h of the external chamber 21, the inner chamber 31 and the multiple extended chambers 41 is 14 mm. Please refer to FIG. 21, which is a relationship diagram between frequency (horizontal axis) and absorption efficiency (vertical axis) obtained through experiments and numerical simulations after the sound-absorbing structure is set according to the aforementioned structural dimensions. The green line is the experimental result obtained by experimenting with the sound-absorbing structure using an impedance tube (SW422, BSWA Technology); the blue line is the theoretical result calculated using the aforementioned equation; and the red line is obtained by finite element method analysis. As shown in the figure, the absorption efficiency peak of this embodiment is located at 97 Hz and has an absorption efficiency of 0.95. Compared with the single-layer series structure of the first preferred embodiment of the invention, the frequency at which the absorption efficiency peak of this embodiment is located is further reduced. In addition, if three of the first preferred embodiments of the present invention are connected in series to form a three-layer series structure, that is, a series design in which six chambers are connected in sequence, the peak absorption efficiency can be reduced to 60 Hz.

Furthermore, by using the particle swarm optimization algorithm (PSO) in conjunction with the aforementioned equation, a specific sound absorption frequency can be set, and the size of the sound absorption structure with the best absorption efficiency can be found under the sound absorption frequency, so that the sound absorption structure can achieve the effect of absorbing sound according to different needs. The sound-absorbing structure can be used to absorb low-frequency noise generated by the operation of mechanical processing (including machine tools), textile plants, hydropower, thermal power, wind power and other power generating units; can be attached to the walls of the engine room of ships, cargo ships, merchant ships, fishing boats, yachts, warships, submarines, aircraft carriers and other ships to absorb the low-frequency noise generated by the engine; can be set to cover the outside of the outdoor air-conditioning compressor and the iron rolling door motor to absorb noise; can be set on the periphery of the ventilation duct to reduce the noise of a specific frequency; can be set inside the air purifier or the mainframe of a large computer to reduce the noise of the fan operation; can be set At the bottom of the washing machine, the noise from the motor operation is reduced; it can be installed at the bottom of the carriage of transportation vehicles such as the MRT, Taiwan Railway and High Speed Rail to reduce the transmission of noise to the interior of the carriage; it can be installed around rocket launch platforms, missile and artillery shells and other military bases to reduce noise of specific frequencies; it can be installed on the outer frame of the window to isolate the noise of specific projects or transportation, and a plurality of the sound-absorbing structures can be installed on the wall over a large area to increase the degree of noise absorption, or a plurality of the sound-absorbing structures with different structural designs can be installed on the wall together to increase the bandwidth of noise absorption.

In summary, the sound-absorbing structure of the present invention can be used to absorb sound. The external structure 20 and the internal structure 30 form a series structure inside the main body 10a~10d to increase the acoustic impedance, thereby reducing the frequency at which the peak of the absorption efficiency of the sound-absorbing structure is located. In this way, when the volume of the main body 10a~10d is limited, the absorption efficiency of the sound-absorbing structure for low-frequency sound is improved. The sound-absorbing structure of the present invention can also be called an ultra-low-frequency sound-absorbing sheet.

1: First structure 2: Second structure 10a~10d: Body 11: Sound absorbing hole 12: Sound absorbing surface 13: Partition wall 14: Upper cover 15: Lower cover 16: Outer wall 20: External structure 21: External chamber 21a: First external chamber 21b: Second external chamber 22: External tube 22a: First external tube 22b: Second external tube 221: External connection end 222: External opening end 223: External section 224: Extension section 30: Internal structure 31: Internal chamber 31a: First internal chamber 31b: Second internal chamber 32: Internal connection tube 32a: First internal connection tube 32b: Second internal connection tube 321: Internal connection end 322: Internal opening end 40: Extension structure 41: Extension chamber 42: Extension tube 43: Extension connection hole D: Diameter of body :Inner diameter h: Chamber height :Length t:Thickness

Figure 1: A three-dimensional schematic diagram of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 2: A decomposed schematic diagram of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 3: A top view schematic diagram of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 4: A top view cross-sectional schematic diagram of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 5: A top view schematic diagram of the interior of the body of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 6: A-A cross-sectional schematic diagram of Figure 3. Figure 7: A three-dimensional schematic diagram of the first preferred embodiment of the sound-absorbing structure of the present invention with an external tube. Figure 8: An equivalent circuit schematic diagram of the acoustic impedance of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 9: A schematic diagram of the experimental and simulation results of the first preferred embodiment of the sound-absorbing structure of the present invention. Figure 10: A three-dimensional schematic diagram of the second preferred embodiment of the sound-absorbing structure of the present invention. Figure 11: A schematic diagram of the decomposition of the second preferred embodiment of the sound-absorbing structure of the present invention. Figure 12: A schematic diagram of the top view of the interior of the body of the second preferred embodiment of the sound-absorbing structure of the present invention. Figure 13: A schematic diagram of the experimental and simulation results of the second preferred embodiment of the sound-absorbing structure of the present invention. Figure 14: A schematic diagram of the decomposition of the third preferred embodiment of the sound-absorbing structure of the present invention. Figure 15: A schematic diagram of the top view of the interior of the body of the third preferred embodiment of the sound-absorbing structure of the present invention. Figure 16: A schematic diagram of the simulation results of the third preferred embodiment of the sound-absorbing structure of the present invention. Figure 17: A three-dimensional schematic diagram of the fourth preferred embodiment of the sound-absorbing structure of the present invention. Figure 18: A schematic diagram of the decomposition of the fourth preferred embodiment of the sound-absorbing structure of the present invention. Figure 19: A schematic diagram of the partial decomposition of the fourth preferred embodiment of the sound-absorbing structure of the present invention. Figure 20: A schematic diagram of the top view of the interior of the body of the fourth preferred embodiment of the sound-absorbing structure of the present invention. Figure 21: A schematic diagram of the experimental and simulation results of the third preferred embodiment of the sound-absorbing structure of the present invention. Figure 22: A schematic diagram of the implementation method of the sound-absorbing structure of the present invention being set on a wall.

10a: ontology

11: Sound-absorbing holes

12: Sound-absorbing surface

13: Partition wall

14: Upper cover

15: Lower cover

16: Outer wall

20: External structure

21: even with external chamber

22: even external pipe

221: External connection terminal

222: External opening end

30: Internal structure

31: Inner chamber

32: Internal connection pipe

321: Internal connection terminal

322: Inner opening end

Claims (10)

A sound-absorbing structure, comprising: A body, a sound-absorbing hole formed on the surface of the body, wherein the ratio of the diameter of the body to the diameter of the sound-absorbing hole is between 9.8:1 and 12.35:1, including end values; An external structure formed inside the body, the external structure having an external cavity and an external tube, the two ends of the external tube passing through and located in the external cavity, one end of the external tube connected to the sound-absorbing hole to connect to the external environment, and the other end of the external tube connected to the external cavity; and An inner structure is formed inside the body, the inner structure has an inner chamber and an inner connecting tube, the two ends of the inner connecting tube are connected and located in the inner chamber, and the inner connecting tube and the outer connecting tube are arranged at intervals, one end of the inner connecting tube is connected to the outer chamber of the outer connecting structure, and the inner chamber is connected to the outer chamber through the inner connecting tube. A sound-absorbing structure as described in claim 1, wherein the main body has a sound-absorbing surface and a partition wall, the sound-absorbing surface is formed on the outer side of the main body, the sound-absorbing hole is located on the sound-absorbing surface, the partition wall is located inside the main body and separates the external cavity and the internal cavity, and one end of the internal connecting pipe is arranged on the partition wall and connected to the external cavity. A sound-absorbing structure as described in claim 1, wherein the two ends of the external tube are respectively defined as an external connection end and an external opening end, the external connection end is connected to the external environment, the external opening end is connected to the external chamber, and the inner diameter of the external tube gradually changes from the external connection end to the external opening end. A sound-absorbing structure as described in claim 2, wherein the two ends of the external tube are respectively defined as an external connection end and an external opening end, the external connection end is connected to the external environment, the external opening end is connected to the external chamber, and the inner diameter of the external tube gradually changes from the external connection end to the external opening end. A sound absorbing structure as described in any one of claims 1 to 4, wherein the two ends of the internal connecting tube are respectively defined as an internal connecting end and an internal opening end, the internal connecting end is connected to the external chamber, the internal opening end is connected to the internal chamber, and the inner diameter of the internal connecting tube gradually changes from the internal connecting end to the internal opening end. A sound-absorbing structure as described in any one of claims 1 to 4, wherein the sound-absorbing structure includes a plurality of extension structures, the plurality of extension structures are connected in sequence and formed inside the main body, the plurality of extension structures respectively have an extension chamber and an extension tube, the extension chambers of the plurality of extension structures are connected in sequence, the extension tube of one of the plurality of extension structures is connected to the inner chamber of the inner structure, and the extension tubes of the remaining extension structures of the plurality of extension structures are connected to the extension chamber of another extension structure. A sound-absorbing structure as described in any one of claims 1 to 4, wherein the outer connecting tube and the inner connecting tube are respectively curved. A sound-absorbing structure as described in any one of claims 1 to 4, wherein the external chamber and the internal chamber are adjacent to each other on a horizontal reference plane, the external tube is connected to the external environment along a Z direction, and the internal connecting tube is connected to the external chamber along an X direction, the Z direction is perpendicular to the horizontal reference plane, and the X direction is parallel to the horizontal reference plane. A sound-absorbing structure as described in claim 8, wherein the external tube includes an external section and an extension section connected to each other, the external section extends along the Z direction, and the extension section is extended on the horizontal reference plane. The sound-absorbing structure as described in claim 8, wherein the main body is in the shape of a disk, the diameter of the main body is located on the horizontal reference plane, the external chamber and the internal chamber each have a chamber height in the Z direction, and the chamber heights of the external chamber and the internal chamber are equal.