Broadband metamaterial silencer for ventilation pipes and its design method and application

Abstract

The objective of the present invention is to provide a broadband metamaterial silencer for ventilation ducts, a design method therefor, and applications thereof, which address the problems existing in broadband noise reduction technology for ventilation ducts, and belong to the noise processing technical field. One technical solution provided by the present invention is a broadband metamaterial silencer for ventilation ducts, which may be a broadband metamaterial silencer installed outside a pipe, a broadband split-flow metamaterial silencer built into a duct, or a broadband metamaterial degenerated sound absorber. The present invention also provides a design method for the broadband metamaterial silencer for ventilation ducts, as well as technical solutions related to its application in wearable devices, indoor and outdoor air conditioning equipment, and home appliances. The silencer of the present invention can effectively reduce broadband noise in pipes.

Description

[Technical Field]

[0001] The present invention relates to the field of noise processing technology, and more particularly to a broadband metamaterial silencer and its design method and application. [Background technology]

[0002] In daily life and industrial production, heat and material accumulation often occur due to various reasons, such as heat generated inside chips and machines operating at high power, dust accumulation during factory work processes, and water vapor accumulation in wearable devices due to human breathing and sweating. Therefore, it is very important to remove excess heat and material through airflow.

[0003] Ducted ventilation is a common solution. Its advantages include high efficiency and simple design. The suction and / or push of the fan system causes air or other gases in the target space to carry heat and accumulated materials, enter the ducting system, and be expelled along a designed path.

[0004] Noise is often a problem when air flows through ducts. This type of noise has two main sources: the inherent mechanical or other internal environmental noise of the equipment, and the additional noise generated by fan systems. These two types of noise have characteristics of a wide frequency range and distinct characteristic frequencies (e.g., the noise generated by a fan has a characteristic frequency corresponding to the fan's rotation speed). This characteristic poses a significant challenge for conventional noise reduction technologies. Conventional porous sound-absorbing materials, such as sponge, rock wool, and glass fiber, have a wide operating frequency range but cannot effectively customize and enhance absorption for characteristic noise frequency bands. On the other hand, conventional acoustic resonance technologies, such as Helmholtz resonators, can highly customize operating frequencies, but their bandwidth is very narrow. Therefore, ensuring both broadband acoustic effects and the ability to customize specific frequencies in ventilation environments is an urgent issue. Summary of the Invention [Problem to be solved by the invention]

[0005] The purpose of the present invention is to provide a broadband metamaterial silencer for ventilation pipes, and its design method and application, in response to the problems existing in existing ventilation pipe broadband noise reduction technologies.

[0006] Generally, the main role of piping is to guide and circulate airflow. Therefore, it is desirable for noise reduction operations to avoid excessive obstruction to the piping itself. The best way to achieve this requirement is to install sound insulation / sound absorption materials on the side walls. For a given broadband target impedance, we can design multiple corresponding resonant units to achieve the acoustic characteristics. [Means for solving the problem]

[0007] Therefore, one of the technical solutions of the present invention is a broadband metamaterial silencer for ventilation pipes, which is a broadband metamaterial silencer outside the pipe, or a broadband branched-flow metamaterial silencer inside the pipe, or a broadband metamaterial degenerate sound absorber.

[0008] The broadband noise reduction metamaterial silencer outside the pipe includes a broadband sound insulator installed outside the pipe, a broadband sound absorber installed outside the pipe, or a combination of a broadband sound insulator and a broadband sound absorber installed outside the pipe.

[0009] The broadband branched-flow metamaterial silencer inside the pipe includes a broadband sound insulator installed inside the pipe, a broadband sound absorber installed inside the pipe, or a combination of a broadband sound insulator and a broadband sound absorber installed inside the pipe.

[0010] The broadband metamaterial degenerate sound absorber includes a plurality of acoustic perforated plates perpendicular to the wind direction inside the pipe, and a broadband metamaterial silencer outside the pipe, or a broadband divergent-flow metamaterial silencer inside the pipe, or a combination of a broadband metamaterial silencer outside the pipe and a broadband divergent-flow metamaterial silencer inside the pipe.

[0011] Furthermore, in the above-mentioned broadband metamaterial silencer for ventilation ducts, the broadband sound insulator installed outside the piping is composed of multiple resonant units installed in parallel and independent of each other, each resonant unit resonating at a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, and each resonant unit achieves a sound insulating effect by reflecting sound waves at and near the resonant frequency. The resonant units are installed on the side walls of the ventilation duct and have openings in the ventilation duct wall, or the resonant units are installed on the side walls of the ventilation duct and have openings in the ventilation duct wall, and a mesh-like covering is installed on the openings of the resonant units.

[0012] The broadband sound absorber installed outside the duct is composed of a plurality of parallel and independent resonant units, each of which has a single-frequency resonant behavior corresponding to a specific frequency band in the broadband noise to be reduced, and which achieves sound absorption by converting noise energy into thermal energy for dissipation. The resonant units are installed on the side walls of the air duct and have openings on the air duct wall, or the resonant units are installed on the side walls of the air duct and have openings on the air duct wall, and a mesh covering is installed on the openings of the resonant units.

[0013] The broadband noise insulator installed inside the piping is composed of a plurality of resonant units arranged in parallel and independent of each other, each resonant unit having a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, and each resonant unit achieves a sound insulation effect by reflecting sound waves at and near its resonant frequency. The resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, or the resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, and a mesh covering is installed at the opening of the resonant unit.

[0014] The broadband sound absorber installed inside the duct is composed of a plurality of resonating units arranged in parallel and independent of each other, each resonating unit resonating at a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, and each resonating unit achieves sound absorption by converting noise energy into thermal energy for dissipation. The resonating units are installed inside the ventilation duct and have their openings in the ventilation duct, or the resonating units are installed inside the ventilation duct and have their openings in the ventilation duct, and a mesh covering is installed at the openings of the resonating units.

[0015] In the broadband metamaterial degenerate sound absorber, each acoustic perforated plate corresponds to a specific frequency band of the broadband noise to be reduced with the broadband metamaterial silencer outside the pipe and / or the broadband branched-flow metamaterial silencer inside the pipe.

[0016] Furthermore, in the broadband metamaterial silencer for an air duct, the resonating unit includes a hard shell having an opening and air in a cavity of the hard shell.

[0017] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the resonant unit includes, but is not limited to, a Fabry-Perot (quarter wavelength) resonator, a Helmholtz resonator, and a resonator with an arbitrary cavity shape, which can block or absorb noise in a specific frequency band.

[0018] Furthermore, in the broadband metamaterial silencer for ventilation pipes, multiple resonant units are geometrically arranged with cavities of the same or different cross-sectional areas, and each cavity is curved and folded on any flat or curved surface, or in three-dimensional space.

[0019] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the acoustic perforated plate is used to filter impurities in the ventilation pipe gas.

[0020] Furthermore, in the above-mentioned broadband metamaterial silencer for ventilation pipes, the mesh covering material includes, but is not limited to, metal mesh, sponge, woven fabric, paper, glass fiber cloth, acoustic perforated plate, and any combination of the above six types of materials.

[0021] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the material of the metamaterial silencer includes, but is not limited to, metal, plastic, wood, leather, paper, ceramic, and any combination of the above six materials.

[0022] Furthermore, in the broadband metamaterial silencer for an air duct, the air duct may have any shape, including a straight pipe, a curved pipe, and a pipe with a constant or variable cross-sectional area.

[0023] The frequency band and its effect can be customized for broadband metamaterial silencers. The operating frequency of each resonant unit can be freely adjusted by designing its geometric shape. The frequency distribution of a broadband resonator can be achieved by designing multiple resonant units with different frequencies. Therefore, in principle, any desired impedance spectrum shape can be achieved by using a series of resonant units. However, in practice, a wider effective frequency band range and better sound insulation performance mean that a larger volume is required to design the resonator. Meanwhile, many noise spectra in real life often have strong frequency characteristics. Therefore, broadband noise reduction metamaterials with a customized spectrum based on the characteristics of a specific noise spectrum are the most space-saving and cost-effective solution.

[0024] Based on this, the second technical solution provided by the present invention is a design method for a broadband metamaterial silencer for an air duct, which includes the following steps:

[0025] 1) Obtain the internal structure data of the ventilation pipe, gas flow velocity and flow rate data, and noise spectrum data to be reduced, including noise intensity information.

[0026] 2) Based on the data obtained in step 1), the internal structure of the ventilation pipe is optimized to reduce the target noise intensity. After that, gas flow velocity and flow rate data and processed target noise spectrum data are obtained again.

[0027] 3) Based on the processed noise spectrum data to be reduced and the upper design volume limit of the metamaterial silencer, a wideband target impedance that will most effectively reduce the noise intensity within the target frequency band of the ventilation pipe is set, and then a type of wideband metamaterial silencer and M resonant units or K acoustic perforated plates and L resonant units in the wideband metamaterial silencer are selected, and the acoustic impedance spectrum shape of the M resonant units or K acoustic perforated plates and L resonant units is made identical to the wideband target impedance.

[0028] in particular, 3.1) When the broadband metamaterial silencer is a broadband metamaterial silencer outside the pipe or a broadband branched-flow metamaterial silencer inside the pipe 3.1.1) Fabry-Perot resonator as the resonating unit: For a given broadband target impedance, M Fabry-Perot resonators with the same cross-sectional area are designed to achieve the acoustic impedance spectrum shape Z(ω) as a function of angular frequency ω. These resonators are arranged in order from longest to shortest, and the length of the mth resonator is L. m and the corresponding primary resonance frequency is ωm=πc / (2L m ) ω m Based on the distribution of the number of modes within a unit frequency, Md Furthermore, the length of each resonator L m By adjusting ω m Distribution of M d satisfies the acoustic impedance spectrum shape Z(ω).

[0029] JPEG2026504657000002.jpg14102

[0030] JPEG2026504657000003.jpg15133

[0031] These Fabry-Perot cavities of different lengths can be folded on demand to form a compact whole for space saving. They can have regular or specific geometric features.

[0032] JPEG2026504657000004.jpg38133

[0033] JPEG2026504657000005.jpg1489

[0034] Here, the unit of Z(ω) is kg / m -2 ·s -1 is.

[0035] JPEG2026504657000006.jpg15133

[0036] JPEG2026504657000007.jpg488

[0037] M is the total number of Helmholtz resonators.

[0038] JPEG2026504657000008.jpg27133

[0039] JPEG2026504657000009.jpg980

[0040] JPEG2026504657000010.jpg20133

[0041] The above equation has the asymptotic expansion form (4).

[0042] JPEG2026504657000011.jpg671

[0043] If the frequency is not very high and the hole diameter and plate thickness are not very large, the second term and other higher-order terms in the above equation (4) can be ignored, so the acoustic impedance of the perforated plate can be approximated as a constant that is independent of frequency.

[0044] JPEG2026504657000012.jpg9133

[0045] 3.2.2) Design of broadband sound insulators or broadband sound absorbers or combinations of broadband sound insulators and broadband sound absorbers

[0046] According to the method of step 3.1), obtain a broadband sound insulator or broadband sound absorber, or a combination of a broadband sound insulator and a broadband sound absorber, whose noise reduction frequency distribution range is equal to or less than the noise reduction frequency of the acoustic perforated plate in step 3.2.1).

[0047] 3.2.3) By combining these two types of acoustic structures, the required broadband degenerate absorber is obtained.

[0048] 4) Based on the broadband metamaterial silencer designed in step 3) and its acoustic impedance spectrum shape, the materials and / or structures of the pipe inner wall, the broadband metamaterial silencer structure, and the mesh coating material are optimized again to achieve the elimination of the target frequency noise.

[0049] Furthermore, in the design method for the broadband metamaterial silencer for an air duct, the method for selecting the type of broadband metamaterial silencer in step 3) is as follows:

[0050] Here, the types of broadband metamaterial sound silencers are broadband sound insulators, broadband sound absorbers, and broadband metamaterial degenerate sound absorbers.

[0051] Step 1: If the reflected energy of broadband noise adversely affects the environment and equipment at the intake side of the ventilation duct, or if this reflected energy is reflected back into the duct, select a broadband sound absorber or a broadband metamaterial degenerate sound absorber. Otherwise, all three are applicable.

[0052] Step 2: If the overall dimension of the broadband metamaterial silencer along the sound propagation direction is less than the upper limit of the noise wavelength in the target frequency band, select a broadband sound insulator, a broadband metamaterial degenerate sound absorber, or a combination of a broadband sound absorber and a broadband sound insulator. Otherwise, all three are applicable.

[0053] Step 3: If the broadband metamaterial silencer is sensitive to the effects of airflow, choose a broadband sound insulator, a broadband sound absorber, or a combination of a broadband sound absorber and a broadband sound insulator. Otherwise, all three are applicable.

[0054] Based on the above-mentioned broadband metamaterial structure and the design method of the broadband metamaterial, the third technical solution of the present invention provides a practical application of the broadband metamaterial silencer in the scene of ventilation pipe broadband noise reduction.

[0055] The first metamaterial application provided by this invention is a broadband metamaterial silencer for ventilation pipes, which is used to reduce noise in wearable devices.

[0056] The material of the wearable device is set to an outwardly protruding hard material, and the hard material may be two or more layers, with multiple sealed cavities between adjacent hard material layers, forming a sealed inner cavity between the innermost hard material layer or a part of the innermost hard material layer and the wearer's skin. The inner cavity is connected to the other sealed cavities through holes in each hard material layer, and the inner cavity and the other cavities jointly form an air duct. The inlet of the air duct is located on the innermost hard material layer or the outermost hard material layer, and the outlet is located on the innermost hard material layer or the outermost hard material layer. The wideband metamaterial silencer is a wideband degenerate sound absorber.

[0057] Furthermore, in the application of the broadband metamaterial silencer for ventilation ducts, the material of the wearable device is set to a hard material that protrudes outward, and the hard material has two layers: an innermost hard material layer and an outer hard material layer. Two sealed cavities are formed between the two hard material layers, Cavity 1 and Cavity 3. A sealed soft pad that comes into contact with the wearer's skin is provided on the inner wall of the innermost hard material layer, forming an inner cavity between a portion of the innermost hard material layer and the wearer's skin, which is Cavity 2. Hole 1 and hole 2 are provided on the innermost hard material layer of the inner cavity. Cavity 1 communicates with Cavity 2 through Hole 1, and Cavity 2 communicates with Cavity 3 through Hole 2, so that the inner cavity, Cavity 1, and Cavity 3 together form a ventilation duct. The inlet of the ventilation pipe is located on the innermost hard material layer of cavity 1 and outside the inner cavity, and the outlet is located on the innermost hard material layer of cavity 3 and outside the inner cavity. The broadband metamaterial silencer is a broadband degenerate sound absorber, and is composed of an acoustic perforated plate and a broadband sound absorber installed outside the pipe, where the acoustic perforated plate is installed on hole 1 and hole 2, and the broadband sound absorber installed outside the pipe is installed on the side wall of cavity 1 and cavity 3, respectively.

[0058] Furthermore, in the application of the broadband metamaterial silencer for the air duct, a fan is installed at the outlet and / or inlet of the air duct.

[0059] Furthermore, in the application of the broadband metamaterial silencer for ventilation pipes, the frequency of noise reduced by the broadband metamaterial degenerate sound absorber is 800 to 8000 Hz.

[0060] Furthermore, in the application of the above-mentioned broadband metamaterial silencer for ventilation pipes, the resonant unit of the broadband sound absorber installed outside the pipe is a Helmholtz resonator, and the cavity of the Helmholtz resonator is folded back and forth to form a maze shape. There are multiple Helmholtz resonators, some of which open to the side wall of cavity 1 and others to the side wall of cavity 3.

[0061] The second application of the metamaterial provided by the present invention is a broadband metamaterial silencer for ventilation pipes, which is used to reduce ventilation pipe noise in indoor air exchange equipment.

[0062] A broadband sound absorber is installed outside the piping on the side wall of the ventilation duct located at the air outlet of the indoor air exchange equipment. The resonance unit of the broadband sound absorber is a Fabry-Perot resonator, and the cavity of the resonance unit is folded back and forth on the same plane, and multiple resonance units installed in parallel and independent of each other form a noise reduction layer that is placed on the outside of the ventilation duct. All resonance units in the noise reduction layer open to the side wall of the ventilation duct, and multiple noise reduction layers are stacked to form the broadband sound absorber.

[0063] The broadband sound absorber reduces noise frequencies in the range of 200 to 8000 Hz.

[0064] The third application of the metamaterial provided by the present invention is a broadband metamaterial silencer for ventilation pipes, which is used to reduce ventilation pipe noise in outdoor heating and ventilation equipment.

[0065] A broadband sound absorber is installed inside the duct of an outdoor heating and ventilation system. The resonating unit of the broadband sound absorber is a Fabry-Perot resonator, and the cavity of the resonating unit is folded back and forth on the same plane, and multiple resonating units installed in parallel and independent of each other form a broadband sound absorber of rectangular, V-shaped, concave-convex, louver-shaped, array-shaped, or other shape, and all resonating units open into the inside of the duct.

[0066] The broadband sound absorber reduces noise frequencies in the range of 200 to 8000 Hz.

[0067] The fourth application of the metamaterial provided by the present invention is a broadband metamaterial silencer for ventilation pipes, which is used to reduce noise from the intake pipe of a gas water heater.

[0068] A broadband noise insulator is installed outside the piping on the side wall of the ventilation duct located at the entrance of the centrifugal fan of a gas water heater.The resonance unit of the broadband noise insulator is a Fabry-Perot resonator, and the cavity of the resonance unit is folded back and forth on the same plane, and the broadband noise insulator that is placed on the outside of the piping is composed of multiple resonance units that are installed in parallel and independent of each other, and all of the resonance units open on the side wall of the ventilation duct.

[0069] The broadband sound insulator reduces noise frequencies in the range of 200 to 4000 Hz.

[0070] The fifth application of the metamaterial provided by the present invention is a broadband metamaterial silencer for ventilation ducts, which is used to reduce noise from the ventilation ducts of power equipment components (including, but not limited to, pumps, compressors, motors, etc.). A broadband silencer installed outside the duct is installed on the sidewall of the duct at the outlet and / or inlet of the duct of the casing of the power equipment component. The resonant unit of the broadband silencer is a Fabry-Perot resonator, and the cavity of the resonant unit is folded back and forth on a single plane. A wide range of resonant units, each installed in parallel and independent of each other, constitute the broadband silencer to be placed over the outside of the duct, with each resonant unit opening onto the sidewall of the duct.

[0071] The broadband sound insulator reduces noise frequencies between 160 and 4000 Hz.

[0072] Compared to existing technologies, the advantages of this invention are as follows:

[0073] 1. The broadband metamaterial silencer of the present invention adopts a broadband metamaterial silencer outside the pipe, or a broadband branched-flow metamaterial silencer or a broadband metamaterial degenerate sound absorber inside the pipe, to efficiently achieve broadband noise reduction in the pipe.

[0074] 2. The metamaterial silencer of the present invention offers significant advantages over other conventional technologies in its application in wearable devices. Because wearable devices come into close contact with the human body, ventilation is essential. However, ventilation inherently contradicts good noise reduction and sound insulation. The ventilation noise reduction properties of metamaterials offer significant advantages for reducing the noise of heat-dissipating components such as fans within devices or for blocking external noise from signal collection within internal devices. Meanwhile, lightweight construction is also crucial for wearable devices. The customizable nature of broadband metamaterial technology allows for maximum acoustic performance with minimal space and material, thereby effectively controlling the overall device weight. Finally, because it is based on materials such as plastic and silicone gel and does not contain conventional porous sound-absorbing materials, this metamaterial silencer structure effectively avoids the absorption of water vapor and various foreign substances generated by human breathing and sweating, and is easily removable and cleaned. This characteristic fully meets the hygienic requirements of wearable devices.

[0075] 3. The metamaterial silencer of the present invention has the following advantages when applied to indoor and outdoor heating and ventilation equipment. First, the function of the metamaterial silencer is based on structural design and does not contain traditional fibrous porous materials, posing no potential harm to human health. Second, its internal structure is free from problems such as water accumulation and mold growth, ensuring a long service life and allowing it to be used in high-standard environments such as clean rooms and dust-free rooms. Furthermore, the operating spectrum of the metamaterial silencer can be customized to suit the different noise characteristics of different equipment, focusing its sound absorption or sound insulation capabilities on the main noise frequency band to more efficiently reduce overall noise. For special applications such as high-temperature resistance, the silencer's resonant unit can be made of pure metal materials, thereby meeting corresponding requirements.

[0076] 4. The metamaterial silencer of the present invention has the following advantages when applied to home appliances. First, by combining the structural design with the limited available space inside the home appliance and customizing it to target key noise energy frequency bands, it can achieve effective noise reduction from 200 Hz in a limited space of within a few centimeters, thereby most efficiently reducing equipment noise without affecting other performance. Furthermore, the resonating unit of the silencer can be made of the same material as the internal connection points, thereby maintaining the integrity of the original structure in appearance. [Brief explanation of the drawings]

[0077] [Figure 1] This is a schematic diagram of the cross-sectional structure of a wideband branched-flow metamaterial silencer inside a pipe that forms a direct air passage inside the pipe. [Figure 2] This is a schematic diagram of the cross-sectional structure of a wideband branched-flow metamaterial silencer inside a pipe that forms a V-shaped air passage inside the pipe. [Figure 3] This is a schematic diagram of the cross-sectional structure of a wideband branched-flow metamaterial silencer inside a pipe that forms a concave-convex air passage inside the pipe. [Figure 4]This is a schematic diagram of the cross-sectional structure of a broadband metamaterial silencer outside a pipe, with a mesh coating material installed on the opening of the resonator unit. [Figure 5] FIG. 1 is a schematic diagram of the cross-sectional structure of a broadband metamaterial degenerate sound absorber. [Figure 6] FIG. 6 is a noise absorption coefficient curve diagram of the broadband metamaterial degenerate sound absorber of FIG. 5. [Figure 7] This is a schematic diagram of the three-dimensional structure of a wideband sound insulator or wideband sound absorber in which multiple resonant unit cavities with different cross-sectional areas are arranged in a rectangular parallelepiped, and each cavity is folded in an L-shape and back-and-forth manner on a single plane. [Figure 8] This is a schematic diagram of the three-dimensional structure of a wideband sound insulator or wideband sound absorber in which multiple resonant unit cavities with different cross-sectional areas are arranged in a rectangular parallelepiped, and each cavity is folded into a U-shape on a single plane. [Figure 9] This is a schematic diagram of the three-dimensional structure of a wideband sound insulator or wideband sound absorber in which multiple resonant unit cavities with different cross-sectional areas are arranged in a rectangular prism outside an inner circle, and each cavity is folded into a U-shape on a single plane. [Figure 10] This is a schematic diagram of the three-dimensional structure of a wideband sound insulator or wideband sound absorber in which multiple resonant unit cavities with the same cross-sectional area are arranged in a rectangular parallelepiped, and each cavity is folded in a U-shape and back-and-forth manner in three-dimensional space. [Figure 11] FIG. 1 is a schematic diagram of the cross-sectional structure of a two-dimensional curved pipe provided with a broadband metamaterial silencer outside the pipe. [Figure 12] This is a schematic diagram of the cross-sectional three-dimensional structure of a three-dimensional curved pipe in which a wideband metamaterial degenerate sound absorber with a resonant unit opening on the side wall is installed. [Figure 13] 1 is a schematic diagram of the three-dimensional structure of a wideband sound absorber outside a pipe according to a first embodiment. FIG. [Figure 14] 1 is a schematic diagram showing the planar structure of a noise reduction piece layer formed in the resonance unit of Example 1. FIG. [Figure 15] FIG. 1 is a noise reduction effect diagram of the wideband metamaterial silencer of Example 1. [Figure 16]FIG. 10 is a partial schematic plan view of the structure of a wideband sound absorber installed inside a pipe according to a second embodiment. [Figure 17] FIG. 10 is a schematic diagram of the three-dimensional structure of a wideband sound absorber inside a pipe that forms a straight air passage in an air duct according to a second embodiment. [Figure 18] FIG. 10 is a diagram showing the layout of a wideband sound absorber in a ventilation pipe inside a piping that forms a straight air passage according to a second embodiment. [Figure 19] FIG. 10 is a schematic diagram of the three-dimensional front structure of the wearable device and the broadband metamaterial silencer for ventilation pipes of Example 3. [Figure 20] FIG. 10 is a schematic diagram of the three-dimensional rear structure of the wearable device and the broadband metamaterial silencer for ventilation pipes of Example 3. [Figure 21] FIG. 10 is a schematic diagram of the back structure of the outer hard material layer of the wearable device of Example 3. [Figure 22] FIG. 10 is a schematic diagram of the cross-sectional structure of a wideband metamaterial silencer for a wearable device according to a third embodiment. [Figure 23] FIG. 10 is a schematic diagram of a cross-sectional structure of a wide-band sound insulator according to a fourth embodiment. [Figure 24] FIG. 10 is a transmission loss spectrum diagram of the wideband sound insulator of Example 4. [Figure 25] FIG. 10 is a schematic diagram of the three-dimensional structure of a wide-band sound insulator according to a fifth embodiment. [Figure 26] FIG. 10 is a transmission loss spectrum diagram of the broadband sound insulator of Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0078] The present invention provides a broadband metamaterial silencer for ventilation pipes and its design method and application.

[0079] Generally, the main role of piping is to guide and circulate airflow. Therefore, it is desirable for noise reduction operations to avoid excessive obstruction to the piping itself. The best way to achieve this requirement is to install sound insulation / sound absorption materials on the side walls. For a given broadband target impedance, we can design multiple corresponding resonant units to achieve the acoustic characteristics.

[0080] A broadband metamaterial silencer for an air duct (1), the metamaterial silencer being a broadband metamaterial silencer (3) outside the duct, or a broadband branched flow metamaterial silencer (2) inside the duct, or a broadband metamaterial degenerate sound absorber.

[0081] Here, the broadband metamaterial silencer outside the pipe includes a broadband sound insulator installed outside the pipe, a broadband sound absorber installed outside the pipe, or a combination of a broadband sound insulator and a broadband sound absorber installed outside the pipe.

[0082] When the pipe diameter is relatively large, such as in a heating, ventilation, and air conditioning system, in addition to installing metamaterials on the pipe sidewalls, several branching metamaterial structures are usually added inside the pipe to increase the design space and opening area of ​​the metamaterial resonator unit and effectively raise the cutoff frequency of the silencer's operation. Branching metamaterial silencers inside pipes include broadband sound insulators installed inside the pipe, broadband sound absorbers installed inside the pipe, or a combination of broadband sound insulators and broadband sound absorbers installed inside the pipe. Branching metamaterial silencers are installed on one or both sides of the pipe, or surrounding the pipe, creating a straight, V-shaped, or concave-convex airway inside the pipe (see Figures 1-3).

[0083] The ability to achieve high sound absorption at scales much smaller than the wavelength is important in practical applications. On the one hand, in many practical scenarios, there may not be enough pipe sidewall area to provide openings for connecting metamaterial structures due to various constraints. On the other hand, minimizing the opening area of ​​the resonant structure can also reduce nonlinear effects on airflow. Therefore, a broadband degenerate sound absorber can be adopted as a sound absorber. Broadband metamaterial degenerate sound absorbers include multiple acoustic perforated plates perpendicular to the wind direction inside the pipe, and a broadband metamaterial sound absorber outside the pipe, a broadband diverging-flow metamaterial sound absorber inside the pipe, or a combination of a broadband metamaterial sound absorber outside the pipe and a broadband diverging-flow metamaterial sound absorber inside the pipe.

[0084] Furthermore, in the above-mentioned broadband metamaterial silencer for ventilation ducts, the broadband sound insulator installed outside the piping is composed of multiple resonant units installed in parallel and independent of each other, each resonant unit resonating at a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, and the resonant units achieve the sound insulation effect by reflecting sound waves at the resonant frequency and its nearby frequencies (in theory, a resonant unit with a high quality factor achieves the sound insulation effect by reflecting sound waves at the resonant frequency, but in reality, due to the dissipation situation of the system during the resonant unit's reflection of sound waves, the quality factor decreases and the resonant bandwidth increases, and the resonant unit reflects sound waves with a certain bandwidth near the resonant frequency). The resonant units are installed on the side wall of the ventilation duct and have an opening on the ventilation duct wall, or the resonant units are installed on the side wall of the ventilation duct and have an opening on the ventilation duct wall, and a mesh covering is installed on the opening of the resonant unit.

[0085] The broadband sound absorber installed outside the duct is composed of a plurality of parallel and independent resonant units, each of which has a single-frequency resonant behavior corresponding to a specific frequency band in the broadband noise to be reduced, and which achieves sound absorption by converting noise energy into thermal energy for dissipation. The resonant units are installed on the side walls of the air duct and have openings on the air duct wall, or the resonant units are installed on the side walls of the air duct and have openings on the air duct wall, and a mesh covering is installed on the openings of the resonant units.

[0086] The broadband sound isolator installed inside the piping is composed of multiple resonant units installed in parallel and independent of each other, each resonant unit resonating at a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, and the resonant units achieve their sound insulation effect by reflecting sound waves at and near their resonant frequency (in theory, a resonant unit with a high quality factor achieves its sound insulation effect by reflecting sound waves at the resonant frequency, but in reality, due to the dissipation of the system during the resonant unit's sound reflection process, the quality factor decreases and the resonant bandwidth increases, and the resonant unit reflects sound waves with a certain bandwidth near the resonant frequency). The resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, or the resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, and a mesh covering is installed at the opening of the resonant unit.

[0087] The broadband sound absorber installed inside the duct is composed of a plurality of resonating units arranged in parallel and independent of each other, each resonating unit resonating at a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, and each resonating unit achieves sound absorption by converting noise energy into thermal energy for dissipation. The resonating units are installed inside the ventilation duct and have their openings in the ventilation duct, or the resonating units are installed inside the ventilation duct and have their openings in the ventilation duct, and a mesh covering is installed at the openings of the resonating units.

[0088] A layer of mesh covering material 4 (see Figure 4), such as metal mesh, sponge, woven fabric, paper, glass fiber cloth, acoustic perforated sheet, or a combination thereof, is added to the opening 5 of the resonator unit. These coverings not only effectively mitigate the whistling problem, but also act as a physical barrier. They prevent foreign objects from entering the resonator unit and generating additional noise or causing safety issues. They also prevent particulate matter such as dust from entering or accumulating at the exit or inside of the resonator unit, which could affect the service life of the metamaterial.

[0089] In the broadband metamaterial degenerate sound absorber, each acoustic perforated plate corresponds to a specific frequency band of the broadband noise to be reduced, such as a broadband metamaterial silencer outside the pipe and / or a broadband branched-flow metamaterial silencer inside the pipe. Figure 5 shows an example of a broadband metamaterial degenerate sound absorber consisting of two acoustic perforated plates 6 and a broadband metamaterial silencer outside the pipe, and as shown in Figure 6, the absorption rate exceeds 94% in both cases in the frequency range of 130 to 3000 Hz.

[0090] Furthermore, in the broadband metamaterial silencer for an air duct, the resonating unit includes a hard shell having an opening and air in a cavity of the hard shell.

[0091] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the resonant unit includes, but is not limited to, a Fabry-Perot resonator, a Helmholtz resonator, and a resonator with an arbitrary cavity shape, which can block or absorb noise in a specific frequency band. The acoustic effect of the resonant unit is related to its geometric shape.

[0092] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the multiple resonant units of the broadband sound insulator or absorber are geometrically arranged in cavities with the same or different cross-sectional areas, and each cavity is curved and folded on a flat or curved surface (see Figures 7 to 9) or in three-dimensional space (see Figure 10). The overall shape of the broadband resonator can be regular or irregular, and can be customized according to the geometric requirements and limitations of specific application scenarios (see Figures 7 to 10).

[0093] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the ventilation pipe can have any shape. In addition to being straight (see Figures 1, 4, and 5), the pipe shape can also be two-dimensionally curved (see Figures 2, 3, and 11), three-dimensionally curved (see Figure 12), etc. Along the sound wave propagation direction, the cross-sectional area of ​​the pipe can be constant (see Figure 1) or can vary (see Figure 11), and the pipe cross-sectional dimensions can vary from a few millimeters to tens of centimeters. A rational curvature of the pipe can increase multiple scattering during the sound wave propagation process, thereby significantly improving the absorption capacity of the resonators located on the side walls of the pipe.

[0094] Furthermore, in the broadband metamaterial silencer for ventilation pipes, the acoustic perforated plate is used to filter impurities in the ventilation pipe gas.

[0095] The introduction of acoustic perforated plates has potential benefits beyond acoustics. For example, their mesh structure can provide a certain level of filtering for particulate matter such as dust. Furthermore, multiple acoustic perforated plate structures can be used to simultaneously achieve multi-stage acoustic and material filtering effects, improving the practicality of the product. Taking Figure 12 as an example, an array of such acoustic perforated plates can divide the ventilation duct into different cavities, thereby preventing cross-contamination between different cavities to some extent. For example, in the ventilation system of a wearable device, the wearing cavity is frequently exposed to water vapor from breathing, while the connected cavity contains a complex metamaterial structure and electronic system. An acoustic perforated plate structure designed into the ventilation system can provide acoustic benefits while effectively preventing water vapor from contaminating adjacent cavities.

[0096] Furthermore, in the above-mentioned broadband metamaterial silencer for ventilation pipes, the mesh covering material includes, but is not limited to, metal mesh, sponge, woven fabric, paper, glass fiber cloth, acoustic perforated plate, and any combination of the above six types of materials.

[0097] Furthermore, in the broadband metamaterial silencer for air ducts, the hard shell can be made of, but is not limited to, metal, plastic, wood, leather, paper, ceramic, and any combination of the above six materials.

[0098] The frequency band and its effect of the broadband metamaterial silencer can be customized. The operating frequency of each resonator unit can be freely adjusted by designing the geometric shape, and the frequency distribution ω of the broadband resonator can be m Since the impedance of a given spectrum can be achieved by designing multiple resonant units with different frequencies, in principle, any desired spectral shape can be realized by a series of resonant units. However, in practice, a wider effective frequency band range and better sound insulation performance mean that a larger volume is required to design the resonators. Meanwhile, many noise spectra in real life often have strong frequency characteristics. Therefore, broadband noise reduction metamaterials with a customized spectrum based on the characteristics of a specific noise spectrum are the most space-saving and cost-effective solution.

[0099] Based on this, the second technical solution provided by the present invention is a design method for a broadband metamaterial silencer for an air duct, which includes the following steps:

[0100] 1) Obtain the internal structure data of the ventilation pipe, gas flow velocity and flow rate data, and noise spectrum data to be reduced, including noise intensity information.

[0101] 2) Based on the data obtained in step 1), the internal structure of the ventilation pipe is optimized to reduce the target noise intensity. After that, gas flow velocity and flow rate data and processed target noise spectrum data are obtained again.

[0102] 3) Based on the processed noise spectrum data to be reduced and the upper design volume limit of the metamaterial silencer, a wideband target impedance that will most effectively reduce the noise intensity within the target frequency band of the ventilation pipe is set, and then a type of wideband metamaterial silencer and M resonant units or K acoustic perforated plates and L resonant units in the wideband metamaterial silencer are selected, and the acoustic impedance spectrum shape of the M resonant units or K acoustic perforated plates and L resonant units is made identical to the wideband target impedance.

[0103] in particular,

[0104] 3.1) When the broadband metamaterial silencer is a broadband metamaterial silencer outside the pipe or a broadband branched-flow metamaterial silencer inside the pipe;

[0105] 3.1.1) Fabry-Perot resonator as the resonant unit

[0106] JPEG2026504657000013.jpg38133

[0107] The constraint between them is expressed by the following relational expression (1).

[0108] JPEG2026504657000014.jpg773

[0109] JPEG2026504657000015.jpg15133

[0110] These Fabry-Perot cavities of different lengths can be folded on demand to form a compact whole for space saving. They can have regular or specific geometric features.

[0111] 3.1.2) When using a Helmholtz resonator as the resonating unit

[0112] JPEG2026504657000016.jpg32133

[0113] The constraint relation (2) between them is as follows:

[0114] JPEG2026504657000017.jpg752

[0115] Here, the unit of Z(ω) is kg / m -2 ·s -1 is.

[0116] JPEG2026504657000018.jpg15133

[0117] JPEG2026504657000019.jpg488

[0118] M is the total number of Helmholtz resonators.

[0119] JPEG2026504657000020.jpg27133

[0120] JPEG2026504657000021.jpg879

[0121] JPEG2026504657000022.jpg20133

[0122] The above equation has the asymptotic expansion form (4).

[0123] JPEG2026504657000023.jpg771

[0124] If the frequency is not very high and the hole diameter and plate thickness are not very large, the second term and other higher-order terms in the above equation (4) can be ignored, so the acoustic impedance of the perforated plate can be approximated as a constant that is independent of frequency.

[0125] JPEG2026504657000024.jpg9133

[0126] 3.2.2) Design of broadband sound insulators or broadband sound absorbers or combinations of broadband sound insulators and broadband sound absorbers

[0127] According to the method of step 3.1), obtain a broadband sound insulator or broadband sound absorber, or a combination of a broadband sound insulator and a broadband sound absorber, whose noise reduction frequency distribution range is equal to or less than the noise reduction frequency of the acoustic perforated plate in step 3.2.1).

[0128] 3.2.3) By combining these two types of acoustic structures, the required broadband degenerate absorber is obtained.

[0129] When using a broadband metamaterial silencer in practice, if the noise reduction requirements are not particularly high, the specific parameters of the perforated plate can be relaxed to some extent at the expense of absorption performance. However, the presence of such a perforated plate in a pipe will inevitably bring about a certain amount of wind resistance, so in practical applications, the balance needs to be optimized according to the airflow requirements.

[0130] 4) Based on the broadband metamaterial silencer designed in step 3) and its acoustic impedance spectrum shape, the materials and / or structures of the pipe inner wall, the broadband metamaterial silencer structure, and the mesh coating material are optimized again to achieve the elimination of the target frequency noise.

[0131] Furthermore, in the design method for the broadband metamaterial silencer for an air duct, the method for selecting the type of broadband metamaterial silencer in step 3) is as follows:

[0132] Here, the types of broadband metamaterial sound silencers are broadband sound insulators, broadband sound absorbers, and broadband metamaterial degenerate sound absorbers.

[0133] Step 1 If the reflected energy of broadband noise adversely affects the environment and equipment at the intake side of the ventilation duct, or if this reflected energy is reflected back into the duct, then a broadband sound absorber or a broadband metamaterial degenerate sound absorber should be selected. Otherwise, all three types are applicable.

[0134] Step 2 If the overall dimensions of the broadband metamaterial silencer along the sound propagation direction are less than the upper limit of the noise wavelength in the target frequency band, then either a broadband sound insulator, a broadband metamaterial degenerate sound absorber, or a combination of a broadband sound absorber and a broadband sound insulator can be selected. Otherwise, all three are applicable.

[0135] Step 3 If the broadband metamaterial silencer is sensitive to the influence of airflow, choose a broadband sound insulator or a broadband sound absorber or a combination of a broadband sound absorber and a broadband sound insulator. Otherwise, all three are applicable.

[0136] The following describes specific applications of the broadband metamaterial silencer and design method based on the technical solution of the present invention.

[0137] Example 1 Noise reduction application of broadband metamaterial silencers in indoor air exchange equipment The indoor air exchange equipment has a circular outlet with a diameter of 160 mm, and its noise energy is mainly concentrated in the frequency range of 250 to 3000 Hz, with a prominent characteristic noise around 290 Hz. The available space for the metamaterial silencer design is such that the external lateral dimensions do not exceed the equipment itself, and the internal dimensions are equal to or larger than the outlet dimensions.

[0138] Through spectral analysis and customization, the broadband metamaterial silencer of this example was selected as a broadband sound absorber installed outside the duct, and the resonant unit of the broadband sound absorber was a Fabry-Perot resonator. The resonant unit aperture was designed to be concentrated on the side wall of the air duct of the indoor air exchange equipment, with the aperture dimensions of 1 cm x 1 cm. The cavity of the resonant unit was folded into a U-shape on the same plane. Eighteen parallel, mutually independent resonant units constituted the noise reduction strip layer 12 to be placed on the outside of the air duct. Multiple noise reduction strip layers were stacked to form a pipe-shaped broadband sound absorber with an inner circle outside (see Figures 13 and 14). Its outer dimensions were 245 mm, and the inner circle maintained the same 160 mm diameter as the original air duct of the indoor air exchange equipment, with a ventilation flow rate of 325 m3. 3 / h. The broadband sound absorber's absorption capacity is focused on the critical noise frequency band, i.e., above 250 Hz, thereby achieving an overall noise reduction of 13 decibels within a half-meter length. This is superior to the 9 decibel noise reduction achieved by the original 1-meter length of traditional noise reduction pipe (glass fiber) (see Figure 15 for a comparison of noise reduction effects). With a total length of 1 meter, an effect of over 26 decibels can be achieved, reducing the final sound power level at the outlet to approximately 40 A-characteristic decibels. The noise frequency range reduced by this broadband sound absorber is 200 to 8000 Hz. At the same time, this broadband sound absorber does not contain any porous or fibrous materials, is free of substances harmful to the human body, such as dust particles, does not absorb water, is not prone to mold, and has a long service life, making it particularly suitable for use in fresh air systems in homes, offices, and commercial facilities, which are closely related to human health.

[0139] Example 2 Noise reduction application of broadband metamaterial silencers in large outdoor heating and ventilation systems. Noise from large outdoor heating and ventilation equipment is generated by the fans above and the compressors below. It primarily covers a broad frequency range from 200 to 4000 Hz, with the lower frequencies accounting for the majority of the energy. This puts high demands on ventilation and heat dissipation requirements for the entire equipment. The metamaterial broadband silencer designed to address this type of industrial noise is a broadband sound absorber designed for installation inside the ventilation duct. The resonant units are Fabry-Perot resonators, and each broadband absorber contains 36 resonant units with reciprocating cavities folded on the same plane. The 36 resonant units are installed in parallel and independent of each other, forming a 100 mm thick flat plate. As shown in Figure 16, a single-reflection absorption coefficient exceeding 0.99 can be achieved across the entire target frequency band.

[0140] The broadband sound absorber of this embodiment can be integrated into various shapes, including rectangular, V-shaped, concave-convex, louver-shaped, array-shaped, and other shapes. A rectangular array is shown in Figure 1, a V-shaped array in Figure 2, and a concave-convex array in Figure 3. Various shapes of air passages 13 can be formed inside the pipe (Figures 17 and 18 show examples of straight air passages). Furthermore, the broadband sound absorber of this embodiment can be customized with parameters such as different thicknesses (30 cm to 200 cm) and ventilation rates (20% to 70%) depending on the actual application, thereby forming a multi-shaped broadband branch-flow metamaterial silencer in the pipe. This can provide a greater ventilation rate than conventional silencers while achieving better noise absorption and insertion loss. The noise frequency that the broadband sound absorber of this embodiment reduces is between 200 and 8,000 Hz.

[0141] Example 3 Noise reduction application of broadband metamaterial silencers in wearable devices The metamaterial silencer of the present invention offers significant advantages over other conventional technologies for application in wearable devices. Because wearable devices come into close contact with the human body, ventilation is essential. However, ventilation inherently contradicts good noise reduction and sound insulation. The ventilated noise reduction properties of metamaterial silencers offer significant advantages for reducing the noise of heat-dissipating components such as fans within devices or for blocking external noise from signal collection within the device. Lightweightness is also crucial for wearable devices. The customizable nature of broadband metamaterial silencer technology allows for maximum acoustic performance with minimal space and material, thereby effectively controlling the overall device weight. Finally, because it is based on materials such as plastic and silicone gel and does not contain conventional porous sound-absorbing materials, the structure and materials of the broadband metamaterial silencer of the present invention effectively prevent the absorption of water vapor and various foreign substances within the device and allow for easy removal and direct cleaning. This characteristic fully meets the hygienic requirements of wearable devices.

[0142] Wearable devices are sensitive to the mass and volume of components, have large ventilation demands, and even require fans to remove water vapor generated by breathing and sweating. This requires a broadband metamaterial silencer to achieve the best possible noise reduction effect while minimizing volume and increasing ventilation. This poses a significant challenge to conventional silencer design concepts. In this solution, as shown in Figures 19-22, the wearable device is made of a hard material with two protruding outward layers: innermost hard material layer 9 and outer hard material layer 10. Two sealed cavities are formed between the two hard material layers, Cavity 1 901 and Cavity 3 902. A sealed soft pad 908 is provided on the inner wall of the innermost hard material layer, which contacts the wearer's skin. An inner cavity, Cavity 2 903, is formed between a portion of the innermost hard material layer and the wearer's skin. The innermost hard material layer of the inner cavity has vias 1 904 and 2 905. Cavity 1 communicates with cavity 2 through vias 1, and cavity 2 communicates with cavity 3 through vias 2. Cavities 2, 1, and 3 jointly form an air duct. The inlet 906 of the air duct is located on the innermost hard material layer of cavity 1 and outside the inner cavity. The outlet 907 of the air duct is located on the innermost hard material layer of cavity 3 and outside the inner cavity. The broadband metamaterial silencer is a broadband degenerate sound absorber, and is composed of an acoustic perforated plate and a broadband sound absorber 11 installed outside the pipe. The acoustic perforated plate is installed on vias 1 and 2, and the broadband sound absorber installed outside the pipe is installed on the sidewalls of cavities 1 and 3, respectively. For the first time, we have designed a nested maze-structured Helmholtz resonator 909 as a resonating unit, which is designed as a curved and intertwined cavity in a maze-like shape.

[0143] In the application of this broadband metamaterial silencer to noise reduction in wearable devices, the airflow is as follows: external air enters cavity 1 through the inlet of the air duct on cavity 1 and then passes through the small holes in the acoustic perforated plate on channel 1 into cavity 2. The air becomes humid in cavity 2 as it carries water vapor exhaled from the human body. This humid air then passes back through the small holes in the acoustic perforated plate on channel 2 into cavity 3 and finally exits through the outlet of the air duct on cavity 3. Fans can be installed at the inlet and / or outlet to increase airflow within the air duct. This circulation keeps the air throughout the air duct, especially in cavity 2, dry, while also providing a more comfortable wearing experience for the wearer in hot weather. It is worth noting that during the design process, we considered two requirements: low wind resistance and uniform airflow across the surface of cavity 2. We conducted multiple iterative optimization simulations to ultimately arrive at the air duct design described in this example.

[0144] The noise reduction process of the broadband metamaterial silencer of this embodiment is as follows: External noise enters cavities 1 and 3 through the inlet and outlet of the ventilation pipe, respectively, and is further attenuated by the Helmholtz resonators, which are the resonating units of the broadband sound absorber installed outside the pipe. The noise then passes through two acoustic perforated plates, holes 1 and 2, for further noise reduction. After most of the sound energy is absorbed, a small amount of the remaining sound energy can enter cavity 2. The broadband sound absorber installed outside the pipe is designed with multiple independent Helmholtz resonators 909 outside cavities 1 and 3, based on the design concept of the broadband metamaterial silencer described above and the spectral characteristics of human auditory sensitivity. Each resonating unit (Helmholtz resonator) is folded into a maze shape and communicates with cavity 1 or cavity 3 through openings 5 ​​with different areas (3.4 to 5.7 square mm, see Figures 21 and 22). Because the opening area is small, it is difficult for airflow and water vapor to enter the resonator through the opening, but sound can easily enter and be absorbed by the resonator due to its resonance behavior. Therefore, this nested labyrinth-structure broadband metamaterial silencer continuously absorbs noise propagating from cavities 1, 2, and 3 without affecting the airflow, thereby achieving effective noise reduction while ensuring sufficient airflow.

[0145] We tested the insertion loss of ten samples of this broadband silencer in a 3m x 3m x 3m anechoic chamber in accordance with the ISO 717-1 2013 standard. The test results showed that the insertion loss of the component was significantly higher than that of a control group without metamaterial in the silencer's design frequency range, i.e., 800 to 8000 Hz. The equivalent insertion loss of the component under white noise testing was 25.3 ± 0.3 A-weighted decibels, and under voice testing it was 21.6 ± 0.3 A-weighted decibels. Meanwhile, the test results for the control group without metamaterial structure design under the same conditions were 17.4 A-weighted decibels (white noise) and 10.3 A-weighted decibels (voice), respectively.

[0146] JPEG2026504657000025.jpg21133

[0147] Example 4 Application of broadband metamaterial silencer in water heater fan noise reduction The noise generated by a gas water heater is primarily generated by a small centrifugal fan inside the water heater housing. The outlet is directed outdoors through an exhaust pipe. However, the air duct at the intake port is exposed on the rear panel of the water heater. Air is typically directed to the fan through an opening in the rear panel, making this the primary path for fan noise propagation indoors. The primary noise energy covers a frequency range of 200 to 3000 Hz, and the interior space is very compact. Through spatial and spectral analysis, a broadband metamaterial silencer corresponding to the fan intake port is designed. The design requirements are to maintain the diameter of the metamaterial silencer's intake port consistent with the original intake port, thereby reducing the impact on ventilation efficiency, and to ensure the entire structure fits within the original lateral area of ​​the fan, avoiding interference with other original structures. The broadband metamaterial silencer employed in this study is a broadband noise isolator for the exterior of the piping (see Figure 23), and the resonating unit of the broadband noise isolator is a Fabry-Perot resonator. The cavity of the resonator unit is folded back and forth on the same plane, and ten resonator units are installed in parallel and independent of each other to form a broadband sound insulator outside the pipe. The opening of the resonator unit is a rectangular structure measuring 10mm x 20mm and is located on the side wall of the pipe. The overall thickness of the sound insulator is 22mm, covering the important noise frequency band, forming a broadband sound insulator from 200 to 4000 Hz, and achieving a noise reduction effect of approximately 8 decibels on a single centrifugal fan (see Figure 24).

[0148] Example 5 Application of broadband metamaterial silencers in the ventilation ducts of power equipment components (including but not limited to pumps, compressors, motors, etc.)

[0149] Under typical conditions, significant noise problems exist in some equipment's power components (including, but not limited to, pumps, compressors, and motors). Due to their heat dissipation requirements, power components cannot be completely sealed, making them a major source of noise transmission within a room. Therefore, effective noise reduction while maintaining ventilation is necessary. Conventional porous materials cannot provide efficient noise reduction at low frequencies due to space limitations, and they are prone to water absorption and damping, making them ineffective noise reduction methods. In this example, a broadband metamaterial silencer is designed as a broadband noise reduction metamaterial silencer for the exterior of a pipe. It is installed at the outlet vent of the equipment's power component housing, while maintaining a constant outlet diameter. The broadband noise reduction metamaterial silencer for the exterior of a pipe is a broadband sound insulator (see Figure 25), and the resonating unit of the broadband sound insulator is a Fabry-Perot resonator. The cavity of the resonating unit is folded back and forth on a single plane, and the exterior of the pipe is composed of ten parallel, mutually independent resonating units. The resonator unit is a rectangular cavity with a diameter of 9mm x 22mm, and its opening is located on the side wall of the circular outlet pipe of the power component housing with a diameter of 41mm. The overall thickness of the broadband noise isolator is approximately 24mm, and its horizontal structure is an irregular quadrilateral. This broadband noise isolator covers the main broadband noise band starting at 160 Hz, reducing noise frequencies from 160 to 4000 Hz with an average transmission loss of over 6 decibels (see Figure 26). Furthermore, based on the characteristics of a pure structural absorption noise reduction principle, it is not affected by factors such as humidity and dust, and can maintain stable noise reduction performance for a long period of time. [Explanation of symbols]

[0150] 1, ventilation pipe; 2. Broadband branched flow metamaterial silencer inside pipe; 3. Broadband metamaterial silencer outside the pipe; 4, mesh covering material; 5, opening; 6, acoustic perforated plate; 7, resonant unit cavity; 8, resonance unit; 9. The innermost hard material layer; 10, outer hard material layer; 11. Broadband sound absorber installed outside the piping; 12. Noise reduction sheet; 13, wind path; 901, cavity one; 902, cavity three; 903, Cavity 2; 904, Kong Luichi; 905, Kong Luji; 906, entrance; 907, exit; 908, sealed soft pad; 909. Helmholtz resonator

Claims

1. A broadband metamaterial silencer for an air duct, comprising: The metamaterial silencer is a broadband metamaterial silencer outside the pipe, or a broadband branched-flow metamaterial silencer inside the pipe, or a broadband metamaterial degenerate sound absorber; The broadband noise reduction metamaterial silencer outside the pipe includes a broadband sound insulator installed outside the pipe, a broadband sound absorber installed outside the pipe, or a combination of a broadband sound insulator and a broadband sound absorber installed outside the pipe, The broadband branched-flow metamaterial silencer inside the pipe includes a broadband sound insulator installed inside the pipe, a broadband sound absorber installed inside the pipe, or a combination of a broadband sound insulator and a broadband sound absorber installed inside the pipe, the broadband metamaterial degenerate sound absorber includes a plurality of acoustic perforated plates perpendicular to the wind direction inside the pipe, and a broadband metamaterial silencer outside the pipe, or a broadband divergent-flow metamaterial silencer inside the pipe, or a combination of a broadband metamaterial silencer outside the pipe and a broadband divergent-flow metamaterial silencer inside the pipe; The broadband sound insulator installed outside the piping is composed of a plurality of resonant units installed in parallel and independent of each other, the resonant behavior of each resonant unit is a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, the resonant unit achieves a sound insulator effect by reflecting sound waves at the resonant frequency and frequencies nearby the resonant frequency, the resonant units are installed on the side wall of the ventilation pipe and have an opening on the ventilation pipe wall, or the resonant units are installed on the side wall of the ventilation pipe and have an opening on the ventilation pipe wall, and a mesh covering material is installed on the opening of the resonant unit, The broadband sound absorber installed outside the piping is composed of a plurality of resonant units installed in parallel and independent of each other, each resonant unit has a single frequency resonant behavior corresponding to a specific frequency band in the broadband noise to be reduced, the resonant units achieve the sound absorption effect by converting noise energy into thermal energy and dissipating it, the resonant units are installed on the side wall of the ventilation duct and have openings on the ventilation duct wall, or the resonant units are installed on the side wall of the ventilation duct and have openings on the ventilation duct wall, and a mesh covering material is installed on the openings of the resonant units, The broadband sound insulator installed inside the piping is composed of a plurality of resonant units installed in parallel and independent of each other, the resonant behavior of each resonant unit is a single frequency and corresponds to a specific frequency band in the broadband noise to be reduced, the resonant unit achieves the sound insulator effect by reflecting sound waves at the resonant frequency and frequencies nearby the resonant frequency, the resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, or the resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, and a mesh covering material is installed at the opening of the resonant unit, The broadband sound absorber installed inside the piping is composed of a plurality of resonant units installed in parallel and independent of each other, the resonant behavior of each resonant unit is a single frequency corresponding to a specific frequency band in the broadband noise to be reduced, the resonant units achieve the sound absorption effect by converting noise energy into thermal energy and dissipating it, the resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, or the resonant units are installed inside the ventilation pipe and have an opening into the ventilation pipe, and a mesh covering material is installed at the opening of the resonant unit, In the broadband metamaterial degenerate sound absorber, each acoustic perforated plate corresponds to a specific frequency band of the broadband noise to be reduced, with the broadband metamaterial silencer outside the pipe and / or the broadband branched-flow metamaterial silencer inside the pipe; the resonating unit includes a hard shell having an opening and air within a cavity of the hard shell; A broadband metamaterial silencer for an air duct, wherein multiple resonant units are geometrically arranged with cavities of the same or different cross-sectional areas, and each cavity is curved and folded on any flat or curved surface, or in three-dimensional space.

2. 2. The broadband metamaterial silencer for an air duct according to claim 1, wherein the resonant unit includes a Fabry-Perot resonator, a Helmholtz resonator, and a resonator with an arbitrary cavity shape, which can block or absorb noise in a specific frequency band.

3. 10. The broadband metamaterial silencer for an air duct according to claim 1, wherein the acoustic perforated plate is used to filter impurities in air duct gases.

4. 2. The broadband noise reduction metamaterial for an air duct according to claim 1, wherein the mesh covering material comprises metal mesh, sponge, woven fabric, paper, glass fiber cloth, acoustic perforated plate, and any combination of the above six types of materials.

5. The broadband metamaterial silencer for an air duct according to any one of claims 1 to 3, wherein the material of the metamaterial silencer includes metal, plastic, wood, leather, paper, ceramic, and any combination of the above six types of materials.

6. The broadband metamaterial silencer for an air duct according to any one of claims 1 to 3, wherein the air duct has any shape, including straight, curved, and piping with a constant or varying cross-sectional area shape.

7. A method for designing a broadband metamaterial silencer for an air duct, comprising: 1) acquiring noise spectrum data to be reduced, including internal structure data of the ventilation pipe, gas flow velocity / flow rate data, and noise intensity information; 2) optimizing the internal structure of the ventilation pipe based on the data obtained in step 1) to reduce the target noise intensity, and then obtaining the gas flow velocity and flow rate data and the processed target noise spectrum data; 3) based on the processed target noise spectrum data and the upper limit of the design volume of the metamaterial silencer, set a wideband target impedance that can most effectively reduce the noise intensity within the target frequency band of the ventilation pipe, and then select a type of wideband metamaterial silencer and M resonant units or K acoustic perforated plates and L resonant units in the wideband metamaterial silencer, and make the acoustic impedance spectrum shape of the M resonant units or K acoustic perforated plates and L resonant units identical to the wideband target impedance; 4) based on the broadband metamaterial silencer designed in step 3) and its acoustic impedance spectrum shape, optimizing the materials and / or structures of the inner wall of the pipe, the broadband metamaterial silencer structure, and the mesh covering material again to eliminate the target frequency noise; The step 3) is 3.1) If the broadband metamaterial silencer is a broadband metamaterial silencer outside the pipe or a broadband branched-flow metamaterial silencer inside the pipe, 3.1.1) When a Fabry-Perot resonator is used as the resonant unit 3.2.2) Design of broadband sound insulators or broadband sound absorbers or combinations of broadband sound insulators and broadband sound absorbers A design method for a broadband metamaterial silencer for an air duct, which, according to the method of step 3.1), obtains a broadband sound insulator or a broadband sound absorber, or a combination of a broadband sound insulator and a broadband sound absorber, whose noise reduction frequency distribution range is equal to or less than the noise reduction frequency of the acoustic perforated plate in step 3.2.1).

8. Step 3) is to select the type of broadband metamaterial silencer: Step 1: If the reflected energy of broadband noise has an adverse effect on the environment and equipment at the intake side of the ventilation duct, or if this reflected energy is reflected back into the duct, select a broadband sound absorber or a broadband metamaterial degenerate sound absorber; otherwise, all three are applicable. Step 2: If the overall dimension of the broadband metamaterial silencer along the sound propagation direction is less than the upper limit of the noise wavelength in the target frequency band, select a broadband sound insulator, a broadband metamaterial degenerate sound absorber, or a combination of a broadband sound absorber and a broadband sound insulator; otherwise, all three are applicable; Step 3: If the broadband metamaterial silencer is sensitive to the influence of airflow, select a broadband sound insulator, a broadband sound absorber, or a combination of a broadband sound absorber and a broadband sound insulator; otherwise, all three are applicable. The design method for a broadband metamaterial silencer for an air duct according to claim 7.

9. An application of a broadband metamaterial silencer for ventilation pipes, used for noise reduction of wearable devices, comprising: The material of the wearable device is set to an outwardly protruding hard material, the hard material is two or more layers, and a plurality of sealed cavities are provided between adjacent hard material layers, forming a sealed inner cavity between the innermost hard material layer or a part of the innermost hard material layer and the wearer's skin, the inner cavity and the other sealed cavities are connected via holes in each hard material layer, and the inner cavity and the other cavities jointly form an air duct, the inlet of the air duct is located on the innermost hard material layer or the outermost hard material layer, and the outlet is located on the innermost hard material layer or the outermost hard material layer, and the wideband metamaterial sound absorber is a wideband degenerate sound absorber.

10. The material of the wearable device is set to be a hard material that protrudes outward, and the hard material has two layers, namely an innermost hard material layer and an outer hard material layer. Two sealed cavities are provided between the two hard material layers, namely Cavity 1 and Cavity 3. A sealed soft pad that comes into contact with the wearer's skin is provided on the inner wall of the innermost hard material layer, and an inner cavity is formed between a part of the innermost hard material layer and the wearer's skin, and the inner cavity is Cavity 2. Hole 1 and hole 2 are provided on the innermost hard material layer of the inner cavity, and Cavity 1 communicates with Cavity 2 through Hole 1, and Cavity 2 communicates with the cavity through Hole 2.

10. The application of the broadband metamaterial silencer for an air duct as claimed in claim 9, wherein the broadband metamaterial silencer is a broadband degenerate sound absorber, which is composed of an acoustic perforated plate and a broadband sound absorber installed outside the pipe, the acoustic perforated plate is installed in the hole 1 and the hole 2, and the broadband sound absorber installed outside the pipe is installed on the side wall of the cavity 1 and the cavity 3, respectively.

11. The application of the broadband metamaterial silencer for an air duct according to claim 9 or 10, wherein a fan is installed at the inlet and / or outlet of the air duct.

12. The application of the broadband metamaterial silencer for ventilation pipes according to claim 9 or 10, wherein the frequency of the noise reduced by the broadband degenerate sound absorber is 800 to 8000 Hz.

13. 11. The application of the broadband metamaterial silencer for ventilation ducts according to claim 10, wherein the resonant unit of the broadband sound absorber installed outside the piping is a Helmholtz resonator, the cavity of the Helmholtz resonator is folded back and forth to form a maze shape, there are multiple Helmholtz resonators, some of the Helmholtz resonators open to the side wall of the first cavity and some of the Helmholtz resonators open to the side wall of the third cavity.

14. The application of the broadband metamaterial silencer for ventilation pipes according to claim 1, which is used to reduce ventilation pipe noise in indoor air exchange equipment, A broadband sound absorber is installed outside the duct on the side wall of the ventilation duct located at the air outlet of the indoor air exchange equipment, the resonance unit of the broadband sound absorber is a Fabry-Perot resonator, the cavity of the resonance unit is folded back and forth on the same plane, and a noise reduction plate layer is formed on the outside of the ventilation duct from a plurality of resonance units installed in parallel and independent of each other, each resonance unit in the noise reduction plate layer is all open to the side wall of the ventilation duct, and a plurality of noise reduction plate layers are stacked to form a broadband sound absorber, and the frequency of the noise reduced by the broadband sound absorber is 200 to 8000 Hz.

15. The application of the broadband metamaterial silencer for ventilation pipes according to claim 1, which is used to reduce ventilation pipe noise in outdoor heating and ventilation equipment, An application of a broadband metamaterial silencer for ventilation ducts, in which a broadband sound absorber is installed inside the duct inside the ventilation duct of an outdoor heating and ventilation equipment, the broadband sound absorber's resonant unit is a Fabry-Perot resonator, the cavity of the resonant unit is folded back and forth on the same plane, and the broadband sound absorber is formed of a plurality of resonant units installed in parallel and independent of each other, and has a rectangular, V-shaped, concave-convex, louvered, arrayed or other shape, and each resonant unit is all open to the inside of the ventilation duct, and the frequency of the noise reduced by the broadband sound absorber is 200 to 8000 Hz.

16. The application of the broadband metamaterial silencer for ventilation pipes according to claim 1, which is used to reduce noise in the intake pipe of a gas water heater, An application of a broadband metamaterial silencer for ventilation ducts, in which a broadband sound insulator installed outside the piping is installed on the side wall of the ventilation duct located at the inlet of the centrifugal fan of a gas water heater, the resonance unit of the broadband sound insulator is a Fabry-Perot resonator, the cavity of the resonance unit is folded back and forth on the same plane, and the broadband sound insulator is configured to cover the outside of the piping from a plurality of resonance units installed in parallel and independent of each other, each resonance unit all opening on the side wall of the ventilation duct, and the frequency of noise reduced by the broadband sound insulator is 200 to 4000 Hz.

17. The application of the broadband metamaterial silencer for ventilation pipes according to claim 1, which is used to reduce ventilation pipe noise of power equipment parts, An application of a broadband metamaterial silencer for ventilation ducts, wherein a broadband sound insulator is installed on the side wall of the duct at the outlet and / or inlet of the ventilation duct of the housing of the power component of the equipment, the broadband sound insulator is installed outside the duct, the resonance unit of the broadband sound insulator is a Fabry-Perot resonator, the cavity of the resonance unit is folded back and forth on a single plane, and the broadband sound insulator is configured to cover the outside of the duct from a plurality of resonance units that are installed in parallel and independent of each other, and each resonance unit is open to the side wall of the ventilation duct, and the frequency of the noise reduced by the broadband sound insulator is 160 to 4000 Hz.

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