A tunable gradient coiled sound barrier structure and method based on 3D printing

Abstract

This invention provides a tunable gradient-curved sound barrier structure and method based on 3D printing, belonging to the field of environmental noise control technology. The sound barrier unit is fabricated using an integrated molding process. Its core lies in the internal construction of a folded, curled topological skeleton with a gradient distribution along the sound wave propagation direction. This skeleton extends vertically to form a three-dimensional solid. The geometry and spacing of the internal folded channels can be parametrically adjusted to achieve precise matching with the target noise spectrum characteristics. In terms of manufacturing process and materials, this invention employs selective laser sintering technology, using modified microporous nylon composite material as raw material. For highway traffic noise scenarios, this structure effectively extends the sound wave propagation path and induces sound energy dissipation by utilizing gradient-changing folded channels, achieving efficient insertion loss in the two energy-concentrated frequency bands of 315-500Hz and 800-1250Hz. Simultaneously, combined with the micropores and high damping characteristics of the material, it effectively suppresses the coincidence effect.

Description

Technical Field

[0001] This invention relates to the field of environmental noise control and additive manufacturing technology, specifically to a tunable gradient curling sound barrier structure and method based on 3D printing, which is particularly suitable for broadband bimodal noise control in traffic scenarios such as highways, urban overpasses, and expressways. Background Technology

[0002] With the acceleration of urbanization and the development of multi-level transportation networks, highways, urban viaducts, and expressways have become the "arteries" of modern cities. However, this multi-level transportation model raises the location of noise sources, directly exposing them to high-rise residential and office areas, leading to increasingly serious environmental noise pollution problems. Acoustic spectrum analysis data shows that modern road traffic noise is not a single-frequency interference, but exhibits significant broadband and dual-energy peak characteristics: Low-frequency energy range (315Hz-500Hz): Noise energy in this frequency band mainly originates from the roar of large-displacement engines of heavy vehicles, low-frequency vibrations of exhaust systems, and aerodynamic turbulence generated by high-speed vehicle travel. Low-frequency sound waves have relatively long wavelengths (approximately 0.7 meters to 1 meter), possess extremely strong diffraction capabilities, attenuate very slowly during atmospheric propagation, and easily penetrate ordinary building components, making them a persistent problem in current environmental governance.

[0003] Mid-to-high frequency energy range (800Hz-1250Hz): Noise in this frequency band mainly originates from the "pumping effect" generated when the tire contacts the road surface and the high-frequency vibration of the tire tread pattern. This frequency band happens to be in the area where human hearing is most sensitive (1kHz-4kHz), and has the greatest impact on the subjective annoyance of the human body.

[0004] Current sound barrier technologies, when dealing with the aforementioned complex noise environments, are limited by fundamental acoustic physics laws, resulting in irreconcilable contradictions: (1) Constraints of the "Law of Mass" and the Challenges of Lightweighting: The sound insulation performance of traditional homogeneous barriers such as concrete, metal sandwich panels, or acrylic panels mainly follows the "Law of Mass," that is, the sound insulation is logarithmically related to the surface density of the material. To effectively block high-energy low-frequency noise below 400Hz, the wall must be extremely thick and heavy (the surface density usually needs to exceed 100kg / m²). This not only causes huge material waste, but also results in excessive self-weight of the barrier. For old bridges or long-span viaducts with limited load-bearing capacity, installing such heavy barriers will bring serious safety hazards; and in vehicle collision accidents, heavy fragments are very likely to cause secondary injuries.

[0005] (2) The "coincidence effect" leading to a low point in sound insulation: Existing single-layer rigid lightweight panels are prone to the "coincidence effect" at certain frequencies. When the wavelength of the incident sound wave matches the wavelength of the bending wave of the panel itself, it will cause the structure to resonate violently, causing the sound wave at that frequency to be transmitted almost without loss, forming a "deep valley" on the sound insulation curve. This "sound transmission" phenomenon often occurs in the mid-to-high frequency range, which seriously weakens the overall protective effectiveness of the barrier.

[0006] The emergence of acoustic metamaterials in recent years, especially structures based on the principle of spatial curling, has provided a new approach to breaking the "mass law." By folding the sound wave transmission path within a confined space, efficient phase delay and impedance modulation of low-frequency sound waves can be achieved at the subwavelength scale. However, existing technologies still have significant limitations in engineering applications: (1) Manufacturing challenges of geometric configurations: In order to achieve broadband impedance matching and viscous heat dissipation, metamaterials often have extremely complex gradient flow channels, labyrinth structures, and a large number of inverted, suspended, and internal cavity features. Traditional injection molding and extrusion molding require demolding and cannot manufacture such complex internal cavity structures; while CNC subtractive manufacturing cannot reach deep curved cavities. This means that many theoretically excellent metamaterial designs can only remain in the numerical simulation stage and cannot be physically realized.

[0007] (2) Uniqueness of frequency band response: Most existing metamaterial structures adopt a single periodic lattice arrangement, which usually results in "narrow band" sound absorption characteristics. This characteristic makes it difficult to cover two peaks that are far apart in traffic noise at the same time (low frequency of engine and high frequency of tire), often resulting in "one thing being addressed but the other not," and poor treatment effect.

[0008] (3) Neglect of acoustic-solid coupling: Existing research focuses on the geometric design of the airborne sound propagation path, while ignoring the characteristics of the skeleton material itself. The photosensitive resin or metal material commonly used has low damping and cannot effectively dissipate the structural vibration energy, making the metamaterial structure itself prone to transmission problems caused by resonance under acoustic excitation.

[0009] In summary, existing technologies cannot achieve efficient isolation of both low-frequency and high-frequency bimodal noise while maintaining extreme lightweight design, and they also struggle to address the issues of large-scale manufacturing and fit-up of complex internal cavity structures. Therefore, there is an urgent need to develop a novel metamaterial sound barrier that can overcome the limitations of traditional manufacturing processes and achieve wideband, bimodal response, and high damping characteristics through a collaborative design of structure, materials, and processes. Summary of the Invention

[0010] This invention addresses the shortcomings of existing technologies by providing a tunable gradient curling sound barrier structure and method based on 3D printing. It solves the problems of traditional sound barriers being bulky, having a significant coincidence effect, being difficult to manufacture acoustic metamaterials, and having a single frequency band response. It achieves lightweight design, precise sound absorption and insulation in both frequency bands, and suppression of the coincidence effect, while also being feasible for engineering manufacturing.

[0011] To achieve the above-mentioned technical features, the objective of this invention is as follows: The first aspect of the present invention provides a tunable gradient curling sound barrier structure based on 3D printing, comprising an integrally formed solid skeleton and internal gradient air channels.

[0012] The cross-section of the solid skeleton is a folded and rolled topology, and the folded and rolled topology is distributed in a gradient along the direction of sound wave propagation. The solid skeleton extends along the vertical height direction to form a three-dimensional column, and the sound wave propagation behavior can be controlled within a limited physical size by utilizing the subwavelength structural characteristics.

[0013] The internal gradient air channel is formed by the folded and rolled topology, which is a connected labyrinthine sound wave transmission path. Its geometric parameters include channel width, folding depth and number of rolls. It can be parameterized according to the center frequency of the target noise band to achieve impedance matching and phase modulation of a specific noise spectrum, breaking the limitation of a single resonant frequency.

[0014] The acoustic impedance matching layer structure is provided on the acoustic wave incident surface of the solid skeleton to reduce the direct reflection of sound waves at the air-barrier interface and guide more acoustic energy into the internal gradient air channel for dissipation.

[0015] Furthermore, the gradient distribution of the folded and rolled topology is characterized by the gradual change in the characteristic dimensions of the folded units of the solid skeleton along the incident direction of the sound wave. Specifically, this includes a gradual increase in the effective channel length and / or a gradual decrease in the channel cross-sectional width. The gradual increase in the effective channel length can adjust the resonant frequency at different depths, covering a wider low-frequency range; the gradual decrease in the channel cross-sectional width can form a broadband acoustic impedance (mainly affecting reflection) and acoustic resistance (mainly affecting absorption) coupling structure inside the sound barrier, ensuring that sound waves can easily enter but are difficult to transmit.

[0016] Furthermore, in response to the bimodal characteristics of highway traffic noise, the parameterized adjustment of the internal gradient air channel is specifically as follows: adjusting the parameters of the first-stage curling structure (such as increasing the number of curls and extending the effective length of the channel) to make the sound barrier form a resonant sound absorption peak in the low-frequency band of 315-500Hz, matching the concentrated energy area of ​​engine noise; adjusting the parameters of the subsequent-stage curling structure (such as reducing the cross-sectional width of the channel and increasing the folding density) to make the sound barrier form a high transmission loss in the mid-high frequency band of 800-1250Hz, matching the concentrated energy area of ​​tire / road noise.

[0017] Furthermore, the physical skeleton includes an outer frame and an inner folding wall panel. The inner folding wall panel is arranged in a maze-like staggered pattern, which forces the incident sound wave to undergo multiple reflections and path folds when passing through the sound barrier. This allows the sound wave to propagate within a finite physical thickness by an equivalent sound path several times the physical thickness, thereby enhancing the dissipation capability of low-frequency sound waves and breaking through the limitations of the traditional mass law.

[0018] Furthermore, the acoustic impedance matching layer structure is a large aperture ratio structure of the incident surface or a gradually changing channel entrance structure. The channel width of the large aperture ratio structure is preferably 15-25mm, which can achieve a high degree of matching between the characteristic acoustic impedance of the structural surface and the characteristic impedance of the air, minimize the incident reflection of sound waves, and form a "sound absorption trap" effect.

[0019] Furthermore, the solid skeleton is made of modified microporous nylon composite material, which is obtained by modifying nylon powder and hollow glass microspheres. It has a micron-level microporous structure formed during laser sintering. The loss factor of the composite material is ≥0.07, preferably η≈0.08. The micropores, combined with the viscoelasticity of the nylon material itself, introduce significant acoustic damping into the structure, converting acoustic energy into heat energy and effectively suppressing the coincidence effect caused by structural resonance.

[0020] A second aspect of this invention provides a method for fabricating a tunable gradient-curved sound barrier based on 3D printing, for fabricating the aforementioned sound barrier structure, comprising the following steps: S1. Three-dimensional model design: Based on the target noise spectrum characteristics (such as center frequency and energy peak range), determine the gradient distribution of the folded and rolled topology of the sound barrier structure to be prepared and the geometric parameters (channel width, fold depth, number of rolls) of the internal gradient air channels. Use three-dimensional modeling software to establish a three-dimensional model of the sound barrier structure. For low-frequency noise of 315-500Hz, increase the number of rolls to make the effective sound path of the internal gradient air channels 1 / 4 of the target sound wave wavelength, and use the Fabry-Perot resonance principle to achieve anti-phase cancellation. For mid-high frequency noise of 800-1250Hz, adjust the cross-sectional width of the subsequent channel to 3-7mm to form a microchannel structure to enhance viscous heat dissipation.

[0021] S2. Preparation of composite powder: Prepare modified microporous nylon composite powder raw materials by mixing nylon powder and hollow glass microspheres in a preset ratio and mixing them evenly using a high-speed mixer to obtain composite powder; wherein the nylon powder is preferably nylon 12 powder, the mass ratio of hollow glass microspheres is 10-20%, and the density of the composite powder is controlled at 0.95-1.05 g / cm³, taking into account both low density and lightweight and high structural strength.

[0022] S3. Selective Laser Sintering (SLS): Using the composite powder as raw material, the three-dimensional model is imported into the 3D printing equipment. After setting the printing process parameters, integrated unsupported printing is performed to form a preliminary sound barrier structure. The preferred printing process parameters are: laser power 40-50W, scanning speed 2000-3000mm / s, and printing layer thickness 0.08-0.12mm. The unsintered composite powder is used as a self-supporting structure to achieve integrated forming of complex suspended, inverted, and labyrinth flow channel structures.

[0023] S4. Post-processing: The initial blank of the sound barrier structure is post-processed. First, high-pressure airflow is used to remove the unsintered powder attached to the surface and internal channels of the initial blank. Then, sandblasting and polishing are performed to make the surface of the structure smooth. Finally, it is placed in a vacuum drying oven to dry and obtain the finished sound barrier structure. The vacuum drying temperature is 60-80℃ and the time is 2-4 hours to remove moisture from the raw materials and prevent the material from absorbing moisture and affecting the acoustic performance.

[0024] S5. Acoustic performance testing and parameter optimization: Conduct acoustic performance testing on the finished sound barrier structure, test its insertion loss, sound insulation and other indicators, and determine whether the target sound absorption and insulation effect has been achieved; if not, return to step S1 to adjust the geometric parameters of the folded and rolled topology and / or step S2 to adjust the raw material ratio and / or step S3 to adjust the printing process parameters, and re-prepare until the target requirements are met.

[0025] Beneficial effects of this invention: 1. This invention, through the parametric design of a gradient curled topology, enables a single structure to simultaneously achieve efficient sound absorption and insulation of highway traffic noise in the low-frequency band of 315-500Hz and the mid-high frequency band of 800-1250Hz. The sound insulation of the low-frequency resonant sound absorption peak can reach more than 35dB, and the sound insulation of the mid-high frequency high transmission loss band can reach more than 50dB. It does not require the combination of multiple materials and is adapted to the dual-peak characteristics of traffic noise.

[0026] 2. The microporous structure and high damping characteristics of the modified microporous nylon composite material of the present invention, combined with the acoustic-solid coupling effect, convert the acoustic energy of structural vibration into thermal energy, fill the sound insulation trough of traditional rigid materials, keep the sound insulation curve smooth across the entire frequency band, and eliminate resonance sound transmission phenomenon.

[0027] 3. This invention uses a modified microporous nylon composite material with a hollowed-out folded and rolled topology structure, which significantly reduces the structural weight compared to a concrete barrier with the same sound insulation performance. The composite powder density is only 0.95-1.05 g / cm³, while maintaining high specific strength, reducing the load on load-bearing structures such as bridges and viaducts and avoiding safety hazards.

[0028] 4. This invention employs selective laser sintering (SLS) technology, utilizing the self-supporting properties of powder to achieve integrated unsupported molding of complex labyrinth flow channels and suspended structures. This solves the problem that traditional processes cannot manufacture complex acoustic metamaterials, transforming theoretical designs into practical products and making large-scale production feasible.

[0029] 5. This invention can flexibly adjust the geometric parameters of the folded and rolled topology, the proportion of composite materials and the printing process parameters according to the spectral characteristics of different noise scenarios (such as highways, railways and urban roads) to achieve accurate matching of the target noise spectrum, and has a wide range of applications.

[0030] 6. The acoustic impedance matching layer structure of the acoustic wave incident surface of the present invention reduces acoustic wave interface reflection, guides more acoustic energy into the internal channel for dissipation, greatly improves the overall sound absorption and insulation efficiency, and avoids ineffective reflection of acoustic energy. Attached Figure Description

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] Figure 1 : A schematic diagram of the basic two-dimensional cross-sectional topology of the sound barrier unit of this invention.

[0033] Figure 2 : A three-dimensional structural schematic diagram of the sound barrier unit of the present invention.

[0034] Figure 3 The insertion loss simulation comparison curves of the embodiment of the present invention and this structure are shown.

[0035] Figure 4 : Under operating condition A, the sound pressure level distribution cloud map of the sound barrier unit of the present invention at 450Hz.

[0036] Figure 5 : Under operating condition A, the sound pressure level distribution cloud map of the sound barrier unit of the present invention at 1050Hz.

[0037] Figure 6 : Under operating condition A, the structural displacement cloud diagram of the sound barrier unit of the present invention at 450Hz.

[0038] Figure 7 : Under operating condition A, the structural displacement cloud diagram of the sound barrier unit of the present invention at 1050Hz.

[0039] Figure 8 : Under operating condition B, the sound pressure level distribution cloud map of the sound barrier unit of the present invention at 450Hz.

[0040] Figure 9 : Under operating condition B, the sound pressure level distribution cloud map of the sound barrier unit of the present invention at 1050Hz. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0042] Example 1: Structural design of gradient curling sound barrier unit: This embodiment provides a sound barrier unit that is parametrically designed based on the spectral characteristics of highway traffic noise (double peaks of 315-500Hz and 800-1250Hz).

[0043] like Figure 1 and Figure 2 As shown, the outer contour of this sound barrier unit is rectangular columnar, with a standard unit size of 200mm × 200mm × 320mm (length × width × height). The internal structure consists of a solid frame and air channels, along the direction of sound wave propagation (…). Figure 1 The distribution (from left to right) exhibits gradient characteristics: Incident impedance matching region (front left section): This region is designed with a relatively wide opening (channel width) w (1≈20mm). A larger opening ratio can effectively adjust the acoustic impedance matching between the air and the surface of the sound barrier, reduce the direct reflection of sound waves at the incident interface, and guide more sound energy into the interior of the structure for processing.

[0044] Low-frequency curling resonance region (middle): The channel gradually narrows and undergoes multiple folds and curls. Through topology optimization design, the effective curling length of the air channel is maximized within a limited physical thickness. L eff The effective path length is significantly increased. According to the Fabry-Perot resonance principle, a strong anti-phase cancellation effect occurs when the effective channel length is approximately 1 / 4 of the sound wave wavelength. In this embodiment, the target frequency is set around 450Hz (corresponding to engine noise), and the effective sound path is achieved to approximately 0.19m through folding.

[0045] High-frequency dissipation and emission region (right rear section): The channel further contracts (channel width) w (2≈5mm) and form a dense labyrinth network. The narrow channel significantly increases the viscous boundary layer effect during sound wave propagation, and utilizes the friction between air and the wall to convert mid-to-high frequency sound energy of 800-1250Hz into heat energy dissipation.

[0046] To further clarify the physical basis of the structural dimensions and material selection of the present invention, this embodiment establishes the following design model based on acoustic metamaterials theory, which serves as the core basis for parametric design: 1. Low-frequency phase modulation model based on spatial curl To address the long wavelength characteristics of low-frequency noise (315-500Hz), this invention breaks through the limitations of the traditional "mass law" by utilizing a folded and rolled topology to construct a subwavelength-scale metasurface. Based on the Fabry-Perot resonance principle, the internal air channel is designed as a quarter-wavelength resonator. Its theoretical resonant frequency... f res With effective sound path L eff The following relationship must be satisfied: ; in, C It is the speed of sound (approximately 343 m / s). n denoted as the modal order.

[0047] This invention achieves structural flexibility in terms of physical thickness by parametrically adjusting the folding depth and the number of rolls. Much smaller than wavelength In the case of ( To achieve an effective sound path The frequency of the incident sound wave is significantly extended. When the incident sound wave frequency is close to the design frequency (such as 450Hz in the embodiment), the reflected wave at the bottom of the channel and the incident wave generate at the entrance. The phase difference creates destructive interference, resulting in a minimum value on the transmission coefficient spectrum, thus achieving efficient blocking of low-frequency sound energy.

[0048] 2. Wideband Impedance Matching and Viscous Dissipation Mechanism of Gradient Channels To address the issue of narrow bandwidth at a single resonant frequency, this invention establishes a gradient acoustic impedance model. Impedance matching end: The incident end has a larger channel width ( This makes the characteristic acoustic impedance of the structural surface... air characteristic impedance Achieve high matching ( This minimizes the direct reflection of sound waves at the air-barrier interface, establishing the "sound-absorbing trap" effect.

[0049] Viscous heat dissipation end: As the channel gradually contracts into a microchannel along the propagation direction ( The propagation characteristics of sound waves within the slit follow Kirchhoff's viscous heat conduction theory. As the hydraulic diameter of the channel decreases, the proportion of the viscous boundary layer thickness of air molecules in the channel cross-section increases significantly. The vibration of air particles caused by sound waves efficiently converts sound energy into heat energy through intense friction with the rough wall surface, thus generating broadband loss in the mid-to-high frequency band of 800-1250Hz.

[0050] 3. Acoustic-structure interaction and complex modulus damping effect To address the sound transmission problem caused by the "matching effect" that is common in traditional rigid metamaterials, this model introduces a complex dynamic modulus design. Modified microporous nylon materials formed using the SLS process exhibit viscoelastic characteristics, and their equivalent elastic modulus can be expressed in complex form: ; in This refers to the material loss factor. For dynamic modulus, It is the equivalent elastic modulus.

[0051] By establishing the acoustic-solid coupling equation, the incident sound wave not only propagates within the air channel but also excites the skeleton to produce micro-amplitude bending vibrations. The micropores within the material and the high loss factor ( The combined effect of these factors introduces additional damping force when the structure resonates, effectively reducing the resonance transmission peak and keeping the sound insulation curve smooth across the entire frequency range, thus eliminating the theoretically low sound insulation trough.

[0052] Example 2: Material Preparation and Additive Manufacturing Process To achieve the aforementioned complex internal suspended and gradient flow channel structure, and to enhance damping by utilizing material properties, this invention employs selective laser sintering (SLS) technology for manufacturing.

[0053] 1. Material Selection: The matrix material is nylon 12 (PA12) powder, modified with 15% hollow glass microspheres. This composite material has a low density (approximately...). It has the characteristics of high toughness.

[0054] 2. Micropore effect: During the powder sintering process, the SLS process retains micron-sized micropores within the material. These micropores, combined with the viscoelasticity of nylon itself, significantly improve the acoustic loss factor of the structure, enabling it to participate in acoustic processes as a "damped elastic body" rather than an "absolute rigid body".

[0055] 3. Printing parameters: Laser power 45W, scanning speed 2500mm / s, layer thickness 0.1mm. Utilizing unsintered powder as a self-supporting structure, integrated supportless molding was achieved.

[0056] Example 3: Acoustic Performance Simulation and Mechanism Verification To verify the effectiveness of the present invention and to reveal the mechanism of the synergistic effect of "structure + material", a finite element model was established using COMSOL Multiphysics software, and comparative simulation analysis was conducted.

[0057] 1. Simulation Settings Comparison To differentiate the contributions of geometry and material properties, two sets of simulation conditions were set up (corresponding to...). Figure 3 (Two curves in the middle) Condition A: Perform acoustic-structure interaction simulation. Assign physical properties (density) to the PA12 composite material skeleton. Young's modulus Loss factor This operating condition reflects the sound absorption and insulation performance under real physical conditions.

[0058] Condition B: Only pressure acoustic simulation is performed. The skeleton boundary is set as a "hard sound field boundary," meaning the skeleton is assumed to be an ideal reflector that is absolutely rigid, vibration-free, and undamped. This condition only reflects the modulating effect of gradient curling geometry on sound waves.

[0059] Figure 4 The comparison of insertion loss for the two operating conditions described above is shown: Geometric effect (condition B): When relying solely on rigid geometry, the curve exhibits a very deep sound insulation trough near 350Hz, and drops extremely rapidly in the high-frequency range after 1100Hz. This is a typical "coincidence effect" or sound transmission phenomenon caused by structural resonance, and due to the lack of damping, the resonance is very sharp.

[0060] Synergistic effect (condition A): After introducing PA12 material and acoustic-structure interaction, the curve was significantly optimized: Filling the trough: The trough near 350Hz is significantly filled, boosting it by more than 20dB. This is because the damping properties of the material suppress severe resonant sound transmission.

[0061] Dual-peak characteristics: Two broadband sound insulation peaks are formed near 450Hz (corresponding to engine noise) and 1150Hz (corresponding to tire noise), with peak IL reaching 35dB and 50dB respectively.

[0062] Smooth curve: Compared with rigid structures, the curve of the present invention is smoother and has a wider effective bandwidth.

[0063] 2. Analysis of the Mechanism of Sound Field and Displacement Field By comparing the sound pressure level contour map and the structural displacement map, its physical mechanism is further revealed: Low-frequency band (450Hz) analysis: Sound pressure level comparison: Figure 4 and Figure 8 The two have similar sound pressure distribution trends, with high sound pressure on the left and low sound pressure on the right, proving that the gradient curl structure itself has a strong reflection effect on low frequencies.

[0064] Structural displacement: such as Figure 6As shown in the figure above, the PA12 skeleton underwent overall bending vibration (red area) at 450Hz. This indicates that the sound wave excited the structural modes of the skeleton. In the "structure plus material" scenario, this vibrational energy was converted into heat energy dissipation by the internal damping of the nylon material, thereby helping to improve the sound insulation and preventing resonant transmission that occurs in rigid structures.

[0065] High-frequency band (1050Hz) analysis: Sound pressure level comparison: In Figure 5 and Figure 9 In the labyrinthine passage, sound waves attenuate rapidly after entering the structure.

[0066] Structural displacement: such as Figure 7 As shown in the figure below, at high frequencies, vibrations are mainly concentrated in localized areas of the inner thin wall. This localized vibration enhances air turbulence within the slit, and combined with viscous heat dissipation, achieves efficient absorption of high-frequency noise.

[0067] In summary, the gradient-curved PA12 metamaterial manufactured by the SLS process in this invention not only controls low frequencies by extending the sound path through geometric topology, but more importantly, it overcomes the coincidence effect defect that is easily generated by simple rigid metamaterials by utilizing the microporous damping characteristics and acoustic-structure coupling effect of the material, thus achieving lightweight, wide-bandwidth, and dual-peak high-efficiency sound insulation.

[0068] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tunable gradient curling sound barrier structure based on 3D printing, characterized in that, It includes a one-piece molded solid frame and internal gradient air channels; The cross-section of the solid skeleton is a folded and rolled topology, and the folded and rolled topology is distributed in a gradient along the direction of sound wave propagation. The solid skeleton extends along the vertical height direction to form a three-dimensional column. The internal gradient air channel is formed by the folded and rolled topology, which is a connected labyrinthine sound wave transmission path. Its geometric parameters are parameterized according to the center frequency of the target noise band to achieve impedance matching and phase modulation of a specific noise spectrum. The acoustic impedance matching layer structure is provided on the acoustic wave incident surface of the solid skeleton.

2. The tunable gradient curling sound barrier structure based on 3D printing according to claim 1, characterized in that, The gradient distribution of the folded and curled topology is characterized by the gradual change in the characteristic dimensions of the folded units of the solid skeleton along the direction of sound wave incidence. The change in characteristic dimensions includes a gradual increase in the effective length of the channel and / or a gradual decrease in the width of the channel cross section, forming a broadband acoustic impedance and acoustic resistance coupling structure inside the sound barrier.

3. The tunable gradient curling sound barrier structure based on 3D printing according to claim 1, characterized in that, The geometric parameters of the internal gradient air channel include channel width, folding depth, and number of rolls; To address highway traffic noise, the parameters of the first-stage coiled structure are adjusted to create a resonant sound absorption peak in the 315-500Hz frequency band of the sound barrier, and the parameters of the subsequent-stage coiled structure are adjusted to create a high transmission loss in the 800-1250Hz frequency band of the sound barrier.

4. A tunable gradient curling sound barrier structure based on 3D printing according to claim 1, characterized in that, The physical skeleton includes an outer frame and an inner folding wall panel. The inner folding wall panel is arranged in a maze-like pattern, causing the incident sound wave to undergo multiple reflections and path folds within the sound barrier, thus extending the equivalent sound path.

5. A tunable gradient curling sound barrier structure based on 3D printing according to claim 1, characterized in that, The acoustic impedance matching layer structure is a large aperture ratio structure of the incident surface or a gradient channel entrance structure, and the channel width of the large aperture ratio structure is 15-25mm.

6. A tunable gradient curling sound barrier structure based on 3D printing according to claim 1, characterized in that, The solid skeleton is made of modified microporous nylon composite material, which has a micron-level microporous structure and a loss factor η ≥ 0.

07.

7. A method for fabricating a tunable gradient-curved sound barrier based on 3D printing, characterized in that, The method for preparing the sound barrier structure as described in any one of claims 1-6 includes the following steps: S1. Based on the target noise spectrum characteristics, determine the gradient distribution of the folded and rolled topology of the sound barrier structure to be prepared and the geometric parameters of the internal gradient air channels, and establish a three-dimensional model of the sound barrier structure. S2. Prepare modified microporous nylon composite powder raw material by mixing nylon powder with hollow glass microspheres in a preset ratio to obtain uniform composite powder. S3. Using selective laser sintering process, the composite powder is used as raw material, and integrated supportless printing is performed according to the three-dimensional model to form a preliminary blank of the sound barrier structure. S4. Post-process the initial blank of the sound barrier structure to obtain the finished sound barrier structure.

8. The preparation method according to claim 7, characterized in that, In step S2, the nylon powder is nylon 12 powder, the mass percentage of the hollow glass microspheres is 10-20%, and the density of the composite powder is 0.95-1.05 g / cm³.

9. The preparation method according to claim 7, characterized in that, In step S3, the parameters of the selective laser sintering process are: laser power 40-50W, scanning speed 2000-3000mm / s, printing layer thickness 0.08-0.12mm, and using unsintered composite powder as a self-supporting structure. In step S1, for low-frequency noise of 315-500Hz, the effective sound path of the internal gradient air channel is made to be 1 / 4 of the target sound wave wavelength by increasing the number of curling cycles; for mid-high frequency noise of 800-1250Hz, the cross-sectional width of the subsequent channel is adjusted to 3-7mm to form a microchannel structure.

10. The preparation method according to claim 7, characterized in that, In step S4, the post-processing includes removing unsintered powder adhering to the surface of the initial blank, sandblasting and polishing, and vacuum drying. The vacuum drying temperature is 60-80℃ and the time is 2-4h. It also includes step S5: conducting acoustic performance testing on the finished sound barrier structure. If the target sound absorption and insulation effect is not achieved, return to step S1 to adjust the geometric parameters and / or step S2 to adjust the raw material ratio and / or step S3 to adjust the printing process parameters, and re-prepare.

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