A small device broadband noise reduction device based on miniaturized composite acoustic wave black hole structure

Abstract

This invention discloses a broadband noise reduction device for small devices based on a miniaturized composite acoustic black hole structure, belonging to the field of fan noise reduction technology in the high-end equipment industry. The device includes at least one miniaturized acoustic black hole unit, which miniaturizes a truncated acoustic black hole structure to a cross-sectional size of approximately 30mm × 30mm. It is constructed by integrating porous sound-absorbing material layers into the power-law contraction of the through-hole walls and lateral cavities. The miniaturized truncated structure promotes low-frequency global resonance to expand the bandwidth, while the porous material layers compensate for low-frequency leakage caused by miniaturization and smooth absorption peaks. This device can be directly integrated as an independent functional component into the cooling fan housing or air guide of high-end equipment, achieving efficient passive absorption of broadband aerodynamic noise above 1000Hz with almost no increase in size or air resistance. It is particularly suitable for noise reduction inside space-constrained electronic equipment, and especially for aerodynamic noise control of miniature fans.

Description

Technical Field

[0001] This invention relates to the field of noise reduction technology for ventilation equipment, and in particular to a broadband noise reduction device for small devices based on a miniaturized composite acoustic black hole structure. Background Technology

[0002] In high-end equipment industries, such as ultra-thin laptops, compact servers, communication equipment, and precision instruments, internal space is extremely limited. Their forced air cooling systems (mainly composed of miniature axial or centrifugal fans and heat sinks) are the primary noise source, generating a wide noise spectrum dominated by mid-to-high frequencies, severely impacting user experience. Traditional fan noise reduction methods, such as optimizing blade shape, adding sound-absorbing cotton, or designing complex cavities, either have a narrow noise reduction bandwidth or significantly increase the size and weight of the equipment and may obstruct airflow, affecting heat dissipation efficiency. Acoustic black holes, acoustic structures based on the theory of gradual changes in the velocity of bending waves in curved thin plates, have been explored in recent years for controlling fan aerodynamic noise.

[0003] However, traditional acoustic black hole structures are relatively large and are mostly used for vibration suppression in structures such as beams and slabs. Directly applying them to small cooling fans with millimeter-scale dimensions presents challenges in structural design, manufacturing processes, and integration. Some existing fan noise reduction structures, such as those using a cylindrical shell, base, and multiple layers of independent microperforated plates, aim to achieve broadband sound absorption through power-law decreasing perforations. However, their typical interlayer assembly structure has inherent engineering flaws: First, the cylindrical shell, multiple microperforated plates, and base, as independent components, require precise alignment and fixation, making manufacturing and assembly complex, and significantly increasing the difficulty and cost at small scales. Second, the connection interfaces between components (such as the contact surface between the microperforated plate and the inner wall of the shell) are prone to fretting wear or stress relaxation under long-term vibration or thermal cycling, leading to a decrease in connection stiffness and potentially altering the dynamic characteristics of the structure. Most importantly, these unavoidable assembly interfaces form microscopic air leakage channels, severely disrupting the precise acoustic impedance gradient conditions and internal sound field integrity required for the acoustic black hole effect, causing a significant attenuation of theoretical sound absorption performance during long-term service, making reliability difficult to guarantee. In the field of high-end equipment manufacturing, the aerodynamic noise problem of micro cooling fans is particularly prominent, and existing fan noise reduction solutions struggle to balance size, air resistance, and broadband sound absorption performance. Therefore, there is an urgent need for a broadband noise reduction solution that can be integrated with the housing or air guide of a miniature fan, without changing the main structure of the fan and with almost no increase in wind resistance. This is directly related to the performance improvement of the fan as a fluid machinery component. Summary of the Invention

[0004] Purpose of the invention: This invention provides a small-scale broadband noise reduction device based on a miniaturized composite acoustic black hole structure, which is extremely compact in structure, has a wide sound absorption bandwidth, is easy to manufacture, and can be conformally integrated with a fan shroud or housing. This device can be directly used as a functional component of a fan (such as a shroud or outlet silencer) in the air-cooling system of high-end equipment. It achieves broadband passive noise reduction without changing the main structure and aerodynamic performance of the fan. It aims to solve the technical problems of the difficulty in broadband noise reduction of aerodynamic noise of existing miniature cooling fans, the large size or high wind resistance of traditional silencer structures, and the difficulty in integrating existing acoustic black hole structures into fan components.

[0005] Technical Solution: The broadband noise reduction device for small devices based on a miniaturized composite acoustic black hole structure of the present invention includes: a rigid outer shell frame with a square channel inside, the cross-section of the channel being square, and N pseudo-periodic units arranged axially inside the channel, where N is a positive integer not less than 10, each unit being composed of a thin partition plate with a central through hole perpendicular to the channel axis; along the direction of sound wave incidence, the size of the central through hole gradually decreases according to a power law function, and the size of the end through hole is non-zero, forming a truncated structure; a porous sound-absorbing material layer is provided on the inner wall surface of the central through hole and / or in the lateral cavity composed of the partition plate.

[0006] Preferably, along the incident direction of the sound wave to the end, the diameter of the central through-hole of the thin partition gradually decreases according to a power law function, and the diameter of the central through-hole of the Nth partition at the very end is not zero, forming a truncated structure; wherein, the center height of the i-th partition is... h i for: , i = N +1, denoted as the unit period length, and m as the power law order, with a value range of 1 ≤ m ≤ 4.

[0007] A porous sound-absorbing material layer is filled or attached to the inner wall surface of the central through hole of the thin partition and / or the lateral cavity formed by the through hole wall surface between adjacent partitions.

[0008] Preferably, the side length H of the square cross-section of the internal channel of the rigid outer shell frame is 25mm to 35mm, preferably 30mm; the axial length L of the channel is 25mm to 35mm, preferably 30mm.

[0009] Preferably, the porous sound-absorbing material layer is a flexible porous material, such as open-cell foam, fiber cotton, or sintered metal porous material, with a flow resistance of 2000 to 15000 N·s / m. 4 This allows for critical coupling in miniaturized structures, balancing energy leakage and loss.

[0010] Preferably, the thickness t of the thin partition is 1 mm to 3 mm. In the truncated structure, the height of the first partition is... R Total height of the passageway H ratio R The condition '0.1≤R'≤0.5' is satisfied to achieve structural miniaturization and induce low-frequency global resonance.

[0011] Preferably, the rigid outer shell frame and thin partition are made of aluminum alloy, engineering plastic or resin material, and are formed by integrated 3D printing technology with a manufacturing accuracy of not less than ±0.1mm.

[0012] Preferably, the noise reduction device is used directly as a shroud for the heat dissipation module, an outer frame for the heat dissipation fin array, or an outlet silencer for a micro fan.

[0013] The present invention also provides a noise reduction method using the above-mentioned device, comprising installing the device in a manner consistent with the airflow direction on the noise radiation path of a small device cooling fan; utilizing the slow sound effect generated by its power-law contraction through-hole to concentrate sound energy, and utilizing the distributed loss provided by the porous sound-absorbing material layer to dissipate sound energy, thereby achieving broadband passive noise reduction.

[0014] Preferably, it includes the following steps: S1: Determine the main noise spectrum of the small device to be noise-reduced and the maximum space size that can be used to integrate the noise reduction structure, and adapt the external size of the device to a cross-section of about 30mm×30mm. S2: Determine the power law order m, number of units N, and truncation height R' based on the target noise reduction frequency band (especially mid-to-high frequencies above 500Hz); S3: Select a porous sound-absorbing material with matching flow resistance and calculate its filling amount in the micro lateral cavity to achieve critical coupling conditions in the target low frequency band. S4: Fabricate the miniaturized composite acoustic black hole structure and integrate it as part of a small device; S5: Wideband noise generated during device operation enters the structure. When the sound wave propagates in the power-law contraction through hole, the speed is slowed down (slow sound effect), and the energy is concentrated at the end of the structure. At the same time, the porous material in the through hole wall and the lateral cavity provides a distributed viscosity and heat loss mechanism, which together converts sound energy into heat energy, realizing wideband and efficient sound absorption from low frequency (such as 1000Hz or lower) to high frequency (such as 5000Hz or higher).

[0015] Compared with the prior art, the present invention has the following significant advantages:

[0016] (1) High integration with the fan: The device of the present invention can directly replace the air guide cover or shell of the existing micro cooling fan, as an integral part of the fan, without changing the main structure of the fan, without increasing the additional installation space, and with minimal impact on the aerodynamic performance of the fan. By optimizing the through hole shrinkage rate and the porous material filling area, while ensuring the broadband noise reduction effect, it minimizes the obstruction of the airflow required for heat dissipation, and is particularly suitable for noise reduction of micro cooling fans in high-end equipment such as servers, ultra-thin laptops, and projectors.

[0017] (2) Extreme miniaturization: By compressing the acoustic black hole structure to a scale of 30mm and adopting a truncated design, it can be directly embedded or used as the shell of a small heat sink or fan, with almost no increase in the size and wind resistance of the original equipment.

[0018] (3) Good structural rigidity and easy integration: The rigid frame and partition are integrated into a design, making the structure stable and suitable as part of a load-bearing or air-guiding structure; advanced manufacturing processes such as 3D printing make it possible to mass-produce this complex microstructure.

[0019] (4) Completely passive and energy-free: No active control components or external energy input are required, resulting in high reliability and long lifespan. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention used as a fan guide cover, where the gray area is the frame and the yellow area is the porous material.

[0021] Figure 2 This is a two-dimensional structural diagram of the present invention.

[0022] Figure 3 The sound pressure level characteristics of the sound-absorbing structure of this invention Figure 1 (Broadband start frequency); freq(141)=1500Hz Surface: Total sound pressure level (dB).

[0023] Figure 4 The sound pressure level characteristics of the sound-absorbing structure of this invention Figure 2 ;freq(491)=5000Hz Surface: Total sound pressure level (dB).

[0024] Figure 5 The diagram shows the sound absorption performance results of the example. Detailed Implementation

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 and Figure 2As shown, this embodiment provides a miniaturized composite acoustic black hole noise reduction device for the exhaust outlet of an ultra-thin laptop CPU cooling fan. This device, as a square sound-absorbing air duct directly connected to the fan outlet, is a component of the fan. Its external dimensions are 32mm x 32mm x 30mm (length). The internal dimensions are the side lengths. H A square channel with a diameter of 30mm. Inside the channel, there are [elements] arranged at equal intervals along the axial direction. N =10 pieces thickness t A thin plastic partition, 1mm thick, has a square through-hole at its center. The side length of the through-hole, from inlet to outlet, follows a power-law function. (Unit: mm) i The size gradually decreases from 1 to 10. The entire square channel, except for the inserted thin plate, is filled with a porous sound-absorbing layer of polyurethane foam. This device is installed at the fan outlet, with a calculation range of 0~5000 Hz. Figure 3 and Figure 4 The sound pressure levels within the structure at 1500 Hz and 5000 Hz are given respectively. As the sound wave enters the structure, the innermost cavity begins to resonate. As the frequency increases, the sound energy is localized within the sound wave black hole and cannot be reflected. Figure 5 The sound absorption coefficient curves for the range of 0 to 5000 Hz are presented. The sound absorption coefficient exceeds 0.8 in the range of 1600 to 5000 Hz, achieving broadband and efficient sound absorption performance, which can effectively reduce the aerodynamic noise of the fan.

[0027] In summary, this invention provides a broadband noise reduction device for small devices based on a miniaturized composite acoustic black hole structure. It creatively combines the geometry of a truncated acoustic black hole with distributed porous sound-absorbing materials, exciting broadband (especially low-frequency) global resonance through a power-law tapering truncated channel design, and incorporating the critical coupling effect of the porous material. This provides a high-performance, highly reliable, easily manufactured, and directly embeddable miniaturized noise reduction solution suitable for micro-cooling fans in high-end small devices.

Claims

1. A broadband noise reduction device for small devices based on a miniaturized composite acoustic black hole structure, characterized in that, include: A rigid outer shell frame with a square cross-section inside, containing axially arranged... N Each pseudo-periodic unit, where N is a positive integer not less than 10, consists of a thin partition plate with a central through hole perpendicular to the channel axis. Along the direction of sound wave incidence, the size of the central through hole gradually decreases according to a power law function, and the size of the end through hole is non-zero, forming a truncated structure. A porous sound-absorbing material layer is provided on the inner wall surface of the central through hole and / or in the lateral cavity formed by the partition plate.

2. The apparatus according to claim 1, characterized in that, The form of the power-law function is: ,in For the first i The height of each through hole i = N +1, The power law order m satisfies 1 ≤ m ≤ 4, where the thickness of the inserted thin partition is... t 1 mm≤ t ≤3 mm; H R is the total height of the channel, i.e., the side length of the square channel; R is the equivalent size of the end through hole; and L is the axial length of the square channel.

3. The apparatus according to claim 1, characterized in that, The total height of the square channel, i.e. the side length of the square channel, is 25~35mm.

4. The apparatus according to claim 1, characterized in that, The axial length of the square channel L It is 25~35mm.

5. The apparatus according to claim 1, characterized in that, The rigid outer shell frame has a thickness of 1-3 mm and is made of any one of aluminum, steel, or plastic.

6. The apparatus according to claim 2, characterized in that, In the truncated structure, the height of the first partition is... R Total height of the passageway H ratio Satisfy 0.1 ≤ ≤ 0.

5.

7. The apparatus according to claim 1, characterized in that, The porous sound-absorbing material layer is made of any one of open-cell foam, fiber material, or sintered porous metal.

8. The apparatus according to claim 1, characterized in that, The thin partition and the rigid outer shell frame are integrally formed using 3D printing technology.

9. The apparatus according to claim 1, characterized in that, The noise reduction device is constructed as a shroud for a cooling fan in a small device, a side plate of a heat sink array, or part of the housing of an electronic device.

10. A noise reduction method using the device of claim 1, characterized in that, include: The device is installed in the noise radiation path of the cooling fan of a small device in a manner consistent with the airflow direction; By utilizing the slow sound effect generated by its power-law contraction through-holes to concentrate sound energy, and by utilizing the distributed loss provided by the porous sound-absorbing material layer to dissipate sound energy, broadband passive noise reduction is achieved.

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