Copper-lanthanum composite acoustic filter screen and laser sintering preparation method thereof

Abstract

The invention provides a copper-lanthanum composite acoustic filter screen and a laser sintering preparation method thereof.The material formula of the copper-lanthanum composite acoustic filter screen comprises copper powder and lanthanum, the D50 of the copper powder is 20 microns, the content range of the copper powder is 98.8-99.5 wt%, the lanthanum exists in the form of La2O3 nanoparticles, the particle size of the lanthanum is 50-100 nm, the content range of the lanthanum is 0.5-1.2 wt%, the lanthanum is distributed on the copper grain boundary, and the particle size of the lanthanum is 10-100 nm. According to the invention, a multi-level structure design is adopted, a surface layer 15 + / -2 [mu] m gradient micropore structure, a middle layer 25 + / -3 [mu] m gradient micropore structure and a bottom layer 35 + / -5 [mu] m gradient micropore structure are arranged in a hexagonal honeycomb shape, the length-diameter ratio is controlled to be 1.2-1.5, and at least one directional gradient modification device such as a bionic spiral gradient pore array and a honeycomb lattice damping structure is combined; an acoustic regulation and control system with accurately matched frequency bands is formed, and the surface layer absorbs gt in a targeted manner; the middle layer realizes acoustic impedance optimization matching, and the bottom layer ensures efficient conduction of airflow, so that the fluctuation of the sound pressure level is controlled at lt; and compared with a metal woven mesh in a traditional scheme, the metal woven mesh is effectively improved by more than three times.

Description

Technical Field

[0001] The present invention relates to the technical field of earphone acoustic appliances, and in particular to a copper-lanthanum composite acoustic filter and a laser sintering preparation method thereof. Background Art

[0002] Existing in-ear headphone back cover filters are usually made of metal woven mesh or tuned filter cotton. However, the metal woven mesh currently on the market (such as 400-mesh stainless steel mesh) faces problems such as significant high-frequency attenuation (10kHz sound transmission loss ≥3.5dB), low porosity (≤32%), insufficient air permeability (45L / min@10Pa), and phase distortion caused by random pore distribution (group delay >0.2ms). The use of tuned filter cotton (PU foam material) has technical bottlenecks such as weak mechanical strength (tensile strength <50MPa), easy moisture absorption leading to degradation of acoustic performance, and severe high-frequency cutoff (20kHz attenuation >8dB).

[0003] At the same time, existing technologies also have limitations when processing filters on the back covers of on-ear headphones. Take the metal woven mesh as an example: the process of using mechanical stirring to achieve rare earth mixing cannot achieve precise control of the micron-level pore structure. In addition, the pore density of traditional copper powder sintered filters is ≤20,000 holes / cm² and the acoustic impedance is >300Rayl. It is difficult to break through the technical barriers of large high-frequency attenuation and the conflicting air permeability and acoustic fidelity. Therefore, it needs to be solved through innovative design of materials and structures. Summary of the Invention

[0004] The embodiments of the present invention provide a copper-lanthanum composite acoustic filter and a laser sintering preparation method thereof, aiming to solve the problems raised by the background technology.

[0005] An embodiment of the present invention provides a copper-lanthanum composite acoustic filter, comprising: wherein the copper-lanthanum composite acoustic filter material formula comprises: copper powder and lanthanum, wherein the copper powder has a D50 of 20 μm and a content range of 98.8-99.5 wt %, the lanthanum exists in the form of La2O3 nanoparticles with a particle size of 50-100 nm and a content range of 0.5-1.2 wt %, and the lanthanum is distributed at the copper grain boundaries;

[0006] Three-layer gradient microporous structure: The surface layer has a pore size of 15±2μm and a porosity of 25%, which is used for high-frequency standing wave sound absorption, targeting frequencies >5kHz; the middle layer has a pore size of 25±3μm and a porosity of 35%, and the bottom layer has a pore size of 35±5μm and a porosity of 45%. The pores of the three-layer gradient microporous structure are arranged in a hexagonal honeycomb shape with an aspect ratio of 1.2-1.5;

[0007] A directional step gradient structure acoustic modification device, comprising at least one of the following structures:

[0008] Bionic spiral gradient pore array structure: It adopts a microporous structure with double helical lines staggered. The inner layer pore size gradient gradually changes from 50μm to 80μm, corresponding to the 3000-6000Hz sensitive frequency band. The outer layer forms an annular damping zone with 120μm equidistant holes. The helix angle is 137.5°.

[0009] Honeycomb lattice damping structure: Constructs a hexagonal honeycomb unit matrix, with a micro-Helmholtz resonant cavity etched 0.05mm deep on the inner wall of each honeycomb. The cavity opening diameter varies with the frequency response gradient: 80μm in the low-frequency range <1kHz, 50μm in the mid-frequency range 1-5kHz, and 30μm in the high-frequency range >5kHz. The unit spacing is arranged using the Fibonacci sequence, gradually varying from 1.2mm-0.8mm-0.5mm.

[0010] Radial fractal branching structure: Based on Koch snowflake fractal geometry, a three-level branched micropore array is generated. The main branch aperture is 100μm, corresponding to 1-3kHz, the secondary branch is 60μm, corresponding to 3-8kHz, and the final branch is 30μm, corresponding to 8-20kHz. The branch angle is designed according to the fractal dimension D=1.85;

[0011] Vortex star composite structure: The central area adopts a 60° star-shaped main hole with a diameter of 200μm, and is surrounded by three layers of vortex-shaped micropore rings with apertures of 120μm, 80μm, and 50μm respectively. The number of vortex blades in each layer increases in prime numbers, namely 7, 11, and 13 pieces respectively.

[0012] In one embodiment of the present invention, the thicknesses of the surface layer, middle layer and bottom layer are 15 μm, 25 μm and 35 μm respectively.

[0013] In one embodiment of the present invention, the length-to-diameter ratio of the channels arranged in the hexagonal honeycomb pattern is 1.3.

[0014] A method for preparing a copper-lanthanum composite acoustic filter screen by laser sintering, for preparing any one of the above-mentioned copper-lanthanum composite acoustic filter screens, comprising the following steps:

[0015] S1, powder pretreatment: copper powder with a D50 of 20 μm and La2O3 nanopowder with a particle size of 50 nm were ball-milled for 2 h at a speed of 300 rpm, so that the tap density after mixing was ≥4.5 g / cm³ and the mixing uniformity CV was ≤5%;

[0016] S2, gradient energy sintering: The three-layer gradient microporous structure is laser sintered, with the surface layer laser power of 150W, the scanning speed of 800mm / s, and the energy density of 80-100J / cm²; the middle layer laser power of 120W, the scanning speed of 1000mm / s, and the energy density of 60-80J / cm²; the bottom layer laser power of 90W, the scanning speed of 1200mm / s, and the energy density of 40-60J / cm²;

[0017] S3, post-treatment: annealing treatment was performed under an argon + 3% H2 protective atmosphere at a temperature of 400°C for 1 h, and then a 5 μm polyurethane hydrophobic layer was sprayed on the filter surface to make the contact angle >120°.

[0018] As an embodiment of the present invention, in the gradient energy sintering of step S2, the energy density of the surface layer is 90 J / cm², the energy density of the middle layer is 70 J / cm², and the energy density of the bottom layer is 50 J / cm².

[0019] In one embodiment of the present invention, during the ball milling process, the grinding medium is agate balls.

[0020] In one embodiment of the present invention, after the annealing treatment, the filter screen is further subjected to ultrasonic cleaning, the cleaning liquid is anhydrous ethanol, and the cleaning time is 15-20 minutes.

[0021] In one embodiment of the present invention, the polyurethane hydrophobic layer is sprayed by electrostatic spraying.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention adopts a multi-level structural design, with three layers of gradient microporous structures (15±2μm surface layer, 25±3μm middle layer, and 35±5μm bottom layer) arranged in a hexagonal honeycomb pattern, with an aspect ratio controlled at 1.2-1.5. Combined with at least one directional gradient modification device, such as a bionic spiral gradient pore array and a honeycomb lattice damping structure, this forms an acoustic control system with precise frequency matching. The surface layer specifically absorbs high-frequency standing waves >5kHz, the middle layer achieves optimized acoustic impedance matching, and the bottom layer ensures efficient airflow conduction, keeping the sound pressure level fluctuation within <±0.8dB, which is more than three times higher than the metal woven mesh in traditional solutions.

[0024] 2) The synergistic effect of the copper-lanthanum composite material formula of the present invention and the gradient energy laser sintering process significantly improves the comprehensive performance of the filter screen, with the acoustic impedance reduced to 120-150Rayl, the air permeability increased to 85±3L / min@10Pa, the attenuation at 10kHz is only 1.2dB, and the fatigue life exceeds 1×10 6Secondly, the directional step gradient structure, in particular, reduces the attenuation of mid- and high-frequency overtone peaks by 4.2-6.8dB through designs such as bionic spiral holes and fractal branches, and optimizes the standing wave ratio from 2.8:1 to 1.5:1, fundamentally resolving the contradiction between high-frequency attenuation and acoustic fidelity of traditional filters, and achieving a comprehensive improvement in the sound quality of headphones. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 A schematic structural diagram of a copper-lanthanum composite acoustic filter provided in an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the gradient microporous structure of a copper-lanthanum composite acoustic filter provided in an embodiment of the present invention.

[0028] Icons: 100, copper-lanthanum composite acoustic filter material; 200, gradient microporous structure; 210, surface layer; 220, middle layer; 230, bottom layer; 300, directional step gradient structure acoustic modification device; 310, bionic spiral gradient hole array structure; 320, honeycomb lattice damping structure; 330, radial fractal branch structure; 340, vortex starburst composite structure. DETAILED DESCRIPTION

[0029] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0031] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0034] In the present invention, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; they may refer to direct connection or indirect connection through an intermediate medium; they may refer to internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0035] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0036] Example

[0037] See also Figure 1-2A copper-lanthanum composite acoustic filter comprises: wherein the copper-lanthanum composite acoustic filter material 100 comprises: copper powder and lanthanum, wherein the D50 of the copper powder is 20 μm and its content ranges from 98.8% to 99.5% by weight, and lanthanum exists in the form of La2O3 nanoparticles with a particle size of 50-100 nm and a content range of 0.5% to 1.2% by weight, and lanthanum is distributed at the copper grain boundaries; a three-layer gradient microporous structure 200: the surface layer 210 has a pore size of 15±2 μm and a porosity of 25%, which is used for high-frequency standing wave sound absorption, for frequencies > 5 kHz; the middle layer 220 has a pore size of 15±2 μm and a porosity of 25%, which is used for high-frequency standing wave sound absorption, for frequencies > 5 kHz; The aperture of the bottom layer 230 is 35±5μm, the porosity is 35%, the aperture of the bottom layer 230 is 35±5μm, the porosity is 45%, the pores of the three-layer gradient microporous structure are arranged in a hexagonal honeycomb shape, and the aspect ratio is 1.2-1.5; the directional step gradient structure acoustic modification device 300 includes at least one of the following structures: a bionic spiral gradient hole array structure 310: a microporous structure with double helices staggered, the inner layer aperture gradient gradually changes from 50μm to 80μm, corresponding to the 3000-6000Hz sensitive frequency band, and the outer layer forms an annular damping with 120μm equidistant holes The spiral angle is 137.5°; honeycomb lattice damping structure 320: a hexagonal honeycomb unit matrix is ​​constructed, and a micro-Helmholtz resonant cavity with a depth of 0.05mm is etched on the inner wall of each honeycomb. The cavity diameter changes with the frequency response gradient. The cavity diameter in the low-frequency range <1kHz is 80μm, in the mid-frequency range 1-5kHz is 50μm, and in the high-frequency range >5kHz is 30μm. The unit spacing is arranged in the Fibonacci sequence, gradually changing from 1.2mm-0.8mm-0.5mm; radial fractal branch structure 330: based on the Koch snowflake fractal geometry Based on the principle of high-performance quantum doping control, a three-level branched micropore array is generated, with a main branch aperture of 100μm, corresponding to 1-3kHz, a secondary branch of 60μm, corresponding to 3-8kHz, and a final branch of 30μm, corresponding to 8-20kHz. The branch angle is designed according to the fractal dimension D=1.85; the vortex star composite structure 340: the central area adopts a 60° star-shaped main hole with a diameter of 200μm, and is surrounded by three layers of vortex-shaped micropore rings with apertures of 120μm, 80μm, and 50μm respectively. The number of vortex blades in each layer increases according to prime numbers, namely 7, 11, and 13 pieces respectively.

[0038] Specifically, in the in-ear headphones, D50=20μm, 98.8-99.5wt% copper powder and 50-100nm, 0.5-1.2wt% La2O3 nanoparticles are distributed at the copper grain boundaries, and the grain boundary segregation effect of lanthanum is used to increase the material damping coefficient by 40%, reducing the energy loss in sound wave propagation. In the three-layer gradient microporous structure 200, the surface layer 210, 15±2μm pore size, 25% porosity forms a dense sound absorption barrier for high-frequency sound waves >5kHz, through The small aperture limits the diffusion of acoustic flow, and the turbulence suppression effect of the hexagonal honeycomb channels with an aspect ratio of 1.2-1.5 reduces high-frequency standing wave reflections. The middle layer 220, with a pore size of 25±3μm and a porosity of 35%, acts as an acoustic impedance transition layer. Through the pore gradient, it adjusts the acoustic wave transmission resistance, stabilizing the 1kHz acoustic impedance at 120-150Rayl. The bottom layer 230, with a pore size of 35±5μm and a porosity of 45%, provides a large-aperture channel to ensure airflow conduction and avoid low-frequency distortion caused by insufficient air permeability.

[0039] The directional order gradient structure acoustic modification device 300 is precisely optimized according to the requirements of different frequency bands: the double helix of the bionic spiral gradient hole array structure 310 has a gradual pore size of 50-80μm in the inner layer and 120μm equidistant holes in the outer layer arranged at a golden section angle of 137.5°, simulating the frequency response of cochlear hair cells, guiding the sound flow to form a spiral channel in the 3000-6000Hz frequency band, reducing the attenuation of the piano overtone peak by 4.2-5.5dB, and the Helmholtz resonance cavity of the honeycomb lattice damping structure 320 has a cavity opening of 80μm in the low frequency zone, 50μm in the mid-frequency zone, and 30μm in the high frequency zone, and is matched with the Fibonacci spacing of 1.2mm-0.8mm-0.5mm, at 2000-3000Hz. The frequency band attenuates standing waves from 7.5dB to 2.3dB, improving language clarity; the radial fractal branch structure 330 generates three-level branches with Koch snowflake geometry, with the main branch being 100μm, the secondary branch being 60μm and the final branch being 30μm. In the 10-16kHz frequency band, the standing waves are attenuated by 18-20dB through the multi-scale diffraction unit, suppressing the diaphragm splitting vibration; the vortex star composite structure 340 has a 200μm star main hole and 120μm, 80μm, and 50μm apertures, and a vortex ring with 7 / 11 / 13 blades to form an acoustic flow convergence-diffusion system, which, combined with a lanthanum content gradient substrate, makes the full-band group delay deviation <±0.8μs, and the left and right channel phase difference is reduced from 15° to 5°, optimizing stereo positioning.

[0040] The specific performance comparison data is as follows:

[0041] parameter The present invention Traditional metal woven mesh Tuning filter cotton Acoustic impedance 1kHz, Rayl 120-150 300-400 50-80 Air permeability L / min@10Pa 85±3 45±5 120±10 10kHz attenuation dB 1.2 3.5 6.8 Fatigue life times <![CDATA[>1×10 6 ]]> <![CDATA[2×10 5 ]]> <![CDATA[5×10 4 ]]>

[0042] Then, the copper-lanthanum composite acoustic filter of the present invention realizes acoustic regulation through the synergistic effect of the material 100 formulation, the three-layer gradient microporous structure 200 and the directional step gradient structure acoustic modification device 300.

[0043] In this embodiment, the thicknesses of the surface layer, the middle layer and the bottom layer are 15 μm, 25 μm and 35 μm respectively.

[0044] Specifically, when the earphones produce sound, high-frequency sound waves >5kHz first contact the 15μm-thick surface layer 210, whose 15±2μm pore size and 25% porosity form a dense sound-absorbing layer. By utilizing the scattering effect of small pores on high-frequency sound waves, the 10kHz attenuation is controlled at 1.2dB; the 25μm-thick middle layer 220 forms an impedance buffer zone in the sound wave transmission path through 25±3μm pore size and 35% porosity, making the sound pressure level fluctuation <±0.8dB; the 35μm-thick bottom layer 230 forms an impedance buffer zone in the sound wave transmission path through 35±5μm pore size and 4 The 5% porosity serves as the main airflow channel, ensuring an air permeability of 85±3L / min@10Pa and avoiding low-frequency response distortion caused by airflow blockage. At the same time, the gradient matching of the three-layer thickness and pore size enables the sound waves to complete progressive regulation from high-frequency absorption, impedance matching to airflow conduction within a total thickness of 0.75μm. Compared with the traditional flat filter with uniform thickness and non-gradient design, the acoustic fidelity is significantly improved, especially in the high-frequency overtone range of 8000-10kHz of the violin, the standing wave attenuation reaches 9dB and the energy retention rate is increased by 22%.

[0045] In this embodiment, the channels arranged in a hexagonal honeycomb pattern have an aspect ratio of 1.3.

[0046] Specifically, in the headphone acoustic cavity environment, the internal angle of the hexagonal geometric structure is 120°, and an equilateral triangle support structure is formed between adjacent channels, which improves the structural strength by 30% compared to circular channels and achieves a tensile strength of 85MPa. At the same time, it reduces the degradation of acoustic performance caused by channel deformation. The design of an aspect ratio of 1.3 makes the channel depth and diameter form the best fluid dynamics ratio. When the sound wave passes through the channel, the turbulence intensity of the sound flow in the channel is reduced by 3-5dB. In the measured 20-20kHz frequency band, additional noise caused by turbulence is avoided. At the same time, the reflection path of the sound wave on the hexagonal hole wall tends to be consistent, reducing phase distortion and making the group delay error below 10kHz <0.3μs. In the high-frequency response of the headphone, this structure, combined with the 15μm aperture of the surface layer 210, improves the ultra-high frequency sensitivity of 20-22kHz by 1.2dB, and retains overtones beyond the upper limit of human hearing. Due to channel turbulence and phase distortion, the traditional filter attenuates the ultra-high frequency energy by more than 8dB.

[0047] The specific acoustic performance tests are as follows:

[0048] Test standard: IEC 60318-4 artificial ear simulation

[0049] result:

[0050] Frequency Hz Sound transmission loss dB Phase delay ms 1000 0.02 0.02 5000 0.04 0.05 10000 0.04 0.08

[0051] A method for preparing a copper-lanthanum composite acoustic filter screen by laser sintering, for preparing any of the above-mentioned copper-lanthanum composite acoustic filter screens, comprising the following steps:

[0052] S1, powder pretreatment: copper powder with a D50 of 20 μm and La2O3 nanopowder with a particle size of 50 nm were ball-milled for 2 h at a speed of 300 rpm, so that the tap density after mixing was ≥4.5 g / cm³ and the mixing uniformity CV was ≤5%;

[0053] S2, gradient energy sintering: laser sintering of three-layer gradient microporous structure, the surface layer laser power is 150W, the scanning speed is 800mm / s, the energy density is 80-100J / cm²; the middle layer laser power is 120W, the scanning speed is 1000mm / s, the energy density is 60-80J / cm²; the bottom layer laser power is 90W, the scanning speed is 1200mm / s, the energy density is 40-60J / cm²;

[0054] S3, post-treatment: annealing treatment was performed under an argon + 3% H2 protective atmosphere at a temperature of 400°C for 1 h, and then a 5 μm polyurethane hydrophobic layer was sprayed on the filter surface to make the contact angle >120°.

[0055] Specifically, when the copper-lanthanum composite acoustic filter is prepared by laser sintering, the structure and performance of the filter are precisely controlled through the synergy of powder pretreatment S1, gradient energy sintering S2 and post-processing S3. In the powder pretreatment stage, 20μm copper powder and 50nm La2O3 nanopowder are ball-milled at 300rpm for 2h to make the lanthanum element evenly distributed at the copper grain boundary, with a mixing uniformity CV≤5% and a tap density ≥4.5g / cm³. During gradient energy sintering, the surface layer 210 adopts 150W laser power and 800mm / s scanning speed, with an energy density of 80-100J / cm². The high energy density ensures the forming accuracy of the 15μm small pore size and avoids powder melting. The middle layer 220 is sintered at 120W power, 1000mm / s speed, and 60-80J / cm² to balance the forming strength and porosity of the 25μm pore size. The bottom layer 230 is sintered at 90W power, 1200mm / s speed, and 40-60J / cm² to reduce the melting depth and ensure the penetration of the 35μm pore size. The 1064nm laser wavelength has a high match with the absorptivity of the copper powder, reducing energy loss. In post-processing, annealing at 400℃ in argon + H2 eliminates sintering stress and improves the ductility of the material. The tensile strength is 85MPa, and the 5μm polyurethane hydrophobic layer with a contact angle of >120° prevents sweat erosion and extends the fatigue life to >1×10 6 Second, the ultrasonic cleaning step removes residual powder on the surface to ensure the cleanliness of the pores.

[0056] In this embodiment: in the gradient energy sintering of step S2, the energy density of the surface layer is 90 J / cm², the energy density of the middle layer is 70 J / cm², and the energy density of the bottom layer is 50 J / cm².

[0057] Specifically, when the energy densities of the surface layer, middle layer, and bottom layer are 90J / cm², 70J / cm², and 50J / cm² respectively, the laser energy is precisely coupled with the three-layer structure. The surface layer 210 fully melts the copper powder and La2O3 nanoparticles with an energy density of 90J / cm², and achieves a pore wall smoothness of Ra<1.6μm at an aperture of 15μm, reducing acoustic flow friction loss. Combined with the 137.5° angle of the bionic spiral hole 310, the attenuation of the mid- and high-frequency overtone peak of 3200-4500Hz is reduced by 4.2-5.5dB; the middle layer 220 forms a semi-molten sintering neck at an aperture of 25μm with an energy density of 70J / cm², which not only ensures structural strength but also retains a porosity of 35% for Acoustic impedance matching, combined with the Helmholtz resonator of the honeycomb lattice damping structure 320, attenuates high-frequency standing waves in the 8000-10kHz range by 9dB. The bottom layer 230 melts only the powder surface at an energy density of 50J / cm², forming a 35μm through-hole. A porosity of 45% ensures airflow, and combined with the final 30μm branches of the radial fractal branch structure 330, the energy retention rate at very high frequencies in the 18-20kHz range is increased by 22%. Therefore, the energy gradient design enables the sintering density of the three-layer structure to be controlled at 88%, 82%, and 75%, respectively. The corresponding acoustic impedance gradually decreases from the surface to the bottom layer, forming a uniform impedance curve of 120-150Rayl, with fluctuations of <±1.5Ω from 1-20kHz.

[0058] In this embodiment, during the ball milling process, the grinding medium is agate balls.

[0059] Specifically, when using agate balls as the ball mill mixing medium, grinding at 300 rpm for 2 hours can achieve impurity-free and uniform dispersion of copper powder and La2O3 nanopowder. Among them, the Mohs hardness of the agate balls reaches 7-7.5, which is higher than that of copper powder and La2O3. The agate balls themselves wear very little during the grinding process, avoiding the introduction of impurities that affect the material's conductivity and acoustic damping properties. The electrical conductivity is 85% IACS.

[0060] By utilizing the collision and rolling action of agate balls during ball milling, 50nm La2O3 nanoparticles are evenly embedded in the 20μm copper powder gaps, distributed on the copper powder surface through the cold welding effect, and precisely positioned at the copper grain boundaries after subsequent sintering, achieving grain boundary segregation of lanthanum elements, and increasing the material's damping coefficient from 0.05 to 0.07, effectively absorbing the mechanical vibration energy during sound wave propagation.

[0061] In this embodiment, after the annealing treatment, the filter screen is further subjected to ultrasonic cleaning, the cleaning liquid is anhydrous ethanol, and the cleaning time is 15-20 minutes.

[0062] Specifically, an ultrasonic cleaning step is added after the annealing treatment. Anhydrous ethanol can be used as the cleaning material for 15-20 minutes to remove the sintering aids and oxides remaining on the surface of the filter, ensuring that the pores are unobstructed.

[0063] During ultrasonic cleaning, anhydrous ethanol produces a cavitation effect under high-frequency vibration, impacting the inner walls and gaps of the channel, peeling off and dissolving impurity particles with a particle size greater than 5μm, and achieving a channel cleanliness level of over 99%. After cleaning, the 15±2μm pore pass rate of the surface layer 210 is increased to 98%, and the air permeability is increased from 80L / min@10Pa to 85±3L / min@10Pa. At the same time, the scattering of impurities on the sound flow is reduced, reducing the 5kHz harmonic distortion from 0.8% to 0.35%. The cleaning effect is particularly significant on the 0.05mm deep Helmholtz resonance cavity of the honeycomb lattice damping structure 320, avoiding the resonance frequency shift caused by cavity blockage and ensuring precise matching of the acoustic resonance effects of the 80μm cavity in the low-frequency region and the 50μm cavity in the mid-frequency region.

[0064] In this embodiment, the polyurethane hydrophobic layer is sprayed by electrostatic spraying.

[0065] Specifically, when a 5μm polyurethane hydrophobic layer is prepared by electrostatic spraying, a uniform and dense protective film is formed on the surface of the filter. During the electrostatic spraying process, the polyurethane droplets are negatively charged under the action of the high-voltage electric field and migrate to the positively charged filter surface. Coulomb force is used to achieve nano-scale spreading, and the film thickness uniformity is controlled within ±0.5μm, avoiding the pore blockage caused by uneven thickness of traditional spraying. In addition, the contact angle of the hydrophobic layer is greater than 120°, which can effectively block the intrusion of liquids such as sweat and water vapor, prevent the oxidation of copper powder and the hydrolysis of La2O3, and ensure that the filter maintains stable acoustic impedance in humid environments.

[0066] For the 200μm star-shaped main pores and 50μm eddy current micropores of the eddy current star-shaped composite structure 340, electrostatic spraying can precisely control the film thickness without affecting the pore size, while improving the surface wear resistance and making the fatigue life exceed 1×10 6 The low surface energy of the hydrophobic layer reduces dust adhesion and maintains a long-term stable density of 27,000 pores / cm², thus avoiding degradation of acoustic performance due to pore blockage.

[0067] In this embodiment, in the gradient energy sintering in step S2, the laser wavelength used is 1064 nm.

[0068] Specifically, when laser sintering uses a wavelength of 1064nm, it matches the optical absorption characteristics of copper powder, improving energy utilization and sintering accuracy. 1064nm belongs to the near-infrared band, and the absorption rate of copper powder at this wavelength is about 30%. The laser energy can effectively penetrate the powder surface, causing the 20μm copper powder and 50nm La2O3 nanoparticles to melt synchronously to form a uniform copper-lanthanum solid solution. Moreover, the focusing spot diameter of the wavelength beam can be controlled within 50μm, meeting the 15±2μm aperture forming requirements of the surface layer 210, avoiding channel adhesion caused by large spots. At the same time, the excitation effect of this wavelength laser on lanthanum is weak, avoiding the decomposition of La2O3 nanoparticles due to overheating, ensuring the uniform distribution of lanthanum at the copper grain boundary, and maintaining the material damping coefficient at a stable value of 0.07.

[0069] In this embodiment: in the powder pretreatment in step S1, the mixed powder is dried at 100-120° C. for 2-3 hours.

[0070] Specifically, during the ball milling process, the surface of the copper powder and the La2O3 nanopowder will absorb moisture in the air, and the moisture will be vaporized during laser sintering to produce pores, resulting in a decrease in the 15μm pore penetration rate of the surface layer 210 and the formation of microcracks inside the filter, reducing the tensile strength from 85MPa to 70MPa. The drying process makes the moisture content of the powder less than 0.05%, avoiding the hole defects caused by gas escape during sintering, and ensuring the forming accuracy of the three-layer gradient microporous structure 200. As for the 0 .05mm Helmholtz resonance cavity, the sintering density of the dried powder is increased by 5%, the cavity wall integrity is better, and the resonance effect is more significant, which makes the 2000-3000Hz mid-frequency standing wave attenuated from 7.5dB to 2.3dB. The fluidity of the powder after drying can also be improved. During the powder spreading process, it can be more evenly filled into the tertiary branch micropores of the radial fractal branch structure 330, avoiding branch breakage caused by powder accumulation, and ensuring the design effect of 18-20dB attenuation of 10-16kHz ultra-high frequency standing waves.

[0071] It should also be added that:

[0072] Lanthanum element replacement: Cerium Ce can be used to partially replace lanthanum La / Ce=7:3, and the acoustic impedance can be maintained at 140-160 Rayl;

[0073] Hole design: Circular hole diameter of 20μm combined with diamond arrangement can still achieve a density of 27,000 holes / cm²;

[0074] Sintering process: Electron beam melting (EBM) replaces laser sintering, and the energy density is adjusted to 50-80 J / cm².

[0075] The above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A copper-lanthanum composite acoustic filter, characterized in that: include: The copper-lanthanum composite acoustic filter material formula (100) comprises: Copper powder and lanthanum, wherein the copper powder has a D50 of 20 μm and a content of 98.8-99.5 wt %, the lanthanum is in the form of La2O3 nanoparticles with a particle size of 50-100 nm and a content of 0.5-1.2 wt %, and the lanthanum is distributed at the copper grain boundaries; Three-layer gradient microporous structure (200): the surface layer (210) has a pore size of 15±2 μm and a porosity of 25%, which is used for high-frequency standing wave sound absorption, targeting frequencies > 5 kHz; the middle layer (220) has a pore size of 25±3 μm and a porosity of 35%, and the bottom layer (230) has a pore size of 35±5 μm and a porosity of 45%. The pores of the three-layer gradient microporous structure are arranged in a hexagonal honeycomb shape with an aspect ratio of 1.2-1.5; A directional step gradient structure acoustic modification device (300) comprising at least one of the following structures: Bionic spiral gradient pore array structure (310): It adopts a microporous structure with double helical lines staggered, with the inner layer pore size gradient gradually changing from 50 μm to 80 μm, corresponding to the 3000-6000 Hz sensitive frequency band, and the outer layer forms an annular damping belt with 120 μm equidistant holes, and the helix angle is 137.5°; Honeycomb lattice damping structure (320): a hexagonal honeycomb unit matrix is ​​constructed, and a micro Helmholtz resonant cavity with a depth of 0.05 mm is etched on the inner wall of each honeycomb. The cavity opening diameter changes with the frequency response gradient. The cavity opening in the low frequency range <1 kHz is 80 μm, in the mid-frequency range 1-5 kHz is 50 μm, and in the high frequency range >5 kHz is 30 μm. The unit spacing is arranged in the Fibonacci sequence, gradually changing from 1.2 mm to 0.8 mm to 0.5 mm. Radial fractal branch structure (330): Based on Koch snowflake fractal geometry, a three-level branched micropore array is generated, with the main branch aperture of 100 μm, corresponding to 1-3 kHz, the secondary branch aperture of 60 μm, corresponding to 3-8 kHz, and the final branch aperture of 30 μm, corresponding to 8-20 kHz. The branch angle is designed according to the fractal dimension D = 1.85; Vortex star composite structure (340): The central area adopts a 60° star-shaped main hole with a diameter of 200 μm, and is surrounded by three layers of vortex-shaped micropore rings with apertures of 120 μm, 80 μm, and 50 μm respectively. The number of vortex blades in each layer increases in prime numbers, namely 7, 11, and 13.

2. A copper-lanthanum composite acoustic filter according to claim 1, characterized in that: The thicknesses of the surface layer, middle layer and bottom layer are 15 μm, 25 μm and 35 μm respectively.

3. The copper-lanthanum composite acoustic filter according to claim 1, characterized in that: The length-to-diameter ratio of the pores arranged in the hexagonal honeycomb pattern is 1.

3.

4. A method for preparing a copper-lanthanum composite acoustic filter by laser sintering, characterized in that: For preparing a copper-lanthanum composite acoustic filter according to any one of claims 1 to 3, the method comprises the following steps: S1, powder pretreatment: copper powder with a D50 of 20 μm and La2O3 nanopowder with a particle size of 50 nm were ball-milled for 2 h at a speed of 300 rpm, so that the tap density after mixing was ≥4.5 g / cm³ and the mixing uniformity CV was ≤5%; S2, gradient energy sintering: The three-layer gradient microporous structure is laser sintered, with the surface layer laser power of 150W, the scanning speed of 800mm / s, and the energy density of 80-100J / cm²; the middle layer laser power of 120W, the scanning speed of 1000mm / s, and the energy density of 60-80J / cm²; the bottom layer laser power of 90W, the scanning speed of 1200mm / s, and the energy density of 40-60J / cm²; S3, post-treatment: annealing treatment was performed under an argon + 3% H2 protective atmosphere at a temperature of 400°C for 1 h, and then a 5 μm polyurethane hydrophobic layer was sprayed on the filter surface to make the contact angle >120°.

5. The laser sintering preparation method of the copper-lanthanum composite acoustic filter according to claim 4, characterized in that: In the gradient energy sintering of step S2, the energy density of the surface layer is 90 J / cm², the energy density of the middle layer is 70 J / cm², and the energy density of the bottom layer is 50 J / cm².

6. The laser sintering preparation method of the copper-lanthanum composite acoustic filter according to claim 4, characterized in that: In the ball milling mixing process, the grinding medium is agate balls.

7. The laser sintering preparation method of the copper-lanthanum composite acoustic filter according to claim 4, characterized in that: After the annealing treatment, the filter screen is ultrasonically cleaned using anhydrous ethanol for 15-20 minutes.

8. The laser sintering preparation method of the copper-lanthanum composite acoustic filter according to claim 4, characterized in that: The polyurethane hydrophobic layer is sprayed by electrostatic spraying.

9. The laser sintering preparation method of the copper-lanthanum composite acoustic filter according to claim 4, characterized in that: In the gradient energy sintering in step S2, the laser wavelength used is 1064 nm.

10. The laser sintering preparation method of the copper-lanthanum composite acoustic filter according to claim 4, characterized in that: In the powder pretreatment in step S1, the mixed powder is dried at 100-120° C. for 2-3 hours.

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