44 results about "Micro perforated plate" patented technology

The invention belongs to the technical field of low-frequency sound absorption, and discloses a micro-perforated plate composite gradient spiral pipe sound absorption device and method.The micro-perforated plate composite gradient spiral pipe sound absorption device comprises a variable cross-section spiral pipe, and the diameter of the inlet end of the variable cross-section spiral pipe is larger than that of the outlet end of the variable cross-section spiral pipe; a plurality of MPP plates are mounted in the variable-cross-section spiral pipe, one MPP plate is embedded into the inlet end of the variable-cross-section spiral pipe, and the other MPP plates are sequentially embedded into the variable-cross-section spiral pipe at equal intervals, so that a multi-stage MPP plate composite sound absorption structure is formed; and the cross-section pipe diameter of the variable cross-section spiral pipe is linearly reduced from the inlet end of the variable cross-section spiral pipe to the outlet end of the variable cross-section spiral pipe. Through the gradient design of the variable cross-section spiral tube integrated micro-perforated plate, low-frequency broadband efficient sound absorption is realized in a compact space, the problem of heavy structure caused by dependence on a deep and large back cavity in the traditional technology is avoided, the limitation of narrow sound absorption frequency band is overcome, and the sound absorption device is particularly suitable for being applied to occasions with limited spaces and has wide application prospects. And low-frequency performance and broadband characteristics are considered in a limited space.

The invention discloses a design method of an array type silencer adaptive to a main ventilation air path between a stator iron core of a hydraulic generator and an air cooler and the array type silencer, and relates to the technical field of suppression or reduction of noise of the hydraulic generator. The method comprises the steps of S1, obtaining aerodynamic noise data and airflow parameters of a main ventilation air path, S2, determining a silencing thought and a micro-perforated plate array core structure according to broadband vortex, discrete rotation, vortex falling and surge noise, S3, determining the boundary dimension and preliminarily calculating the airflow parameters, S4, designing plate parameters in combination with a micro-perforated resonance formula, and S5, calculating the noise of the micro-perforated plate array. S5, performing simulation optimization and S6, accurately accounting airflow parameters, and locking a scheme meeting requirements; the silencer comprises a shell and a plurality of micro-perforated plates, and the multiple layers of micro-perforated plates are arranged in series. The invention has the advantages of no sound absorption material, low wind resistance (the air volume attenuation is less than or equal to 5%, and the pressure loss is less than or equal to 200Pa), the noise of the main wind path is reduced by 5-7dB (A), the service life is long, the operation and maintenance cost is low, and the requirements of the main wind path are met.

The invention discloses a low-turbulence noise-reduction hydro-generator rotor and a hydro-generator, and relates to the technical field of hydro-generators. Inter-pole wind shields are assembled between salient poles of the rotor, the peripheral cambered surfaces of the inter-pole wind shields are consistent with the peripheral radiuses of the poles, and the inner sides of the inter-pole wind shields are attached to magnetic pole transition surfaces, provided with ventilation holes and fixed through tensioning screws; and the fans at the two ends of the rotor adopt wing-shaped fan blades such as NACA0012 / 0016 / 0018 and the like. According to the hydro-generator, a metal micro-perforated plate is assembled on a main ventilation air path between a stator iron core and an air cooler, the array resistance-resistance performance of a non-sound-absorption material conforms to a silencer type silencer, plate bodies are arranged in series, an air inlet / outlet is bent by 45 degrees, and parameters are accurately designed through a resonance formula. Rotor hidden polarization and precise noise elimination of a main air path are achieved, double noise reduction enables the noise of the whole machine to be smaller than or equal to 65 dB (A), the wind resistance is low (the air volume attenuation is smaller than or equal to 5%), heat dissipation reaches the standard, the structure is stable, the operation and maintenance cost is low, and the requirements of a large-capacity and high-rotating-speed unit are met.

The invention relates to a multi-physical mechanism synergistic light sound absorption and insulation integrated sandwich structure and a manufacturing method thereof.The multi-physical mechanism synergistic light sound absorption and insulation integrated sandwich structure comprises a panel, a sandwich layer and a micro-perforated panel which are arranged from top to bottom, a cavity is formed in the sandwich layer, and multiple sets of cantilever beam type harmonic oscillators arranged in an array are arranged in the cavity; the cantilever beam type harmonic oscillator comprises a cantilever beam base body and a metal rubber mass block fixed at the top end of the cantilever beam base body. According to the invention, through the coupling design of the micro-perforated plate and the internal grating cavity of the sandwich layer, the sound absorption frequency band is further widened, the sound absorption coefficient of the whole structure in a middle-high frequency band is improved, collaborative optimization of broadband sound absorption and low-frequency sound insulation is realized, the problem that a traditional harmonic oscillator is easy to lose efficacy in high-temperature and low-temperature environments is effectively solved, and the sound absorption efficiency is improved. And meanwhile, due to the design of the integrated sandwich structure, the problems of aging and layering of the adhesive layer in severe environments such as high temperature and damp and hot environments are avoided, and the integrity and durability of the structure are also remarkably improved.

The utility model relates to the technical field of silencers, and discloses a high temperature resistant pipeline type silencer, which comprises a static pressure box and a sound absorption sheet, the inside of the static pressure box is fixedly connected with a silencing pipe, the inside of the silencing pipe is fixedly connected with the sound absorption sheet, the back surface of the silencing pipe is fixedly connected with a fixing device, the sound absorption sheet comprises a sound absorption body, and the fixing device is fixedly connected with the sound absorption body. The front face and the back face of the sound absorption body are fixedly connected with a flow guide cover, air grooves are formed in the two sides of the interior of the sound absorption body, micro-penetrating holes are formed in the two sides of the sound absorption body, and the micro-penetrating holes are evenly distributed and communicate with the air grooves. Air flow enters the silencer and is separated by the sound absorption sheets, sound enters the air grooves through the micro-perforated holes, the micro-perforated plate where the micro-perforated holes are located and the air grooves form a resonance sound absorption structure, the sound is absorbed, the sound absorption sheets are simple in structure, easy to clean and resistant to high temperature, and the silencer can be used in a high-temperature environment easily.

This invention discloses a low-frequency noise reduction and sound insulation device for industrial applications, belonging to the field of noise control technology. The device includes an outer soundproof cover, an inner composite sound-absorbing structure, and an active noise control system. The outer soundproof cover is constructed of high-density board. The inner composite sound-absorbing structure is located on the inner wall of the outer soundproof cover and includes an acoustic metamaterial layer and a micro-perforated plate layer, which are spaced apart to form a first resonant cavity. The active noise control system includes: an error microphone embedded in the inner wall of the outer soundproof cover; a controller electrically connected to the error microphone; and a secondary sound source electrically connected to the controller and installed on the inner wall of the outer soundproof cover. This invention achieves broadband passive sound absorption through the composite structure of acoustic metamaterial and micro-perforated plate, providing a high signal-to-noise ratio environment for the active control system. Furthermore, the active control system based on the FxLMS algorithm precisely cancels residual low-frequency line spectra, achieving efficient and stable low-frequency noise reduction.

The utility model discloses a composite absorption device for enhancing low frequency sound absorption, which belongs to the technical field of pipeline acoustics black holes, and comprises a sound tube, a plurality of micro-perforated plates and a Helmholtz sound absorber, the micro-perforated plates are distributed at equal intervals along the axial direction of the inlet end of the sound tube and are arranged from large to small according to the perforated distribution area, and the Helmholtz sound absorber is arranged on the sound tube. Micro-pores are uniformly distributed in each micro-perforated plate; every two adjacent micro-perforated plates are connected through a separation ring; the Helmholtz sound absorbers are distributed at equal intervals in the axial direction of the outlet end of the sound tube, the diameters of the gradually-changed embedded necks are gradually reduced, the center of each Helmholtz sound absorber is provided with a gradually-changed embedded neck, and the inner diameter of each gradually-changed embedded neck is gradually reduced from the inlet end to the outlet end; every two adjacent Helmholtz sound absorbers are connected through a sound absorber cavity. According to the utility model, through the combination of the composite gradually-changed micro-perforated plate and the gradually-changed cascaded Helmholtz sound absorbers which are embedded in the neck part, low-frequency sound absorption and medium-high frequency broadband sound absorption are realized under the sub-wavelength length.

The invention relates to the technical field of building noise control, and discloses a building noise control method based on sound absorption cavity design, which comprises the following steps: arranging a plurality of sound absorption cavities in a concrete truss, filling a porous sound absorption material in the cavities, covering a micro-perforated plate, and optimizing the noise reduction effect by adjusting the geometric dimensions and the arrangement mode of the cavities. According to the method, the internal space of the concrete truss can be fully utilized, the design parameters are optimized in combination with experimental testing and numerical simulation, low-frequency noise propagation is effectively inhibited, and the additional burden on a building structure is relieved. The sound absorption cavity is formed in the inner space of the concrete truss, and the porous sound absorption material and the micro-perforated plate are combined, so that the inner space of the concrete truss is fully utilized, and the additional burden of a traditional sound insulation measure on a building structure is avoided; the geometric dimension and the arrangement mode of the sound absorption cavities can be flexibly adjusted according to the building floor height and the noise frequency characteristic, and therefore the low-frequency noise suppression capacity is improved.

This invention discloses a superstructure design method for suppressing noise loads in aircraft under high-speed environments, relating to the field of aircraft design. The method includes: obtaining characteristic noise frequencies through simulation using a typical cavity model; introducing various designable structures such as micro-perforated plates, Helmholtz resonators, and porous materials to construct acoustic superstructures capable of suppressing or phase-shifting noise loads at these frequencies; and solidifying the acoustic superstructure assembly style through ground tests or wind tunnel tests to facilitate its physical realization. This invention addresses the problem that commonly used cavity noise reduction methods cannot be applied to high-speed cavity structures by designing and optimizing various acoustic superstructure assemblies capable of suppressing or phase-shifting noise loads to achieve optimized suppression of noise loads in aircraft cavities under high-speed environments.

This application discloses a low-noise air supply system for cleanrooms, comprising an air supply power module, a silencing module, and an air outlet module. The silencing module includes a housing, connecting pipes, two noise sensors, and a noise reduction mechanism. Two connecting pipes are provided, each located at an opening at one end of the housing. The two noise sensors are respectively located at both ends of the housing. The noise reduction mechanism includes two square plates, four outer micro-perforated plates, and four inner micro-perforated plates. The four outer micro-perforated plates and two square plates form an outer noise reduction cavity, and the four inner micro-perforated plates, four outer micro-perforated plates, and two square plates form an inner noise reduction cavity. The noise reduction mechanism also includes multiple partitions that divide the outer and inner micro-perforated plates into multiple unit plates, which are connected by a connecting mechanism. The low-noise air supply system provided by this application can achieve noise reduction effects at different noise frequencies depending on different air supply conditions.

This invention relates to the field of bearings, specifically to a noise-reducing bearing with an integrated micro-perforated plate sound-absorbing structure. Rolling elements are disposed between the inner and outer rings of the bearing, and these rolling elements are positioned at intervals by a cage. A sealing ring is disposed on one side of the outer ring. The sealing ring has a mounting structure for installing the micro-perforated plate. The micro-perforated plate is annular and installed at the sealing ring, with a uniform array of micropores. An air cavity is formed between the micro-perforated plate and the sealing ring, constituting the back cavity of the sound-absorbing structure. In this invention, by setting a micro-perforated plate sound-absorbing structure at the bearing's sealing structure, the bearing maintains its original sealing function while possessing active sound absorption capability. When noise generated during bearing operation propagates to the micro-perforated plate, sound waves enter the micropores, generating viscous friction and heat exchange between the air and the pore walls within the micropore channels, thereby converting some of the sound energy into heat energy and dissipating it.

The utility model belongs to the technical field of musical instrument manufacturing, and particularly relates to a micro-perforated plate adjusting device for a bottom drum. Comprising a drum body shell and a drum beating surface arranged on the front side of the drum body shell, and further comprises a micro-perforated plate arranged in the drum body shell; the supporting mechanism comprises a supporting frame arranged in the drum body shell and located behind the micro-perforated plate and a supporting sleeve arranged in the middle of the supporting frame; the translation adjusting mechanism comprises a translation threaded rod of which the front end is connected with the middle part of the micro-perforated plate and the rear end is arranged in the supporting sleeve in a penetrating manner, a belt wheel part for driving the translation threaded rod to rotate so as to change the distance between the micro-perforated plate and the drumbeat surface, and an anti-rotation part for preventing the micro-perforated plate from rotating during translation. According to the utility model, the distance between the micro-perforated plate and the drumbeat surface is changed through the translation adjusting mechanism, so that the bottom drum has the effects of sound absorption and sound quality improvement at the same time.

The utility model provides a kind of road noise barrier based on sound-absorbing material, including barrier support assembly and barrier body, barrier support assembly includes the barrier support post of pair arrangement, and the sliding slot upper end of barrier support post is connected with buffer sliding block, and one barrier hanging pole is connected between buffer sliding block, barrier hanging pole is connected with barrier assembly support by hinged link, and barrier assembly support is connected with barrier body by bolt.The utility model in barrier body is converted into heat energy dissipation by the sound hole hole of sound hole board body, and the sound-absorbing micropore on microporous attraction cloth layer is based on micro-perforated plate theory, and the sound-absorbing coefficient is excellent in full frequency band, especially in low frequency part, further improve sound-absorbing effect, significantly improve the sound-absorbing performance of low frequency band by sound-absorbing cotton layer, and the porous structure of sound-absorbing cotton layer effectively insulates internal air convection and heat radiation, significantly reduce heat loss, while large aperture area absorbs and reflects sound wave, effectively reduce noise.

The utility model provides a composite sound absorption structure and a vehicle provided with the composite sound absorption structure, the composite sound absorption structure comprises a perforated plate, a sound absorption part and a support part; a gap exists between the sound absorption part and the perforated plate, a square containing cavity is defined by the micro-perforated plate in the sound absorption part, and the honeycomb filler is arranged in the square containing cavity; the perforated plate is provided with a plurality of through holes to form a sound transmission channel in the compartment body, so that noise reaches the sound absorption component connected with the perforated plate through the through holes, the micro-perforated plate of the sound absorption component is a direct reflection surface of the noise, and sound waves consume energy due to a viscous friction effect when passing through micropores of the micro-perforated plate. Cavities and micropores in the honeycomb filler form resonance sound absorption; and compared with a single-layer micro-perforated plate which can only cover low and medium frequency sound, the micro-perforated plates encircle to form the square accommodating cavity to form three groups of double-layer micro-perforated plate structures, namely an up-down double-layer micro-perforated plate structure, a left-right double-layer micro-perforated plate structure and a front-back double-layer micro-perforated plate structure, so that the sound absorption frequency band can be expanded to

The present application relates to a kind of sound barrier noise reduction structure and its design method, comprising: the high-frequency valley of high-frequency noise of the measured noise spectrum is determined as the valley frequency of the high-frequency sound insulation amount of the resonant unit, the low-frequency peak of low-frequency noise is determined as the peak frequency of the low-frequency sound insulation amount of the composite waveguide layer, according to the number of low-frequency peak determines the number of Helmholtz cavity;According to valley frequency, obtain the thickness of micro-perforated plate layer, the diameter of small hole on micro-perforated plate layer, the thickness of hollow cavity layer and its cross-sectional size parameter relationship formula, so as to optimize the selection of relevant parameters;According to each peak frequency, respectively calculate and obtain the volume of corresponding Helmholtz cavity, and the effective area, cross-sectional length relationship of its corresponding throat pipe, so as to optimize the selection of effective area.The structure designed by resonance system controls high-frequency noise, utilizes the Helmholtz cavity of composite waveguide layer to control low-frequency noise, realizes selective sound insulation in large frequency range.

The utility model discloses an exhaust silencer which comprises a first silencer body, one side of the first silencer body is in threaded connection with a hollow threaded connection pipe, and one side of the hollow threaded connection pipe is in threaded connection with a second silencer body. By means of the structure, the outer threads are arranged on one side of the first silencer body and one side of the second silencer body, the first inner threads are arranged on the other side of the first silencer body and the other side of the second silencer body, the sliding grooves are formed in the side walls of the first silencer body and the second silencer body, the sliding blocks are arranged in the sliding grooves, the sliding covers are arranged at the upper ends of the sliding blocks, and therefore silencing materials can be replaced conveniently; micro-perforated plates are arranged in the first silencer body and the second silencer body, flow guide plates are arranged on one sides of the micro-perforated plates, silencing material layers are arranged on one sides of the flow guide plates, filter cotton is arranged on one sides of the silencing material layers, and sound absorption cotton, metal fiber layers, glass fiber layers, porous ceramics and foam materials are arranged in the silencing material layers, so that the silencing effect of the silencer is better.

This invention discloses a multi-layer composite sound-absorbing device. The double-layer micro-perforated plate of this invention includes an upper micro-perforated plate and a lower micro-perforated plate, which are connected by a disc spring device. The upper and lower micro-perforated plates are connected around their perimeter by a frame, ensuring the disc spring device between them is compressed. The density gradient porous sound-absorbing material layer is composed of at least two layers of sound-absorbing material with different densities stacked together. This multi-layer composite sound-absorbing device is composed of resonant and resistive sound-absorbing materials, achieving excellent low-frequency broadband sound absorption, effectively solving low-frequency noise pollution problems in substations, converter stations, and other fields. By adjusting the plate spacing to change the compression state of the disc springs, different stiffness characteristics are obtained, thereby enhancing the resonant sound absorption effect for specific frequency bands of noise and specifically improving the sound absorption coefficient of the device for specific frequency bands of noise.

The utility model discloses a movable anti-impact sound insulation board, and particularly relates to the technical field of noise reduction, the movable anti-impact sound insulation board comprises a base, the top of the base is fixedly connected with a barrier board, an observation window is installed in the barrier board, and contraction wheel mechanisms are arranged on the top of the base and located on the two sides of the barrier board; the barrier plate is composed of a supporting layer, a damping layer and a micro-perforated plate, the micro-perforated plate is arranged on the outermost layer, and the damping layer and the supporting layer are sequentially arranged on the rear side of the micro-perforated plate. A good sound insulation effect is conveniently achieved through combination of the supporting layer, the damping layer and the micro-perforated plate, the bottom of the barrier plate is connected with the base, the contraction wheel mechanism is installed on the base, the whole sound insulation barrier can be conveniently moved and stably placed by controlling the wheels to ascend and descend, and position deviation is not prone to occurring in the using process.

The invention belongs to the technical field of engine sound insulation and noise resistance, and particularly discloses an aero-engine acoustic liner structure based on a polymorphic three-period minimal curved surface and a construction method.The aero-engine acoustic liner structure comprises a micro-perforated plate, a polymorphic TPMS core layer is fixedly connected under the micro-perforated plate, the polymorphic TPMS core layer comprises P-type TPMS cell elements and I-WP-type TPMS cell elements, and the P-type TPMS cell elements and the I-WP-type TPMS cell elements are connected with the micro-perforated plate. The P-type TPMS cell element and the I-WP-type cell element are gradually connected into a whole through a Sigmoid function, and the lower end of the polymorphic TPMS core layer is fixedly connected with the rigid panel. The low-frequency sound absorption material has excellent low-frequency sound absorption performance, and the noise of the aero-engine is effectively controlled within the low-frequency range of 100-400 Hz; the material shows a double-platform stress characteristic in the aspect of mechanical properties, and has excellent energy absorption capacity; besides, TPMS structures with different sizes, types and porosities can be designed by adjusting TPMS structure parameters, and the multi-form TPMS structure is multifunctional and has more flexible design freedom.

The invention belongs to the technical field of noise energy harvesting, and particularly relates to an adjustable sound absorption energy harvesting device and electronic equipment. The adjustable sound absorption energy harvesting device comprises a sound absorption structure which comprises a containing shell with a containing cavity and an adjusting baffle connected with the containing shell in a sliding mode, and the cavity top of the containing cavity is provided with a tuning slit communicating with the external space; the energy harvesting structure comprises a micro-perforated plate located in the containing cavity and a piezoelectric plate arranged at an interval with the micro-perforated plate, the edge of the micro-perforated plate is connected with the cavity wall of the containing cavity, and the piezoelectric plate is located at the cavity bottom of the containing cavity; the adjusting baffle has a first position state and a second position state, and when the adjusting baffle is in the first position state, the adjusting baffle completely shields the tuning slit; when the adjusting baffle is in the second position state, the adjusting baffle at least partially opens the tuning slit. The electric energy output efficiency of the piezoelectric plate can be remarkably improved, and the dual functions of sound absorption and energy recovery are achieved.

The utility model discloses a mute treadmill which comprises a bottom plate, the top of the bottom plate is fixedly connected with an installation frame, the top of the installation frame is fixedly connected with a micro-perforated plate, the inner wall of the installation frame is fixedly connected with sound absorption glass wool, the inner wall of the sound absorption glass wool is fixedly connected with glass cloth, and the glass cloth is fixedly connected with a sound absorption plate. And the bottom of the mounting frame is fixedly connected with a sound absorption plate, the bottom end of the bottom plate is fixedly connected with a connecting plate, and the bottom end of the connecting plate is fixedly connected with a piston rod. The mounting frame is additionally arranged on the bottom plate, when a user runs on the running machine, noise generated by shoes and the running plate enters the mounting frame and enters the resonant cavity through the micro-perforated plate, and the noise sequentially passes through the glass cloth and the sound absorption glass wool to generate friction with the glass cloth and the sound absorption glass wool, so that energy in the noise is consumed, and the noise reduction effect is achieved. And the glass cloth and the sound absorption glass wool are both rough planes, so that noise is reflected or refracted in the resonant cavity in a reciprocating manner, and the noise reduction effect of the treadmill is further improved.

The utility model provides a composite sound barrier structure which comprises a sound barrier main body, and the sound barrier main body comprises a supporting device; the micro-perforated plate layer is located on the first side of the supporting device in the thickness direction, and the micro-perforated plate layer is connected with the supporting device; the noise reduction cavity layer is located on the second side of the supporting device in the thickness direction, the noise reduction cavity layer is connected with the supporting device, the noise reduction cavity layer is provided with a plurality of noise reduction cavities, and the noise reduction cavities are used for exciting sound energy to resonate with the air columns so as to consume the sound energy; and the gradient density sound absorption material layer is located between the micro-perforated plate layer and the noise reduction cavity layer, and the densities of at least part of sound absorption materials of the gradient density sound absorption material layer are different in the thickness direction of the supporting device. The problem that in the prior art, the noise reduction effect of a passive sound barrier is poor is solved.

The invention discloses an aircraft noise load suppression superstructure design method in a high-speed environment, and relates to the field of aircraft design, and the method comprises the steps: obtaining a characteristic noise frequency through the simulation of a typical cavity model; various designable structures such as a micro-perforated plate, a Helmholtz resonator and a porous material are introduced to construct an acoustic superstructure capable of suppressing noise load or performing phase transfer, and the acoustic superstructure assembly style is solidified through methods such as ground test or wind tunnel test verification so as to facilitate materialization. In order to solve the problem that a common cavity noise reduction method cannot be applied to a high-speed cavity structure, multiple acoustic superstructure assemblies capable of suppressing noise load or performing phase transfer are designed for optimization, so that suppression optimization of the noise load of an aircraft cavity in a high-speed environment is realized.

The invention relates to the field of energy-absorbing materials, in particular to an energy-absorbing plate based on a three-period extremely-small curved surface and a manufacturing method and application thereof.The plate comprises a three-period extremely-small curved surface plate, a micro-perforated plate and a back plate, and the three-period extremely-small curved surface plate is formed by arranging a plurality of three-period extremely-small curved surface units in the X direction, the Y direction and the Z direction in an array mode; the micro-perforated plate and the back plate are respectively arranged on the upper and lower surfaces of the three-period extremely-small curved plate; the thicknesses of the inner hole walls of the supporting columns in six directions of each three-period minimal curved surface unit are changed in a stepped manner; the micro-perforated plate, the stepped hole walls of the three-period extremely-small curved surface units and the curved surface cavities jointly act to achieve medium-frequency, high-frequency and broadband sound absorption effects, meanwhile, the structure is excellent in mechanical property, good in limit stress and energy absorption effect, the needed structure is designed according to needs, meanwhile, the structure is excellent in lightweight performance, and the structure is suitable for large-scale popularization and application. The composite material can be applied to the vibration isolation and sound absorption fields of aerospace, railway transportation, commercial sound insulation boards and the like or automobile energy absorption boxes.

The present application belongs to the technical field of low-frequency sound absorption, and discloses a micro-perforated panel composite gradient spiral pipe sound absorption device and method, which comprises a variable cross-section spiral pipe, the diameter of the inlet end of the variable cross-section spiral pipe is larger than the diameter of the outlet end of the variable cross-section spiral pipe; a plurality of MPP plates are installed in the variable cross-section spiral pipe, one of the MPP plates is embedded in the inlet end of the variable cross-section spiral pipe, and the other MPP plates are sequentially embedded in the inside of the variable cross-section spiral pipe at the same interval, forming a multi-stage MPP plate composite sound absorption structure; the cross-section pipe diameter of the variable cross-section spiral pipe linearly decreases from the inlet end of the variable cross-section spiral pipe to the outlet end of the variable cross-section spiral pipe. The gradient design of the variable cross-section spiral pipe integrated with the micro-perforated panel realizes low-frequency broadband high-efficiency sound absorption in a compact space, avoids the problem of heavy structure caused by the deep and large back cavity in the traditional technology, and overcomes the limitation of narrow sound absorption frequency band, and is especially suitable for space-limited occasions, and can balance the low-frequency performance and broadband characteristics in a limited space.

The invention provides an acoustic metamaterial suitable for a leading edge slat, a design method and the slat, and belongs to the field of aircraft noise reduction. The acoustic metamaterial comprises a plurality of acoustic metamaterial subunits, and each subunit is composed of a micro-perforated plate and a cavity. And at least one of the plurality of subunits is linear and the internal channel of the cavity is linear, and at least one of the plurality of subunits is curved and the internal channel of the cavity is curved. The linear and curved subunits form a conformal unitary structure by an adaptive arrangement including profile adaptation within the airfoil profile and location distribution and combination within a profile perpendicular to the airfoil profile and along the leading and trailing edges. According to the invention, extremely limited space in the slat is utilized to the maximum extent through conformal design, a sound wave propagation path is prolonged at a sub-wavelength scale through linear and curved cavity channels, efficient low-frequency sound absorption is realized, broadband noise is covered through combination of multiple subunits, and the problem of insufficient low-frequency sound absorption in a slat space in a traditional scheme is effectively solved.

This invention discloses a mid-to-low frequency ventilation and sound insulation metamaterial comprising two main areas: sound absorption and ventilation. The sound absorption area is divided into inner and outer rings, each composed of multiple circumferentially arranged sound-absorbing functional cavities. Each functional cavity includes a resonant cavity formed by partitions and a perforated cavity formed by micro-perforated plates. The perforations on the plates are positioned according to the centroid of the vertical projection of the functional cavities. The ventilation area is a cylindrical region enclosed by the inner ring functional cavities, forming a complete resonant cavity via a ring-shaped base plate. This material combines the resonant characteristics of a Helmholtz resonator, achieving mid-to-low frequency broadband sound insulation through multiple parallel HR combinations. The hollow tube design ensures ventilation, and the mid-to-low frequency band utilizes a non-local coupling sound absorption mechanism for sound insulation. A 4.6cm thick specimen can block 90% of incident wave energy (TL≥10dB) in the 435~1700Hz range, and customized designs can be achieved simply by adjusting the aperture. The improved design incorporates a connecting small hole in the center of the inner and outer functional cavity partitions to form a connected functional cavity, bridging the gap between resonance absorption peaks and enhancing low-frequency sound absorption. The improved unit can achieve the same sound insulation effect in the range of 385~1700Hz.

According to the method for widening the sound absorption frequency band of the micro-perforated plate sound absorber array under the excitation of the free field oblique incidence plane wave, the coupling sound absorption rule between units in the array is analyzed and fully utilized according to the excitation condition of the free field oblique incidence plane wave; unit structure parameters in the array are subjected to optimization design, the optimal sound absorption performance is achieved, the effective sound absorption frequency band of the MPPA array is greatly widened, and broadband efficient sound absorption of the MPPA array under free field oblique incidence excitation is achieved. The invested cost is low, the sound absorption frequency band broadening effect of the MPPA array is obvious, and therefore the MPPA array has important engineering application value.

This invention provides a cavity-adjustable array micro-perforated sound absorber and its design method, belonging to the field of low-frequency vibration reduction and noise reduction. The sound absorber has a rectangular modular structure, consisting of an array of micro-perforated plates (assembled from multiple micro-perforated plates), a main frame, a sliding cavity plate assembly, and a rear-sealed large back plate, arranged sequentially along the sound wave incident direction. Here, and represent the number of rows and columns on one side of the independent cavity channels divided within the main frame. The perforated plates exhibit a perforation rate gradient distribution characteristic, and each cavity-adjustable sub-micro-perforated sound absorber has an effective cavity depth exhibiting an in-plane gradient distribution characteristic. Furthermore, the array of micro-perforated plates is arranged in a concentric matrix topology. This invention achieves extreme broadband impedance matching and targeted low-frequency absorption enhancement under finite thickness constraints by constructing an adjustable cavity, a dual-gradient evolution mechanism of perforation rate and cavity depth under constant aperture, and combining this with a concentric matrix topology arrangement radiating outwards from the low-frequency core.

The invention discloses a composite sound absorption structure with a double-porosity back cavity and a performance prediction method of the composite sound absorption structure. The composite sound absorption structure comprises a micro-perforated plate, a curled space, a structural frame, a porous material, an air channel and a side plate. The micro-perforated plate is mounted at the opening of the structural frame; a closed space defined by the micro-perforated plate, the structural frame and the side plates is a curled space; the porous materials are mounted around the inner surface of the structural frame and are separated from one another to form air channels; the air channels and the porous material form a dual-porosity back cavity. Performance in the performance prediction method is represented by an acoustic absorption coefficient spectrum, and the performance prediction method specifically can be realized through the following steps: calculating surface acoustic impedance of the micro-perforated plate; respectively calculating the effective mass density and the effective volume modulus of the air channel and the effective mass density and the effective volume modulus of the porous material; calculating the surface acoustic impedance of the double-porosity back cavity by using a double-porosity medium theory; and calculating the sound absorption coefficient frequency spectrum of the composite sound absorption structure.