A mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism

Abstract

The present invention relates to a mode-switchable thin-film acoustic metamaterial structure based on a magnetic control mechanism, and relates to the technical field of noise control. The steps are as follows: (1) constructing a thin-film metamaterial acoustic vibration coupling model; (2) establishing a magnetic control force relationship of the thin-film metamaterial; (3) designing the thin-film metamaterial structure; (4) calibrating the magnetic force of the circular mass block; (5) preparing the thin-film metamaterial to realize mode switching based on the magnetic control mechanism. The mode-switchable thin-film acoustic metamaterial structure based on the magnetic control mechanism of the present invention has the characteristic of strong designability, and finally realizes non-contact and discontinuous regulation.

Description

Technical Field

[0001] The present invention relates to an acoustic metamaterial with adjustable acoustic performance, and particularly to a mode-switchable thin-film acoustic metamaterial structure based on a magneto-control mechanism, belonging to the technical field of noise control. Background Art

[0002] Due to the weak inherent dissipation of natural materials in the low-frequency band, there has always been a huge challenge in the control of low-frequency sound waves. Although traditional porous sound-absorbing materials and impedance matching designs can achieve good sound-absorbing effects in the medium and high-frequency bands, there are still inadaptabilities in realizing small-size control of large wavelengths.

[0003] With the in-depth study of the acoustic performance of composite materials and structures, it has been found that they have properties different from natural acoustic materials, and such structures are collectively referred to as acoustic artificial structures. Among them, "acoustic metamaterials" refer to structures designed by combining materials in a specific way to obtain some acoustic properties that natural materials do not possess. Its important feature is that the working wavelength is much larger than the geometric size of its unit cell, and it can be characterized by equivalent parameters. The elastic constants and densities of natural materials are all positive values. Acoustic metamaterials enrich the optional range of material parameters, such as negative equivalent material parameters and zero-coefficient equivalent material parameters, etc. Therefore, through the design of acoustic metamaterial structures, the control ability of sound waves can be improved, and it has good application prospects.

[0004] Using the local resonance mechanism, thin-film metamaterials can achieve strange phenomena such as negative mass, negative modulus, double-negative parameters, and "perfect sound absorption" in the low-frequency band. However, affected by its action mechanism, passive metamaterials have a narrow working frequency band and cannot adapt to changes in the environment and requirements, and have a single function. Therefore, researchers have proposed to design adjustable acoustic metamaterials by using intelligent materials and controlling the change of the structure state. For example, it has been reported that a thin-film acoustic metamaterial based on piezoelectric materials can achieve continuous regulation of equivalent parameters within a certain range; it has been reported that an elastic metamaterial that realizes the switching of passbands and stopbands by using structure buckling to induce changes in the geometric shape of the structure. However, the acoustic metamaterials using the electro-control method utilize the force-electric coupling effect of intelligent materials, require a high input voltage, have a limited regulation range, and belong to contact control. The existing regulation mechanism based on circuit feedback requires a relatively complex system, requires the application of a strong electromagnetic field, and most of them are continuous control of acoustic performance.

[0005] Therefore, providing a mode-switchable thin-film acoustic metamaterial structure based on a magneto-control mechanism, using a magnetic field to achieve non-contact regulation, inducing changes in the internal force of the structure, breaking the symmetry of the internal force of the structure, exciting implicit asymmetric modes, and realizing sudden changes in acoustic properties, to solve the problem that the thin-film metamaterials based on the electromagnetic intelligent material parameter regulation mechanism require the application of a strong electromagnetic field, and the control method is simple and convenient for design, has become an urgent technical problem to be solved in this technical field. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism. By using a magnetic field, non-contact regulation is achieved, internal forces of the structure are induced to change, symmetry of the internal forces of the structure is broken, implicit asymmetric modes are excited, sudden changes in acoustic properties are realized, and the problem that thin-film metamaterials based on the parameter regulation mechanism of electromagnetic intelligent materials require the application of strong electromagnetic fields is solved. The control method is simple and convenient for design.

[0007] The above objective of the present invention is achieved through the following technical solutions:

[0008] A mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism includes: an elastic film, a paramagnetic metal ring piece, and a ring mass block; the elastic film is fixed to the paramagnetic metal ring piece, and the ring mass block is composed of a ferromagnetic material and a paramagnetic material and is adhesively connected to the elastic film to form an axisymmetric structure.

[0009] Preferably, the ring mass block has a uniform areal density.

[0010] Preferably, the ferromagnetic material is iron with a density of 7800 kg / m 3 .

[0011] Preferably, the paramagnetic material is copper with a density of 8900 kg / m 3 .

[0012] Preferably, the area ratio of the ferromagnetic material in the ring mass block is 1 / 8 - 1 / 4.

[0013] Preferably, the area ratio of the ferromagnetic material in the ring mass block is 1 / 6.

[0014] Preferably, it further includes a flange device, and the axisymmetric structure is fixed in the flange device.

[0015] Preferably, the axisymmetric structure is screwed to the flange device.

[0016] Another objective of the present invention is to provide a preparation method for the above-mentioned mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism. By using a magnetic field, non-contact regulation is achieved, internal forces of the structure are induced to change, symmetry of the internal forces of the structure is broken, implicit asymmetric modes are excited, sudden changes in acoustic properties are realized, and the problem that thin-film metamaterials based on the parameter regulation mechanism of electromagnetic intelligent materials require the application of strong electromagnetic fields is solved. The control method is simple and convenient for design.

[0017] The above objective of the present invention is achieved through the following technical solutions:

[0018] A preparation method for a mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism comprises the following steps:

[0019] (1) Construct a coupled acoustic - vibration model of thin - film metamaterials

[0020] Construct a coupled acoustic - vibration model of thin - film metamaterials to form a composite structure with a circular - ring mass bonded to the center of an elastic thin - film. Among them, the circular - ring mass is composed of ferromagnetic and paramagnetic materials and has a uniform areal density;

[0021] (2) Establish the magneto - control force relationship of thin - film metamaterials

[0022] According to the coupled acoustic - vibration model of thin - film metamaterials in step (1), solve the influence of different magnetic forces on the internal forces of the thin - film structure, and calculate the modal frequencies and vibration modes of the thin - film metamaterials under different magnetic forces;

[0023] (3) Design the structure of thin - film metamaterials

[0024] According to the coupled acoustic - vibration model of thin - film metamaterials in step (1), establish the relationship between the film tension, geometric parameters, and design parameters of the circular - ring mass and the vibration characteristics of the structure, and calculate the modal frequencies and vibration modes of the thin - film metamaterials in the concerned frequency band. According to the requirements of the target working frequency band, design the structure of the thin - film metamaterials, and determine the magnetic force required for regulation according to the magneto - control force relationship of the thin - film metamaterials established in step (2);

[0025] (4) Calibrate the magnetic force of the circular - ring mass

[0026] Determine the magnetic - force application method, using a permanent magnet or an electromagnet to apply magnetic force to the circular - ring mass;

[0027] (5) Fabricate thin - film metamaterials to achieve mode - switchable based on the magneto - control mechanism

[0028] According to the design parameters determined in step (3), fix a thin - film with uniform tension on a paramagnetic metal circular - ring sheet, and bond the circular - ring mass composed of a composite of ferromagnetic and paramagnetic materials to the center of the thin - film to form an axisymmetric structure.

[0029] Preferably, in step (1), the area ratio of the ferromagnetic material in the circular - ring mass is 1 / 6.

[0030] Preferably, in step (1), when constructing the coupled acoustic - vibration model of thin - film metamaterials, the dynamic equation is:

[0031]

[0032] In the formula, η is the displacement of the transverse vibration of the elastic film, σ0 is the radial stress generated by the initial tension of the elastic film, ρ is the density of the elastic film, and f is the sound pressure load; the circular ring mass block and the film boundary follow the displacement and velocity continuity conditions. Considering the continuity of the velocities on both sides of the film and neglecting the high-order scattered waves, the relationship between the sound pressure load and the transmission coefficient is established as follows:

[0033] f = 2(1 - T0)

[0034] In the formula, T0 is the transmission coefficient under the incidence of plane waves.

[0035] Preferably, in step (1), considering the modulation effect of the magnetic force on the modal frequency and vibration mode of the film-type metamaterial, the magnetic control force relationship of the film-type metamaterial is established, specifically as follows:

[0036] Considering the influence of the magnetic force, the dynamic equation of the circular film vibration is established:

[0037]

[0038] Among them, σ m is the radial stress generated by the initial tension of the elastic film. Through the numerical solution method, the distribution of the internal tension of the circular film is obtained, and the modal vibration mode function and frequency related to the magnetic force are calculated.

[0039] Preferably, in step (2), specifically as follows: control the first-order modal natural frequency through the tension design and the circular ring block mass design, control the third-order modal natural frequency through the circular ring block mass size design, and determine the magnitude of the magnetic force to achieve the target frequency by calculating the dynamic equation of the circular film vibration after applying the magnetic field.

[0040] Preferably, in step (4), if a permanent magnet is used, it is necessary to calibrate the change of the magnetic force with the distance between the permanent magnet and the circular ring mass block, and determine the distance between the permanent magnet and the circular ring mass block in step (3) according to the magnetic field modulation frequency requirement.

[0041] Preferably, in step (4), the permanent magnet magnetic force loading module is a hollow cylindrical magnet composed of 14 small magnets (Nd-FeB) joined together.

[0042] Preferably, in step (4), the inner diameter of the hollow cylindrical magnet is 52 mm, the outer diameter is 80 mm, and the height is 100 mm.

[0043] Preferably, in step (4), if an electromagnet is used, it is necessary to calibrate the change of the magnetic force with the current intensity of the electromagnet, and determine the current intensity of the electromagnet in step (3) according to the magnetic field modulation frequency requirement.

[0044] Beneficial effects:

[0045] Compared with the prior art, for the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure of the present invention, first, a thin - film metamaterial acoustic - vibration coupling model is constructed, the relationship between key design parameters and structural vibration characteristics is established, and the design parameters of the thin - film metamaterial structure are selected according to the target frequency band. Then, the magnetic force of the ring mass is calibrated, and the magneto - controlled force relationship of the thin - film metamaterial is established. Finally, the thin - film metamaterial is prepared and the magneto - controlled conditions are determined, realizing the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure.

[0046] The magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure proposed by the present invention can achieve non - contact and non - continuous regulation, realize the sudden change of structural acoustic performance, and provide novel means for band - gap regulation, equivalent parameter dispersion control, etc. Moreover, the regulation of the thin - film acoustic metamaterial based on the magneto - controlled mechanism is simple and highly designable. Parameters such as film tension, geometric parameters, ring mass, and magnetic force can be designed according to the application scenario and target frequency band, improving the adaptability to different application scenarios.

[0047] The present invention will be further described below with reference to the drawings and specific embodiments, but this does not mean any limitation to the protection scope of the present invention. Brief Description of the Drawings

[0048] Figure 1 It is a flowchart of the preparation method of the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial in Embodiment 1 of the present invention;

[0049] Figure 2-1 It is a schematic structural diagram of the thin - film metamaterial acoustic - vibration coupling model in the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure in Embodiment 1 of the present invention.

[0050] Figure 2-2 It is a physical photo of the thin - film metamaterial acoustic - vibration coupling model in the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure in Embodiment 1 of the present invention.

[0051] Figure 3-1 It is a schematic structural diagram of the hollow cylindrical magnet - loading module composed of 14 small magnets (Nd - FeB) joined together in the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure in Embodiment 1 of the present invention.

[0052] Figure 3-2 It is the distribution of the radial tension of the film before and after the application of the magnetic field in Embodiment 1 of the present invention.

[0053] Figure 4 It is the magneto - controlled mechanism diagram of the magneto - controlled mechanism - based mode - switchable thin - film acoustic metamaterial structure of the present invention.

[0054] Figure 5-1This is the energy band diagram of the thin-film acoustic metamaterial without applying a magnetic field in Embodiment 1 of the present invention.

[0055] Figure 5-2 This is the simulation result and experimental verification result of the transmission coefficient of the thin-film acoustic metamaterial without applying a magnetic field in Embodiment 1 of the present invention.

[0056] Figure 6-1 This is the energy band diagram of the thin-film acoustic metamaterial after applying an external magnetic field in Embodiment 1 of the present invention.

[0057] Figure 6-2 This is the simulation result and experimental verification result of the transmission coefficient of the thin-film acoustic metamaterial after applying an external magnetic field in Embodiment 1 of the present invention.

[0058] Figure 7 This is the assembly schematic diagram of the mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism in Embodiment 1 of the present invention. Detailed implementation manners

[0059] Unless otherwise specified, the components used in the present invention are all conventional commercially available components in the technical field, and their connection methods are conventional connection methods in the technical field; the materials used are conventional materials in the technical field.

[0060] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific implementation manners. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. For those embodiments where specific conditions are not indicated, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0061] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is 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 construed as limiting the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0062] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0063] Embodiment 1

[0064] As Figure 1 shown, it is a flowchart of the preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism in Embodiment 1 of the present invention;

[0065] The preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism of the present invention is as follows:

[0066] S1. Construct a thin-film metamaterial acoustic-vibration coupling model;

[0067] S2. Calculate the influence of different magnetic forces on the internal force of the thin-film structure, obtain the modal frequencies and vibration modes of the thin-film metamaterial under different magnetic forces, and establish the magneto-control force relationship of the thin-film metamaterial;

[0068] S3. According to the design objective, based on the relationship between the design parameters such as thin-film tension, geometric parameters, and ring mass blocks and the structural vibration characteristics, design the thin-film metamaterial structure, and determine the magnetic force required to be applied for regulation based on the magneto-control force relationship of the thin-film metamaterial;

[0069] S4. Determine the magnetic force application method and calibrate the influence of the magnetic force control parameters on the magnetic force of the ring mass block;

[0070] S5. Prepare a thin-film acoustic metamaterial based on the magneto-control mechanism to realize a switchable sound propagation mode.

[0071] In a specific embodiment:

[0072] In S1, the thin-film metamaterial acoustic-vibration coupling model is composed of an elastic thin film and concentric ring mass blocks. As Figure 2-1 shown, it is a schematic structural diagram of the thin-film metamaterial acoustic-vibration coupling model in the structure of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism in Embodiment 1 of the present invention; As Figure 2-2As shown in the figure, it is a physical photo of the thin-film metamaterial acoustic vibration coupling model in the mode-switchable thin-film type acoustic metamaterial structure based on the magneto-control mechanism in Embodiment 1 of the present invention; the thin-film metamaterial acoustic vibration coupling model is formed by bonding an elastic thin film with concentric ring masses to form a composite structure. Among them, the concentric ring masses are composed of ferromagnetic materials and paramagnetic materials and have a uniform areal density; since the stiffness of the concentric ring masses is much greater than that of the elastic thin film, they can be regarded as rigid bodies. The concentric ring masses are composed of copper and iron composites. Through height matching design, the areal density is ensured to be consistent. On the physical model, it can still be regarded as an axisymmetric system. The dynamic equation of the circular film vibration can be expressed as:

[0073]

[0074] where η is the displacement of the transverse vibration of the elastic thin film, σ0 is the radial stress generated by the initial tension of the elastic thin film, ρ is the density of the elastic thin film, f is the acoustic pressure load, t is the width of the ring mass, and r is the radial coordinate; at the boundary between the concentric ring mass and the elastic thin film, the displacement and velocity continuity conditions are followed;

[0075] Considering the continuity of the velocities on both sides of the thin film and ignoring the higher-order scattered waves, the relationship between the acoustic pressure load and the transmission coefficient is established as:

[0076] f = 2(1 - T0)

[0077] where T0 is the transmission coefficient under the incidence of plane waves;

[0078] The transverse deflection of the thin-film metamaterial is expressed by the modal superposition method. The selected vibration mode function is related to the target frequency band and is expressed as:

[0079]

[0080] where a total of N-order modes are selected, W n (R,θ) is the vibration mode function of the nth order in the polar coordinate system, q n (t) is the modal coefficient corresponding to the nth order mode. Considering the low-frequency band below the cut-off frequency of the waveguide and ignoring the influence of higher-order scattered waves, the far-field transmission coefficient is obtained as:

[0081] T0 = ρ a c a ωη>

[0082] where T0 is the transmission coefficient of the plane wave transmitted from the thin-film metamaterial to the far field, ρ a and c a are the density and wave speed of air respectively, ω is the excitation circular frequency of the plane wave, and <η> represents the average value of the transverse vibration displacement of the elastic thin film;

[0083] Considering the continuity of the velocities on both sides of the thin film and using the orthogonality of the thin-film metamaterial modes, the modal coefficients of each order are obtained by solving:

[0084]

[0085] where q n is the modal coefficient corresponding to the nth order mode, W n (R,θ) is the eigenfunction of the nth order mode in the polar coordinate system, ω n is the excitation circular frequency of the plane wave, T0 is the transmission coefficient of the plane wave transmitted from the thin-film metamaterial to the far field, ρ is the density of the thin-film metamaterial, and ω is the excitation circular frequency of the plane wave.

[0086] For an axisymmetric structural system, it can be divided into axisymmetric modes and antisymmetric modes. Under plane wave excitation, the integral of the antisymmetric mode eigenfunction on the surface of the structure is 0, and the corresponding modal coefficient is 0, which can be called a hidden mode. Therefore, under the condition of no magnetic field, the axisymmetric mode frequency and eigenfunction are the main factors determining the thin-film metamaterial;

[0087] In the S2, a permanent magnet is used to apply the magnetic field, and a permanent magnet magnetic force loading module is selected. It is a hollow cylindrical magnet composed of 14 small magnets (Nd-FeB) joined together, as Figure 3-1 shown, which is the structural schematic diagram of the hollow cylindrical magnet loading module composed of 14 small magnets (Nd-FeB) in Embodiment 1 of the present invention; in order to match the impedance tube, its inner diameter is designed to be 52 mm, the outer diameter is 80 mm, and the height is 100 mm; it can provide a magnetic field range of 0-1 T, and has a gradient magnetic field in the axial direction. By changing the relative distance between the magnetic field and the test sample, the magnetic force loading is realized;

[0088] To illustrate the influence of the magnetic force on the vibration mode of the thin film, the radial stress of the thin film in the states of no magnetic force and with magnetic force is selected, as Figure 3-2 shown, which is the distribution of the radial tension of the thin film before and after the magnetic field is applied in Embodiment 1 of the present invention; since the magnetic force only acts on the magnetic material part of the concentric ring mass block, the axisymmetry of the internal force of the circular film is changed by the magnetic force, and the structural vibration mode loses axisymmetry and antisymmetry. After the magnetic field is applied, the dynamic equation of the circular film vibration can be expressed as:

[0089]

[0090] where η is the displacement of the transverse vibration of the elastic thin film, σ0 is the radial stress generated by the initial tension of the elastic thin film, ρ is the density of the elastic thin film, f is the sound pressure load, t is the width of the ring mass, r is the radial coordinate, and σ m is the radial stress generated by the initial tension of the elastic thin film, and the distribution of the internal tension of the circular film can be obtained by numerical solution methods;

[0091] The first three modes of the thin film metamaterial are as follows Figure 4 As shown in the figure, the local force caused by the magnetic field changes the axisymmetry of the structural stress state, destroys the axisymmetric mode of the structure, and realizes the switching of the acoustic wave control mode; under the condition of no magnetic field, the first and third order modal vibration modes are both axisymmetric modes, and the second order modal vibration mode is an antisymmetric mode; under the condition of magnetic field, the symmetry of the model is broken, and the first three order modal vibration modes no longer have axisymmetry or antisymmetry. Under the action of plane waves, they are all dominant modes.

[0092] The first-order modal natural frequency is controlled by tension design and ring block mass design, the third-order modal natural frequency is controlled by ring block mass size design, and the magnetic force required to achieve the target frequency is determined by calculating the dynamic equation of circular membrane vibration after applying a magnetic field.

[0093] The film-type metamaterial and structure disclosed by the present invention have the characteristics of strong designability. It can be known from the modal vibration type that the first-order mode can be approximated as a spring-mass system, the elastic film outside the annular mass block (concentric annular mass block) is analogous to a spring, and the annular mass block is analogous to a mass block. Therefore, the first-order modal natural frequency can be controlled by tension design and annular block mass design; the third-order mode is mainly based on the vibration of the elastic film outside the annular mass block, which is similar to the vibration mode of the inner and outer diameter constrained annular membrane. Therefore, the third-order modal natural frequency can be controlled by the annular block mass size design, and the magnetic force size for achieving the target frequency is determined by calculating the dynamic equation of the vibration of the annular membrane after applying a magnetic field, and the relative position relationship between the permanent magnet and the film-type metamaterial is determined by magnetic force calibration;

[0094] When designing the annular mass block, the power consumption can be further reduced by increasing the proportion of magnetic material and reducing the requirement for the external magnetic field strength. In this embodiment 1, the proportion of the area of ​​the annular mass block occupied by the ferromagnetic material is 1 / 6;

[0095] In S3, the design target frequency is that the first and third order natural frequencies are 170 Hz and 1700 Hz respectively under the condition of no magnetic field; after the magnetic field is applied, the second order natural frequency appears at 600 Hz. Based on the acoustic-vibration coupling model of thin film metamaterials and the relationship between the magnetic control force, the structural parameters of the thin film metamaterials are designed as follows:

[0096] Table 1 Main design parameters of thin film metamaterial in Example 1

[0097]

[0098]

[0099] In S4, according to the structural design parameters, a mode-switchable thin-film type acoustic metamaterial structure based on the magneto-control mechanism is prepared. The thin film with a pre-tension is fixed to a paramagnetic metal circular sheet, and a circular mass block composed of a ferromagnetic material and a paramagnetic material is bonded to the center of the thin film to form an axisymmetric structure. The structure is fixed in a flange device for easy testing, assembly and application.

[0100] As Figure 7 shown, it is an assembly schematic diagram of the mode-switchable thin-film type acoustic metamaterial structure based on the magneto-control mechanism in Embodiment 1 of the present invention; the mode-switchable thin-film type acoustic metamaterial structure based on the magneto-control mechanism includes: a flange device, an elastic thin film, a paramagnetic metal circular sheet (which can be aluminum or other paramagnetic materials), a permanent magnet magnetic force loading module, and a circular mass block; the elastic thin film is fixed to the paramagnetic metal circular sheet, and the circular mass block composed of a ferromagnetic material and a paramagnetic material is bonded to the center of the thin film to form an axisymmetric structure. The axisymmetric structure is fixed in the flange device, and the distance between the permanent magnet magnetic force loading module and the axisymmetric structure is determined according to the magnetic force calibration result. The area ratio of the ferromagnetic material in the circular mass block is 1 / 6; the axisymmetric structure is fixed in the flange device; the axisymmetric structure is screwed to the flange device.

[0101] The permanent magnet magnetic force loading module is a hollow cylindrical magnet composed of 14 small magnets (Nd-FeB) joined together. As Figure 3-1 shown, it is a structural schematic diagram of the hollow cylindrical magnet loading module composed of 14 small magnets (Nd-FeB) in Embodiment 1 of the present invention; in order to match the impedance tube, its inner diameter is designed to be 52 mm, the outer diameter is 80 mm, and the height is 100 mm; the magnetic field range it can provide is 0 - 1 T, and it has a gradient magnetic field in the axial direction. By changing the relative distance between the magnetic field and the test sample, the magnetic force loading can be realized.

[0102] According to the acoustic vibration coupling model of the thin-film type metamaterial, using the design parameters adopted in Table 1, the band diagram is calculated. As Figure 5-1 shown, it is the band diagram of the thin-film type acoustic metamaterial without applying a magnetic field in Embodiment 1 of the present invention; as Figure 5-2 shown, it is the simulation result and experimental verification result of the transmission coefficient of the thin-film type acoustic metamaterial without applying a magnetic field in Embodiment 1 of the present invention; among them, the gray area indicates that the wave vector is a complex number and decays along the acoustic wave propagation direction, that is, a band gap appears; adopting the local resonance mechanism, the band gap width of the thin-film type acoustic metamaterial is determined by the resonance frequency and the anti-resonance frequency. Therefore, by regulating the local resonance characteristics of the structure, the control of the acoustic wave transmission mode can be realized; further, through the standing wave tube test method, the transmission performance of the thin-film type acoustic metamaterial designed in Embodiment 1 without a magnetic field is measured and compared with the design target for verification, proving the effectiveness of the present invention.

[0103] According to the magneto-control force relationship of the thin-film acoustic metamaterial and using the magnetic force control requirements in Table 1, the energy band diagram under the action of a magnetic field is calculated, as Figure 6-1 shown, which is the energy band diagram of the thin-film acoustic metamaterial after applying an external magnetic field in Embodiment 1 of the present invention; as Figure 6-2 shown, which are the simulation results and experimental verification results of the transmission coefficient of the thin-film acoustic metamaterial after applying an external magnetic field in Embodiment 1 of the present invention; the local resonance characteristics of the thin-film acoustic metamaterial are regulated, and a new forbidden band appears near the second-order modal frequency, that is, the transmission energy of sound waves can be controlled by a magnetic field to achieve the function of an acoustic switch device; similarly, through the standing wave tube test method, the transmission performance of the thin-film acoustic metamaterial designed in this Embodiment 1 under a magnetic field is measured and compared with the design target for verification, verifying the effectiveness of the mode-switchable thin-film metamaterial based on the magneto-control mechanism.

[0104] Under the condition of plane wave incidence, without the action of a magnetic field, the axisymmetry of the excitation and the structure makes the structure vibration mainly dominated by the axisymmetric mode; after applying a magnetic field, the local magnetic force breaks the axisymmetry of the internal force of the structure, exciting more dominant modes, realizing the magneto-control mechanism, and based on the modal vibration mode characteristics, the mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism has the characteristic of strong designability, and finally realizes non-contact and discontinuous regulation.

[0105] The regulation of the thin-film acoustic metamaterial based on the magneto-control mechanism is simple and has strong designability. The parameters such as film tension, geometric parameters, ring mass blocks, and magnetic force can be designed according to the application scenario and target frequency band, improving the adaptability to different application scenarios. The mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism proposed by the present invention can realize non-contact, discontinuous regulation, realizing a sudden change in the structural acoustic performance, providing a new means for bandgap regulation, equivalent parameter dispersion control, etc.

[0106] The present invention adopts the above method. For the thin-film metamaterial composed of additional mass blocks and a thin film, first establish an acoustic-vibration coupling model, and then establish the influence relationship of the magnetic force on the vibration performance of the thin-film structure. According to the design target, design the thin-film metamaterial structure, determine the magnetic force required to be applied for regulation, then calibrate the magnetic force of the ring mass block according to the magnetic force action mode, and finally prepare the thin-film acoustic metamaterial based on the magneto-control mechanism to realize the switchable sound propagation mode.

[0107] The mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism proposed by the present invention can realize non-contact, discontinuous, and rapid regulation, realizing a sudden change in the structural acoustic performance, providing a new means for bandgap regulation, equivalent parameter dispersion control, etc.; moreover, the regulation of the thin-film acoustic metamaterial based on the magneto-control mechanism is simple and has strong designability, improving the adaptability to different application scenarios.

[0108] The mode-switchable thin-film acoustic metamaterial structure based on the magneto-control mechanism of the present invention utilizes a magnetic field to achieve non-contact regulation, induces changes in internal structural forces, breaks the symmetry of internal structural forces, excites implicit asymmetric modes, realizes sudden changes in acoustic properties, solves the problem that thin-film metamaterials based on the parameter regulation mechanism of electromagnetic intelligent materials require the application of strong electromagnetic fields, has a simple control method, and is convenient for design.

[0109] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of a mode-switchable thin-film acoustic metamaterial structure based on a magneto-control mechanism, the steps are as follows: (1) Construct a thin-film metamaterial acoustic-vibration coupling model Construct a thin-film metamaterial acoustic-vibration coupling model to form a composite structure with a mass block bonded to the center of an elastic thin film. Among them, The circular ring mass is composed of ferromagnetic material and paramagnetic material, and has a uniform areal density; (2) Establish the magneto-control force relationship of the thin-film metamaterial According to the thin-film metamaterial acoustic-vibration coupling model in step (1), solve the influence of different magnetic forces on the internal force of the thin-film structure, and calculate the modal frequencies and vibration modes of the thin-film metamaterial under different magnetic forces; (3) Design the thin-film metamaterial structure According to the thin-film metamaterial acoustic-vibration coupling model in step (1), establish the relationship between the film tension, geometric parameters, and design parameters of the circular ring mass and the structural vibration characteristics, and calculate the modal frequencies and vibration modes of the thin-film metamaterial in the concerned frequency band. According to the requirements of the target working frequency band, design the thin-film metamaterial structure, and determine the magnetic force required for regulation according to the magneto-control force relationship of the thin-film metamaterial established in step (2); (4) Calibrate the magnetic force of the circular ring mass Determine the magnetic force application method, and use a permanent magnet or an electromagnet to apply magnetic force to the circular ring mass; (5) Prepare the thin-film metamaterial to achieve mode switching based on the magneto-control mechanism According to the design parameters determined in step (3), fix the thin film with uniform tension on the paramagnetic metal circular ring sheet, and bond the circular ring mass composed of the composite of ferromagnetic material and paramagnetic material to the center of the thin film to form an axisymmetric structure; In step (1), when constructing the thin-film metamaterial acoustic-vibration coupling model, the dynamic equation is: In the formula, η is the displacement of the transverse vibration of the elastic thin film, σ0 is the radial stress generated by the initial tension of the elastic thin film, ρ is the density of the elastic thin film, f is the sound pressure load; t is the width of the circular ring mass, r is the radial coordinate; the circular ring mass and the thin film boundary follow the displacement and velocity continuity conditions. Considering the continuity of the velocities on both sides of the thin film and ignoring the high-order scattered waves, the relationship between the sound pressure load and the transmission coefficient is established as: f = 2(1 - T0) In the formula, Τ0 is the transmission coefficient under the condition of plane wave incidence.

2. The preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism according to claim 1, characterized in that In step (1), the area ratio of the ferromagnetic material in the circular ring mass is 1 / 6.

3. According to the preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism described in claim 2, in step (1), considering the regulation effect of the magnetic force on the modal frequencies and vibration modes of the thin-film metamaterial, establish the magneto-control force relationship of the thin-film metamaterial, specifically: Considering the influence of the magnetic force, establish the dynamic equation of the circular film vibration: Among them, σ m is the radial stress of the film in the magnetized state. By means of numerical solution methods, the distribution of the internal tension of the circular film is obtained, and the modal vibration shape functions and frequencies related to the magnetic force are calculated.

4. According to the preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism described in claim 3, in step (2), specifically as follows: control the first-order modal natural frequency through the tension design and the circular ring mass design, control the third-order modal natural frequency through the circular ring mass size design, and determine the magnetic force magnitude to achieve the target frequency by calculating the dynamic equation of the circular film vibration after applying the magnetic field.

5. The preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism according to claim 3. In step (4), when using a permanent magnet, it is necessary to calibrate the variation of the magnetic force with the distance between the permanent magnet and the ring mass, and determine the distance between the permanent magnet and the ring mass in step (3) according to the magnetic field regulation frequency requirement.

6. The preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism according to claim 5. In step (4), the permanent magnet is a permanent magnet magnetic force loading module, which is a hollow cylindrical magnet composed of 14 small magnets joined together.

7. The preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism according to claim 6. In step (4), the inner diameter of the hollow cylindrical magnet is 52 mm, the outer diameter is 80 mm, and the height is 100 mm.

8. The preparation method of the mode-switchable thin-film acoustic metamaterial based on the magneto-control mechanism according to claim 3. In step (4), when using an electromagnet, it is necessary to calibrate the variation of the magnetic force with the current intensity of the electromagnet, and determine the current intensity of the electromagnet in step (3) according to the magnetic field regulation frequency requirement.

Images