A semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency

Abstract

The present invention provides a semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency. It is composed of a thin-film acoustic metamaterial, an axial magnetic field, and a control circuit part. The thin-film acoustic metamaterial is composed of a natural rubber film, two NdFeB magnets, and an acrylic ring frame. The NdFeB magnets adsorbed on both sides of the film can serve as both the central mass block of the semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency and the force-bearing object of the axial magnetic field. Current is passed into the axial magnetic field, and the force on the NdFeB magnet is changed by controlling the current intensity, thereby changing the pre-tension of the film and realizing the directional adjustment of the natural frequency of the sound insulation peak of the material. The control circuit part is composed of a sound level meter sensor, a display screen, and a potentiometer. When the sound insulation peak frequency shifts due to material fatigue, the model received by the sound level meter sensor is observed on the display screen, and the input current intensity is changed by the potentiometer to realize semi-automatic control.

Description

Technical Field

[0001] The present invention relates to the technical field of acoustic metamaterials for low-frequency noise control, and in particular to a semi-automatic thin-film acoustic metamaterial capable of adjusting and controlling the peak frequency of sound insulation. Background Art

[0002] With the expansion of cities, substations have gradually moved from suburbs to cities, and noise pollution from substations has attracted more and more attention. The noise frequency of substations is mainly concentrated in 40-120Hz, with the characteristics of low frequency and wide bandwidth. However, due to the long wavelength and slow attenuation of low-frequency noise, controlling low-frequency noise has become a challenging problem. Traditional sound insulation and noise reduction materials are limited by the law of mass. In order to achieve better sound insulation effects in the low-frequency range, they usually need to be designed to be thicker and more complex, and their applications are limited. Thin-film acoustic metamaterials have been widely studied in the field of vibration reduction and noise reduction because of their better low-frequency acoustic performance.

[0003] In order to solve the problem that low-frequency noise is difficult to control, Hang Rui et al. designed a thin-film active acoustic metamaterial based on electromagnetic force tuning. The structure consists of a energized solenoid and a thin film with fixed boundaries and a neodymium iron boron magnet attached to the center. The acoustic performance was analyzed in detail through numerical simulation and experiments. The results show that the structure has good sound insulation performance in the range of 100-200Hz. In order to isolate low-frequency noise, He Zihou et al. designed a controllable thin-film acoustic metamaterial based on piezoelectric materials. The material is made of a piezoelectric mass block embedded in an elastic film. A finite element analysis model of the material was established. The experimental results show that this acoustic metamaterial can adjust the resonant frequency of the circuit by changing the parameters of the external circuit, thereby achieving the regulation of the sound insulation performance.

[0004] However, the sound insulation frequency of most thin-film acoustic metamaterials is mostly in the frequency domain above 100Hz, and there is little research in the frequency range of 20-100Hz. However, some mechanical noises such as substation equipment are mainly concentrated in the low frequency band of 40-100Hz. In addition, the existing thin-film acoustic metamaterials will become fatigued due to long-term use, which will cause the sound insulation peak frequency to shift, making its noise reduction effect worse. Therefore, this application designs a semi-automatic thin-film acoustic metamaterial that can adjust the sound insulation peak frequency. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and provide a semi-automatic thin film acoustic metamaterial with adjustable sound insulation peak frequency. The thin film acoustic metamaterial is made by combining NdFeB magnets with different shapes and distributions with natural rubber films, which can generate sound insulation band gaps of different frequencies and broaden the low-frequency noise control range.

[0006] The technical solution adopted by the present invention is: a semi-automatic thin-film acoustic metamaterial capable of adjusting the peak frequency of sound insulation, comprising a thin-film acoustic metamaterial, an axial magnetic field and a control circuit; the thin-film acoustic metamaterial comprises a natural rubber film, two NdFeB magnets and an acrylic ring frame, the natural rubber film is fixed in the acrylic ring frame by means of screws, and the two NdFeB magnets are respectively fixed on both sides of the center of the natural rubber film; the axial magnetic field comprises an energized solenoid and two insulating partition plates, and the two insulating partition plates are located on both sides of the energized solenoid; the control circuit comprises a sound level meter sensor, a display screen and a potentiometer, the sound level meter sensor communicates with the display screen by means of a serial port, and the potentiometer is connected in series with a wire and a DC power supply of the energized solenoid; the thin-film acoustic metamaterial is placed at the center of the energized solenoid, and the N pole of the NdFeB magnet is in the same direction as the N pole of the energized solenoid.

[0007] Furthermore, the energized solenoid comprises a PVC tube, an enameled copper wire and an insulating tape, wherein the enameled copper wire is evenly wound on the PVC tube, and the insulating tape is coated on the surface of the enameled copper wire.

[0008] Furthermore, the radius of the natural rubber film is 50 mm, and the thickness is 1.0-1.5 mm; the radius of the NdFeB magnet is 5-7.5 mm, and the thickness is 1-3 mm; the inner radius of the acrylic ring frame is 50 mm, the outer radius is 60 mm, and the thickness is 3 mm.

[0009] Furthermore, the PVC pipe has an inner radius of 60 mm, an outer radius of 62 mm, a length of 200 mm, and 800 turns.

[0010] Furthermore, the insulating partition sheet has an inner radius of 62 mm, an outer radius of 65 mm, and a thickness of 3 mm. The insulating partition sheet is fixed on both sides of the energized solenoid by means of AB glue.

[0011] Furthermore, the current range of the potentiometer is 0-30A.

[0012] Furthermore, the NdFeB magnet is circular in shape.

[0013] The beneficial effects obtained by the present invention are as follows: the present invention places the thin film acoustic metamaterial in an axial magnetic field controlled by current, applies an axial magnetic force to the central mass block, and uses the magnetic force to supplement the film restoring force. The sound insulation peak frequency change of the thin film acoustic metamaterial is monitored in real time by a sound level meter sensor, and the current intensity of the axial magnetic field is adjusted by a potentiometer to change the force on the central mass block, thereby realizing directional adjustment of the natural frequency of the sound insulation peak of the material, effectively alleviating the problem of sound insulation peak frequency deviation caused by material fatigue, and achieving the effect of semi-automatic control.

[0014] The invention has simple preparation and structure, and the raw materials are easily available, and the raw materials are easily available, and large-scale production can be realized. For the 50-100Hz frequency noise of the substation, the invention has excellent sound insulation effect, and the sound transmission loss reaches 130dB, and it is convenient and adjustable according to different sound insulation characteristics requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of thin film acoustic metamaterial;

[0016] Figure 2 This is a cross-sectional view of the thin film acoustic metamaterial;

[0017] Figure 3 A diagram of a semi-automatic thin-film acoustic metamaterial device capable of adjusting the peak frequency of sound insulation;

[0018] Figure 4 A cross-sectional view of a semi-automatic thin-film acoustic metamaterial device capable of adjusting the peak frequency of sound insulation;

[0019] Figure 5 The effect of mass block thickness on the low-frequency sound insulation properties of thin-film acoustic metamaterials;

[0020] Figure 6 The effect of film thickness on the low-frequency sound insulation properties of thin film acoustic metamaterials;

[0021] Figure 7 The effect of mass block diameter on the low-frequency sound insulation properties of thin film acoustic metamaterials;

[0022] Figure 8 This is a semi-automatic thin film acoustic metamaterial sound intensity streamline cloud diagram with a valley value of 21Hz;

[0023] Fig. 9 This is a semi-automatic thin-film acoustic metamaterial sound intensity streamline cloud diagram with a peak value of 51Hz;

[0024] Fig.10 This is a semi-automatic film acoustic metamaterial vibration mode displacement cloud map with a valley value of 21Hz;

[0025] Fig.11 This is a semi-automatic film acoustic metamaterial vibration displacement cloud diagram with a peak value of 51Hz;

[0026] Fig.12 It is the sound insulation curve of materials under different current intensities;

[0027] Among them: 1-NdFeB magnet; 2-natural rubber film; 3-acrylic ring frame; 4-energized solenoid; 5-current inflow direction; 6-current outflow direction; 7-potentiometer; 8-sound level meter sensor. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely 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, rather than all the embodiments.

[0029] like Figure 1-4 As shown, a semi-automatic thin-film acoustic metamaterial capable of adjusting the peak frequency of sound insulation comprises a thin-film acoustic metamaterial, an axial magnetic field and a control circuit; the thin-film acoustic metamaterial comprises a natural rubber film 2, two NdFeB magnets 1 and an acrylic ring frame 3, the natural rubber film 2 is fixed in the acrylic ring frame 3 by means of screws, and the two NdFeB magnets 1 are respectively fixed on both sides of the center of the natural rubber film 2; the axial magnetic field comprises an energized solenoid 4 and two insulating partition plates, and the two insulating partition plates are located on both sides of the axial direction of the energized solenoid 4; the control circuit comprises a sound level meter sensor 8, a display screen and a potentiometer 7, the sound level meter sensor 8 communicates with the display screen by means of a serial port, and the potentiometer 7 is connected in series with the wire and the DC power supply of the energized solenoid 4; the thin-film acoustic metamaterial is placed at the center of the energized solenoid 4, and the N pole of the NdFeB magnet 1 is in the same direction as the N pole of the energized solenoid 4. The energized solenoid 4 comprises a PVC tube, an enameled copper wire and an insulating tape. The enameled copper wire is evenly wound on the PVC tube, and the insulating tape is coated on the surface of the enameled copper wire.

[0030] The radius of the natural rubber film 2 is 50mm, and the thickness is 1.0-1.5mm; the radius of the NdFeB magnet 1 is 5-7.5mm, and the thickness is 1-3mm; the inner radius of the acrylic ring frame 3 is 50mm, the outer radius is 60mm, and the thickness is 3mm. The inner radius of the PVC pipe is 60mm, the outer radius is 62mm, the length is 200mm, and the number of turns is 800 turns. The inner radius of the insulating partition is 62mm, the outer radius is 65mm, and the thickness is 3mm. The insulating partition is fixed on both sides of the energized solenoid 4 with the help of AB glue. The current range of the potentiometer is 0-30A. The shape of the NdFeB magnet 1 is circular.

[0031] The NdFeB magnet 1 adsorbed on both sides of the natural rubber film 2 can serve as the central mass block of the semi-automatic thin film acoustic metamaterial with adjustable sound insulation peak frequency, and can also serve as a force-bearing object of the axial magnetic field, and current is passed into the axial magnetic field to generate a magnetic field. When the sound insulation peak frequency shifts due to material fatigue, the sound level meter sensor receives the signal and displays it on the display screen, and the input current intensity is changed by the potentiometer to achieve directional adjustment of the sound insulation peak natural frequency of the material. When the sound insulation peak frequency shifts due to material fatigue, the internal magnetic field intensity of the axial magnetic field is controlled by adjusting the potentiometer, and then the tension of the natural rubber film 2 of the thin film acoustic metamaterial is controlled to achieve directional adjustment of the sound insulation peak natural frequency of the material, achieving the effect of semi-automatic control.

[0032] Specific implementation: Step 1: Place a 1.5 mm thick natural rubber film 2 flat on the laboratory table, and cut a circular natural rubber film 2 with a radius of 60 mm using a slicer;

[0033] Step 2: Use a laser cutting machine to cut two pieces Figure 2 The acrylic ring frame 3 shown is used to press the natural rubber film 2 with two pieces of acrylic ring frames 3, punch the screw holes with a puncher, and fix them with screws;

[0034] Step 3: Fix two NdFeB magnets 1 with a radius of 6 mm and a thickness of 2 mm at the center positions on both sides of the natural rubber film 2;

[0035] Step 4: Place the sound level meter sensor 8 probe at the end away from the sound source, and connect the potentiometer 7 to the energized solenoid 4;

[0036] Step 5: Place the thin film acoustic metamaterial into the center of the axial magnetic field and fix the edges with AB glue. After the AB glue solidifies, a semi-automatic thin film acoustic metamaterial with adjustable sound insulation peak frequency is completed.

[0037] Step 6: Connect the axial magnetic field to the power supply, adjust the current intensity, and obtain the acoustic transmission loss curve of the acoustic metamaterial under different current intensities.

[0038] Table 1 shows the material parameters of the thin film acoustic metamaterial.

[0039] Table 1 Material parameters

[0040]

[0041] A semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency was simulated and analyzed by finite element method using the "acoustic-solid coupling, frequency domain" module in COMSOL Multiphysics5.6 finite element software.

[0042] The present invention studies the influence of natural rubber films of different thicknesses and NdFeB magnets of different radii and thicknesses on the sound insulation properties of the material, and further determines the parameters of the most ideal sound insulation effect for 50 Hz frequency noise.

[0043] The calculation results are as follows Figure 5 As shown. Figure 5 It can be seen that when the thickness of the mass block increases from 1mm to 3mm in steps of 1mm, the peak values ​​of the sound transmission loss appear at 63Hz, 51Hz, and 43Hz, respectively, showing a trend of shifting to low frequencies. The sound insulation at 63Hz reaches 106dB, at 51Hz reaches 130dB, and at 43Hz reaches 126dB. Figure 6It can be seen that as the mass block diameter increases from 10mm to 12mm and 15mm, the sound insulation peak frequency and Figure 5 The sound insulation is consistent with that of the other two frequencies, shifting to low frequencies, reaching 111dB, 130dB and 101dB at 54Hz, 51Hz and 47Hz respectively. Figure 7 It can be seen that with the increase of film thickness, the sound insulation peak frequency tends to move toward high frequency. When the thickness is 1mm, the sound insulation reaches 135dB at 29Hz. When the thickness is 1.2mm, the sound insulation reaches 100dB at 38Hz. When the thickness is 1.5mm, the sound insulation reaches 130dB at 51Hz.

[0044] In summary, when the center mass block has a radius of 6mm, a thickness of 2mm, and a film thickness of 1.5mm, its sound transmission loss not only reaches 130dB at 51Hz, but also exceeds 50dB in the frequency range of 44Hz to 58Hz, showing a broadband characteristic. In view of the fact that the peak noise of the substation is at 50Hz, the material has excellent sound insulation performance.

[0045] In order to further explore the sound insulation properties of a semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency, the sound intensity streamlines, vibration mode displacement and sound pressure level were calculated at the peak frequency and valley frequency of sound transmission loss. Fig. 9 and Fig.11 They are the sound intensity streamline composite vibration displacement diagram and mode displacement diagram at the valley value of 21Hz. It can be seen that at 21Hz, the oscillator and the sound wave form a phase resonance, and the sound wave can pass through the thin film metamaterial with almost no loss. Figure 8 and Fig.10 They are the sound intensity streamline composite vibration displacement diagram and mode displacement diagram with a peak value of 51Hz. It can be seen that at 51Hz, the oscillator and the sound wave form an anti-phase resonance, and the sound wave energy is continuously dissipated in this vibration mode.

[0046] Depend on Fig.12 It can be seen that within the research frequency range of 20 to 80 Hz, as the current increases, the sound insulation peak frequency of the acoustic metamaterial moves toward high frequency. Therefore, the designed semi-automatic thin film acoustic metamaterial with adjustable sound insulation peak frequency can solve the problem of sound insulation peak frequency shift caused by fatigue softening of thin film materials. By adjusting the current to apply axial electromagnetic force to the central magnet, the sound insulation peak can be adjusted within the low frequency range, thereby realizing non-contact semi-automatic control of the sound insulation peak of the thin film acoustic metamaterial.

[0047] According to the above characteristics of the semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency of the present invention, it can be applied to sound insulation and noise reduction in aspects such as 50Hz low-frequency noise in substations, and has potential application value in the field of low-frequency noise reduction.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A semi-automatic thin-film acoustic metamaterial with adjustable sound insulation peak frequency. Features: The invention comprises a thin film acoustic metamaterial, an axial magnetic field and a control circuit; the thin film acoustic metamaterial comprises a natural rubber film (2), two NdFeB magnets (1) and an acrylic ring frame (3); the natural rubber film (2) is fixed in the acrylic ring frame (3) by means of screws; the two NdFeB magnets (1) are respectively fixed on both sides of the center of the natural rubber film (2); the axial magnetic field comprises an energized solenoid (4) and two insulating partition plates; the two insulating partition plates are located on both sides of the axial direction of the energized solenoid (4); the control circuit comprises a sound level meter sensor (8), a display screen and a potentiometer (7); the sound level meter sensor (8) communicates with the display screen by means of a serial port; the potentiometer (7) is connected in series with the wire of the energized solenoid (4) and a DC power supply; the thin film acoustic metamaterial is placed at the center of the energized solenoid (4); the N pole of the NdFeB magnet (1) is in the same direction as the N pole of the energized solenoid (4); The energized solenoid (4) comprises a PVC tube, an enameled copper wire and an insulating tape, wherein the enameled copper wire is evenly wound on the PVC tube, and the insulating tape is coated on the surface of the enameled copper wire; The radius of the natural rubber film (2) is 50 mm, and the thickness is 1.0-1.5 mm; the radius of the NdFeB magnet (1) is 5-7.5 mm, and the thickness is 1-3 mm; the inner radius of the acrylic ring frame (3) is 50 mm, the outer radius is 60 mm, and the thickness is 3 mm; The PVC tube has an inner radius of 60 mm, an outer radius of 62 mm, a length of 200 mm, and 800 turns.

2. A semi-automatic thin film acoustic metamaterial capable of adjusting the peak frequency of sound insulation according to claim 1, Features: The insulating partition sheet has an inner radius of 62 mm, an outer radius of 65 mm and a thickness of 3 mm. The insulating partition sheet is fixed to both sides of the energized solenoid (4) by means of AB glue.

3. A semi-automatic thin film acoustic metamaterial capable of adjusting the peak frequency of sound insulation according to claim 1, Features: The current range of the potentiometer (7) is 0-30A.

4. A semi-automatic thin film acoustic metamaterial capable of adjusting the peak frequency of sound insulation according to claim 1, Features: The NdFeB magnet (1) is circular in shape.

Images