CN114339535A - Acoustic metamaterial filter - Google Patents

Abstract

The invention discloses an acoustic metamaterial filter, which comprises a cylindrical main body, wherein a tubular hollow sound transmission channel is formed in the center of the cylindrical main body, one end of the sound transmission channel is a closed end, and the other end of the sound transmission channel is an open end; meanwhile, two resonance spaces with the same size are also formed in the cylindrical main bodies on the two sides of the sound transmission channel, and the whole cross section of each resonance space is of a fan-shaped structure; two sympathetic response spaces pass through the choke and communicate each other with the transaudient passageway and constitute two resonators, are left side resonator and right side resonator respectively, and the choke of left side resonator is close to the blind end of transaudient passageway, and the choke of right side resonator is close to the open end of transaudient passageway, a transaudient passageway of two resonator commonalities. The filter has the advantages that the structural size belongs to the sub-wavelength size, the filter has a strong filtering function, the structural size and the filtering frequency band can be strictly matched, and a high-quality filtering signal with the bandwidth of about 400Hz can be obtained after the cavity action.

Description

An acoustic metamaterial filter

technical field

The invention relates to an acoustic metamaterial filter, which belongs to the technical field of acoustics.

Background technique

The emergence of acoustic metamaterials enables people to continuously break through the limits of traditional acoustic structures on the manipulation of sound waves and solve practical difficulties in various acoustic scenarios. In recent years, related work on filtering acoustic signals by constructing subwavelength acoustic structures has been emerging, and the design of acoustic structures with excellent performance and simple structure has become the goal of many researchers.

At present, most of the traditional acoustic filter devices have two ports, and these structures are mostly filter devices formed by connecting Helmholtz resonators on both sides of the pipeline or inserting variable-section tubes into the pipeline. Usually, researchers perform electro-acoustic analogy to obtain the corresponding analog circuit diagram, and match it with filter circuits such as typical Butterworth filter circuits in electricity, so as to achieve the function of designing acoustic structures to filter incident sound waves.

In the previous design, because people mostly retained the remaining sound waves after absorbing and filtering the incident sound waves, the output end of the two-port filter element was required to be non-closed (non-rigid wall), but this has a negative impact on the usage scenario. certain restrictions. Moreover, the basic structure of this filter is mostly based on basic structures such as Helmholtz cavity and expansion tube. The single shape makes the structure size larger, and the overall size is not as small as subwavelength.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies in the prior art, the present invention proposes an acoustic metamaterial by deforming and combining the Helmholtz resonator and sealing the end of the main pipe from the perspective of the design of acoustic metamaterials. material filter.

The technical solution adopted in the present invention is: an acoustic metamaterial filter, the filter includes a cylindrical body, a tubular hollow sound transmission channel is opened in the center of the cylindrical body, and both ends of the sound transmission channel One end is a closed end, and the other end is an open end; at the same time, two resonance spaces of the same size are opened in the cylindrical body on both sides of the sound transmission channel. The two resonance spaces pass through the throat and the sound transmission. The channels communicate with each other.

Further, the resonant space and the throat tube constitute two resonators, which are a left resonator and a right resonator respectively. The throat tube of the left resonator is close to the closed end of the sound transmission channel, and the right resonator The throat is close to the open end of the sound transmission channel, and the left resonator and the right resonator share a sound transmission channel.

Further, the length of the throat pipe is: l ₀ =0.8mm, the diameter is: a = 0.2mm; and the distance between the two throat pipes is: d ₀ =1.7mm.

Further, the distance between the throat near the open end and the open end is: x ₁ =1.05mm.

Further, the inner and outer side walls of the resonance space are arcs, and the overall cross section of the resonance space is a fan-shaped structure.

Further, the arc radians of the inner and outer side walls of the resonance space are: α=2π/3.

Further, the radius of curvature of the inner wall surface of the resonator space is: l ₁ =2.75mm, and the radius of curvature of the outer wall surface is: l ₂ =4.75mm.

Further, the height of the resonance space is: l ₃ =3.6mm.

Further, the wall thickness between the inner wall of the upper end of the resonance space close to the sound transmission channel and the top of the cylindrical body provided with the closed end is: t=0.2 mm.

Further, the length of the cylindrical body is: l _t =4 mm, the diameter is: D = 13.8 mm; the diameter of the sound transmission channel is: d = 3.9 mm.

The beneficial effects of the present invention are as follows:

(1) The filter structure size of the present invention belongs to the sub-wavelength size, the formed filter (metamaterial unit) has a strong filtering function, and the structure size and the filter frequency band can be strictly matched;

(2) Near the closed pipe end of the main pipe, after the action of the cavity, a high-quality filtered signal with a bandwidth of about 400 Hz can be obtained.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

Fig. 1 is the longitudinal sectional view of the present invention;

Fig. 2 is the transverse sectional view of the present invention;

Fig. 3 is the internal structure equivalent schematic diagram of the present invention;

Fig. 4 is the simulation schematic diagram of the present invention; wherein (a) is a schematic diagram of a simulation structure, and (b) is a comparison diagram of the transfer function result obtained by theoretical derivation calculation and the simulation result;

FIG. 5 is an equivalent circuit diagram of the filter structure of the present invention.

Marked in the figure: 1-cylindrical body; 2-sound transmission channel, 3-left resonator, 4-right resonator, 5-closed end, 6-open end, 7-throat.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Figures 1-3, an embodiment provided by the present invention: an acoustic metamaterial filter, the filter includes a cylindrical body 1, and a tubular hollow sound transmission channel is opened in the center of the cylindrical body 1 2. Among the two ends of the sound transmission channel 2, one end is a closed end 5 and the other end is an open end 6; at the same time, two resonances of the same size are also opened in the cylindrical body 1 on both sides of the sound transmission channel 2. Space, the inner and outer side walls of the resonance space are arcs, and the overall cross-section of the resonance space is a fan-shaped structure; the two resonance spaces are communicated with each other through the throat pipe and the sound transmission channel, and the resonance space and the throat pipe 7 form two parts. Resonators are the left resonator 3 and the right resonator 4 respectively, the throat 7 of the left resonator is close to the closed end 5 of the sound transmission channel, and the throat 7 of the right resonator is close to the sound transmission channel 2 The open end 6, the left resonator and the right resonator share a sound transmission channel 2.

When working, the sound wave is incident from the side of the open end, passes through the right resonator and the left resonator in turn, and finally reaches the rigid wall and is reflected back. But because of the two resonators, not all frequencies of sound waves will reach the rigid wall with the same intensity, only waves of certain frequencies will.

The structural parameters of the present invention are as follows:

Main body structure length: l _t = 4mm;

Main structure diameter: D=13.8mm;

The diameter of the main sound transmission channel: d=3.9mm;

Resonator throat length: l ₀ =0.8mm;

Resonator throat diameter: a=0.2mm;

The distance between the throats of the two resonators: d ₀ =1.7mm;

The distance between the throat of the resonator on the open side and the open end: x ₁ =1.05mm;

The radius of curvature of the inner side of the resonator: l ₁ =2.75mm;

The radius of curvature of the outer side of the resonator: l ₂ =4.75mm;

Resonator height: l ₃ =3.6mm;

The arc corresponding to the inner (outer) side of the resonator: α=2π/3;

The wall thickness between the top of the main structure and the top of the resonator: t=0.2mm.

In Figure 4(a), a probe is placed at the closed end of the main structure, a shooting field is added directly in front of the main structure, and a perfect matching layer is added to the range enclosed by the dotted line. Figure 4(b) shows the comparison between the transfer function results obtained through theoretical derivation and the simulation results; the dashed line marked with an asterisk is the simulation result, and the solid line is the calculation result.

共鸣器之间的阻抗为Z_a0＝jωM_a0(管直径相对较小，产生的声容可以忽略)，开口端波导管产生的阻抗Z_a1＝jωM_a1。考虑到未封闭端口存在管端修正，其产生阻抗的真实长度为

因为管道末端为刚性壁，阻抗为Z_al＝∞。使用转移阻抗法可以求出在亥姆霍兹左侧共鸣器处的阻抗,Z_a0＝-jR₀cot(kx₁)，其中

为主管道的阻抗，S_m为主管道截面积。经过推导，得到传递函数T(ω)为Figure 5 shows the equivalent circuit diagram of the filter structure. When this filter product is in use, the sound pressure is to be measured from an unclosed pipe, and the incident sound pressure is P ₀ , and a sound pressure detector (a small hole can be opened, the diameter of which is far away from the pipe) is placed at the end (closed end) of the pipe. It can be smaller than the diameter of the pipe), and the measured sound pressure at the end of the pipe is P. The transfer function of the equivalent circuit diagram of the internal structure corresponding to the invention can be obtained by using the voltage division theorem. Let the impedance of each Helmholtz resonator be

The impedance between the resonators is Z _a0 =jωM _a0 (the tube diameter is relatively small and the resulting sound capacity is negligible), and the impedance Z _a1 =jωM _a1 produced by the open-end waveguide. Considering the existence of pipe end correction in the unclosed port, the true length of the resulting impedance is

Since the end of the pipe is a rigid wall, the impedance is Z _al = ∞. The impedance at the left-hand Helmholtz resonator can be found using the transfer impedance method, Z _a0 =-jR ₀ cot(kx ₁ ), where

is the impedance of the main pipe, and S _m is the cross-sectional area of the main pipe. After derivation, the transfer function T(ω) is obtained as

where Z _t is the impedance of the entire system,

Finally, through the following table, the meaning of the symbols in the text and the parameter values used in the calculation process are supplemented:

The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those of ordinary skill in the art should understand that the above-mentioned embodiments do not limit the protection scope of the present invention in any form, and all technical solutions obtained by means of equivalent replacement and the like all fall within the protection scope of the present invention.

The parts not involved in the present invention are the same as the prior art or can be implemented by using the prior art.

Claims (10)

1. The acoustic metamaterial filter is characterized by comprising a cylindrical main body, wherein a tubular hollow sound transmission channel is formed in the center of the cylindrical main body, one end of the two ends of the sound transmission channel is a closed end, and the other end of the two ends of the sound transmission channel is an open end; and two resonance spaces with the same size are also arranged in the cylindrical main bodies on the two sides of the sound transmission channel, and the two resonance spaces are communicated with the sound transmission channel through the throat pipe.

2. An acoustic metamaterial filter as claimed in claim 1, wherein the resonating space and the throat form two resonators, a left resonator and a right resonator, respectively, the throat of the left resonator is close to the closed end of the acoustic transmission channel, the throat of the right resonator is close to the open end of the acoustic transmission channel, and the left resonator and the right resonator share the acoustic transmission channel.

3. An acoustic metamaterial filter as claimed in claim 1 or 2, wherein the throat has a length of: l₀0.8mm, diameter: a is 0.2 mm; and the distance between the two throats is as follows: d₀＝1.7mm。

4. A method as claimed in claim 2The acoustic super-structure material filter is characterized in that the distance between a throat close to the opening end and the opening end is as follows: x is the number of₁＝1.05mm。

5. An acoustic metamaterial filter according to claim 1 or 2, wherein the inner and outer side wall surfaces of the resonance space are both circular arcs, and the overall cross section of the resonance space is a fan-shaped structure.

6. The acoustic metamaterial filter of claim 5, wherein the arc radians of the inner and outer sidewall surfaces of the resonance space are: α is 2 π/3.

7. An acoustic metamaterial filter as claimed in claim 5, wherein the resonator volume has an inner sidewall surface radius of curvature: l₁2.75mm, the outside wall curvature radius is: l₂＝4.75mm。

8. An acoustic metamaterial filter as claimed in claim 1 or 2, wherein the height of the resonating space is: l₃＝3.6mm。

9. An acoustic metamaterial filter as claimed in claim 1 or 2, wherein the wall thickness of the resonance space between the inner wall of the upper end near the sound transmission channel and the top of the cylindrical body having the closed end is: t is 0.2 mm.

10. An acoustic metamaterial filter as claimed in claim 1, wherein the cylindrical body has a length of: l_t4mm, diameter: d is 13.8 mm; the diameters of the sound transmission channels are as follows: d is 3.9 mm.

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