CN114061733B - Gradient reflection acoustic grating sensing structure - Google Patents
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Abstract
The invention relates to the field of sound grating metamaterials, in particular to a gradient reflection sound grating sensing structure which comprises a plurality of vertical plates and a reflection plate, wherein the vertical plates are sequentially arranged, the reflection plate is arranged on one side of each vertical plate, the width of an air slit between every two adjacent vertical plates is increased in an equal difference mode, an air interlayer is reserved between the reflection plate and the side edge of each vertical plate, a region between every two adjacent vertical plates and the reflection plate can form an FP-like resonant cavity, sound wave transmission can be effectively controlled, sound energy is limited in the slit, the working bandwidth of the FP-like resonant cavity is widened by combining frequency bands of the FP-like resonant cavities with different sizes, the volume of the resonant cavity is changed, the working frequency of the resonant cavity is adjusted, and therefore the problems that the working bandwidth of a traditional sound grating metamaterials is narrow, the size of the resonant cavity is large and the like are solved, and directional positioning of all angles is also realized.
Description
Technical Field
The invention relates to the field of acoustic grating metamaterials, in particular to a gradient reflection acoustic grating sensing structure.
Background
The acoustic sensing technology has been widely used in the fields of sound source localization, state monitoring, and the like. However, when an acoustic signal is drowned out by strong background noise, the conventional acoustic sensing detection apparatus cannot detect the acoustic signal because of the limitation of the minimum detection pressure. In addition, the traditional sound source positioning method based on the microphone array is influenced by complex installation, complex operation and the like, and is limited in industrial application.
In recent years, acoustic metamaterials have gained wide attention due to their unique acoustic wave manipulation characteristics. The characteristics of rainbow capture, supernormal acoustic transmission, acoustic tunneling and the like continuously promote the development of acoustic sensing technology based on metamaterials. The acoustic metamaterial can be used as an acoustic device for pre-enhancing acoustic signals and sound source positioning by utilizing the acoustic wave manipulation characteristics of the acoustic metamaterial. To date, some important research efforts have provided good technical support for the development of metamaterial-based acoustic enhancement devices. Besides sound enhancement devices, some sound source positioning devices based on acoustic metamaterials have also been developed, such as topological acoustic antennas based on valley-Hall topological insulators to achieve directional positioning and coupled sub-wavelength Helmholtz resonators that can be used for all-angle directional sensing. However, in engineering practice, the design and manufacture of such metamaterials is often quite complex.
Compared with the metamaterial, the grating metamaterial composed of the rectangular plate and the slit periodic array is simple in structure and easy to manufacture in engineering practice. Previous researches show that each slit of the traditional periodic acoustic grating metamaterial with the slits with the same width can be used as a Fabry-Perot (FP) resonant cavity, the resonant frequency corresponding to incident sound waves can be effectively captured, the sound pressure amplitude of the resonant frequency can be amplified by more than 80 times, and the resonant frequency is very sensitive to the incident angle of zero-order transmission, so that the resonant frequency provides potential application value for the acoustic sensing technology. However, due to the high quality factor characteristic of the resonant structure, the operating frequency band of the conventional acoustic grating metamaterial is narrow. Multi-resonator coupling, a common method for broadening the operating bandwidth, can combine multiple resonance bands to effectively broaden the operating bandwidth, and is also applicable to sonogram metamaterials.
In engineering practice, such as in the detection of rub-impact signals, manipulation of acoustic waves by the sonogram metamaterial is typically required at lower frequencies or at deep sub-wavelength scales. However, the FP resonant cavity typically has a length greater than or equal to the wavelength of the resonant frequency, which makes the device bulky and unsuitable for use in compact or small devices. Although in past studies, a spatial convolution has proven successful in reducing the operating band, it is not suitable for coupling with a sonotrode material due to its significant loss in thermal viscosity. In recent years, a reflective grating metamaterial proposed in the optical field can realize deep sub-wavelength sensing in the optical field by manipulating a reflection phase at a boundary of the reflective grating metamaterial, and provides a thought for realizing the deep sub-wavelength acoustic grating metamaterial, however, it is not clear whether the deep sub-wavelength acoustic sensing can be realized by manipulating the reflection phase at the boundary of the acoustic grating.
It should be noted that the above background description is only for the convenience of clear and complete description of the technical solutions of the present application and for the understanding of those skilled in the art. Such solutions are not considered to be known to the person skilled in the art merely because they have been set forth in the background section of the present application.
Disclosure of Invention
Compared with the traditional periodic grating metamaterial, the grating metamaterial with the gradually increased slit width can be regarded as a group of combined resonators capable of capturing different frequency components, a plurality of resonance bands can be combined, and the working bandwidth is widened.
In order to achieve the purpose, the invention provides a gradient reflection acoustic grating sensing structure which comprises a plurality of vertical plates arranged in sequence and a reflection plate arranged on one side of each vertical plate, wherein the widths of air slits between two adjacent vertical plates are increased in an equal difference mode, and an air interlayer is reserved between the reflection plate and the side edge of each vertical plate.
Wherein the width increasing rule of the air slit satisfies w n ＝w 1 + (n-1). times.d, wherein w 1 Is an initial width, w n Is the width of the nth air slot and d is the step size.
Wherein the initial width w of the air slit 1 The step length d is 1mm, 7 mm.
Wherein the total number of air slits is 15.
The gradient reflection acoustic grating sensing structure is prepared through 3D printing, and the vertical plate and the reflecting plate are made of photosensitive resin.
Wherein the density ρ of the photosensitive resin 2 ＝1190kg/m 3 Speed of sound c 2 1700m/s, modulus of elasticity E 2 ＝2.65×10 3 MPa, shear modulus G 2 ＝2.22×10 3 MPa。
The vertical plates are rectangular plates, the rectangular plates are arranged in a mode that long sides of the rectangular plates are aligned, the plate thickness t of each rectangular plate is 8mm, and the plate length h of each rectangular plate is 100 mm.
The thickness b of the reflecting plate is 8mm, the length L of the reflecting plate is 338mm, and the width H of the reflecting plate is 100 mm.
Wherein the thickness g of the air interlayer is 1.5 mm.
Meanwhile, the air slits and the air interlayer can be adjusted according to actual requirements.
The scheme of the invention has the following beneficial effects:
according to the gradient reflection acoustic grating sensing structure provided by the invention, the region between the adjacent vertical plates and the reflection plate can form an FP-like resonant cavity, so that acoustic energy can be effectively limited in the slits, the acoustic energy density is obviously increased, meanwhile, an evanescent wave attenuation phenomenon exists outside the gradient reflection acoustic grating sensing structure and is coupled with zero-order resonance modes of the slits, the transmission from an acoustic energy cavity to the cavity is realized, and the function of widening a working frequency band is further realized;
in the invention, the working frequency of the gradient reflection acoustic grating sensing structure can be adjusted by changing the geometric parameters (w and g) of the structure, the resonance frequency of each slit is changed along with the size of the volume of the resonant cavity, and the control on deep sub-wavelength acoustic waves can be realized;
In the invention, the sound pressure response of the gradient reflection acoustic grating sensing structure is influenced by the sound wave incidence angle, different pressure field distribution conditions exist, the direction response is sensitive, and the sound source positioning can be realized;
in addition, the photosensitive resin is adopted, the preparation is carried out by a 3D printing technology, the structure is simple, the manufacturing is convenient, and the production cost is lower;
other advantages of the present invention will be described in detail in the detailed description that follows.
Drawings
FIG. 1(a) is a front view of the overall structure of the present invention;
FIG. 1(b) is a three-dimensional view of the overall structure of the present invention;
fig. 2(a) is the normalized sound pressure response of the 2 nd, 8 th, 14 th slits;
FIG. 2(b) is a normalized pressure field distribution at different resonant frequencies;
FIG. 2(c) is a comparison of resonance frequencies at different slit positions with and without a reflective plate;
FIG. 3(a) is a graph showing the effect of air slit width w on the resonant frequency;
FIG. 3(b) is a graph showing the effect of air interlayer width g on the resonant frequency;
FIG. 4(a) is a schematic diagram of a directional response test;
FIG. 4(b) is a directional response normalized sound pressure;
fig. 4(c) shows the sound field distribution at different incident angles.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The various features and embodiments described in the embodiments may be combined in any suitable manner, for example, different embodiments may be formed by combining different features/embodiments, and in order to avoid unnecessary repetition, various possible combinations of features/embodiments in the present invention will not be described in detail.
It should be noted that the terms "disposed" and "connected" should be interpreted broadly, and may be, for example, directly disposed, installed and connected, or indirectly disposed and connected through intervening components and intervening structures. In addition, the directions or positional relationships indicated by "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like in the present invention are based on the directions or positional relationships shown in the drawings or the conventional placing states or using states, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the structures, features, devices or elements referred to must have a specific direction, be configured and operated in a specific direction, and thus, cannot be construed as limiting the present invention.
As shown in fig. 1, an embodiment of the present invention provides a gradient reflection acoustic grating sensing structure, which includes a plurality of vertical plates 1 arranged in sequence and a reflection plate 2 arranged on one side of the vertical plates 1, that is, the gradient reflection acoustic grating sensing structure is formed by vertically arranging a plurality of "plate-air-plate" type unit structures, and the middle of each two adjacent unit structures shares one vertical plate 1. The widths of the air slits 3 between two adjacent vertical plates 1 are in equal difference and gradually increased, namely the widths of the plate-air-plate type units are sequentially increased, an air interlayer 4 is reserved between the reflecting plate 2 and the side edge of the vertical plate 1, and a region between the adjacent vertical plate 1 and the reflecting plate 2 forms a FP-like resonant cavity.
In the present embodiment, the increasing rule of the width of the air slit 3 satisfies w n ＝w 1 + (n-1) x d, wherein the initial width w 1 ＝7mm，w n The width of the nth air slit 3 is set to 1mm as the step d, and the total number of air slits 3 in the present embodiment is preferably 15, that is, the maximum value of n is 15.
In the present embodiment, the vertical plates 1 are rectangular plates, each rectangular plate is arranged with its long sides aligned, and preferably, the plate thickness t of the rectangular plate is 8mm, the plate length H is 100mm, the thickness b of the reflection plate 2 is 8mm, the plate length L is 338mm, the plate width H is 100mm, and the thickness g of the air interlayer 4 is 1.5 mm.
In the embodiment, the gradient reflection acoustic grating sensing structure is prepared by 3D printing, and the raw materials of the vertical plate 1 and the reflecting plate 2 are photosensitive resin with density ρ of photosensitive resin 2 ＝1190kg/m 3 Speed of sound c 2 1700m/s, modulus of elasticity E 2 ＝2.65×10 3 MPa, shear modulus G 2 ＝2.22×10 3 MPa。
In the gradient reflection acoustic grating sensing structure provided by this embodiment, the region between the adjacent vertical plates 1 and the reflection plate 2 may form an FP-like resonant cavity, so that the acoustic energy can be effectively confined in the slit, and the acoustic energy density is significantly increased. Meanwhile, evanescent wave attenuation exists outside the gradient reflection acoustic grating sensing structure, and the evanescent wave attenuation phenomenon is coupled with zero-order resonance modes of all slits, so that the transmission from an acoustic wave energy cavity to the cavity is realized, and the function of widening a working frequency band is further realized.
The working frequency of the gradient reflection acoustic grating sensing structure can be adjusted by changing the geometric parameters (w and g) of the structure, the resonance frequency of each slit is changed along with the size of the resonant cavity, and the control on deep sub-wavelength acoustic waves can be realized.
The sound pressure response of the gradient reflection acoustic grating sensing structure is influenced by the sound wave incidence angle, different pressure field distribution conditions exist, the direction response is sensitive, and the sound source positioning can be realized.
In addition, the structure adopts photosensitive resin, is prepared by a 3D printing technology, and has the advantages of simple structure, convenience in manufacturing and lower production cost.
Referring to fig. 2, the following is demonstrated by specific examples:
the gradient reflection acoustic grating sensing structure adopts t as 8mm and w 1 ＝7mm，n max ＝15，d＝1mm，h＝100mm, g 1.5mm, b 8mm, L338 mm, H100 mm. The structure is simplified to a two-dimensional acoustic system, considering only the zeroth order mode. The gradient reflection acoustic grating sensing structure is set to be rigid boundaries up and down, the distance between the upper rigid boundary and the lower rigid boundary is 200mm, the distance between the upper rigid boundary and the upper boundary of the structure is 25mm, broadband plane waves are incident from the right side to the FP-like cavity in a perpendicular mode, the distance between the incident end and the left side of the structure is 230mm, initial sound pressure is set to be 1Pa, and sound pressure response analysis is conducted on the structure.
By normalizing the sound pressure gain of the 2 nd, 8 th and 14 th air slits 3, it can be seen that each air slit 3 has a distinct resonance peak. In the sound pressure field distribution of different resonance frequencies, it can be clearly observed that the sound waves of the corresponding frequencies are concentrated in the respective air slits 3. Compared with the acoustic grating metamaterial without the reflecting plate 2, the working frequency of the gradient reflecting acoustic grating sensing structure is reduced by at least 140Hz, and the maximum reduction amplitude can exceed 280 Hz. Taking the 2 nd air slit 3 as an example, the wavelength is 281mm, which is 35 times (w) the width of the air slit 3 2 8mm), which indicates that the gradient reflection grating sensing structure is more suitable for applications at the deep sub-wavelength scale. Furthermore, as the width of the air slit 3 increases, its corresponding resonant frequency decreases. The gradient reflection acoustic grating sensing structure not only can effectively widen the working bandwidth, but also can reduce the working frequency band on the deep sub-wavelength scale.
Referring to FIG. 3, the width of the air slit 3 is changed to change the initial width w of the air slit 3 1 Increasing from 6mm to 8.5mm the corresponding resonance frequency decreases, i.e. the resonance frequency of each air slit 3 can be adjusted by changing the volume of the resonance chamber. The resonance frequency of each air slit 3 is increased by increasing the thickness g of the air interlayer 4, and the resonance frequency tends to be constant after increasing g to 15 mm. Satisfies the conditions
(m is an integer representing an m-order FP resonance;
the reflection phases at the upper and lower boundaries, respectively; n is k Effective refractive index of slit), resonanceThe imaginary part of the factor is zero and a zero order resonance mode occurs. In this case, the diffracted surface waves at the upper and lower boundaries of the gradient reflection grating sensing structure are coupled with the slit mode, so that the unsealed air slit 3 forms an FP-like resonant cavity. The resonance frequency increases with increasing thickness of the air interlayer 4 because the phase can be modulated by the reflection coefficient associated with the air interlayer 4. That is, by compressing the air interlayer 4, a deep sub-wavelength FP-like resonance can be obtained.
Referring also to fig. 4, the gradient reflection grating is placed in the circular sound absorption boundary with the center of the 8 th air slit 3 coinciding with the dots of the circular boundary. The inner diameter of the circular boundary is 600mm and a trapezoidal opening is provided. The plane wave is horizontally incident at the opening. The gradient reflection acoustic grating sensing structure is rotated by taking a circular point of a circular boundary as a center, so that incident waves are incident on the structure at different angles. The results show that the directional response of the gradient reflecting acoustic grating sensing structure is sensitive to the acoustic incident angle. When the angle of incidence is 0 °, a maximum sound pressure occurs because the resonance phenomenon of the gradient reflective grating sensing structure is caused by diffracted waves along the periodic surface; when the incident angle is increased to 180 degrees, the slit cannot capture sound energy due to the phenomenon of serious sound wave impedance mismatching existing at the boundary of the air and the gradient reflection sound grating sensing structure. Due to the presence of the reflective plate 2, there is a slight asymmetry in the directional response of the gradient reflective grating sensing structure. Therefore, in theory the gradient reflection grating sensing structure can distinguish acoustic signals in various directions. Based on this characteristic, the gradient reflection acoustic grating sensing structure can be used as a sound source positioning sensor.
In summary, the gradient reflection acoustic grating sensing structure constructed by the application can effectively control the propagation of sound waves through similar FP resonance, and the sound energy is limited in the slit; the frequency bands of FP-like resonant cavities with different sizes can be combined, so that the working bandwidth of the FP-like resonant cavities is widened; the volume of the resonant cavity is changed, and the working frequency of the resonant cavity can be adjusted, so that the problems of narrow working bandwidth, large volume and the like of the traditional acoustic grating metamaterial are solved, and the directional positioning of all angles is realized.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. The gradient reflection acoustic grating sensing structure is characterized by comprising a plurality of vertical plates which are sequentially arranged and a reflection plate which is arranged on one side of each vertical plate, wherein the widths of air slits between every two adjacent vertical plates are increased in an equidifferent mode, and an air interlayer is reserved between the reflection plate and the side edge of each vertical plate.
2. A gradient reflection acoustic grating sensing structure as claimed in claim 1, wherein the increasing law of the width of the air slit satisfies w n ＝w 1 + (n-1). times.d, where w 1 Is the initial width, w n Is the width of the nth air slot and d is the step size.
3. A gradient reflection acoustic grating sensing structure as claimed in claim 2, wherein the initial width w of the air slit 1 The step length d is 1mm, 7 mm.
4. A gradient reflection acoustic grating sensing structure as claimed in claim 2, wherein the total number of air slits is 15.
5. The gradient reflection acoustic grating sensing structure according to claim 1, wherein the gradient reflection acoustic grating sensing structure is prepared by 3D printing, and the vertical plate and the reflective plate are made of photosensitive resin.
6. A gradient reflection acoustic grating sensing structure as claimed in claim 5, wherein the photosensitive resin has a density p 2 ＝1190kg/m 3 Speed of sound c 2 1700m/s, modulus of elasticity E 2 ＝2.65×10 3 MPa, shear modulus G 2 ＝2.22×10 3 MPa。
7. The gradient reflection acoustic grating sensing structure according to claim 1, wherein the vertical plates are rectangular plates, each rectangular plate is arranged with its long sides aligned, and the thickness t of the rectangular plate is 8mm, and the length h of the rectangular plate is 100 mm.
8. A gradient reflection acoustic grating sensing structure as claimed in claim 1, wherein said reflecting plate has a thickness b of 8mm, a length L of 338mm and a width H of 100 mm.
9. A gradient reflecting acoustic grating sensing structure according to claim 1, wherein the thickness g of the air interlayer is 1.5 mm.
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