CN106228971A - Broadband sound focusing lens based on fractal acoustic metamaterial and preparation method thereof - Google Patents
Broadband sound focusing lens based on fractal acoustic metamaterial and preparation method thereof Download PDFInfo
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/18—Methods or devices for transmitting, conducting or directing sound
- G10K11/26—Sound-focusing or directing, e.g. scanning
- G10K11/30—Sound-focusing or directing, e.g. scanning using refraction, e.g. acoustic lenses
Abstract
The present invention discloses a kind of broadband sound focusing lens based on fractal acoustic metamaterial and preparation method thereof, these broadband sound focusing lens include base material and the fractal structure cell array being positioned on this base material, this fractal structure cell array is arranged to make up by multiple fractal periodic units, and each fractal periodic unit is corresponding to a refraction point of condenser lens；Fractal periodic unit includes fractal unit and air two parts, and the refractive index of fractal unit that arbitrary refraction point is corresponding is consistent with the theoretical refractive index of this refraction point.The present invention uses fractal unit to form Acoustic focusing lens first, provides the new paragon of design new material for acoustic engineering, increases the actual path length that sound wave is propagated in cellular construction, improve the refractive index of cellular construction by the way of fractal；These Acoustic focusing lens have broadband character, can realize the well focussed effect of sound wave in broad frequency range.
Description
Technical field
The present invention relates to a kind of condenser lens and preparation method thereof, particularly to a kind of width based on fractal acoustic metamaterial
Band sound focusing lens and preparation method thereof.
Background technology
Along with Novel manual electromagnetic material theoretical research and application and development are goed deep into by people, Meta Materials is at acoustic direction
Application also result in the interest of numerous research worker.Meta Materials at acoustics with the similar corresponding relation on electromagnetism front
Being confirmed in the middle of the research of people, the probability that the concept of Meta Materials expands to sound wave section is also being ground by the expert in this field
Study carefully.Non-natural parameter characteristic can also be obtained at sound wave wave band at research acoustically, cellular construction based on Meta Materials before,
Such as DNG feature (negative density and negative elastic modelling quantity), zero refractive index, even negative index, acoustic imaging, stealthy, conversion sound
Learn, and acoustic surface.The design of acoustic elements mainly has two kinds of strategies: resonant element and effective medium theory composite.Closely
Coming, the feasibility of the design of the disresonance unit based on folding space structure proposes the most in theory and is also tested
Confirm.These structures can be used to design some specific parameters, such as low absorption and wide bandwidth of operation, but in unit design
There is also the challenge of impedance matching.
Fractal structure is common in the fractal geomorphic feature in nature landform, is usually applied to architectural design, antenna, microwave
Device designs.Fractal acoustic metamaterial is the space folding structure of a kind of self similarity, also in that this self-similarity, fractal sound
Learn Meta Materials and have excellent characteristics.Fractal structure looks the most complicated, but it can pass through computer program design, and leads to
Cross 3D printer printing speed molding, have and have good application prospect.
Summary of the invention
Goal of the invention: the first object of the present invention is to provide a kind of broadband based on fractal acoustic metamaterial sound focusing saturating
Mirror, the second object of the present invention is to provide the preparation method of these broadband sound focusing lens.
Technical scheme: a kind of broadband sound focusing lens based on fractal acoustic metamaterial of the present invention, this broadband sound
Condenser lens includes base material and the fractal structure cell array being positioned on this base material, this fractal structure cell array
Being arranged to make up by multiple fractal periodic units, each fractal periodic unit is corresponding to a refraction point of condenser lens；Fractal week
Phase unit includes fractal unit and air two parts, the refractive index of the fractal unit that arbitrary refraction point is corresponding and the reason of this refraction point
Opinion refractive index is consistent.
Concrete, the fractal unit that arbitrary refraction point is corresponding is selected from the one in the fractal unit of single order～N rank, and wherein, N is
Integer, and N >=2.
Further, the fractal unit in every rank is that this fractal unit of rank standard carries out shape after opening part reason on acoustic propagation direction
The deformation unit become, the structure of the fractal unit of standard and size by Computer Fractal program according to the cycle chi of fractal periodic unit
Very little automatically generate.
Further, this periodic dimensions operating frequency range based on equivalent medium theory, according to condenser lens determines.
Preferably, base material and fractal unit are formed through 3D printing by photosensitive resin material.
Further, fractal unit is the fractal unit of Hilbert.
The preparation method of broadband sound focusing lens based on fractal acoustic metamaterial of the present invention, including walking as follows
Rapid:
Step 1, determines the theoretical refractive index value of each refraction point of condenser lens to be prepared；
Step 2, realizes the theoretical refractive index of each refraction point by fractal periodic unit, determines that each refraction point is corresponding
The structure of fractal unit and size in typing periodic unit；
Step 3, the fractal unit that each refraction point of step 2 being obtained is corresponding requires to arrange shape according to sound focusing lens theory
Become fractal building block array, and be fixed on base material, form the structural model of broadband sound focusing lens, pass through 3D
Print this structural model and obtain broadband sound focusing lens.
In above-mentioned steps 1, according to hyperbolic secant function n (y)=n0Sech (α y) determines each refraction point of condenser lens
Theoretical refractive index value, wherein,n0For the refractive index value of condenser lens center, h is half condenser lens
Height, nhRefractive index value for condenser lens edge.
Concrete, in step 2, structure and the size of fractal unit determine by the following method:
Step 21, according to refractive index of the centre value n of condenser lens to be prepared0, determine dividing for analog focus lens
The top step number N, N≤n of shape unit0≤ N+1, N are integer；
Step 22, according to the working band of condenser lens to be prepared, determines the periodic dimensions of fractal periodic unit；By week
The phase fractal program of size input computer, by this programming automatic generation single order～the structure of the N rank fractal unit of standard and size；
Step 23, extracts single order～the performance parameter of the N rank fractal unit of standard, respectively with the folding of condenser lens to be prepared
The rate Gradient distribution of penetrating is compared, according to comparison result respectively on acoustic propagation direction to single order～the N rank fractal unit of standard
Structure carries out opening process, obtains structure and the size of the fractal unit of single order～N rank for analog focus lens；
Step 24, extracts single order～the performance parameter of the fractal unit in N rank, obtains the refraction of the fractal unit in each rank by sweeping ginseng
Rate, compares the theoretical refractive index of each refraction point of condenser lens to be prepared, determines the fractal unit that each refraction point is corresponding.
Further, in step 3, fractal unit is formed fractal structure cell array according to periodic dimensions arrangement, and will
It is fixed on base material, obtains the structural model of broadband sound focusing lens, uses photosensitive resin material to print this structure mould
Type, obtains broadband sound focusing lens.
Beneficial effect: compared with prior art, it is an advantage of the current invention that: (1) present invention uses fractal unit to use first
In forming Acoustic focusing lens, provide the new paragon of design new material for acoustic engineering, by the way of fractal, increase sound wave
The actual path length propagated in cellular construction, improves the refractive index of cellular construction；And, along with the exponent number of fractal unit
Raising, be also easier to obtain high index of refraction, fractal unit the lens formed or wave absorbing device have more excellent performance；(2)
The Acoustic focusing lens of the present invention have broadband character, can realize the well focussed effect of sound wave in broad frequency range；(3)
The Acoustic focusing lens preparation method simple and fast of the present invention, and raw material uses photosensitive resin, and prepared Acoustic focusing is saturating
Mirror has the feature of lightweight and low cost, is suitable to popularization and application.
Accompanying drawing explanation
Fig. 1 is the structural representation of the broadband sound focusing lens of the present invention；
Fig. 2 a is the structural representation of the fractal unit of single order in embodiment；
Fig. 2 b is the structural representation of the fractal unit of second order in embodiment；
Fig. 2 c is the structural representation of the three fractal unit in rank in embodiment；
Fig. 3 a be single order fractal unit equivalent refractive index in 2kHz～5kHz frequency range in embodiment, equiva lent impedance, etc.
Effect density and the change curve of concrete moduli；
Fig. 3 b be second order fractal unit equivalent refractive index in 2kHz～5kHz frequency range in embodiment, equiva lent impedance, etc.
Effect density and the change curve of concrete moduli.
Fig. 3 c be the three fractal unit in rank equivalent refractive index in 2kHz～5kHz frequency range in embodiment, equiva lent impedance, etc.
Effect density and the change curve of concrete moduli.
Fig. 4 is that single order in embodiment, second order, the three fractal unit in the rank variations in refractive index in 2kHz～5kHz frequency range is bent
Line；
Fig. 5 be Acoustic focusing lens to be prepared in embodiment ideal refractive rate distribution and fractal unit attainable from
Dissipate index distribution；
Fig. 6 is the structural representation of the condenser lens prepared in embodiment；
Fig. 7 a be the actual test acoustic lens that records under 2kHz and 5kHz operating frequency and emulation acoustic lens in the x-direction
Output acoustic pressure amplitude scattergram；
Fig. 7 b is the actual test acoustic lens that records under 2kHz and 5kHz operating frequency and emulation acoustic lens in the y-direction defeated
Go out acoustic pressure amplitude scattergram；
The acoustic pressure distribution that acoustic pressure distribution and the actual test lens of lens emulation when Fig. 8 a is 2kHz obtains；
The acoustic pressure distribution that acoustic pressure distribution and the actual test lens of lens emulation when Fig. 8 b is 3kHz obtains；
The acoustic pressure distribution that acoustic pressure distribution and the actual test lens of lens emulation when Fig. 8 c is 4kHz obtains；
The acoustic pressure distribution that acoustic pressure distribution and the actual test lens of lens emulation when Fig. 8 d is 5kHz obtains.
Detailed description of the invention
Below in conjunction with the accompanying drawings technical scheme is described further.
The broadband sound focusing lens based on fractal acoustic metamaterial of the present invention, such as Fig. 1, these broadband sound focusing lens include
Fractal structure cell array 2 and base material 1, fractal structure cell array 2 is positioned on this base material 1, for simulated sound
Learning the refractive index of each refraction point of condenser lens, base material 1 is used for supporting fractal structure cell array 2.
Fractal structure cell array 2 is arranged to make up by multiple fractal periodic units, and each fractal periodic unit is corresponding to poly-
One refraction point of focus lens.Each fractal periodic unit has identical periodic dimensions U, and periodic dimensions U uses effective medium
Theoretical method, operating frequency range according to condenser lens determine.
Fractal periodic unit includes fractal unit 3 and air two parts, the refraction of the fractal unit 3 that arbitrary refraction point is corresponding
Rate is consistent with the theoretical refractive index of this refraction point.The fractal unit 3 that arbitrary refraction point is corresponding is all selected from the fractal list of single order～N rank
One in unit, wherein, N is integer, and N >=2；Can first according to the periodic dimensions U of fractal periodic unit by Computer Fractal journey
Sequence generates structure and the size of each rank fractal unit of standard, then opens each rank fractal unit of standard on acoustic propagation direction
Mouth processes, and obtains structure and the size of the final fractal unit in each rank；Processed by opening, make corresponding fractal of each refraction point
The refractive index of unit 3 is consistent with theoretical refractive index, makes Acoustic focusing lens realize wide working band.
Fractal unit 3 can be Hilbert fractal structure, and it can effectively improve the refractive index of cellular construction, it is achieved thin
The design of lens.
Base material 1 and fractal unit 3 can be formed through 3D printing by photosensitive resin material.
The Acoustic focusing lens of the present invention have broadband character, can realize the well focussed of sound wave in broad frequency range
Effect.Compared with prior art, fractal unit 3 is used for forming Acoustic focusing lens by the present invention first, these Acoustic focusing lens
Be equivalent to a kind of acoustic metamaterial, including the fractal structure list formed by periodic dimensions U periodic arrangement by a series of fractal unit 3
Element array 2, increases the actual path length that sound wave is propagated in cellular construction by the way of fractal, improves cellular construction
Refractive index；And, along with the raising of the exponent number of fractal unit, be also easier to obtain high index of refraction, by fractal unit 3 formed saturating
Mirror or wave absorbing device have more excellent performance；Meanwhile, by the cellular construction of its fractal unit of engineer, material can be controlled
Effective dielectric constant, pcrmeability, refractive index, the electromagnetic parameter such as natural impedance, it is achieved the material that nature exists does not has
Character.
The preparation method of the broadband sound focusing lens based on fractal acoustic metamaterial of the present invention, comprises the steps:
(1) the theoretical refractive index value of each refraction point of condenser lens to be prepared is determined；
Changing owing to the refractive index of the every bit of condenser lens is as longitudinal position, therefore, design acoustics gathers
During focus lens (hereinafter referred to as " condenser lens "), the distribution of its refractive index is it suffices that hyperbolic secant function: n (y)=n0sech
(α y), α is by formulaDefinition obtains；Wherein, n0Being the refractive index value of condenser lens center, h is half
The height of individual condenser lens, nhIt it is the refractive index value of condenser lens edge.
(2) simulated the theoretical refractive index of each refraction point by fractal periodic unit, determine corresponding the dividing of each refraction point
The structure of fractal unit 3 and size in type periodic unit；
First, according to refractive index of the centre value n of condenser lens to be prepared0, determine for analog focus lens is fractal
The top step number N, N≤n of unit 30≤ N+1, N are integer；In embodiments of the invention, 3 ＜ n0＜ 4, therefore, fractal unit 3
Top step number is N=3, i.e. uses single order, the fractal unit of second order and three rank to carry out analog focus lens.
Secondly, according to the working band (i.e. operating frequency range) of condenser lens to be prepared, fractal periodic unit is determined
Periodic dimensions U, by the periodic dimensions fractal program of U input computer, by this programming automatic generation single order～the N rank fractal list of standard
The structure of unit and size.In the present embodiment, the working band of Acoustic focusing lens to be prepared is 2kHz to 5kHz, by equivalence matchmaker
Matter theory understands, and each fractal unit 3 suffers from identical periodic dimensions, in the working band that this example is selected, and its periodic dimensions U
=0.94cm；By Computer Fractal Program Generating standard single order, the fractal unit of standard second order and standard three rank, this fractal unit 3
For the fractal unit of Hilbert.
Again, single order～the performance parameter of the N rank fractal unit of standard are extracted respectively, with the refraction of condenser lens to be prepared
Rate Gradient distribution is compared, and is finely adjusted structure and the size of the 1～N fractal unit of rank standard according to comparison result, respectively
Acoustic propagation direction carries out opening process to the structure of single order～the N rank fractal unit of standard, obtains for analog focus lens
The structure of the fractal unit of single order～N rank and size, the performance parameter of the fractal unit of this single order～N rank and condenser lens folding
Penetrate rate Gradient distribution closest.
The opening purpose of fractal unit is the theoretical refractive index value obtaining this point, and therefore whether opening number is can be somebody's turn to do
The refractive index of point is as the criterion, and opening number is generally 1～3；The opening number of the fractal unit in every rank may be identical, it is also possible to no
With.
In the present embodiment, respectively extract standard single order, the equivalent refractive index of the fractal unit of standard second order and standard three rank, etc.
The parameters such as effect impedance, equivalent density and concrete moduli, to standard single order, the structure of the fractal unit of standard second order and standard three rank
It is finely adjusted, obtains single order, the fractal unit of second order and three rank, the height H=13mm of the fractal unit in every rank, thickness D=0.5mm；
Concrete, such as Fig. 2 a, the fractal unit of single order 31 is that unit fractal to standard single order has carried out deformation process, i.e. in acoustic propagation direction
On it carried out opening processed, length and width size W of the fractal unit of single order 311=4.5mm, opening size S1=1.5mm,
Its parameter characteristic in the working band of Acoustic focusing lens 2kHz～5kHz such as Fig. 3 a；Such as Fig. 2 b, the fractal unit of second order 32
It is that unit fractal to standard second order has carried out deformation process, i.e. on acoustic propagation direction, it has been carried out an opening and processed, two
Length and width size W of the fractal unit in rank 322=6.5mm, minor matters length L=2.5mm stretched into inside it, opening size S2=
1.5mm, outward opening size J=1.5mm, its parameter characteristic in the working band of 2kHz～5kHz such as Fig. 3 b；Such as Fig. 2 c, three
The fractal unit in rank 33 is that the fractal unit in standard three rank has been carried out deformation process, i.e. on acoustic propagation direction, it has been carried out two
Opening processes, length and width size W of the three fractal unit in rank 333=8.4mm, acoustic wave inlet size K=0.5mm, opening size S3=
1.5mm, its parameter characteristic in the working band of 2kHz～5kHz such as Fig. 3 c.
Finally, extract single order～the performance parameter of the fractal unit in N rank, obtain the refractive index of the fractal unit in each rank by sweeping ginseng
Distribution, compares the theoretical refractive index of each refraction point of condenser lens to be prepared, determines the fractal list that each refraction point is corresponding
Unit 3.In the present embodiment, single order, second order, the three fractal unit in rank index distribution such as Fig. 4 in working band, wherein, single order
Fractal unit is for realizing the refraction point that refractive index value in condenser lens is close to 1, and the fractal unit of second order is used for realizing condenser lens
The middle refractive index value refraction point close to 2, the three fractal unit in rank are for realizing the refraction point that refractive index value is close to 3.
(3) after the structure analyzing the fractal unit 3 determining that each refraction point is corresponding and size, according to sound focusing lens theory
Requirement, forms fractal structure unit by corresponding fractal unit 3 according to periodic dimensions arrangement according to the distribution situation of each refraction point
Array 2, and be fixed on base material 1, obtain the structural model of broadband sound focusing lens, use photosensitive resin material 3D
Print this structural model, obtain broadband sound focusing lens.
In the present embodiment, using photosensitive resin material printed substrates material 1 and fractal unit 3, the Acoustic focusing prepared is saturating
The structural representation of mirror sample such as Fig. 6, it is made up of the fractal cell array of two-layer 2, and the total length of this sample is Lf=
19.74cm, the cycle is U=0.94cm, and gross thickness is Wf=1.73cm, two minimum ranges arranged between fractal unit are Ws=
0.5mm.Such as Fig. 5, it can be seen that the attainable discrete index distribution of Acoustic focusing lens formed by the arrangement of fractal unit
It is distributed with the ideal refractive rate of Acoustic focusing lens and complies fully with.The Acoustic focusing lens of prepared in accordance with the method for the present invention are original
Sample is a layer unit structure, can realize the well focussed effect of sound wave, for further enhancing its sound in broad frequency range
Focusing performance, highlights the advantage of this method further, uses the fractal cell array of two-layer 2, such as " the Measured in Fig. 8 d
Field " shown in figure, when 5kHz, experiment records its output sound focusing energy and reaches 5:1 with input acoustic energy ratio, and sound wave gathers
Burnt effect is notable；If continuing to increase the number of plies, then its thickness will substantially increase, and this will cause acoustic lens materials cost to improve,
Also result in acoustic lens impedance to increase further simultaneously, in turn result in acoustic reflection loss and sound focusing energy reduces, affect sound wave
The shortcomings such as focusing effect, therefore, use two-layer cellular construction in the present embodiment.
In order to verify the correctness of this method, the performance of prepared sample is tested.
Concrete method of testing is: prepared Acoustic focusing lens are placed in test zone, total by sweep test region
Sonic pressure field, obtains the scattergram of acoustic pressure, concrete, is placed in by sample in two-dimensional acoustic field near-field scan platform, and sample is positioned at raises one's voice
Between device array and mike, lucite is slightly compressed on sample, obtains plane wave by loudspeaker array, and comes with mike
Near scanning sample, the acoustic pressure of test zone, obtains its output acoustic pressure amplitude scattergram (Fig. 7 a～7b) in x direction and y direction
And acoustic pressure distribution situation (Fig. 8 a～8d).Meanwhile, it is simulated emulating to Expected Results to these Acoustic focusing lens, sound will be emulated
The acoustic pressure distribution of lens compares with the actual test result of the acoustic lens prepared.
Fig. 7 a～7b is the actual test acoustic lens recorded under 2kHz and 5kHz operating frequency and emulates the defeated of acoustic lens
Go out acoustic pressure amplitude scattergram, Fig. 7 a represents in the x-direction along acoustic propagation direction, Fig. 7 b represents in the y-direction in focal spot
Vertical direction along acoustic propagation direction.In Fig. 7 a and Fig. 7 b, two curves in top are the simulation figure under 5kHz working band and reality
Border test image, it can be seen that two curve distribution are almost consistent, illustrates that the experiment of 5kHz acoustic lens coincide very with simulation architecture
Good, and, obtaining sound field amplitude gain at distance acoustic lens about 120mm is the focusing effect of 11.3dB；Under in Fig. 7 a～7b
Two, side curve is the emulating image under 2kHz working band and actual test image, it can be seen that experiment during 2kHz is with imitative
True result is the most identical, and to record its focusing effect be 8dB, and actual test herein is owing to during 2kHz, sound is real with the error of emulation
Test what slit source acoustic conductance in platform caused, i.e. the upper poly (methyl methacrylate) plate of experiment porch and sample room has less space, in low frequency work
Owing to its wavelength is long, there is certain sound diffraction ability when making, in turn result in certain sound capacity loss, have impact on low
Frequently focusing effect time.
The acoustic pressure distribution feelings of the actual test lens recorded under Fig. 8 a～8b respectively different operating frequency and emulation lens
Condition, wherein, the acoustic pressure distribution that acoustic pressure distribution and the actual test lens of lens emulation when Fig. 8 a is 2000Hz obtains, Fig. 8 b is
The acoustic pressure distribution that acoustic pressure distribution and the actual test lens of lens emulation during 3000Hz obtains, lens emulation when Fig. 8 c is 4000Hz
The acoustic pressure distribution that obtains with actual test lens of acoustic pressure distribution, the acoustic pressure distribution of lens emulation when Fig. 8 d is 5000Hz and reality
The acoustic pressure distribution that test lens obtains.In experimental result picture, for the sound-filed simulation figure of lens emulation in white dashed line frame, white is empty
It is the sound-filed simulation figure of actual test lens on the left of wire frame, by contrast it can be seen that actual test case is kissed with simulation scenarios
Close.
Claims (10)
1. broadband sound focusing lens based on fractal acoustic metamaterial, it is characterised in that described broadband sound focusing lens bag
Include base material (1) and the fractal structure cell array (2) being positioned on this base material (1), this fractal structure cell array
(2) being arranged to make up by multiple fractal periodic units, each fractal periodic unit is corresponding to a refraction point of condenser lens；Described
Fractal periodic unit includes fractal unit (3) and air two parts, the refractive index of the fractal unit (3) that arbitrary refraction point is corresponding with
The theoretical refractive index of this refraction point is consistent.
Broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 1, it is characterised in that arbitrary folding
The fractal unit (3) that exit point is corresponding is selected from the one in the fractal unit of single order～N rank, and wherein, N is integer, and N >=2.
Broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 2, it is characterised in that every rank are divided
Shape unit is the deformation unit formed after this fractal unit of rank standard carries out opening part reason on acoustic propagation direction, the fractal list of standard
Structure and the size of unit are automatically generated according to the periodic dimensions of fractal periodic unit by Computer Fractal program.
Broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 3, it is characterised in that this cycle
The size operating frequency range based on equivalent medium theory, according to condenser lens determines.
Broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 1, it is characterised in that described base
Bottom material (1) and fractal unit (3) are formed through 3D printing by photosensitive resin material.
Broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 1, it is characterised in that described point
Shape unit (3) is the fractal unit of Hilbert.
7. a preparation method for the broadband sound focusing lens based on fractal acoustic metamaterial described in claim 1, its feature
It is, comprises the steps:
Step 1, determines the theoretical refractive index value of each refraction point of condenser lens to be prepared；
Step 2, realizes the theoretical refractive index of each refraction point by fractal periodic unit, determines corresponding fractal of each refraction point
The structure of fractal unit (3) and size in periodic unit；
Step 3, the fractal unit (3) that each refraction point of step 2 being obtained is corresponding requires arrangement shape according to sound focusing lens theory
Become fractal building block array (2), and be fixed on base material (1), form the structural model of broadband sound focusing lens,
Print this structural model by 3D and obtain broadband sound focusing lens.
The preparation method of broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 7, its feature
It is, in step 1, according to hyperbolic secant function n (y)=n0Sech (α y) determines the theoretical refraction of each refraction point of condenser lens
Rate value, wherein,n0For the refractive index value of condenser lens center, h is the height of half condenser lens,
nhRefractive index value for condenser lens edge.
The preparation method of broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 8, its feature
Being, in step 2, structure and the size of described fractal unit (3) determine by the following method:
Step 21, according to refractive index of the centre value n of condenser lens to be prepared0, determine the fractal unit for analog focus lens
(3) top step number N, N≤n0≤ N+1, N are integer；
Step 22, according to the working band of condenser lens to be prepared, determines the periodic dimensions of fractal periodic unit, by cycle chi
The fractal program of very little input computer, by this programming automatic generation single order～the structure of the N rank fractal unit of standard and size；
Step 23, extracts single order～the performance parameter of the N rank fractal unit of standard, respectively with the refractive index of condenser lens to be prepared
Gradient distribution is compared, according to comparison result respectively on acoustic propagation direction to single order～the structure of the N rank fractal unit of standard
Carry out opening process, obtain structure and the size of the fractal unit of single order～N rank for analog focus lens；
Step 24, extracts single order～the performance parameter of the fractal unit in N rank, obtains the refractive index of the fractal unit in each rank by sweeping ginseng,
Compare the theoretical refractive index of each refraction point of condenser lens to be prepared, determine the fractal unit (3) that each refraction point is corresponding.
The preparation method of broadband sound focusing lens based on fractal acoustic metamaterial the most according to claim 9, its feature
It is, in step 3, described fractal unit (3) is formed fractal structure cell array (2) according to periodic dimensions arrangement, and by it
It is fixed on base material (1), obtains the structural model of broadband sound focusing lens, use photosensitive resin material to print this structure mould
Type, obtains broadband sound focusing lens.
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