CN110442907B - Numerical simulation analysis method for basic characteristics of piezoelectric MEMS loudspeaker - Google Patents
Numerical simulation analysis method for basic characteristics of piezoelectric MEMS loudspeaker Download PDFInfo
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
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Abstract
The invention discloses a numerical simulation analysis method of basic characteristics of a piezoelectric MEMS loudspeaker, which comprises the following steps: 1) Establishing an MEMS speaker simulation geometric model; 2) Setting physical fields and boundary conditions, wherein the physical fields comprise a material model, a piezoelectric constitutive relation, damping, constraint conditions, impedance boundaries, voltage loads and the like in a solid mechanics, an electric field, a pressure acoustics, a frequency domain, a hot viscosity acoustics and a frequency domain physical field respectively; 3) Defining material parameters; 4) Setting the type and the size of the grid, and dividing the grid. 5) And (3) solving and calculating: the finite element model is solved by respectively adopting frequency domain and characteristic frequency researches; 6) Post-processing results: the sound pressure level frequency response curve, sound pressure and sound pressure level distribution diagram, capacitance value change relation along with frequency, the size and distribution diagram of stress/strain/displacement/speed/acceleration on the vibration component, and the resonance frequency and vibration mode of the MEMS speaker are obtained through post-processing.
Description
Technical Field
The invention belongs to the field of MEMS speaker design, and relates to a numerical simulation analysis method of micro-electromechanical systems (MEMS), piezoelectric effect, structural mechanics, electric field and sound field. By adopting the numerical simulation analysis method disclosed by the invention, the sound pressure level frequency response curve, sound pressure and sound pressure level distribution, the change relation of capacitance value along with frequency, the size and distribution diagram of stress/strain/displacement/speed/acceleration on the vibration part, and the resonance frequency and vibration mode of the MEMS loudspeaker can be obtained. These simulation analysis results can be used to guide the structural design and improvement of MEMS speakers to improve their performance.
Background
The MEMS speaker is a novel speaker designed by combining transducer theory and MEMS technology. The device has the advantages of small volume, light weight, low power consumption, easy integration with acoustic equipment and the like. The piezoelectric MEMS loudspeaker adopts the structural design of the piezoelectric cantilever beam, and has the advantages of stable structure, good consistency, easy mass production and the like.
Piezoelectric MEMS speakers are a new type of speaker that has only emerged in recent years, and there are the following problems in research and design: 1) The design theory is imperfect and the design threshold is high. This is because it is difficult to fully meet the design requirements using conventional speaker design theory (equivalent circuit), and generally only repeated sample preparation and testing can be relied on; 2) The sample preparation cost is high, and the test difficulty is high. The MEMS speaker is not mature in manufacturing process, and the working principle is changed, so that the test of the MEMS speaker is different from that of the traditional moving-coil speaker to a certain extent, and the test difficulty is increased.
Disclosure of Invention
The invention aims to provide a numerical simulation analysis method for basic characteristics of a piezoelectric MEMS loudspeaker, which solves the problems of imperfect design theory, high design threshold, high development cost and the like of the existing MEMS product.
The invention can calculate the sound pressure level frequency response curve, sound pressure and sound pressure level distribution diagram, the size and distribution diagram of stress/strain/displacement/speed/acceleration on the vibrating component, and the resonance frequency and vibration mode of the loudspeaker by establishing the finite element simulation analysis model of the piezoelectric MEMS loudspeaker. The basic characteristics of the MEMS speaker can be estimated according to the simulation analysis results, and the structural design and improvement of the MEMS speaker are guided.
The invention discloses a numerical simulation analysis method of basic characteristics of a piezoelectric MEMS loudspeaker, which uses a physical field interface of pressure acoustics, frequency domain, hot viscosity acoustics, frequency domain, electric field and solid mechanics, and a multi-physical field coupling interface of piezoelectric material, sound-structure boundary and sound-hot viscosity acoustics boundary. The numerical simulation analysis method mainly comprises the following steps:
(1) Establishing a finite element model
1) The method comprises the following steps of establishing a geometric model for basic characteristic simulation analysis of the piezoelectric MEMS loudspeaker:
A. establishing a geometric model of a loudspeaker: leading the MEMS loudspeaker geometric model into finite element analysis software, wherein the geometric model of the loudspeaker is drawn by adopting three-dimensional drawing software or is built by adopting the self-contained geometric function of the finite element analysis software, and redundant points, lines, planes and bodies in the model are required to be cleaned after the geometric model is built so as to improve the quality of the geometric model;
B. establishing 711 a coupler acoustic cavity equivalent model: the sound pressure level frequency response curve of a MEMS speaker is typically tested in 711 coupler: in order to make the simulation analysis method more universal, an acoustic cavity equivalent model (comprising a connecting pipe) of the 711 coupler is established and is correctly connected with the loudspeaker; the 711 coupler refers to a human ear simulator;
2) The physical field and boundary conditions are set, and the detailed steps are as follows:
A. selecting a corresponding domain of pressure acoustics and frequency domain, namely an air domain of a front cavity and a rear cavity of the loudspeaker and an air domain of a non-narrow area in a 711 coupler;
B. under the condition of pressure acoustics and frequency domain, adopting serial coupling RCL impedance boundary, and performing simulation analysis 711 on acoustic impedance of the surface of the test microphone in the coupler, wherein R is equivalent acoustic impedance, C is equivalent acoustic compliance, and L is equivalent acoustic inertia;
C. the pressure balance holes (the size of the balance holes is very small, about 10 a) in the speaker were simulated using "user-defined impedance boundaries" under "pressure acoustics, frequency domain -1 mm magnitude) acoustic impedance when radiating sound waves into air;
D. setting the symmetry plane of the air domain as a symmetry boundary condition under the pressure acoustics and frequency domain;
E. selecting a corresponding domain of 'hot tack acoustics and frequency domain', namely an air domain in a narrow area in a 711 coupler acoustic cavity model;
F. in the "hot tack acoustic, frequency domain", a temperature value is set that affects the hot tack parameters of air;
G. setting the symmetry plane of the air region of the narrow region as a symmetry boundary condition under the condition of hot tack acoustics and frequency domain;
H. selecting a corresponding domain of 'solid mechanics', namely a piezoelectric cantilever beam and a vibrating diaphragm domain;
I. under the condition of 'solid mechanics', the piezoelectric cantilever beam and the vibrating diaphragm domain are set as 'linear elastic material', and the damping type and the damping value are set;
J. under the condition of 'solid mechanics', a 'piezoelectric material' functional interface is added and applied to a piezoelectric material domain, and a piezoelectric material model and a piezoelectric material polarization direction are arranged at the interface;
K. under the condition of 'solid mechanics', setting the fixed edges of the piezoelectric cantilever beam and the vibrating diaphragm of the loudspeaker as 'fixed constraint' boundary conditions;
setting symmetry planes of vibration components such as piezoelectric cantilever beams as symmetry boundary conditions under the condition of solid mechanics;
m, selecting a field corresponding to the electric field, namely a piezoelectric material field;
n, under the ' electric field ', adding ' charge conservation ', piezoelectricity ', and applying the same to a piezoelectric material;
setting a designated voltage value on an electrode surface of a piezoelectric material under an electric field by adopting a terminal and a grounding function interface;
and P, under the interface of multiple physical fields, respectively setting a piezoelectric effect, an acoustic-structure boundary and an acoustic-thermal viscous acoustic boundary.
3) Defining material parameters: the material parameters required by the finite element simulation model are related to physical fields, material models and boundary conditions, and the material parameters of the vibrating diaphragm, the dome and the piezoelectric cantilever in the MEMS loudspeaker are required to be respectively set, and mainly comprise Young modulus, density, poisson ratio, damping and sound velocity, and an elastic matrix, a coupling matrix and a relative dielectric constant matrix of the piezoelectric material.
4) Dividing grids: specifying the type and the size of the grid unit and dividing the grid; here, it is also necessary to make the calculation result more accurate by appropriately performing local mesh refinement by setting the size of the mesh unit.
(2) Post-processing of solutions and results
1) Solving: in the simulation analysis of the basic characteristics of the piezoelectric MEMS loudspeaker, the finite element model is solved by respectively adopting the research of frequency domain and characteristic frequency; the frequency domain and characteristic frequency researches are research methods built in finite element software, and the calculation process is completed by an algorithm built in the software;
2) Post-processing results: after the solution is completed, post-processing operation is adopted to obtain the basic characteristics of the MEMS loudspeaker, and the basic characteristics mainly comprise: A. the MEMS speaker has a sound pressure level frequency response curve under 711 coupler test environment; B. the MEMS speaker is distributed with sound pressure and sound pressure level in the sound cavity of the speaker and 711 coupler under any working frequency; C. a capacitance value change curve of the MEMS speaker along with frequency; D. the MEMS loudspeaker has distribution patterns of stress, strain, displacement, speed and acceleration on structures such as a vibrating diaphragm, a cantilever beam and the like at any working frequency; E. the resonance frequency and mode of the MEMS speaker. The post-processing operation is a conventional operation of obtaining a result by finite element software; the basic characteristics A-D of the loudspeaker are the results obtained by post-processing by adopting a frequency domain, and E is the results obtained by post-processing by adopting a characteristic frequency.
The geometrical model of the MEMS loudspeaker simulation analysis is a reasonably simplified model. The model simplification method is many, and can be achieved by adopting professional three-dimensional drawing software (such as SolidWorks, proE and the like) or adopting the "geometric" related function in finite element software.
The finite element analysis software is COMSOL Multiphysics (COMSOL for short), which is a multi-physical-field simulation analysis software and has the main functions of establishing a geometric model, meshing, setting and solving a physical field, displaying a result image and the like.
The invention has the advantages that: 1) The complete simulation analysis model of the MEMS loudspeaker is established, so that the piezoelectric effect, structural mechanics, electric field and sound field characteristics of the piezoelectric MEMS loudspeaker can be more comprehensively considered, and the structural design and optimization of the loudspeaker can be guided; 2) The defect of MEMS loudspeaker design theory is made up, and the threshold of engineering application is reduced; 3) And the characteristics of the MEMS speaker are estimated by adopting numerical simulation analysis, so that the sample preparation and test times are reduced, the development efficiency is improved, and the cost is saved.
Drawings
FIG. 1 is a flow chart of an embodiment of the present invention.
Fig. 2 is an external view of a piezoelectric MEMS speaker.
Fig. 3 is a block diagram of an equivalent acoustic cavity of 711 coupler.
Fig. 4 is an exploded view of the piezoelectric MEMS speaker structure.
Fig. 5 is a diagram of a piezoelectric cantilever structure.
Fig. 6 is a basic characteristic simulation analysis geometric model of a piezoelectric MEMS speaker.
FIG. 7 shows the physical field settings corresponding to the air domain during the simulation analysis.
Fig. 8 is a physical field setting corresponding to the vibration member at the time of simulation analysis.
Fig. 9 is an acoustic impedance of the microphone surface in the set 711 coupler.
FIG. 10 is an acoustic impedance of a surface of a pressure balance orifice.
Fig. 11 is a graph showing the material parameter values input during simulation analysis.
Fig. 12 is an elastic matrix of piezoelectric material (PZT 4).
Fig. 13 is a coupling matrix of piezoelectric material (PZT 4).
Fig. 14 shows the relative dielectric constant of the piezoelectric material (PZT 4).
Fig. 15 is a simulation finite element mesh model of basic characteristics of a piezoelectric MEMS speaker.
Fig. 16 is a sound pressure level frequency response curve of the piezoelectric MEMS speaker.
Fig. 17 is a sound pressure distribution diagram in the air domain.
Fig. 18 is an air domain acoustic pressure level distribution diagram.
Fig. 19 shows the change of the capacitance value of the piezoelectric MEMS speaker with frequency.
Fig. 20 is a graph of stress distribution on a piezoelectric cantilever.
Fig. 21 is a graph of strain distribution on a piezoelectric cantilever.
Fig. 22 is a diagram showing a displacement distribution on the diaphragm.
Fig. 23 is a velocity profile on a diaphragm.
FIG. 24 is a graph showing the acceleration profile across a diaphragm.
Fig. 25 shows the resonance frequency and the mode of the speaker vibration member.
Detailed Description
The invention is further described below with reference to the drawings and examples.
Taking a piezoelectric MEMS loudspeaker as an example, the basic characteristics of the loudspeaker in an electric field, structural mechanics and sound field are analyzed by the numerical simulation method disclosed by the invention. FIG. 1 is a flowchart of the present invention, which comprises the following steps:
(1) Preparation of
Fig. 2 and 3 are three-dimensional block diagrams of piezoelectric MEMS speakers (simplified structure, dimensions about 6.5mm x 4.5mm x 1.5 mm) and 711 coupler equivalent acoustic cavities, respectively. Fig. 4 is an exploded view of the MEMS speaker structure, which includes a front chamber housing (1), a diaphragm (2), a piezoelectric cantilever (3), and a rear chamber housing (4). Fig. 5 shows a piezoelectric cantilever structure of the loudspeaker, which comprises a silicon material substrate (5), a piezoelectric material (6) and an H-shaped connecting piece (7), wherein the H-shaped connecting piece (7) is used for connecting the cantilever and the vibrating diaphragm and plays a role in lifting the vibrating diaphragm (preventing the wiping between the vibrating diaphragm and the cantilever when the loudspeaker works). The MEMS speaker and 711 coupler acoustic cavity structures can be drawn by adopting professional three-dimensional drawing software such as SolidWorks and the like, and can also be drawn by adopting a geometric function in COMSOL software.
(2) Establishing a finite element model
1) Adding spatial dimensions, physical field interfaces and study types: opening COMSOL software, setting the space dimension as three-dimensional, sequentially selecting and adding pressure acoustics, frequency domain, hot viscosity acoustics, frequency domain, electric field and solid mechanics physical field, and selecting the research type as the frequency domain.
2) A simulated analytical geometric model is built as shown in fig. 6. The modeling process is as follows:
A. establishing a geometrical model of the MEMS speaker basic characteristic simulation analysis: the 3D assembled digital-to-analog of the MEMS speaker and 711 coupler acoustic cavity (including the connection tube (8)) prepared in advance is imported into the simulation analysis program using the "import" function under "geometry". Because the structure such as the flexible electrode in the MEMS loudspeaker has small influence on the loudspeaker characteristics, a simplified loudspeaker model is adopted here, so that the calculated amount is reduced, and the calculation speed is improved; in view of the symmetry of the structure, a 1/2 symmetric model is adopted during simulation analysis, so that the calculated amount is further reduced, and the calculation speed is improved;
B. geometric cleaning: and adopting a geometric cleaning function under the geometric operation to clean redundant points, lines, planes and bodies in the model.
3) The physical field and boundary conditions are set. The detailed setting steps are as follows:
A. selecting a corresponding domain (9) at a ' pressure acoustics ' frequency domain ' physical field interface, wherein the domain comprises an air domain of a front cavity and a rear cavity of the MEMS loudspeaker and an air domain of a non-narrow area in an acoustic cavity of a 711 coupler, as shown in FIG. 7;
B. in the "hot tack acoustic, frequency domain" physical field interface selects the corresponding domain (10), which includes 711 the narrow area air domain in the coupler acoustic cavity, see FIG. 7;
C. selecting a corresponding domain (11) at a 'solid mechanics' physical field interface, wherein the domain comprises a piezoelectric cantilever beam (piezoelectric material domain, silicon-based and H-shaped connectors) and a vibrating diaphragm, as shown in figure 8;
D. selecting a corresponding domain (12) at an "electric field" physical field interface, which includes all piezoelectric material domains, see fig. 8;
E. in the "piezoacoustic, frequency domain" case, the face (13) where the 711 coupler tests the microphone is set to the "impedance" boundary, see fig. 9. The "series coupled RCL" impedance model was selected and equivalent acoustic resistance r=1.19e8 [ kg/(m) was set, respectively 4 ·s)]Equivalent acoustic compliance c=6.2e-14 [ m ] 4 ·s 2 /kg]And equivalent acoustic inertia l=710 [ kg/m ] 4 ]；
F. In the "pressure acoustic, frequency domain" case, the pressure balance hole outer surface (14) is set to the "impedance" boundary, see fig. 10. Selecting a "user-defined" impedance model and specifying an impedance value zi=30 [ pa·s/m ];
G. setting a symmetry plane in an air domain as a symmetry boundary under the pressure acoustics and the frequency domain;
H. setting a symmetry plane in the air of a narrow area as a symmetry boundary under a ' hot-tack acoustics ' frequency domain ' physical field;
I. under the physical field of 'solid mechanics', adding 'damping' for 'linear elastic material', setting damping type as 'Rayleigh damping', and setting mass damping parameter alpha=0 and stiffness damping parameter beta=2/(2×pi×1400[ Hz ]);
J. under the condition of 'solid mechanics', a 'piezoelectric material' functional interface is added and applied to a piezoelectric material domain, and the piezoelectric material constitutive relation is set as 'stress-charge', and the piezoelectric material is polarized along the Y axis (namely, the thickness direction of the piezoelectric material);
K. setting the symmetry plane of the loudspeaker vibrating component as a symmetry boundary under a solid mechanics physical field;
setting the outer side edges of the piezoelectric cantilever beam and the vibrating diaphragm as 'fixed' boundaries under a 'solid mechanics' physical field;
m, under the ' electric field ', adding ' charge conservation ', piezoelectricity ', and applying the same to a piezoelectric material;
n. under "electric field" the upper and lower surface potentials in each piezoelectric material domain are set using "terminal" and "ground" boundary conditions. In the embodiment, the upper surface of the piezoelectric material is grounded, the lower surface adopts a terminal, and 15V (peak value) voltage is loaded;
and O, under the interface of multiple physical fields, adding a piezoelectric effect, an acoustic-structure boundary and an acoustic-thermal viscous acoustic boundary. Setting a piezoelectric effect to be applied to a piezoelectric material, and establishing a coupling relation between an electric field and a solid mechanics physical field; setting an ' acoustic-structural boundary ' to be applied to a contact surface of a vibration component and air, and establishing a coupling relation between ' solid mechanics ' and ' pressure acoustics ' and frequency domain ' physical fields; the acoustic-thermal adhesive acoustic boundary is set to be applied to the interface between a narrow air domain and a general air domain, and a coupling relation is established between a pressure acoustic, frequency domain and a thermal adhesive acoustic, frequency domain physical field.
4) Material parameters are defined. And setting material parameters of piezoelectric material (PZT 4), silicon base, vibrating diaphragm, connecting piece and air in the simulation analysis model by adopting material related operation. The values of the material parameters defined in this example are shown in fig. 11 to 14, respectively.
5) And (5) dividing grids. Fig. 15 is a finite element mesh model employed in this example, and the mesh division steps are as follows:
A. grid dividing narrow air space: firstly, adding 'mapping', carrying out grid division on the upper surface of each narrow air domain, and controlling the grid size of the upper surface through 'distribution'; then, adding 'sweeping', carrying out grid division on the narrow air domain, and controlling the grid quantity in the thickness direction of the narrow air domain through 'distribution'; in this example, in order to reduce the "hot tack acoustics" calculation error, the thickness direction "cell number distribution" is set to 4. Finally, adding 'conversion', and converting quadrilateral units on the boundary of the narrow area into triangular units through 'inserting diagonal edges', so as to ensure compatibility with the free tetrahedral grid;
B. dividing grids of vibrating components such as a diaphragm: adding a 'free tetrahedral mesh', and manually defining the size of the mesh; in addition, as the vibrating parts such as the vibrating diaphragm and the like are thinner, the size of the vibrating parts in the thickness direction is far smaller than the transverse size of the vibrating parts, and the vibrating parts are required to be stretched in the thickness direction when the grids are divided, so that the grid quality in the thickness direction is improved; in this example, the mesh "maximum cell size" is manually defined to be 0.06mm, and the thickness direction "stretch ratio" is 5;
C. grid dividing common air domain: the "free tetrahedral mesh" is added, and the mesh size is manually defined. In the solution of the piezoacoustic problem, in order to ensure the calculation accuracy, the maximum unit size of the grid needs to be not more than lambda/6, where lambda is the minimum wavelength of the acoustic wave in the solution frequency range. In this example, the maximum cell size of the mesh is set to 0.8mm.
(3) Solving and post-processing
1) "frequency domain" study
A. Setting the frequency range (unit Hz) of "frequency domain" study 1 to 10 { range (log 10 (20), 1/21, log10 (20000));
B. after the setting is completed, the finite element model is solved, and the calculation process is completed by an algorithm built in the COMSOL software.
2) "characteristic frequency" study
A. Add "characteristic frequency" study 2; disabling pressure acoustics, frequency domain "," hot-tack acoustics, frequency domain "," damping "," acoustic-structure boundary "and" acoustic-hot-tack acoustic boundary "in the" model configuration of the "physical field and variable selection > modification study step;
B. after the setting is completed, the finite element model is solved, and the calculation process is completed by an algorithm built in the COMSOL software.
3) And (5) post-treatment. The results that can be viewed by post-processing are as follows:
A. sound pressure level frequency response curve: firstly, adding a three-dimensional intercept point under a data set, inputting coordinates of a midpoint position on the surface of a microphone, and setting the data set as a data set of research 1; then, adding a 'one-dimensional drawing group > dot diagram', setting a 'data set' as a 'three-dimensional intercept point', inputting a sound pressure level expression 'acpr.lp' under pressure acoustics, and drawing to obtain a sound pressure level frequency response curve of the MEMS loudspeaker as shown in fig. 16;
B. sound pressure distribution: adding a three-dimensional drawing group (body 1 and body 2) respectively, selecting a data set of research 1 and a frequency point to be checked, inputting a sound pressure expression acpr.p_t under pressure acoustics and a sound pressure expression ta.p_t under hot viscosity acoustics respectively into the body 1 and the body 2, and drawing to obtain sound pressure distribution as shown in figure 17;
C. sound pressure distribution: adding a three-dimensional drawing group (body 1 and body 2) respectively, selecting a data set of research 1 and frequency points to be checked, inputting a sound pressure expression acpr.lp under pressure acoustics and a sound pressure expression ta.lp under hot viscosity acoustics in the body 1 and the body 2 respectively, and drawing to obtain sound pressure distribution as shown in figure 18;
D. capacitance value varies with frequency: adding a one-dimensional drawing group > global ", selecting a data set of research 1, inputting an expression (es.Q0_1/es.V0_1) x 2, and drawing to obtain the change of the capacitance value of the MEMS speaker along with the frequency as shown in FIG. 19;
E. stress distribution on piezoelectric cantilever: adding a 'three-dimensional drawing group' body, setting a data set and a viewing frequency point of the study 1, inputting stress expressions solid.mises, right clicking the 'body', adding 'selection', selecting a cantilever Liang Yu, and drawing to obtain stress distribution on the cantilever beam, wherein the stress distribution is shown in figure 20;
F. strain distribution on piezoelectric cantilever: adding a 'three-dimensional drawing group' body, setting a data set and a viewing frequency point of the study 1, inputting a strain expression solid.evol, right clicking the 'body', adding 'selection', selecting a cantilever Liang Yu, and drawing to obtain strain distribution on the cantilever beam, wherein the strain distribution is shown in figure 21;
G. displacement distribution on diaphragm: adding a 'three-dimensional drawing group > body', setting a data set and a viewing frequency point of research 1, inputting a displacement expression solid.disp, right clicking the 'body', adding 'selection', selecting a diaphragm corresponding domain, and drawing to obtain displacement distribution on the diaphragm, wherein the displacement distribution is shown in figure 22;
H. speed distribution on diaphragm: adding a 'three-dimensional drawing group' body, setting a data set and a view frequency point of the study 1, inputting a speed expression sol.vel, right clicking the 'body', adding 'selection', selecting a diaphragm corresponding domain, and drawing to obtain speed distribution on the diaphragm, wherein the speed distribution is shown in figure 23;
I. acceleration distribution on diaphragm: adding a 'three-dimensional drawing group > body', setting a data set and a viewing frequency point of research 1, inputting an acceleration expression solid.acc, right clicking the 'body', adding 'selection', selecting a diaphragm corresponding domain, and drawing to obtain acceleration distribution on the diaphragm, wherein the acceleration distribution is shown in figure 24;
J. resonance frequency of the vibration member: the three-dimensional drawing group surface deformation is added in sequence, a data set and a minimum frequency point of the research 2 are set, a displacement expression solid. Disp is input, and the mode of first-order resonance (fundamental frequency) of the MEMS loudspeaker vibration system is drawn and obtained as shown in figure 25, and the resonance frequency value is 2725.7Hz.
The above embodiments are only for illustrating the implementation procedure of the present invention and not for limiting the technical solution described in the present invention. Although the invention has been described in detail with reference to the above-described embodiments, it will be understood by those skilled in the art that the present invention may be modified or equivalently replaced, and all technical solutions and modifications thereof, which do not depart from the spirit and scope of the present invention, should be covered by the scope of the appended claims.
Claims (4)
1. The method is characterized in that the method uses a plurality of physical field coupling interfaces of pressure acoustics, frequency domain, hot viscosity acoustics, frequency domain, electric field and solid mechanics, and a plurality of physical field coupling interfaces of piezoelectric materials, sound-structure boundary and sound-hot viscosity acoustics boundary; the numerical simulation analysis method at least comprises the following steps:
(1) Establishing a finite element model
1) Establishing a geometric model
A. Establishing a geometric model of a loudspeaker: the MEMS loudspeaker geometric model is imported into finite element analysis software, the geometric model of the loudspeaker is drawn by adopting three-dimensional drawing software or built by adopting the self-contained geometric function of the finite element analysis software, and redundant points, lines, planes and bodies in the model are required to be cleaned after the geometric model is built so as to improve the quality of the geometric model;
B. establishing 711 an acoustic cavity equivalent model of the coupler: the sound pressure level frequency response curve of the MEMS loudspeaker is usually tested in a 711 coupler, so that the simulation analysis method is more universal, and an acoustic cavity equivalent model of the 711 coupler is established, wherein the acoustic cavity equivalent model comprises a connecting pipe and is correctly connected with the loudspeaker;
2) Setting physical field and boundary conditions
A. Selecting a corresponding domain of pressure acoustics and frequency domain, namely an air domain of a front cavity and a rear cavity of the loudspeaker and an air domain of a non-narrow area in a 711 coupler;
B. under the condition of pressure acoustics and frequency domain, adopting serial coupling RCL impedance boundary, and performing simulation analysis 711 on acoustic impedance of the surface of the test microphone in the coupler, wherein R is equivalent acoustic impedance, C is equivalent acoustic compliance, and L is equivalent acoustic inertia;
C. under the pressure acoustics and frequency domain, adopting a user-defined impedance boundary to simulate and analyze the acoustic impedance of a pressure balance hole in the loudspeaker when the pressure balance hole radiates sound waves to the air; the size of the balance hole 10 -1 magnitude of mm;
D. setting the symmetry plane of the air domain as a symmetry boundary condition under the pressure acoustics and frequency domain;
E. selecting a corresponding domain of 'hot tack acoustics and frequency domain', namely an air domain in a narrow area in a 711 coupler acoustic cavity model;
F. in the "hot tack acoustic, frequency domain", a temperature value is set that affects the hot tack parameters of air;
G. setting the symmetry plane of the air region of the narrow region as a symmetry boundary condition under the condition of hot tack acoustics and frequency domain;
H. selecting a corresponding domain of 'solid mechanics', namely a piezoelectric cantilever beam and a vibrating diaphragm domain;
I. under the condition of 'solid mechanics', the piezoelectric cantilever beam and the vibrating diaphragm domain are set as 'linear elastic material', and the damping type and the damping value are set;
J. under the condition of 'solid mechanics', a 'piezoelectric material' functional interface is added and applied to a piezoelectric material domain, and a piezoelectric material model and a piezoelectric material polarization direction are arranged at the interface;
K. under the condition of 'solid mechanics', setting the fixed edges of the piezoelectric cantilever beam and the vibrating diaphragm of the loudspeaker as 'fixed constraint' boundary conditions;
setting symmetry planes of vibration components such as piezoelectric cantilever beams as symmetry boundary conditions under the condition of solid mechanics;
m, selecting a field corresponding to the electric field, namely a piezoelectric material field;
n, under the ' electric field ', adding ' charge conservation ', piezoelectricity ', and applying the same to a piezoelectric material;
setting a designated voltage value on an electrode surface of a piezoelectric material under an electric field by adopting a terminal and a grounding function interface;
p, under the interface of multiple physical fields, respectively setting a piezoelectric effect, an acoustic-structure boundary and an acoustic-thermal viscosity acoustic boundary;
3) Defining material parameters: the material parameters required by the finite element simulation model are related to physical field, material model and boundary conditions, wherein the material parameters of the vibrating diaphragm, the dome and the piezoelectric cantilever in the MEMS loudspeaker are required to be respectively set, and the material parameters mainly comprise Young modulus, density, poisson's ratio, damping and sound velocity, and an elastic matrix, a coupling matrix and a relative dielectric constant matrix of the piezoelectric material;
4) Dividing grids: specifying a grid cell type and a grid size, and generating a finite element grid cell; the grid type and the grid size of each component and the air domain in the MEMS loudspeaker are respectively specified, and partial grid refinement is properly carried out, so that the calculation result is more accurate;
(2) Post-processing of solutions and results
1) Solving: the finite element model is solved by respectively adopting frequency domain and characteristic frequency researches;
2) Post-processing results: after the calculation is completed, post-processing operation is adopted to obtain the basic characteristics of the MEMS loudspeaker, and the basic characteristics mainly comprise: A. the MEMS speaker has a sound pressure level frequency response curve under 711 coupler test environment; B. the MEMS speaker is distributed with sound pressure and sound pressure level in the sound cavity of the speaker and 711 coupler under any working frequency; C. a capacitance value change curve of the MEMS speaker along with frequency; D. the MEMS loudspeaker has distribution patterns of stress, strain, displacement, speed and acceleration on structures such as a vibrating diaphragm, a cantilever beam and the like at any working frequency; E. the resonance frequency and mode of the MEMS speaker.
2. The method of claim 1, wherein the simulated analysis conditions are known as geometry of the speaker, material properties of materials used for the components of the speaker, constraints of the speaker, and loading conditions.
3. The method of claim 1, wherein the MEMS speaker is a piezoelectric speaker that uses a piezoelectric cantilever structure to drive the diaphragm to vibrate.
4. The method for numerical simulation analysis of basic characteristics of a piezoelectric MEMS speaker according to claim 1, wherein the finite element analysis software comprises COMSOL or ANSYS finite element simulation analysis software; the three-dimensional drawing software comprises SolidWorks or ProE drawing software.
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