CN107565013B - Longitudinal gradient short fiber piezoelectric composite material and preparation method thereof - Google Patents
Longitudinal gradient short fiber piezoelectric composite material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a longitudinal gradient short fiber piezoelectric composite material and a preparation method thereof, and relates to the technical field of material preparation. The longitudinal gradient short fiber piezoelectric composite material comprises an interdigital electrode and a piezoelectric fiber composite layer located between an upper electrode and a lower electrode of the interdigital electrode, wherein the piezoelectric fiber composite layer comprises a plurality of short fiber piezoelectric composite units which are sequentially bonded along the axis direction, the axial lengths of the short fiber piezoelectric composite units are in gradient change, and each short fiber piezoelectric composite unit comprises a plurality of polarized short piezoelectric fibers and a plurality of polymer fibers. The polarization is completed before packaging, the polarization is complete and uniform, the problem of polarization 'dead zones' does not exist, and meanwhile, the adaptability to non-planar structures is enhanced. According to the preparation method of the longitudinal gradient short fiber piezoelectric composite material, the longitudinal gradient short fiber piezoelectric composite material is prepared, the structure size of the composite material is accurate and controllable, and the serial and batch preparation of the structure and the performance of the piezoelectric fiber composite material is easy to realize.
Description
Technical Field
The invention relates to the technical field of material preparation, in particular to a longitudinal gradient short fiber piezoelectric composite material and a preparation method thereof.
Background
The piezoelectric composite material is a functional composite material based on the mutual coupling effect between electric energy and mechanical energy, and has various varieties according to different composite principles and structures, the piezoelectric fiber composite material is formed by compounding piezoelectric fibers and polymer fibers, has the characteristics of excellent piezoelectric performance of piezoelectric crystal materials, flexibility of the polymer fibers and the like, overcomes the defects of large brittleness and poor flexibility of the piezoelectric crystal materials, has the characteristics of prominent unidirectional performance, excellent designability and the like, and is widely applied to the fields of sensing, driving, structure control, structure health monitoring, energy acquisition and the like. The piezoelectric fiber composite material with MFC (micro fiber composites) structure proposed by NASA Langly research center of America is formed by combining and packaging a piezoelectric fiber composite layer and a flexible Interdigital electrode, the cross section of the fiber is rectangular, and the composite material can be made by means of the unique electric field distribution characteristics of Interdigital electrodes (IDEs)Material composition d33The mode is operated, and the longitudinal (along the axial direction of the piezoelectric fiber) strain performance of the piezoelectric fiber composite material is effectively exerted.
At present, based on d33The MFC structure piezoelectric fiber composite material mainly takes continuous long piezoelectric fibers as a functional phase, and due to the working mode of the composite material and the special structure of the piezoelectric fibers, the polarization of the piezoelectric fibers in the piezoelectric fiber composite material can be carried out only after the piezoelectric fiber composite layer and the flexible fork electrode are packaged. Due to the special structure and the unique electric field distribution state of the interdigital electrode, the electric field distribution in the piezoelectric fiber is not uniform, a polarization 'dead zone' is generated under the interdigital electrode of the interdigital flexible electrode, the piezoelectric fiber is easily polarized non-uniformly, the piezoelectric fiber is difficult to be polarized sufficiently, and the piezoelectric performance of the piezoelectric fiber cannot be effectively exerted. In addition, the uneven distribution of the electric field inside the piezoelectric fibers is easy to generate stress concentration on the interfaces among the piezoelectric fibers, the electrodes and the polymer in the polarization process of the composite material, the structure of the composite material is damaged, and the stability and the service cycle of the piezoelectric fiber composite material can be greatly reduced. The simple cross-value electrode structure enables the intensity of a driving electric field of the piezoelectric fiber composite material to be uneven in the application process, the performance of the composite material is difficult to effectively exert, and the application field of the piezoelectric fiber composite material is limited.
Disclosure of Invention
The invention aims to provide a longitudinal gradient short fiber piezoelectric composite material, which aims to solve the problem that a piezoelectric fiber is easy to generate a polarization dead zone in a polarization process and enhance the adaptability to a non-planar structure.
Another object of the present invention is to provide a method for preparing a longitudinally graded short fiber piezoelectric composite material, which performs polarization before encapsulation, has low requirements for the strength of equipment, and prevents the occurrence of a polarization dead zone.
The technical problem to be solved by the invention is realized by adopting the following technical scheme.
The invention provides a longitudinal gradient short fiber piezoelectric composite material, which comprises an interdigital electrode and a piezoelectric fiber composite layer positioned between an upper electrode and a lower electrode of the interdigital electrode, wherein the piezoelectric fiber composite layer comprises a plurality of short fiber piezoelectric composite units which are sequentially bonded along the axial direction, the axial length of the plurality of short fiber piezoelectric composite units is changed in a gradient manner, each piezoelectric composite unit comprises a plurality of polarized short piezoelectric fibers and a plurality of polymer fibers, the plurality of polarized short piezoelectric fibers and the plurality of polymer fibers are alternately bonded, two sides of each polymer fiber are respectively connected with one polarized short piezoelectric fiber, and the polarization directions of the polarized short piezoelectric fibers in two adjacent short fiber piezoelectric composite units are opposite.
The invention also provides a preparation method of the longitudinal gradient short fiber piezoelectric composite material, which comprises the following steps:
alternately superposing a plurality of piezoelectric thin layers and a plurality of polymer thin layers to obtain a piezoelectric composite structure, wherein two sides of each polymer thin layer are respectively connected with one piezoelectric thin layer, the length direction of the plane where the piezoelectric thin layers are located is a first direction, and the width direction of the plane where the piezoelectric thin layers are located is a second direction;
cutting once along a direction perpendicular to a plane where the piezoelectric thin layer is located, dividing the piezoelectric composite structure into a plurality of piezoelectric composite units along a first direction, polarizing the plurality of piezoelectric composite units along the first direction, and sequentially bonding the plurality of polarized piezoelectric composite units to obtain a polarized piezoelectric composite structure;
the distance between two adjacent cutting surfaces in the primary cutting process is a cutting distance, the cutting distances are in gradient change, the bonding surface in the bonding process is the cutting surface in the primary cutting process, and the polarized electric field intensities of the two adjacent piezoelectric composite units are the same and the polarization directions are opposite;
carrying out secondary cutting on the polarized piezoelectric composite structure along the direction perpendicular to the plane of the piezoelectric thin layer, and dividing the polarized piezoelectric composite structure into a plurality of piezoelectric fiber composite layers along a second direction;
and packaging the piezoelectric fiber composite layer and the interdigital electrode.
The embodiment of the invention provides a longitudinal gradient short fiber piezoelectric composite material and a preparation method thereof, and the longitudinal gradient short fiber piezoelectric composite material has the beneficial effects that: the longitudinal gradient short fiber piezoelectric composite material provided by the invention is formed by splicing a plurality of polarized short piezoelectric fibers and a plurality of polymer fibers to form a short fiber piezoelectric composite unit, and then splicing a plurality of short fiber piezoelectric composite units to form a piezoelectric fiber composite layer, so that the problem that the conventional structure is difficult to prepare in batch due to the high length of the piezoelectric fibers is solved. In addition, the short fiber piezoelectric composite material provided by the invention completes polarization before packaging, the requirement of the polarization process on equipment is low, and the short piezoelectric fiber is completely and uniformly polarized in the polarization process without the problem of polarization 'dead zones'. The invention also provides a preparation method of the longitudinal gradient short fiber piezoelectric composite material, the process is simple and feasible, the structural size of the composite material is accurate and controllable, and the preparation of the piezoelectric fiber composite material with serialized and batched structure and performance is easy to realize.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a schematic structural diagram of a longitudinal gradient short fiber piezoelectric composite material provided in an embodiment of the present invention;
FIG. 2 is a schematic diagram of a process for preparing the longitudinal gradient short fiber piezoelectric composite material in FIG. 1;
FIG. 3 is a schematic diagram of the piezoelectric fiber composite layer packaging process of FIG. 1.
Icon: 1-polarizing the short piezoelectric fibers; 2-polymer fibers; 4-face electrodes; 3-interdigital electrodes; 31-upper electrodes of interdigital electrodes; 32-lower electrodes of interdigital electrodes; 11-a piezoelectric thin layer; 22-a thin polymer layer; 5-a piezoelectric composite structure; 6-a piezoelectric composite unit; 7-piezoelectric fiber composite layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "connected" and "connected" are to be construed broadly, e.g., as meaning either a fixed connection or a removable connection, or an integral part; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
The longitudinal gradient short fiber piezoelectric composite material and the preparation method thereof provided by the embodiment of the invention are specifically described below.
Referring to fig. 1 and 3, an embodiment of the present invention provides a longitudinal gradient short fiber piezoelectric composite material, including an interdigital electrode 3 and a piezoelectric fiber composite layer 7 located between an upper electrode and a lower electrode of the interdigital electrode 3, where the piezoelectric fiber composite layer 7 includes a plurality of short fiber piezoelectric composite units sequentially bonded along an axial direction, axial lengths of the plurality of short fiber piezoelectric composite units vary in a gradient manner, each short fiber piezoelectric composite unit includes a plurality of polarized short piezoelectric fibers 1 and a plurality of polymer fibers 2, the plurality of polarized short piezoelectric fibers 1 and the plurality of polymer fibers 2 are alternately bonded, two sides of each polymer fiber 2 are respectively connected to one polarized short piezoelectric fiber 1, and polarization directions of the polarized short piezoelectric fibers 1 in two adjacent short fiber piezoelectric composite units are opposite.
It should be noted that, in the longitudinal gradient short fiber piezoelectric composite material provided in the embodiment of the present invention, the short fiber piezoelectric composite unit is formed by splicing a plurality of polarized short piezoelectric fibers 1 and a plurality of polymer fibers 2, the piezoelectric fiber composite layer 7 is formed by splicing a plurality of short fiber piezoelectric composite units, and the piezoelectric fiber composite layer 7 and the interdigital electrode 3 are encapsulated to form the longitudinal gradient short fiber piezoelectric composite material. Because the short piezoelectric fibers are adopted, the polarization can be carried out before packaging, the requirement on equipment in the polarization process is low, and the polarization is complete and uniform without the problem of polarization 'dead zones'. The axial lengths of the short fiber piezoelectric composite units are changed in a gradient manner, so that the matching characteristic of the piezoelectric fiber composite material to a non-planar structure is improved, and the application of the piezoelectric material is expanded. The composite material is designed into different gradients in the invention, so that the composite material can meet different production and use requirements.
In addition, in the preparation process of the longitudinal gradient short fiber piezoelectric composite material provided by the embodiment of the invention, if a certain short piezoelectric fiber composite unit has a problem, the short fiber piezoelectric composite unit can be directly replaced, rather than discarding the whole piezoelectric fiber composite layer. The complete and uniform polarization of the short fiber piezoelectric composite material can promote the effective performance of the piezoelectric fiber, provide a uniform and comprehensive driving electric field for the piezoelectric fiber in the application process, overcome the problem of stress concentration among the piezoelectric fiber, the electrode and the polymer fiber 2, and improve the application stability and the service cycle of the piezoelectric fiber composite material.
It is to be supplemented that, because the length of the piezoelectric fiber is higher, the traditional piezoelectric composite material is generally polarized after being packaged and has higher requirements on equipment, a polarization 'dead zone' is easy to appear in the polarization process, and if a problem occurs in the use process, the whole composite material needs to be replaced, so that the manufacturing cost and the use cost are higher.
Specifically, the axial length of the plurality of short fiber piezoelectric composite units is not limited in the form of gradient change, and may be continuously monotonically increasing or decreasing, increasing first and then decreasing, decreasing first and then increasing second, or a combination of the above forms.
Specifically, in fig. 3, the interdigital electrode 3 includes an upper electrode 31 of the interdigital electrode, a lower electrode 32 of the interdigital electrode, and the entire piezoelectric fiber composite layer 7 includes a plurality of surface electrodes 4 formed by bonding short fiber piezoelectric composite units. The interdigital electrode 3 adopts a flexible interdigital electrode, and the substrate of the interdigital electrode can be bent to meet the requirements of various use environments.
The axial direction in the present invention is the longitudinal direction of the piezoelectric fibers and the polymer fibers 2 on the piezoelectric fiber composite layer 7, and the polymer fibers 2 in the present invention are general polymer fibers.
Specifically, the polymer fibers 2 are made of epoxy resin, phenolic resin or polyester resin, so that the piezoelectric fibers can be well bonded and protected, and the flexibility of the material is improved. The polarized short piezoelectric fibers 1 are made of piezoelectric ceramics or piezoelectric single crystals, and can provide diversified electromechanical coupling characteristics for composite materials. Polymer fibers and piezoelectric fibers made of different materials can be selected according to different performance requirements of the composite material.
Furthermore, the short fiber piezoelectric composite units are sequentially bonded along the axis direction, and the bonding material is conductive adhesive. The plurality of short fiber piezoelectric composite units are spliced in sequence in a bonding mode, and the bonding material is conductive adhesive, which is caused by the cutting and bonding processes in the manufacturing process.
Specifically, the conductive adhesive is a polymer conductive adhesive, the polymer system of the polymer conductive adhesive is epoxy resin or silicone, and the electrical conductor system of the polymer conductive adhesive is Cu, Ag or Ni, so that moderate conductivity can be maintained while the bonding performance is ensured.
Further, the axial length of the polarized short piezoelectric fiber 1 is adapted to the distance between adjacent ones of the interdigital electrodes 3. In the process of packaging the piezoelectric fiber composite layer 7 and the interdigital electrode 3, the distance between adjacent interdigital electrodes in the interdigital electrode 3 is required to be ensured to be adapted to the axial length of the polarized short piezoelectric fiber 1.
In addition, it is necessary to align the conductive paste with the center of the finger electrode of the interdigital electrode 3 during the packaging process. The conductive adhesive is formed by bonding a plurality of short fiber piezoelectric composite units with each other, and the conductive adhesive is aligned with the center of a finger electrode in the interdigital electrode 3, so that an electric field transmitted by the electrode is more uniform.
Specifically, the base material of the interdigital electrode 3 is polyimide or a polyester film, and the electrode material of the interdigital electrode 3 is Cu, Ag, or Au. The base material and the electrode material of the interdigital electrode 3 may be the material of the conventional interdigital electrode 3, and are not described herein in detail.
Referring to fig. 2 and fig. 3, an embodiment of the present invention further provides a method for preparing a longitudinal gradient short fiber piezoelectric composite material, including the following steps:
and S1, alternately stacking a plurality of piezoelectric thin layers 11 and a plurality of polymer thin layers 22 to obtain the piezoelectric composite structure 5, wherein two sides of each polymer thin layer 22 are respectively connected with one piezoelectric thin layer 11.
For the sake of clarity in the following description, it is specified that the length direction along the plane of the piezoelectric thin layer 11 is the first direction and the width direction along the plane of the piezoelectric thin layer 11 is the second direction.
Specifically, a plurality of piezoelectric thin layers 11 and a plurality of polymer thin layers 22 are alternately spliced, wherein the piezoelectric thin layers 11 are located at the top and the bottom of the piezoelectric composite structure 5. The connection manner of the piezoelectric thin layer 11 and the polymer thin layer 22 is not limited, and the piezoelectric composite structure 5 may be prepared by a cut-and-fill method or a lamination-and-cut method.
Specifically, in order to meet the process requirements in the use process, the thickness of the piezoelectric thin layer 11 is 0.05-2mm, and the thickness of the polymer thin layer 22 is 0.01-1 mm.
And S2, cutting once along the direction perpendicular to the plane of the piezoelectric thin layer 11, dividing the piezoelectric composite structure 5 into a plurality of piezoelectric composite units 6 along the first direction, polarizing the piezoelectric composite units 6 along the first direction, and sequentially bonding the polarized piezoelectric composite units 6 to obtain the polarized piezoelectric composite structure.
The interval between two adjacent cutting surfaces in the primary cutting process is a cutting interval, the cutting intervals are in gradient change, the bonding surface in the bonding process is the cutting surface in the primary cutting process, and the polarized electric field intensities of the two adjacent piezoelectric composite units 6 are the same and the polarization directions are opposite. Namely, resetting is carried out according to the original cutting surface which is cut once, and attention is paid to ensure that the polarization directions of two adjacent piezoelectric composite units 6 are opposite.
Specifically, the mechanical device used in the one-time cutting process and the conductive adhesive used in the bonding process are not described herein, and reference is made to the contents of the material portion in the embodiments of the present invention. In the process of one-time cutting, the cutting distance is 0.2-5mm, and the difference value of two adjacent cutting distances is 0.05-1 mm. The distance between two adjacent cutting surfaces needs to be adapted to the distance between two adjacent finger electrodes of the interdigital electrode 3, and the process parameter of the distance between two adjacent cutting surfaces needs to be controlled.
And S3, performing secondary cutting on the polarized piezoelectric composite structure along the direction perpendicular to the plane of the piezoelectric thin layer 11, and dividing the polarized piezoelectric composite structure into a plurality of piezoelectric fiber composite layers 7 along the second direction.
The piezoelectric fiber composite layer 7 in the introduction of the short fiber piezoelectric composite material can be obtained through a secondary cutting process, and the cuts of a plurality of piezoelectric composite units in the piezoelectric fiber composite layer 7 are formed in the primary cutting process.
Specifically, the thickness of the piezoelectric fiber composite layer 7 can be adjusted to 0.01-2mm according to the cutting distance.
And S4, packaging the piezoelectric fiber composite layer 7 and the interdigital electrode 3.
The piezoelectric fiber composite layer 7 and the interdigital electrode 3 need to be packaged and then sold or used. The packaging process is to assemble the piezoelectric fiber composite layer 7 and the interdigital electrode 3, in the process, the axial length of the polarized short piezoelectric fiber 1 needs to be controlled to be adapted to the distance between adjacent finger electrodes in the interdigital electrode 3, and the center of the surface electrode 4 is aligned with the center of the finger electrode in the interdigital electrode 3.
The preparation method of the longitudinal gradient short fiber piezoelectric composite material provided by the embodiment of the invention has the advantages of simple and easy process, accurate and controllable structure and size of the composite material, and easy realization of serial and batch production of the structure and performance of the piezoelectric fiber composite material.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a preparation method of a longitudinal gradient short fiber piezoelectric composite material, which takes PZT as a piezoelectric phase and epoxy resin as a polymer phase, and adopts the method to prepare the longitudinal gradient short fiber reinforced piezoelectric composite material, and the specific process is as follows:
1. the piezoelectric composite structure 5 shown in figure 2 is prepared by using PZT ceramic and epoxy resin as raw materials and adopting a laminating-cutting method, wherein the number of the piezoelectric thin layers 11 is 9, the thickness is 0.3mm, the number of the polymer thin layers 22 is 8, the thickness is 0.2mm, the thickness of the piezoelectric composite structure 5 is 4.3mm which is the sum of the thicknesses of all the piezoelectric thin layers 11 and the polymer thin layers 22, and the length and the width of the piezoelectric fiber composite structure 5, the piezoelectric thin layers 11 and the polymer thin layers 22 are consistent and are 50 × 30 mm.
2. And (3) cutting the piezoelectric composite structure 5 obtained in the step (1) perpendicular to the piezoelectric thin layer 11 for one time along the width direction, and obtaining the piezoelectric composite units 6 with gradually increased thickness (distance between two cutting surfaces) in a gradient manner by adjusting the distance between cutting tools, wherein the initial thickness is 0.5mm, the incremental thickness is 0.1mm, the maximum thickness is 1.5mm, the other dimensions are 30 × 4.3.3 mm (length × width), and the total number is 11 in total.
3. And (3) coating a thin layer of epoxy resin silver paste on the cutting surfaces of the piezoelectric composite units 6 obtained in the step (2) to serve as surface electrodes 4, and polarizing the 2-2 type piezoelectric composite units in the thickness direction under the condition that an external electric field E is 3kV/mm to obtain uniformly polarized piezoelectric composite units 6.
4. And (3) alternately arranging the 11 polarized piezoelectric composite units 6 obtained in the step (3) in the direction of polarization P, molding the polarized piezoelectric composite units 6 into a polarized piezoelectric composite structure by using epoxy resin silver paste as a binder, and performing secondary cutting on the polarized piezoelectric composite structure along the polarization direction to obtain a piezoelectric fiber composite layer 7 with the size of 11 × 4.3.3 4.3 × 0.2.2 mm (the length is ×, the width is ×, and the thickness is the distance between two cutting surfaces.
5. The flexible fork value electrode is prepared by adopting a printed circuit board technology, the flexible substrate material is polyimide, the electrode material is metal copper, the center distance gradient of the electrode is gradually increased, the initial value of the distance is 0.5mm, the increment of the distance is 0.1mm, the maximum distance is 1.5mm, the width of the electrode is 0.1mm, the thickness of the electrode is 0.02mm, and the upper electrode and the lower electrode are in mirror symmetry.
6. Aligning the piezoelectric fiber composite layer 7 obtained in the step 4 and the flexible fork value electrode obtained in the step 5 with the piezoelectric fiber composite layer 7 and packaging the flexible fork value electrode 3 according to the structure shown in fig. 3 to obtain the longitudinal gradient short fiber piezoelectric composite material.
The embodiment provides a longitudinal gradient short fiber piezoelectric composite material, which is prepared by the preparation method.
In other embodiments, the initial thickness value and the incremental thickness of the piezoelectric composite unit 6, the piezoelectric fiber composite layer 7 and two adjacent cutting surfaces of one cutting can be controlled to be other dimensions.
In summary, the longitudinal gradient short fiber piezoelectric composite material provided by the invention is formed by splicing a plurality of polarized short piezoelectric fibers and a plurality of polymer fibers to form piezoelectric composite units, splicing a plurality of piezoelectric composite units to form a piezoelectric fiber composite layer, and packaging the piezoelectric fiber composite layer and the interdigital electrodes. Because the short piezoelectric fibers are adopted, the polarization can be carried out before packaging, the requirement on equipment in the polarization process is low, and the polarization is complete and uniform without the problem of polarization 'dead zones'. The axial lengths of the piezoelectric composite units are in gradient change, the matching characteristic of the piezoelectric fiber composite material to a non-planar structure is improved, and the application of the piezoelectric material is expanded.
The preparation method of the longitudinal gradient short fiber piezoelectric composite material provided by the embodiment of the invention has the advantages of simple and easy process, accurate and controllable structure and size of the composite material, and easy realization of serial and batch production of the structure and performance of the piezoelectric fiber composite material.
The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (7)
1. A longitudinal gradient short fiber piezoelectric composite material is characterized by comprising an interdigital electrode and a piezoelectric fiber composite layer positioned between an upper electrode and a lower electrode of the interdigital electrode, wherein the piezoelectric fiber composite layer comprises a plurality of short fiber piezoelectric composite units which are sequentially bonded along the axis direction, the axial length of the short fiber piezoelectric composite units is changed in a gradient manner, each short fiber piezoelectric composite unit comprises a plurality of polarized short piezoelectric fibers and a plurality of polymer fibers, the plurality of polarized short piezoelectric fibers and the plurality of polymer fibers are alternately bonded, two sides of each polymer fiber are respectively connected with one polarized short piezoelectric fiber, and the polarization directions of the polarized short piezoelectric fibers in two adjacent short fiber piezoelectric composite units are opposite;
the distance between adjacent interdigital electrodes in the interdigital electrodes is adapted to the axial length of the plurality of piezoelectric composite units, and the polymer fiber is made of epoxy resin, phenolic resin or polyester resin;
the bonding material sequentially bonded by the short fiber piezoelectric composite units is conductive adhesive, and the conductive adhesive is aligned with the center of a finger electrode in the interdigital electrode.
2. The longitudinal gradient short fiber piezoelectric composite material according to claim 1, wherein the conductive adhesive is a polymer conductive adhesive, a polymer system of the polymer conductive adhesive is epoxy resin or silicone, and an electrical conductor system of the polymer conductive adhesive is Cu, Ag or Ni.
3. The longitudinal gradient short fiber piezoelectric composite material according to claim 1, wherein the interdigital electrode is a flexible interdigital electrode, the base material of the flexible interdigital electrode is polyimide or a polyester film, and the electrode material of the flexible interdigital electrode is Cu, Ag or Au.
4. The longitudinal gradient short fiber piezoelectric composite material as claimed in claim 1, wherein the material of the polarized short piezoelectric fibers is piezoelectric ceramic or piezoelectric single crystal.
5. A preparation method of a longitudinal gradient short fiber piezoelectric composite material is characterized by comprising the following steps:
alternately superposing a plurality of piezoelectric thin layers and a plurality of polymer thin layers to obtain a piezoelectric composite structure, wherein two sides of each polymer thin layer are respectively connected with one piezoelectric thin layer, the length direction of the plane where the piezoelectric thin layers are located is a first direction, and the width direction of the plane where the piezoelectric thin layers are located is a second direction;
cutting once along a direction perpendicular to the plane of the piezoelectric thin layer, dividing the piezoelectric composite structure into a plurality of piezoelectric composite units along the first direction, polarizing the piezoelectric composite units along the first direction, and sequentially bonding the polarized piezoelectric composite units to obtain a polarized piezoelectric composite structure;
the distance between two adjacent cutting surfaces in the primary cutting process is a cutting distance, the cutting distances are in gradient change, the bonding surface in the bonding process is the cutting surface in the primary cutting process, and the polarized electric field intensities of the two adjacent piezoelectric composite units are the same and the polarization directions are opposite;
carrying out secondary cutting on the polarized piezoelectric composite structure along the direction perpendicular to the plane of the piezoelectric thin layer, and dividing the polarized piezoelectric composite structure into a plurality of piezoelectric fiber composite layers along the second direction;
and packaging the piezoelectric fiber composite layer and the interdigital electrode.
6. The method for preparing a longitudinal gradient short fiber piezoelectric composite material as claimed in claim 5, wherein the thickness of the piezoelectric thin layer is 0.1-2mm, and the thickness of the polymer thin layer is 0.01-1 mm.
7. The method for preparing a longitudinal gradient short fiber piezoelectric composite material as claimed in claim 6, wherein in the one cutting process, the cutting distance is 0.2-5mm, and the difference between two adjacent cutting distances is 0.05-1 mm.
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