Nested composite coform piezoelectric vibrator and regulation method

Abstract

The application discloses a nested composite coformable piezoelectric vibrator and a regulation method, and belongs to the field of piezoelectric materials and sensing. The coformable piezoelectric vibrator is a three-phase nested composite coformable piezoelectric vibrator composed of a piezoelectric material, a rigid polymer and a flexible polymer, and adopts 1-3 type and 2-2 type nested communication in structure, so that the piezoelectric vibrator has the dual functions of high-strength mechanical vibration and coformable application, and meets the application requirements of various curved surfaces. The piezoelectric vibrator is integrally formed by a plurality of periodically arranged piezoelectric elements and a flexible polymer, and the structure presents the characteristics of a transducer array. The application provides a regulation method for the structure of the nested composite coformable piezoelectric vibrator, and the width of a piezoelectric column in each piezoelectric element is a, the width of the rigid polymer is b, the width of the flexible polymer is c, the number of long edges of the piezoelectric column array in each piezoelectric element is q, and the number of short edges is w, so that the high electromechanical coupling coefficient performance of the coformable piezoelectric vibrator is regulated.

Description

TECHNICAL FIELD

[0001] The application relates to a nested composite coformable piezoelectric vibrator and a regulation method, and belongs to the technical field of piezoelectric materials and sensing. BACKGROUND

[0002] Ultrasonic waves are important carriers for sensing human body and ocean information so far. As a kind of mechanical wave, the sound signal has the advantages of strong projection, low loss and long transmission distance in biological tissues and water, which is the main factor for its wide application in medical imaging, ocean exploration and underwater guidance. An ultrasonic transducer is an electronic device that realizes the interaction of electrical and acoustic signals with ultrasonic waves as the carrier. Its internal structure is usually composed of a piezoelectric vibrator, a backing, a matching layer and a packaging layer. Since the vibration mode, piezoelectric coefficient and resonance characteristics of the piezoelectric vibrator play a leading role in the electrical and acoustic performance of the ultrasonic transducer, the performance optimization and structural improvement of the piezoelectric vibrator have always been a hot research topic.

[0003] A 1-3 type piezoelectric vibrator is a two-phase piezoelectric vibrator composed of one-dimensional piezoelectric material and three-dimensional rigid polymer. It is currently commonly used to develop sensitive elements of medium / high frequency ultrasonic transducers, and has the characteristics of high thickness vibration energy, low characteristic impedance and good stability. However, in recent research, it has been found that there are certain technical bottlenecks in the design of 1-3 type piezoelectric vibrator and its transducer array: first, from the composition of the vibrator, since the polymer of the 1-3 type piezoelectric vibrator is generally made of rigid epoxy resin, the vibrator has high hardness and is a flat structure that cannot be bent. However, the ultrasonic transducer in the underwater application scenario is generally installed on the ship in the form of an array, and the outer side of the ship is basically a curved shell. Therefore, the traditional 1-3 type piezoelectric vibrator cannot meet the application requirements of complex curved surfaces. Second, the epoxy resin material itself has high rigidity, which will limit the mechanical vibration of the piezoelectric material, which will limit the further improvement of the electromechanical coupling coefficient of the piezoelectric vibrator (the electromechanical coupling coefficient of the 1-3 type piezoelectric vibrator is generally about 0.6). Third, from the aspect of array, the ultrasonic transducer array is currently made in the form of manual positioning, that is, a plurality of 1-3 type piezoelectric vibrator elements are spliced in a customized frame according to the geometric structure, and finally the curved surface of the array as a whole is realized. Large opening angle, curved surface focusing, high power transmission and other specific functions, however, such transducer array has the problems of large volume, long process time, high technical requirements and difficult to control the consistency of the elements. In addition, since the positioning frame of the array is designed according to the shape of the ship, the current transducer array cannot meet the design of multiple curved surfaces. In summary, it is an important prerequisite to develop a piezoelectric vibrator that has high electromechanical coupling coefficient, meets the application of multiple curved surfaces and is easy to form an array structure, which is an important prerequisite for expanding the application of the current ultrasonic transducer and its array. SUMMARY

[0004] In order to solve the problems of the existing 1-3 type piezoelectric vibrator, such as difficult surface forming, low electromechanical coupling coefficient, and the problems of the spliced transducer array, such as large volume, long preparation period, high technical requirements, low element consistency, etc., the present application provides a nested composite coformable piezoelectric vibrator and a control method. First, the present application provides a coformable piezoelectric vibrator composed of piezoelectric material, rigid polymer and flexible polymer. The structure belongs to 1-3 type and 2-2 type nested communication, that is, the piezoelectric material and the rigid polymer are combined to form a piezoelectric element with 1-3 type matrix characteristics, and then the piezoelectric element is embedded in a two-dimensional connected flexible polymer to form a stable 2-2 type structure. The flexible polymer not only effectively promotes the mechanical vibration of the piezoelectric vibrator to improve the electromechanical coupling coefficient, but also has high elasticity to make the piezoelectric vibrator have stretching and bending characteristics to meet the curved surface application requirements of the transducer. Secondly, the present application provides a corresponding control method for the nested composite coformable piezoelectric vibrator structure. By controlling the width of the piezoelectric column in the piezoelectric element as a, the width of the rigid polymer as b, the width of the flexible polymer as c, the number of long edges of the piezoelectric column array in each piezoelectric element as q, and the number of short edges as w, the control of the coformable piezoelectric vibrator with high electromechanical coupling coefficient is realized, and theoretical guidance is provided for the preparation of the piezoelectric vibrator. In addition, the coformable piezoelectric vibrator provided by the present application is integrally formed by a plurality of periodically arranged piezoelectric elements and flexible polymers, and has the characteristics of transducer array in structure, which has great prospects in the development of coformable transducer array with small size, light weight and good element consistency.

[0005] The purpose of the present application is realized by the following technical solutions:

[0006] The nested composite coformable piezoelectric vibrator disclosed by the present application is mainly composed of a piezoelectric element, a flexible polymer and an electrode layer.

[0007] The piezoelectric element is made of piezoelectric material and rigid polymer, and the structure retains the characteristics of 1-3 type communication structure. The rigid polymer has good pressure resistance, which not only improves the stability of the piezoelectric element, but also enables the vibration mode of the composite material to be concentrated in the thickness direction, thereby meeting the high-power emission conditions of the transducer. In the preferred example, the piezoelectric material is PZT piezoelectric ceramic or piezoelectric single crystal. These types of piezoelectric materials have high piezoelectric coefficient and electromechanical coupling coefficient, which can make the transducer have excellent electroacoustic performance. The rigid polymer is WRS series epoxy resin, which has a large Young's modulus and can enhance the mechanical clamping effect between the piezoelectric columns.

[0008] The flexible polymer is embedded on both sides of the piezoelectric element in the form of a two-dimensional array, so that the piezoelectric element and the flexible polymer form a 2-2 type communication structure. The Young's modulus of the flexible polymer is low, which not only effectively reduces the coupling between the piezoelectric elements and the piezoelectric elements, but also promotes the vibration of the piezoelectric columns on both sides of the piezoelectric element, thereby promoting the improvement of the electromechanical coupling coefficient. On the other hand, the size of the flexible polymer is determined by the size of the piezoelectric element and the application requirement, that is, the thickness of the flexible polymer is strictly consistent with the thickness of the piezoelectric element, the length of the flexible polymer is strictly consistent with the length of the piezoelectric element, and the width of the flexible polymer is determined according to the ship structure. However, in order to meet the conformable requirement of the present application, the width of the flexible polymer should not be set too small. In a preferred embodiment, the flexible polymer is prepared by using 704 silicone rubber material. After curing, the silicone rubber material of this type has good decoupling and elasticity, which can effectively isolate the piezoelectric element and greatly promote the mechanical vibration intensity of the piezoelectric column.

[0009] Further, the electrode layer comprises a bottom electrode layer and a top electrode layer, which are uniformly covered on the upper and lower end surfaces of the conformable matrix, for conducting the electrical signal of the piezoelectric element. The bottom electrode layer is a uniform electrode plane for connecting the lower end surfaces of all piezoelectric elements, and the top electrode layer is an array electrode plane or a uniform electrode plane. When the top electrode layer is an array electrode plane, the present application can be used to make a matrix type transducer, each piezoelectric element being an independent element, so the units of the array electrode plane should be matched with the upper end surfaces of the piezoelectric elements one by one, and the piezoelectric element part is in a hollow state; when the top electrode layer is a uniform electrode plane, the whole is a transducer element, and the size of the electrode plane should be consistent with the size of the upper end surface of the conformable piezoelectric vibrator, so as to ensure the communication of the upper end surfaces of all piezoelectric elements. In a preferred embodiment, the electrode layer is prepared by using magnetron sputtering or silver paste brushing method.

[0010] Further, the conformable piezoelectric vibrator is composed of three phases of piezoelectric material, rigid polymer and flexible polymer. The piezoelectric element composed of piezoelectric material and rigid polymer satisfies the 1-3 communication structure, and the piezoelectric element and the flexible polymer satisfy the 2-2 type communication structure, so the constitutive relation of the whole conformable piezoelectric vibrator should be established in turn according to the 1-3 type and the 2-2 type.

[0011] Second part, the present application provides a nested composite conformable piezoelectric vibrator regulation method for regulating the size parameters of the conformable piezoelectric vibrator.

[0012] Step one, in the piezoelectric element, the polarized piezoelectric material expands according to the e type stress equation, as shown in formula (1):

[0013]

[0014] where T i represents stress components, S i represents strain components, E k represents electric field intensity, D h is electric displacement, is elastic constant components under constant electric field, e ij is piezoelectric stress constant components, is dielectric constant components under constant strain (i, j = 1, 2,..., 6, h, k = 1, 2, 3).

[0015] Step two, the rigid polymer is a uniform isotropic medium, the piezoelectric equation is shown as formula (2):

[0016]

[0017] Step three, since the piezoelectric material is polarized along the thickness direction, the co-type piezoelectric vibrator is concentrated in the thickness capacity mode, the shear strain is zero, then:

[0018] S4= S5= S6= 0 (3)

[0019] The electrode layer is uniformly covered on the upper and lower end surfaces of the co-type piezoelectric vibrator, and there is no electric field and electric displacement in the transverse and shear directions, then:

[0020] E1= E2= D1= D2= 0 (4)

[0021] The piezoelectric element composed of the piezoelectric material and the rigid polymer has significant symmetry in the xoy plane, the transverse strains S1 and S2 are equal, that is:

[0022] S1= S2 (5)

[0023] Step four, formula (3)~formula (5) are substituted into formula (1) and formula (2) respectively to simplify, formula (6) and formula (7) are obtained:

[0024]

[0025]

[0026] In formula (6) and formula (7), the upper subscript c represents the piezoelectric material phase, and e represents the rigid polymer phase.

[0027] Step five, in the z direction, the piezoelectric material phase and the rigid polymer phase are connected in parallel, the vertical strain of the piezoelectric element is equal to the vertical strain of its internal components, and the vertical stress of the piezoelectric element is affected by the piezoelectric material phase and the rigid polymer phase, then:

[0028]

[0029] The vertical electric field of the piezoelectric element is the same as that of the internal components, and the vertical electric displacement of the whole vibrator is affected by both the piezoelectric material phase and the rigid polymer phase, so that:

[0030]

[0031] In formula (8) and formula (9), the upper index m represents the piezoelectric element, v c and v e respectively represent the volume fraction of the piezoelectric material and the rigid polymer in the piezoelectric element, wherein v e =1-v c .

[0032] Step six, in the x direction and the y direction, the piezoelectric material phase and the rigid polymer phase are connected in series, the lateral stress of the piezoelectric element is equal to that of the internal components, and the lateral strain of the piezoelectric element is affected by both the piezoelectric material phase and the rigid polymer phase, so that:

[0033]

[0034] Step seven, after transforming formula (6) and formula (7) into a matrix equation with T1, S3 and E3 as independent variables and S1, T3 and D3 as dependent variables, and then according to the relationship of formula (8) to formula (10), then:

[0035]

[0036] In the above formula (11), a ij There is a relationship as follows: (i, j = 1, 2, 3)

[0037]

[0038]

[0039]

[0040] Step eight, transform formula (11) into a standard e-type piezoelectric equation according to formula (1), so that:

[0041]

[0042] In the above formula (12),

[0043]

[0044] Step nine, in the y direction, the piezoelectric element and the flexible polymer form a 2-2 composite structure, and the electro-elastic parameters of the structure satisfy the following relationship:

[0045]

[0046]

[0047]

[0048] In formula (13) to formula (15), the upper index n represents a co-typed piezoelectric vibrator, the upper index s represents a flexible polymer phase, v1 represents a volume fraction of the piezoelectric element in the co-typed piezoelectric vibrator, v s represents a volume fraction of the flexible polymer in the co-typed piezoelectric vibrator.

[0049] Step ten, the parameters in formula (13) to formula (15) are brought into formula (16) to solve the electromechanical coupling coefficient k t of the piezoelectric vibrator.

[0050]

[0051] Step eleven, by solving formula (16), the highest electromechanical coupling coefficient k t is obtained under the condition that v c and v1 correspond, and finally the specific structural size of the nested composite co-typed piezoelectric vibrator is obtained. The width of the piezoelectric column in the piezoelectric element is a, the width of the rigid polymer is b, the width of the flexible polymer is c, the number of long edges of the piezoelectric column array in each piezoelectric element is q, and the number of short edges is w, then the volume fraction v c of the piezoelectric material in the piezoelectric element and the volume fraction v1 of the piezoelectric element in the co-typed piezoelectric vibrator are respectively:

[0052]

[0053] Third part, according to the structural size a, b, c and w provided in the second part, the application also discloses a preparation method of the nested composite co-typed piezoelectric vibrator, and the specific steps are as follows:

[0054] Step one, preparing a primary cutting skeleton; a piezoelectric material with a proper size is fixed on a cutting machine sample table, cutting parameters are set, the cutting blade is uniformly cut transversely, and the piezoelectric material is ensured not to be cut through, so that the primary cutting skeleton is formed.

[0055] Step two, pouring the rigid polymer material; a certain amount of rigid polymer glue solution is prepared, and the rigid polymer glue solution is poured into the cutting seam of the primary cutting skeleton, vacuum is extracted, and curing is performed at room temperature for 24 hours to form. Further, the rigid polymer needs to be prepared by a proportion of a softener and a curing agent, so that the piezoelectric element has good pressure resistance.

[0056] Step three, preparing the second cutting skeleton; grinding the surface of the product of step two with an abrasive disc, removing the rigid polymer impurities, making the surface of the sample flat and smooth, and then fixing it on the sample table of the cutting machine again. Set the cutting parameters to make the cutting blade cut the sample longitudinally to form a second cutting skeleton. Further, the cutting step must be strictly set to ensure that the length and width of the piezoelectric column are consistent, and the longitudinal and transverse cutting depths are completely consistent.

[0057] Step four, filling the rigid polymer material; take the second cutting skeleton and fill the rigid polymer material as in step two, vacuumize and cure at room temperature for 24 hours to shape, forming a number of piezoelectric cell structures composed of piezoelectric material and rigid polymer.

[0058] Step five, preparing the third cutting skeleton; grinding the surface of the product of step four with an abrasive disc, removing the residual epoxy resin impurities, and then fixing it on the sample table of the cutting machine. Set the cutting parameters and adjust the cutting position in the cutting machine operation interface to make the cutting blade cut off the piezoelectric material in the gap between the piezoelectric cells to make a third cutting skeleton.

[0059] Step six, filling the flexible polymer material; take the third cutting skeleton and fill it with flexible polymer material, vacuumize and cure at room temperature for 24 hours to make a nested composite piezoelectric vibrator.

[0060] Step seven, grinding the piezoelectric vibrator base. Grind the upper and lower surfaces of the nested composite piezoelectric vibrator in step six flat, fix the base upwards on the sample table of the cutting machine, and set the cutting parameters to grind the piezoelectric vibrator base.

[0061] Step eight, preparing the electrode layer. Take the piezoelectric vibrator after grinding the base, clean the impurities on the upper and lower surfaces, and then plate the electrode to complete the preparation of a nested composite co-molded piezoelectric vibrator. The electrode layer includes the upper and lower end faces of the piezoelectric vibrator, and after preparation, the surface resistance of the electrode needs to be tested with a multimeter to control it within 1.0Ω. If the top electrode of the electrode layer is an array electrode, a mask plate with a hollow array needs to be prepared, and the hollow part needs to be completely matched with the piezoelectric cell part during electrode preparation.

[0062] Advantages:

[0063] 1. The nested composite co-molded piezoelectric vibrator and the control method disclosed by the present application are composed of three phases of piezoelectric material, rigid polymer and flexible polymer, which retains the high pressure resistance and thickness mode concentration advantages of traditional 1-3 type rigid composite materials, and at the same time makes the piezoelectric vibrator have the ability of curved surface co-molding, improving the acoustic application field of the piezoelectric vibrator.

[0064] 2. The nested composite coformable piezoelectric vibrator and the regulation method, which utilize the piezoelectric composite structure integrated transducer array, compared with the traditional splicing type array, greatly simplify the preparation process, not only effectively reduce the development cost, but also ensure the consistency of piezoelectric elements in performance.

[0065] 3. The nested composite coformable piezoelectric vibrator and the regulation method, which adopt silicone rubber as a decoupling material filled between the piezoelectric elements, which not only realizes the elimination of crosstalk and plane coupling between the piezoelectric elements, but also weakens the rigid restraint force on both sides of the piezoelectric elements, and can further improve the overall electromechanical coupling coefficient of the piezoelectric vibrator. BRIEF DESCRIPTION OF DRAWINGS

[0066] Figure 1 It is a three-dimensional structure schematic diagram of a nested composite coformable piezoelectric vibrator.

[0067] Figure 2 It is Figure 1 It is a three-dimensional structure schematic diagram of a piezoelectric element.

[0068] Figure 3 It is an array structure diagram of a nested composite coformable piezoelectric vibrator.

[0069] Figure 4 It is a relationship curve diagram of the electromechanical coupling coefficient and v c under different v1 conditions.

[0070] Figure 5 It is a preparation flowchart of a nested composite coformable piezoelectric vibrator provided in embodiment 1.

[0071] Figure 6 It is a finite element modeling of a nested composite coformable piezoelectric vibrator provided in embodiment 1.

[0072] Figure 7 It is a vibration displacement diagram of a nested composite coformable piezoelectric vibrator provided in embodiment 1 at the resonance point.

[0073] Figure 8 It is a nested composite coformable piezoelectric vibrator admittance curve diagram provided in embodiment 1.

[0074] In the figure, 1 is a piezoelectric element, 2 is a flexible polymer, 3 is an electrode layer, 4 is a piezoelectric material column, 5 is a rigid polymer, and 6 is an array electrode. DETAILED DESCRIPTION

[0075] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application is further described in detail below with specific examples and drawings.

[0076] Figure 1It is a schematic diagram of a nested composite coformable piezoelectric vibrator three-dimensional structure, the overall structure is composed of a plurality of piezoelectric elements 1, flexible polymer 2 and electrode layer 3, wherein the flexible polymer 2 plays a role in series connection to the piezoelectric element 1, allowing each piezoelectric element to have high elasticity and minimal mechanical restraint on both sides, not only promoting the thickness vibration of the high piezoelectric vibrator, but also reducing the coupling between the piezoelectric elements 1. The piezoelectric element 1 is composed of a plurality of piezoelectric material columns 4 and rigid polymer 5, as shown in Figure 2 The piezoelectric material column 4 is arranged in one dimension and each column has the same size parameters, and the rigid polymer 5 is arranged in three dimensions, both of which form a 1-3 connected structure, so that the piezoelectric element has significant compression resistance.

[0077] Figure 3 A nested composite coformable piezoelectric vibrator array structure is given, the upper end surface of each piezoelectric element 1 is connected to an array electrode 7, the area size of each array electrode 7 is consistent with the area size of the upper end surface of the piezoelectric element 1, and the structure is the same. When developing a transducer array, the array electrode 7 can be aligned and attached to a flexible circuit board (not shown in the figure) on top to achieve independent control of the piezoelectric element 1.

[0078] Example 1

[0079] The electromechanical coupling coefficient of the piezoelectric vibrator is closely related to the sensitivity index of the ultrasonic transducer. When using an ultrasonic transducer to sense a human body or underwater acoustic signal, the higher the sensitivity, the stronger the signal captured by the ultrasonic transducer, and the more acoustic information it carries. In addition, the current 1-3 two-phase piezoelectric vibrator used in the ultrasonic transducer does not have the bending coformability, and if it is made into an array form, not only the cycle is long and the process requirement is high, but also the consistency of the array element is difficult to control. Based on this problem, the present application provides a nested composite coformable piezoelectric vibrator with light weight, small volume, coformability, easy preparation and excellent performance, which can not only further improve the electromechanical coupling coefficient of the vibrator and strengthen the sensitivity of the ultrasonic transducer and the ability to sense signals, but also can realize the coformability effect, so that the piezoelectric vibrator meets the curved surface application demand in various environments. The present application provides an analysis method for a nested composite coformable piezoelectric vibrator, by changing the piezoelectric layer column width a, the rigid polymer width b, the number of long edges of the piezoelectric column array q, the number of short edges w and the flexible polymer width c, so as to change the volume fraction v of the piezoelectric material in the piezoelectric element c and the volume fraction v1 of the piezoelectric element in the coformable piezoelectric vibrator, finally realizing the preparation of high electromechanical coupling coefficient and coformable piezoelectric vibrator, the specific design process is as follows:

[0080] Step one, in the piezoelectric element, the polarized piezoelectric material is expanded according to the e-type stress equation, as shown in formula (1):

[0081]

[0082] where T i represents stress components, S i represents strain components, E k represents electric field intensity, D h is electric displacement, is elastic constant components under constant electric field, e ij is piezoelectric stress constant components, is dielectric constant components under constant strain (i, j = 1, 2,..., 6, h, k = 1, 2, 3).

[0083] Step two, the rigid polymer is a uniform isotropic medium, the piezoelectric equation is shown in equation (2):

[0084]

[0085] Step three, the piezoelectric material is polarized along the thickness direction, the co-type piezoelectric vibrator is concentrated in the thickness capacity mode, the shear strain is zero, then:

[0086] S4 = S5 = S6 = 0 (3)

[0087] The electrode layer is uniformly covered on the upper and lower end surfaces of the co-type piezoelectric vibrator, so there is no transverse and shear direction electric field and electric displacement, then:

[0088] E1 = E2 = D1 = D2 = 0 (4)

[0089] The piezoelectric element composed of piezoelectric material and rigid polymer has significant symmetry in the xoy plane, the transverse strain S1 and S2 are equal, that is:

[0090] S1 = S2 (5)

[0091] Step four, according to the setting of step three, equation (1) and equation (2) are simplified to obtain equation (6) and equation (7) respectively:

[0092]

[0093]

[0094] In equation (6) and equation (7), the upper subscript c represents the piezoelectric material phase, and e represents the rigid polymer phase.

[0095] Step five, in the z direction, the piezoelectric material phase and the rigid polymer phase are connected in parallel, the vertical strain of the piezoelectric element is equal to the vertical strain of its internal components, and the vertical stress of the piezoelectric element is affected by the piezoelectric material phase and the rigid polymer phase, then:

[0096]

[0097] The vertical electric field of the piezoelectric element is the same as that of the internal components, and the vertical electric displacement of the vibrator is affected by both the piezoelectric material phase and the rigid polymer phase, so that:

[0098]

[0099] In the formula (8) and formula (9), the upper index m represents the piezoelectric element, v c and v e respectively represent the volume fraction of the piezoelectric material and the rigid polymer in the piezoelectric element, wherein v e =1-v c .

[0100] Step six, in the x direction and the y direction, the piezoelectric material phase and the rigid polymer phase are in series, so that the lateral stress of the piezoelectric element is equal to that of its internal components, and the lateral strain of the piezoelectric element is affected by both the piezoelectric material phase and the rigid polymer phase, so that:

[0101]

[0102] Step seven, after transforming the formula (6) and formula (7) into a matrix equation with T1, S3 and E3 as independent variables and S1, T3 and D3 as dependent variables, and then according to the relationship of formula (8)~formula (10), then:

[0103]

[0104] In the above formula (11), a ij There is a relationship as follows: (i,j=1,2,3)

[0105]

[0106]

[0107]

[0108] Step eight, transforming formula (11) into formula (1) into a standard e-type piezoelectric equation, then:

[0109]

[0110] In the above formula (12),

[0111]

[0112] Step nine, in the y direction, the piezoelectric element and the flexible polymer phase constitute a 2-2 composite structure, and the electro-elastic parameters under this structure satisfy the following relationship:

[0113]

[0114]

[0115]

[0116] In formula (13) to formula (15), the upper index n represents a co-formable piezoelectric vibrator, the upper index s represents a flexible polymer phase, v1 represents a volume fraction of the piezoelectric element in the co-formable piezoelectric vibrator, v s represents a volume fraction of the flexible polymer in the co-formable piezoelectric vibrator.

[0117] In step ten, the parameters in formula (13) to formula (15) are brought into formula (16) to solve the electromechanical coupling coefficient k t of the piezoelectric vibrator.

[0118]

[0119] In this example, piezoelectric ceramic PZT-5A is selected as the piezoelectric material phase, 618 epoxy resin and 704 silicone rubber are respectively selected as the rigid polymer phase and the flexible polymer phase, and the material parameters are shown in Table 1 as follows:

[0120] Table 1. Material parameter table of PZT-5A

[0121]

[0122] The data in Table 1 is brought into formula (12) and formula (13) by using MATLAB software, and the electromechanical coupling coefficient k Figure 4 is obtained as shown in the following table. t The theoretical relationship between v1 and v c . When the percentage of v1 gradually increases, the electromechanical coupling coefficient first gradually increases and then stabilizes at about 0.67, which indicates that the introduction of silicone rubber will promote the electromechanical conversion ability of the piezoelectric vibrator, and the co-forming ability of the piezoelectric vibrator is also enhanced, but the introduction of too much silicone rubber will also affect the thickness energy conversion. When v c ≤0.4, the content of piezoelectric ceramic in the piezoelectric vibrator is small, and the k t value increases significantly; when 0.6≤v c ≤0.7, the k t value of the composite material increases slowly until it increases to the maximum value. When v c ≥0.8, the content of piezoelectric ceramic gradually reaches saturation, and the planar coupling of the composite material is more significant, which will affect the thickness vibration energy of the whole piezoelectric vibrator, and the k t value decreases. In summary, in order to make the whole piezoelectric vibrator have a high electromechanical coupling coefficient and a certain co-forming ability, v1=0.5 and vc = 0.7.

[0123]

[0124] Step eleven, from the above analysis, the width of the piezoelectric column in the piezoelectric element is 1 mm, the size of the piezoelectric ceramic column array in the piezoelectric element is 5x2, and v1=0.5 and v2=0.7 are given in step nine. From equation (14), the width of the rigid polymer b=0.2 mm, and the width of the flexible polymer c=2.2 mm. c = 0.7.

[0125] Figure 5 A preparation flow chart of the nested composite coformable piezoelectric vibrator is given. According to the size parameters of the nested composite coformable piezoelectric vibrator provided in step ten, the sample is prepared by cutting-filling technology, and the specific steps are as follows:

[0126] Step one, preparation of the first cutting skeleton; fix the PZT piezoelectric ceramic of appropriate size on the cutting machine sample table, and the size of the PZT piezoelectric ceramic should be equivalent to the designed sample size of the nested composite coformable piezoelectric vibrator. Set the cutting step to 1.2 mm, so that the cutting blade cuts uniformly in the transverse direction and ensures that the piezoelectric material is not cut through, forming the first cutting skeleton.

[0127] Step two, filling of epoxy resin material; configure a certain amount of epoxy resin solution according to the relationship of epoxy resin: curing agent: softener = 10:1:1, and fill it into the cutting seam of the first cutting skeleton. Vacuum and cure at room temperature for 24 hours to form.

[0128] Step three, preparation of the second cutting skeleton; polish the surface of the rigid polymer filled skeleton product in step two to remove surface residual epoxy resin impurities. Fix the sample on the cutting machine sample table again, set the cutting step to 1.2 mm, and cut the sample vertically with the cutting blade to form the second cutting skeleton.

[0129] Step four, filling of epoxy resin material; take the second cutting skeleton and fill the epoxy resin material according to the method in step two. Vacuum and cure at room temperature for 24 hours to shape, forming the PZT-epoxy resin piezoelectric element structure prototype.

[0130] Step five, preparation of the third cutting skeleton; polish the surface of the rigid polymer skeleton product filled in step four, remove the epoxy resin impurities, and fix it on the cutting machine sample table. Set the cutting step to 4.4 mm, and adjust the cutting position in the cutting machine operation interface to cut off the piezoelectric material in the gap between the piezoelectric elements, and make the third cutting skeleton.

[0131] Step six, filling the silicon rubber; taking three cutting skeletons, filling the inside with flexible polymer material, vacuumizing and curing at room temperature for 24 hours to make the nested composite piezoelectric vibrator.

[0132] Step seven, polishing the piezoelectric vibrator base. The upper and lower surfaces of the nested composite piezoelectric vibrator in step six are polished flat, the base is fixed on the cutting machine sample table with the base facing up, and the cutting parameters are set to polish the piezoelectric vibrator base.

[0133] Step eight, preparing the electrode layer. After polishing the piezoelectric vibrator base, the upper and lower surfaces are cleaned of impurities, and conductive silver paste with a purity of 99% is applied. The piezoelectric vibrator is placed in an oven at 150°C for 2 hours. The piezoelectric vibrator is removed from the oven, and the surface resistance of the electrode is tested using a multimeter. When the resistance of both ends of the sample is <1.0Ω, the preparation of the nested composite piezoelectric vibrator is complete.

[0134] The performance of the nested composite piezoelectric vibrator prepared in this example is tested, and ANSYS finite element analysis software is used to simulate the nested composite piezoelectric vibrator. The piezoelectric vibrator is modeled according to the parameters shown in Table 2, and the grid size is set to 1mm. The model is swept to obtain the finite element model as shown in Figure 6 .

[0135] Table 2. Size of the simulation model of the piezoelectric vibrator

[0136]

[0137] In the general post-processing block of the harmonic response analysis, the vibration mode corresponding to the resonance frequency point of the piezoelectric vibrator is read, and the vibration displacement graph as shown in Figure 7 is obtained. From Figure 7 , it can be seen that the piezoelectric vibrator proposed in the present application is a concentrated thickness vibration mode, and the deformation of the silicon rubber is larger, while the deformation of the epoxy resin is smaller, indicating that the silicon rubber has little effect on the vibration of the piezoelectric ceramic column, and the thickness energy is further concentrated. Although the epoxy resin can also promote the vibration of the piezoelectric column, its rigidity still slightly suppresses the vibration of the ceramic column.

[0138] Figure 8 The admittance curve of the piezoelectric vibrator in this example is given. From Figure 8 , it can be seen that the admittance curve is relatively pure, without other significant coupling peaks, indicating that the piezoelectric vibrator provided in the present application has a high-purity thickness vibration mode. The resonance frequency and anti-resonance frequency in the admittance curve are read to solve the electromechanical coupling coefficient k t The test results are shown in Table 3.

[0139] Table 3. Simulation results of the piezoelectric vibrator

[0140]

[0141] According to Table 3, the k t value can be as high as 0.68, indicating that the thickness vibration effect is significantly enhanced with the promotion of silicone rubber; in addition, the test result is close to the theoretical calculation result, and there is only a 1% error between them, verifying the feasibility of the theoretical model proposed in the present application and the guidance to the experiment. Compared with the traditional 1-3 type pure rigid piezoelectric vibrator, the k t value can be increased by 11.8%, and the improvement of the piezoelectric vibrator has achieved remarkable results in the improvement of energy conversion. According to the above simulation results, the nested composite conformable piezoelectric vibrator provided in the present application has a significantly high electromechanical coupling coefficient and conformable bending ability, which is expected to not only improve the sensitivity of the ultrasonic transducer, but also meet the conformable application effect, and achieve the expected design requirements.

[0142] The above specific description further details the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A nested composite conformal piezoelectric oscillator, characterized in that: It is mainly composed of piezoelectric elements, flexible polymers, and electrode layers; The piezoelectric unit is made of piezoelectric material and rigid polymer composite, and retains the 1-3 type interconnect structure characteristics in structure; The flexible polymer is embedded on both sides of the piezoelectric element in the form of a two-dimensional array, so that the piezoelectric element and the flexible polymer form a 2-2 type connected structure; the thickness of the flexible polymer is strictly consistent with the thickness of the piezoelectric element, the length of the flexible polymer is strictly consistent with the length of the piezoelectric element, and the width of the flexible polymer is determined according to the hull structure. The electrode layer comprises a bottom electrode layer and a top electrode layer, which are uniformly covered on the upper and lower end faces of the conformal piezoelectric oscillator for conducting electrical signals of the piezoelectric elements; the bottom electrode layer is a uniform electrode plane for connecting the lower end faces of all piezoelectric elements, and the top electrode layer is an array electrode plane or a uniform electrode plane. The conformable piezoelectric oscillator is composed of a three-phase composite of piezoelectric material, rigid polymer and flexible polymer. The piezoelectric unit composed of piezoelectric material and rigid polymer satisfies the 1-3 type interconnection structure, and the piezoelectric unit and flexible polymer satisfy the 2-2 type interconnection structure. Therefore, the constitutive relation of the conformable piezoelectric oscillator as a whole should be established in the order of 1-3 type and 2-2 type.

2. The nested composite conformal piezoelectric oscillator as described in claim 1, characterized in that: The piezoelectric material is selected from PZT piezoelectric ceramics or piezoelectric single crystals; the rigid polymer is selected from WRS series epoxy resins.

3. The nested composite conformal piezoelectric oscillator as described in claim 1, characterized in that: The flexible polymer is prepared using 704 silicone rubber material.

4. The nested composite conformal piezoelectric oscillator as described in claim 1, characterized in that: When the top electrode layer is an array electrode plane, it is used to fabricate an array transducer. Each piezoelectric element is an independent element. Therefore, the units of the array electrode plane should match the upper surface of the piezoelectric element one by one, and the piezoelectric element part is hollow.

5. A nested composite conformal piezoelectric oscillator as described in claim 1, characterized in that: When the top electrode layer is a uniform electrode plane, the whole is a transducer element. The size of the electrode plane should match the size of the upper end face of the conformal piezoelectric vibrator to ensure that the upper end faces of all piezoelectric elements are connected.

6. A nested composite conformal piezoelectric oscillator as described in claim 5, characterized in that: The electrode layer is prepared using magnetron sputtering or silver paste coating.

7. A method for controlling a nested composite conformal piezoelectric oscillator, used to control the dimensional parameters of a nested composite conformal piezoelectric oscillator as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: Includes the following steps, Step 1: In the piezoelectric element, the polarized piezoelectric material phase is expanded according to the e-type stress equation, as shown in equation (1): In the formula T i S represents the stress component. i E represents the strain component. k D represents the electric field strength. h For electric displacement, Let e ​​be the elastic constant component under a constant electric field. ij For the piezoelectric stress constant components, The dielectric constant components under constant strain are (i,j=1,2,...,6,h,k=1,2,3); Step 2: The rigid polymer is a homogeneous isotropic medium, and the piezoelectric equation is shown in equation (2): Step 3: Since the piezoelectric material is polarized along the thickness direction, the conformal piezoelectric oscillator is concentrated in the thickness capability mode, and the shear strain is zero. Therefore: S4=S5=S6=0 (3) The electrode layer uniformly covers the upper and lower end faces of the conformal piezoelectric oscillator. Since there is no electric field or electric displacement in the transverse or shear directions, then: E1=E2=D1=D2=0(4) The piezoelectric unit cell, composed of piezoelectric material and rigid polymer, exhibits significant symmetry in the xoy plane, with equal transverse strains S1 and S2, i.e.: S1 = S2 (5) Step 4: Substitute equations (3) to (5) into equations (1) and (2) respectively and simplify to obtain equations (6) and (7): In equations (6) and (7), the superscript c represents the piezoelectric material phase and e represents the rigid polymer phase; Step 5: In the z-direction, the piezoelectric material phase and the rigid polymer phase are connected in parallel. The vertical strain of the piezoelectric element is equal to the vertical strain of its internal components, while the vertical stress of the piezoelectric element is influenced by both the piezoelectric material phase and the rigid polymer phase. Therefore: The vertical electric field of the piezoelectric element is the same as that of the internal components. The overall vertical electric displacement of the oscillator is influenced by both the piezoelectric material phase and the rigid polymer phase. Therefore: In equations (8) and (9), the superscript m represents the piezoelectric element, v c and v e V represents the volume fraction of the piezoelectric material and the rigid polymer in the piezoelectric unit, respectively. e =1-v c ; Step six: In both the x and y directions, the piezoelectric material phase and the rigid polymer phase are connected in series. The transverse stress of the piezoelectric element is equal to the transverse stress of its internal components. The transverse strain of the piezoelectric element is influenced by both the piezoelectric material phase and the rigid polymer phase. Therefore: Step 7: After transforming equations (6) and (7) into matrix equations with T1, S3, and E3 as independent variables and S1, T3, and D3 as dependent variables, and then according to the relationship between equations (8) to (10), we get: In the above formula (11), a ij The following relationship exists: (i,j=1,2,3) Step 8: Transform equation (11) into the standard e-type piezoelectric equation according to equation (1), then: In the above formula (12), Step nine: In the y-direction, the piezoelectric element and the flexible polymer form a 2-2 composite structure, under which the electroelastic parameters satisfy the following relationship: In equations (13) to (15), the superscript n represents the conformable piezoelectric oscillator, the superscript s represents the flexible polymer phase, v1 represents the volume fraction of the conformable piezoelectric oscillator occupied by the piezoelectric element, and v s This indicates the volume fraction of the flexible polymer in the conformable piezoelectric oscillator; Step 10: Substitute the parameters from equations (13) to (15) into equation (16) to solve for the electromechanical coupling coefficient k of the piezoelectric oscillator. t ; Step 11: Solve equation (16) to obtain the highest electromechanical coupling coefficient k. t v under the condition c And v1, finally a specific structural dimension of a nested composite conformal piezoelectric oscillator is obtained; the width of the piezoelectric pillar in the piezoelectric unit is a, the width of the rigid polymer is b, the width of the flexible polymer is c, the number of long sides of the piezoelectric pillar array in each piezoelectric unit is q, and the number of short sides is w, then the volume fraction v of the piezoelectric material in the piezoelectric unit is... c And the volume fraction v1 of the coherent piezoelectric oscillator occupied by the piezoelectric element are respectively:

8. A method for preparing a nested composite conformal piezoelectric oscillator as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: Includes the following steps, Step 1: Prepare a primary cutting skeleton; Fix a piece of piezoelectric material of appropriate size on the sample stage of the cutting machine, set the cutting parameters to make the cutting blade cut evenly in the transverse direction, and ensure that the piezoelectric material is not cut through, thus forming a primary cutting skeleton; Step 2: Injecting rigid polymer material; prepare a certain mass of rigid polymer liquid and inject it into the cut of the first-cut skeleton, vacuum and cure at room temperature for 24 hours to form; furthermore, the rigid polymer needs to be prepared with a softener and a curing agent in proportion to ensure that the piezoelectric element has good compressive strength; Step 3: Prepare the secondary cutting skeleton; grind the surface of the skeleton product with rigid polymer poured in Step 2 with a grinding disc to remove impurities from the rigid polymer, so that the sample surface is flat and smooth, and then fix it on the sample stage of the cutting machine again; set the cutting parameters so that the cutting blade cuts the sample longitudinally to form the secondary cutting skeleton; furthermore, the cutting step must be strictly set during cutting to ensure that the length and width of the piezoelectric column are consistent, and at the same time ensure that the longitudinal cutting depth and the transverse cutting depth are completely consistent. Step 4: Infuse rigid polymer material; Take the secondary cut skeleton, infuse rigid polymer material using the same method as in Step 2, vacuum and cure at room temperature for 24 hours to set the shape, forming several piezoelectric unit structures composed of piezoelectric material and rigid polymer. Step 5: Prepare the three-stage cutting skeleton; grind the surface of the skeleton product with rigid polymer poured in Step 4 with a grinding disc to remove residual epoxy resin impurities and then fix it on the sample stage of the cutting machine; set the cutting parameters and adjust the cutting position in the cutting machine operation interface so that the cutting blade cuts off the piezoelectric material in the gap of the piezoelectric unit to make the three-stage cutting skeleton. Step 6: Infuse flexible polymer material; Take the skeleton cut three times, fill its interior with flexible polymer material, vacuum and cure at room temperature for 24 hours to make a nested composite piezoelectric oscillator; Step 7: Grind the piezoelectric vibrator substrate; Grind the upper and lower surfaces of the nested composite piezoelectric vibrator from Step 6 until smooth, place it with the substrate facing up on the sample stage of the cutting machine, and set the cutting parameters to grind the piezoelectric vibrator substrate. Step 8: Prepare the electrode layer; Take the piezoelectric oscillator after polishing the substrate, clean the impurities on its upper and lower surfaces, and then plate the electrodes to complete the preparation of a nested composite conformal piezoelectric oscillator; The electrode layer includes the upper and lower end faces of the piezoelectric oscillator. After preparation, the surface resistance of the electrodes needs to be tested with a multimeter to ensure that it is controlled within 1.0Ω; If the top electrode of the electrode layer is an array electrode, a mask template with a hollow array needs to be prefabricated. During electrode preparation, ensure that the hollow part is completely attached to the piezoelectric element part.

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