RU2686492C1 - Sensitive element from connectivity piezocomposite 1-3 and method of its production - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: group of inventions relates to piezoelectric transducers of ceramic-polymer type with cohesion of 1–3 and can be used to increase receiving sensitivity of hydroacoustic antennae. Sensitive element from connectivity piezocomposite 1–3 comprises rods made of lead-zirconate-titanate-based piezoelectric material having longitudinal polarization arranged uniformly in polymer matrix and provided on electrodes with ends, wherein polymer matrix is made of mixture in equal-volume ratio of polyurethane and hollow ceramic balls uniformly distributed throughout matrix volume, and the matrix and the piezoceramic rods are located between the in-series current-conducting grid and the thin elastic plates of the material having Young's modulus value of not less than 2.5⋅10⁹ Pa, wherein electrodes of rods, mesh and plate are rigidly glued to each other, and current conducting grid and electrodes are electrically connected.

EFFECT: technical result is increased sensitivity of sensing element from connectivity piezocomposite 1–3.

7 cl, 6 dwg, 1 tbl

Description

The invention relates to the design of the sensitive element and the method of its manufacture from a composite piezomaterial of connectivity 1-3 [1] for piezoelectric transducers, which are designed to create both single sonar receivers and multielement sonar antennas operating in receive mode.

Piezocomposites of connectivity 1-3 are a two-phase system in which the structural elements of one of the components form a monolithic system, called a matrix, and the structural elements of the second component are polarized piezoceramic rods of square or circular cross section immersed in it and in parallel. Such structures are called matrix. In this case, the matrix is characterized by three dimensions, and the active element, made of a monolithic piezoelectric ceramic material, has the form of an extended thin rod, characterized by one dimension. Piezocomposite connectivity 1-3 is characterized by a number of properties that are not present in any single component [2].

For obtaining piezocomposites of connectivity 1-3 on the basis of piezoceramics, over the past three decades, various methods have been proposed and tested [3, 4]. The first attempts to create piezocomposites of connectivity 1-3 were concluded in the use of coarse-grained powder of ferroelectric solid solution Pb (Zr, Ti) O ₃ and polyurethane. The average grain size of such a powder was approximately equal to the thickness of the composite sample, which facilitated its further polarization in an external electric field. Later, a powder with grains in the shape of a sphere or disks was used, and these grains filled the polymer medium, creating a continuous distribution in one direction. Subsequently, a method was proposed for immersion in the polymer matrix of a system of ceramic rods fixed in a special holder. In an improved form, this method, called “pick and place”, was used to obtain piezocomposites of connectivity 1–3 “ferro piezo ceramics - polymer” with different volumetric concentrations of ceramic rods, as well as with different microgeometry corresponding to the size of rods, their spatial distribution, cross-sectional shape, etc.

In the prior art a method of obtaining a block piezocomposite of connectivity 1-3 for low-frequency sensors operating in the frequency range up to 100 kHz [5]. The structure of the sensitive element of the piezocomposite of connectivity 1-3 contains active elements in the form of two blocks of piezoceramic rods installed oppositely to the end and having a counter polarization direction. At the ends of piezoceramic rods, electrodes with current leads are applied. The blocks of piezoceramic rods are immersed in a dielectric matrix.

The main advantages of using piezocomposites as a sensitive element of hydroacoustic receivers are based on the following considerations.

A hydroacoustic receiver is a device that converts the acoustic pressure P (acting on the receiver from all sides) into an electrical voltage U that occurs at the electrical output of the receiver. It is obvious that the sonar receiver is the better, the higher its sensitivity - M _u , equal to

Consider piezoelectric elements made of classical monolithic piezoceramics, for example, from the PTS system piezoelectric material, which is characterized by g ₃₃ piezo-constants (piezo-constant in the direction of polarization) and g ₃₁ (piezo-constant in the direction perpendicular to polarization). If this piezoelectric element is exposed to the all-round acoustic pressure P, then its sensitivity will be directly proportional to the size of the volume piezoelectric constant g _v .

Since for all modern monolithic piezomaterials g ₃₃ ≈ –2g ₃₁ , then g _v → 0. Thus, a sound receiver made of monolithic piezoelectric ceramics will have sensitivity M _u → 0. Therefore, all sonar receivers contain additional structural units that provide such acoustic shielding of the piezoelectric element, in which the piezoelectric element is exposed to acoustic effects only in one particular direction, for example, in the direction of polarization. In this case, the sensitivity of the sound receiver is determined only by the constant g ₃₃ , since g _v = g ₃₃ .

It is obvious that such sound receivers have a complex structure, which can be greatly simplified by using as a basis a sensitive element made of piezocomposite material in which the g ₃₁ piezoconstant is suppressed due to the combined properties of the matrix and the piezo element. Therefore, the main characteristic piezocomposites 1-3 connectivity for manufacturing transducers operating at low frequency, is the volume of the composite piezoelectric constant g _v, mV⋅m / H. [6].

The designs of sensitive elements of hydroacoustic transducers with a high value of the longitudinal piezoelectric constant g ₃₃ , with structurally suppressed transverse component g ₃₁ , in which the active component is made of a monolithic piezoelectric ceramic material, are widely known [7]. However, the volumetric sensitivity of sensitive elements of hydroacoustic transducers based on monolithic piezoelectric materials as shown above has low values. The possibilities of further increasing the sensitivity of sensitive elements of hydroacoustic transducers based on monolithic piezoelectric materials are limited.

Promising for the creation of sensitive elements of hydroacoustic transducers are piezocomposites of connectivity 1-3, which have longitudinal sensitivity with strongly suppressed transverse sensitivity, which ensures a high volumetric piezoelectric constant g _v .

When designing piezoelectric transducers, the most widely used piezocomposites of connectivity are 1-3, in which the following piezoceramic materials are used as the piezoelectric component: barium titanate, lead titanate, lead zirconate titanate, magnesium niobate, lead zirconate, zinc niobate, lithium niobate, lithium tantalate, lithium tantalate. bismuth strontium calcium, and as a binder, various organic polymeric materials [8].

A piezo-composite of connections 1-3 is known, containing damping particles in the binder composition, in which piezo-active components (rods) are evenly spaced [6, 9]. Piezoelectric rods are obtained either by injection molding, or by sawing a piezo-ceramic block. Piezocomposite connectivity 1-3 is obtained by subsequent filling of the block, consisting of ceramic rods, liquid reactive polymer, in particular, epoxy polymer, which has a low viscosity in the uncured state, high adhesive and mechanical properties.

However, the curing of epoxy resins leads to shrinkage of the polymer matrix and the occurrence of internal stresses. This can lead to a prestressing of the active component of the piezocomposite of connectivity 1-3, distortion of the rods, reduction of parallelism between the sides of the rods, and as a result, distortion of the system.

Part of the solution to this problem is achieved by incorporating particles of cement and graphite into the polymer matrix, which contributes to the increase in the viscoelastic and damping properties of the polymer matrix [10]. The sensing element from the piezoelectric composite of connectivity 1-3 and the method of its manufacture, described in article [10], are taken as the prototype of the present invention.

The active component of the piezocomposite of connectivity 1-3 has the form of rods made of a piezoelectric material PZT (PZT), having a longitudinal polarization and evenly spaced in an epoxy resin polymer matrix with inclusions of particles of cement and graphite. The piezoelectric, electromechanical, and damping properties of the piezo-composite of connectivity 1-3 were investigated. High values of the piezoelectric constant g ₃₃ = 13.3 mV⋅m / N were obtained, the values of which are approximately equal to the volume piezoelectric constant g _v , since g _v = g ₃₃ -2g ₃₁ , and the values of the transverse piezoelectric constant g ₃₁ = 0 [6].

However, the prototype has not sufficiently high values of bulk piezoelectric constant g _v, mV⋅m / H, which is necessary for efficient operation of hydroacoustic transducers in receiving mode.

The present invention is to develop a sensitive element from a piezocomposite of connectivity 1-3, having high values of the volume piezoconstant g _v mV m / N and a sufficiently high strength for operation at great depths.

The task is solved by achieving new technical results:

- the creation under the influence of external pressure in the monolithic piezoceramic rods of additional transverse mechanical stresses;

- increase the longitudinal mechanical stretching / compression of piezoceramic rods under the influence of external pressure;

- increase the stiffness and decrease the speed of the acoustic wave in the polymer matrix;

- increase mechanical strength.

These technical results are achieved by the fact that the sensitive element from the piezocomposite of connectivity 1-3 contains rods made of piezoelectric material based on lead zirconate titanate (PZT), having longitudinal polarization and located evenly in a polymer matrix with hollow ceramic balls and fitted with electrodes at the ends .

According to the invention, conductive grids are successively glued to the ends of the piezoceramic rods, which allow to avoid large local stresses at the point of contact of the piezoceramic rod and, as a consequence, loss of electrical contact, and thin elastic plates made of a material that has a Young's modulus of at least 2.5⋅10 ⁹ Pa, Young's modulus for the material of the plates is chosen experimentally on the basis of flexibility and strength under static compression, and the conductive grids and electrodes are electrically connected.

In the particular case of execution:

- elastic plates are made of polymethyl methacrylate with a Young's modulus of 3⋅10 ⁹ Pa;

- elastic plates have a thickness of 0.5-0.7 mm.

The method of obtaining the sensitive element from the piezocomposite of connectivity 1-3 consists in sintering the piezoceramic block from the PTS system piezoelectric material with subsequent sawing into thin square rods, applying electrodes of the piezoceramic rods to the ends, polarizing and placing the piezoceramic rods in the polymer matrix.

According to the invention, a polymer matrix is prefabricated; to do this, liquid polyurethane with the addition of hollow ceramic balls in an equal ratio by volume is poured into the mold for manufacturing a matrix having a specified distribution of holes in the matrix volume corresponding to the geometry of the piezoceramic rods, insert the piezoceramic rods into the holes of the polymer matrix, solder the conductive grids with the current to the electrodes of the piezoceramic rods by conclusions, a thin elastic plate with a Young's modulus of elasticity of not less than 2.510 ⁹ Pa is glued to the surface of each conductive mesh, the resulting blank of the piezoelectric composite is placed in a mold, filled with liquid polyurethane and held until the end of polymerization.

In the particular case of execution:

- thin rods have a cross section equal to (4.5 × 4.5) mm;

- the number of piezoceramic rods is nine;

- piezoceramic rods are polarized in air at a voltage of 1 kV / mm.

This new sequence of operations of the method allows for the polarization and rejection of piezoceramic rods by electrophysical parameters before being placed in a polymer matrix, which increases the yield of suitable products.

The presence of hollow ceramic balls in the polymer matrix leads to an increase in its rigidity and prevents the acoustic impact on the piezoceramic rods in the direction perpendicular to polarization. Consequently, the proposed polymer matrix provides acoustic shielding of the side surfaces of the piezoceramic rods, thereby performing the function of additional acoustic screens of classical sound receivers.

In the prototype, the polymer matrix has inclusions of graphite and cement, which contribute to an increase in the propagation speed of the acoustic wave in the transverse direction and do not suppress the acoustic impact on the lateral surfaces of the piezoelectric cores.

When external pressure P is applied to the sensitive element of the piezocomposite of connection 1-3 along the direction of polarization of the piezoceramic rods, which are the active component, thin elastic plates that have a Young's modulus of at least 2.5-10 ⁹ Pa in the areas between the piezoceramic rods bend towards each other other, which leads to the appearance in the plates in the areas mated with the piezoceramic rods, additional mechanical stresses aimed at stretching the elastic plates, and, consequently, rigidly fastened by gluing with them piezoceramic rods in the direction perpendicular to the polarization and the effect of pressure P (see Fig. 5). Thus, the proposed design of the sensing element provides a simultaneous effect on the piezoceramic rods of the superposition of two components of mechanical stresses, which are squeezing in the direction of polarization, and stretching in the perpendicular direction. Therefore, equation (2) for the proposed piezoceramic composition takes the form:

Considering that for piezostama of the PZT system, the piezoconstants g ₃₃ and g ₃₁ have different signs, the change in the sign of mechanical stress in the proposed piezocomposite in the direction perpendicular to polarization (not compression, but stretching) in accordance with equation (3) leads to a significant increase in g _v , and hence the volumetric sensitivity of the hydroacoustic receiver as a whole. After the cessation of exposure to acoustic pressure, the elastic plates take on their original shape.

The thickness range of thin elastic plates is 0.5-0.7 mm, which is optimal for providing a combination of sufficient strength and weight of a sensitive element made from a piezo-composite.

Known piezocomposite converter connectivity 1-3 for hydroacoustic antennas operating in surface Arctic waters. On one surface of each piezoelectric transducer there is a steel protective layer, and on the other surface there is a matching layer of glass polymer [11, paragraphs 10-35 of the patent description]. In contrast to [11], the claimed converter, due to the presence of identical elastic plates with the specified characteristics from two sides, ensures the operability of the sensitive element in the sensors at a depth of 5 km and simultaneously leads to an increase in volumetric sensitivity, which does not follow from [11] and is obvious from the prior art. In this case, the function of the matching layer is performed by the polyurethane body of the piezoelectric transducer, and not by a special matching layer in the form of a plate made of glass polymer.

Brief Description of the Drawings

FIG. 1 - Piezocomposite with connectivity 1-3, in a perspective view - the prototype.

FIG. 2 - The inventive sensitive element of the piezocomposite connection 1-3, side view.

FIG. 3 - The inventive sensitive element of the piezocomposite connection 1-3, top view.

FIG. 4 - Form for the manufacture of the polymer matrix, top view.

FIG. 5 - Deformation scheme of the inventive sensitive element from a piezocomposite of connectivity 1-3 under the influence of acoustic longitudinal pressure P, where F is the force that stretches the piezoceramic rods, which are the active component, in the transverse direction.

FIG. 6 is a diagram of the deformation of a sensitive element from a piezocomposite of connectivity 1-3 under the influence of acoustic longitudinal pressure P in the absence of thin elastic plates.

The implementation of the invention

The sensing element of the piezocomposite connectivity 1-3 (Fig. 2) contains a block of piezoceramic rods 1, which are the active component, evenly located in the polymer matrix 2, made of polyurethane with the addition of hollow ceramic balls in an equal volume ratio. At the ends of the piezoceramic rods 1, the silver paste was applied by applying the electrodes 3, 4 soldered to conductive grids 5, 6 with current leads 7, 8, respectively. Thin elastic plates 9, 10 with a Young's modulus of elasticity of at least 2.5⋅10 ⁹ Pa are glued to the surfaces of each conductive mesh 5, 6, and the whole structure is covered with a polyurethane sheath 11, which serves as a matching layer.

When external pressure P (Fig. 5) is applied to a sensitive element from a piezocomposite of connectivity 1-3 along the direction of polarization of piezoceramic rods, thin elastic plates 9 and 10 bend towards each other, and a force F arises, which leads to additional pressure on the ends of the piezoelectric rods 1, which leads to stretching of the piezoceramic rods 1 in the transverse direction. In the absence of thin elastic plates 9, 10 additional pressure on the ends of the piezoceramic rods does not occur (Fig. 6).

An example of a specific implementation of the method of manufacturing a sensitive element of the piezoelectric composite connectivity 1-3.

The piezoceramic block from the PZT-19 material was sawn on a cutting machine into rods with dimensions (4.5 × 4.5 × 7.5) mm, at the ends of which silver electrodes were applied using silver paste paste. The polarization of the samples was carried out in the air at the PVA-2 polarization unit (manufactured by the Piezopribor NKTB SFU) at a voltage of 1 kV / mm and a temperature of 360 ° C. A polymer matrix was prepared by adding ceramic hollow spheres with a particle size of 120 μm to an equal volume ratio of liquid polyurethane of the brand Germokast 7980285.

Liquid polyurethane with ceramic hollow balls was poured into a mold with a hole profile 12 of rectangular cross section (Fig. 4), corresponding to the thickness of piezoceramic rods 1 and kept at room temperature for 12 hours until complete polymerization. The obtained polymer matrix 2 was uniformly filled with piezoceramic rods 1. Then, a conductive grid 6 with current terminal 8 was soldered to the positive electrodes of the piezoelectric rod 1, and a conductive grid 5 was soldered to the negative electrodes of piezoceramic rods 1 with adhesive terminal 7. BF-2 in one thin elastic plate 9, 10 made of a material with a Young's modulus not less than 2.5⋅10 ⁹ Pa. In the particular case of making thin elastic plates 9, 10 are made of polymethyl methacrylate and have a thickness of 0.5 mm. The resulting design was placed in a mold and poured with liquid polyurethane brand Hermokast 7980285.

On the installation for measuring the volumetric sensitivity of the Pascal-4 piezoelectric elements, the manufacturer of the Piezopribor NPTB, Rostov-on-Don, was measured for the voltage sensitivity M _u . The values of the volume piezoelectric constant g _{v were} calculated by the formula:

g _v = M _u / h,

where M _u is the voltage sensitivity, µV / Pa;

h is the distance between the electrodes of the active component of the sensitive element of the piezoelectric composite equal to 7.5 mm.

Comparative data for the piezoelectric constant g _v mV⋅m / N, the electromechanical coupling coefficient k _t of the longitudinal piezoelectric modulus d ₃₃ values and the dielectric loss tangent of the angle tgδ active component of the sensor element 1-3 piezocomposite connected as a percentage of the values of the prototype (Line 1), the claimed of a sensitive element from a piezoelectric composite of connectivity 1-3 (line 2) and a sensitive element of a piezocomposite of connectivity 1-3 without dielectric plates at the ends of piezoceramic rods made of piezoceramics with iem longitudinal piezoelectric modulus d ₃₃ = 500 pC / N. (line 3) are given in the table.

As follows from the table, the volumetric sensitivity value of the inventive sensitive element from the piezocomposite of connectivity 1-3 (line 2) is g _v = 20 mV мm / H, which is 1.5 times higher than that of the prototype (line 1), which has g _v = g ₃₃ = 13.3 mV⋅m / H. The value g _v = 16.8 mV⋅m / H was obtained for a sensitive element from a piezocomposite of connectivity 1–3 without thin elastic plates 9, 10 at the ends of piezoceramic rods (line 3), which confirms their influence on the increase in piezo-sensitivity. At lower values of the longitudinal piezoelectric modulus d _{33 of the} active component (d ₃₃ = 500 pC / H) compared with the prototype (d ₃₃ = 600 pC / H), higher values of g _v were obtained. An experimental sample of the inventive sensitive element from a piezocomposite of connectivity 1-3 has been developed.

Information sources

1. R.Е. Newnham, D.P. Skinner, and L.E. Cross, "Connectivity and piezoelectric-pyroelectric composites," MaterialcRes. Bull., Vol. 13, pp. 525-536, 1978.

2. Modeling 1-3 Composite Piezoelectrics: Thickness-Mode Oscillations. W. Smith and B. Auld, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS AND FREQUENCY CONTROL. Vol. 38. NO. I. JANUARY 1991.

3. FABRICATION OF PIEZOELECTRIC CERAMIC / POLYMER COMPOSITES BY INJECTION MOLDING, Leslie J. Bowen and Kenneth W. French, Materials Systems Inc. 53 Hillcrest Road, Concord, MA 01742.

4. US 5539965 A, Method for making piezoelectric composites.

5. Method for making an acoustic transducer. WO 2007012604 (A2), IPC B06B 1/06, H01L 41/37, publ. 2007-02-01.

6. V.Yu. Topolov, A.E. Panin. Piezocomposites: obtaining, properties, application (training manual), Rostov-on-Don, 2009, p. 43.

7. RU 2080743 C1, IPC ⁶ H04R 1/44, published: 05/27/1997.

8. WO 2011005535 (A1) 2011-01-13 CERAMIC-POLYMER COMPOSITES A61L 27/40; A61L 31/12; C04B 35/117; C04B 35/185; C08J 5/24; C09K 8/58; C09K 8/80; H01L 41/18.

and G. Hayward, "Investigation into the effects of modification of the passive phase of improved manufacture of 1-3 connectivity piezocomposite transducers," IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 46, pp. 511-516, 1999.9. Piezoelectric Composites for Sensor and Actuator Applications. E. Koray Akdogan et al. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency control, vol. 52, no. 5, may 2005, 756) [2], (RL

and G. Hayward, "Investigation of the transient transducers," IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol. 46, pp. 511-516, 1999.

10. Design, fabrication and property of the cement / polymer based 1-3 connectivity piezo-damping composites. Xu Dongyu, Cheng Xin, Guo Xiaojing, Huang Shifeng. Conduction and Building Materials 84 (2015) 219-223. Journal homepage: www.elsevier.com/locate/conbuildmat - prototype.

11. US 6806622 (B1) - 2004-10-19, Impact-reinforced piezocomposite transducer array, B06B 1/06; G10K 11/00; H04R 17/00; H04R 1/44; (IPC1-7): H01L 41/04.

Claims (7)

1. The sensing element from the piezoelectric composite connectivity 1-3. containing rods made of piezoelectric material based on lead zirconate titanate (PZT), having longitudinal polarization, located evenly in the polymer matrix and provided with electrodes at the ends, characterized in that the polymer matrix is made of a mixture in an equal ratio of polyurethane and hollow ceramic balls uniformly distributed throughout the matrix, and the matrix and piezoceramic rods are located between the successively installed conductive grid and thin elastic plates Astinas from a material with a Young's modulus of at least 2.5⋅10 ⁹ Pa, with the rod electrodes, grid and plate rigidly glued to each other, and the conductive grid and electrodes are electrically connected. 2. The sensing element according to claim 1, characterized in that the elastic plates are made of polymethyl methacrylate. 3. The sensing element according to p. 1, characterized in that the elastic plates have a thickness of 0.5-0.7 mm. 4. A method of obtaining a sensitive element from a piezocomposite of connectivity 1-3, which consists in sintering a piezoceramic block from a PTS piezo material with subsequent sawing into thin square rods, applying to the ends of piezoceramic rods of electrodes and polarization, placing piezoceramic rods in a polymer matrix, different that the polymer matrix is made of a uniform mixture of polyurethane and hollow ceramic balls in an equal ratio by volume, for this purpose in the mold for izgoto Matrix having a specified distribution in the matrix of holes corresponding to the geometric dimensions of the piezoceramic rods, pour the mixture and maintain the resulting composition until the end of polymerization, insert the piezoceramic rods into the holes of the polymer matrix, solder the grids with current leads to the electrodes of the piezoceramic rods, then assemble the resulting electrodes between the piezoceramic rods thin elastic plates, pre-applied to the contacting surface of the grids and plates of cells Eve layer, after which the resulting package is maintained under conditions suitable for the closure process of forming the desired mechanical properties of the adhesive layer, and the resulting preform is set in a form to fill the sensing element, is filled with liquid polyurethane and is maintained until the end of the polymerization process. 5. The method according to p. 4, characterized in that the thin rods have a cross section equal to (4.5 × 4.5) mm. 6. The method according to p. 4, characterized in that the number of piezoceramic rods is nine. 7. The method according to p. 4, characterized in that the piezoceramic rods are polarized in air at a voltage of 1 kV / mm.

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