AU2021100869A4

AU2021100869A4 - A Type of Sensitive Element Used for Manufacturing a High-sensitivity Underwater Acoustic Transducer and its Preparation Method

Info

Publication number: AU2021100869A4
Application number: AU2021100869A
Authority: AU
Inventors: Qiguo HUANG; Hongwei Wang
Original assignee: Beijing Information Science And Technology Univ; Beijing Information Science and Technology University
Current assignee: Beijing Information Science and Technology University
Priority date: 2021-02-12
Filing date: 2021-02-12
Publication date: 2021-05-06
Anticipated expiration: 2029-02-12

Abstract

The present invention relates to a type of sensitive element used for manufacturing a high sensitivity underwater acoustic transducer and its preparation method. The sensitive element consists of a piezoelectric small column array with substrate, and a metal plate fixedly installed on the upper surface of the piezoelectric small column array; and the gaps between the piezoelectric small columns in the said piezoelectric small column array are filled with air. The preparation method consists of: cutting the piezoelectric material pieces along the X direction; cutting the piezoelectric material pieces along the Y direction, and thus, form a piezoelectric small column array with substrate; in addition, there is a metal plate is bonded on the upper surface of the piezoelectric small column array. Therefore, an underwater acoustic transducer can be further manufactured by using this sensitive element. The present invention replaces the polymer filled in the piezoelectric material with air, and covers metal plate on the upper surface at the same time, and thus, can effectively improve the electromechanical coupling coefficient and the receiving sensitivity. Drawings of Descriptions Metal Plate 1 IICeramic Substrate Air Gap X Electrode Ceramic Small Column Figure 1 z Z x X Piezoelectric Ceramic Piece (a) (b) Metal Plate Z X~ 010ICeramic Substrate ~Air- Gap Ceramic Substrate Ceramic Small Column Electrode Ceramic Small Column (c) (d) Figure 2 1/5

Description

Drawings of Descriptions

Metal Plate

1 IICeramic Substrate Air Gap

X Electrode Ceramic Small Column

Figure 1

z Z

x X Piezoelectric Ceramic Piece

(a) (b) Metal Plate

Z

X~ 010ICeramic Substrate ~Air- Gap

Ceramic Substrate Ceramic Small Column Electrode Ceramic Small Column

(c) (d)

Figure 2

1/5

Descriptions A Type of Sensitive Element Used for Manufacturing a High-sensitivity Underwater Acoustic Transducer and its Preparation Method

Technical Field

[0001] The present invention belongs to the technical field of piezoelectric material and underwater acoustic transducer, particularly relates to a type of sensitive element, which is made of piezoelectric materials and air, used for manufacturing a high-sensitivity underwater acoustic transducer and its preparation method.

Background Technology

[0002] Currently, various researches on underwater acoustic transducer mainly focus on following aspects: (1) further reduce the operating frequency (which is mainly aims at low-frequency transducers), and increase the transmitting sound power, so that extent the propagation distance for emitting and receiving sound wave by the transducer. (2) Expand the operation bandwidth of the transducer. (3) Improve the sensitivity of the transducer, i.e., improve the performance of electromechanical conversion of the transducer, that is, improve the transmitting voltage response and receiving sensitivity. In view of this, the ability of the transducer to emit sound waves can be enhanced through improving the transmitting voltage response, and the ability to detect weak signals (such as silent submarines) can be enhanced through improving the receiving sensitivity as well.

[0003] To improve the sensitivity of the transducer is mainly by means of improving the efficiency of electromechanical conversion of the transducer. The transmitting voltage response and receiving sensitivity of the transducer reflect the level of efficiency of electromechanical conversion. The efficiency of electromechanical conversion is in direct proportion to the square of the electromechanical coupling coefficient, and the improved efficiency of electromechanical conversion will be ultimately translated into the increase of the electromechanical coupling coefficient. Increasing the electromechanical coupling coefficient is the eternal goal for the research on the transducer, and is also the difficulty existed in studies of transducer in the world. For all materials, the electromechanical coupling coefficient k33 of the longitudinal stretching vibration mode is greater than the electromechanical coupling coefficient kt of the thickness vibration mode. Therefore, if the thickness vibration mode of the piezoelectric material can be converted into the longitudinal stretching vibration mode, the electromechanical coupling coefficient will be increased accordingly. The researchers realized that the vibration mode of the piezoelectric material inside the composite material is the main factor affecting the properties of the composite material. For example, the 1-3 type of piezoelectric composite material improves the property by converting the thickness vibration of the whole piece of piezoelectric material into the longitudinal stretching vibration of lots of piezoelectric small columns. Furthermore, after changing the vibration mode of the material, the electromechanical coupling coefficient of equivalent thickness of the 1-3 type of piezoelectric composite material can be increased by about 20% than the electromechanical coupling coefficient of the thickness of the pure piezoelectric material. Through researches on various composite materials, due to such materials have the characteristics of simple preparation process, strong piezoelectricity, and large electromechanical coupling coefficient, the public basically tends to use 1-3 type and 1-3-2 type of piezoelectric composite materials. In conclusion, the thickness vibration mode of the piezoelectric material can be transformed into the longitudinal stretching vibration mode of the piezoelectric small column through the composite material, and thus increase the electromechanical coupling coefficient, so that improve the sensitivity of the transducer.

Summary of the Invention

[0004] The purpose of the present invention is to provide a type of sensitive element used for manufacturing a high-sensitivity planar underwater acoustic transducer and its preparation method. In addition, how to increase the electromechanical coupling coefficient and improve the sensitivity of the transducer are the main problems studied in the present invention.

[0005] The technical scheme adopted by the present invention is as follows:

[0006] A type of sensitive element used for manufacturing a high-sensitivity underwater acoustic transducer, which consists of a piezoelectric small column array with substrate, and a metal plate fixedly installed on the upper surface of the piezoelectric small column array; and the gaps between the piezoelectric small columns in the said piezoelectric small column array are filled with air.

[0007] Further, the piezoelectric material used in the said piezoelectric small column array with substrate is piezoelectric ceramic or piezoelectric single crystal.

[0008] Further, the shape of the said piezoelectric small column array with substrate and the said metal plate is one of the following: square, rectangle or circle.

[0009] Further, there are electrodes are plated on the lower surface of the said substrate.

[0010] A kind of method for preparing the said sensitive element for manufacturing a high-sensitivity underwater acoustic transducer, which consists of following steps:

[0011] Cut the piezoelectric material pieces which have been plated with electrodes on the upper and lower surfaces and polarized in the thickness direction along the X direction;

[0012] Cut the piezoelectric material pieces along the Y direction, and thus, form a piezoelectric small column array with substrate;

[0013] There is a metal plate (such as a copper plate) is bonded on the upper surface of the piezoelectric small column array.

[0014] A type of underwater acoustic transducer, which consists of sensitive element for manufacturing a high-sensitivity underwater acoustic transducer, and there are electrode leads are led out from the upper and lower surfaces of the said sensitive element, and there are acoustic absorption layer and metal back cover plate are bonded on the lower surface (i.e., the reverse side) of the said sensitive element, as well as there is a waterproof acoustically transparent layer is equipped outside the said sensitive element, the acoustic absorption layer and the metal back cover plate.

[0015] Further, the said acoustic absorption layer is a kind of rigid foam, and the material of the said metal back cover plate is stainless steel.

[0016] Further, the said waterproof acoustically transparent layer is formed after glue sealing and curing by polyurethane.

[0017] The present invention replaces the polymer filled in the piezoelectric small column with air, and thus, can effectively improve the electromechanical coupling coefficient and the receiving sensitivity, which has advantages and beneficial effects of:

[0018] (1) From macroscopical view, it can avoid the existence of non-thickness vibration mode of the whole piece of material, and thus, makes the thickness vibration mode of the whole piece of material simple, and increases the effective electromechanical coupling coefficient.

[0019] (2) The thickness vibration of the whole piece of material composed of piezoelectric small columns is translated into a kind of collective behavior of the longitudinal vibration of the piezoelectric small columns, i.e., the electromechanical coupling coefficient of the piezoelectric material is changed from kt to k33, and thus, increases the electromechanical coupling coefficient, so that improves the transmitting voltage response and receiving sensitivity of the transducer.

[0020] (3) The sound pressure in the sound field is transmitted to the piezoelectric

small column through the metal plate on the upper surface, and thus plays a role of stress amplification as well as further improves the receiving sensitivity of the transducer.

[0021] The transducer of the present invention is conducive to improving the detecting

precision of high-frequency sonar, especially the receiving sensitivity of receiving sonar.

Brief Description of the Drawings

[0022] Figure 1 is a schematic diagram of the structure of "piezoelectric small column

array with substrate + metal plate".

[0023] Figure 2 is a schematic diagram of the preparation process of the sensitive element

with the structure of "piezoelectric small column array with substrate + metal plate".

[0024] Figure 3 is a schematic diagram of the packaging structure of the transducer.

[0025] Figure 4 is a 1/4 structure chart of a piezoelectric small column unit.

[0026] Figure 5 is a conductance curve graph of the structure of piezoelectric small

column array with cooper cover plate.

[0027] Figure 6 is a vibration displacement diagram of the structure of piezoelectric

small column array structure with a metal plate at the position of resonance, wherein, figure (a) is the case where the vibration phase angle 0 is 00, and figure (b) is the case where the vibration phase angle 0 is 180 °.

[0028] Figure 7 is a graph of the transmitting voltage response and receiving sensitivity

of the transducer with the structure of "PZT small column array with epoxy resin", wherein, figure (a) is the transmitting voltage response, and figure (b) is the receiving sensitivity.

[0029] Figure 8 is a graph of the transmitting voltage response and receiving sensitivity

of the transducer with the structure of "PZT small column array without polymer", wherein, figure (a) is the transmitting voltage response, and figure (b) is the receiving sensitivity.

Detailed Description of the Presently Preferred Embodiments

[0030] For the purpose of making the abovesaid objects, characteristics, and advantages of the present invention clearer and easy to understand, the text below will further describe the present invention in detail through specific embodiments and drawings.

[0031] The present invention develops a type of high-sensitivity planar underwater

acoustic transducer, which has main characteristic of high-sensitivity. High-sensitivity is realized through increasing the electromechanical coupling coefficient and stress amplification effect.

[0032] The sensitivity of transducer refers to transmitting voltage response in terms of the

transmitting transducer, and refers to receiving sensitivity in terms of the receiving transducer. The improvement of sensitivity can be realized by increasing the electromechanical coupling coefficient. In addition, in terms of the receiving transducer, stress amplification can also improve the receiving sensitivity. The present invention adopts the structure of "piezoelectric small column array with substrate + metal plate" as the sensitive element. Wherein, the piezoelectric material used in the structure of piezoelectric small column array with substrate can be piezoelectric ceramic (such as PZT), piezoelectric single crystal, and so on. The text below will mainly take piezoelectric ceramic as an example to illustrate.

[0033] 1. The structure of the sensitive element: piezoelectric small column array with

substrate + metal plate

[0034] Figure 1 is a schematic diagram of the sensitive element with the structure of "piezoelectric small column array with substrate + metal plate". Such structure consists of piezoelectric small columns with substrate formed by vertically cutting piezoelectric ceramic, and the gaps of the piezoelectric small columns are filled with air instead of polymer, as well as there is a metal plate is bonded on the piezoelectric small columns, and there are electrodes are plated on the bottom surface of substrate of the piezoelectric ceramic.

[0035] The characteristics of such structure of "piezoelectric small column array with

substrate + metal plate" are:

[0036] 1) Adopt the structure of piezoelectric small column array without polymer, and thus can increase the electromechanical coupling coefficient.

[0037] People usually get used to preparing 1-3 type of piezoelectric composite

materials through the method of cutting piezoelectric materials and pouring polymers (such as epoxy resins), which transforms the thickness vibration mode of piezoelectric materials into the longitudinal stretching vibration of the piezoelectric small columns, and thus, increases the electromechanical coupling coefficient. However, due to the addition of polymers, results in the increase of wastage and is prejudicial to the increase of electromechanical coupling coefficient at the same time. The structure of "piezoelectric small column array without polymer" of the present invention replaces air with polymer to fill the gaps of the piezoelectric small columns, so that can completely highlight the longitudinal vibration behavior of the piezoelectric small columns, and thus, translate the thickness vibration of the piezoelectric material into the longitudinal vibration behavior of the piezoelectric small column to a greater extent, so that maximize the electromechanical coupling coefficient.

[0038] The structure of "piezoelectric small column array with substrate + metal plate" is an improvement based upon the 1-3-2 type of composite materials (i.e., remove the polymer part of the 1-3-2 type of piezoelectric composite materials), which reflects the d33 vibration mode of the piezoelectric small column array, and thus obtains a high electromechanical coupling coefficient; on the one hand, the electromechanical coupling coefficient of the piezoelectric material is changed from kt to k33, and thus improves the electromechanical coupling coefficient; on the other hand, it removes the horizontal coupling between the piezoelectric small columns, and thus makes the thickness vibration mode of the whole piece of material simple, and increases the effective electromechanical coupling coefficient.

[0039]2) The metal plate can transmit the sound pressure from the sound field to each

piezoelectric small column, and thus increase stress inside the piezoelectric small column, so that plays a role of stress amplification as well as improves the receiving sensitivity of transducing material through the stress amplification effect of the piezoelectric small column. That is, in terms of the receiving transducer, the receiving sensitivity can be improved through stress amplification. In addition, the metal plate can also play a role of frame support.

[0040] It should be noted that the shape of the structure of "piezoelectric small column array with substrate + metal plate" (from the top view) is not limited to the square displayed in Figure 1, which can also be rectangle, circle, or the like. The text below will mainly take the square structure shown in Figure 1 as an example to illustrate.

[0041]2. The preparation method of sensitive element

[0042] Figure 2 is a schematic diagram of the preparation process of the sensitive element with the aforesaid structure of "piezoelectric small column array with substrate + metal plate", which consists of following steps:

[0043] 1) Obtain a piezoelectric ceramic piece, as shown in Figure 2 (a); and the piezoelectric ceramic piece is a piezoelectric ceramic piece which has been plated with electrodes on the upper and lower surfaces and polarized in the thickness direction;

[0044]2) Cut the piezoelectric ceramic piece along the X direction, as shown in Figure 2 (b) after cutting;

[0045]3) Cut the piezoelectric ceramic piece along the Y direction to form a square small column array of piezoelectric material with substrate, as shown in Figure 2 (c);

[0046] 4) Bond a metal plate on the piezoelectric small column (the thickness of the metal plate is much smaller than the wavelength of the sound wave, the more the Young's modulus of the metal plate, the better, the smaller the density, the better) to form the structure of "piezoelectric small column array with substrate + metal plate", as shown in Figure 2 (d).

[0047] 3. The integral packaging of the transducer

[0048] The packaging structure of the transducer prepared by using the sensitive element with the aforesaid structure of "piezoelectric small column array with substrate + metal plate" is shown in Figure 3. The electrodes plated on the upper and lower surfaces of the sensitive element (the upper surface uses the metal layer as the electrode, and there is electrode is plated on the lower surface) lead out the electrode leads, and then bond with the rigid foam (acoustic absorption layer) and the metal back cover plate, after that, complete glue-sealing with polyurethane, and thus form a waterproof acoustically transparent layer after curing to complete the manufacture of the transducer. Then, place the transducer in an anechoic tank, and conduct whole performance test (including the transmitting voltage response, receiving sensitivity, bandwidth, and directivity of the transducer, etc.) according to relevant standards.

[0049]4. Feasibility analysis and experimental test

[0050] 1) The feasibility of using the structure of "piezoelectric small column array with

substrate + metal plate" to improve the sensitivity

[0051] The receiving sensitivity of the transducer can be improved by means of stress

amplification. As shown in Figure 4, the sound pressure from the sound field, i.e., the intensity of pressure applied on the upper surface of the sensitive element is p, and the longitudinal stress on the piezoelectric small column is T 3 , in addition, due to the metal plate is very thin (the thickness of the metal plate is much smaller than the wavelength of the sound wave in the metal plate), the sound pressure p acts on the piezoelectric small column through the metal plate, and the stress applied on the piezoelectric small column can be approximated as:

[0052] T W22 3 P W,

[0053] In the formula, w and wi represent the widths of the array unit and the

piezoelectric small column respectively.

[0054] The stress acting on the piezoelectric small column is greater than the sound

pressure in the external sound field, and the electric field generated by the mechanical electric coupling on the piezoelectric small column becomes larger, and thus, makes the voltage between the upper and lower plates become larger, so that improves the receiving sensitivity of the transducing material.

[0055] Using the g-type piezoelectric equation:

[0056] E3 = -gT+ p3D3

[0057] In the formula, E3 represents the electric field intensity along the lengthwise direction of the piezoelectric small column, g33 represents the piezoelectric (the stiffness)

constant, A3 represents the dielectric impermeability under constant stress, and D 3 represents the electric displacement along the lengthwise direction of the piezoelectric small column. In the case of only taking stress into consideration, E3=-g33T3, and thus, the voltage generated on the piezoelectric small column is:

[0058] V=-g33T3hi

[0059] In the formula, hi represents the height of the small column, and h represents the

height of the piezoelectric material (substrate + piezoelectric small column), and the 2 w receiving sensitivity of the transducer is improved by about times.

[0060] Therefore, the receiving sensitivity of the transducer is improved by the metal plate.

[0061]2) The performance test and comparison of transducer

[0062] In this embodiment, the PZT-5A piezoelectric ceramic material is cut to obtain

the structure of piezoelectric small column array with substrate, and then, bonds the metal copper plate and the cut piezoelectric ceramic small column array together with conductive adhesive, and thus, obtains the structure of PZT small column array with copper cover plate. After that, using impedance analysis meter and laser vibrometer respectively to test the components with structure of "PZT small column array with copper cover plate", and the test results are shown in Figures 5 and 6. It can be seen from the conductance curve of Figure 5 that the resonance frequency is 175kHz; furthermore, the vibration displacement graph of Figure 6 (in the figure, the 0 represents the vibration phase angle) shows that the entire copper cover plate vibrates up and down in unison during resonance.

[0063] The present invention manufactured the transducer with the structure of "PZT

small column array with substrate + metal plate without polymer" and the transducer with the structure of "PZT small column array with substrate + metal plate with polymer" in the same size. Transducer, and the transmitting voltage response and receiving sensitivity of which were tested in an anechoic tank respectively. Figure 7 shows the transmitting voltage response (figure (a)) and the receiving sensitivity (figure (b)) of the transducer with the structure of "PZT small column array with substrate +

metal plate with polymer", and Figure 8 shows the transmitting voltage response (figure (a)) and the receiving sensitivity (figure (b)) of the transducer with the structure of "PZT small column array with substrate + metal plate without polymer".

[0064] In Figure 7, the transmitting voltage response of the transducer with the structure

of "PZT small column array with substrate + metal plate with polymer" reaches 157dB and the receiving sensitivity reaches -195dB. In Figure 8, the transmitting voltage response of the transducer with the structure of "PZT small column array with substrate + metal plate without polymer" reaches 163dB, which increases 6dB, and the receiving sensitivity reaches -169dB, which increases 26dB. It shows that the performance of the transducer with the structure of "PZT small column array with substrate + metal plate without polymer" is superior to that of the transducer with the structure of "PZT small column array with substrate + metal plate with polymer".

[0065] In conclusion, the characteristics and innovations of the present invention mainly

consist of:

[0066] 1) Replacing air with polymer to fill the gaps of the piezoelectric small columns,

so that can completely highlight the longitudinal vibration behavior of the piezoelectric small columns, and thus increase the electromechanical coupling coefficient.

[0067] 2) The stress of the piezoelectric small column is amplified by the metal cover

plate to improve the receiving sensitivity of the transducer.

[0068] 3) Adopting the structure of "piezoelectric small column array with substrate

+ metal plate", and thus can obtain larger electromechanical coupling coefficient and higher receiving sensitivity.

[0069] The above embodiments are only used to illustrate the technical scheme of the present invention rather than limiting it. Those skilled in the art can modify or equivalently replace the technical scheme of the present invention without deviating from the principle and scope of the present invention. The scope of protection of the present invention shall be subject to the descriptions of claims.

Claims

1. A type of sensitive element used for manufacturing a high-sensitivity underwater acoustic transducer, characterized in that consisting of a piezoelectric small column array with substrate, and a metal plate fixedly installed on the upper surface of the piezoelectric small column array; and the gaps between the piezoelectric small columns in the said piezoelectric small column array are filled with air.

2. The said sensitive element according to Claim 1, characterized in that the piezoelectric material used in the said piezoelectric small column array with substrate is piezoelectric ceramic or piezoelectric single crystal.

3. The said sensitive element according to Claim 1, characterized in that the shape of the said piezoelectric small column array with substrate and the said metal plate is one of the following: square, rectangle or circle.

4. The said sensitive element according to Claim 1, characterized in that there are electrodes are plated on the lower surface of the said substrate.

5. A kind of method for preparing the sensitive element for manufacturing a high sensitivity underwater acoustic transducer described in Claim 1, characterized in that consisting of following steps: Cut the piezoelectric material pieces which have been plated with electrodes on the upper and lower surfaces and polarized in the thickness direction along the X direction; Cut the piezoelectric material pieces along the Y direction, and thus, form a piezoelectric small column array with substrate; In addition, there is a metal plate is bonded on the upper surface of the piezoelectric small column array.

6. The said method according to Claim 5, characterized in that further consisting of steps of plating electrodes on the lower surface of the substrate.

7. The said method according to Claim 5, characterized in that the said piezoelectric material is piezoelectric ceramic or piezoelectric single crystal.

8. A type of underwater acoustic transducer, characterized in that consisting of the sensitive element for manufacturing a high-sensitivity underwater acoustic transducer described in any one of Claims 1 to 4, and there are electrode leads are led out from the upper and lower surfaces of the said sensitive element, and there are acoustic absorption layer and metal back cover plate are bonded on the lower surface of the said sensitive element, as well as there is a waterproof acoustically transparent layer is equipped outside the said sensitive element, the acoustic absorption layer and the metal back cover plate.

9. The said underwater acoustic transducer according to Claim 8, characterized in that the said acoustic absorption layer is a kind of rigid foam, and the material of the said metal back cover plate is stainless steel.

10. The said underwater acoustic transducer according to Claim 8, characterized in that the said waterproof acoustically transparent layer is formed after glue-sealing and curing by polyurethane.