A piezoelectric stack point focusing transducer

Abstract

The present invention provides a piezoelectric stack point focusing transducer, including a truncated cone wedge, a backing sound absorbing layer, a protective shell and a plurality of piezoelectric stack composite material sensing units; the truncated cone wedge is inverted in the protective shell, the backing sound absorbing layer is arranged between the large end surface of the truncated cone wedge and the top wall of the protective shell, a plurality of the piezoelectric stack composite material sensing units are evenly distributed on the side of the truncated cone wedge along the circumferential direction, and the piezoelectric stack composite material sensing unit is formed by connecting a plurality of layers of piezoelectric elements and a plurality of layers of epoxy resin in parallel. The present invention realizes multi-point focusing of ultrasonic beams through physical focusing based on truncated cone wedges, excites ultrasonic beams with high energy, and has a good focusing function on the beams, thereby improving the energy utilization rate, and utilizes the orthogonal anisotropy of the piezoelectric stack composite material sensing unit to enhance the signal in the length direction, weaken the signal in the width direction, and effectively suppress the interference caused by the complex resonance frequency of the signal.

Description

Technical Field

[0001] The invention relates to the field of nondestructive testing of block structures, and in particular to a piezoelectric stack point focusing transducer. Background Art

[0002] Research and development of structural health diagnostic technology is of great significance for the safe operation and maintenance of facilities. Compared with other conventional non-destructive testing methods, acoustic emission technology has the advantages of real-time dynamics and wide coverage. Piezoelectric composite materials are obtained by complementing the advantages of piezoelectric phase and polymer phase to obtain materials with strong piezoelectricity and good toughness. Piezoelectric transducers designed based on piezoelectric composite materials are increasingly widely used in structural non-destructive testing in mechanical engineering, civil engineering and other fields.

[0003] However, when traditional focused transducers are used for acoustic emission detection or health monitoring, there are problems such as narrow signal resonance frequency and low energy conversion rate. They do not have the ability to measure stress in a specific direction and stress wave driving and sensing, which brings certain difficulties to the extraction of effective structural damage characteristic information. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a piezoelectric stack point focusing transducer to solve the problems of narrow signal resonance frequency and low energy conversion rate in the current focusing transducer.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A piezoelectric stack point focusing transducer for block structure damage detection, comprising a truncated cone wedge, a backing sound absorbing layer, a protective shell and a plurality of piezoelectric stack composite material sensing units;

[0007] The truncated cone wedge is inverted in the protective shell, the backing sound absorption layer is arranged between the large end surface of the truncated cone wedge and the top wall of the protective shell, and a plurality of piezoelectric stack composite material sensing units are evenly distributed on the side of the truncated cone wedge along the circumferential direction. The piezoelectric stack composite material sensing unit includes a plurality of layers of piezoelectric elements and a plurality of layers of epoxy resin, and the plurality of layers of piezoelectric elements and the plurality of layers of epoxy resin are connected in parallel.

[0008] Furthermore, the matrix material phase of the piezoelectric stack composite material sensing unit includes two epoxy resin polymers, wherein the epoxy resin polymer used as an electrode is epoxy conductive glue, and the epoxy resin polymer used as a non-conductive material is epoxy resin.

[0009] Furthermore, the piezoelectric element of the piezoelectric stack composite material sensor unit is a PZT-5 type piezoelectric ceramic.

[0010] Furthermore, the number of the piezoelectric stack composite material sensing units is three.

[0011] Furthermore, the large end surface of the frustum cone wedge is serrated.

[0012] Furthermore, the backing sound absorbing layer is made of epoxy resin and tungsten powder, wherein the mass ratio of the epoxy resin to the tungsten powder is 1:1.

[0013] Furthermore, the protective shell includes a top wall, a bottom wall and side walls, the bottom wall is made of organic glass, and the top wall and side walls are made of metal.

[0014] Furthermore, the thickness of the bottom wall is 200 μm.

[0015] Furthermore, the material of the frustum cone wedge is aluminum.

[0016] Furthermore, the total displacement of the piezoelectric stack composite material sensing unit is:

[0017]

[0018] Where n is the number of piezoelectric element layers; δ is the total displacement of the piezoelectric stack composite sensor unit; δ i is the displacement of each piezoelectric element; U is the driving voltage value applied to the piezoelectric element; d 33 is the piezoelectric strain constant; F is the force on the piezoelectric element; k i is the stiffness of the piezoelectric film; K 0 is the equivalent static stiffness of the piezoelectric element, K 0 =k i / n;d 0 is the equivalent piezoelectric constant, d = nd 33 .

[0019] Beneficial effects of the present invention:

[0020] The present invention realizes multi-point focusing of ultrasonic beams through physical focusing based on truncated cone wedges, excites high-energy ultrasonic beams, and has a good focusing function on the beams, thereby improving energy utilization. The orthogonality of the piezoelectric stack composite material sensing unit is used to enhance the signal in the polarization direction and weaken the signal in the width direction, thereby having the ability to drive and sense stress and stress waves in specific directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a piezoelectric stack point focusing transducer according to an embodiment of the present invention Figure 1 ;

[0022] Figure 2 A schematic diagram of a piezoelectric stack point focusing transducer according to an embodiment of the present invention Figure 2 ;

[0023] Reference numerals:

[0024] 1: wire and interface; 2: backing sound absorption layer; 3: protective shell; 301: bottom wall; 4: truncated cone wedge; 5: piezoelectric stack composite material sensor unit. DETAILED DESCRIPTION

[0025] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0026] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0027] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] The following first describes in detail the piezoelectric stack point focusing transducer according to an embodiment of the present invention in conjunction with the accompanying drawings, which is used for block structure damage detection, including a truncated cone wedge 4, a backing sound absorbing layer 2, a protective shell 3 and a plurality of piezoelectric stack composite material sensing units 5;

[0029] The frustum of cone wedge 4 is inverted in the protective shell 3, the large end face of the frustum of cone wedge 4 is located at the top, and the small end face of the frustum of cone wedge 4 is located at the bottom, the backing sound absorption layer 2 is arranged between the large end face of the frustum of cone wedge 4 and the top wall of the protective shell 3, and a plurality of piezoelectric stack composite material sensing units 5 are evenly distributed on the side of the frustum of cone wedge 4 along the circumferential direction, and the piezoelectric stack composite material sensing units include a plurality of layers of piezoelectric elements and a plurality of layers of epoxy resin, and the plurality of layers of piezoelectric elements and the plurality of layers of epoxy resin are connected in parallel.

[0030] Furthermore, the matrix material phase of the piezoelectric stack composite material sensor unit 5 includes two epoxy resin polymers, wherein the epoxy resin polymer used as the electrode is epoxy conductive glue, with a room temperature shear strength of 14.7Mpa and a volume resistivity of ≤1.0×10-3Ω·cm. The non-conductive epoxy resin polymer is epoxy resin, with an elastic modulus Ep=3.5GPa

[0031] Furthermore, in this embodiment, the piezoelectric stack composite material sensing unit 5 includes 32 layers of piezoelectric elements. The piezoelectric elements are PZT-5 type piezoelectric ceramics with dual functions of sensing and driving, and the elastic modulus Ec33=117 GPa.

[0032] Furthermore, for a sensing unit composed of n piezoelectric elements with the same geometric and physical parameters, under ideal conditions and the same voltage drive, there is no energy loss between the piezoelectric elements, and their output displacement à and phase are the same. Therefore, the total displacement output of the sensing unit can be considered as the linear superposition of the output displacements of each piezoelectric element. Therefore, the total displacement of the piezoelectric stack composite material sensing unit 5 in this embodiment is:

[0033]

[0034] Where n is the number of piezoelectric element layers; δ is the total displacement of the piezoelectric stack composite sensor unit 5; δ i is the displacement of each piezoelectric element; U is the driving voltage value applied to the piezoelectric element; d 33 is the piezoelectric strain constant; F is the force on the piezoelectric element; k i is the stiffness of the piezoelectric film; K 0 is the equivalent static stiffness of the piezoelectric element, K 0 =k i / n;d 0 is the equivalent piezoelectric constant, d = nd 33 .

[0035] Furthermore, in the present embodiment, there are three piezoelectric stack composite material sensing units 5, which are equally spaced and attached to the side of the truncated cone wedge 4 by epoxy resin to form the main part of the transducer, thereby realizing three-point focusing of the ultrasonic beam, and reducing the interference of the back-reflected wave through the filtering effect of the piezoelectric composite material array element, and efficiently acquiring the reflected wave signal with wide bandwidth and concentrated energy, thereby integrating driving and sensing to realize high-sensitivity excitation and receiving functions.

[0036] Furthermore, the material of the truncated cone wedge 4 is aluminum, with a density of 2700 kg / m 3 , the elastic modulus is 6.8×10 10 N / m 2 , Poisson's ratio is 0.32. The large end surface of the truncated cone wedge 4 is serrated, which can reduce the interference of the reflected wave on the sensor unit.

[0037] Furthermore, the backing sound absorbing layer 2 is made of epoxy resin and tungsten powder, wherein the mass ratio of epoxy resin to tungsten powder is 1: 1. Epoxy resin has a strong sound absorption capacity, which can cause the reverse radiated sound waves to be scattered randomly around the backing material particles, so that part of the energy is converted into heat energy dissipation.

[0038] Furthermore, the protective shell 3 includes a top wall, a bottom wall 301 and side walls. The bottom wall 301 is made of organic glass with a thickness of 200 μm. It has good impedance matching with the transducer body and can reduce energy loss. The top wall and side walls are made of metal to provide necessary protection for the main body.

[0039] The piezoelectric stack point focusing transducer of the embodiment of the present invention is bonded to the block to be tested by using a butter coupling agent, which can provide multiple tests and facilitate the adjustment of the test position.

[0040] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0041] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A piezoelectric stack point focusing transducer for block structure damage detection, characterized in that: It comprises a truncated cone wedge (4), a backing sound absorbing layer (2), a protective shell (3) and a plurality of piezoelectric stack composite material sensing units (5); The truncated cone wedge (4) is inverted in the protective shell (3), the backing sound absorption layer (2) is arranged between the large end surface of the truncated cone wedge (4) and the top wall of the protective shell (3), the large end surface of the truncated cone wedge (4) is serrated, and a plurality of piezoelectric stack composite material sensing units (5) are evenly distributed on the side of the truncated cone wedge (4) along the circumferential direction, and the piezoelectric stack composite material sensing units (5) include a plurality of layers of piezoelectric elements and a plurality of layers of epoxy resin, and the plurality of layers of piezoelectric elements and the plurality of layers of epoxy resin are connected in parallel.

2. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The matrix material phase of the piezoelectric stack composite material sensing unit (5) comprises two epoxy resin polymers, wherein the epoxy resin polymer used as an electrode is epoxy conductive glue, and the epoxy resin polymer used as a non-conductive material is epoxy resin.

3. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The piezoelectric element of the piezoelectric stack composite material sensing unit (5) is a PZT-5 type piezoelectric ceramic.

4. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The number of the piezoelectric stack composite material sensing units (5) is three.

5. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The backing sound absorbing layer (2) is made of epoxy resin and tungsten powder, and the mass ratio of the epoxy resin to the tungsten powder is 1:

1.

6. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The protective shell (3) comprises a top wall, a bottom wall (301) and side walls; the bottom wall (301) is made of organic glass, and the top wall and side walls are made of metal.

7. The piezoelectric stack point focusing transducer according to claim 6, characterized in that: The thickness of the bottom wall is 200 μm.

8. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The material of the truncated cone wedge (4) is aluminum.

9. The piezoelectric stack point focusing transducer according to claim 1, characterized in that: The total displacement of the piezoelectric stack composite material sensing unit (5) is: Where n is the number of piezoelectric element layers; δ is the total displacement of the piezoelectric stack composite sensor unit (5); δ i is the displacement of each piezoelectric element; U is the driving voltage value applied to the piezoelectric element; d 33 is the piezoelectric strain constant; F is the force on the piezoelectric element; k i is the stiffness of the piezoelectric sheet; K0 is the equivalent static stiffness of the piezoelectric element, K0 = k i / n; d0 is the equivalent piezoelectric constant, d = nd 33 .

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