CN205958518U - A piezoelectric transducer that is used for pipeline supersound guided wave to detect a flaw - Google Patents

Abstract

The utility model discloses a piezoelectric transducer used for ultrasonic guided wave flaw detection of pipelines. In the piezoelectric transducer of the present invention, the upper surfaces of n curved surface transducer plate units are evenly bonded to the lower surface of the flexible base, the upper surface of each curved surface transducer plate unit is a plane, and the lower surface is a curved surface, as The working surface is close to the outer surface of the tested pipeline, and n parallel curved surface transducer units surround the outer surface of the tested pipeline; the zero-order torsional guided wave T(0 , 1); The piezoelectric transducer proposed by the utility model has high energy conversion efficiency, small size and compact size, and can be directly attached to the surface of the pipeline, which is very suitable for pipeline health monitoring. It can be predicted that the utility model will strongly promote the Development of guided waves for pipeline health monitoring.

Description

A Piezoelectric Transducer Used in Pipeline Ultrasonic Guided Wave Flaw Detection

technical field

The utility model relates to intelligent material and structural health monitoring technology, in particular to a piezoelectric transducer used for ultrasonic guided wave flaw detection of pipelines.

Background technique

As an important means of transportation, pipelines play an irreplaceable role in petroleum, chemical and other fields. By the end of 2013, my country had built more than 60,000 kilometers of natural gas pipelines, more than 26,000 kilometers of crude oil pipelines, and more than 20,000 kilometers of refined oil pipelines. Pipelines have become important infrastructure related to the lifeline of the national economy. In recent years, due to corrosion, accidental damage, wear and other factors, pipeline safety accidents at home and abroad have occurred frequently, resulting in huge loss of life and property. Therefore, the detection and evaluation of pipeline integrity is of great significance. The non-destructive testing method based on ultrasonic guided waves has become an important technical method for pipeline integrity testing because of its long detection distance and low cost. At present, the pipeline inspection technology based on ultrasonic guided waves is still mainly in the laboratory research stage, and there are not many instruments and systems that can be used for actual industrial pipeline inspection. One of the main reasons is that the ducted guided wave has complex characteristics of multi-mode and high-frequency dispersion. Taking an aluminum tube with an outer diameter of 100mm and a wall thickness of 3mm as an example, in the range of 0kHz to 200kHz, there are more than 50 guided wave modes propagating along the axial direction. Each frequency corresponds to more than two guided wave modes. If the single-mode guided wave cannot be excited, it will be difficult to identify the echo information related to the defect from many guided waves. On the other hand, except for the zero-order torsional guided wave T(0, 1), all ducted guided waves have serious dispersion characteristics, that is, the wave velocity changes with frequency. Since most guided waves are excited by special waveforms modulated by window functions, the dispersion characteristics make the shape of the excitation signal distorted as the wave propagation distance increases, and the amplitude of the guided waves decays rapidly, making it difficult to achieve long-distance detection. Therefore, how to excite single-mode and non-dispersive guided waves is the core issue of pipeline guided wave detection.

The longitudinal mode guided wave L(0,2) is the most widely studied and relatively mature guided wave mode because it is easy to excite and has small dispersion in a certain frequency range. However, due to the radial displacement of the longitudinal guided wave mode, when there is liquid inside or outside the pipe, part of the guided wave energy will leak into the liquid, which seriously affects the detection distance. Compared with the longitudinal mode guided wave L(0,2), the zero-order torsional guided wave T(0,1) has obvious advantages. The zero-order torsional guided wave T(0,1) is the only non-dispersive guided wave mode in the pipeline. At the same time, since the zero-order torsional guided wave T(0,1) has only tangential displacement, and the liquid cannot bear shear, the energy of the guided wave will not leak into the liquid transported by the pipeline. Therefore, the zero-order torsional guided wave T(0,1) has an important application prospect in the field of pipeline integrity detection. However, there are still very few transducers that can excite single-mode zero-order torsional guided waves T(0,1), which greatly limits the application of T(0,1) guided waves in pipeline integrity testing. At present, two types of torsional guided wave transducers have been proposed successively, and commercial applications have been successfully realized. One type is an electromagnetic ultrasonic transducer (U.S. Pat. No. 6429650B1) developed by the Southwest Research Institute (Southwest Research Institute). The transducer passes an alternating current through the coil to form an alternating magnetic field, and the alternating magnetic field induces deformation of the ferromagnetic material through the magnetostrictive effect, thereby forming a guided wave in the pipeline. However, the electromagnetic ultrasonic transducer needs to apply a strong bias magnetic field, so the volume of the transducer is relatively large. In addition, the energy conversion efficiency of the electromagnetic ultrasonic transducer is low, which requires a strong excitation source to improve the signal-to-noise ratio. The above factors make electromagnetic ultrasonic transducers only suitable for non-destructive testing and not suitable for structural health monitoring. Another type is the dry-coupled piezoelectric transducer developed by Imperial College of Technology (A. Demma, P. Cawly and M. Lowe, The reflection of the fundamental torsional mode from cracks and notches in pipes, J. Acoust . Soc. Am. 114(2), 2003). China National Offshore Oil Corporation and other units have also developed similar dry-coupled piezoelectric transducers (ZL 201010605979.7). The dry-coupled piezoelectric transducer achieves excitation and reception of torsional guided waves by arranging thickness-shear piezoelectric sheets circumferentially. However, the deformation of the thickness-shear piezoelectric transducer tends to be simple shear when no pressure is applied, so the shear deformation is difficult to be effectively transmitted to the pipeline. The pressurizing device makes the volume of the dry-coupled piezoelectric transducer larger. On the other hand, the thickness-shear piezoelectric transducer has a high resonant frequency, usually much higher than the excitation frequency of the guided wave, so the transducer cannot be excited near the resonant frequency to improve energy conversion efficiency. The above two points make the dry-coupled piezoelectric transducer only suitable for non-destructive testing of pipelines but not for health monitoring of pipelines.

Compared with pipeline non-destructive testing, pipeline health monitoring technology can predict the safety status of pipelines in real time, and can save manpower and time costs at the same time, so it is currently a research hotspot and trend in the field of pipeline integrity testing at home and abroad. Therefore, it is urgent to develop transducers suitable for pipeline health monitoring. Faxin Li's research group at Peking University recently developed a new in-plane shear piezoelectric transducer (ZL 201620284659.9), which can excite a single-mode horizontal shear guided wave mode (SH0) in a flat plate structure. , but not suitable for direct use in pipelines, the transducer is small in size and high in energy conversion efficiency, so it is suitable for structural health inspection. Since the horizontal shear guided wave mode (SH0) in the flat plate structure is similar to the zero-order torsional guided wave mode (T(0,1)) in the pipe, it is hopeful to develop a suitable Torsional guided wave piezoelectric transducers for pipeline health monitoring, and then promote the development of pipeline health monitoring.

Utility model content

Aiming at the current lack of guided wave transducers suitable for pipeline health monitoring, this utility model proposes a piezoelectric transducer that can excite and receive single-mode zero-order torsional guided waves T(0,1) in pipelines. The transducer has the characteristics of light weight, small size and high energy conversion efficiency, which is suitable for pipeline health monitoring.

The piezoelectric transducer used for pipeline ultrasonic guided wave flaw detection of the utility model includes: n curved surface transducer plate units and a flexible base; wherein, the upper surface of each curved surface transducer plate unit is a plane, bonded on a flexible The surface of the substrate, the shape of the upper surface of the curved transducer plate unit is rectangular, and the four sides are perpendicular to the upper surface; the lower surface of the curved transducer plate unit is a curved surface, and the projection of the curved surface along the thickness direction is congruent with the upper surface, and the curved surface The curvature is consistent with the curvature of the outer surface of the pipeline under test, and the lower surface is used as the working surface; the curved transducer plate unit is made of polarized piezoelectric material, and the polarization direction is along the chord length direction of the working surface, with a piezoelectric coefficient d24; The two opposite sides parallel to the polarization direction are electrode surfaces; the upper surfaces of the n curved transducer plate units are evenly bonded to the lower surface of the flexible substrate, and the polarization directions of the n curved transducer plate units are aligned in the same direction; The electrode surfaces on the same side of n curved surface transducer board units are respectively electrically connected to an electrode column by a wire, so that n curved surface transducer board units are connected in parallel; the working surface of each curved surface transducer board unit is close to the pipeline under test The outer surface of the flexible base, the n curved surface transducer plate units evenly distributed on the lower surface of the flexible base are evenly distributed along the outer surface of the pipeline under test, and circle around the outer surface of the pipeline under test; the two sides of the flexible base Each end is provided with a snap-lock mechanism, and the two ends of the flexible substrate are connected and fixed by the snap-lock mechanism, so that the piezoelectric transducer forms an integral ring and is fixed on the outer surface of the pipeline under test, and n is a natural number ≥ 2.

The piezoelectric transducer is used as a brake to excite the ultrasonic guided wave of the pipeline under test, or as a sensor to receive the ultrasonic guided wave of the pipeline under test; when used as a brake, the excitation signal sent by the signal generator is amplified by the power amplifier and connected to two electrodes The column excites n curved surface transducing plate units at the same time, through the d24 mode of the inverse pressure point effect, the in-plane shear deformation is generated on the working surface, and the load is applied to the measured pipeline to excite the ultrasonic guided wave; when used as a sensor, the measured pipeline The ultrasonic guided wave causes the in-plane shear deformation of the working surface of each curved transducer plate unit, so that the electric displacement is formed on the electrode surface through the d24 mode of the positive piezoelectric effect, and the n parallel curved surface transducer plate units average the signal Finally, it is connected to the preamplifier through two electrode columns for amplification, and is transmitted to the signal processing and analysis system through the data acquisition digital analog A/D card.

The upper surface of the curved transducer plate unit is rectangular, the length of the side along the length direction of the flexible substrate is the long side a, the length of the side along the width direction of the flexible substrate is the short side b, and the minimum thickness of the curved transducer plate unit is the working surface The distance from the highest point of the upper surface to the upper surface is h, satisfying

The length of the flexible substrate is L, the width is W, and the thickness is H, satisfying b≤W≤4b, 0.1h≤H≤4h. The length of the flexible base is equal to the outer circumference of the pipeline under test, and the flexible base has a certain degree of elasticity, so that the n curved surface transducer plate units can tightly surround the outer surface of the pipeline under test through a snap-lock mechanism.

The piezoelectric material of the curved surface transducer plate unit is PZT ceramics, ferroelectric ceramics or ferroelectric piezoelectric single crystal; if ceramics are used, the remanent polarization should reach the maximum value during polarization; Electric single crystal, it should be ensured that it has a large piezoelectric coefficient d24 when it is polarized. The flexible base adopts low elastic modulus, high elastic material, such as rubber.

When the piezoelectric transducer is used as a brake to excite the ultrasonic guided wave, the signal generator generates the excitation signal modulated by the window function. The center frequency of the signal is f ₀ , and the signal frequency width is [f _min , f _max ]. This frequency band is called the working frequency band. In order to suppress the torsional wave of the high-order mode, f _max should be less than the first-order cut-off frequency of the torsional guided wave of the pipeline under test; in order to suppress the generation of bending wave within the frequency range, the number n of the curved transducer plate unit should be greater than the measured pipeline in [0 , f _max ] the highest circumferential order of the curved guided wave mode in the frequency range. The wave velocity of the torsional wave excited by the piezoelectric transducer is c _g , and the wavelength is λ=c _g /f ₀ . In order to make the piezoelectric transducer have higher energy conversion efficiency, the preferred short side b of the curved transducer plate unit satisfies: 0.25λ≤b≤0.6λ. A piezoelectric transducer that satisfies the above relationship can excite a single-mode zero-order torsional guided wave T(0,1) at the center frequency f ₀ of the working frequency band.

Similarly, when a piezoelectric transducer is used as a sensor to receive ultrasonic guided waves, the center frequency of the received signal is f ₀ , and the signal frequency width is [f _min , f _max ]. This frequency band is called the working frequency band. In order to suppress the torsional wave of the high-order mode, f _max should be less than the first-order cut-off frequency of the torsional guided wave of the pipeline under test; in order to suppress the generation of bending wave within the frequency range, the number n of the curved transducer plate unit should be greater than the measured pipeline in [0 , f _max ] the highest circumferential order of the curved guided wave mode in the frequency range. The velocity of the torsional wave received by the piezoelectric transducer is c _g , and the wavelength is λ=c _g /f ₀ . In order to make the piezoelectric transducer have higher energy conversion efficiency, the preferred short side b of the curved transducer plate unit satisfies: 0.25λ≤b≤0.6λ. A piezoelectric transducer that satisfies the above relationship can receive a single-mode zero-order torsional guided wave T(0,1) at the center frequency f ₀ of the working frequency band.

The piezoelectric transducer of the utility model can filter the bending guided wave mode at the center frequency f ₀ of the working frequency band, and only receive the twisted guided wave.

The principle that the piezoelectric transducer of the present invention is used as a brake to only excite the torsional guided wave T(0, 1) of a single mode is as follows: after the excitation transducer is installed on the pipeline to be tested, n curved surface transducer plate units along the The pipeline under test is evenly distributed in the circumferential direction; when n curved transducer plate units are excited by the AC signal at the same time, the curved surface transducer unit produces in-plane shear deformation on the working surface due to the d24 mode of the inverse piezoelectric effect. The measured pipeline forms a shear stress uniformly distributed along the circumferential direction; since the number of curved transducer plate units is greater than the highest circumferential order of the bending wave in the pipeline in the working frequency band, the gap between adjacent curved transducer plate units is smaller than the excited torsion The half-wavelength of the guided wave, so it can be approximated that the load imposed by the piezoelectric transducer on the pipeline under test is an axisymmetric load along the circumferential direction; the bending guided wave mode is a non-axisymmetric mode, so the axisymmetric load is not will excite the bending guided wave mode; on the other hand, the main displacement of the longitudinal axisymmetric guided wave is along the axial direction of the measured pipe, and there is no circumferential displacement, so the axisymmetric load along the circumferential direction will only excite the torsional guided wave; and The frequency of the excitation signal is below the first-order cut-off frequency of the torsional wave, so only the zero-order torsional wave T(0,1) of a single mode can be excited. In the same way, the principle that the piezoelectric transducer of the present invention is used as a sensor to only detect the zero-order torsional wave T(0,1) of a single mode is as follows: the received signal is in the working frequency band, and when the received signal is a torsional wave, the measured When there is a torsional wave in the pipeline, the torsional wave only has a displacement component along the circumferential direction of the tested pipeline, and is evenly distributed along the circumferential direction of the tested pipeline. The circumferential displacement component causes the in-plane Shear deformation, so that the electric displacement is formed on the electrode surface through the d24 mode of the positive piezoelectric effect; when there is a bending wave in the measured pipeline, although the bending wave contains a circumferential displacement component, it is unevenly distributed along the circumferential direction of the measured pipeline, Therefore, only a small part of the piezoelectric sheet of the transducer will form an electric displacement; since the circuits between the n curved surface transducer plate units are connected in parallel, the detected signal is actually approximately equal to the average of the n curved surface transducer plate unit signals, so The superimposed bending wave signal will be very weak, so as to realize the function of filtering bending wave.

Advantage of the utility model:

The utility model provides a piezoelectric transducer that can excite and receive a zero-order torsional guided wave T(0,1) of a single mode in the pipeline under test. The piezoelectric transducer proposed by the utility model has high energy conversion efficiency , Small in size and compact in size, can be directly attached to the surface of the pipeline, and is very suitable for pipeline health monitoring. It can be predicted that the utility model will effectively promote the development of pipeline health monitoring based on ultrasonic guided waves.

Description of drawings

Fig. 1 is the schematic diagram that the piezoelectric transducer of the present utility model is close on the pipeline under test, and wherein, (a) is the three-dimensional structure schematic diagram, (b) is the side view;

Fig. 2 is the schematic diagram of the curved surface transducer plate unit of the piezoelectric transducer of the present invention;

Fig. 3 is the expanded schematic diagram of the piezoelectric transducer of the present utility model;

Fig. 4 is the group velocity dispersion curve of the guided wave in the range of 0-250kHz for an aluminum tube with a wall thickness of 3mm and an outer diameter of 100mm;

Fig. 5 is the waveform structure diagram of zero-order torsional guided wave T (0,1);

Fig. 6 is that the embodiment one of piezoelectric transducer of the present utility model is 3mm in wall thickness as brake, and the aluminum tube center frequency that external diameter is 100mm is the experimental result of 150kHz signal excitation T (0,1);

Fig. 7 is the experimental result of the second embodiment of the piezoelectric transducer of the present invention as a sensor receiving ultrasonic guided waves, and the ultrasonic guided waves are excited by piezoelectric transducers with 12 curved surface transducer plate units, where (a) is There are only 12 piezoelectric transducers of curved surface transducing plate units as the waveform diagram received by the sensor, (b) is the waveform received by the piezoelectric transducer of 32 curved surface transducing plate units of the present utility model as the sensor picture.

detailed description

Below in conjunction with accompanying drawing, through specific embodiment, further set forth the utility model.

As shown in Figure 1, the piezoelectric transducer of the present embodiment comprises: n curved surface transducer plate units 15 and a flexible substrate 12; The surface of the n curved surface transducer plate units on the same side is electrically connected to an electrode column with a wire, so that the n curved surface transducer plate units connected in parallel are respectively connected to the positive electrode column 17 and the negative electrode 19 The working surface is close to the outer surface of the tested pipeline 10, and n curved surface transducer plate units are evenly distributed along the outer surface of the tested pipeline 10, and surround the outer surface of the tested pipeline for a week.

The number of curved surface transducer plate units is n, and n is greater than the highest circumferential order of the curved guided wave mode of the measured pipeline 10 within the [0,f _max ] frequency band. The length of the flexible base 12 is equal to the outer circumference of the pipe 10 to be tested.

As shown in FIG. 2 , the upper surface of the curved transducer plate unit 15 is flat and rectangular in shape; The lower surface is a working surface, which is closely attached to the outer surface of the pipeline 10 during operation. The projection of the working surface along the thickness direction of the transducer plate 15 is equal to the upper surface of the transducer plate 15, that is, the chord length of the working surface is equal to the side length a of the upper surface. The two opposite side surfaces of the curved transducer plate unit 15 that are parallel to the polarization direction and perpendicular to the upper surface are electrode surfaces.

Fig. 3 shows the expanded view of the piezoelectric transducer of the present invention. When the transducer is pasted on the pipeline 10, since the base 12 is a flexible material, it can be unfolded into a long strip. When the piezoelectric transducer needs to be closely attached to the pipeline under test 10, the flexible base 12 is connected end to end by a snap-lock mechanism 14, and the flexible base has elasticity, so that the piezoelectric transducer is sleeved on the pipeline under test 10, as shown in FIG. 1 Show. As can be seen from FIG. 3 , the curved transducer plate units are evenly distributed on the surface of the flexible substrate 12 , and the channel wires 18 realize the circuit parallel connection of the curved transducer plate units.

In order to further illustrate the advantages of the zero-order torsional wave T (0, 1) excited by the transducer of the present invention in the field of pipeline integrity detection, Fig. 4 shows that an aluminum tube with a wall thickness of 3 mm and an outer diameter of 100 mm is in the Group velocity dispersion diagram of an ultrasonic guided wave propagating axially along an aluminum tube from 0 to 250 kHz. It can be seen that there are three types of guided waves propagating along the axial direction in the pipeline under test: one is the axisymmetric longitudinal guided wave mode L(0, m), and m is the modulus of the guided wave (m=1,2 ,3,···), the other is the torsional axisymmetric torsional guided wave mode T(0, m), and the other is the non-axisymmetric curved guided wave mode F(N,m), where N is the guided wave mode Circumferential order of waves (N=1,2,3, . . . ). It can be seen that the zero-order torsional guided wave T(0, 1) is the only non-dispersive guided wave mode, that is, its wave velocity does not change with frequency. The non-dispersive characteristic of T(0, 1) can keep the excitation signal shape and propagation speed of the guided wave unchanged during the propagation process, thereby increasing the detection distance and reducing the difficulty of signal analysis. On the other hand, Fig. 5 shows the waveform structure diagram of the zero-order torsional guided wave T(0, 1). It can be seen that T(0,1) only has the component of circumferential displacement U _θ , since the liquid cannot withstand shear deformation, the energy of the torsional guided wave T(0,1) will not leak into the liquid, thus ensuring the detection distance , which makes T(0,1) very suitable for detecting pipelines transporting liquids. Further, Fig. 5 shows that the displacement component of the zero-order torsional guided wave T(0, 1) is almost uniformly distributed along the wall thickness of the tested pipe, which shows that the T(0, 1) wave has an impact on the surface and interior of the tested pipe The defects have the same detection sensitivity, thus ensuring that the defect detection is not affected by the position of the defect on the pipe wall.

Embodiment one

In order to further illustrate the effectiveness of the zero-order torsional guided wave T (0, 1) of the piezoelectric transducer of the present utility model to excite a single mode, a design is used to excite an aluminum tube with a wall thickness of 3 mm and an outer diameter of 100 mm. Zero-order torsional guided wave T(0,1) piezoelectric transducer. The design center frequency of the piezoelectric transducer is 150kHz, and the five-period sinusoidal signal modulated by the Hanning window is used as the excitation signal, so the highest frequency in the working frequency band is 210kHz. It can be seen from FIG. 4 that within 0-210 kHz, the highest circumferential order of the curved guided wave F(N,1) is 31, so the number of curved transducer plate units is 32. The curved surface transducer plate unit is made of polarized PZT-5H ceramics, the shape is square, the length of the upper surface is 6mm, and the minimum thickness h is 1.9mm. The flexible base is made of rubber, the length is 314mm, the width is 12mm, and the thickness is 2mm. For the convenience of the experiment, a piezoelectric transducer with 12 curved transducer plate units was prepared at the same time.

Figure 6 shows that the prepared piezoelectric transducers with 32 curved surface transducer plate units are used as brakes, and the voltage with a center frequency of 150kHz and an amplitude of 20V is used to excite on an aluminum tube with a wall thickness of 3mm and an outer diameter of 100mm Experimental results for T(0,1). The signal is received by a piezoelectric transducer with 12 curved surface transducer units. Since the number of curved surface transducer units is lower than the highest circumferential order of the curved guided wave F(N,1), the transducer is both It can receive both torsional wave and bending guided wave mode. Fig. 6 shows that the piezoelectric transducers of 32 curved surface transducer plate units prepared by the utility model have successfully excited the zero-order torsional wave T(0,1) of a single mode and high signal-to-noise ratio, without any other Bending mode guided waves are excited. The interval between the excitation point and the receiving point is 600mm, so that the wave velocity of the zero-order torsional wave T (0, 1) excited by the piezoelectric transducer of the present utility model can be calculated as 3050m/s, which is the same as T (0 in the aluminum tube. , 1) is very close to the theoretical value of 3099m/s. It can be seen that the waveform of the zero-order torsional wave T(0, 1) excited by the utility model is completely consistent with the waveform of the excitation signal without any dispersion.

Embodiment two

In this embodiment, the piezoelectric transducers with 32 curved transducer plate units prepared in Embodiment 1 are used as sensors.

Fig. 7(a) shows the ultrasonic guided wave signal received by the piezoelectric transducer with 12 transducer plates as the actuator excited at 150kHz and received by the piezoelectric transducer with 12 transducer plates. It can be seen that in addition to the zero-order torsional guided wave T(0, 1), there are also curved guided wave modes excited. Figure 7(b) shows that when the piezoelectric transducers of 32 curved surface transducer plate units prepared by the present invention are used as sensors, only the zero-order torsional guided wave T(0, 1) is detected, and the curved guided wave Modals are filtered out. This shows that the utility model can be used as a filter sensor, can greatly reduce the complexity of receiving signals, and has important application value.

Finally, it should be noted that the purpose of announcing the embodiments is to help further understand the utility model, but those skilled in the art can understand that various replacements and Modifications are possible. Therefore, the utility model should not be limited to the content disclosed in the embodiments, and the protection scope of the utility model is subject to the scope defined in the claims.

Claims (8)

1. a kind of piezoelectric transducer for pipe ultrasonic guide wave flaw detection is it is characterised in that described piezoelectric transducer includes：N Curved surface transducing Slab element and flexible substrates；Wherein, the upper surface of each curved surface transducing Slab element is plane, is bonded in soft The surface of property substrate, the upper surface of described curved surface transducing Slab element be shaped as rectangle, four sides are perpendicular to upper surface；Curved surface The lower surface of transducing Slab element is curved surface, curved surface along the projection and upper surface congruence of thickness direction, the curvature of curved surface with tested The outer surface curvature of pipeline is consistent, and lower surface is as work surface；Curved surface transducing Slab element is using the piezoelectric after polarization, polarization Direction, along the chord length direction of work surface, has piezoelectric coefficient d 24；The two relative sides parallel with polarised direction are electrode Face；The upper surface of n curved surface transducing Slab element is equably bonded in the lower surface of flexible substrates, n curved surface transducing Slab element Polarised direction orientation is consistent；The electrode surface of the homonymy of n curved surface transducing Slab element is respectively adopted a wire and is electrically connected one Electrode column, thus n curved surface transducing Slab element is in parallel；The work surface of each curved surface transducing Slab element is close to tested pipeline Outer surface, n curved surface transducing Slab element being evenly distributed on the lower surface of flexible substrates is circumferential along the outer surface of tested pipeline It is uniformly distributed, and around the outer surface one week along tested pipeline；It is respectively arranged at two ends with locking mechanism in flexible substrates, pass through Locking mechanism the two ends of flexible substrates are connected so that piezoelectric transducer formed the annular that links into an integrated entity and be fixed on by The outer surface in test tube road, n is >=2 natural number.

2. piezoelectric transducer as claimed in claim 1 is it is characterised in that the upper surface of described curved surface transducing Slab element is square Shape, the length of side along flexible substrates length direction is long side a, and the length of side along flexible substrates width is minor face b, and curved surface changes Can Slab element minimum thickness be the distance away from upper surface for the peak of work surface be h, meet

3. it is characterised in that the width of described flexible substrates is W, thickness is H to piezoelectric transducer as claimed in claim 2, full Sufficient b≤W≤4b, 0.1h≤H≤4h.

4. piezoelectric transducer as claimed in claim 1 is it is characterised in that the length of described flexible substrates is equal to tested pipeline Outer perimeter.

5. piezoelectric transducer as claimed in claim 1 is it is characterised in that the piezoelectric of described curved surface transducing Slab element adopts The piezoelectric monocrystal of PZT pottery, ferroelectric ceramics or ferroelectric type.

6. piezoelectric transducer as claimed in claim 1 is it is characterised in that described flexible substrates adopt low elastic modulus.

7. piezoelectric transducer as claimed in claim 1 is it is characterised in that described piezoelectric transducer is ultrasonic as brake excitation Guided wave, the mid frequency of the pumping signal that signal generator produces is f₀, signal frequency width is [f_min,f_max], this frequency band claims For working band；f_maxReverse the single order cut-off frequency of guided wave less than tested pipeline；Quantity n of described curved surface transducing Slab element is big In tested pipeline [0, f_max] the interior highest circumference order bending guided wave modal appearance of frequency band range；Piezoelectric transducer excites The velocity of wave of torsional wave is c_g, wavelength is λ=c_g/f₀；The minor face b of described curved surface transducing Slab element meets：0.25λ≤b≤0.6λ.

8. piezoelectric transducer as claimed in claim 1 is it is characterised in that described piezoelectric transducer is ultrasonic as sensor reception Guided wave, the mid frequency of receipt signal is f₀, signal frequency width is [f_min,f_max], this frequency band is referred to as working band；f_maxLittle Reverse the single order cut-off frequency of guided wave in tested pipeline；Quantity n of described curved surface transducing Slab element be more than tested pipeline [0, f_max] the interior highest circumference order bending guided wave modal appearance of frequency band range；The velocity of wave of torsional wave that piezoelectric transducer receives is c_g, wavelength is λ=c_g/f₀；The minor face b of described curved surface transducing Slab element meets：0.25λ≤b≤0.6λ.