CN102706964B

CN102706964B - Point-focusing ultrasonic transducer for Lamb wave velocity testing

Info

Publication number: CN102706964B
Application number: CN201210152249.5A
Authority: CN
Inventors: 何存富; 吕炎; 宋国荣; 胡跃刚; 谭博涛; 吴斌
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2012-05-16
Filing date: 2012-05-16
Publication date: 2014-01-22
Anticipated expiration: 2032-05-16
Also published as: CN102706964A

Abstract

The invention relates to a point-focusing ultrasonic transducer for Lamb wave velocity testing, which belongs to the technical field of acoustic transducers. The point-focusing ultrasonic transducer has the functions of converting a pulse electric signal generated by an excitation source into vibration of a piezoelectric film so as to generate an ultrasonic signal, simultaneously receiving a reflection echo of a tested sample, and converting the ultrasonic signal into an electric signal. According to the point focusing ultrasonic transducer, a piezoelectric macromolecular polymer is taken as an excitation receiving element, and the ultrasonic signal with the central frequency of 14MHz can be generated by a joint, a metal spring, an upper metal shell, a lower metal shell, an insulated sleeve, a backing, insulated cement, an evaporation electrode and the like. A stretch operation is avoided in a polarization process, so that the polarization difficulty is greatly reduced. The point-focusing ultrasonic transducer has the advantages of long defocusing distance, wide frequency band, high signal to noise ratio and the like, and can completely meet the requirements on experiment analysis.

Description

A kind of point focusing ultrasonic transducer detecting for Lamb wave velocity of wave

Technical field

The present invention relates to a kind of ultrasonic transducer that leaks the detection of Lamb wave velocity of wave for material, belong to acoustic transducer technical field, thereby its effect is the pulse electrical signal of driving source generation to be converted to the vibration generation ultrasonic signal of piezoelectric membrane, receive the reflection echo of tested sample simultaneously, and ultrasonic signal is converted to electric signal.By the signal analysis collecting being understood to the wave characteristic of measured material, be finally inversed by the mechanical property of material.

Background technology

The dedicated transducer of material character Non-Destructive Testing is the key of whole test macro, and numerous scholars are doing fruitful work aspect the focused transducer development that is applied to material character detection.From early stage to being applied to lens type ZnO, PZT or the LiNbO of ultrasonic imaging ₃deng piezoelectric membrane focused transducer, improve, obtain and to be applied to the large angle transducer that material character detects, to adopt PVDF piezoelectric membrane without lens type focused transducer, the scope that the development of its manufacture craft detects material character constantly expands.But use ZnO, PZT or LiNbO ₃deng piezoelectric during as excitation/receiving element, need to make a very accurate quartz or sapphire camera lens, be limited to its material expensive, make difficulty, and the factors such as acoustic impedance does not mate between exciting element and camera lens, cause conventional microscope mostly to operate under narrow frequency or single-frequency, and the acoustic impedance of camera lens and water also differs greatly, can cause the reduction of energy transmission efficiency, therefore traditional lens type transducer is not popularized.PVDF after being proved and thering is piezoelectricity, the acoustic impedance that it is lower, good pliability makes to become without lens type transducer the research emphasis of Chinese scholars.

In recent years, the multipolymer of PVDF, for example P (VDF-TrFE) high molecular polymer, due to its good piezoelectric property, is used as the excitation/receiving element of ultrasonic transducer widely.Although the piezoelectric property of pure PVDF is fine, but need to carry out unidirectional or two-way stretch in the process of polarization, so directly limit itself and other components and parts and carried out integrated ability, and because stretching, needs polarize, more than the thickness of PVDF film is limited in 10 μ m, make the transducer frequency made relatively low.

Summary of the invention

The object of the present invention is to provide a kind of point focusing formula ultrasonic transducer detecting for leaking Lamb wave velocity of wave, excitation/reception can be unified in a transducer.

To achieve these goals, the present invention has comprised as lower member: joint 1, metal spring 2, upper metal shell 3A, lower metal shell 3B, insulating sleeve 4, backing 5, insulating gel 6, piezoelectric membrane 7, electrode evaporation 8 and be positioned at the boss 9 on upper metal shell 3A top, as shown in Figure 1, section as shown in Figure 2 and Figure 3 for the integral body assembling outward appearance of transducer.Backing 5 is positioned at the inside of open circles column type insulating sleeve 4 and coaxial, it is R that the upper surface of cylindrical backing 5 has a radius, subtended angle is the concave spherical surface of θ, the centre of sphere of concave spherical surface and the central axis of cylindrical backing are on same straight line, on concave spherical surface, covering a layer thickness is the piezoelectric membrane 7 of h, the upper surface at piezoelectric membrane 7 edges flushes with the upper surface of insulating sleeve 4, and the upper surface at piezoelectric membrane 7 edges and the upper surface of insulating sleeve 4 are coated with insulating gel 6, on central fovea sphere, the upper surface of the upper surface of piezoelectric membrane 7 and insulating gel 6 is coated with electrode evaporation 8, insulating sleeve 4 is positioned at the inside of metal shell 3A on hollow cylinder and coaxial, upper metal shell 3A is coaxial with lower metal shell 3B, lower metal shell 3B is by being threaded into upper metal shell 3A, a protruding male is arranged at the top of joint 1, male is partly overlapped metal spring 2, the two ends of spring contact with joint 1 with backing 5 respectively, joint 1 is fixed under hollow cylinder in metal shell 3B, the spring compressing makes the upper surface at electrode evaporation 8 edges contact with the inside surface of boss 9.

As shown in Figure 4, the piezoelectric membrane of making in said process, thickness is h=10-50 μ m; In said process, the subtended angle of backing concave spherical surface can be θ=60-120 °, and radius is R=10-25mm.

This transducer is excitation/reception one transducer, adopt general pulse excitation/receiving trap to encourage/receive, during use, need carry out water logging coupling, system as shown in Figure 5, comprising: four axle mobile platforms 9, motion control card 10, embedded controller 11, oscillograph 12, pulse excitation/receiving instrument 13 and the transducer 14 and sample 15 made.The present invention realizes the measurement to isotropic thin plate material Lamb wave velocity of wave, has that centre frequency is high, a bandwidth, signal to noise ratio (S/N ratio) advantages of higher, can meet the needs of experimental analysis completely.

Accompanying drawing explanation

Fig. 1 is the whole assembling of the present invention schematic diagram;

Fig. 2 is the whole assembling of the present invention diagrammatic cross-section;

Fig. 3 is piezoelectricity partial cutaway schematic of the present invention;

Fig. 4 is backing of the present invention, sleeve, piezoelectric membrane and electrode schematic diagram;

Fig. 5 test macro schematic diagram;

Fig. 6 transducer test result figure.

Embodiment

Take subtended angle as θ=90 °, and the transducer that focused radius is R=10mm is that example describes in detail concrete embodiment.

As shown in Figure 1, this transducer comprises: joint 1, metal spring 2, upper metal shell 3A, lower metal shell 3B, insulating sleeve 4, backing 5, insulating gel 6, P (VDF-TrFE) piezoelectric membrane 7, electrode evaporation 8 etc.Backing is as supporting construction and the negative pole of P (VDF-TrFE) piezoelectric membrane 7, need to carry out finishing to it, the concave spherical surface of made is positioned at cylindrical upper surface, being centered close on cylindrical axis of concave spherical surface, the radian of concave spherical surface and subtended angle have determined radian and the subtended angle of P (VDF-TrFE) piezoelectric membrane, by concave spherical surface is carried out to fine gtinding, make its surface reach minute surface grade, roughness Ra≤0.2 μ m.On the concave spherical surface completing, preparing thickness is the macromolecule piezoelectric membrane of 10-12 μ m, treat that film inserts backing in insulating sleeve after solidifying completely, make to there is one end of piezoelectric membrane and one end of sleeve flushes, then use insulating gel that both are bonded together, play fixing effect, play the object of isolation backing (positive pole) and copper shell (negative pole) simultaneously.After treating that insulating gel solidifies, at the surperficial evaporation layer of metal electrode of P (VDF-TrFE) piezoelectric membrane, this metal level forms electrical connection as negative pole by the mechanical type contact with copper shell, plays the function of shielding simultaneously.Upper and lower two

metal shell

3A and 3B are screwed, and UHF joint collocation metal spring is screwed in to transducer, complete the assembling of transducer, then by high voltage polarization device, P (VDF-TrFE) piezoelectric membrane is polarized, make it there is piezoelectric effect, the low roughness of backing concave spherical surface, by the point discharge effect reducing in polarization process, improves and is polarized to power.

Use rectangular build tungsten carbide as reflecting body (sample), it is of a size of 40mm * 40mm * 10mm, and at the pulse time-domain signal of focusing surface and frequency-region signal as shown in Figure 6, the centre frequency of transducer can reach 14MHz to the transducer of development,-6dB bandwidth is about 11MHz, and signal to noise ratio (S/N ratio) is very high.This transducer is measured and designs for leaking Lamb wave velocity of wave, simple in structure, easy to make, by test result, can find out that it can be competent at the needs of measurement.

Claims

1. the point focusing ultrasonic transducer detecting for Lamb wave velocity of wave, this transducer has comprised as lower member: backing, piezoelectric membrane, electrode evaporation,

It is characterized in that: this transducer has also comprised as lower member: joint (1), metal spring (2), upper metal shell (3A), lower metal shell (3B), insulating sleeve (4), insulating gel (6) and be positioned at the boss (9) on upper metal shell (3A) top;

Backing (5) is positioned at the inside of open circles column type insulating sleeve (4) and coaxial, it is R that the upper surface of cylindrical backing (5) has a radius, subtended angle is the concave spherical surface of θ, the centre of sphere of concave spherical surface and the central axis of cylindrical backing are on same straight line, on concave spherical surface, cover the piezoelectric membrane that a layer thickness is h (7), the upper surface at piezoelectric membrane (7) edge flushes with the upper surface of insulating sleeve (4), and the upper surface at piezoelectric membrane (7) edge and the upper surface of insulating sleeve (4) are coated with insulating gel (6), the upper surface of the upper surface of piezoelectric membrane on central fovea sphere (7) and insulating gel (6) is coated with electrode evaporation (8), insulating sleeve (4) is positioned at the inside of metal shell on hollow cylinder (3A) and coaxial, upper metal shell (3A) is coaxial with lower metal shell (3B), lower metal shell (3B) is by being threaded into upper metal shell (3A), a protruding male is arranged at the top of joint (1), male is partly overlapped metal spring (2), the two ends of spring contact with joint (1) with backing (5) respectively, joint (1) is fixed in metal shell under hollow cylinder (3B), the spring compressing makes the upper surface at electrode evaporation (8) edge contact with the inside surface of boss (9), above-mentioned piezoelectric membrane, thickness is h=10-50 μ m, the subtended angle of above-mentioned concave spherical surface is θ=60-120 °, and radius is R=10-25mm.