CN201034982Y - A double-layer PVDF piezoelectric film line focused ultrasonic probe - Google Patents

Abstract

The utility model relates to a double-layer PVDF piezoelectric film line focused ultrasonic probe, which belongs to the technical field of non-destructive testing. It includes a probe shell, a piezoelectric element for excitation, a piezoelectric element for reception, a protective layer, an excitation-reception coupling layer, a backing layer, an excitation signal input channel and a receiving signal output channel. The piezoelectric element for excitation is an excitation PVDF piezoelectric film (14) with the negative electrode (11) of the piezoelectric element for excitation attached to the upper surface and the positive electrode (12) of the piezoelectric element for excitation attached to the lower surface; The receiving piezoelectric element is a receiving PVDF piezoelectric film (7) with a receiving piezoelectric element positive electrode (9) attached to its upper surface and a receiving piezoelectric element negative electrode (10) attached to its lower surface. This probe is designed for the time-domain waveform analysis method of the acoustic measurement of the elastic constant of the material. It can measure the surface wave velocity and the longitudinal wave velocity of the material at the same time. The signal-to-noise ratio is high and the measurement blind zone is small.

Description

A double-layer PVDF piezoelectric film line focused ultrasonic probe

Technical field:

A line-focused ultrasonic probe using a double-layer PVDF piezoelectric film as a transducer element is used to measure the wave velocity of longitudinal waves and leaky surface waves, thereby realizing the evaluation of the mechanical properties of materials, and belongs to the technical field of non-destructive testing.

Background technique:

With the rapid development of material science, various new materials are constantly emerging, and many materials show extraordinary mechanical properties, such as: the hardness of nano-copper or palladium block materials is 50 times higher than that of conventional materials, and the yield strength is 12 times higher; nano-silicon carbide The fracture toughness is 100 times higher than that of conventional materials; the fracture strength of nano-iron polycrystals is 12 times higher than that of conventional iron; the copper sheets densely packed with nano-copper ions have amazing super-ductility, reaching 5100%, far exceeding ordinary iron with the same purity. Ductility of copper sheet. To accurately evaluate the mechanical properties of various new materials, it is necessary to test the mechanical properties of the materials. However, many new materials have the characteristics of one-time molding, small size, and high manufacturing cost due to special preparation processes. Depending on the technology, the sizes that can be prepared are also different. In this case, conventional mechanical performance testing methods such as destructive testing cannot be used to test the mechanical properties of materials. Exploring and developing new testing methods and instruments has become a research hotspot for scholars at home and abroad. In recent years, people have researched and proposed many new mechanical property testing methods, such as: nano-indentation technology, acoustic microscope technology, surface acoustic wave technology, laser ultrasonic technology, etc.

The acoustic microscope is designed for high-resolution imaging of the internal properties of materials. Its main purpose is to study the difference in mechanical properties at different points inside the material. Its focus is on the microscopic properties of materials. Because traditional piezoelectric ceramics or piezoelectric crystals are used as transducer elements, ultrasonic waves are focused into points through spherical acoustic lenses, the aperture is small, the equipment is complex and expensive, and it cannot be used to analyze the anisotropy of materials. For the measurement of material elastic constant and the analysis of anisotropy, we often pay more attention to the macroscopic properties of the material, and high resolution is not necessary. Therefore, for the measurement of small-sized material elastic constant and anisotropy analysis, a simple and practical The line focusing probe is necessary for the evaluation of the mechanical properties of materials.

Patent ZL.2005200053518 proposes a single-layer PVDF film line focusing probe that can simultaneously measure surface wave velocity and longitudinal wave velocity. This type of probe can be used to measure elastic constants of small-sized materials by simultaneously measuring surface wave velocity and longitudinal wave velocity of materials. The probe includes a piezoelectric element, a backing layer cast on the piezoelectric element, and several main parts of the shell consisting of a shell and a shell cover. The transducer element in this type of probe adopts a single-layer PVDF film, which is used as both an excitation transducer and a receiving transducer. In actual use, the PVDF film first acts as an excitation transducer to excite ultrasonic excitation, and after a certain time interval, it also acts as a receiving transducer to receive ultrasonic echoes. The PVDF film will be excited by a strong electrical signal. After the excitation, there will be a saturation phenomenon, and the saturation will last for a period of time. During this time, PVDF will not be able to receive ultrasonic echoes normally. Therefore, this type of probe has a large measurement blind area, and the normal detection effect cannot be obtained when the distance between the probe and the test piece is close during use.

Utility model content:

The purpose of this utility model is to develop a double-layer PVDF piezoelectric film line focused ultrasonic probe, which generates and receives ultrasonic signals through a dedicated excitation layer and a receiving layer, which can be used to measure the surface wave velocity and longitudinal wave velocity of materials, and then measure The elastic constant of the material (Young's modulus and Poisson's ratio) overcomes the shortcoming of a single-layer PVDF film line focusing probe with a large measurement blind area, and still obtains good experimental results when the probe is relatively close to the tested object.

A double-layer PVDF piezoelectric film line focused ultrasonic probe, as shown in Figure 1, the probe includes a probe shell, a piezoelectric element for excitation, a piezoelectric element for reception, a protective layer, an excitation receiving coupling layer, a backing layer, an excitation Signal input channel and received signal output channel.

It is characterized by:

The probe housing is composed of a hollow cube lower surface processed into an upwardly concave arc-shaped housing 6 and the top of which is matched with a housing cover 3;

The piezoelectric element for excitation is an excitation PVDF piezoelectric film 14 with the negative electrode 11 of the piezoelectric element for excitation attached to the upper surface and the positive electrode 12 of the piezoelectric element for excitation attached to the lower surface;

The receiving piezoelectric element is a receiving PVDF piezoelectric film 7 with a receiving piezoelectric element positive electrode 9 attached to the upper surface and a receiving piezoelectric element negative electrode 10 attached to the lower surface;

The radian of the lower surface of the housing 6 is greater than twice the Rayleigh angle of the material to be tested;

The PVDF piezoelectric film 14 for excitation is closely adhered to the lower surface of the housing 6, and is in an upwardly concave arc shape consistent with the radian of the lower surface of the housing 6;

The excitation-receiving coupling layer 8 is closely adhered to the upper surface of the excitation PVDF piezoelectric film 14, and is in an upwardly concave arc shape consistent with the radian of the upper surface of the excitation piezoelectric film 14;

The PVDF piezoelectric film 7 for receiving is closely adhered to the upper surface of the excitation receiving coupling layer 8, and is in an upwardly concave arc shape consistent with the radian of the upper surface of the excitation receiving coupling layer 8;

The protective layer 13 is closely attached to the lower surface of the PVDF piezoelectric film 14 for excitation, and is in an upwardly concave arc shape consistent with the radian of the lower surface of the PVDF piezoelectric film 14 for excitation;

The excitation signal input channel is composed of a signal positive path of the excitation signal input channel and a signal negative path of the excitation signal input channel;

The excitation signal output channel is composed of a signal positive path of the excitation signal output channel and a signal negative path of the excitation signal output channel;

The positive signal path of the excitation signal input channel is formed by connecting the positive electrode 12 of the piezoelectric element for excitation, the positive electrode lead wire 17 of the piezoelectric element for excitation, and the positive pole of the excitation signal input socket 1;

The signal negative path of the excitation signal input channel is formed by connecting the negative electrode 11 of the piezoelectric element for excitation, the negative electrode lead wire 16 of the piezoelectric element for excitation, and the negative electrode of the excitation signal input socket 1;

The signal positive path of the receiving signal output channel is formed by connecting the positive electrode 9 of the piezoelectric element for receiving, the positive electrode lead wire 5 of the piezoelectric element for receiving, and the positive electrode of the receiving signal output socket 2;

The signal negative path of the receiving signal output channel is formed by connecting the negative electrode 10 of the piezoelectric element for receiving, the negative electrode lead wire 4 of the piezoelectric element for receiving, and the negative electrode of the receiving signal output socket 2;

The backing layer 15 is cast on the receiving PVDF piezoelectric film 7 .

The PVDF piezoelectric film used above has a thickness less than 100 μm and a length greater than 20 μm.

This probe is a dual-channel probe for ultrasonic transmission and reception. It uses a general-purpose pulse excitation receiving device to excite and receive signals, and must be coupled in water when used. This probe is designed for the time-domain waveform analysis method of the acoustic measurement of the elastic constant of the material. It can measure the surface wave velocity and the longitudinal wave velocity of the material at the same time. The signal-to-noise ratio is high and the measurement blind area is small.

Description of drawings:

Figure 1: Schematic diagram of probe structure

1. Exciting signal input socket, 2. Receiving signal output socket, 3. Shell cover, 4. Negative electrode lead of piezoelectric element for receiving, 5. Positive electrode lead of piezoelectric element for receiving, 6. Shell, 7. Receiving PVDF film, 8. Exciting and receiving coupling layer, 9. Positive electrode of piezoelectric element for receiving, 10. Negative electrode of piezoelectric element for receiving, 11. Negative electrode of piezoelectric element for exciting, 12. Positive electrode of piezoelectric element for exciting, 13. Protective layer, 14. PVDF film for excitation, 15. Backing layer, 16. Negative electrode lead wire of piezoelectric element for excitation, 17. Positive electrode lead wire of piezoelectric element for excitation, 18. Countersunk screw

Figure 2: Schematic Diagram of Probe Application System

19. Probe, 20. Water, 21. Material test block, 22. Pulse transmitter and receiver, 23. Oscilloscope, 24. Computer

Detailed ways:

The concrete technical scheme of the utility model is referring to Fig. 1.

The probe shell 6 and shell cover 3 are made of stainless steel. The shell 6 is designed as a 35×20×30mm (length×width×height) rectangle that runs through the shell up and down, with a wall thickness of 2mm, the upper end is flush, and the two sides (width ) are flush at the bottom, and the bottom ends of the other two opposite sides are processed into circular arcs. Because the focusing parameter of the probe depends on the radian of the piezoelectric film 14, and for this probe, the radian of the piezoelectric film after the probe is made depends on the radian of the probe shell, so the arc size of the arc end of the probe shell depends on the radian of the probe shell. Designed according to the required focusing aperture angle. The determination of the focusing aperture angle is mainly to consider the generation of surface waves. According to acoustic theory, surface waves are waves that are generated when the incident angle is equal to the Rayleigh angle of the material and propagate along the surface of the material. If surface waves are generated on the surface, the lower limit of the semi-aperture angle of the probe must be greater than the Rayleigh angle of the material to be tested; and if the arc is too large, it will increase the difficulty of making the probe, and at the same time shorten the propagation path of the surface wave, which is not conducive to waveform analysis. According to the Rayleigh angle data when ultrasonic waves are incident on different materials, the aperture angle of the probe should be in the range of 60° to 80°. In the actual design of the probe, the aperture angle is 72°.

PVDF piezoelectric film 14 and PVDF piezoelectric film 7 are used as piezoelectric transducer elements, both of which are devices of the same type, respectively exert their inverse piezoelectric effect and positive piezoelectric effect, and play the role of ultrasonic generation and reception. The most important component of the sensor, its performance directly determines the quality of the probe function. The main parameters to be considered in the design are the thickness of the piezoelectric film and the shape and size of the electrodes covering its surface. Piezoelectric films with different thicknesses have different inherent center frequencies. The thicker the piezoelectric film, the lower the center frequency, which will reduce the overall center frequency of the probe and reduce the measurement resolution. For this probe, it is necessary to use The measurement accuracy is guaranteed, and the center frequency of the probe should be above 5MHz. To meet this requirement, the thickness of the piezoelectric film used should be less than 50μm. The probe measures the surface wave velocity through the waveform time domain analysis method, so the propagation time of the surface wave is required to be long enough, so the probe diameter should not be too small, that is, the piezoelectric film length should not be too small, and the design length should be more than 20mm. Theoretically speaking, when conditions permit, the smaller the thickness of the piezoelectric film, the better. However, because the piezoelectric film is an outsourced component, the thickness and electrode shape and size are limited to the specific conditions of the manufacturer's products, so it can only meet the requirements. appropriate selection under the circumstances. The thickness of the piezoelectric film used in this probe is 28μm, and the electrode size is 30×12mm.

PVDF piezoelectric film is a very thin film material with limited high temperature resistance, generally not exceeding 100°C, so the connection between the electrode wire and the surface electrode of the piezoelectric film cannot use conventional welding methods. In the production of other kinds of piezoelectric film sensors, the electrode leads are mostly connected by mechanical fixing, such as riveting. The structure of the probe determines that the electrode leads cannot occupy too much space, and at the same time, the fixing problem between the piezoelectric film and the shell must be considered, so the mechanical fixing method is not applicable. The probe adopts the method of conductive adhesive bonding. The upper and lower surfaces of the piezoelectric film used in this probe are covered with electrodes. In the actual design, after one end of the piezoelectric film is bent upward for a section, the positive electrode of the bent section is bonded to the positive lead, and the negative electrode of the bent section is bonded to the negative lead.

The excitation-receiving coupling layer 8 is located between the PVDF piezoelectric film 14 for excitation and the PVDF piezoelectric film 7 for reception, and is used to bond two independent piezoelectric films together. This layer is made of silicone rubber with a thickness of less than 0.5 mm.

When the piezoelectric element is excited by an electric pulse, it not only radiates sound energy forward, but also radiates backward. The echo signal from the front contains the information of the inspected material, but the interference clutter reflected from the back increases the complexity of the received signal and brings great difficulties to the actual detection. This part of the clutter signal needs to be eliminated. Therefore, it is necessary to design a backing layer in the design of an ultrasonic probe; in addition, if there is no backing layer, the piezoelectric element is excited by electricity and vibrates, but when the electric pulse stops exciting, the piezoelectric element will not stop vibrating immediately, but will continue It will stop after a while. In this way, the pulse-echo duration will be very long, which reduces the resolution of the probe. Another function of the backing layer is to make the piezoelectric element stop vibrating instantly after the excitation pulse stops, so that the received pulse width is relatively small, which can improve the resolution of the probe. The backing is prepared by using epoxy resin and tungsten powder mixed curing agent according to known technology, using WSR6101 epoxy resin and T31 epoxy resin curing agent.

The electrode leads are Φ0.2 enameled wires, the excitation and receiving signals of the probe are connected to other instruments through the radio frequency socket 9, the shell 1 and the shell cover 2 are fixed by countersunk screws 10, and the screws are coated with silicone rubber to prevent water.

The protective layer 13 of the probe is made by spraying waterproof paint on the lower surface of the PVDF piezoelectric film 14 for excitation.

In actual application, the probe forms a measurement system with other instruments. As shown in Figure 2, the pulse transmitter and receiver sends out excitation pulses to make the probe generate ultrasonic pulses, which are coupled with water to generate surface waves on the surface of the incident material and are reflected back to the probe to be received. The oscilloscope shows that the data is collected by the computer for subsequent processing.

Because the focused PVDF piezoelectric thin film ultrasonic probe of this line is used to measure the surface wave velocity of materials, it is a non-destructive testing method, which is different from the traditional tensile test, and its measurement principle determines the feasibility of the probe for measuring the elastic constant of small-sized materials; The probe is a line focusing probe, which has focusing directionality, so it can be used for the analysis of material anisotropy.

Claims (2)

1. A double-layer PVDF piezoelectric film line-focused ultrasonic probe, comprising a probe shell, a piezoelectric element, a protective layer, a backing layer, and a signal channel; the probe shell is a hollow cube lower surface processed into an upper concave arc The top of the shell (6) is combined with the shell cover (3). The radian of the lower surface of the shell (6) is greater than twice the Rayleigh angle of the material to be tested. It is characterized in that: the piezoelectric element is divided into Piezoelectric elements, piezoelectric elements for receiving, signal channels are divided into excitation signal input channels and receiving signal output channels, and also include excitation and receiving coupling layers; The piezoelectric element for excitation is an excitation PVDF piezoelectric film (14) with the negative electrode (11) of the piezoelectric element for excitation attached to the upper surface and the positive electrode (12) of the piezoelectric element for excitation attached to the lower surface; The receiving piezoelectric element is a receiving PVDF piezoelectric film (7) with a receiving piezoelectric element positive electrode (9) attached to the upper surface and a receiving piezoelectric element negative electrode (10) attached to the lower surface; The PVDF piezoelectric film (14) for excitation is closely adhered to the lower surface of the casing (6), and is in an upwardly concave arc shape consistent with the curvature of the lower surface of the casing (6); The excitation-receiving coupling layer (8) closely adheres to the upper surface of the excitation PVDF piezoelectric film (14), and is in an upwardly concave arc shape consistent with the radian of the upper surface of the excitation piezoelectric film (14); The PVDF piezoelectric film (7) for receiving is closely adhered to the upper surface of the excitation receiving coupling layer (8), and is in an upwardly concave arc shape consistent with the radian of the upper surface of the excitation receiving coupling layer (8); The protective layer (13) is closely attached to the lower surface of the PVDF piezoelectric film (14) for excitation, and is in an upwardly concave arc shape consistent with the radian of the lower surface of the PVDF piezoelectric film (14) for excitation; The excitation signal input channel is composed of a signal positive path of the excitation signal input channel and a signal negative path of the excitation signal input channel; The excitation signal output channel is composed of a signal positive path of the excitation signal output channel and a signal negative path of the excitation signal output channel; The signal positive path of the excitation signal input channel is formed by connecting the positive electrode (12) of the piezoelectric element for excitation, the positive electrode lead (17) of the piezoelectric element for excitation, and the positive pole of the excitation signal input socket (1); The signal negative path of the excitation signal input channel is formed by connecting the negative electrode (11) of the piezoelectric element for excitation, the negative electrode lead (16) of the piezoelectric element for excitation, and the negative pole of the excitation signal input socket (1); The signal positive path of the receiving signal output channel is formed by connecting the positive electrode (9) of the receiving piezoelectric element, the positive electrode lead wire (5) of the receiving piezoelectric element, and the positive electrode of the receiving signal output socket (2); The signal negative path of the receiving signal output channel is formed by connecting the negative electrode (10) of the piezoelectric element for receiving, the lead wire (4) of the negative electrode of the piezoelectric element for receiving, and the negative electrode of the receiving signal output socket (2); The backing layer (15) is cast on a receiving PVDF piezoelectric film (7). 2. A double-layer PVDF piezoelectric film line-focused ultrasonic probe according to claim 1, characterized in that: the thickness of the PVDF piezoelectric film used is less than 100 μm, and the length is greater than 20 μm.

Images