A high-frequency piezoelectric transducer, a high-frequency ultrasonic probe, and a method for their fabrication.

Abstract

This invention relates to a high-frequency piezoelectric transducer, a high-frequency ultrasonic probe, and a manufacturing method, used for rail defect monitoring, belonging to the field of measurement technology. The high-frequency piezoelectric transducer includes a first electrode layer, a flexible piezoelectric transducer layer, a second electrode layer, and a conductive epoxy solder mixture layer. The first electrode layer is connected to the front side of the flexible piezoelectric transducer layer and has a positive lead connected thereto. The upper surface of the second electrode layer is connected to the back side of the flexible piezoelectric transducer layer and has a negative lead connected thereto. The lower surface of the second electrode layer is connected to the conductive epoxy solder mixture layer. The high-frequency piezoelectric transducer of this invention is used in a high-frequency ultrasonic probe, which enables real-time, online, automated, and accurate detection of rail head defects.

Description

Technical Field

[0001] This invention belongs to the field of measurement technology, specifically relating to a high-frequency piezoelectric transducer, a high-frequency ultrasonic probe, and a preparation method thereof. Background Technology

[0002] In existing technologies, rails used for train operation often develop cracks, fissures, or breaks during long-term train operation. Therefore, rail damage detection is necessary. Current methods involve coupling an ultrasonic probe to the rail head tread and utilizing the reflection of ultrasonic waves from the damaged area. The amplitude of the reflected sound waves is measured to determine the location of the rail defect. However, this method of using ultrasonic waves at the rail head cannot be implemented while the train is running on the same track, making real-time online monitoring of rail head defects impossible. Consequently, it is difficult to determine the shape of the rail damage and its changes. Because these highly hazardous rail head defects cannot be detected in a timely manner, the potential for rail breakage due to defect expansion poses a significant threat to train safety. Summary of the Invention

[0003] The purpose of this invention is to provide a high-frequency piezoelectric transducer, a high-frequency ultrasonic probe, and a preparation method to solve the above-mentioned problems existing in the prior art.

[0004] A high-frequency piezoelectric transducer for rail defect monitoring includes a first electrode layer, a flexible piezoelectric transducer layer, a second electrode layer, and a conductive epoxy solder mixture layer.

[0005] The first electrode layer is connected to the front side of the flexible piezoelectric transducer layer and is connected to a positive electrode lead;

[0006] The upper surface of the second electrode layer is connected to the back surface of the flexible piezoelectric transducer layer and is connected to a negative electrode lead;

[0007] The lower surface of the second electrode layer is connected to the conductive epoxy solder mixture layer.

[0008] Furthermore, the flexible piezoelectric transducer layer is a copolymer PVDF layer with a certain thickness.

[0009] Furthermore, the copolymer PVDF layer is a 20 μm thick polyvinylidene fluoride-trifluoroethylene film or a polyvinylidene fluoride-tetrafluoroethylene film.

[0010] Furthermore, both the first electrode layer and the second electrode layer are two-layer vapor-deposited structures.

[0011] Furthermore, the two-layer vapor-deposited structure consists of a 10nm thick titanium (Ti) vapor-deposited electrode layer and a 200nm thick gold (Au) vapor-deposited electrode layer covering it, from the inside out.

[0012] Furthermore, the high-frequency piezoelectric transducer is a cube with a side length of 3mm × 3mm.

[0013] The present invention also provides a method for fabricating a high-frequency piezoelectric transducer element, the method comprising the following steps:

[0014] S1. Prepare the flexible piezoelectric transducer layer;

[0015] S2. A first electrode layer and a second electrode layer are respectively connected to both sides of the flexible piezoelectric transducer layer;

[0016] S3. A conductive epoxy solder mixture layer is connected to the lower surface of the second electrode layer, and the first electrode layer, the flexible piezoelectric transducer layer, the second electrode layer and the conductive epoxy solder mixture form a multilayer structure;

[0017] S4. Place the multilayer structure in an oven at 30-60°C and cure for 3-6 hours, then polarize it in room temperature silicone oil with a 2000V DC electric field for 20-40 minutes.

[0018] S5. Cut the polarized multilayer structure to obtain a high-frequency piezoelectric transducer.

[0019] Furthermore, in step S5, after cutting to obtain the high-frequency piezoelectric transducer element, the positive electrode lead and the negative electrode lead are welded to the first electrode layer and the second electrode layer, respectively.

[0020] The present invention also provides a high-frequency ultrasonic probe, the high-frequency ultrasonic probe comprising a high-frequency piezoelectric transducer, a flexible adhesive layer, a positive electrode connecting wire, a negative electrode connecting wire, a multi-core high-frequency cable and a waterproof connector, wherein the high-frequency piezoelectric transducer is bonded to the flexible adhesive layer.

[0021] Furthermore, the flexible adhesive bonding layer is a polydimethylsiloxane (PDMS) layer, and multiple high-frequency piezoelectric transducers are provided, with a spacing of 1 mm between each high-frequency piezoelectric transducer.

[0022] Beneficial effects of the present invention

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The flexible piezoelectric transducer layer of this invention uses copolymer PVDF to fabricate the high-frequency piezoelectric transducer element. This copolymer PVDF is a flexible piezoelectric material that combines the characteristics of fluoropolymers and general-purpose resins. Therefore, the high-frequency piezoelectric transducer element has good chemical corrosion resistance, high temperature resistance, oxidation resistance, good mechanical properties, is soft and non-brittle, lightweight, impact resistant, and has good piezoelectric properties and good acoustic transmission characteristics. Since all online monitoring locations are outdoors, the performance of copolymer PVDF does not change under high and low temperatures, resulting in a long service life. Furthermore, copolymer PVDF has a temperature resistance of -40 degrees to 140 degrees Celsius and strong anti-aging properties. In addition, this invention uses polyvinylidene fluoride-trifluoroethylene or polyvinylidene fluoride-tetrafluoroethylene copolymers in copolymer PVDF with good piezoelectric properties.

[0025] (2) A high-frequency piezoelectric transducer element is fabricated using a flexible piezoelectric transducer layer and fixed by a flexible adhesive bonding layer to fabricate a high-frequency ultrasonic probe. The flexible adhesive bonding layer is made of polydimethylsiloxane (PDMS). PDMS has strong flexibility, good elasticity, low Young's modulus, excellent gas permeability, chemical stability and thermal stability, which makes the high-frequency ultrasonic probe have good flexibility and bending characteristics. It can be placed at any position on the rail. Especially when monitoring rail head core defects, the high-frequency ultrasonic probe can be completely attached to the lower jaw of the rail to form a good ultrasonic incident surface, which can perform real-time online automated detection of core defects in the rail head. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a high-frequency piezoelectric transducer.

[0027] Figure 2 This is a schematic diagram of the structure of a high-frequency ultrasonic probe;

[0028] Figure 3 This is a schematic diagram of a high-frequency ultrasonic probe installed on a steel rail.

[0029] In the diagram: 1. High-frequency piezoelectric transducer; 2. First electrode layer; 3. Flexible piezoelectric transducer layer; 4. Second electrode layer; 5. Conductive epoxy solder mixture layer; 6. Positive lead; 7. Negative lead; 8. High-frequency ultrasonic probe; 9. Flexible adhesive connection layer; 10. Positive connection wire; 11. Negative connection wire; 12. Multi-core high-frequency cable; 13. Epoxy resin; 14. Rivet hole; 15. Waterproof connector; 16. Multi-core shielded cable. Detailed Implementation

[0030] To better understand the technical solution of this invention, the content of this invention includes, but is not limited to, the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of this invention. To make the technical problems to be solved, the technical solutions, and advantages of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0031] It should be understood that the embodiments described in this invention are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0032] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0033] To achieve the above objectives, the present invention provides a high-frequency piezoelectric transducer element, such as... Figure 1 As shown, the high-frequency piezoelectric transducer 1 includes a first electrode layer 2, a flexible piezoelectric transducer layer 3, a second electrode layer 4, and a conductive epoxy solder mixture layer 5.

[0034] Wherein: the first electrode layer 2 is connected to the front side of the flexible piezoelectric transducer layer 3 and is connected to a positive electrode lead 6;

[0035] The upper surface of the second electrode layer 4 is connected to the back side of the flexible piezoelectric transducer layer 3 and is connected to the negative electrode lead 7;

[0036] The lower surface of the second electrode layer 4 is connected to the conductive epoxy solder mixture layer 5.

[0037] Preferably, the copolymer PVDF combines the characteristics of both fluoropolymers and general-purpose resins. The resin itself possesses excellent chemical resistance, high-temperature resistance, oxidation resistance, good mechanical properties, flexibility, light weight, and impact resistance. Therefore, the high-frequency ultrasonic probe made from this material exhibits good bending characteristics. The flexible piezoelectric transducer layer 3 of this invention is implemented using copolymer PVDF, such as... Figure 1As shown, in order to fabricate the high-frequency piezoelectric transducer 1, in the embodiments of the present invention, the copolymer PVDF layer is selected as a polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) film or a polyvinylidene fluoride-tetrafluoroethylene film with a thickness of 20μm. Polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) or polyvinylidene fluoride-tetrafluoroethylene copolymers have high crystallinity, so the piezoelectric properties determined by crystallinity are also relatively good. Moreover, the higher the crystallinity, the greater the piezoelectric response, so it has a higher piezoelectric constant and excellent acoustic performance.

[0038] The fabrication steps for this high-frequency piezoelectric transducer are as follows:

[0039] (1). Prepare a 12mm×12mm polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or vinylidene fluoride-tetrafluoroethylene film layer with a thickness of 20μm;

[0040] (2). Connect the first and second electrode layers to both sides of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or polyvinylidene fluoride-tetrafluoroethylene film layer. In this embodiment, the bonding method is adopted, that is, the first electrode layer 2 is bonded to the front side of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or polyvinylidene fluoride-tetrafluoroethylene film layer, and the upper surface of the second electrode layer 4 is bonded to the back side of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or polyvinylidene fluoride-tetrafluoroethylene film layer. The first electrode layer 2 and the second electrode layer 4 are both vapor-deposited electrode structures. The vapor deposition process is to deposit conductive material on the corresponding electrode layer by heating the electrode material to form vapor and then adsorbing it onto the target object.

[0041] In a preferred embodiment, the first electrode layer 2 and the second electrode layer 4 are both two-layer vapor-deposited electrode structures, namely, from the inside out, a titanium (Ti) vapor-deposited electrode layer with a thickness of 10 nm bonded to a polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or vinylidene fluoride-tetrafluoroethylene film layer, and a gold (Au) vapor-deposited electrode layer with a thickness of 200 nm covering the titanium (Ti) vapor-deposited electrode layer.

[0042] (3). The conductive epoxy solder (E-Solder) 3022 and the hardener are mixed at a certain mass ratio and centrifuged at 10,000 rpm for 10 minutes to obtain the centrifuged conductive epoxy solder mixture. Then the centrifuged conductive epoxy solder mixture layer is connected to the lower surface of the second electrode layer 4. In this embodiment, the casting method is used.

[0043] (4) The multilayer structure formed by the first electrode layer 2, polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or vinylidene fluoride-tetrafluoroethylene film layer, the second electrode layer 4, and the conductive epoxy solder mixture layer 5 is placed in an oven and cured at a temperature of 30-60°C, preferably 45°C, for 3-6 hours, preferably 5 hours. It is then polarized in room temperature silicone oil with a 2000V DC electric field for 20-40 minutes, preferably 30 minutes, to form a multilayer structure with high-frequency piezoelectric properties.

[0044] (5) Using a cutting saw or other cutting tools, the polarized multilayer structure is cut into 16 cubes with a side length of 3mm×3mm. Each cube is a high-frequency piezoelectric transducer element. The positive lead 6 of the first electrode layer 2 and the negative lead 7 of the second electrode layer 4 are welded to each cube. The positive / negative leads are connected to an external power supply to excite the high-frequency piezoelectric transducer element with electrical pulses to generate ultrasonic waves with high-frequency narrow pulse characteristics.

[0045] This invention employs a flexible adhesive layer to bond a high-frequency piezoelectric transducer element, fabricating a high-frequency ultrasonic probe. The flexible adhesive layer is made of polydimethylsiloxane (PDMS), a high-molecular-weight elastic polymer prepared using a special process. PDMS possesses good elasticity, low Young's modulus, excellent gas permeability, chemical stability, thermal stability, and low-temperature flexibility, maintaining excellent performance, especially within a temperature range of -60 to 200°C. Due to these unique mechanical properties, the use of PDMS as the adhesive layer in this invention results in a high-frequency ultrasonic probe with excellent bending characteristics.

[0046] The high-frequency ultrasonic probe comprises multiple high-frequency piezoelectric transducers and a polydimethylsiloxane (PDMS) bonding layer. Each high-frequency piezoelectric transducer is embedded and bonded to the PDMS bonding layer, and the spacing between each high-frequency piezoelectric transducer is set to 1 mm. The distribution structure of all high-frequency piezoelectric transducers is as follows: Figure 2 As shown, in this embodiment, the high-frequency ultrasonic probe uses multiple high-frequency piezoelectric transducers. In this embodiment, 16 high-frequency piezoelectric transducers are used, and four are arranged in a row to form a 4x4 square. This allows the high-frequency ultrasonic probe to fit fully against the lower jaw arc surface of the rail during use, for monitoring the damaged parts of the rail head, making the detected signal more accurate and reliable.

[0047] The rear of the high-frequency ultrasonic probe is designed as a combined planar structure. The entire rear of the high-frequency ultrasonic probe also includes a positive electrode connection wire 10, a negative electrode connection wire 11, a multi-core high-frequency cable 12, epoxy resin 13, rivet holes 14, and a waterproof connector 15. The positive electrode leads 6 of each high-frequency piezoelectric transducer element 1 are coated, but need to be led out separately from each high-frequency piezoelectric transducer element 1 to ensure that the positive electrodes of each high-frequency piezoelectric transducer element 1 are not interconnected. The individually led-out positive electrode leads 6 are connected in parallel to form the positive electrode connection wire 10 of the high-frequency ultrasonic probe 8. The negative electrode connection wire 11 of the high-frequency ultrasonic probe 8 is formed as follows: The negative electrode leads 7 of each high-frequency piezoelectric transducer element 1 are also coated according to... Figure 2 The wires are connected together to form a common negative terminal, which serves as the negative terminal connection line 11 for the high-frequency ultrasonic probe 8. All positive and negative terminal connection lines 10 and 11 are evenly arranged and coated to allow them to be led out. Rivet holes 14 are drilled on each positive and negative terminal connection line 10 and 11 to secure them. A multi-core high-frequency cable 12 is then connected to a waterproof connector 15. One end of the multi-core high-frequency cable 12 is soldered to all the positive and negative terminal connection lines 10 and 11 to form a signal transmission cable. The other end is soldered to the waterproof connector 15, which is a multi-core structure. Finally, epoxy resin 13 is used to seal the high-frequency cable 12 and the waterproof connector 15. The waterproof connector 15 is used to connect measuring instruments. The sealing epoxy resin 13 is used to waterproof the high-frequency ultrasonic probe. To ensure waterproofing and driving safety, the waterproof connector 15 should be placed at the bottom of the rail during on-site installation and connected to the multi-core shielded cable 16 of the ultrasonic instrument during actual use.

[0048] In this embodiment, the high-frequency ultrasonic probe is used for rail damage detection. Lateral fatigue cracks at the rail head, commonly known as rail head core damage, or simply core damage, refer to the extremely complex stress distribution and state within the rail head under repeated train loads. This causes small cracks to propagate laterally into core damage until the surrounding steel is insufficient to resist the stress under wheel loads, leading to sudden brittle fracture of the rail. Rail head core damage is the most threatening type of steel damage to train operation and is the most dangerous rail damage. Due to continuous impact from vehicles, rail head core damage is relatively easy to develop and expand, leading to rail breakage. Rail head core damage generally appears on the inner side of the rail head where the compressive stress is greatest, and at a certain angle (approximately 14 degrees) to the perpendicular section of the rail. Conventional ultrasonic testing of rail head core damage typically involves incident sound waves from the rail surface. However, under online monitoring conditions, due to vehicle operation restrictions, the probe cannot be placed at the rail surface, and due to the presence of the wheel flange, the monitoring probe cannot be placed on the inner side of the rail head. The high-frequency ultrasonic probe of this embodiment has good bending characteristics and flexibility, therefore, the high-frequency ultrasonic probe 8 can be placed on the lower jaw part of the outer side of the rail head, such as... Figure 3 As shown, this system is unaffected by the movement of trains on the rails and can automatically monitor the rail head in real time without manual intervention. It uses ultrasonic longitudinal waves generated by a high-frequency ultrasonic probe to detect core defects on the inner side of the rail head. The detected measurement signals are sent to a multi-channel ultrasonic instrument connected to the high-frequency ultrasonic probe (e.g., a 16-channel ultrasonic transmitter and receiver). This multi-channel ultrasonic instrument analyzes the measurement signals acquired by the high-frequency ultrasonic probe to construct a defect contour image of the rail. Based on this contour image, the edge and shape of the core defects in the rail head are determined. Furthermore, if the core defects in the rail head expand or deform under the impact stress of a train, the signals measured by the high-frequency ultrasonic probe provided in this embodiment can also monitor the change in the defect shape before and after expansion, allowing for timely decision-making.

[0049] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a high-frequency piezoelectric transducer, characterized in that, include: The high-frequency piezoelectric transducer includes a first electrode layer, a flexible piezoelectric transducer layer, a second electrode layer, and a conductive epoxy solder mixture layer. The first electrode layer is connected to the front side of the flexible piezoelectric transducer layer and has a positive electrode lead. The upper surface of the second electrode layer is connected to the back side of the flexible piezoelectric transducer layer and has a negative electrode lead. The lower surface of the second electrode layer is connected to the conductive epoxy solder mixture layer. The flexible piezoelectric transducer layer is a copolymer PVDF layer of a certain thickness, which is a 20 μm thick polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) film or a polyvinylidene difluoride-tetrafluoroethylene film. The preparation method includes the following steps: S1, prepare a 12mm×12mm polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or vinylidene fluoride-tetrafluoroethylene film layer with a thickness of 20μm. S2, the first and second electrode layers are connected to both sides of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or polyvinylidene fluoride-tetrafluoroethylene film layer by an adhesive method, that is, the first electrode layer is bonded to the front side of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or polyvinylidene fluoride-tetrafluoroethylene film layer, and the upper surface of the second electrode layer is bonded to the back side of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or polyvinylidene fluoride-tetrafluoroethylene film layer. Both the first and second electrode layers are vapor-deposited electrode structures. The vapor deposition process is to deposit conductive material on the corresponding electrode layer by heating the electrode material to form vapor and then adsorbing it onto the target object. The first electrode layer and the second electrode layer are both two-layer vapor-deposited electrode structures, namely, from the inside out, a titanium (Ti) vapor-deposited electrode layer with a thickness of 10nm bonded to a polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or vinylidene fluoride-tetrafluoroethylene film layer, and a gold (Au) vapor-deposited electrode layer with a thickness of 200nm covering the titanium (Ti) vapor-deposited electrode layer. S3, mix conductive epoxy solder (E-Solder) 3022 with hardener at a preset mass ratio, and centrifuge at 10000 rpm for 10 minutes to obtain centrifuged conductive epoxy solder mixture. Then, connect the centrifuged conductive epoxy solder mixture layer to the lower surface of the second electrode layer by casting. S4. The multilayer structure formed by the first electrode layer, polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) or vinylidene fluoride-tetrafluoroethylene film layer, second electrode layer and conductive epoxy solder mixture layer is placed in an oven and cured at 30-60℃ for 3-6 hours. Then, it is polarized in room temperature silicone oil with a DC electric field of 2000V for 20-40 minutes to form a multilayer structure with high frequency piezoelectric properties. S5. Using a cutting tool, the polarized multilayer structure is cut into 16 cubes with a side length of 3mm×3mm. Each cube is a high-frequency piezoelectric transducer element. The positive lead of the first electrode layer and the negative lead of the second electrode layer are welded to each cube. The positive / negative leads are connected to an external power supply to excite the high-frequency piezoelectric transducer element with electrical pulses, thereby generating ultrasonic waves with high-frequency narrow pulse characteristics.

2. A high-frequency ultrasonic probe, characterized in that, The high-frequency ultrasonic probe includes the high-frequency piezoelectric transducer element as described in claim 1, a flexible adhesive bonding layer, a positive electrode connecting wire, a negative electrode connecting wire, a multi-core high-frequency cable, and a waterproof connector, wherein the high-frequency piezoelectric transducer element is bonded to the flexible adhesive bonding layer.

3. The high-frequency ultrasonic probe according to claim 2, characterized in that, The flexible adhesive bonding layer is a polydimethylsiloxane (PDMS) layer, and multiple high-frequency piezoelectric transducers are provided, with a spacing of 1 mm between each high-frequency piezoelectric transducer.

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