Flexible piezoelectric ultrasonic fiber transducer and preparation method and application thereof

Abstract

The invention relates to the field of flexible sensing fabrics, and discloses a flexible piezoelectric ultrasonic fiber transducer and a preparation method and application thereof.The preparation method includes the steps that a thin film A and a thin film B are stacked according to the sequence of A, B, A and B, the thin film A is a non-conductive high-molecular polymer thin film, and the thin film B is a conductive high-molecular polymer thin film; the laminated film is subjected to hot pressing, and a hot stretching prefabricated part with the piezoelectric ultrasonic circuit structure wrapped inside is prepared; and fixing the thermal stretching prefabricated part in a low-temperature polymer wire drawing tower, and performing thermal stretching and feeding in a wire to obtain the flexible piezoelectric ultrasonic fiber transducer. The flexible non-conductive high-molecular polymer film is used for coating a piezoelectric ultrasonic circuit system to prepare the fiber, the non-conductive high-molecular polymer film can also be used as a matching layer and a backing layer of an ultrasonic transducer system while serving as a coating layer, and the non-conductive high-molecular polymer film is non-toxic and harmless, has certain flexibility and flexibility, and is wear-resistant, good in elasticity, easy to process and easy to prepare.

Description

Technical Field

[0001] The invention relates to the field of flexible sensing fabrics, and in particular to a flexible piezoelectric ultrasonic fiber transducer and a preparation method and application thereof. Background Art

[0002] With the continuous expansion of ultrasonic application scenarios, piezoelectric materials and their applications are constantly developing and researching. Ultrasonic transducers made of piezoelectric materials as the core, with backing layers, matching layers, and wires can be applied to industries such as industry, medicine, military industry, and clothing. At present, ultrasonic sensors used in practical applications are generally hard sensors, which are large in size, rigid, and cannot be bent. Hard sensors cannot achieve complete coupling when used in workpiece angles, human joints, and other parts, and there will be errors in the detection results. Intelligent flexible ultrasonic transducers are flexible, small in size, and flexible. They can be bent and stretched to a great extent, completely fit the workpiece or human body structure, and eliminate interference signals to the maximum extent. Therefore, under the premise of ensuring its stable and excellent sensing performance, how to develop a low-cost, continuously produced, and integrated ultrasonic transceiver piezoelectric ceramic flexible transducer fiber has become a major challenge in current research.

[0003] Styrene-ethylene-butylene-styrene block copolymer (SEBS) is a thermoplastic elastomer that can be used to modify plastics or mixed into thermoplastic rubber. SEBS has excellent aging resistance, is both plastic and highly elastic, can be processed and used without vulcanization, and scraps can be reused. It is widely used in the production of high-end elastomers, plastic modification, adhesives, lubricant thickeners, fillers and sheathing materials for wires and cables, etc. It is a suitable material for the coating of flexible wearable fibers and is widely used in the fields of flexible wearable strain sensors, smart clothing, etc.

[0004] Carbon-doped polyethylene (CPE) is a carbon-doped polymer material that combines the heat resistance, corrosion resistance, thermoplastic characteristics and excellent conductivity of polymer materials. In recent years, CPE has been widely used in optical sensing, brain-computer interfaces, ultrasonic transducers and other scenarios. It is a flexible electrode material widely used in flexible wearable systems.

[0005] Yoel Fink et al. published an article titled "Multimaterial piezoelectric fibres" in the journal Nature Materials (Nature materials, 2010, 9(8): 643-648.) reporting a flexible piezoelectric ultrasonic transducer fiber with PC as the coating layer, P (VDF-TrFE) as the piezoelectric ultrasonic material, CPC and Indium as the conductive material. The fiber has a certain degree of flexibility and can be prepared continuously. However, the PC and CPC materials used in the coating layer and the conductive polymer layer are brittle and cannot be bent at a large angle. In addition, the piezoelectric fiber prepared by this method has good performance in the audible frequency band, but relatively poor performance in the ultrasonic frequency band.

[0006] Wei et al. published the article "Flexible Piezoelectric Fibers for Acoustic Sensing and Positioning" in the journal Advanced Electronic Materials (Adv Elect Materials, 2017, 3 (3): 1600449.) on a flexible piezoelectric ultrasonic fiber transducer for acoustic sensing and positioning and its preparation method. The polymer material polyvinylidene fluoride-co-trifluoroethylene [P(VDF-TrFE)] is used as a piezoelectric element. The P(VDF-TrFE) film is sandwiched between two layers of carbon-supported polyethylene (CPE) to ensure that there is a large active area between the piezoelectric material and the conductive material. The eutectic alloy bismuth tin (BiSn) is selected as the metal electrode connected to the external circuit. The entire structure is wrapped between two rectangular polycarbonate (PC) blocks and hot-pressed into a hot-stretched preform. The preform is heated and stretched by a low-temperature polymer drawing tower to prepare a flexible piezoelectric ultrasonic fiber transducer. The produced fiber is both flexible and continuously processable, but its piezoelectric element is made of piezoelectric polymer material, whose piezoelectric performance is relatively poor compared to piezoelectric ceramics and piezoelectric single crystal materials, affecting the ultrasonic transceiver performance of the ultrasonic transducer. Summary of the invention

[0007] Based on this, the present invention provides a method for preparing a flexible piezoelectric ultrasonic fiber transducer, and develops a piezoelectric fiber device based on piezoelectric ceramics to address the application bottleneck of low piezoelectric constant of piezoelectric materials in traditional polymer piezoelectric fibers, which leads to poor ultrasonic emission and sensing performance. The thermal pulling technology can integrate functional materials with different thermal, acoustic, electrical, and mechanical properties into a tiny fiber through a simple one-step thermal pulling, and accurately control the delicate multi-scale structure of the material, which is most suitable for the integrated large-scale forming preparation of ultrasonic fibers.

[0008] To achieve the above object, on the one hand, the present invention provides a method for preparing a flexible piezoelectric ultrasonic fiber transducer, comprising the following steps:

[0009] S1. Stack two films A and B in the order of ABABA, wherein A is a non-conductive high molecular polymer film, and B is a conductive high molecular polymer film, and the center position of the non-conductive high molecular polymer film located in the middle layer is provided with a plurality of piezoelectric element grooves with through-hole structures arranged at intervals along its length direction, a piezoelectric element is placed in the piezoelectric element groove, and the positive and negative electrodes of the piezoelectric element are respectively attached to the conductive high molecular polymer films on both sides, and the conductive high molecular polymer film is embedded with Teflon wires arranged along the arrangement direction of the piezoelectric element grooves;

[0010] S2, hot-pressing the film laminated in step S1 and then extracting the Teflon wire from the preform to obtain a hot-stretched preform with a piezoelectric ultrasonic circuit structure and metal wire through holes;

[0011] S3, fixing the hot-stretched preform obtained in step S2 in a low-temperature polymer drawing tower, and preparing a flexible piezoelectric ultrasonic fiber transducer by hot stretching and feeding the metal wire into the metal wire through hole during the hot stretching.

[0012] As a further preferred technical solution of the present invention, the piezoelectric element is a piezoelectric ceramic material such as lead-containing piezoelectric ceramics (lead zirconate titanate, barium titanate or lead titanate), lead-free piezoelectric ceramics (zinc oxide or barium strontium titanate), or a piezoelectric single crystal material such as binary piezoelectric single crystal (PMN-PT, PZN-PT), ternary piezoelectric single crystal (PMN-PIN-PT, PMN-PZ-PT), and the center frequency of the piezoelectric element is 1kHz-10 MHz. The piezoelectric element is arranged in a single / multiple rows at a spacing of 0.1-10mm, and the size of the piezoelectric element is 0.0025cm 2 -1 cm 2 . Further preferably, the length and width specifications of the piezoelectric element range from 0.1 to 5 mm, and the height dimension is designed according to the required center frequency. Specifically: when the width of the element is less than 0.1 mm, the circuit system is prone to short circuit or open circuit if the size is too small, and the ultrasonic emission and reception performance decreases after the element is coated with a polymer, and it cannot be applied in actual scenarios. When it is less than 0.1 mm, the ultrasonic half-wavelength is too small, and the interval between the piezoelectric elements needs to be controlled in an extremely small range to fully utilize its piezoelectric performance; when the element length is higher than 5 mm, although the ultrasonic signal will be greatly improved, due to the rigidity of the piezoelectric element, the overly long element cannot take into account the flexible characteristics, and its half-wavelength is large, which will cause the signals in several planes to be received and superimposed on each other, reducing the detection quality.

[0013] As a further preferred technical solution of the present invention, the polymer material of the non-conductive high molecular polymer film is styrene-ethylene-butylene-styrene block copolymer (SEBS), polycarbonate (PC), polymethyl methacrylate (PMMA) or polyetherimide (PEI). Since styrene-ethylene-butylene-styrene block copolymer is a thermoplastic elastomer, it has excellent aging resistance, plasticity, high elasticity, and can be processed and used without vulcanization. As a matching layer and backing layer of a piezoelectric ultrasonic system, it can provide excellent elasticity, flexibility, and tensile cycle performance for a flexible piezoelectric ultrasonic fiber transducer. In addition, it can also be replaced by other materials with good elasticity or flexibility, such as polycarbonate, polymethyl methacrylate or polyetherimide.

[0014] As a further preferred technical solution of the present invention, the polymer material of the conductive polymer film is carbon-doped polyethylene (CPE) or carbon-doped polycarbonate (CPC). Carbon-doped polyethylene is a carbon-doped polymer material that combines the heat resistance, corrosion resistance, thermoplasticity and excellent conductivity of polymer materials, and is suitable as a flexible electrode in the fiber. In addition, it can also be replaced by other conductive polymers, such as carbon-doped polycarbonate and other materials.

[0015] As a further preferred technical solution of the present invention, the wire is carbon fiber, copper wire, silver wire or tungsten wire, and more preferably, the wire diameter is 20 to 50 μm.

[0016] As a further preferred technical solution of the present invention, the high molecular polymer raw material for preparing the film in step S1 needs to be dried before preparing the film, the drying time is 5 to 10 days, and the drying temperature is 60°C; the hot pressing temperature in step S2 is 105 to 160°C; the thickness of the hot-stretched preform obtained in step S2 is 7 to 12 mm.

[0017] As a further preferred technical solution of the present invention, in step S3, the low-temperature polymer drawing tower is divided into three temperature zones, and the hot-stretched preform is heat-stretched in the three temperature zones in turn, wherein the upper and lower temperature zones are regulated according to the physical properties of the preform and the surrounding environment, and the temperature of the middle temperature zone is set to 130-160°C. Specifically, when the temperature of the middle temperature zone is lower than 130°C, the preform cannot reach the softening temperature, and the polymer cannot be transformed into a viscous flow state for hot stretching to prepare the fiber; when the temperature of the middle temperature zone is higher than 160°C, the temperature of the preform is too high, the viscosity is reduced, and the uniform fiber cannot be stably prepared, which easily causes the fiber to break prematurely, and the excessively high temperature will cause the piezoelectric constant (d33) and other properties of the ultrasonic element to decay, which has a certain influence on the ultrasonic emission and receiving performance of the flexible piezoelectric ultrasonic fiber transducer finally prepared. By selecting different materials to conduct experiments at different temperatures, it is finally found that a flexible piezoelectric ultrasonic fiber transducer with uniform distribution and good performance can be obtained within the temperature range of 130-160°C.

[0018] As a further preferred technical solution of the present invention, in order to make the conductive high polymer film cover the inside of the heat-stretched preform without being exposed, and at the same time make the surface of the heat-stretched preform smooth after hot pressing, in step S1, conductive dielectric grooves adapted to the conductive high polymer film (referring to the same length, width and height dimensions) are respectively opened on the non-conductive high polymer film located in the middle layer and one of the non-conductive high polymer films located on the outside, and the two conductive high polymer films are respectively embedded in the conductive dielectric grooves; the conductive high polymer film is also provided with a metal wire groove adapted to the wire, and the Teflon wire is embedded in the metal wire groove before hot pressing the heat-stretched preform.

[0019] According to another aspect of the present invention, the present invention further provides a flexible piezoelectric ultrasonic fiber transducer, which is prepared by the above method.

[0020] According to another aspect of the present invention, the present invention also provides an application of a flexible piezoelectric ultrasonic fiber transducer as a flexible sensing fabric, wherein the flexible piezoelectric ultrasonic fiber transducer is used to simultaneously transmit and receive fixed frequency ultrasonic waves. Specifically, the fiber transducer is woven into a fabric of appropriate size by a weaving method, and then used as an ultrasonic transducer fabric that can transmit and receive ultrasonic signals in real time for detecting defects in industrial workpieces, imaging human tissues, and non-invasive treatment.

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0022] 1) The present invention uses a flexible non-conductive polymer film to coat the piezoelectric ultrasonic circuit system to prepare the fiber. The non-conductive polymer film can be used as a matching layer and backing layer of the ultrasonic transducer system while serving as a coating layer. It is non-toxic and harmless, has a certain degree of flexibility and elasticity, is wear-resistant, has good elasticity, and is easy to process and prepare;

[0023] 2) The flexible piezoelectric ultrasonic fiber transducer prepared by the present invention has a stable structure, good flexibility, can be bent at a large angle, can simultaneously transmit and receive ultrasonic signals in real time, and has a wide range of application scenarios, such as as a flexible sensing fabric;

[0024] 3) The flexible piezoelectric ultrasonic fiber transducer prepared by the present invention adopts a conventional heat stretching process, has controllable costs, mature technology, and can be industrially produced continuously. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0026] Figure 1 It is a schematic structural diagram of the hot-drawn preform of the flexible piezoelectric ultrasonic fiber transducer of the present invention before hot pressing.

[0027] Figure 1 In the figure: 1. Matching layer; 2. Teflon wire; 3. Conductive medium; 4. Piezoelectric element; 5. Insulation layer; 6. Backing layer; 7. Conductive medium slot; 8. Metal wire slot; 9. Ultrasonic element slot.

[0028] Figure 2 The actual image (a) and the enlarged image (b) of the flexible piezoelectric ultrasonic fiber transducer prepared in Example 1.

[0029] Figure 3 This is a test diagram of the ultrasonic emission performance of the flexible piezoelectric ultrasonic fiber transducer prepared in Example 1.

[0030] Figure 4 This is a test diagram of the ultrasonic receiving performance of the flexible piezoelectric ultrasonic fiber transducer prepared in Example 1.

[0031] Figure 5 This is the ultrasonic emission spectrum of the flexible piezoelectric ultrasonic fiber transducer prepared in Example 1.

[0032] Figure 6 The piezoelectric constant test of 1-3PZT piezoelectric ceramics after heating at different temperatures for 30 minutes.

[0033] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0035] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0036] The following is a 1-3PZT piezoelectric ceramic (Japan Fine Geramigs Go.LTO PZT-Pb(Zr·Ti)O 3 -C-201), copper wire (Cu, Goodfellow CU00-WR-000115), carbon-doped polyethylene (CPE, Hillas LAD 5710), styrene-ethylene-butylene-styrene block copolymer (SEBS, Karton G1657) are preferred raw materials for explanation and implementation.

[0037] like Figure 1As shown, the following embodiments use 1-3PZT piezoelectric ceramics as piezoelectric elements 4, which have high piezoelectric constants and rigid structural characteristics, excellent piezoelectric ultrasonic performance, and the 1-3 composite structure formed with epoxy resin can match the impedance with the coupling agent, and is a piezoelectric ceramic material commonly used in ultrasonic transducers; 1-3PZT piezoelectric ceramics are embedded in the SEBS film as the insulating layer 5; carbon-doped polyethylene (CPE) is selected as the conductive medium 3 to completely fit the positive and negative electrodes of the piezoelectric element 4 to ensure stable reception of ultrasonic electrical signals; copper wires are embedded in the conductive high molecular polymer as conductors to ensure electrical signal transmission; finally, two SEBS films are used to cover the front and back surfaces as matching layers 1 and backing layers 6, and completely cover the conductive medium 3. In practical applications, encapsulation layers can also be laminated on the outside of the matching layer 1 and the backing layer 6 for coating, and the material of the encapsulation layer can be a film of SEBS, PC, PMMA or PEI material.

[0038] A hot-stretched preform (1-3PZT piezoelectric ceramic as a piezoelectric element, SEBS film as an insulating layer 5, a matching layer 1, a backing layer 6, CPE as a conductive medium 3, and a copper wire as a conductor is prepared. Figure 1 ) is heated in a low-temperature polymer drawing tower and then stretched. The CPE and copper wire are tightly fitted with the piezoelectric element through stretching to obtain a complete current path. The SEBS is tightly wrapped around the ultrasonic circuit system through stretching to finally obtain a flexible piezoelectric ultrasonic fiber transducer. By leading out the circuit at both ends of the fiber to connect to the signal generator and waveform generator, the ultrasonic signal can be transmitted and received through the fiber.

[0039] Example 1

[0040] The preparation method of the flexible piezoelectric ultrasonic fiber transducer of this embodiment is as follows:

[0041] Step 1: Preparation of hot-stretched preforms:

[0042] 1) The SEBS raw material was vacuum dried in an oven at 60°C for 7 days, and a SEBS film with a thickness of 2 mm was obtained by hot pressing at 160°C, and the film was cut into 3 rectangular films of 20×200 mm; 10 square ultrasonic element grooves with a length and width of 0.5×0.5 mm, a depth of 0.4 mm, and a spacing of 1 mm were engraved in the center of one of the SEBS films along the length direction, and a rectangular conductive dielectric groove with a length and width of 8×180 mm and a depth of 1.6 mm was engraved at the center of the back of the film, and the SEBS film was used as an insulating layer; a rectangular conductive dielectric groove with a length and width of 8×180 mm and a depth of 1.6 mm was engraved in the center of another film along the length direction, and the SEBS film was used as a matching layer; the remaining SEBS film was used as a backing layer;

[0043] 2) The CPE raw material was vacuum dried in an oven at 60°C for 7 days, and hot pressed at 105°C to obtain a CPE film with a thickness of 1.6 mm, which was cut into two 8×180 mm rectangular films as conductive media; and a rectangular metal wire groove with a length and width of 1×180 mm and a depth of 1 mm was engraved in the center along the length direction;

[0044] 3) The conductive medium 3 is embedded in the rectangular conductive medium groove 7, the piezoelectric element 4 (0.4×0.4×0.28 mm) is embedded in the square ultrasonic element groove 9, and the 1 mm diameter Teflon wire 2 is embedded in the rectangular metal wire groove 8. The above-mentioned SEBS film and CPE film are stacked in the configuration of ABABA (A is SEBS film, B is CPE film), wherein the outermost two layers of SEBS film are the matching layer 1 and the backing layer 6, respectively, and the middle SEBS film is the insulating layer, and then pressed in a hot press at 105° C. The specific structure is as follows Figure 1 As shown, the Teflon wire 2 is finally drawn out to obtain a heat-drawn preform (also called a preform rod). After the Teflon wire 2 is drawn out, a metal wire through hole is formed on the heat-drawn preform to facilitate subsequent feeding of wires.

[0045] Step 2: High temperature heat stretching to prepare fibers

[0046] The hot-stretched preform was fixed in a low-temperature polymer drawing tower, and the upper temperature zone was set to 120°C, the middle temperature zone was set to 215°C, and the lower temperature zone was set to 60°C. After heating for 18 minutes, the preform was transformed into a viscous flow state and stretched and thinned. The feeding speed was set to 1mm / min and the pulling speed was set to 0.4m / min, so that the hot stretching ratio was 1:20. At the same time, the copper wire was fed into the metal wire through hole during the fiber stretching process, and finally a flexible piezoelectric ultrasonic fiber transducer was obtained. The appearance of the fiber is shown in Figure 2 shown.

[0047] It should be noted that the copper wire is fed into the final fiber transducer during the hot-drawing process of the hot-drawn preform, and its operation belongs to conventional technology and will not be described in detail here. The present invention embeds the metal wire groove into the Teflon wire with a diameter of 1 mm during hot pressing to prevent the metal wire groove from collapsing during hot pressing. After hot pressing, the Teflon wire can be pulled out, so that a metal wire through hole is formed at the position of the metal wire groove.

[0048] For the flexible piezoelectric ultrasonic fiber transducer of this embodiment, a commercial ultrasonic probe (Olympus 5MHz) is used as the transmitting or receiving module in the test system, a signal generator (Keysight 33500B) is used to provide an electrical signal for the piezoelectric ultrasonic fiber or the commercial ultrasonic probe, and a wide-band amplifier (Aigtek ATA-1200C) is used to characterize the ultrasonic signal received by the piezoelectric ultrasonic fiber or the commercial ultrasonic probe using a digital oscilloscope (SiglentSDS1202X-E). The results are as follows:

[0049] (1) The flexible piezoelectric ultrasonic fiber transducer and the commercial ultrasonic probe were completely immersed in deionized water to achieve coupling between the fiber and the probe. The fiber was excited by a 5MHz AC signal to emit ultrasonic waves. The distance between the fiber and the commercial probe was kept at 5mm. The signal generator output voltage intensity was 5Vpp and applied to the fiber through a widescreen amplifier with a gain of 20dB. The ultrasonic signal received by the commercial probe was characterized by a digital oscilloscope, as shown in Figure 2. Figure 3 . It shows that the flexible ultrasonic piezoelectric fiber transducer has good ultrasonic emission performance and can be applied in practical scenarios through structural weaving.

[0050] (2) The flexible piezoelectric ultrasonic fiber transducer and the commercial ultrasonic probe were completely immersed in deionized water to achieve coupling between the fiber and the probe. The commercial ultrasonic probe was excited with a 5MHz AC signal to emit ultrasonic waves. The distance between the fiber and the commercial probe was kept at 5mm. The signal generator output voltage intensity was 6Vpp and applied to the commercial probe through a widescreen amplifier with a gain of 20dB. According to the characterization of the ultrasonic signal received by the fiber by a digital oscilloscope, Figure 4 . It shows that the flexible ultrasonic piezoelectric fiber transducer has good ultrasonic receiving performance and can be applied in practical scenarios through structural weaving.

[0051] (3) The flexible piezoelectric ultrasonic fiber transducer and the commercial ultrasonic probe were bonded to both sides of the standard test block through a coupling agent, and the fiber was excited with an alternating current signal of 3.5-6 MHz to emit ultrasonic waves. The thickness of the test block between the fiber and the commercial probe was 50 mm, and the input voltage intensity was 60 Vpp. According to the characterization of the fiber spectrum data by a digital oscilloscope, Figure 5 It shows that the center frequency of the flexible ultrasonic piezoelectric fiber transducer is around 5 MHz, and the center frequency does not shift significantly after the piezoelectric element is hot-pulled into the fiber.

[0052] The 1-3PZT piezoelectric ceramic in the flexible ultrasonic piezoelectric fiber transducer prepared in this embodiment has high temperature resistance. The high temperature resistance test is performed on it. Figure 6 The piezoelectric constant of 1-3PZT piezoelectric ceramics after heating at different temperatures for 30 minutes is tested. The d33 of the sample PZT piezoelectric ceramic sheet at room temperature is 540×10 -12 C / N, d33 decreased to 350×10 after heating at 170℃ for 30min -12 C / N, retains 64.814% of the performance of the raw materials, can withstand the temperature of the preform during hot drawing, and still maintains a high advantage over traditional piezoelectric polymer acoustic fibers.

[0053] Example 2

[0054] The fiber transducer was prepared by a method basically the same as that in Example 1, with the only difference being that the hot stretching process parameters of step 2 were different, specifically: the temperature of the low-temperature polymer drawing tower was set to 120°C in the upper temperature zone, 210°C in the middle temperature zone, and 60°C in the lower temperature zone. After heating for 25 minutes, the preform was converted into a viscous flow state and stretched to become thinner. The feeding speed was set to 1 mm / min and the pulling speed was set to 0.4 m / min, so that the hot stretching ratio was 1:20. At the same time, the copper wire was fed into the fiber together with the fiber stretching process.

[0055] Example 3

[0056] The fiber transducer was prepared by a method basically the same as in Example 1, with the only difference being that the hot stretching process parameters of step 2 were different, specifically: the temperature of the low-temperature polymer drawing tower was set to 110°C in the upper temperature zone, 235°C in the middle temperature zone, and 50°C in the lower temperature zone. After heating for 9 minutes, the preform was converted into a viscous flow state and stretched to become thinner. The feeding speed was set to 1 mm / min and the pulling speed was set to 0.4 m / min, so that the hot stretching ratio was 1:20. At the same time, the copper wire was fed into the fiber together with the fiber stretching process.

[0057] Example 4

[0058] The fiber transducer was prepared by a method substantially the same as that in Example 1, except that the piezoelectric element in step 1 was different, specifically: a 1-3PMN-PT piezoelectric single crystal (0.4×0.4×0.28 mm) was used as an ultrasonic element to prepare a hot-drawn preform.

[0059] A comprehensive comparison is made between the different flexible piezoelectric ultrasonic fiber transducers prepared in the above embodiments (as shown in Table 1). Compared with Embodiment 1, Embodiments 2, 3 and 4 also have good ultrasonic emission and reception performance. In addition, the fibers have good flexibility and can also meet the weaving requirements.

[0060] Table 1 Performance comparison of flexible piezoelectric ultrasonic fiber transducers prepared with different parameters

[0061] Example 1 Example 2 Example 3 Example 4 Medium temperature zone 215℃ 210℃ 235℃ 215℃ Initial heating time 18min 25min 9min 15min Fiber diameter 1.5 mm 3 mm 0.8mm 1mm Piezoelectric constant <![CDATA[350×10 -12 C / N]]> <![CDATA[380×10 -12 C / N]]> <![CDATA[300×10 -12 C / N]]> <![CDATA[650×10 -12 C / N]]>

[0062] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a flexible piezoelectric ultrasonic fiber transducer, characterized in that: The following steps are involved: S1. Stack two films A and B in the order of ABABA, wherein A is a non-conductive high molecular polymer film, and B is a conductive high molecular polymer film, and the center position of the non-conductive high molecular polymer film located in the middle layer is provided with a plurality of piezoelectric element grooves with through-hole structures arranged at intervals along its length direction, a piezoelectric element is placed in the piezoelectric element groove, and the positive and negative electrodes of the piezoelectric element are respectively attached to the conductive high molecular polymer films on both sides, and the conductive high molecular polymer film is embedded with Teflon wires arranged along the arrangement direction of the piezoelectric element grooves; S2, hot-pressing the film laminated in step S1 and removing the Teflon wire to obtain a hot-stretched preform with a piezoelectric ultrasonic circuit structure and metal wire through holes; S3, fixing the hot-stretched preform obtained in step S2 in a low-temperature polymer drawing tower, and producing a flexible piezoelectric ultrasonic fiber transducer by hot stretching and feeding the wire into the metal wire through-hole during the hot stretching.

2. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to claim 1, characterized in that: The piezoelectric element is made of piezoelectric ceramic material or piezoelectric single crystal material, and the center frequency of the piezoelectric element is 1kHz-10MHz.

3. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to claim 1, characterized in that: The piezoelectric elements are arranged in single or multiple rows with a spacing of 0.1-10 mm, and the size of the piezoelectric element is 0.0025 cm 2 -1 cm 2 .

4. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to claim 1, characterized in that: The polymer material of the non-conductive high molecular polymer film is styrene-ethylene-butylene-styrene block copolymer, polycarbonate, polymethyl methacrylate or polyetherimide, and the polymer material of the conductive high molecular polymer film is carbon-doped polyethylene or carbon-doped polycarbonate.

5. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to claim 1, characterized in that: The conductive wire is carbon fiber, copper wire, silver wire or tungsten wire.

6. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to claim 5, characterized in that: The wire diameter is 20-50 μm.

7. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to claim 1, characterized in that: In step S3, the low-temperature polymer drawing tower is divided into three temperature zones, and the hot-stretched preform is hot-stretched in the three temperature zones in turn, wherein the temperature of each temperature zone is set to 130-160°C.

8. The method for preparing a flexible piezoelectric ultrasonic fiber transducer according to any one of claims 1 to 7, characterized in that: In step S1, the non-conductive high polymer film located in the middle layer and one of the non-conductive high polymer films located on the outside are both provided with conductive dielectric grooves adapted to the conductive high polymer film, and the two conductive high polymer films are respectively embedded in the conductive dielectric grooves; the conductive high polymer film is provided with a metal wire groove adapted to the wire, and the Teflon wire is embedded in the metal wire groove before the hot-stretched preform is hot-pressed.

9. A flexible piezoelectric ultrasonic fiber transducer, characterized in that: The method is prepared by any one of claims 1 to 8.

10. An application of the flexible piezoelectric ultrasonic fiber transducer according to claim 9 as a flexible sensing fabric, characterized in that: The flexible piezoelectric ultrasonic fiber transducer is used for transmitting and receiving fixed-frequency ultrasonic waves.

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