A piezoelectric-fiber composite ultrasonic sensor and detection method thereof

Abstract

The present invention discloses a piezoelectric-fiber composite ultrasonic sensor and a detection method thereof, which belongs to the field of sensors. The sensor includes an optical fiber, a piezoelectric film, and an electrode structure. The testing steps of the structure of the present invention are: 1) gluing the end of the optical fiber away from the piezoelectric film to the structure to be tested or embedding it into the structure to be tested through a coupling agent; 2) the optical fiber acts as a waveguide to transmit the high-frequency vibration signal or ultrasonic signal on the structure to be tested to the piezoelectric film, and generates a corresponding voltage signal based on the positive piezoelectric effect; 3) the electrode transmits the voltage signal to the data conditioner, which is finally received by the data acquisition system. The sensor combines the advantages of optical fiber such as wide temperature application range, anti-electromagnetic interference, corrosion resistance, and good waveguide ability with the advantages of piezoelectric film such as excellent sensing performance, simple processing, high designability, and low cost. It can effectively realize high-performance ultrasonic detection in extreme environments such as high temperature and low temperature.

Description

Technical Field

[0001] The present invention relates to the field of sensors, and in particular to a piezoelectric-fiber composite ultrasonic sensor and a detection method thereof. Background Art

[0002] Ultrasonic testing is a crucial nondestructive testing technique in modern industrial manufacturing. It assesses defects and damage by analyzing changes in the propagation characteristics of ultrasound within a structure. Sensor performance is a key factor influencing the accuracy of ultrasonic testing. Currently, piezoelectric sensors are one of the most widely used ultrasonic sensors in ultrasonic testing due to their wide bandwidth, high sensitivity, and reliability. The main principle of piezoelectric sensors is to measure the mechanical force applied to a piezoelectric material using the direct piezoelectric effect. The acquired data is converted into an electrical signal to represent the measured value. However, piezoelectric sensors have difficulties operating in extreme environments. For example, the sensor's mechanical structure is susceptible to corrosion by strong acids and bases; the accuracy of the piezoelectric signal is susceptible to strong electromagnetic interference; and due to the Curie temperature, piezoelectricity changes significantly at high temperatures, causing the piezoelectric effect to disappear. At low temperatures, the piezoelectric effect not only attenuates but also causes brittle cracking in the sensor. To address these issues, a conventional approach is to connect a waveguide to the object being tested, directing the ultrasonic signal from the test environment to the piezoelectric sensor in the normal environment, thereby isolating it from interference from the test environment. This method still has some shortcomings, including: the waveguide probe is bulky and heavy, making it difficult to secure, and the ultrasonic wave attenuation from the object under test to the waveguide probe is significant. Furthermore, the complex waveguide probe structure complicates ultrasonic modal conversion, hindering subsequent ultrasonic mode-based signal processing. The metal waveguide probe also has a limited temperature range. Therefore, in the face of increasingly diverse and demanding test environments, the application of single or traditional piezoelectric sensors with waveguide probes has certain limitations.

[0003] As a new sensing medium, optical fiber offers excellent resistance to high and low temperatures, as well as immunity to electromagnetic interference, making it adaptable to a variety of harsh operating environments. Furthermore, optical fiber is compact, lightweight, and simple in structure, making it easy to secure to the object being measured. It also exhibits a low ultrasonic attenuation coefficient and avoids the complexities of ultrasonic mode conversion. However, compared to piezoelectric sensors, optical fiber sensors offer lower ultrasonic detection sensitivity and are insufficient for detecting small-amplitude ultrasonic signals.

[0004] In summary, there is an urgent need to combine the advantages of piezoelectric sensors and optical fibers to develop a piezoelectric-optical fiber composite sensor suitable for harsh environments and capable of detecting ultrasonic waves, so as to solve the problem of ultrasonic detection in extreme environments in modern industry. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention discloses a piezoelectric-fiber composite sensor, which can detect the ultrasonic detection problem of materials in harsh environments such as high temperature and low temperature.

[0006] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0007] A piezoelectric-fiber composite sensor, characterized in that the sensor comprises an optical fiber, a piezoelectric film, and an electrode; the optical fiber is coated with a piezoelectric film on the outside, and electrodes are coated on the top and bottom, or front and back of the piezoelectric film, connected to a data acquisition system via wires. The optical fiber, piezoelectric film, and electrodes constitute the sensor, and the sensor as a whole is connected to the data acquisition system via the electrode connecting wires, and the collected signals are processed on the data acquisition system. The sensor of the present invention is based on the transmission of ultrasonic waves through optical fibers, causing the piezoelectric film on the optical fiber to produce a piezoelectric effect, generating an electrical signal to enable ultrasonic detection of materials in extreme environments such as high and low temperatures.

[0008] The piezoelectric film, the sensor's sensitive element, is tightly coated onto an optical fiber using a thin film forming process. The preparation process involves: 1) preparing a piezoelectric precursor solution. Tetrabutyl titanate, lead acetate trihydrate, and zirconium nitrate dihydrate are weighed in a stoichiometric ratio of Pb:Zr:Ti = 2:1:1 and dissolved in ethylene glycol methyl ether. Mixing and stirring for 90 minutes yields a uniform, stable, and transparent precursor solution. 2) Applying the precursor sol to form a gel. After 1-3 days of hydrolysis and polycondensation, the precursor solution forms a sol. A cleaned bare optical fiber is then dipped into the sol and allowed to stand in air to polymerize the gel particles, forming a wet gel. The solution is then dried at 100°C to form a porous dry gel. 3) Heat treatment is performed. The optical fiber with the dry gel is placed at 200-300°C for 100 seconds to cause the remaining organic matter to decompose and the internal pores to collapse. The temperature is then raised to 620-850°C and maintained for 5 minutes. The piezoelectric gel on the optical fiber surface undergoes oxidation, solid-phase reaction, and surface diffusion, ultimately forming a continuous piezoelectric film (2) on the optical fiber. 4) The piezoelectric film is stacked layer by layer by repeating the above process to control the thickness of the piezoelectric film on the optical fiber surface.

[0009] The size and thickness of the piezoelectric film of the present invention, as well as the size, distance and arrangement of the electrodes can be designed according to the specific requirements of sensitivity, bandwidth and the like in ultrasonic detection, thereby realizing broadband ultrasonic detection similar to that of ordinary piezoelectric transducers or resonant ultrasonic detection of a specific frequency.

[0010] Furthermore, the types of the piezoelectric film include: inorganic piezoelectric film, organic piezoelectric film or composite piezoelectric film; the inorganic piezoelectric film adopts piezoelectric ceramics, and the organic piezoelectric film adopts piezoelectric polymers.

[0011] Furthermore, the material of the optical fiber is ordinary quartz optical fiber or sapphire optical fiber; the temperature application range of the ordinary quartz optical fiber is -200°C to 900°C; the temperature application range of the sapphire optical fiber is -200°C to 1600°C; the structure of the optical fiber includes solid optical fiber, hollow optical fiber or microstructured optical fiber.

[0012] Furthermore, the electrodes are fixed on the piezoelectric film by spot welding silver paste, and the electrodes are arranged front to back or up and down on the piezoelectric film.

[0013] The present invention also discloses a detection method for a piezoelectric-fiber composite ultrasonic sensor, which is characterized in that the method is used for detecting various high-frequency vibration signals or ultrasonic signals. The ultrasonic signal generated by material destruction in extreme environments such as high temperature and low temperature is transmitted through a long-distance optical fiber to the piezoelectric film on the optical fiber in a normal temperature environment, causing the piezoelectric film to deform, and then charge movement occurs, which accumulates on the electrode and is transmitted to the data acquisition system through a wire connected to the electrode. By observing the changes in the electrical signal, ultrasonic detection of material structures in extreme environments such as high temperature and low temperature can be achieved.

[0014] The specific steps are:

[0015] 1) The end of the optical fiber away from the piezoelectric film is glued to the structure to be measured or embedded inside the structure to be measured using a coupling agent; 2) The optical fiber acts as a waveguide to transmit the high-frequency vibration signal or ultrasonic signal from the structure to be measured to the piezoelectric film, and based on the positive piezoelectric effect, a corresponding voltage signal is generated; 3) The electrode transmits the voltage signal to the data conditioner, and finally it is received by the data acquisition system.

[0016] In this method, a piezoelectric film is coated on the surface of an optical fiber. One end of the optical fiber is placed on the material to be tested, while the end covered by the piezoelectric film is away from the test environment, effectively isolating the ultrasonic testing process from environmental interference. Ultrasonic waves within the material to be tested pass through the damaged area and are transmitted through the optical fiber, causing polarization of the piezoelectric film. The inverse piezoelectric effect causes charge movement in the piezoelectric film, which is transmitted through the coated electrodes to the data acquisition system, generating an electrical signal change. This enables ultrasonic testing in extreme environments such as high and low temperatures.

[0017] Furthermore, the structure to be tested can be placed in different test environments, including room temperature or high or low temperature environments, strong corrosion environments, high humidity environments, and strong electromagnetic interference environments.

[0018] The beneficial effects of the present invention and the prior art are:

[0019] This invention overcomes the limitations of traditional piezoelectric or fiber optic sensing measurement technologies, combining the advantages of both to enable ultrasonic testing of material structures. Compared to a single piezoelectric sensor, this method allows one end of the optical fiber to be placed in the test environment, while the piezoelectric film portion is kept at room temperature. This effectively avoids the negative impact of environmental factors on the piezoelectric sensor and enables long-distance ultrasonic testing in harsh environments such as high and low temperatures. Compared to a single fiber optic sensor, this method does not require a complex demodulation system and offers high sensitivity.

[0020] The present invention features a simple structure, low cost, and flexible application. Optical fiber, as an excellent waveguide element, is compact, corrosion-resistant, temperature-resistant, and exhibits low ultrasonic loss. Piezoelectric film is simple and inexpensive to process, and the resulting sensor is highly sensitive. The present invention's flexibility is demonstrated by: 1) determining the type of optical fiber and piezoelectric film based on test requirements; and 2) designing the position, length, and thickness of the piezoelectric film coated on the optical fiber, as well as the location of the electrodes, based on the ultrasonic characteristics being measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an overall diagram of the electrodes arranged and coated above and below the piezoelectric film in the sensor according to an embodiment of the present invention;

[0022] Figure 2 This is an overall diagram of electrodes arranged in a front-to-back arrangement and coated on a piezoelectric film in a sensor according to an embodiment of the present invention;

[0023] Figure 3 Schematic diagram of the detection system of the present invention;

[0024] Figure 4 is a schematic diagram of a chirp excitation signal in an embodiment of the present invention;

[0025] Figure 5 Schematic diagram of chirp signal acquisition in an embodiment of the present invention;

[0026] Figure 6 is a schematic diagram of a burst excitation signal in an embodiment of the present invention;

[0027] Figure 7 Schematic diagram of burst acquisition signal in an embodiment of the present invention.

[0028] Among them, 1-electrode, 2-piezoelectric film, 3-optical fiber. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the following examples are given to further illustrate the present invention in detail. It should be noted that the specific implementation described here is only used to explain the present invention and is not intended to limit the present invention.

[0030] like Figures 1-3 As shown, the piezoelectric-fiber composite sensor of the present invention comprises: an electrode 1, a piezoelectric film 2, and an optical fiber 3. The optical fiber 3 is covered with the piezoelectric film 2, and the piezoelectric film 2 is coated with the electrode 1 and connected to a data collector via a wire.

[0031] The piezoelectric film 2, serving as the sensor's sensitive element, is tightly coated onto the optical fiber using a thin film forming process. Its preparation process involves: 1) preparing a piezoelectric precursor solution. Tetrabutyl titanate, lead acetate trihydrate, and zirconium nitrate dihydrate are dissolved in ethylene glycol methyl ether to produce a uniform, stable, and transparent precursor solution. 2) The precursor sol is dipped into the solution to form a gel. After 1-3 days of hydrolysis and polycondensation, the precursor solution forms a sol. A cleaned bare optical fiber is dipped into the sol and allowed to stand in air to polymerize the gel particles, forming a wet gel. The solution is then dried at 100°C to form a porous dry gel. 3) Heat treatment is performed. The optical fiber with the dry gel is placed at 200-300°C for 100 seconds to cause the remaining organic matter to crack and the internal pores to collapse. The temperature is then raised to 620-850°C and maintained for 5 minutes. The piezoelectric gel on the surface of the optical fiber undergoes oxidation, solid-phase reaction, and surface diffusion to eventually form a continuous piezoelectric film 2 on the optical fiber. The sensor is based on the transmission of ultrasonic waves by optical fiber, causing the piezoelectric film on the optical fiber to produce a positive piezoelectric effect, generating an electrical signal to realize ultrasonic detection of materials in extreme environments.

[0032] This embodiment takes active acoustic-ultrasonic testing on a metal aluminum plate as an example. The specific implementation is as follows: First, a piezoelectric transducer is arranged on the aluminum plate and connected to a signal generator to generate an active ultrasonic signal. In order to enhance the sound transmission ability of the ultrasonic wave, a layer of liquid sound-transmitting medium, called a coupling agent, needs to be applied between the transducer and the workpiece surface. Its function is to exclude the air between the probe and the workpiece so that the ultrasonic wave can effectively penetrate the workpiece being tested and ensure sufficient sound intensity transmittance on the detection surface. Then, at a distance of 10 mm from the piezoelectric transducer, the end of the optical fiber 3 away from the piezoelectric film 2 is attached to the aluminum plate to serve as a waveguide to receive the ultrasonic wave propagating in the aluminum plate. The end covering the piezoelectric film 2 is away from the ultrasonic source, thereby simulating the ultrasonic detection scenario under extreme environment. Finally, the electrode 1 on the piezoelectric film 2 of the optical fiber is connected to the data acquisition system through electrodes and wires.

[0033] like Figure 4 As shown in Figure 1, the control function signal generator generates a chirp ultrasonic signal with a sweep frequency range of 10kHz to 1 MHz and a sweep time of 100 µs. Figure 5 It can be seen that under the stimulation of the chirp signal, the present invention can collect the corresponding ultrasonic signal, which proves that the present invention has the ability to detect broadband ultrasonic signals. Figure 6It means that the signal generator generates a 5-cycle trigger excitation signal with a frequency of 500 kHz and a signal duration of 30 μs. For this burst signal, the present invention can also correctly collect it, such as Figure 7 shown.

[0034] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A piezoelectric-fiber composite ultrasonic sensor, characterized in that: The sensor comprises an electrode (1), a piezoelectric film (2) and an optical fiber (3); one end of the optical fiber (3) is covered with a piezoelectric film (2), and an electrode (1) is arranged on the piezoelectric film (2); the other end of the optical fiber (3) is connected to the object to be measured, and the electrode (1) is connected to a data conditioner and a data acquisition system in sequence through a wire; the sensor is based on the transmission of ultrasonic waves by an optical fiber, causing the piezoelectric effect of the piezoelectric film on the optical fiber to generate an electrical signal to realize ultrasonic detection of materials in extreme environments; the piezoelectric film (2) serves as a sensitive element of the sensor, and the piezoelectric film (2) is tightly coated on the optical fiber using a film forming process, and its preparation process is as follows: 1) Prepare a piezoelectric precursor solution; use tetrabutyl titanate, lead acetate trihydrate, and zirconium nitrate dihydrate as raw materials, dissolve them in ethylene glycol methyl ether solution to obtain a uniform, stable, and transparent precursor solution; 2) Dipping the precursor sol and forming a gel; After 1-3 days of hydrolysis and polycondensation, the precursor solution forms a sol. A cleaned bare optical fiber is dipped into the sol and allowed to stand in the air to polymerize the particles, forming a wet gel. The sol is then dried at 100°C to form a porous dry gel. 3) Heat treatment: Place the optical fiber with dry gel at 200-300°C for 100 seconds to cause the remaining organic matter to crack and the internal pores to collapse. Then raise the temperature to 620-850°C and keep it for 5 minutes. The piezoelectric gel on the surface of the optical fiber undergoes oxidation, solid-phase reaction, and surface diffusion to form a continuous piezoelectric film on the optical fiber (2). 4) By repeating the above preparation process, the thickness of the piezoelectric film (2) on the optical fiber surface can be controlled.

2. The piezoelectric-fiber composite ultrasonic sensor according to claim 1, characterized in that: The types of the piezoelectric film (2) include: inorganic piezoelectric film, organic piezoelectric film or composite piezoelectric film; the inorganic piezoelectric film adopts piezoelectric ceramics, and the organic piezoelectric film adopts piezoelectric polymers.

3. The piezoelectric-fiber composite ultrasonic sensor according to claim 1, characterized in that: The material of the optical fiber (3) is ordinary quartz optical fiber or sapphire optical fiber; the applicable temperature range of the ordinary quartz optical fiber is -200°C to 900°C; the applicable temperature range of the sapphire optical fiber is -200°C to 1600°C; the structure of the optical fiber (3) includes solid optical fiber, hollow optical fiber or microstructured optical fiber.

4. The piezoelectric-fiber composite ultrasonic sensor according to claim 1, characterized in that: The electrodes (1) are fixed on the piezoelectric film (2) by spot welding silver paste, and the electrodes (1) are arranged front to back on the piezoelectric film (2), or arranged up and down on the piezoelectric film (2).

5. A detection method for a piezoelectric-fiber composite ultrasonic sensor according to claim 1, characterized in that: The method is used to detect various high-frequency vibration signals or ultrasonic signals, and the specific steps are as follows: 1) bonding one end of the optical fiber (3) away from the piezoelectric film (2) to the structure to be measured or embedding it into the structure to be measured through a coupling agent; 2) The optical fiber (3) acts as a waveguide to transmit the high-frequency vibration signal or ultrasonic signal on the structure to be measured to the piezoelectric film (2), causing the piezoelectric film (2) to deform and convert it into a voltage output according to the positive piezoelectric effect; 3) The electrode (1) transmits the voltage signal to the data conditioner, which is finally received by the data acquisition system. The ultrasonic detection of material structure in extreme environment is realized by observing and analyzing the characteristics of the electrical signal.

6. The detection method of the piezoelectric-fiber composite ultrasonic sensor according to claim 5, characterized in that: During the test, one end of the optical fiber can be placed in the test environment, and the piezoelectric film part can be placed in the room temperature environment; the structure to be tested can be placed in different test environments, including: room temperature or high and low temperature environments, strong corrosion environments, high humidity environments, and strong electromagnetic interference environments.

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