A fiber optic Fabry-Perot weak ultrasonic sensor

Abstract

This invention discloses a fiber optic Fabry-Perot weak ultrasonic sensor, comprising: a microphone and a fiber optic Fabry-Perot ultrasonic sensor; the microphone is horn-shaped, and its small-diameter end is connected to the signal receiving end of the fiber optic Fabry-Perot ultrasonic sensor; the inner wall of the microphone includes serrated steps. The technical solution provided by this invention improves the detection sensitivity of the fiber optic Fabry-Perot sensor.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic sensing technology, specifically to a fiber optic Fabry-Perot weak ultrasonic sensor. Background Technology

[0002] Because partial discharge in high-voltage power equipment is accompanied by the generation of ultrasonic signals, ultrasonic signal monitoring can be used to promptly locate faults in the equipment and facilitate timely maintenance. However, the presence of significant noise in the actual monitoring environment and the complex structure of the power equipment leading to rapid attenuation of the partial discharge ultrasonic signals add considerable difficulty to ultrasonic signal detection.

[0003] The commonly used fiber optic Fabry-Perot ultrasonic sensors in existing technologies have relatively low sensitivity, making them difficult to apply to the detection of weak ultrasonic signals. Therefore, improving the detection sensitivity of fiber optic Fabry-Perot sensors is an urgent problem to be solved in practical applications. Summary of the Invention

[0004] In view of this, the present invention provides a fiber optic Fabry-Perot weak ultrasonic sensor, which improves the detection sensitivity of the fiber optic Fabry-Perot sensor.

[0005] According to a first aspect, embodiments of the present invention provide a fiber optic Fabry-Perot weak ultrasonic sensor, comprising: a microphone and a fiber optic Fabry-Perot ultrasonic sensor; the microphone is horn-shaped, and the small-diameter end of the microphone is connected to the signal receiving end of the fiber optic Fabry-Perot ultrasonic sensor; the inner wall of the microphone includes serrated steps.

[0006] Optionally, the fiber optic Fabry-Perot ultrasonic sensor includes: a quartz diaphragm, a first quartz tube, a second quartz tube, and a single-mode optical fiber; one side of the quartz diaphragm covers the small-diameter end of the receiver; the other side of the quartz diaphragm covers one end of the second quartz tube; the second quartz tube is sleeved outside the first quartz tube, and the first quartz tube is sleeved outside the single-mode optical fiber; a preset distance exists between the first end face and the second end face, and the inner walls of the two quartz tubes, the first end face, the second end face, and the preset distance together constitute the fiber optic Fabry-Perot cavity, wherein the first end face is the end face of the first quartz tube near the quartz diaphragm, and the second end face is the end face of the quartz diaphragm connected to the second quartz tube; the end face of the single-mode optical fiber inserted into the first quartz tube is located on the same plane as the first end face.

[0007] Optionally, the inclined surface of the serrated step forms an angle A with the plane of the quartz diaphragm, and the value of the angle A is in the range of 3~12°.

[0008] Optionally, the quartz diaphragm is coated with an anti-reflection film on the end face of the quartz diaphragm near the fiber Fabry-Perot cavity and the end face of the single-mode fiber near the fiber Fabry-Perot cavity.

[0009] Optionally, the connection between the microphone and the quartz diaphragm, between the quartz diaphragm and the second quartz tube, between the second quartz tube and the first quartz tube, and between the first quartz tube and the single-mode optical fiber are all achieved by CO2 laser welding.

[0010] Optionally, the inner diameter of the first quartz tube ranges from 0.1 to 1.3 mm, and the outer diameter ranges from 1.2 to 2.5 mm; the inner diameter of the second quartz tube ranges from 1.2 to 2.5 mm, and the outer diameter ranges from 3 to 4 mm.

[0011] Optionally, the diameter of the quartz diaphragm ranges from 3 to 4 millimeters, and the thickness ranges from 60 to 80 micrometers.

[0012] Optionally, the preset distance is in the range of 30 to 50 micrometers.

[0013] Optionally, the microphone and the fiber optic Fabry-Perot ultrasonic sensor are made of silicon dioxide.

[0014] The technical solution provided in this application has the following advantages: The technical solution provided in this application uses a horn-shaped microphone to improve signal collection efficiency. At the same time, the inner wall of the microphone is micro-processed into a serrated step to enhance the focusing ability of the ultrasonic signal, thereby further increasing the detection sensitivity of weak ultrasonic signals.

[0015] Furthermore, all components of the ultrasonic sensor are joined using CO2 laser welding, resulting in a tight and secure connection that extends the sensor's lifespan. All components are made of silicon dioxide, which has the same coefficient of thermal expansion and thermo-optical coefficient, thus effectively improving the sensor's stability. Attached Figure Description

[0016] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings: Figure 1 A schematic diagram of the structure of a fiber optic Fabry-Perot weak ultrasonic sensor is shown in one embodiment of the present invention. Figure 2 This diagram illustrates another structural schematic of a fiber optic Fabry-Perot weak ultrasonic sensor according to one embodiment of the present invention.

[0017] The numbers in the diagram are as follows: 1- microphone, 2- microphone inner wall, 3- quartz diaphragm, 4- antireflective coating, 5- fiber optic Fabry-Perot cavity, 6- second quartz tube, 7- first quartz tube, 8- single-mode fiber, 9- weak ultrasonic signal, 10- fiber optic Fabry-Perot ultrasonic sensor. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figure 1 In one embodiment, the fiber optic Fabry-Perot weak ultrasonic sensor provided by this invention specifically includes a microphone 1 and a fiber optic Fabry-Perot ultrasonic sensor 10. The microphone 1 is horn-shaped, and its small-diameter end is connected to the signal receiving end of the fiber optic Fabry-Perot ultrasonic sensor 10. The inner wall 2 of the microphone 1 is processed by femtosecond laser micromachining to form a sawtooth-shaped step.

[0020] Specifically, in this embodiment of the invention, a horn-shaped receiver 1 is installed at the signal receiving end of the fiber optic Fabry-Perot ultrasonic sensor 10. The horn-shaped receiver 1 is made of a quartz tube processed into a horn shape. By using the horn-shaped receiver 1, the signal collection efficiency is improved, and the signal diverging from all directions is collected to the small-diameter end through the inner wall of the horn shape. At the same time, the inner wall 2 of the receiver is micro-processed. In this embodiment of the invention, the inner wall 2 of the receiver is processed into a sawtooth-shaped step, which enhances the focusing ability of the ultrasonic signal, makes the signal more concentrated in the center, avoids the loss of ultrasonic signal, and improves the sensitivity of signal acquisition. Specifically, in one embodiment, such as Figure 2 As shown, the aforementioned fiber optic Fabry-Perot ultrasonic sensor 10 includes: a quartz diaphragm 3, a first quartz tube 7, a second quartz tube 6, and a single-mode optical fiber 8.

[0021] The quartz diaphragm 3 is made by polishing a common circular quartz membrane. The quartz diaphragm 3 is positioned at the small-diameter end of the receiver and one end of the second quartz tube 6, covering both ends to receive the signal focused by the receiver 1. In this embodiment, the diameter of the quartz diaphragm 3 can be 3-4 mm, and the thickness 60-80 micrometers. This size makes the quartz diaphragm 3 sufficiently thin, allowing for immediate response to even weak ultrasonic signals. It deforms upon receiving weak ultrasonic signals, further preventing the signal from being undetectable due to low signal strength, thus improving the sensitivity of ultrasonic signal acquisition. In practical applications, the specific dimensions of the quartz diaphragm can be flexibly adjusted according to actual needs; this embodiment is not limited to this.

[0022] In this embodiment, two different specifications of quartz tubes are used. The inner diameter of the second quartz tube is larger than that of the first quartz tube, and the second quartz tube 6 is fitted over the first quartz tube 7. In this embodiment, the inner diameter of the first quartz tube 7 ranges from 0.1 to 1.3 mm, and the outer diameter ranges from 1.2 to 2.5 mm. The inner diameter of the second quartz tube ranges from 1.2 to 2.5 mm, and the outer diameter ranges from 3 to 4 mm. In practical applications, when the outer diameter of the first quartz tube and the inner diameter of the second quartz tube are specifically chosen within the above ranges, it is only necessary to ensure that the outer diameter of the first quartz tube is smaller than the inner diameter of the second quartz tube so that the second quartz tube can be fitted over the first quartz tube. The specific values ​​can be flexibly adjusted according to the user's actual needs, and this embodiment of the invention does not impose any special limitations. For example, in this embodiment, the inner diameter of the first quartz tube is 0.126 mm, the outer diameter is 1.8 mm, and the inner diameter of the second quartz tube 6 is 1.81 mm, and the outer diameter is 3.5 mm.

[0023] One side of the quartz diaphragm covers the small-diameter end of the microphone; the other side of the quartz diaphragm covers one end of the second quartz tube; the second quartz tube is fitted over the first quartz tube, and the first quartz tube is fitted over the single-mode optical fiber. There is a preset distance between the first end face and the second end face. The inner walls of the two quartz tubes, the first end face, the second end face, and the preset distance together form the fiber Fabry-Perot cavity. The first end face is the end face of the first quartz tube that is close to the quartz diaphragm, and the second end face is the end face of the quartz diaphragm that is connected to the second quartz tube. The end face of the single-mode optical fiber inserted into the first quartz tube is located on the same plane as the first end face.

[0024] A preset distance exists between the first end face and the second end face. Based on this preset distance, the first end face, the second end face, and the inner wall of the second quartz tube 6, a cavity is formed. This cavity is the fiber optic Fabry-Perot cavity 5, and the preset distance is the original cavity length of the fiber optic Fabry-Perot cavity 5. In this embodiment of the invention, the preset distance can be set between 30 and 50 micrometers. Since a shorter cavity length results in higher sensitivity, but an excessively short cavity length increases the difficulty of adjustment, a preset distance of 30 to 50 micrometers can achieve high sensitivity of the optical signal while reducing the difficulty of adjustment. Furthermore, a single-mode fiber 8 is inserted into the first quartz tube 7. The outer diameter of the single-mode fiber 8 is consistent with the inner diameter of the first quartz tube 7 to ensure that the single-mode fiber 8 is tightly inserted into the first quartz tube 7. The end face of the single-mode fiber 8 and the first quartz tube 7 closest to the fiber optic Fabry-Perot cavity 5 are flush, and both end faces are located on the same plane. When an ultrasonic signal is detected, the signal acts on the quartz diaphragm 3, causing the quartz diaphragm 3 to deform. This causes a change in the cavity length of the fiber optic Fabry-Perot cavity 5, which in turn causes a corresponding change in the intensity of the Fabry-Perot interference light. By monitoring this change, the partial discharge ultrasonic signal can be detected, thereby detecting weak ultrasonic signals and improving the sensitivity of the monitoring signal.

[0025] Specifically, in one embodiment, the inclined surface of the serrated step in the aforementioned microphone forms an angle A with the plane of the quartz diaphragm 3, and the angle A is set between 3 and 12°. For example, in this embodiment of the invention, the angle is set to 5°. Thus, when the angle between the inclined surface of the serrated step and the plane of the quartz diaphragm 3 is between 3 and 12°, the concentration of the ultrasonic signal towards the center is further improved, thereby increasing the sensitivity of the ultrasonic signal acquisition.

[0026] Specifically, in one embodiment, the end face of the single-mode fiber 8 is flattened and placed in a coating machine along with the quartz diaphragm 3. An anti-reflection coating 4, with a thickness of 100 nanometers, is deposited on the end face of the single-mode fiber 8 near the fiber Fabry-Perot cavity 5 and the end face of the quartz diaphragm 3 near the fiber Fabry-Perot cavity 5. The anti-reflection coating 4 increases the surface reflectivity of the quartz diaphragm 3, and the anti-reflection coating 4 on the end face of the single-mode fiber 8 matches the reflectivity of the two reflecting surfaces constituting the Fabry-Perot cavity, thereby further improving the sensitivity of the fiber optic Fabry-Perot weak ultrasonic sensor when acquiring ultrasonic signals and increasing the success rate of weak ultrasonic signal acquisition.

[0027] Specifically, in one embodiment, the microphone and the fiber Fabry-Perot cavity structure of the quartz diaphragm 3 are welded together using a CO2 laser to form a horn-shaped fiber Fabry-Perot weak ultrasonic sensor. The quartz diaphragm 3 and the second quartz tube 6 are spot-welded using a CO2 laser. The second quartz tube 6 is fitted onto the first quartz tube 7 and welded using a CO2 laser. The end face of the single-mode fiber 8 coated with the anti-reflection film 4, which is flush with the end face of the first quartz tube 7, is spot-welded using a CO2 laser. In this embodiment, the microphone, quartz diaphragm 3, first quartz tube 7, second quartz tube 6, and single-mode fiber 8 are connected together by CO2 laser welding, resulting in a tight and secure connection, thereby improving the lifespan of the sensor.

[0028] Specifically, in one embodiment, the fiber optic Fabry-Perot weak ultrasonic sensor provided by this invention has a microphone and all components of the fiber optic Fabry-Perot ultrasonic sensor made of silicon dioxide. As a result, all components of the overall fiber optic Fabry-Perot weak ultrasonic sensor have the same coefficient of thermal expansion and thermo-optic coefficient, thus effectively improving the stability of the sensor.

[0029] Specifically, in one embodiment, the fiber optic Fabry-Perot weak ultrasonic sensor provided in this invention has multiple through holes at the connection between the second quartz tube 6 and the quartz diaphragm 3 to connect the fiber optic Fabry-Perot cavity 5 to the outside. Considering that when the external temperature rises, if the fiber optic Fabry-Perot cavity 5 is a closed space, the pressure generated by the temperature will compress the quartz diaphragm 3, causing a change in the length of the fiber optic Fabry-Perot cavity 5. This could lead to inaccurate ultrasonic signal acquisition due to temperature factors during the acquisition process. Therefore, by setting through holes, the internal and external air pressures of the fiber optic Fabry-Perot cavity 5 are balanced, thus avoiding acquisition errors caused by temperature increases. Furthermore, when the fiber optic Fabry-Perot weak ultrasonic sensor is located in different gas environments, the refractive index inside the fiber optic Fabry-Perot cavity 5 differs from the refractive index of air under standard atmospheric pressure. This change in refractive index within the cavity alters the intensity of the interference light. Based on the change in light intensity, monitoring results for any gas environment can be obtained, further improving the applicability of the fiber optic Fabry-Perot weak ultrasonic sensor and enabling it to adapt to more gaseous application environments.

[0030] Thus, through the combination of the components in the above embodiments, the fiber optic Fabry-Perot weak ultrasonic sensor is connected to the fiber optic Fabry-Perot sensing demodulation system during use. When the weak ultrasonic signal 9 acts on the sensor, the horn-shaped receiver 1 collects the weak ultrasonic signal 9 with minimal signal loss. This signal passes through the stepped inner wall and is concentrated on the quartz diaphragm 3, causing the quartz diaphragm 3 to deform, resulting in a change in the length of the fiber optic Fabry-Perot cavity, which in turn causes a corresponding change in the intensity of the Fabry-Perot interference light. The partial discharge ultrasonic signal is then detected by monitoring this change.

[0031] Through the above steps, the technical solution provided in this application uses a horn-shaped microphone to improve signal collection efficiency. At the same time, the inner wall of the microphone is micro-processed into a sawtooth-shaped step to enhance the focusing ability of the ultrasonic signal, thereby further increasing the detection sensitivity of weak ultrasonic signals.

[0032] Furthermore, all components of the ultrasonic sensor are joined using CO2 laser welding, resulting in a tight and secure connection that extends the sensor's lifespan. All components are made of silicon dioxide, which has the same coefficient of thermal expansion and thermo-optical coefficient, thus effectively improving the sensor's stability.

[0033] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A fiber optic Fabry-Perot weak ultrasonic sensor, characterized in that, include: Microphone and fiber optic Fabry-Perot ultrasonic sensor; The microphone is horn-shaped, and the small-diameter end of the microphone is connected to the signal receiving end of the fiber optic Fabry-Perot ultrasonic sensor. The fiber optic Fabry-Perot ultrasonic sensor includes: a quartz diaphragm, a first quartz tube, a second quartz tube, and a single-mode optical fiber; one side of the quartz diaphragm covers the small-diameter end of the receiver; the other side of the quartz diaphragm covers one end of the second quartz tube; the second quartz tube is sleeved outside the first quartz tube, and the first quartz tube is sleeved outside the single-mode optical fiber; a preset distance exists between the first end face and the second end face, and the inner wall of the second quartz tube, the first end face, the second end face, and the preset distance together constitute the fiber optic Fabry-Perot cavity, wherein the first end face is the end face of the first quartz tube near the quartz diaphragm, and the second end face is the end face of the quartz diaphragm connected to the second quartz tube; the end face of the single-mode optical fiber inserted into the first quartz tube is located on the same plane as the first end face. The inner wall of the microphone is processed by micro-machining technology to form a sawtooth-shaped step. The inclined surface of the sawtooth-shaped step forms an angle A with the plane of the quartz diaphragm. The value of the angle A is in the range of 3~12°. The connections between the microphone and the quartz diaphragm, between the quartz diaphragm and the second quartz tube, between the second quartz tube and the first quartz tube, and between the first quartz tube and the single-mode optical fiber are all made by CO2 laser welding.

2. The fiber optic Fabry-Perot weak ultrasonic sensor according to claim 1, characterized in that, The quartz diaphragm is coated with an anti-reflection coating on the end face of the fiber Fabry-Perot cavity and on the end face of the single-mode fiber near the fiber Fabry-Perot cavity.

3. The fiber optic Fabry-Perot weak ultrasonic sensor according to claim 1, characterized in that, The inner diameter of the first quartz tube ranges from 0.1 to 1.3 mm, and the outer diameter ranges from 1.2 to 2.5 mm; the inner diameter of the second quartz tube ranges from 1.2 to 2.5 mm, and the outer diameter ranges from 3 to 4 mm.

4. The fiber optic Fabry-Perot weak ultrasonic sensor according to claim 3, characterized in that, The diameter of the quartz diaphragm ranges from 3 to 4 millimeters, and the thickness ranges from 60 to 80 micrometers.

5. The fiber optic Fabry-Perot weak ultrasonic sensor according to claim 1, characterized in that, The preset distance ranges from 30 to 50 micrometers.

6. The fiber optic Fabry-Perot weak ultrasonic sensor according to claim 1, characterized in that, The microphone and the fiber optic Fabry-Perot ultrasonic sensor are made of silicon dioxide.

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