CN209841783U - Reflection type optical fiber acoustic emission system - Google Patents

Abstract

The utility model discloses a reflective optical fiber acoustic emission system, which comprises an optical fiber acoustic emission sensor, a wavelength measurement module, a circulator, a coupler, a tunable narrowband light source, a photoelectric detector, a preamplifier, an acoustic emission acquisition card and a computer; The optical fiber launch sensor is a fiber Bragg grating, the circulator is connected with the tunable narrowband light source, the coupler and the photodetector through the optical fiber in sequence, the two ports on the same side of the coupler are connected with the wavelength measurement module and the circulator through the optical fiber, and the other side It is connected with the optical fiber acoustic emission sensor through optical fiber, the wavelength measurement module and the tunable narrowband light source are respectively connected with the computer through the electrical signal line, the preamplifier is connected between the photodetector and the acoustic emission acquisition card through the electrical signal line, and the acoustic emission acquisition card It is connected with the computer through an electrical signal line. The system has a response speed of microseconds, and can accurately monitor the failure process of solid structure damage and failure in a narrow space.

Description

A reflective optical fiber acoustic emission system

technical field

The utility model relates to the technical field of material performance testing, in particular to a reflective optical fiber acoustic emission system suitable for temperature shock tests in narrow spaces.

Background technique

Acoustic emission system can be used to obtain damage, destruction or failure information of solid structures under variable temperature conditions. Existing acoustic emission systems use piezoelectric materials as sensors, and the probes are bulky and cannot be installed in slit spaces. Optical fiber sensors can be installed in slit spaces due to their slender volume and flexibility. There have been relevant literatures to establish optical fiber acoustic emission systems, but most systems cannot be applied to variable temperature experiments due to the temperature limitation of the sensing principle.

Utility model content

In order to overcome the above-mentioned technical defects, the utility model provides a reflective optical fiber acoustic emission system, which has a microsecond response speed and can accurately monitor the damage and failure process of solid structures in a narrow space.

In order to achieve the above technical effects, the utility model provides the following technical solutions:

A reflective optical fiber acoustic emission system, comprising an optical fiber acoustic emission sensor, a wavelength measurement module, a circulator, a coupler, a tunable narrowband light source, a photodetector, a preamplifier, an acoustic emission acquisition card and a computer; the optical fiber emission sensor It is a fiber Bragg grating, the circulator is connected to the tunable narrowband light source, the coupler and the photodetector through the optical fiber in sequence, the two ports on the same side of the coupler are connected to the wavelength measurement module and the circulator through the optical fiber, and the other The side is connected to the optical fiber acoustic emission sensor through an optical fiber, the wavelength measurement module and the tunable narrowband light source are respectively connected to the computer through an electrical signal line, and the preamplifier is connected through an electrical signal line between the photodetector and the acoustic emission acquisition card , the acoustic emission acquisition card is connected to the computer through an electrical signal line.

A further technical solution is that the optical fiber acoustic emission sensor is an optical fiber Bragg grating with no coating layer and a length within the range of 9-11 mm.

A further technical solution is that the linear region of the fiber Bragg grating is >80pm and the reflectivity is >=80%.

A further technical solution is that the wavelength measurement module has a built-in broadband light source with a wavelength range of 1520-1570nm and a power of less than 1mW.

A further technical solution is that the wavelength of the tunable narrowband light source can be continuously tuned, the tuning range is 1520nm-1570nm, the precision is ≤50pm, the width is ≤10pm, and the power is ≥5mW.

The utility model is further described below. The wavelength measurement module in the device is used to measure the central wavelength λ _B of the optical fiber acoustic emission sensor in real time. It has a built-in wide-spectrum light source with a wavelength range of 1520-1570nm and a power of less than 1mW. It uses a fiber Bragg grating As a fiber optic acoustic emission sensor, its reflection spectrum is an arc-shaped peak, λ _B is the central wavelength, half of the wave peak corresponds to a spectral width of 2λ _b , and the computer obtains λ _B (t ₁ ) at time t1 through the wavelength measurement module , in this system, the light source enters the fiber optic acoustic emission sensor through a circulator and a coupler, the reflected light of the fiber optic acoustic emission sensor is divided into two beams through the coupler, and the wavelength measurement module tracks the wavelength of the fiber optic acoustic emission sensor through the coupler. The wavelength value λ _L (t ₂ ) is assigned by the λ _B (t ₁ ) obtained by the computer, so that λ _L (t ₂ )=λ _B (t ₁ )+λ _b , or λ _L (t ₂ )=λ _B ( t ₁ )-λ _b , t ₂ -t ₁ >50μs and the closer to 50μs, the better, indicating that the wavelength of the light source is consistent with the wavelength response of the fiber optic acoustic emission sensor, and can distinguish acoustic emission signals above 20kHz (1/50μs). This application The circulator has three ports, which are ① port, ② port, and ③ port. These three ports realize the unidirectional transmission function of light, that is, ① port → ② port → ③ port. Among them, the optical loss from ① port to ② port The smaller the better, the light intensity from ① port to ③ port is 0; the smaller the light intensity from ② port to ① port, the better, and the smaller the optical loss from ② port to ③ port, the better; the smaller the light intensity from ③ port to ② port is, the better , The light intensity from port ③ to port ① is 0. The higher the sensitivity of the photodetector in this application, the better, and the acoustic emission light intensity signal is converted into an analog voltage signal. In this system, the photodetector receives the total light intensity I reflected by the optical fiber acoustic emission sensor through the circulator. The total light intensity I includes two parts: the built-in broadband light source I _W of the wavelength measurement module and the tunable narrowband light source I _N. The latter is much greater than the former, so it can be considered that the total light intensity I is close to _{IN, and the light intensity I W of} the broadband light source is very small and is not displayed. In this application, the preamplifier is used to receive the analog voltage signal and amplify it, and the acoustic emission acquisition card is used to collect the acoustic emission signal amplified by the preamplifier and input it to the computer.

Compared with the prior art, the utility model has the following beneficial effects:

The utility model provides an optical fiber Bragg grating as an acoustic emission sensor, uses a wavelength measurement module and a coupler to track the central wavelength of the optical fiber Bragg grating in real time, and combines an acoustic emission acquisition card and a preamplifier to establish a monitoring method for monitoring the temperature-varying damage of solid structures process fiber optic acoustic emission system. The system has a response speed of microseconds, and can accurately monitor the failure process of solid structure damage and failure in a small space in a special temperature-changing environment.

Description of drawings

Fig. 1 is a schematic diagram of the overall structure of the reflective optical fiber acoustic emission system of the present invention;

Fig. 2 is a schematic diagram of reflection spectrum of the reflective optical fiber acoustic emission sensor of the present invention;

Fig. 3 is a schematic diagram of the spectrum reaching the photodetector in this system.

Detailed ways

Example 1

A reflective fiber optic acoustic emission system as shown in Figure 1, comprising a fiber optic acoustic emission sensor, a wavelength measurement module, a circulator, a coupler, a tunable narrowband light source, a photodetector, a preamplifier, and an acoustic emission acquisition card and a computer; the optical fiber launch sensor is a fiber Bragg grating, the circulator is connected to the tunable narrowband light source, a coupler and a photodetector through an optical fiber in sequence, and the two ports on the same side of the coupler are connected to the wavelength measurement module and The circulator is connected through an optical fiber, and the other side is connected with the optical fiber acoustic emission sensor through an optical fiber. The wavelength measurement module and the tunable narrowband light source are respectively connected to the computer through an electrical signal line. The preamplifier is connected between the photodetector and the acoustic emission acquisition The cards are connected by electrical signal wires, and the acoustic emission acquisition card is connected with the computer by electrical signal wires. The circulator has three ports, the smaller the optical loss from port ① to port ②, the better, the light intensity from port ① to port ③ is 0; the smaller the light intensity from port ② to port ①, the better, and the smaller the optical loss from port ② to port ③ The better; the smaller the light intensity from port ③ to port ②, the better, and the light intensity from port ③ to port ① is 0. The coupler is arranged between the fiber circulator and the fiber Bragg grating, and the optical loss of the coupler is as small as possible, that is, the smaller the difference between the light intensity of the ① port and the ② port and the ③ port light intensity, the smaller the better. it is good. In this system, the photodetector receives the total light intensity I reflected by the optical fiber acoustic emission sensor through the circulator. The total light intensity I includes two parts: the built-in broadband light source I _W of the wavelength measurement module and the tunable narrowband light source I _N. The latter is much greater than the former, so it can be considered that the total light intensity I is close to _{IN, and the light intensity I W of} the broadband light source is very small and is not displayed. The optical fiber acoustic emission sensor is an optical fiber Bragg grating with no coating layer and a length within the range of 9-11 mm. The linear region of the fiber Bragg grating is >80pm and the reflectivity is >80%. The wavelength measurement module has a built-in wide-spectrum light source with a wavelength range of 1520-1570nm and a power of less than 1mW. The wavelength of the tunable narrowband light source can be continuously tuned, the tuning range is 1520nm-1570nm, the precision is ≤50pm, the width is ≤10pm, and the power is ≥5mW. In this system, the light source is incident on the fiber optic acoustic emission sensor through the circulator, and the wavelength value λ _L (t ₂ ) is assigned by the λ _B (t ₁ ) obtained by the computer, so that λ _L (t ₂ )=λ _B (t ₁ ) +λ _b , or λ _L (t ₂ )=λ _B (t ₁ )-λ _b , t ₂ -t ₁ >50μs and the closer to 50μs, the better, indicating that the wavelength of the light source is consistent with the wavelength response of the fiber optic acoustic emission sensor, and can Distinguish the acoustic emission signal above 20kHz (1/50μs), use the preamplifier in this application to receive the analog voltage signal, and amplify it, and the acoustic emission acquisition card is used to collect the acoustic emission signal amplified by the preamplifier, and input it to computer.

The wavelength measurement module obtains the center wavelength λ _B of the fiber Bragg grating through the coupler, and the computer assigns the offset wavelength and λ _B to the tunable narrow-band light source. The reflected light intensity information is incident to the photodetector through the coupler and the circulator. When the measured solid with the fiber Bragg grating attached is damaged and destroyed, the dynamic light intensity information obtained by the photodetector can be converted into an electrical signal, which is amplified by the preamplifier, obtained by the acoustic emission acquisition card, and stored and displayed in the calculation. The advantage is that when the measured solid is in a variable temperature environment, the optical fiber acoustic emission system of the present invention will not fail due to the change of the wavelength of the optical fiber grating, and can still effectively monitor the solid damage signal.

Although the utility model has been described here with reference to the explanatory embodiments of the utility model, the above-mentioned embodiment is only a preferred implementation mode of the utility model, and the implementation mode of the utility model is not limited by the above-mentioned embodiment, it should be understood that, Those skilled in the art can devise many other modifications and implementations that will fall within the scope and spirit of the principles disclosed in this application.

Claims (5)

1. A reflective optical fiber acoustic emission system is characterized in that it comprises an optical fiber acoustic emission sensor, a wavelength measurement module, a circulator, a coupler, a tunable narrowband light source, a photodetector, a preamplifier, an acoustic emission acquisition card and a computer The fiber optic acoustic emission sensor is a fiber Bragg grating, the circulator is connected to the tunable narrowband light source, the coupler and the photodetector through the optical fiber in sequence, and the two ports on the same side of the coupler are connected to the wavelength measurement module and the ring The sensor is connected through an optical fiber, and the other side is connected with the optical fiber acoustic emission sensor through an optical fiber. The wavelength measurement module and the tunable narrowband light source are respectively connected to the computer through an electrical signal line. The preamplifier is connected between the photodetector and the acoustic emission acquisition card. They are connected by electric signal lines, and the acoustic emission acquisition card is connected with the computer by electric signal lines. 2 . The reflective fiber optic acoustic emission system according to claim 1 , wherein the fiber optic acoustic emission sensor is a fiber Bragg grating with no coating layer and a length in the range of 9-11 mm. 3 . 3. The reflective fiber optic acoustic emission system according to claim 1, characterized in that, the linear region of the fiber Bragg grating > 80pm and the reflectivity > 80%. 4. The reflective optical fiber acoustic emission system according to claim 1, wherein the wavelength measurement module has a built-in broadband light source with a wavelength range of 1520-1570nm and a power of less than 1mW. 5. The reflective optical fiber acoustic emission system according to claim 1, wherein the wavelength of the tunable narrowband light source can be tuned continuously, the tuning range is 1520nm-1570nm, the precision is ≤50pm, the width is ≤10pm, and the power is ≥5mW light source.