CN204666246U - A kind of fiber grating geosound of debris flow sensor-based system - Google Patents

Abstract

A fiber grating debris flow geoacoustic sensing system, comprising a broadband light source, a first optical circulator, a first transmission optical fiber, an optical power splitter, a second optical circulator, a second transmission optical fiber, a broadband light source and the first optical circulator The first port of the first optical circulator is connected to the first transmission fiber, the third port of the first optical circulator is connected to the input port of the optical power splitter; the first output port of the optical power splitter is connected to the first output port of the optical power splitter The first port of the second optical circulator is connected, the second port of the second optical circulator is connected with the second transmission fiber, the third port of the second optical circulator is connected with the optical intensity differential demodulation device, and the optical power splitter The second output port is connected with the light intensity differential demodulation device. The first transmission fiber and the second transmission fiber are respectively connected with the sensing probe. The sensing probe is suspended and packaged with a wavelength sampling grating and a sensing grating. The system of the utility model has the advantages of high sensitivity, resistance to temperature influence, simple layout, multi-point multiplexing, and high cost performance.

Description

A Fiber Bragg Grating Debris Flow Geoacoustic Sensing System

technical field

The utility model relates to the technical field of sensors, in particular to an optical fiber grating debris flow geoacoustic sensing system.

Background technique

Debris flow, earthquake and other disasters have the characteristics of sudden outbreak, ferocious and rapid onset, and the dual effects of collapse, landslide and flood damage, and their harm is more extensive and serious than a single geological disaster. During the flow of debris flow, the mixed particles will collide with the mountains along the way, generating vibrations with a specific frequency. This kind of transmission along the rocks along the ditch bank will produce the sound of debris flow. By monitoring the ground sound of debris flow, it is possible to give an alarm in the early stage of debris flow, maximize the time for disaster prevention and mitigation, and effectively reduce the degree of disaster loss. In recent years, many scholars and experts at home and abroad have proposed the development of a debris flow monitoring system as a preliminary measure for debris flow prevention, hoping to give an alarm to residents in areas endangered by debris flow before the debris flow occurs, so as to ensure the safety of their lives and property. At present, most debris flow alarm systems are electronic alarms. For example, the Chengdu Institute of Mountain Hazards and Environment, Ministry of Water Resources, Chinese Academy of Sciences, launched the third-generation debris flow electronic alarm DFW-1 III, which is compatible with world-renowned brands MODEL4190 (B&KG, Denmark), MK222 (made in Germany) of the same nature and precision. However, these electronic geoacoustic monitoring devices need to provide energy in the field, or supplemented by solar power devices, which complicates the sensing system, and the remote signal backhaul is severely attenuated, susceptible to interference, and remote monitoring is difficult.

Optical fiber sensing technology has the characteristics of high sensitivity, easy multi-point multiplexing, anti-electromagnetic interference, passive remote monitoring, etc., and has gradually gained favor in the field of vibration sensors. The application of fiber optic vibration sensors to geoacoustic monitoring, giving full play to their advantages of resistance to harsh environments and long-distance transmission, has become a new direction for research on geohazard monitoring technology. Existing research shows that the significant frequency of debris flow ground sound is lower than 250Hz, and the acceleration amplitude of the minimum vibration is about 0.2m/s2, which belongs to the category of low-frequency weak vibration signals, and is close to the sensitivity limit of the acceleration sensor with the traditional single grating cantilever beam structure. In order to effectively monitor the ground sound of debris flow, the sensitivity of the fiber grating sensor needs to be improved, and some cost-effective technical solutions have been proposed one after another. Among them, the intensity demodulation solution based on the slope method has both high sensitivity and easy multi-point multiplexing. characteristics have become a research hotspot.

Zhu Fangdong from Wuhan University of Technology and others ("Zhu Fangdong. Research on WDM Fiber Bragg Grating Vibration Sensing Network Demodulation System [D]. Wuhan: Wuhan University of Technology, 2012.") proposed to use DFB-LD as the light source, incident to the transmission On the spectral slope of the grating, the wavelength change caused by the acceleration is converted into the change of the intensity of the reflected light signal through the sensing grating. This method can increase the sensitivity of the sensing system by an order of magnitude, but this method is limited by the wavelength of the laser light source. The influence of stability and temperature drift of the sensor grating is not very practical.

Liu Tongyu's research team from the Key Laboratory of Optical Fiber Sensing Technology in Shandong Province improved the above-mentioned system by monitoring the DC component in the reflection signal of the grating to analyze the influence of temperature, and then adjusted the wavelength of the laser to eliminate it, but the system design is complicated and the long-term stability Poor (“Binxin Hu, Tongyu Liu, et al. Distributed fiber optic micro-seismic monitoring system for coal mines[C]. Proc. of SPIE, Vol.8924, 89242F, 2013”).

Utility model content

The technical problem to be solved by the utility model is to provide a fiber grating debris flow geoacoustic sensing system, which has the advantages of high sensitivity, temperature resistance, simple layout, multi-point multiplexing, and high cost performance.

The technical scheme that the utility model takes is:

A fiber grating debris flow geoacoustic sensing system, comprising a broadband light source, a first optical circulator, a first transmission optical fiber, an optical power splitter, a second optical circulator, a second transmission optical fiber, a broadband light source and the first optical circulator The first port of the first optical circulator is connected to the first transmission fiber, the third port of the first optical circulator is connected to the input port of the optical power splitter; the first output port of the optical power splitter is connected to the first output port of the optical power splitter The first port of the second optical circulator is connected, the second port of the second optical circulator is connected with the second transmission fiber, the third port of the second optical circulator is connected with the optical intensity differential demodulation device, and the optical power splitter The second output port is connected with the light intensity differential demodulation device. The first transmission fiber and the second transmission fiber are respectively connected with the sensing probe. The sensing probe is suspended and packaged with a wavelength sampling grating and a sensing grating.

The number of the sensing probes can also be extended by using wavelength division multiplexing (WDM) technology, and multiple sensing probes are serially connected through the first transmission optical fiber and the second transmission optical fiber.

The power ratio of the first output port and the second output port of the optical power splitter is 2:1.

The peak wavelength of the wavelength sampling grating is located at the half power point of the static reflection spectrum of the sensing grating.

The sensing grating is connected with the cantilever beam mechanical structure, and the cantilever beam mechanical structure senses the change of the external acceleration, thereby causing the change of the tensile strain of the grating.

The wavelength sampling grating is used to select and reflect the optical signal of a specific wavelength from the broadband light source, and sense the change of the ambient temperature inside the probe.

The wavelength sampling grating and sensing grating have the same temperature sensitivity coefficient.

The light intensity differential demodulator performs photoelectric conversion and amplification on the reference light (from the optical power splitter) and the signal light (from the sensor grating) of the two input ports respectively, and then makes a difference between the two electrical signals. Since the intensity of the signal light reflected by the sensor grating is equal to that of the reference light when it is static, the intensity of the output electrical signal after the difference is zero. And when the sensing grating is affected by acceleration and the intensity of the reflected light signal changes with the magnitude of the acceleration, the intensity of the output electrical signal after the difference will directly reflect the magnitude and frequency characteristics of the acceleration. In addition, the light intensity differential demodulation device can also well suppress power fluctuations caused by the light source and the transmission fiber. For example, when the light source works for a long time and the output power drops, both the reference signal and the sensing signal will decrease in equal proportion, and the influence of the light source can be well eliminated by the differential method.

For the signals of multiple sensor probes with different wavelengths passing through WDM, it is necessary to add a WDM demultiplexer (or band-pass filter) corresponding to the working wavelength in the optical intensity differential demodulation device, and then the method of single sensor demodulation Perform demodulation of the wavelength sensor of each channel.

A fiber grating debris flow ground acoustic sensing method, the continuous optical power signal sent by the broadband light source enters the first optical circulator, and enters the wavelength sampling grating array through the second port of the first optical circulator, and the wavelength sampling grating is used for broadband light source signal Reflection is performed to form reflection spectra of various specific wavelengths, and then divided into two paths through an optical power splitter: one path is used as a reference signal for direct photoelectric conversion, and the other path enters the sensing grating array through a second optical circulator.

When the sensing probe is static, the incident light signal with matching wavelength is reflected by the sensing grating. Since the incident light is at the half power point of the sensing grating spectrum, the reflected light intensity signal is about half of the power of the incident light intensity signal;

When the sensing probe is affected by the acceleration, the spectrum of the sensing grating shifts, the position of the slope reflection point changes, and the reflected optical power fluctuates accordingly. After the dynamic optical signal is photoelectrically converted, it is compared with the reference signal By making a difference, a stable electrical signal corresponding to the acceleration change can be obtained, and then analyzed by a computer to extract the frequency and amplitude signals related to the acceleration.

A cantilever beam sensing probe includes a stainless steel shell, a wavelength sampling grating, a sensing grating, a spring piece, and a quality block. One end of the spring piece is matched with the quality block and then laser welded, and the other end is matched with the inside of the shell and then laser welded. One end of the sensing grating is glued to the introduction of the stainless steel housing, and the other end is glued to the transition arc of the mass block. One end of the wavelength sampling grating is glued to the introduction of the stainless steel housing, and the other end can be glued to the inner wall of the stainless steel housing. When the probe is working, ground acoustic vibrations such as debris flow are transmitted to the mass block through the stainless steel shell, and the mass block is affected by the acceleration change to produce reciprocating motion in the vertical direction, resulting in the stress change of the sensing grating, which causes the slope position of the grating reflection spectrum to change. Changes, the reflectivity of the corresponding wavelength changes, and the relevant information of vibration can be extracted by detecting the change of light intensity; the wavelength sampling grating is suspended in the stainless steel shell, used to sense the change of the ambient temperature in the stainless steel shell, and balance the temperature due to The influence causes the error caused by the slope change of the sensing grating 8, and improves the stability and application range of the probe.

The utility model is a fiber grating debris flow geoacoustic sensing system, which has the advantages of:

1) The wavelength sampling grating and sensing grating with the same temperature drift coefficient are packaged in the same cavity, and the influence of temperature on the sensing probe is eliminated through optical compensation, so as to ensure that the sensing system has high sensitivity and can work stably for a long time;

2) Using wavelength sampling grating to separate signals from broadband light sources, reducing requirements on light sources and simplifying system costs;

3) The sensing probes can work at different wavelengths, and are easy to multiplex multiple wavelengths, forming a multi-probe series structure.

4) According to the characteristics of debris flow ground sound and complex practical environment, the optical fiber sensing system is optimized to realize passive, multi-point and high-sensitivity monitoring of debris flow ground sound.

Description of drawings

Fig. 1 is a schematic diagram of a fiber grating debris flow geoacoustic sensing system of the present invention;

In the figure: 1—broadband light source, 2—first optical circulator, 3—first transmission fiber 3, 4—sensing probe, 5—optical power splitter, 6—second optical circulator, 7—second transmission Optical fiber, 8—wavelength sampling grating, 9—sensing grating, 10—light intensity differential demodulation device.

Fig. 2 is a kind of specific structural diagram of the cantilever beam sensing probe of the present utility model:

In the figure: 8—wavelength sampling grating, 9—sensing grating, 11—stainless steel shell, 12—spring leaf, 13—mass block.

Fig. 3 A realization principle diagram of light intensity differential demodulation device.

Detailed ways

Below in conjunction with accompanying drawing, specific embodiment of the present utility model is described in further detail:

As shown in Figure 1, a fiber grating debris flow geoacoustic sensing system includes a broadband light source 1, a first optical circulator 2, a first transmission fiber 3, an optical power splitter 5, a second optical circulator 6, a second Transmission fiber 7, broadband light source 1 is connected with the first port of the first optical circulator 2, the second port of the first optical circulator 2 is connected with the first transmission optical fiber 3, the third port of the first optical circulator 2 is connected with optical Input port of power splitter 5. The first output port of the optical power splitter 5 is connected to the first port of the second optical circulator 6, the second port of the second optical circulator 6 is connected to the second transmission fiber 7, and the third port of the second optical circulator 6 The ports are connected to the optical intensity differential demodulation device 10 , and the second output port of the optical power splitter 5 is connected to the optical intensity differential demodulation device 10 . The first transmission optical fiber 3 and the second transmission optical fiber 7 are respectively connected to the sensing probe 4 .

The sensing probe 4 is suspended and packaged with a wavelength sampling grating 9 and a sensing grating 8 .

The number of sensing probes 4 can also be expanded by using wavelength division multiplexing (WDM) technology, and multiple sensing probes 4 are connected in series through the first transmission optical fiber 3 and the second transmission optical fiber 7 .

The power ratio of the first output port and the second output port of the optical power splitter 5 is 2:1. After the optical power of the first output port is reflected by the half-power point of the sensing grating 8, it can obtain the same intensity as the reference signal light of the second output port, so as to facilitate differential processing.

The peak wavelength of the wavelength sampling grating 9 is located at the half power point of the static reflection spectrum of the sensing grating 8 . The spectrum at the half-power point of the grating has good linearity and can make the sensing system have the largest dynamic range.

The sensing grating 8 is connected with a cantilever beam mechanical structure, and the beam mechanical structure senses changes in external acceleration, thereby causing changes in tensile strain of the grating. The cantilever beam mechanical structure is mature and reliable, and the split structure is easy to process (the key parts of the stainless steel shell 11 can be completed by one wire cutting), and it is convenient to adjust the resonant frequency and sensitivity, which is convenient for the test and monitoring of the low frequency band of debris flow.

The wavelength sampling grating 9 is used to select and reflect an optical signal of a specific wavelength from the broadband light source 1 , and to sense changes in the ambient temperature inside the probe. When the temperature of the probe content changes, the wavelength of the sampling grating 9 will drift, and after the broadband light source 1 is reflected by the sampling grating 9, the wavelength of the reflected signal will faithfully reflect the change of the sampling grating 9.

The wavelength sampling grating 9 and the sensing grating 8 have the same temperature sensitivity coefficient. When the ambient temperature in the probe changes, since the two gratings have the same temperature sensitivity coefficient, that is, for the same temperature change, both have the same wavelength drift range, thus ensuring the stability of the half-power reflection point.

A schematic diagram of an implementation scheme of the light intensity differential demodulation device 10 is shown in Figure 3, which includes a first photoelectric converter, a first adjustable amplifier, a second photoelectric converter, a second adjustable amplifier, a difference operation circuit, and an analog-to-digital converter. Conversion and data acquisition card, computer. One end of the first photoelectric converter is connected to the optical fiber, the other end is connected to the first adjustable amplifier, and the other end of the first adjustable amplifier is connected to the difference operation circuit; one end of the second photoelectric converter is connected to the optical fiber, and the other end is connected to the second adjustable amplifier. The other end of the second adjustable amplifier is connected with the difference operation circuit; the other end of the difference operation circuit is connected with the analog-to-digital conversion and data acquisition card, and the other end of the analog-to-digital conversion and data acquisition card is connected with the computer.

The light intensity differential demodulation device 10 performs photoelectric conversion and amplification on the reference light (from the optical power splitter 5 ) and the signal light (from the sensor grating 8 ) of the two input ports respectively, and then differentiates the two electrical signals. Since the intensity of the signal light reflected by the sensing grating 8 is equal to that of the reference light when it is static, the intensity of the output electrical signal after the difference is zero. And when the sensing grating 8 is affected by acceleration, the intensity of the reflected light signal changes with the magnitude of the acceleration, and the intensity of the output electrical signal after the difference will directly reflect the magnitude of the acceleration and the frequency characteristics. In addition, the light intensity differential demodulation device 10 can also well suppress power fluctuations caused by the light source 1 and the transmission fiber 3 . For example, when the light source 1 works for a long time and the output power decreases, both the reference signal and the sensing signal will decrease in an equal proportion, and the influence of the light source can be well eliminated by the differential method.

For the signals of multiple sensor probes 4 with different wavelengths passing through WDM, it is necessary to add a WDM demultiplexer (or band-pass filter) corresponding to the working wavelength in the light intensity differential demodulation device 10, and then single sensor demodulation Method The demodulation of the wavelength sensor of each channel is carried out separately.

A fiber grating debris flow geoacoustic sensing method, the continuous optical power signal sent by the broadband light source 1 enters the first optical circulator 2, enters the wavelength sampling grating 9 array through the second port of the first optical circulator 2, and the wavelength sampling grating 9 Reflect the broadband light source 1 signal to form reflection spectra of various specific wavelengths, and then divide it into two paths through the optical power splitter 5: one path is used as a reference signal for direct photoelectric conversion, and the other path enters the sensing spectrum through the second optical circulator 6 grating 8 array;

When the sensing probe 4 is static, the incident light signal of matching wavelength is reflected by the sensing grating 8, and since the incident light is at the half power point of the spectrum of the sensing grating 8, the reflected light intensity signal is about half of the power of the incident light intensity signal;

When the sensing probe 4 is affected by the acceleration, the spectrum of the sensing grating 8 shifts, the position of the slope reflection point changes, and the reflected optical power fluctuates accordingly. The reference signal is differentiated to obtain a stable electrical signal corresponding to the acceleration change, and then the computer is used for analysis to extract the frequency and amplitude signals related to the acceleration.

As shown in FIG. 2 , a cantilever sensor probe includes a stainless steel shell 11 , a wavelength sampling grating 9 , a sensing grating 8 , a spring piece 12 , and a mass 13 . One end of the spring piece 12 is matched with the mass block 13 and then laser welded, and the other end is matched with the stainless steel shell 11 and then laser welded. One end of the sensing grating 8 is glued to the introduction of the stainless steel housing 11 , and the other end is glued to the transition arc of the proof mass 13 . One end of the wavelength sampling grating 9 is glued to the introduction part of the stainless steel housing 11 , and the other end may be glued to the inner wall of the stainless steel housing 11 . When the probe is working, ground acoustic vibrations such as debris flow are transmitted to the mass block 13 through the stainless steel shell 11, and the mass block 13 reciprocates in the vertical direction under the influence of the acceleration change, resulting in the stress change of the sensor grating 8, so that the reflection spectrum of the grating When the position of the slope changes, the reflectivity corresponding to the wavelength changes. By detecting the change of light intensity, the relevant information of vibration can be extracted; the wavelength sampling grating 9 is suspended in the stainless steel shell 11, and the stainless steel shell 11 used for sensing When the wavelength sampling grating 9 and the sensing grating 8 are affected by the ambient temperature at the same time, since they have the same temperature sensitivity coefficient, they will produce the same wavelength drift, thus ensuring the peak point of the sensing grating 8 It is always at the half power point, so as to balance the error caused by the slope change of the sensing grating 8 due to the influence of temperature, and improve the stability and application range of the probe.

Claims (7)

1. A fiber grating debris flow geoacoustic sensing system, including a broadband light source (1), a first optical circulator (2), a first transmission optical fiber (3), an optical power splitter (5), and a second optical circulator (6) The second transmission optical fiber (7), characterized in that the broadband light source (1) is connected to the first port of the first optical circulator (2), and the second port of the first optical circulator (2) is connected to the second port of the first optical circulator (2). A transmission fiber (3) is connected, the third port of the first optical circulator (2) is connected to the input port of the optical power splitter (5); the first output port of the optical power splitter (5) is connected to the second optical circulator (6) is connected to the first port, the second port of the second optical circulator (6) is connected to the second transmission fiber (7), the third port of the second optical circulator (6) is connected to the light intensity differential demodulation device (10) connection, the second output port of the optical power splitter (5) is connected to the light intensity differential demodulation device (10); the first transmission fiber (3) and the second transmission fiber (7) are respectively connected to the sensor The probe (4) is connected; the sensing probe (4) is suspended and packaged with a wavelength sampling grating (9) and a sensing grating (8). 2. A fiber grating debris flow geoacoustic sensing system according to claim 1, characterized in that the wavelength sampling grating (9) is used to select and reflect optical signals of specific wavelengths from the broadband light source (1), and sense Changes in the temperature of the environment inside the probe. 3. A fiber grating debris flow geoacoustic sensing system according to claim 1, characterized in that the wavelength sampling grating (9) and sensing grating (8) have the same temperature sensitivity coefficient. 4. A fiber grating debris flow geoacoustic sensing system according to claim 1, characterized in that the power ratio of the first output port and the second output port of the optical power splitter (5) is 2:1. 5. A fiber grating debris flow geoacoustic sensing system according to claim 1, characterized in that the peak wavelength of the wavelength sampling grating (9) is located at the half power point of the static reflection spectrum of the sensing grating (8). 6. A fiber grating debris flow geoacoustic sensing system according to claim 1, characterized in that a plurality of sensing probes (4) are connected in series through the first transmission optical fiber (3) and the second transmission optical fiber (7). 7. A fiber grating debris flow geoacoustic sensing system according to claim 1, characterized in that the light intensity differential demodulation device (10) includes a first photoelectric converter, a first adjustable amplifier, a second photoelectric converter , a second adjustable amplifier, a differential operation circuit, an analog-to-digital conversion and a data acquisition card, and a computer; one end of the first photoelectric converter is connected to the optical fiber, the other end is connected to the first adjustable amplifier, and the other end of the first adjustable amplifier is connected to the first adjustable amplifier. The difference operation circuit is connected; one end of the second photoelectric converter is connected to the optical fiber, the other end is connected to the second adjustable amplifier, and the other end of the second adjustable amplifier is connected to the difference operation circuit; the other end of the difference operation circuit is connected to the analog-to-digital conversion And the data acquisition card, the analog-to-digital conversion and the other end of the data acquisition card are connected with the computer.