CN108844615B - Distributed optical fiber sensing device and method based on chaotic Brillouin phase spectrum measurement - Google Patents
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Abstract
The invention discloses a distributed optical fiber sensing device based on chaotic Brillouin phase spectrum measurement, which comprises a chaotic laser (1), a first optical isolator (2), a 1 x 2 optical fiber coupler (3), a first optical fiber polarization controller (4), a variable optical delay line (5), an optical amplifier (6), an optical scrambler (7), a second optical isolator (8), a 2 x 2 optical fiber coupler (9), a sensing optical fiber (10), a second optical fiber polarization controller (11), a 3 x 3 optical fiber coupler (12), an electro-optical modulator (13), a microwave signal source (14), a tunable optical attenuator (15), a third optical isolator (16), a balance detector (17) and a real-time oscilloscope (18). The Brillouin frequency shift amount is extracted through the Brillouin phase spectrum, so that the temperature or strain information along the optical fiber is sensed. Compared with the chaotic Brillouin gain spectrum, the chaotic Brillouin phase spectrum-based optical fiber interferometer can sense external vibration information by combining an interferometer structure.
Description
Technical Field
The invention relates to the field of distributed optical fiber sensing, in particular to a distributed optical fiber sensing device and method based on chaotic Brillouin phase spectrum measurement.
Background
The distributed optical fiber sensing technology is to sense the change of information such as external temperature, strain and the like by utilizing physical parameters such as phase, wavelength, light intensity or polarization state and the like of optical signals transmitted in sensing optical fibers, has the advantages of integration of sensing and transmission, light weight, electromagnetic interference resistance, high temperature/corrosion resistance, low loss and the like, and is widely applied to important fields such as aerospace, petrochemical industry, nuclear industry, electric power industry, civil engineering, military frontier defense and the like. The distributed optical fiber sensing technology is further divided into distributed optical fiber sensing technologies based on the rayleigh scattering effect, the raman scattering effect and the brillouin scattering effect according to the scattering effect in the sensing optical fiber. Compared with other distributed optical fiber sensing technologies, the distributed optical fiber sensing technology based on the brillouin scattering effect has unique advantages in sensing distance, spatial resolution and measurement accuracy, can realize simultaneous measurement of temperature or strain information, and has gradually become a great research hotspot in the field of optical fiber sensing.
Distributed optical fiber sensing technologies based on the brillouin scattering effect can be divided into time domain systems and related domain systems. The time domain system comprises: brillouin Optical Time Domain Reflectometry (BOTDR) and Brillouin Optical Time Domain Analyzer (BOTDA). The correlation domain system includes: brillouin Optical Correlation Domain Reflectometry (BOCDR) and Brillouin Optical Correlation Domain Analyzer (BOCDA). A correlation domain system using continuous light whose frequency is sinusoidally modulated as a detection signal can achieve a higher spatial resolution than a time domain system using a pulse signal as a detection signal. For example, k.hotate et al, tokyo university, japan, implements a BOCDR system (optics express,2008,16(16),12148) with a sensing distance of 100m and a spatial resolution of 40cm, and a BOCDA system (Photonics Technology Letters,2007,19(23),1928) with a sensing distance of 20m and a spatial resolution of 10 cm. However, the coherent domain system based on sinusoidal modulation of continuous light frequency has a limited sensing distance while ensuring high spatial resolution due to the contradiction between the sensing distance and the spatial resolution. In order to solve the problem, the chaotic laser is used as a new sensing signal in a distributed optical fiber sensing related domain system (ZL201110217936.6, ZL201310045097.3, ZL201510531253.6, ZL201510531180.6, ZL201610306001.8, ZL 201610305960.8). The correlation domain system based on the chaotic laser detection utilizes the Brillouin gain spectrum to extract Brillouin frequency shift quantity, so that the temperature or strain information along the optical fiber is sensed. Because the distribution of the brillouin gain spectrum is of a lorentz type, the brillouin gain spectrum can be obtained only in a very wide sweep frequency range near the brillouin frequency shift, so that a relative domain system based on the measurement of the chaotic brillouin gain spectrum needs very long measurement time for sensing temperature or strain once, and the measurement real-time performance of the sensing system is influenced.
Disclosure of Invention
In the existing distributed optical fiber sensing related domain system, continuous light with frequency subjected to sinusoidal modulation is used as a detection signal, the contradiction that the measurement distance and the spatial resolution cannot be taken into consideration exists, and the chaotic laser is used as the detection signal, so that the difficulty that the measurement real-time performance is poor and the vibration information cannot be sensed exists. The invention provides a distributed optical fiber sensing device and method based on chaotic Brillouin phase spectrum measurement.
The invention is realized by adopting the following technical scheme:
a distributed optical fiber sensing device based on chaotic Brillouin phase spectrum measurement comprises a chaotic laser, a first optical isolator, a 1 x 2 optical fiber coupler, a first optical fiber polarization controller, a variable optical delay line, an optical amplifier, an optical deflector, a second optical isolator, a 2 x 2 optical fiber coupler, a sensing optical fiber, a second optical fiber polarization controller, a 3 x 3 optical fiber coupler, an electro-optical modulator, a microwave signal source, a tunable optical attenuator, a third optical isolator, a balance detector and a real-time oscilloscope.
The chaotic laser, the first optical isolator, the 1 x 2 optical fiber coupler (upper emergent end), the first optical fiber polarization controller, the variable optical delay line, the optical amplifier, the optical polarization scrambler, the second optical isolator and the I port of the 2 x 2 optical fiber coupler are connected by a single-mode optical fiber jumper in sequence.
The other exit end (lower exit end) of the 1 × 2 optical fiber coupler, the electro-optical modulator, the tunable optical attenuator, the third optical isolator and the b port of the 3 × 3 optical fiber coupler are connected by a single-mode optical fiber jumper in sequence.
The electro-optical modulator is connected with a microwave signal source.
The d port of the 3 multiplied by 3 optical fiber coupler is connected with the m port of the 2 multiplied by 2 optical fiber coupler through a single mode optical fiber jumper; a sensing optical fiber is connected between the n port of the 2 x 2 optical fiber coupler and one port of the second optical fiber polarization controller; the other port of the second optical fiber polarization controller is connected with the e port of the 3 multiplied by 3 optical fiber coupler through a single mode optical fiber jumper; the port a and the port c of the 3 x 3 optical fiber coupler are respectively connected with the negative port and the positive port of the balance detector; the output end of the balance detector is connected with the real-time oscilloscope.
Based on the device, a specific implementation scheme of the distributed optical fiber sensing method based on the measurement of the chaotic Brillouin phase spectrum is as follows:
broadband chaotic laser (with center frequency v) output by chaotic laser0) After passing through the first optical isolator, the optical fiber is divided into two paths through a 1 multiplied by 2 optical fiber coupler: one path output by the upper emergent end is used as a pump (pump) optical signal, and the other path output by the lower emergent end is used as a probe (probe) optical signal. The pump light signal is subjected to polarization control and delay through the first optical fiber polarization controller and the variable optical delay line, and then amplified through the optical amplifier. The amplified pump light sequentially passes through the optical polarization scrambler and the second optical isolator, and enters a Sagnac Interferometer (SI) ring consisting of the 2 × 2 optical fiber coupler, the sensing optical fiber, the second optical fiber polarization controller and the 3 × 3 optical fiber coupler through a port I of the 2 × 2 optical fiber coupler. The detection optical signal output from the lower emitting end of the 1 x 2 optical fiber coupler is modulated into a carrier-suppressed double-sideband detection optical signal by a sinusoidal signal output by a microwave signal source after passing through an electro-optical modulator. The frequency (v ═ 10GHz to 11GHz) of the sinusoidal signal is set at a Brillouin frequency shift value (v ═ 10GHz to 11GHz)B10.6 GHz). Carrier suppressed double sideband (v)0V) the detection optical signal enters the Seganic interference ring from the b port of the 3X 3 optical fiber coupler through the tunable optical attenuator and the third optical isolator in sequence. The double-sideband detection optical signal entering the Seganic interference ring is divided into two beams of optical signals, namely probe1 which is transmitted along the Seganic interference ring in a clockwise direction and probe2 which is transmitted along the Seganic interference ring in a counterclockwise direction, by a 3 x 3 optical fiber coupler, a pump optical signal is introduced into the Seganic interference ring by a 2 x 2 optical fiber coupler, and only the probe2 which is transmitted along the Seganic interference ring in the counterclockwise direction and the pump in the sensing optical fiber generate stimulated Brillouin gain action at the meeting position, namely low-frequency sideband (v) in the probe20-v) the signal is amplified by the pump optical signal. Probe1 transmitted clockwise along the Seganic interference ring is used as a reference signal, and after passing through the second optical fiber polarization controller together with the amplified Probe2 low-frequency sideband signal,interference occurs in a 3 x 3 fiber coupler. The interference effect converts the phase information of the amplified probe2 low-frequency sideband signal into intensity information for subsequent detection. By adjusting the second fiber polarization controller, the polarization states of the two beams of light, probe1 and probe2, can be controlled, so that complete interference is realized. And the interfered optical signal is converted into an electric signal through a balance detector, and is acquired and stored through a real-time oscilloscope.
By changing the frequency of the modulation sinusoidal signal, the intensity information of the interfered probe2 low-frequency sideband signal under each frequency is recorded, so that the chaotic Brillouin phase spectrum is obtained. Brillouin frequency shift quantity is extracted through a Brillouin phase spectrum, and temperature or strain information along the optical fiber is sensed through adjustment of the variable optical delay line. Meanwhile, the phase change of the probe2 low-frequency sideband signal caused by vibration can be converted into the change of the intensity of the interference effect by using the Sagnac interference ring, so that the vibration information can be sensed. Because the chaotic Brillouin phase spectrum has linear distribution, the Brillouin frequency shift quantity can be extracted in a relatively narrow sweep frequency range near the Brillouin frequency shift. Therefore, the sensing method has shorter measuring time and can realize real-time measurement of temperature or strain. In addition, compared with the chaotic Brillouin gain spectrum, the chaotic Brillouin phase spectrum based interferometer structure can sense external vibration information.
Compared with the existing distributed optical fiber sensing system, the distributed optical fiber sensing device and method based on the chaotic Brillouin phase spectrum measurement have the following advantages:
1. compared with a distributed optical fiber sensing system which takes pulse light or continuous light with frequency subjected to sinusoidal modulation as a detection signal, the distributed optical fiber sensing system adopts chaotic laser as the detection signal, and can overcome the contradiction between sensing distance and spatial resolution in the distributed optical fiber sensing system.
2. Compared with a distributed optical fiber sensing system (ZL201110217936.6, ZL201310045097.3, ZL201510531253.6, ZL201510531180.6, ZL201610306001.8 and ZL201610305960.8) based on chaotic Brillouin gain spectrum measurement, the method extracts Brillouin frequency shift quantity based on the chaotic Brillouin phase spectrum, senses the change of temperature or strain of the sensing optical fiber along the line, and enables the sweep frequency range of a microwave source to be smaller due to the linear distribution characteristic of the phase spectrum, so that the measurement time can be shortened by 1-2 orders of magnitude.
3. Compared with the distributed optical fiber sensing system based on the chaotic Brillouin phase spectrum measurement, the distributed optical fiber sensing system based on the chaotic Brillouin phase spectrum measurement not only can acquire temperature or strain information on the sensing optical fiber along the line, but also can convert phase change caused by vibration into intensity change through interference, thereby realizing the measurement of the vibration.
Drawings
Fig. 1 shows a schematic structural view of the apparatus of the present invention.
FIG. 2 shows a schematic diagram of the structure of a Sagnac Interferometer (SI) ring of the present invention.
In the figure: the optical fiber polarization control device comprises a 1-chaotic laser, a 2-first optical isolator, a 3-1 x 2 optical fiber coupler, a 4-first optical fiber polarization controller, a 5-variable optical delay line, a 6-optical amplifier, a 7-optical scrambler, an 8-second optical isolator, a 9-2 x 2 optical fiber coupler, a 10-sensing optical fiber, an 11-second optical fiber polarization controller, a 12-3 x 3 optical fiber coupler, a 13-electro-optical modulator, a 14-microwave signal source, a 15-tunable optical attenuator, a 16-third optical isolator, a 17-balance detector and an 18-real-time oscilloscope.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
A distributed optical fiber sensing device based on chaotic Brillouin phase spectrum measurement is shown in figure 1 and comprises a chaotic laser 1, a first optical isolator 2, a 1 x 2 optical fiber coupler 3 (an upper emergent port), a first optical fiber polarization controller 4, a variable optical delay line 5, an optical amplifier 6, an optical deflector 7, a second optical isolator 8 and a port I of the 2 x 2 optical fiber coupler 9 which are connected in sequence, wherein eight single-mode optical fiber jumpers are used for connecting the ports in sequence; the other exit end (lower exit port) of the 1 × 2 optical fiber coupler 3 is sequentially connected with an electro-optical modulator 13, a tunable optical attenuator 15, a third optical isolator 16 and a port b of the 3 × 3 optical fiber coupler 12, four single-mode optical fiber jumpers are sequentially used for connection among the two ports, and the electro-optical modulator 13 is connected with a microwave signal source 14; the d port of the 3 × 3 optical fiber coupler 12 is connected with the m port of the 2 × 2 optical fiber coupler 9 through a single-mode optical fiber jumper; a sensing optical fiber 10 is connected between the n port of the 2 x 2 optical fiber coupler and the second optical fiber polarization controller 11; the other port of the second optical fiber polarization controller 11 is connected with the e port of the 3 × 3 optical fiber coupler 12 through a single-mode optical fiber jumper; the port a and the port c of the 3 × 3 optical fiber coupler 12 are respectively connected with the negative port and the positive port of the balanced detector 17; the output of the balance detector 17 is connected to a real-time oscilloscope 18.
The chaotic laser 1 is composed of an F-P semiconductor laser without a built-in optical isolator, two random DFB semiconductor lasers, a linear chirped fiber grating, an adjustable optical attenuator, a polarization controller and a fiber coupler. Specifically, two arbitrary DFB semiconductor lasers are adopted to output optical signals with different wavelengths, and the optical signals are injected into an F-P semiconductor laser with an optical fiber feedback loop. The chaotic laser signal output with the center wavelength of 1530-1565 nm, adjustable spectral width and spectral width larger than 100GHz can be realized by utilizing the connection of a double-light injection and light feedback combined disturbance mode and adjusting the feedback intensity, the injection intensity and the injection frequency detuning amount.
Broadband chaotic laser (with center frequency v) output by chaotic laser 10) After passing through the first optical isolator 2, the optical fiber is divided into two paths through a 1 × 2 optical fiber coupler 3: one path output by the upper outgoing end is used as a pump (pump) optical signal, and the other path output by the lower outgoing end is used as a probe (probe) optical signal. The pump light signal is subjected to polarization control and delay through a first optical fiber polarization controller 4 and a variable optical delay line 5, and then amplified through an optical amplifier 6. The amplified pump light sequentially passes through the optical polarization scrambler 7 and the second optical isolator 8, and enters a Sagnac Interferometer (SI) ring composed of a sensing fiber 10, a second fiber polarization controller 11 and a 3 × 3 fiber coupler 12 through a port l of the 2 × 2 fiber coupler 9. The detection light signal output from the lower emitting end of the 1 x 2 optical fiber coupler 3 passes through the electro-optical modulator 13, and is modulated into a carrier-suppressed bilateral signal by the sinusoidal signal output from the microwave signal source 14The strip detects the optical signal. The frequency (v) of the sinusoidal signal is set equal to the Brillouin frequency shift value (v)B10.6 GHz). Carrier suppressed double sideband (v)0V) the probe optical signal enters the seebeck interference ring from the b port of the 3 × 3 fiber coupler 12 through the tunable optical attenuator 15 and the third optical isolator 16 in sequence. The double-sideband detection optical signal entering the Seganic interference ring is divided into two optical signals of probe1 transmitted clockwise along the Seganic interference ring and probe2 transmitted anticlockwise along the Seganic interference ring by the 3 x 3 optical fiber coupler 12, the pump optical signal is introduced into the Seganic interference ring by the 2 x 2 optical fiber coupler 9, only the probe2 transmitted anticlockwise along the Seganic interference ring in the sensing optical fiber 10 and the pump generate stimulated Brillouin gain action at the meeting position, namely the low-frequency sideband (v 2) in the probe20-v) the signal is amplified by the pump optical signal. Probe1 transmitted clockwise along the seebeck interference ring is used as a reference signal, and interferes with the amplified probe2 low-frequency sideband signal in the 3 × 3 optical fiber coupler 12 after passing through the second optical fiber polarization controller 11. The interference effect converts the phase information of the amplified probe2 low-frequency sideband signal into intensity information for subsequent detection. By adjusting the second fiber polarization controller 11, the polarization states of the two beams of light from probe1 and probe2 can be controlled, so that complete interference can be realized. The interfered optical signal is converted into an electric signal by a balance detector 17, and is collected and stored by a real-time oscilloscope 18. By changing the frequency of the modulation sinusoidal signal, recording the intensity information of the interfered probe2 low-frequency sideband signal under each frequency, thereby acquiring the chaotic Brillouin phase spectrum information; when external disturbance, namely temperature change, strain and vibration, acts on the sensing optical fiber arm of the Mach-Zehnder ring, the Brillouin frequency shift amount extracted from the chaotic Brillouin phase spectrum is correspondingly changed, so that corresponding disturbance information of the temperature, the strain or the vibration can be quickly obtained in real time.
Fig. 2 shows a specific process of acquiring the chaotic brillouin phase spectrum.
Let probe2 optical signal low frequency (v)0-v) the light intensity of the sidebands is:
probe2 high frequency (v) optical signal0+ v) the light intensity of the sidebands is:
wherein v is0The phase delay in the equation, i.e., the phase shift introduced by the 3 x 3 fiber coupler 12, is the center frequency of the pump optical signal, and G and a are the brillouin gain or loss, respectively. Further expressed as:
wherein, PpFor pump light power,. DELTA.z for spatial resolution, gB(v) is the brillouin gain or loss coefficient, defined as:
wherein g ispIs a Brillouin gain factor of (5 · 10)-11m/W)，AeffV is the amount of frequency shift of the modulated sinusoidal signal, v is the effective areaBBeing Brillouin frequency shift, Δ vBIs the bandwidth of the brillouin gain spectrum.
Substituting equations (3) and (4) into equation (1) or (2) can result:
from equation (5), E1Intensity of end-output optical signal | E1|2Is proportional to its phase σ (v), and is a function of the modulation frequency v.
Similarly, | E2|2The expression of (2) is as above.
The light intensities of the output optical signals corresponding to the port a and the port c in FIG. 1 are respectively | E1|2、|E2|2Then enter into balance detection respectivelyNegative input port and positive input port of detector 17, balancing output | E of detector 171|2-|E2|2Namely the required stimulated brillouin phase spectrum.
The central frequency of the stimulated brillouin phase spectrum in the sensing optical fiber changes correspondingly in a temperature or strain region, wherein the brillouin frequency shift value shows a linear relation with the temperature and the strain along the optical fiber, and can be expressed as follows:
v in the formulaB-ν0Is the variation of Brillouin frequency shift in the sensing optical fiber, and the delta T and the delta epsilon are the variation of temperature and strain,
the temperature and strain coefficient of the brillouin frequency shift. T.R.Parke et al experimentally measured temperature coefficient and strain coefficient obtained from Brillouin frequency shift are respectively
From equation (6), temperature or strain information along the sensing fiber 10 can be obtained.
Meanwhile, the phase change of the probe2 low-frequency sideband signal caused by vibration can be converted into the change of the intensity of the interference effect by using the Sagnac interference ring, so that the vibration information can be sensed.
It should be noted that modifications and applications may occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (2)
1. A distributed optical fiber sensing device based on chaotic Brillouin phase spectrum measurement is characterized in that: the device comprises a chaotic laser (1), a first optical isolator (2), a 1 x 2 optical fiber coupler (3), a first optical fiber polarization controller (4), a variable optical delay line (5), an optical amplifier (6), an optical deflector (7), a second optical isolator (8), a 2 x 2 optical fiber coupler (9), a sensing optical fiber (10), a second optical fiber polarization controller (11), a 3 x 3 optical fiber coupler (12), an electro-optical modulator (13), a microwave signal source (14), a tunable optical attenuator (15), a third optical isolator (16), a balance detector (17) and a real-time oscilloscope (18);
the chaotic laser comprises a chaotic laser (1), a first optical isolator (2), a 1 x 2 optical fiber coupler (3), a first optical fiber polarization controller (4), a variable optical delay line (5), an optical amplifier (6), an optical polarization scrambler (7), a second optical isolator (8) and ports I of the 2 x 2 optical fiber coupler (9), which are connected by single-mode optical fiber jumpers in sequence;
the other outgoing end of the 1 x 2 optical fiber coupler (3), the electro-optical modulator (13), the tunable optical attenuator (15), the third optical isolator (16) and the b port of the 3 x 3 optical fiber coupler (12) are connected by single-mode optical fiber jumpers in sequence;
the electro-optical modulator (13) is connected with a microwave signal source (14);
the d port of the 3 multiplied by 3 optical fiber coupler (12) is connected with the m port of the 2 multiplied by 2 optical fiber coupler (9) through a single mode optical fiber jumper; a sensing optical fiber (10) is connected between the n port of the 2 x 2 optical fiber coupler (9) and one port of the second optical fiber polarization controller (11); the other port of the second optical fiber polarization controller (11) is connected with the e port of the 3 multiplied by 3 optical fiber coupler (12) through a single-mode optical fiber jumper; the port a and the port c of the 3 x 3 optical fiber coupler (12) are respectively connected with the negative port and the positive port of the balance detector (17); the output end of the balance detector (17) is connected with a real-time oscilloscope (18).
2. A distributed optical fiber sensing method based on chaotic Brillouin phase spectrum measurement is characterized in that: after passing through the first optical isolator (2), the broadband chaotic laser output by the chaotic laser (1) is divided into two paths through the 1 multiplied by 2 optical fiber coupler (3): one path output by one emergent end of the 1 x 2 optical fiber coupler (3) is used as a pumping optical signal, and the other path output by the second emergent end is used as a detection optical signal; after polarization control and delay of a pump light signal are realized through a first light polarization controller (4) and a variable light delay line (5), the pump light signal is amplified through an optical amplifier (6); the amplified pump light sequentially passes through the optical polarization scrambler (7) and the second optical isolator (8) and enters a Selenk interference ring consisting of the 2 x 2 optical fiber coupler (9), the sensing optical fiber (10), the second optical fiber polarization controller (11) and the 3 x 3 optical fiber coupler (12) through a port I of the 2 x 2 optical fiber coupler (9);
the detection optical signal output from the other emitting end of the 1 multiplied by 2 optical fiber coupler (3) is modulated into a carrier-suppressed double-sideband detection optical signal by a sinusoidal signal output by a microwave signal source (14) after passing through an electro-optical modulator (13); the carrier-suppressed double-sideband detection optical signal enters a Seganic ring from a port b of a 3 multiplied by 3 optical fiber coupler (12) after sequentially passing through a tunable optical attenuator (15) and a third optical isolator (16);
the double-sideband detection optical signal entering the Seganic ring is divided into two optical signals of probe1 transmitted clockwise along the Seganic ring and probe2 transmitted anticlockwise along the Seganic ring by a 3 x 3 optical fiber coupler (12), a pump optical signal is introduced into the Seganic ring by a 2 x 2 optical fiber coupler (9), and only probe2 transmitted anticlockwise along the Seganic ring in a sensing optical fiber (10) and the pump light have stimulated Brillouin gain action at the meeting position, namely the low-frequency sideband signal in the probe2 is amplified by the pump optical signal; probe1 transmitted clockwise along the Sagnac ring is used as a reference signal, and after passing through a second optical fiber polarization controller (11), the reference signal and the amplified probe2 low-frequency sideband signal interfere in a 3 x 3 optical fiber coupler (12); the polarization states of the two beams of light of probe1 and probe2 are controlled by adjusting a second optical fiber polarization controller (11), so that complete interference is realized; the interfered optical signal is converted into an electric signal through a balance detector (17), and is collected and stored through a real-time oscilloscope (18);
by changing the frequency of the modulation sinusoidal signal, recording the intensity information of the interfered probe2 low-frequency sideband signal under each frequency, thereby acquiring the chaotic Brillouin phase spectrum information; when external disturbance, namely temperature change, strain and vibration, acts on the sensing optical fiber arm of the Mach-Zehnder ring, the Brillouin frequency shift amount extracted from the chaotic Brillouin phase spectrum is correspondingly changed, so that corresponding disturbance information of the temperature, the strain or the vibration can be quickly obtained in real time.
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