CN117288314A - Optical fiber acoustic wave sensor for simultaneously detecting transverse wave and longitudinal wave - Google Patents
Optical fiber acoustic wave sensor for simultaneously detecting transverse wave and longitudinal wave Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention discloses an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves, and relates to the technical field of acoustic wave detection. In the invention, a first light source and a second light source are coupled into the same optical fiber through a wavelength division multiplexer and then transmitted to a sensing unit through a circulator; the sensing unit modulates the received transverse wave signals and longitudinal wave signals to optical signals corresponding to the first light source and the second light source respectively; the modulated reflected optical signal is transmitted to a demultiplexer through a circulator; the optical signals corresponding to the first light source and the second light source are separated by the wavelength division demultiplexer; the optical signals corresponding to the first light sources after separation correspond to the transverse wave signals one by one; the optical signals corresponding to the second light sources after separation correspond to the longitudinal wave signals one by one; after the two paths of signals respectively pass through the first photoelectric detector and the second photoelectric detector, the optical signals are converted into electric signals to complete demodulation of transverse wave signals and longitudinal wave signals.
Description
Technical Field
The invention relates to the technical field of sound wave detection, in particular to an optical fiber sound wave sensor for simultaneously detecting transverse waves and longitudinal waves.
Background
The sound wave is formed by the vibration of an object propagating in a medium, the propagating form is divided into two types, and when the vibration direction of medium particles is consistent with the sound propagating direction in the sound wave propagating process, the sound wave is called longitudinal wave; when the vibration direction of the medium particles is perpendicular to the propagation direction of sound, the medium particles are called transverse waves.
Because the transverse wave and longitudinal wave propagation characteristics are different, the detection mechanisms of the corresponding sensor measurements are also different. The longitudinal wave detector mainly senses the change of longitudinal wave sound pressure through the sensing film so as to cause the sensing film to deform, and then the deformation of the diaphragm is converted into an electric signal; the transverse wave detector mainly senses the change of transverse wave acceleration through a mass block or a cantilever beam structure, so that the strain of the cantilever beam or the displacement of the mass block is caused, and the strain of the cantilever beam or the displacement of the mass block is converted into an electric signal.
In the prior art, the electronic acoustic wave sensing technology is relatively mature, but has some defects, such as high cable load, resonance effect of a connecting cable, high low-frequency noise and poor stability and reliability; the signal is easy to be subjected to electromagnetic interference of an external complex environment, and the impedance matching difficulty of low-frequency measurement is high; the transverse wave sensor and the longitudinal wave sensor are separated, have poor integration, low sensitivity and large volume, and cannot meet the requirements of some special application environments. If the pipeline leaks, the interaction between the fluid in the pipeline and the pipeline wall can send out longitudinal wave signals propagating in the pipeline and transverse wave signals transmitted along the pipeline wall, so that the leakage condition of the pipeline can be monitored in real time by detecting the leakage sound wave mode. The difficulty of installing the sensor in the old pipeline is high, so that the sensor is required to be high in integration level, small in size and high in sensitivity, the transverse sensor and the longitudinal sensor of the existing detector are separated, and only the longitudinal wave detector is generally installed, so that the detection precision is reduced. The acoustic wave detection can also be used for the resource exploration of petroleum, natural gas and the like, the natural early warning of earthquakes, debris flows and the like, and the noise monitoring of ships, airplanes and the like. The measuring precision in the corresponding field can be effectively improved by a mode of combining transverse wave and longitudinal wave detection, so that the development of high-sensitivity acoustic wave sensing for simultaneously detecting transverse wave and longitudinal wave is necessary.
Disclosure of Invention
In order to address the above-mentioned drawbacks and improvements of the prior art, the present invention provides an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves, comprising:
the sensing unit, link to each other with the circulator for survey transversal wave and longitudinal wave simultaneously, the sensing unit includes:
a support plate;
one end of the hollow eccentric optical fiber penetrates through the supporting plate and is fixed with the supporting plate, and the other end of the hollow eccentric optical fiber is inserted into the hollow glass capillary tube to form a cantilever structure;
the optical fiber grating is carved on one side of the fixed end of the hollow eccentric optical fiber;
a long period grating carved on the other side of the fixed end of the hollow eccentric optical fiber;
the sensing film is adhered to the end face of the hollow glass capillary tube;
the protective shell is fixed on the supporting plate and used for protecting the internal sensing structure;
the sound transmission hole is formed in the side belt of the protective shell, and an external longitudinal wave sound signal acts on the sensing film through the sound transmission hole;
the hollow eccentric optical fiber in the sensing unit is a cantilever beam, the hollow glass capillary is a mass block, and the hollow glass capillary and the mass block form a cantilever beam structure together for transverse wave detection; the end face of the hollow eccentric optical fiber in the sensing unit and the sensing film form a Fabry-Perot interferometer for longitudinal wave detection.
Further, the optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves provided by the invention further comprises:
the first input port and the second input port of the wavelength division multiplexer are respectively connected with the output ends of the first light source and the second light source;
the first input port of the circulator is connected with the output port of the wavelength division multiplexer, and the first output port of the circulator is connected with the hollow eccentric optical fiber in the sensing unit;
the input port of the demultiplexer is connected with the second output port of the circulator, and the first output port and the second output port of the demultiplexer are respectively connected with the first photoelectric detector and the second photoelectric detector;
the wavelength division multiplexer couples lasers with different wavelengths into the same optical fiber, the circulator directionally transmits reflected light of the sensing unit to the wavelength division demultiplexer, the wavelength division demultiplexer separates light emitted by the first light source and light emitted by the second light source, a first output port of the wavelength division demultiplexer outputs light with the wavelength corresponding to the first light source, a second output port of the wavelength division multiplexer outputs light with the wavelength corresponding to the second light source, the first photoelectric detector and the second photoelectric detector respectively convert two paths of optical signals into electric signals, the first photoelectric detector outputs a transverse wave signal, and the second photoelectric detector outputs a longitudinal wave signal.
Further, the hollow eccentric optical fiber and the hollow glass capillary form a cantilever structure for detecting transverse wave signals;
the end face of the hollow eccentric optical fiber and the sensing film form a Fabry-Perot cavity for detecting longitudinal wave signals.
Further, the fiber bragg grating is used for sensing cantilever strain transformation and reflecting part of light of the first light source to the demultiplexer for demodulating by using a transverse wave signal;
the long period grating couples the light transmitted by the first light source into the fiber grating to be lost, so that interference of longitudinal wave signals on transverse wave detection is isolated.
Furthermore, the hollow eccentric optical fiber is used as a cantilever structure, the cross section area of the optical fiber is small, and the fiber core is close to the outer surface of the optical fiber, so that when a transverse wave signal is induced, the strain sensitivity is one order of magnitude higher than that of a common single-mode optical fiber, and the transverse wave detection is facilitated;
the fiber core of the hollow eccentric optical fiber faces to the central position of the sensing film, and when the sensing film senses a longitudinal wave signal, the sensitivity of the central position is the largest.
Furthermore, the wall thickness of the hollow glass capillary tube is 30-100 mu m, and the hollow glass capillary tube is used as a mass block of a cantilever beam and is also used for fixing a sensing film.
Further, the central wavelength of the first light source is located in the bandwidth corresponding to the first input port of the wavelength division multiplexer;
the center wavelength of the second light source is positioned in the bandwidth corresponding to the second input port of the wavelength division multiplexer;
the central wavelength of the first light source is consistent with the central wavelength of the long-period grating and is positioned in the middle area of the bevel edge of the reflection spectrum of the fiber grating, so that the sensor is ensured to have high transverse wave detection sensitivity.
Further, the wavelength division multiplexer and the demultiplexer have the same performance parameters.
Furthermore, the first output port of the circulator is connected with the hollow eccentric optical fiber by adopting core butt fusion, so that the insertion loss of the system is reduced.
Further, the detection range of the first photoelectric detector comprises light waves emitted by the first light source;
the second photodetector detection range includes light waves emitted by the second light source.
Compared with the prior art, the invention provides the optical fiber acoustic wave sensor for simultaneously detecting the transverse wave and the longitudinal wave, which has the beneficial effects that:
(1) The sensing unit can sense transverse wave signals and longitudinal wave signals at the same time, the cantilever beam structure formed by the hollow eccentric optical fiber and the hollow glass capillary tube converts the transverse wave signals into strain changes of the fiber bragg grating, and the fabry-perot cavity formed by the end face of the hollow eccentric optical fiber and the sensing film senses the longitudinal wave signals;
(2) The sensing unit has high transverse wave detection sensitivity, the hollow eccentric optical fiber is used as the cantilever beam, the cross section area of the optical fiber is greatly reduced, and meanwhile, the fiber core is close to the outer surface of the optical fiber, so that the strain change of the root of the cantilever beam caused by transverse wave signals is easier to sense;
(3) The sensing unit has high longitudinal wave detection sensitivity, the material of the adopted sensing film is not limited, and the longitudinal wave detection sensitivity of the sensor can be obviously improved by reducing the thickness of the sensing film;
(4) The sensing unit does not contain any electric device, external transverse wave and longitudinal wave are modulated by optical signals, and the sensing unit has strong electromagnetic interference resistance and can be used in application environments such as remote sensing, flammable and explosive environments and the like.
(5) The sensor can realize the simultaneous power demodulation of transverse wave and longitudinal wave signals through the wave selection characteristics of the wavelength division multiplexer, the de-wavelength division multiplexer, the fiber bragg grating and the long period fiber, the crosstalk between the transverse wave and the longitudinal wave signals is almost 0, the demodulation precision is high, and the signal-to-noise ratio is higher than 50dB.
Drawings
FIG. 1 is a schematic diagram of a fiber optic acoustic wave sensor for detecting both transverse and longitudinal waves according to the present invention;
FIG. 2 is a schematic diagram of a sensing unit in a fiber optic acoustic wave sensor for detecting both transverse and longitudinal waves according to the present invention;
FIG. 3 is a cross-sectional view of a hollow eccentric fiber in a fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves according to the present invention;
FIG. 4 is a cross-sectional view of a hollow eccentric optical fiber and a hollow glass capillary tube of an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves, which is provided by the invention;
FIG. 5 is a schematic diagram of the overall structure of an optical fiber acoustic sensor for detecting both transverse and longitudinal waves according to the present invention;
fig. 6 is an information flow chart of an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves.
In the figure: 1. a first light source; 2. a second light source; 3. a wavelength division multiplexer; 4. a circulator; 5. a demultiplexer; 6. a sensing unit; 7. a first photodetector; 8. a second photodetector; 9. a long period grating; 10. an optical fiber grating; 11. hollow eccentric optical fiber; 12. a hollow glass capillary; 13. a sensing film; 14. a support plate; 15. a protective shell; 16. a sound-transmitting hole; 17. glue.
Detailed Description
Embodiments of the present invention will be further described with reference to fig. 1 to 6. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
Example 1: as shown in fig. 1 and 6, the present invention provides an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves, wherein:
a schematic structural diagram of the sensor unit 6 is shown in fig. 2. The sensing unit 6 comprises a long period grating 9, a fiber bragg grating 10, a hollow eccentric fiber 11, a hollow glass capillary 12, a sensing film 13, a supporting plate 14, a protective shell 15 and an acoustic hole 16.
One end of the hollow eccentric optical fiber 11 passes through the supporting plate 14 and is fixed with the supporting plate 14, the other end of the hollow eccentric optical fiber is inserted into the hollow glass capillary 12 to form a cantilever structure, and an optical fiber grating 10 is carved on one side close to the fixed end of the hollow eccentric optical fiber 11 and is used for sensing transverse wave signals; the other end of the hollow eccentric optical fiber 11 is engraved with a long period grating 9 for isolating the interference of longitudinal wave signals on transverse wave detection. A sensing film 13 is stuck on the end face of the hollow glass capillary tube 12, and a fabry-perot interferometer is formed between the end face of the hollow eccentric optical fiber 11 and the sensing film 13 for detecting longitudinal wave signals. The protective housing 15 is fixed on the backup pad 14 for protecting the internal sensing structure, and protective housing 15 one side has the sound hole 16 that passes through, and outside longitudinal wave acoustic signal can be acted on sensing film 13 through the sound hole 16.
The end surface section of the hollow glass capillary tube 12 is shown in fig. 3, and an air hole is formed in the middle; the cladding is annular; the core is in an annular cladding.
The hollow glass capillary 12 and the hollow eccentric optical fiber 11 are fixed together through glue 17, and the section view after fixing is shown in fig. 4, so that the fiber core of the hollow eccentric optical fiber 11 is ensured to be near the center of the hollow glass capillary 12.
In this embodiment, the reflectivity corresponding to the center wavelength of the fiber bragg grating 10 is more than 90%, and the transmissivity corresponding to the center wavelength of the long-period grating 9 is less than 10%, so as to isolate the interference of the reflected signal of the fabry-perot interferometer on the transverse wave detection.
In this embodiment, the distance from the support plate 14 to the sensing film 13 of the hollow eccentric optical fiber 11 is 2-8 cm, so that the sensor can be ensured to detect the transverse wave signal with high sensitivity and have a wider frequency detection range, the length of the hollow eccentric optical fiber 11 can be adjusted according to the actual measurement frequency range, and the measurement of the transverse wave signal in the frequency range of 1 Hz-100 kHz can be realized.
In this embodiment, the smaller the cross-sectional area of the hollow eccentric optical fiber 11, the higher the sensor shear wave detection sensitivity, but the higher the manufacturing cost and the higher the manufacturing difficulty, the inner diameter of the hollow eccentric optical fiber 11 is preferably 30 to 60 μm, and the outer diameter is preferably 100 to 150 μm.
In this embodiment, the diameter of the core of the hollow eccentric optical fiber 11 is 8-10 μm, which is convenient for welding with a single-mode optical fiber and has small insertion loss.
In the embodiment, the fiber core of the hollow eccentric optical fiber 11 is near the center of the hollow glass capillary 12, so that the fiber core of the hollow eccentric optical fiber 11 is ensured to be opposite to the center of the sensing film 13, and the sensor can obtain the maximum longitudinal wave detection sensitivity, and the sensitivity is 100-200 mV/g.
In this embodiment, the hollow glass capillary 12 has a wall thickness of 30 to 100 μm, which facilitates fixing the sensor film 13.
In this embodiment, the sensing film 13 is made of a silica film, and the same material as that of the hollow glass capillary 12 and the hollow eccentric optical fiber 11, so that thermal noise of the sensor can be effectively reduced.
In the embodiment, the distance from the end face of the hollow eccentric optical fiber 11 to the sensing film 13 is 50-200 μm, and the Fabry-Perot interferometer in the range has higher contrast and the sensor has high longitudinal wave detection sensitivity.
In this embodiment, the thinner the thickness of the sensor film 13, the higher the sensor longitudinal wave detection sensitivity, but the detection frequency range is about, and considering comprehensively that the thickness of the sensor film 13 is preferably 0.5-2 μm, the thickness of the sensor film 13 can be set according to the actual measurement frequency range, and the measurement of longitudinal wave signals in the frequency range of 1 Hz-100 kHz can be realized, and the sensitivity is 100-500 mV/Pa.
In this embodiment, the support plate 14 is an aluminum square plate, which is light and convenient for perforating and maintenance, and for fixing the sensing unit on the surface of the detecting structure.
The structure of the optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves is shown as a figure 5, and the optical fiber acoustic wave sensor comprises a first light source 1 and a second light source 2; a wavelength division multiplexer 3 and a demultiplexer 5; a circulator 4; a sensor unit 6; a first photodetector 7 and a second photodetector 8.
The output ends of the first light source 1 and the second light source 2 are respectively connected with a first input port and a second input port of the wavelength division multiplexer 3, and lasers with different wavelengths are coupled into the same optical fiber through the wavelength division multiplexer 3; the circulator 4 directionally transmits the reflected light of the sensing unit 6 to the demultiplexer 5, a first input port of the circulator 4 is connected with an output port of the wavelength division multiplexer 3, a first output port of the circulator 4 is connected with a hollow eccentric optical fiber 11 in the sensing unit 6, and a second output port of the circulator 4 is connected with an input port of the demultiplexer 5; the first port of the demultiplexer 5 outputs light with the wavelength corresponding to the first light source 1 and is connected with the first photoelectric detector 7, and the second output port of the demultiplexer 5 outputs light with the wavelength corresponding to the second light source 2 and is connected with the second photoelectric detector 8; the first photodetector 7 and the second photodetector 8 convert the two optical signals into telecommunications, respectively.
In this embodiment, the first light source 1 is a narrow-band laser, the linewidth is smaller than 1MHz, the working center wavelength λ1 is in the working wavelength range of the first input port of the wavelength division multiplexer 3, the linewidth of the first light source 1 is far smaller than the bandwidth of the fiber bragg grating 10, the weak wavelength drift of the fiber bragg grating 10 can cause the change of the reflected power, and the sensor is guaranteed to have very high transverse wave detection sensitivity; the second light source 2 is a narrow-band laser, the linewidth is smaller than 1GHz, the Fabry-Perot interferometer can be guaranteed to have higher contrast, the working center wavelength lambda 2 is in the working wavelength range of the second input port of the wavelength division multiplexer 3, and the sensor is guaranteed to have very high longitudinal wave detection sensitivity.
In this embodiment, the central wavelength of the first light source 1 is substantially identical to the transmission central wavelength of the long period grating 9, so as to isolate the interference of the longitudinal wave signal on the transverse wave detection.
In this embodiment, the first output port of the circulator 4 is connected to the hollow eccentric optical fiber 11 of the sensing unit by adopting a core-to-core connection, so as to reduce the connection insertion loss.
In this embodiment, when no signal acts on the sensor, the optical reflectivity of the fiber bragg grating 10 to the light emitted by the first light source 1 is 40-60%, and the initial working wavelength is located in the middle of the oblique side of the reflection spectrum of the fiber bragg grating 10, so that the sensor has larger sensitivity and larger dynamic detection range during transverse wave detection.
In the embodiment, the fiber grating 10 adopts a phase shift fiber grating, the reflection spectrum bevel edge of the phase shift fiber grating is steeper, and the sensitivity is higher in transverse wave detection and can reach 300-500 mV/g.
In this embodiment, the long-period grating 9 is inscribed near one end of the sensing film, when the sensor detects the transverse wave signal, the strain borne by the long-period grating 9 is negligible, so that the central projection wavelength of the long-period grating 9 is ensured to be consistent with the central wavelength of the first light source 1 all the time, and the interference of the longitudinal wave signal on the transverse wave detection is completely isolated.
In this embodiment, the wavelength division multiplexer 3 and the demultiplexer 5 are dual-channel coarse wavelength division multiplexers, which are low in price, small in mutual crosstalk between channels, small in insertion loss and stable in performance.
The signal flow of the optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves provided by the invention is shown in fig. 6, the first light source 1 and the second light source 2 are all narrow-band lasers, the center wavelength corresponding to the emitted laser is divided into lambda 1 and lambda 2, and the laser emitted by the first light source 1 and the second light source 2 is coupled into the same optical fiber through the wavelength division multiplexer 3 and then transmitted to the sensing unit 6 through the circulator 4. The hollow eccentric optical fiber 11 in the sensing unit 6 is a cantilever beam, the hollow glass capillary 12 is a mass block, and the hollow glass capillary and the mass block form a cantilever beam structure together for transverse wave detection; the end face of the hollow eccentric optical fiber 11 in the sensing unit 6 and the sensing film 13 form a Fabry-Perot interferometer for longitudinal wave detection. When transverse and longitudinal wave signals act on the sensing unit at the same time, the cantilever beam structure is only sensitive to the transverse wave signals, and the cantilever beam and the transverse wave signals vibrate synchronously, so that the fiber grating 10 is subjected to strain modulation of corresponding frequency, and the reflection spectrum of the fiber grating 10 is periodically shifted; the Fabry-Perot interferometer is only sensitive to the longitudinal wave signal, and the sensing film can sense the longitudinal wave signal, so that the cavity length of the Fabry-Perot interferometer is periodically modulated, and the modulation frequency is consistent with the longitudinal wave signal. The light emitted by the first light source 1 is partially reflected by the fiber bragg grating 10, and the rest of the light is coupled into the cladding by the long-period fiber 9 and is lost, so that the transverse wave signal mainly modulates the light emitted by the first light source 1; the light emitted by the second light source 2 is not within the reflection bandwidth of the fiber grating 10 and within the transmission bandwidth of the long period grating 9, and can be transmitted to the fabry-perot interferometer entirely, so that the longitudinal wave signal is mainly modulated by the light emitted by the second light source 2. The reflected light λ1 and λ2 modulated by the signal are transmitted to the demultiplexer 5 through the circulator 4, the demultiplexer 5 separates the light with wavelength divided into λ1 and λ2, and transmits the light to the first photodetector 7 and the second photodetector 8 respectively, the first photodetector 7 and the second photodetector 8 finally convert the optical signal into an electrical signal, the transversal wave signal is output by the first photodetector 7, and the longitudinal wave signal is output by the second photodetector 8.
In a general sense, the invention provides an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves, which has the following beneficial effects:
(1) The sensing unit can sense transverse wave signals and longitudinal wave signals at the same time, the cantilever beam structure formed by the hollow eccentric optical fiber and the hollow glass capillary tube converts the transverse wave signals into strain changes of the fiber bragg grating, and the fabry-perot cavity formed by the end face of the hollow eccentric optical fiber and the sensing film senses the longitudinal wave signals;
(2) The sensing unit has high transverse wave detection sensitivity, the hollow eccentric optical fiber is used as the cantilever beam, the cross section area of the optical fiber is greatly reduced, and meanwhile, the fiber core is close to the outer surface of the optical fiber, so that the strain change of the root of the cantilever beam caused by transverse wave signals is easier to sense;
(3) The sensing unit has high longitudinal wave detection sensitivity, the material of the adopted sensing film is not limited, and the longitudinal wave detection sensitivity of the sensor can be obviously improved by reducing the thickness of the sensing film;
(4) The sensing unit does not contain any electric device, external transverse wave and longitudinal wave are modulated by optical signals, and the sensing unit has strong electromagnetic interference resistance and can be used in application environments such as remote sensing, flammable and explosive environments and the like.
(5) The sensor can realize the simultaneous power demodulation of transverse wave and longitudinal wave signals through the wave selection characteristics of the wavelength division multiplexer, the de-wavelength division multiplexer, the fiber bragg grating and the long period fiber, the crosstalk between the transverse wave and the longitudinal wave signals is almost 0, the demodulation precision is high, and the signal-to-noise ratio is higher than 50dB.
The above embodiments are merely preferred embodiments of the present invention, the protection scope of the present invention is not limited thereto, and any simple changes or equivalent substitutions of technical solutions that can be obviously obtained by those skilled in the art within the technical scope of the present invention disclosed in the present invention belong to the protection scope of the present invention.
Claims (10)
1. An optical fiber acoustic wave sensor for simultaneously detecting transverse and longitudinal waves, comprising:
the sensing unit (6), link to each other with circulator (4) for survey transversal wave and longitudinal wave simultaneously, sensing unit (6) include:
a support plate (14);
a hollow eccentric optical fiber (11), one end of which passes through the supporting plate (14) and is fixed with the supporting plate (14), and the other end of which is inserted into the hollow glass capillary (12) to form a cantilever structure;
the optical fiber grating (10) is carved on one side of the fixed end of the hollow eccentric optical fiber (11);
a long period grating (9) carved on the other side of the fixed end of the hollow eccentric optical fiber (11);
a sensing film (13) adhered to the end face of the hollow glass capillary tube (12);
a protective shell (15) fixed on the support plate (14) for protecting the internal sensing structure;
the sound transmission hole (16) is formed in the side belt of the protective shell (15), and an external longitudinal wave sound signal acts on the sensing film (13) through the sound transmission hole (16);
the hollow eccentric optical fiber (11) in the sensing unit (6) is a cantilever beam, the hollow glass capillary (12) is a mass block, and the hollow glass capillary and the mass block form a cantilever beam structure together for transverse wave detection; the end face of the hollow eccentric optical fiber (11) in the sensing unit (6) and the sensing film (13) form a Fabry-Perot interferometer for longitudinal wave detection.
2. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, further comprising:
the first input port and the second input port of the wavelength division multiplexer (3) are respectively connected with the output ends of the first light source (1) and the second light source (2);
the first input port of the circulator (4) is connected with the output port of the wavelength division multiplexer (3), and the first output port of the circulator is connected with the hollow eccentric optical fiber (11) in the sensing unit (6);
the input port of the demultiplexer (5) is connected with the second output port of the circulator (4), and the first output port and the second output port of the demultiplexer are respectively connected with the first photoelectric detector (7) and the second photoelectric detector (8);
the wavelength division multiplexer (3) couples lasers with different wavelengths into the same optical fiber, the circulator (4) directionally transmits reflected light of the sensing unit (6) to the wavelength division demultiplexer (5), the wavelength division demultiplexer (5) separates light emitted by the first light source (1) and light emitted by the second light source (2), a first output port of the wavelength division demultiplexer (5) outputs light with the corresponding wavelength of the first light source (1), a second output port of the wavelength division demultiplexer (5) outputs light with the corresponding wavelength of the second light source (2), the first photoelectric detector (7) and the second photoelectric detector (8) respectively convert two paths of optical signals into electric signals, the first photoelectric detector (7) outputs transverse wave signals, and the second photoelectric detector (8) outputs longitudinal wave signals.
3. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, wherein:
the hollow eccentric optical fiber (11) and the hollow glass capillary (12) form a cantilever structure and are used for detecting transverse wave signals;
the end face of the hollow eccentric optical fiber (11) and the sensing film (13) form a Fabry-Perot cavity for detecting longitudinal wave signals.
4. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:
the fiber bragg grating (10) is used for sensing cantilever strain transformation and reflecting part of light of the first light source (1) to the wavelength division demultiplexer (5) for demodulation by transverse wave signals;
the long period grating (9) couples the light transmitted by the first light source (1) into the fiber grating (10) into the cladding for loss, and isolates the interference of the longitudinal wave signal on the transverse wave detection.
5. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, wherein:
the hollow eccentric optical fiber (11) is used as a cantilever structure, the cross section area of the optical fiber is small, the fiber core is close to the outer surface of the optical fiber, and when a transverse wave signal is induced, the strain sensitivity is one order of magnitude higher than that of a common single-mode optical fiber, so that transverse wave detection is facilitated;
the fiber core of the hollow eccentric optical fiber (11) is opposite to the central position of the sensing film (13), and when the sensing film (13) senses longitudinal wave signals, the sensitivity of the central position is the largest.
6. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, wherein:
the wall thickness of the hollow glass capillary tube (12) is 30-100 mu m, and the hollow glass capillary tube is used as a mass block of a cantilever beam and is also used for fixing a sensing film (13).
7. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:
the central wavelength of the first light source (1) is positioned in the bandwidth corresponding to the first input port of the wavelength division multiplexer (3);
the central wavelength of the second light source (2) is positioned in the bandwidth corresponding to the second input port of the wavelength division multiplexer (3);
the central wavelength of the first light source (1) is consistent with the central wavelength of the long period grating (9), and the first light source is positioned in the middle area of the reflection spectrum bevel edge of the fiber grating (10), so that the sensor has high transverse wave detection sensitivity.
8. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:
the wavelength division multiplexer (3) and the demultiplexer (5) have the same performance parameters.
9. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:
the first output port of the circulator (4) is connected with the hollow eccentric optical fiber (11) by adopting butt fusion, so that the insertion loss of the system is reduced.
10. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:
the detection range of the first photoelectric detector (7) comprises light waves emitted by the first light source (1);
the detection range of the second photodetector (8) comprises the light waves emitted by the second light source (2).
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