CN116520390A - Fiber bragg grating medium-high frequency geophone based on lever amplification structure - Google Patents
Fiber bragg grating medium-high frequency geophone based on lever amplification structure Download PDFInfo
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Abstract
A mass block is connected to one side wall of a U-shaped base through a flexible hinge beam, the mass block is in a suspended state, the flexible hinge beam and the mass block form a hinge mechanism, one end upper surface of the mass block, which is far away from the flexible hinge beam, is connected with a lever mechanism through a connecting plate, the lever mechanism comprises a support, a flexible support plate and a lever plate, the support is arranged on a bottom plate of the U-shaped base, the support is provided with the flexible support plate and the lever plate, one end of the lever plate is connected with the mass block, the other end of the lever plate is located right above the other side wall of the U-shaped base and is flush with the outer side surface of the other side wall of the U-shaped base, one end of an optical fiber is arranged on the other end face of the lever plate, the other end of the optical fiber is arranged on the outer side surface of the other side wall of the U-shaped base, and a grating is inscribed on the suspended optical fiber between the other side wall of the U-shaped base and the other end of the lever plate. The invention obviously increases the sensitivity of the detector and enhances the capability of resisting transverse cross interference.
Description
Technical Field
The invention belongs to the technical field of measurement and test, and particularly relates to a fiber bragg grating medium-high frequency geophone based on a lever amplification structure.
Background
At present, most of instruments used in the field engineering production test of oil and gas fields are electric detectors mainly based on piezoelectric, magnetoelectric and eddy current mechanisms, and most of the instruments have the advantages of high signal-to-noise ratio, convenient interface, stable performance, high reliability, simple structure, wide use and the like, but the instruments have essential defects in detection sensitivity, response frequency band, dynamic range, spatial resolution, electromagnetic field interference resistance, reusability, high temperature resistance and the like.
Compared with the traditional electric detectors, the optical fiber geophone has the advantages of large dynamic range, wide working frequency band, high sensitivity and resolution, electromagnetic interference resistance, easiness in long-distance transmission, good reusability, long-term stability in severe environments, high temperature and high pressure resistance, corrosion resistance, safety and reliability in flammable and explosive environments, and fills the defects of the electric detectors in underground seismic exploration.
Among the fiber geophones, there are mainly four methods of distributed acoustic wave sensing (Distributed Acoustic Sensing, DAS), fiber laser (Distributed Feed Back Fiber Laser, DFB-FL), fiber grating (FBG), and fiber interference. Compared with the other three optical fiber detection technologies, the FBG technology has the advantages of wavelength coding and multiplexing capability. FBGs can be written on a length of photosensitive quartz fiber less than 10mm in length and are sensitive to axial strain, which makes possible high sensitivity vibration signal acquisition through compact, small-sized structures.
The research on the high frequency band of the fiber grating geophone is rapidly developing, however, the high resonance frequency of the fiber grating geophone inevitably reduces the sensitivity, so that the realization of the high sensitivity of the high frequency band becomes an important evaluation index for evaluating the performance of the geophone.
Bing Yan (Yan B, liang L.A Novel Fiber Bragg Grating Accelerometer Based on Parallel Double Flexible Hinges [ J ]. IEEE Sensors Journal,2020,20 (9): 4713-4718.), et al designed a novel Fiber Bragg Grating (FBG) accelerometer based on parallel double flexible hinges, the accelerometer being of a right circular double hinge structure, consisting of a block and two parallel flexible hinges, with a grating suspended between them, the accelerometer having a sensitivity of 54pm/g, a characteristic frequency of 800Hz, a quality factor of 43200. There are problems of low sensitivity at high frequencies, and the quality factor (product of natural frequency and sensitivity) is not high.
Chinese patent application No.: 202010896491.8, name: a medium-high frequency elliptical hinge dual fiber grating acceleration sensor and a measuring method. The sensor designed by the invention has the resonance frequency of about 780Hz, and the advantages of large motion range of the elliptical hinge are utilized, so that the single optical fiber sensitivity is 59.22pm/g, the quality factor is 46191.6, the problems of high frequency and low sensitivity exist, and the quality factor is not high. However, the invention starts from the demodulation aspect, and adopts a demodulation mode of a differential method to improve the differential sensitivity of the double optical fibers.
Journal photoelectron laser discloses a medium-high frequency fiber Bragg grating acceleration detector based on double-lever amplification in volume 33 of 7 months in 2022, and experimental results show that the natural frequency of the detector is 612Hz, the range of a flat area is 20-250Hz, the acceleration sensitivity is 106.7pm/g, and the quality factor is 65300.4. The detector has low sensitivity and a small flat area range.
Therefore, there is an urgent need for a mid-high frequency geophone with excellent performance such as sensitivity, quality factor, and anti-transverse interference capability.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the fiber bragg grating medium-high frequency geophone based on the lever amplification structure, which has the advantages of reasonable design, simple structure, high sensitivity, high quality factor and strong lateral interference resistance.
The technical scheme adopted for solving the technical problems is as follows: a mass block is connected to one side wall of a U-shaped base through a flexible hinge beam, the mass block is in a suspended state, the flexible hinge beam and the mass block form a hinge mechanism, one end upper surface of the mass block, which is far away from the flexible hinge beam, is connected with a lever mechanism through a connecting plate, the lever mechanism comprises a support, a flexible support plate and a lever plate, the support is arranged on a bottom plate of the U-shaped base, the support is provided with the flexible support plate and the lever plate, one end of the lever plate is connected with the connecting plate, the other end of the lever plate is located right above the other side wall of the U-shaped base and is flush with the outer side surface of the other side wall of the U-shaped base, one end of an optical fiber is arranged on the other end of the lever plate, the other end of the optical fiber is arranged on the outer side surface of the other side wall of the U-shaped base, and a grating is inscribed on the suspended optical fiber between the other side wall of the U-shaped base and the other end of the lever plate.
As a preferable technical scheme, the lever plate is provided with a supporting plate positioning hole, and the distance between the supporting plate positioning hole and the mass block is less than 1/2 times the length of the lever plate.
As a preferred technical scheme, the flexible supporting plate comprises a vertical plate and a horizontal mounting plate, wherein the horizontal mounting plate is arranged at the top of the vertical plate to form a T-shaped structure, the horizontal mounting plate is arranged on the bottom surface of the lever plate, the vertical plate is aligned with a supporting plate positioning hole on the lever plate, and through holes which are uniformly distributed are processed on the vertical plate along the length direction.
As a preferable technical scheme, the diameter of the through holes is 1-3 mm, and the center distance between adjacent through holes is 1.5-3.5 mm.
As a preferable technical scheme, the thickness of the vertical plate is 0.3-1.5 mm.
As a preferable technical scheme, the vertical plate, the horizontal mounting plate and the support are connected into a whole.
As a preferred technical scheme, the flexible supporting plate is replaced by a lug hinge structure, the lug hinge structure comprises two lugs, a lug boss and a rotating shaft, the two lugs are arranged on the upper surface of the support at a certain distance, the lug boss is positioned between the two lugs and arranged at the bottom of the lever plate, the two lugs are coincident with the central line of the lug boss, and the rotating shaft penetrates through the two lugs and the lug boss, so that the lever plate is hinged on the support.
As a preferred technical scheme, the thickness of one side wall of the U-shaped base is larger than the thickness of the other side wall.
As a preferable technical scheme, the U-shaped base, the flexible hinge beam, the mass block, the connecting plate and the lever plate are connected into a whole, the width of the side wall of the U-shaped base is the same as the width of the flexible hinge beam and the width of the mass block, and the flexible hinge beam is positioned at the center of the side wall of the mass block.
As a preferable technical solution, the sensitivity S of the geophone is:
lambda in B Is the center wavelength of the fiber bragg grating, P e Is the effective elasto-optical coefficient of the optical fiber, n 1 The distance between the center of mass of the lever mechanism and the lever fulcrum is m is the weight of the mass block, d is the distance between the center of the hinge beam and the center of the mass block, L is the grating area length of the grating on the optical fiber, and k f Is the axial rigidity constant of the optical fiber, h is the height of the mass block, and k 1 Is the rigidity of the hinge mechanism.
The beneficial effects of the invention are as follows:
according to the invention, the lever mechanism is connected to the hinge mechanism, one end of the optical fiber is arranged on the lever mechanism, the lever mechanism is used for amplifying the inertial strain of the hinge mechanism, so that the sensitivity of the detector is obviously increased, the transverse cross interference resistance is enhanced, the advantage of micro-displacement amplification without additional directional displacement and motion precision of the lever mechanism is fully displayed, and the transverse interference resistance of the detector is enhanced. The lever mechanism is used as the rigid self-vibration of the rigid beam, so that the telescopic transformation of the grating is increased, and the sensitivity and the quality factor are improved to the maximum extent on the premise of guaranteeing the high frequency band.
Drawings
Fig. 1 is a schematic structural view of embodiment 1 of the present invention.
Fig. 2 is a schematic view of the structure of the flexible support plate 6 in fig. 1.
Fig. 3 is a schematic structural view of embodiment 2 of the present invention.
FIG. 4 is a simulation analysis diagram of a simulation example of embodiment 1 of the present invention.
FIG. 5 is a graph of the amplitude-frequency response of the experimental test of example 1 of the present invention.
FIG. 6 is a plot of a linear fit of sensitivity at 100Hz for the experimental test vibration frequency of example 1 of the present invention.
FIG. 7 is a plot of a linear fit of sensitivity at 300Hz for the experimental test vibration frequency of example 1 of the present invention.
FIG. 8 is a graph showing comparison of amplitude-frequency response curves of the transverse interference resistance test of example 1 of the present invention.
FIG. 9 is a simulation analysis diagram of a simulation example of embodiment 2 of the present invention.
Fig. 10 is a frequency response graph of embodiment 2 of the present invention.
Wherein: u-shaped base 1, flexible hinge roof beam 2, quality piece 3, connecting plate 4, backup pad locating hole 5, flexible backup pad 6, horizontal mounting panel 6-1, riser 6-2, through-hole 6-3, lever board 7, support 8, optic fibre 9, grating 10, pivot 11, lug 12, boss 13.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, but the present invention is not limited to the following embodiments.
Example 1
In fig. 1 and 2, the fiber bragg grating medium-high frequency geophone based on the lever amplification structure of the present embodiment includes a U-shaped base 1, a flexible hinge beam 2, a mass block 3, a connecting plate 4, a support 8, a flexible support plate 6, a lever plate 7, an optical fiber 9, and a grating 10.
A cuboid-shaped mass block 3 is connected to one side wall of a U-shaped base 1 through a flexible hinge beam 2, the flexible hinge beam 2 is a straight round flexible hinge beam, the width of the side wall of the U-shaped base 1 is identical to the width of the flexible hinge beam 2 and the width of the mass block 3, the flexible hinge beam 2 is located in the middle of the side face of the mass block 3, the mass block 3 is in a suspended state, the bottom face of the mass block 3 is parallel to the bottom face of the U-shaped base 1, a lever plate 7 is connected to the upper surface of one end of the mass block 3 far away from the hinge beam through a connecting plate 4, the lever plate 7 is in a horizontal state, a supporting plate locating hole 5 is machined in the lever plate 7, the distance between the supporting plate locating hole 5 and the connecting plate 4 is less than 1/2 times the length of the lever plate 7, the U-shaped base 1, the flexible hinge beam 2, the mass block 3, the connecting plate 4 and the lever plate 7 are connected into a whole, a support 8 is installed on a bottom plate of the U-shaped base 1 located on one side of the mass block 3, a flexible supporting plate 6 is arranged on the support 8, the flexible supporting plate 6 is connected with the support 8 into a whole, the flexible supporting plate 6 comprises a vertical plate 6-2 and a horizontal mounting plate 6-1, the vertical plate 6-1 and a horizontal mounting plate 6-1, the top of the vertical plate 6-1 is arranged on the top of the vertical plate 6-2, the vertical plate 6-1 is aligned with the horizontal mounting plate 6-7, and the horizontal mounting plate 6-7 is aligned with the vertical plate 6, and the vertical plate 2 is fixed on the bottom plate 2The thickness of the supporting plate locating holes 5 on the vertical plate 6-2 is 0.3-1.5 mm, through holes 6-3 which are uniformly distributed are processed on the vertical plate 6-2 along the length direction and are used for improving the elasticity of the vertical plate 6-2, the diameter of each through hole is 2mm, the center distance of adjacent through holes is 2.5mm, the diameter of each through hole is 1mm, the center distance of adjacent through holes is 1.5mm, the diameter of each through hole is 3mm, the center distance of adjacent through holes is 3.5mm, the support 8, the flexible supporting plate 6 and the lever plate 7 form a lever mechanism, the flexible support plate 6 is used for further improving sensitivity, the other end of the lever plate 7 is positioned right above the other side wall of the U-shaped base 1, the end face of the lever plate is flush with the outer side face of the other side wall of the U-shaped base 1, one end of the optical fiber 9 is fixed on the end face of the other end of the lever plate 7, the other end of the optical fiber 9 is fixed on the outer side face of the other side wall of the U-shaped base 1, a grating 10 is inscribed on the suspended optical fiber 9 between the other side wall of the U-shaped base 1 and the other end of the lever plate 7, and the central wavelength lambda of the grating B 1548nm and a gate length L of 5mm. When the mass block 3 is stressed to vibrate up and down, the vertical plate 6-2 of the flexible supporting plate 6 is bent and rebounded through the lever plate 7, so that the lever plate 7 generates reciprocating motion with one end descending and the other end ascending, and finally the fiber bragg grating generates stretching or shrinking.
The U-shaped base 1, the flexible hinge beam 2, the mass block 3 and the lever plate 7 of the embodiment are all made of steel AISI304, and the support 8 and the flexible support plate 6 are all made of aluminum alloy 1060 alloy materials.
In the embodiment, a power arm is arranged between the support plate positioning hole 5 on the lever plate 7 and the mass block 3, the rest is a resistance arm, and the length of the power arm is less than that of the resistance arm, so that the sensitivity is obviously improved.
Example 2
In fig. 3, the fiber bragg grating medium-high frequency geophone based on the lever amplifying structure of the present embodiment includes a U-shaped base 1, a flexible hinge beam 2, a mass block 3, a connection plate 4, a support 8, a lever plate 7, an optical fiber 9, a grating 10, a rotation shaft 11, a bump 12, and a boss 13.
The thickness of the left side wall of the U-shaped base 1 is larger than the thickness of the right side wall and is used for fixing the left end of the flexible hinge, so that the left side wall of the U-shaped base is prevented from vibrating along with the mass block 3, and the left side wall of the U-shaped base 1 is connected with a long part through the flexible hinge beam 2The side wall width of the U-shaped base 1 is the same as the width of the flexible hinge beam 2 and the width of the mass block 3, the flexible hinge beam 2 is a cycloid flexible hinge beam, the flexible hinge beam 2 is positioned in the middle of the side surface of the mass block 3, the mass block 3 is in a suspended state, the bottom surface of the mass block 3 is parallel to the bottom surface of the U-shaped base 1, the upper surface of one end of the mass block 3 far away from the hinge beam is connected with a lever plate 7 through a connecting plate 4, the lever plate 7 is in a horizontal state, the U-shaped base 1, the flexible hinge beam 2, the mass block 3, the connecting plate 4 and the lever plate 7 are connected into a whole, a support 8 is arranged on the bottom plate of the U-shaped base 1 at one side of the mass block 3, a bump hinge structure is arranged between the support 8 and the lever plate 7 and comprises two bumps 12, a boss 13 and a rotating shaft 11, the two bumps 12 are arranged on the upper surface of the support 8 at a certain distance, the boss 13 is positioned between the two bosses 12 and fixed at the bottom of the lever plate 7, the outer surface of the boss 13 is an arc surface and is contacted with the upper surface of the mass block 3, the boss 13 is used for supporting the lever plate 7, the distance between the boss 13 and the connecting plate 4 is less than 1/2 times the length of the lever plate 7, the two bosses 12 are overlapped with the central line of the boss 13, the rotating shaft 11 passes through the two bosses 12 and the boss 13 to enable the lever plate 7 to be hinged on the support 8, the other end of the lever plate 7 is positioned right above the right side wall of the U-shaped base 1, the end face of the lever plate 7 is flush with the outer side face of the right side wall of the U-shaped base 1, one end of the optical fiber 9 is fixed on the end face of the other end of the lever plate 7, the other end of the optical fiber 9 suspended between the other side wall of the U-shaped base 1 and the other end of the lever plate 7 is inscribed with the grating 10, and the central wavelength lambda of the grating B 1548nm and a gate length L of 5mm. When the mass block 3 is stressed to vibrate up and down, the lever plate 7 generates reciprocating motion with one end descending and the other end ascending around the rotating shaft 11, and finally, the fiber bragg grating generates stretching or shrinking.
The U-shaped base 1, the flexible hinge beam 2, the mass block 3 and the lever plate 7 of the embodiment are all made of steel AISI304, and the support 8 and the flexible support plate 6 are all made of aluminum alloy 1060 alloy materials.
In the embodiment, a power arm is arranged between the support plate positioning hole 5 on the lever plate 7 and the mass block 3, the rest is a resistance arm, and the length of the power arm is less than that of the resistance arm, so that the sensitivity is obviously improved.
The working principle of the invention is as follows:
when external acceleration is applied to the mass block 3, the flexible hinge beam 2 is deformed, the lever mechanism further amplifies the displacement variation of the mass block 3, and the magnitude of the acceleration is measured through the reflection wavelength drift amount of the fiber bragg grating, namely, the cycloid flexible hinge strain amplified by the lever mechanism is determined. The lever amplifying mechanism greatly improves the sensitivity to load, so that the micro-displacement amplifying advantages of no additional directional displacement and motion precision of the lever mechanism are fully displayed.
The invention firstly obtains a moment equation of a hinge mechanism formed by a flexible hinge and a mass block 3 to obtain initial acceleration, then obtains a final acceleration value of a detector after a lever amplifying mechanism is added by adopting a method for obtaining terminal acceleration of the lever mechanism, and further obtains final sensitivity, and the invention comprises the following specific steps:
the mass block 3 vibrates with the flexible hinge as the center, and the initial acceleration a is obtained by a moment balance equation 0 ,
Wherein, kappa f Is the axial rigidity constant of the optical fiber, delta L is the displacement variation of the left end displacement input quantity/mass block vibration direction of the lever mechanism, and k 1 The rigidity of the hinge mechanism is h is the height of the mass block 3, m is the weight of the mass block 3, and d is the distance between the center of the hinge beam and the center of the mass block 3;
terminal acceleration a generated by lever mechanism 1 Expressed as:
wherein τ is moment applied to the left end of the lever mechanism by inertial vibration of the mass block through the connecting plate, m 1 N is the weight of the lever mechanism 1 Is the distance between the center of mass of the lever mechanism and the lever fulcrum;
according to the law of conservation of energy, it is possible to obtain:
τΔL＝m 1 a 0 ΔL (3)
from formulas (2) and (3):
the sensitivity S of the detector is then,
wherein lambda is B Is the center wavelength of the fiber bragg grating, P e Is the effective elasto-optical coefficient of the optical fiber, n 1 The distance between the center of mass of the lever mechanism and the lever fulcrum is m is the weight of the mass block, d is the distance between the center of the hinge beam and the center of the mass block, L is the grating area length of the grating on the optical fiber, and k f Is the axial rigidity constant of the optical fiber, h is the height of the mass block, and k 1 Is the rigidity of the hinge mechanism.
Experiment 1
In order to verify the benefits of the present invention, the inventors performed simulation experiments and vibration experiments on the fiber bragg grating medium-high frequency geophone based on the lever amplification structure of example 1.
1. Simulation experiment
And (3) establishing a mathematical model of the proposed geophone by adopting SOLIWORKS professional mathematical modeling software, and performing frequency simulation on the geophone mathematical model which is completely modeled by using Simulation premium plug-ins in SOLIWORKS.
Modal analysis is performed on the geophone model, as shown in fig. 4, and the resonant frequencies of the obtained first-order mode and second-order mode are 759.54Hz and 2427.7Hz respectively. The first-order mode is simple harmonic vibration, which indicates that the geophone model vibrates along the Y axis under the external excitation. The second-order mode is a rotation vibration mode, which indicates that the geophone model rotates along the X axis under the external excitation effect.
By comparing the mode data of each order, the difference between the resonant frequency of the first-order mode and the resonant frequency of the second-order mode is larger, which indicates that the cross coupling of the geophone with the structure is small, and the cross interference can be effectively reduced.
2. Vibration experiment
The experimental system mainly comprises a vibration testing system and a signal demodulation system, wherein the vibration testing system comprises a high-frequency vibration table, a signal generator and a power amplifier; the signal demodulation system comprises a circulator and a fiber grating dynamic signal demodulator. In the experimental process, the signal generator amplifies the generated signal through the power amplifier to enable the vibrating table to drive the geophone to vibrate. The magnitude of the effective amplitude of acceleration is controlled by manually rotating an adjusting knob on a power amplifier, the magnitude of the acceleration amplitude is checked on a sensor sensitivity and frequency response calibration interface of a sine wave control system of a vibration table of Vib-SIN of computer software, and meanwhile, the value of the frequency of a control signal is input on the interface of the software by a keyboard so as to change the magnitude of the frequency of the control signal; the fiber grating dynamic signal demodulator is used for demodulating the optical signal, reflected light waves of the fiber grating of the geophone are transmitted to the fiber grating dynamic signal demodulator through the transmission fiber intervening circulator, and information carried by wavelength changes of the light waves is demodulated. All recording, processing and analyzing experimental data are carried out on a notebook computer.
1. And (3) testing the natural frequency of the detector:
the amplitude-frequency characteristic of the detector determines the frequency response range of the detector, and the acceleration of the vibrating table is set to be 5m/s for testing the amplitude-frequency response characteristic of the detector 2 The initial frequency of vibration is set to 20Hz, then from 50Hz, the step length is 50Hz to 500Hz, the natural frequency is approached, the step length is changed to 5Hz, the test is carried out, the step length is ended from 700Hz, the measured data are recorded and processed, and the amplitude-frequency response curve of the sensor is obtained as shown in figure 5.
As can be seen from FIG. 5, the natural frequency of the high-frequency geophone in the fiber bragg grating based on the lever amplification structure is 525Hz, and the curve below 400Hz is relatively gentle, which is beneficial to the realization of intermediate frequency measurement.
2. Detector sensitivity test
In order to ensure that the detector has good performance below 400Hz, the sensitivity linearity test is required to be carried out on the detector, 100Hz and 300Hz are selected to apply sine excitation signals to the detector, and the acceleration amplitude takes the value of 2m/s 2 、5m/s 2 、7m/s 2 、9m/s 2 、11m/s 2 、13m/s 2 、15m/s 2 The wavelength drift amount of different accelerations of the detector under the same excitation frequency is measured, and a sensitivity fitting curve of the sensor is obtained by fitting the linear relation between the wavelength drift amount and the acceleration, as shown in fig. 6.
As can be seen from fig. 6, the sensitivity was 107.426pm/g at a vibration frequency of 100Hz, and the fitting determination coefficient r2=0.9997;
as can be seen from fig. 7, the sensitivity was 144.885pm/g at a vibration frequency of 300Hz, and the coefficient r2=0.99968 was determined by fitting.
3. Test of lateral interference resistance
The detector is rotated by 90 degrees to test the transverse anti-interference capability, the amplitude-frequency response characteristic of the sensor after the detector is rotated by 90 degrees is tested, and the acceleration of the vibrating table is set to be 5m/s 2 The vibration starting frequency was set to 20Hz, then from 50Hz, with 50Hz as the step size, to 500Hz, at which time the natural frequency was approached, the test was performed with the step size changed to 5Hz, and to 700 Hz. The measured data are recorded and processed to obtain an amplitude-frequency response curve of the sensor after 90 degrees of rotation, and the amplitude-frequency response curve is compared with an amplitude-frequency response curve of the main shaft direction, as shown in fig. 8. It can be seen from fig. 7 that the resonance frequency in the cross-axis direction is almost 0, so that the sensor has excellent lateral anti-interference capability.
In summary, the fiber bragg grating medium-high frequency geophone based on the lever amplification structure of the embodiment 1 of the invention can realize medium-frequency measurement in a frequency range of 20 Hz-400 Hz, has sensitivity of about 145pm/g, resonance frequency of about 526Hz, quality factor as high as 76270pm & Hz/g, sensitivity fitting determination coefficient as high as 0.9997, and has the characteristics of high sensitivity, high quality factor and strong transverse anti-interference capability.
Experiment 2
Simulation experiments were performed on the fiber bragg grating medium-high frequency geophone based on the lever amplification structure of example 2:
modal analysis is performed on the geophone model, and the natural frequency of the first-order mode of the geophone is 1638.5Hz, which shows that the lever mechanism can amplify the displacement of micro-deformation of the cycloid flexible hinge caused by vibration of the inertial mass along the y direction and generate obvious strain, as shown in fig. 9 (a).
The natural frequency of the second order mode of the geophone is 2935.6Hz. It is shown that only the inertial mass vibrates in the x-direction about the cycloidal compliant hinge, while the strain of the lever mechanism in the transverse direction is not so pronounced, so the geophone has little disturbing influence in the transverse direction, as shown in fig. 9 (b).
FIG. 9 shows that the natural frequency of the geophone is related to the structural stiffness, and the y-direction structural stiffness of the first-order mode of the geophone model is much less than the x-direction structural stiffness of the second-order mode of the geophone model, so the natural frequency of the modes is proportional to the model structural stiffness. Therefore, the difference between the structural rigidity in the first-order mode and the structural rigidity in the second-order mode is large, so that the crosstalk in the sensitive direction and the insensitive direction of the geophone is small.
Harmonic response analysis of geophone model, determination of frequency range of sweep in analysis setup, application of 10m/s to mass in y-direction 2 Applying a fixed constraint to the bottom of the geophone and analyzing the system dynamic response of the geophone under sinusoidal loading at different frequencies. The sweep frequency range is 20Hz:20Hz:2000Hz, a plot of the detector frequency response is obtained as shown in fig. 10.
As can be seen from fig. 10, the natural frequency of the high-frequency geophone in the fiber bragg grating based on the lever amplification structure in the embodiment 2 of the present invention is about 1643.6Hz, and the curve below 1500Hz is relatively gentle, which is favorable for realizing high-frequency measurement.
Claims (10)
1. A fiber bragg grating medium-high frequency geophone based on a lever amplification structure is characterized in that: a side wall of the U-shaped base is connected with a mass block through a flexible hinge beam, the mass block is in a suspended state, the flexible hinge beam and the mass block form a hinge mechanism, one end upper surface of the mass block, which is far away from the flexible hinge beam, is connected with a lever mechanism through a connecting plate, the lever mechanism comprises a support, a flexible supporting plate and a lever plate, the support is arranged on a bottom plate of the U-shaped base, the support is provided with the flexible supporting plate, the flexible supporting plate is provided with the lever plate, one end of the lever plate is connected with the connecting plate, the other end of the lever plate is located right above the other side wall of the U-shaped base and the end face of the lever plate is flush with the outer side face of the other side wall of the U-shaped base, one end of an optical fiber is arranged on the end face of the other end of the lever plate, the other end of the optical fiber is arranged on the outer side face of the other side wall of the U-shaped base, and a grating is inscribed on the suspended optical fiber between the other end of the lever plate.
2. The fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 1, wherein: the lever plate is provided with a supporting plate positioning hole, and the distance between the supporting plate positioning hole and the mass block is less than 1/2 times the length of the lever plate.
3. The fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 1 or 2, wherein: the flexible supporting plate comprises a vertical plate and a horizontal mounting plate, wherein the horizontal mounting plate is arranged at the top of the vertical plate to form a T-shaped structure, the horizontal mounting plate is arranged on the bottom surface of the lever plate, the vertical plate is aligned with a supporting plate positioning hole on the lever plate, and through holes which are uniformly distributed are processed on the vertical plate along the length direction.
4. A fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 3, wherein: the diameter of the through holes is 1-3 mm, and the center distance between adjacent through holes is 1.5-3.5 mm.
5. A fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 3, wherein: the thickness of the vertical plate is 0.3-1.5 mm.
6. A fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 3, wherein: the vertical plate, the horizontal mounting plate and the support are connected into a whole.
7. The fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 1, wherein: the flexible supporting plate is replaced by a lug hinge structure, the lug hinge structure comprises two lugs, a boss and a rotating shaft, the two lugs are arranged on the upper surface of the support at a certain distance, the boss is arranged between the two lugs and at the bottom of the lever plate, the two lugs are coincident with the center line of the boss, and the rotating shaft penetrates through the two lugs and the boss to enable the lever plate to be hinged on the support.
8. The fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 7, wherein: the thickness of one side wall of the U-shaped base is larger than that of the other side wall.
9. The fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 1 or 8, wherein: the U-shaped base, the flexible hinge beam, the mass block, the connecting plate and the lever plate are connected into a whole, the width of the side wall of the U-shaped base is the same as the width of the flexible hinge beam and the width of the mass block, and the flexible hinge beam is positioned at the center of the side wall of the mass block.
10. The fiber bragg grating medium-high frequency geophone based on a lever amplification structure according to claim 1 or 7, wherein: the sensitivity S of the geophone is as follows:
lambda in B Is the center wavelength of the fiber bragg grating, P e Is the effective elasto-optical coefficient of the optical fiber, n 1 The distance from the center of mass of the lever mechanism to the fulcrum of the lever is defined as m, the weight of the mass block is defined as m,d is the distance between the center of the hinge beam and the center of the mass block, L is the grating region length of the grating on the optical fiber, and k f Is the axial rigidity constant of the optical fiber, h is the height of the mass block, and k 1 Is the rigidity of the hinge mechanism.
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| CN202310467069.4A CN116520390A (en) | 2023-04-27 | 2023-04-27 | Fiber bragg grating medium-high frequency geophone based on lever amplification structure |
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