CN111025381B - Piezoresistive geophone based on graphene - Google Patents
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 115
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 30
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 26
- 229910052681 coesite Inorganic materials 0.000 claims abstract description 24
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
- G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
- G01V1/181—Geophones
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H11/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties
- G01H11/06—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties by electric means
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Abstract
The invention relates to a piezoresistive geophone based on a graphene film, wherein graphene is applied to the piezoresistive geophone, so that the sensitivity of the piezoresistive geophone is improved; the graphene film can bear 20% of self deformation, so that the dynamic range of the geophone is greatly improved; the hollow SiO2 is adopted to directly take the graphene film as a vibration conversion structure, the frequency response of the sensitive unit is irrelevant to the substrate material and the structure, and the modal analysis of the graphene film shows that the first-order natural frequency is several MHz, and the linearity of the theoretical frequency response of the geophone in the invention from direct current to several MHz is good; the graphene film can respond to deformation generated by single molecule adsorption, and the resolution ratio is extremely high; a symmetrical double-Wheatstone bridge structure is adopted, wherein the Wheatstone bridge on the cylindrical substrate at the top end is used as a reference bridge to only sense the variation of the temperature field, the Wheatstone bridge on the cylindrical substrate at the top end simultaneously senses the temperature field and vibration, and the outputs of the Wheatstone bridge and the vibration are subjected to hardware difference to improve the temperature influence.
Description
Technical Field
The invention belongs to the technical field of sensors, particularly relates to a geophone, and particularly relates to a piezoresistive geophone based on graphene.
Background
Seismic instruments are widely used in geological structure exploration, subsurface resource exploration, and monitoring of seismic activity. The geophone is used as the front end of a seismic instrument, the direct wave of a seismic source and the reflected wave of each stratum are converted into electric signals by vibration signals to be output, and performance indexes such as sensitivity, dynamic range, frequency response and the like directly influence the accuracy of the seismic instrument, so that the quality of acquired data is influenced.
According to the working principle of the geophone, the geophone can be divided into an electromagnetic geophone, an electrochemical geophone, an optical fiber geophone, an MEMS geophone and the like. Among them, electromagnetic geophones and piezoelectric geophones are widely used in current geological exploration. The former is mainly applied to land seismic exploration, the main internal structure of the former is a coil and a permanent magnet, and the mechanical structure is complex and the whole mass is large. Due to the low dynamic range, after a vibration signal with large amplitude is picked up, the internal structure of the electromagnetic geophone is extremely easy to be damaged irreversibly. Piezoelectric geophones have excellent overall performance with other types, but have poor low frequency characteristics, which makes them unsatisfactory for current seismic exploration.
The geophone is one of the vibration sensors, which converts the vibration of the earth into an electrical signal for output, and thus, is analyzed from the most basic principle.
Piezoresistive sensors are one of the most widely used vibration sensors. There are mainly four types depending on the sensitive unit: the first type is a strain gauge type piezoresistive vibration sensor, which is manufactured by sticking a metal strain gauge on an elastic cantilever beam structure. The resistance of metal foil gage is directly proportional with the resistivity and the size of material itself, and after external vibration was picked up by the cantilever beam structure, its self can produce deformation, and the size changes, and then makes the resistance of itself change, changes this resistance change into voltage variation through signal conditioning circuit, can be gathered by data acquisition system. The piezoresistive sensor has good temperature stability, but the strain coefficient is extremely low, so that the sensitivity of the sensor is low. The second is a semiconductor piezoresistive type sensor, which usually uses an N-type silicon wafer as a substrate. The silicon chip is made into an elastic stress component with a certain geometric shape, four P-type diffusion resistors are manufactured at the stress position of the silicon chip along different crystal directions, then the four resistors form a four-arm Wheatstone bridge, and the change of the resistance value is changed into an electric signal to be output under the action of external force. The sensor has a voltage coefficient of variation of 200, but has poor temperature stability, and the maximum deformation of the sensor cannot exceed 2% due to the extremely high rigidity of the material, so that the sensor has a low dynamic range when used for vibration measurement. The third type is a thick film piezoresistive sensor, where the resistive structure is printed on a base element (e.g. of a ceramic base) using a thick film process and then fired at high temperature. The resistance change here is also due to the deformation of the diaphragm, and the temperature stability of such a sensor is improved, but the dynamic range and sensitivity are mediocre, and it is difficult to realize the measurement of weak vibration. A fourth type of piezoresistive sensor is piezoresistive sensing with graphene as the sensitive unit. Novosclov et al discovered graphene (Novoseov K S, Geim A K, Morozov S V, et al. electric field in atomic thin films [ J ]) in 2004, which was of interest to researchers, had extremely high Young' S modulus and breaking strength, about 1TPa and 125GPa, respectively. Schedulin et al found that even small deformations caused by single molecules can be detected using graphene films (Schedulin F, Geim A K, Morozov S V, et al. detection of induced viral gas molecules adsorbed on graphene [ J ]). In the same year, J.S.Bunch et al made a prototype of a suspended Graphene vibration sensor (Bunch J S, Van Der Zande A M, Verbridge S S, et al, electrochemical detectors from Graphene Sheets [ J ] Science,2007,315(5811):490-493.) by covering a Graphene film on a cavity, and then O.K.Kwon et al improved the suspended Graphene vibration sensor, increased the deformation of the Graphene film under unit action force by the action of an additional support, and further improved the sensitivity of the sensor (Kwon O K, Lee J H, Kim K-S, et al. In addition, the graphene film can bear large deformation, so that the sensor has a high dynamic range. And the low-frequency characteristic can be extended to near direct current.
The suspension graphene vibration sensor has extremely high sensitivity and extremely large dynamic range, and the frequency band ranges from direct current to dozens of megahertz, so the suspension graphene vibration sensor can be used for detecting weak seismic signals. However, the temperature characteristic of the sensor is poor, the zero drift is large after the sensor passes through a conditioning circuit, and when the detected vibration signal is a low-frequency signal, the signal-to-noise ratio of the output signal is extremely low.
Disclosure of Invention
The invention aims to provide a piezoresistive geophone based on graphene aiming at the performance defects of the geophone in the prior art, which can enhance the low-frequency performance of the geophone to be close to direct-current frequency while ensuring higher sensitivity and dynamic range of the geophone; two Wheatstone bridges with completely consistent parameters are designed by utilizing the graphene film in the same temperature field in the geophone and are respectively recorded as a measuring Wheatstone bridge and a reference Wheatstone bridge, the graphene films forming the four arms of the measuring Wheatstone bridge are fixed on the cavity and used for picking up vibration quantity and sensing temperature quantity, and the graphene films forming the four arms of the reference Wheatstone bridge are tightly attached to SiO (silicon dioxide) film2On the substrate, the detector cannot deform correspondingly along with the vibration of the detector, so that the detector cannot sense external vibration and can only sense the temperature, the output of the two Wheatstone bridges is subjected to hardware difference, the influence of the temperature on the vibration sensitive unit in the detector can be eliminated, and the temperature stability of the piezoresistive seismic detector can be improved.
The purpose of the invention is realized by adopting the following technical scheme:
the utility model provides a piezoresistive geophone based on graphite alkene film, includes a cylindrical hollow geophone shell, and the casing below of geophone shell is equipped with geophone caudal vertebra, its characterized in that:
a bottom cylindrical substrate is fixed on the inner lower bottom surface of the casing of the detector, cross-shaped grooves are symmetrically distributed on the upper surface of the bottom cylindrical substrate, a reserved square area is arranged in the center of the upper surface of the bottom cylindrical substrate, and the cross-shaped grooves are divided into four symmetrically distributed grooves by the square area; four temperature compensation graphene films are respectively bonded in the four grooves;
a top end cylindrical substrate is fixed above the bottom end cylindrical substrate, a cross-shaped groove and a square area reserved in the center are also formed in the upper surface of the top end cylindrical substrate, and the cross-shaped groove is divided into four symmetrically distributed grooves by the square area; a limiting block with a central hole is arranged above the square area; four hollow-out SiO2The substrate is respectively arranged in four grooves on the cylindrical substrate at the top end, and the four hollow SiO layers2Four vibration conversion graphene films are correspondingly arranged on the upper surface of the substrate;
the vibration pickup lever is arranged above the limiting block and comprises four cantilevers, a vertical rod and cylindrical support legs, the four cantilevers are symmetrically distributed by taking the central vertical rod as a symmetry axis, the lower surface of each cantilever is provided with three cylindrical support legs, the upper end of each vertical rod is integrated into a hollow cup-shaped structure, and the lower end of each vertical rod is provided with an installation head matched with the central hole of the limiting block; the four cantilevers are parallel to the edges of the four vibration conversion graphene thin films respectively, and three cylindrical support legs under each cantilever are in contact with the upper surface of the corresponding vibration conversion graphene thin film respectively, so that the vibration conversion graphene thin film is not deformed;
the four vibration conversion graphene films and the four temperature compensation graphene films are electrically connected according to a Wheatstone bridge to respectively form a vibration measurement Wheatstone bridge and a temperature compensation Wheatstone bridge; the power supply ends and the ground ends of an upper Wheatstone bridge and a lower Wheatstone bridge which are composed of graphene films are respectively connected together to supply power through a voltage source, two output ends of the upper Wheatstone bridge and the lower Wheatstone bridge are respectively subjected to differential processing, and the subsequent signals are amplified through a differential circuit.
Further, the depth of the groove on the bottom cylindrical substrate is three times of the thickness of the temperature compensation graphene film.
Furthermore, the bottom end cylindrical substrate is bonded with the inner lower bottom surface of the casing of the detector by AB glue, the upper surface of the bottom end cylindrical substrate is bonded with the lower surface of the top end cylindrical substrate by the AB glue, and the bottom end cylindrical substrate and the top end cylindrical substrate are coaxially matched.
Further, the four hollow-out SiO2The lower surface of the substrate is tightly attached to the surfaces of the four grooves on the top cylindrical substrate, and the contacted planes are bonded through an adhesive; the four vibration conversion graphene films are bonded to four hollow SiO films through adhesives2An upper surface of the substrate.
Furthermore, the hollow SiO2The substrate is formed by SiO in a cuboid2The upper surface of the substrate is formed by etching three grooves at equal intervals and equal depths.
Furthermore, the limiting blocks are arranged on four hollow-out SiO2In the square groove formed by the substrate, the lower surface of the limiting block is tightly attached to the upper surface of the square area of the top cylindrical substrate, and the limiting block is attached to the hollowed-out SiO2The surfaces of the substrate and the top cylindrical substrate which are contacted with each other are bonded by an adhesive.
Furthermore, a detector top cover is arranged at the top end of the detector shell, an integrated circuit board is arranged between the vibration pickup lever cup-shaped structure and the detector top cover, and the integrated circuit board is respectively connected with a vibration measurement Wheatstone bridge formed by a vibration conversion graphene film and a temperature compensation Wheatstone bridge formed by a temperature compensation graphene film through wires; the integrated circuit board comprises a direct-current voltage source, a double-end input single-end output differential amplification circuit, a single-end input single-end output voltage amplification circuit, a filter circuit, a data acquisition circuit and a data transmission circuit.
Furthermore, the outputs of the vibration measurement Wheatstone bridge formed by the vibration conversion graphene film and the temperature compensation Wheatstone bridge formed by the temperature compensation graphene film are differentially amplified, and signals after differential amplification sequentially pass through the low-pass filtering module and the A \ D conversion module and transmit data to the outside through the wireless module.
Further, the geophone top cover is matched with the geophone shell through threads, and an airtight glue is used for sealing between the threaded matching.
Further, the detector tail cone is used for coupling the detector with the ground.
Compared with the prior art, the invention has the beneficial effects that:
1. the sensing element is made of graphene piezoresistive material, and compared with a sensitive unit of a traditional detector, the low-frequency characteristic of the sensing element is excellent; the piezoresistive material influences the output of the sensor through the change of the resistance value, the change of the resistance value does not change along with the change of the frequency, the amplitude of the excitation signal is relevant, and therefore the low-frequency range of the piezoresistive material can reach direct current.
2. The graphene sensor element has a very high strain coefficient GF compared with piezoresistive materials such as piezoresistive semiconductors, thick film resistors and metal strain gauges, so that a detector using the graphene sensor element as a sensitive unit has very high sensitivity.
3. The sensitive material graphene used in the invention can bear nearly 20% of self deformation, and the hollow suspension structure can sense the stress close to 0N, so that the detector made of the sensitive material graphene has an extremely high dynamic range.
4. According to the invention, two cross cantilever beam sensitive units with the same structural parameters are designed, and the graphene film arranged on the bottom cylindrical substrate can not pick up vibration and can only sense temperature due to the extremely high substrate rigidity. Is arranged in the hollow SiO2The graphene film on the surface of the substrate can simultaneously sense temperature and vibration, and the output results of the temperature and the vibration are subjected to hardware difference, so that the influence of the temperature on the piezoresistive sensor is completely counteracted.
5. According to the invention, the signal output of the Wheatstone bridge formed by the vibration conversion graphene film and the signal output of the Wheatstone bridge formed by the temperature compensation graphene film are subjected to hardware difference, the obtained output is subjected to difference amplification, and then is subjected to A/D conversion after being filtered, so that an analog signal is converted into a digital signal, noise and distortion generated by various interferences in the long-distance transmission process of the analog signal can be avoided, and the sensitivity and the anti-interference capability of the detector are greatly improved.
Drawings
Fig. 1 is a schematic diagram of the overall structure of a piezoresistive geophone based on graphene according to the present invention;
fig. 2 is a schematic view of a vibration pickup and conversion structure of a piezoresistive geophone based on graphene according to the present invention;
fig. 3 is a schematic bottom substrate view of a vibration pickup conversion structure of a graphene-based piezoresistive geophone according to the present invention;
FIG. 4 is an exploded view of a vibration pickup transducing structure of a graphene-based piezoresistive geophone in accordance with the present invention;
fig. 5 is a block diagram of a signal conditioning module of a piezoresistive geophone based on graphene according to the present invention.
In the figure: 1. vibration conversion graphene film 2. hollow SiO2The detector comprises a substrate 3, a limiting block 4, a vibration pickup lever 5, a top cylindrical substrate 6, a temperature compensation graphene film 7, a bottom cylindrical substrate 8, a detector top cover 9, a detector shell 10, a detector tail cone 11 and an integrated circuit board.
Detailed Description
The invention is described in detail below with reference to the attached drawing figures:
the utility model provides a pressure drag geophone based on graphite alkene, includes a cylindrical cavity geophone shell, and geophone shell lower surface is provided with a geophone caudal vertebra, and geophone shell internally mounted vibrates and picks up conversion structure, and this vibration is picked up the structure and is picked up cylindrical SiO with two structural parameters unanimity2The substrates are assembled as a matrix, and the upper surfaces of the two cylindrical substrates are respectively carved with a cross-shaped groove. Four graphene films are symmetrically and flatly laid in a cross-shaped groove of the cylindrical substrate arranged on the inner surface of the bottom end of the shielding shell, so that the film is prevented from deforming due to external vibration. The four graphene films serve as four arms of a wheatstone bridge and are electrically connected according to a schematic diagram of the wheatstone bridge circuit. And installing another cylindrical substrate on the substrate, respectively installing four hollowed-out substrates in the cross-shaped groove of the substrate, respectively installing four graphene films on the upper surfaces of the four hollowed-out substrates to form a suspended graphene film, and still electrically connecting the four graphene films according to a Wheatstone bridge principle diagram. The above-mentionedThe four vibration conversion graphene films and the four temperature compensation graphene films respectively form a vibration measurement Wheatstone bridge and a temperature compensation Wheatstone bridge. A vertical rod is installed at the intersection of the cross-shaped groove, four cantilevers which are perpendicular to each other in pairs are arranged above the vertical rod, the lower surface of each cantilever is separated from one another by a certain distance to integrate three cylindrical support legs, and a hollow cup-shaped structure is installed at the top end of the vertical rod. The method comprises the steps of respectively connecting power supply ends and ground ends of an upper Wheatstone bridge and a lower Wheatstone bridge which are formed by graphene films together, supplying power through a voltage source to ensure that working voltages of the upper Wheatstone bridge and the lower Wheatstone bridge are consistent, respectively carrying out differential processing on two output ends of the upper Wheatstone bridge and the lower Wheatstone bridge, and amplifying a subsequent signal through a differential circuit. The integrated circuit board is arranged on the inner surface of the top end of the detector shell. A closed shielding shell for electromagnetic shielding is arranged between the integrated circuit board and the two cross cantilevers and is fixed through a clamping groove type structure. The integrated circuit board comprises a direct-current voltage source, a double-end input single-end output differential amplification circuit, a single-end input single-end output voltage amplification circuit, a filter circuit, a data acquisition circuit and a data transmission circuit.
The top end of the detector shell is provided with a detector top cover, an integrated circuit board is arranged between the vibration pickup lever cup-shaped structure and the detector top cover, and the integrated circuit board is respectively connected with a vibration measurement Wheatstone bridge formed by vibration conversion graphene films and a temperature compensation Wheatstone bridge formed by temperature compensation graphene films through wires; the integrated circuit board comprises a direct-current voltage source, a double-end input single-end output differential amplification circuit, a single-end input single-end output voltage amplification circuit, a filter circuit, a data acquisition circuit and a data transmission circuit. The output of a vibration measurement Wheatstone bridge formed by the vibration conversion graphene film and the output of a temperature compensation Wheatstone bridge formed by the temperature compensation graphene film are subjected to differential amplification, and signals after differential amplification sequentially pass through the low-pass filtering module and the A \ D conversion module and transmit data to the outside through the wireless module. The detector top cover is matched with the detector shell through threads, and airtight glue is used for sealing between the thread matching. The detector tail cone is used for coupling the detector with the ground. The upper surface and the lower surface of the detector shell are fixed by adopting a threaded nut structure.
The threaded connection part is bonded by using a polyurethane adhesive to ensure the air tightness inside the protective sleeve, so that the graphene piezoresistive sensitive units are ensured to be converted into the graphene film 1 and four hollow SiO (silicon dioxide) films by four pieces of vibration2The integrated circuit board comprises a substrate 2, a limiting block 3, a vibration pickup lever 4, a top end cylindrical substrate 5, four temperature compensation graphene films 6 and a bottom end cylindrical substrate 7, and is high in overall stability and safety.
The bottom cylindrical substrate and the inner surface of the bottom end of the casing of the detector are bonded and installed by using AB glue; the lower surface of the top end cylindrical substrate is bonded with the upper surface of the top end cylindrical substrate through AB glue, and the lower surface of the top end cylindrical substrate and the upper surface of the top end cylindrical substrate are coaxially matched.
The hollow SiO2The base is arranged at the cross-shaped groove of the cylindrical base at the top end and is bonded through AB glue.
When the vertical rod arranged on the top cylindrical substrate is installed through the aperture matching, the four arms of the vertical rod are guaranteed to be just opposite to (parallel to) the four hollow SiO2 substrates, and the installation depth of the vertical rod is adjusted, so that the cylindrical support legs on the four arms are just in contact with the graphene film and the film is not deformed.
Examples
As shown in fig. 1-4, the piezoresistive geophone according to the present invention comprises four vibration-converted graphene thin films 1 and four hollow-out SiO thin films2The detector comprises a substrate 2, a limiting block 3, a vibration pickup lever 4, a top cylindrical substrate 5, four temperature compensation graphene films 6, a bottom cylindrical substrate 7, a detector top cover 8, a detector shell 9, a detector tail cone 10 and an integrated circuit board 11. Graphene as a novel piezoresistive material has strong piezoresistive performance and good flexibility.
As shown in FIG. 1, the geophone casing 9 is a cylindrical hollow shielding shell, and a vibration pickup conversion structure is arranged inside the casing.
As shown in fig. 2, the vibration pickup conversion structure includes a top end cylindrical base 5 and a bottom end cylindrical base 7, and an upper surface of the bottom end cylindrical base 7 and a lower surface of the top end cylindrical base 5 are bonded by an AB paste. Four hollowed-out SiO positioned on the top cylindrical substrate 52Four vibration conversion graphene films 1 are respectively arranged on the upper surface of the substrate 2. Vibration conversion graphite alkene film 1 and vibration pick up lever 4 and are located the top of whole wave detector, and the four arms that vibration picked up lever 4 have three equidistant cylindrical stabilizer blade respectively. During installation, four arms of the vibration pickup lever 4 are parallel to the edges of the four vibration conversion graphene films 1 respectively, and cylindrical support legs of the vibration pickup lever 4 are just in contact with the upper surfaces of the four vibration conversion graphene films 1.
As shown in fig. 3, a cross-shaped groove is etched on the upper surface of the bottom cylindrical substrate 7 bonded to the lower surface of the top cylindrical substrate 5, the depth of the cross-shaped groove is three times of the thickness of the temperature compensation graphene film 6, a square area at the center of the bottom cylindrical substrate 7 is reserved, the four temperature compensation graphene films 6 are respectively bonded in the cross-shaped groove through a polyurethane adhesive, and the symmetry is ensured at the installation positions of the four temperature compensation graphene films 6.
As shown in fig. 4, the vibration pickup lever 4 installed just above has a vertical bar at the geometric center, a cup-shaped structure at the top end of the vertical bar, the wall thickness of the cup-shaped structure being 1mm, the inner diameter of the cup-shaped structure being 5 times the inner diameter of the vertical bar, and a cylindrical mounting head at the bottom end of the vertical bar, the diameter of the mounting head being smaller than the diameter of the vertical bar. Four cantilevers are symmetrically distributed on the circumferential plane by taking the vertical rod as a symmetry axis, and the four cantilevers are mutually spaced by 90 degrees. The lower surfaces of the four cantilevers are respectively and symmetrically distributed with three cylindrical supporting feet, and the positions of the cylindrical supporting feet are formed by hollow SiO2The recess of the substrate 2.
As shown in fig. 4, the upper surface of the top end cylindrical substrate 5 is distributed with "cross" grooves with equal arm length, and a square area at the center of the top end cylindrical substrate 5 is reserved. Hollowed-out SiO2The substrate 2 is formed by coating a rectangular SiO film on a substrate2The upper surface of the substrate is equidistant and equal in depthAnd etching the three grooves. Hollowed-out SiO2The length and width of the bottom surface of the substrate 2 are equal to the length and width of four grooves divided by the reserved square area on the cylindrical substrate 5. The center of the limiting block 3 is provided with a round hole, the diameter of the round hole is equal to the diameter of a lower end joint of a vertical rod of the vibration pickup lever 4, the upper surface of the limiting block 3 is square, and the side length of the upper surface of the limiting block 3 is equal to that of a square area reserved on the upper surface of the top cylindrical substrate 5.
As shown in figures 2 and 4, the matching relation and the assembly mode of all parts of the geophone are that four hollow SiO2The substrate 2 is respectively arranged in four grooves on the upper surface of the top cylindrical substrate 5, and four hollowed-out SiO2The lower surface of the substrate 2 is closely attached to the surfaces of the four grooves, and the contact planes are bonded through an adhesive. Four vibration conversion graphene films 1 are bonded to the hollow SiO through an adhesive2The upper surface of the substrate 2. The limiting block 3 is arranged on the four hollow SiO2In the square groove formed by the substrate 2, the lower surface of the limiting block 3 is tightly attached to the upper surface of the square area of the top cylindrical substrate 5, and the limiting block 3 is connected with the hollow SiO2The surfaces of the substrate 2 and the top cylindrical substrate 5 which are in contact with each other are bonded by an adhesive. The joint at the lower end of the vertical rod of the vibration pickup lever 4 is arranged at the central circular hole of the limiting block 3, and the long edges under four cantilevers of the vibration pickup lever 4 and four hollow SiO2The long edges of the substrate 2 are kept parallel, and the vibration pickup lever 4 selects a proper installation depth, so that the lower surfaces of the cylindrical support legs on the four cantilevers of the vibration pickup lever 4 are just contacted with the upper surface of the vibration conversion graphene film 1, and the vibration conversion graphene film 1 is not deformed. The temperature compensation graphene film 6 is bonded in the groove of the bottom cylindrical substrate 7 through a bonding agent. The upper surface of the bottom cylindrical base 7 is bonded to the front surface of the top cylindrical base 5 by an adhesive while being held in a concentric relationship.
As shown in fig. 5, the signal conditioning circuit of the present invention includes a wheatstone bridge, a differential amplifying module, a low-pass filtering module and an a/D converting module. The vibration conversion graphene film 1 is respectively used as four arms of a Wheatstone bridge, output signals of the Wheatstone bridge simultaneously contain vibration information and temperature information, the temperature compensation graphene film 6 is respectively used as four arms of another Wheatstone bridge, the output signals of the Wheatstone bridge only contain the temperature information, the output signals of the Wheatstone bridge are subjected to differential operation through a differential circuit to remove the temperature information, then the output signals are subjected to filtering conditioning through a low-pass filtering module, and analog signals are converted into digital signals through an A/D conversion module. Finally, the signal after A/D conversion is transmitted to the outside of the geophone through the wireless module, so that noise and distortion generated by various interferences in the long-distance transmission process of the analog signal can be avoided, and the anti-interference capability and the detection sensitivity of the piezoelectric geophone are greatly improved.
The invention applies the graphene to the piezoresistive geophone, and compared with materials such as a metal strain gauge, a doped semiconductor, a thick film resistor and the like, the piezoresistive geophone has the advantage of extremely high pressure variable coefficient GF, so that the sensitivity of the piezoresistive geophone is greatly improved. The graphene film can bear 20% of self-deformation, which is far higher than that of a doped semiconductor with a relatively large strain coefficient (the maximum self-deformation which can be borne by the graphene film is 2%). The dynamic range of the geophone is greatly improved. Adopts hollow SiO2The graphene film is directly used as a vibration conversion structure, so that the frequency response of the sensitive unit is irrelevant to a substrate material and a structure, and the modal analysis of the graphene film can know that the first-order natural frequency of the sensitive unit is several MHz, so that the linearity of the theoretical frequency response of the geophone in the design from direct current to several MHz is good. The graphene film can respond to deformation even caused by single molecule adsorption, so that the resolution ratio is extremely high. A symmetrical double-Wheatstone bridge structure is adopted, wherein the Wheatstone bridge on the cylindrical substrate at the bottom end is used as a reference bridge to only sense the variation of the temperature field, the Wheatstone bridge on the cylindrical substrate at the top end simultaneously senses the temperature field and vibration, and the output of the Wheatstone bridge and the vibration is subjected to hardware difference to improve the temperature influence.
Claims (10)
1. The utility model provides a piezoresistive geophone based on graphite alkene film, includes a cylindrical hollow geophone shell (9), and geophone caudal vertebra (10), its characterized in that are equipped with to the casing below of geophone shell (9):
a bottom cylindrical substrate (7) is fixed on the inner lower bottom surface of the detector shell (9), cross-shaped grooves are symmetrically distributed on the upper surface of the bottom cylindrical substrate (7), a reserved square area is arranged in the center of the upper surface of the bottom cylindrical substrate (7), and the cross-shaped grooves are divided into four symmetrically distributed grooves by the square area; four temperature compensation graphene films (6) are respectively bonded in the four grooves;
a top end cylindrical substrate (5) is fixed above the bottom end cylindrical substrate (7), a cross-shaped groove and a square area reserved in the center are also formed in the upper surface of the top end cylindrical substrate (5), and the cross-shaped groove is divided into four symmetrically distributed grooves by the square area; a limiting block (3) with a central hole is arranged above the square area; four hollow-out SiO2The substrate (2) is respectively arranged in four grooves on the top cylindrical substrate (5), and the four hollow SiO layers2The upper surface of the substrate (2) is correspondingly provided with four vibration conversion graphene films (1);
the vibration pickup lever (4) is arranged above the limiting block (3), the vibration pickup lever (4) comprises four cantilevers, a vertical rod and cylindrical support legs, the four cantilevers are symmetrically distributed by taking the central vertical rod as a symmetry axis, the lower surface of each cantilever is provided with three cylindrical support legs, the upper end of each vertical rod is integrated into a hollow cup-shaped structure, and the lower end of each vertical rod is provided with an installation head matched with a central hole of the limiting block (3); the four cantilevers are respectively parallel to the edges of the four vibration conversion graphene films (1), and three cylindrical support legs under each cantilever are respectively in contact with the upper surface of the corresponding vibration conversion graphene film (1), so that the vibration conversion graphene film (1) is not deformed;
the four vibration conversion graphene films (1) and the four temperature compensation graphene films (6) are electrically connected according to a Wheatstone bridge to respectively form a vibration measurement Wheatstone bridge and a temperature compensation Wheatstone bridge; the power supply ends and the ground ends of an upper Wheatstone bridge and a lower Wheatstone bridge which are composed of graphene films are respectively connected together to supply power through a voltage source, two output ends of the upper Wheatstone bridge and the lower Wheatstone bridge are respectively subjected to differential processing, and the subsequent signals are subjected to differential amplification.
2. The graphene film based piezoresistive geophone according to claim 1, wherein: the depth of the groove on the bottom cylindrical substrate (7) is three times of the thickness of the temperature compensation graphene film (6).
3. The graphene film based piezoresistive geophone according to claim 1, wherein: the bottom end cylindrical substrate (7) is bonded with the inner lower bottom surface of the wave detector shell (9) through AB glue, the upper surface of the bottom end cylindrical substrate (7) is bonded with the lower surface of the top end cylindrical substrate (5) through the AB glue, and the bottom end cylindrical substrate and the top end cylindrical substrate are coaxially matched.
4. The graphene film based piezoresistive geophone according to claim 1, wherein: the four hollow-out SiO2The lower surface of the substrate (2) is clung to the surfaces of the four grooves on the top cylindrical substrate (5), and the contacted planes are bonded by an adhesive; the four vibration conversion graphene films (1) are bonded to four hollow SiO films through adhesives2An upper surface of the substrate (2).
5. The graphene film based piezoresistive geophone according to claim 4, wherein: the hollow SiO2The substrate (2) is formed by SiO in a cuboid2The upper surface of the substrate is formed by etching three grooves at equal intervals and equal depths.
6. The graphene film based piezoresistive geophone according to claim 1, wherein: the limiting blocks (3) are arranged on four hollow SiO2In the square groove formed by the substrate (2), the lower surface of the limiting block (3) is tightly attached to the upper surface of the square area of the top cylindrical substrate (5), and the limiting block (3) is tightly attached to the hollowed-out SiO2The mutual contact plane between the substrate (2) and the top cylindrical substrate (5) is bonded by an adhesive.
7. The graphene film based piezoresistive geophone according to claim 1, wherein: a detector top cover (8) is arranged at the top end of the detector shell (9), an integrated circuit board (11) is arranged between the cup-shaped structure of the vibration pickup lever (4) and the detector top cover (8), and the integrated circuit board (11) is respectively connected with a vibration measurement Wheatstone bridge formed by the vibration conversion graphene film (1) and a temperature compensation Wheatstone bridge formed by the temperature compensation graphene film (6) through wires; the integrated circuit board comprises a direct-current voltage source, a double-end input single-end output differential amplification circuit, a single-end input single-end output voltage amplification circuit, a filter circuit, a data acquisition circuit and a data transmission circuit.
8. The graphene film based piezoresistive geophone according to claim 7, wherein: the differential amplification is carried out on the outputs of a vibration measurement Wheatstone bridge formed by the vibration conversion graphene film and a temperature compensation Wheatstone bridge formed by the temperature compensation graphene film, and signals after the differential amplification sequentially pass through the low-pass filtering module and the A \ D conversion module and transmit data to the outside through the wireless module.
9. The graphene film based piezoresistive geophone according to claim 7, wherein: the detector top cover (8) is matched with the detector shell (9) through threads, and airtight glue is used for sealing between the thread matching.
10. The graphene film based piezoresistive geophone according to claim 1, wherein: the detector tail cone (10) is used for coupling the detector with the ground.
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