A piezoelectric sensor based on asymmetric electrodes for separating transverse and longitudinal waves and stress inversion method

Abstract

This invention provides a piezoelectric sensor for separating transverse and longitudinal waves based on asymmetric electrodes and a stress inversion method, relating to the field of tunnel engineering detection technology. This invention utilizes the structural characteristics of spherical symmetrical and asymmetric partitioned external electrode groups to fundamentally solve the technical problem that traditional sensors cannot directly monitor transverse and longitudinal wave signals. It introduces an asymmetric partitioned external electrode group structure with a geometrically non-external electrode region, breaking the linear correlation of the charge response matrix and achieving independent decoupling of the three-dimensional full tensor stress. By constructing the inverse matrix of the calibration matrix and introducing a numerical noise floor threshold denoising mechanism, it suppresses error amplification and crosstalk during the stress inversion process, improving the purity of longitudinal and transverse wave separation and the tracking accuracy of the wave source spatial orientation. Therefore, this invention can achieve direct separation and monitoring of elastic waves at the hardware level, providing high-resolution physical parameter support for the identification of adverse geological bodies ahead during tunnel construction.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering detection technology, specifically to a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes and a stress inversion method. Background Technology

[0002] During tunnel construction and underground engineering excavation, the uncertainty of the geological structure ahead of the tunnel face is a significant factor inducing engineering disasters such as water and mud inrushes and surrounding rock instability. Advanced detection technology, through the acquisition and analysis of multi-source physical field information within the rock mass, enables the prediction of geological structure and the distribution of anomalies. Among these, the detection method based on elastic wave propagation has become one of the most widely used techniques due to its high sensitivity to mechanical responses. As tunnel engineering develops towards deeper burial, ultra-long, and complex geological conditions, the requirements for the accuracy and stability of advanced detection are continuously increasing.

[0003] The detection method based on seismic wave propagation theory is one of the important technical approaches for advanced tunnel detection. By exciting wave signals in the rock mass and using sensors to record the wave field response, the vibration characteristics of particles and stress change information can be extracted, thereby enabling inversion analysis of the geological structure.

[0004] Most of the sensors disclosed in the current literature use accelerometers or velocity sensors, which mainly acquire particle vibration information. They require mathematical algorithms to separate longitudinal and transverse waves through post-processing. However, these processing algorithms are prone to component aliasing in complex wave fields and strong noise environments, which leads to a decrease in signal-to-noise ratio and affects the accuracy and stability of subsequent inversion. Secondly, when it is necessary to acquire information in multiple directions, multiple single-axis sensors are usually combined to form an array to achieve multi-component detection. However, such schemes are complex to deploy and have unstable coupling, making them difficult to apply to engineering environments with limited space or complex working conditions.

[0005] Therefore, how to achieve direct decoupling of stress components at the physical level through sensor structure design and obtain complete three-dimensional wave field information on a single sensing unit, thereby reducing dependence on post-processing algorithms and array layout, is a key technical problem that urgently needs to be solved in the field of elastic wave detection. Summary of the Invention

[0006] The purpose of this invention is to provide a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes and a stress inversion method to solve the problem that existing sensors are unable to perform high-precision transverse and longitudinal wave separation detection of elastic waves.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes, comprising: A spherical piezoelectric functional body with radial polarization distribution. The common internal electrode is located inside the spherical piezoelectric functional body. In addition, an asymmetric partitioned external electrode group is disposed on the outer surface of the spherical piezoelectric functional body; the asymmetric partitioned external electrode group includes six mutually insulated spherical cap-shaped electrode blocks, which are distributed along the positive and negative directions of the three coordinate axes of the three-dimensional orthogonal coordinate system, and the two spherical cap-shaped electrode blocks along the positive and negative directions of the same coordinate axis are arranged asymmetrically.

[0008] According to the present invention, a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes is provided, wherein the spherical piezoelectric functional body is a self-supporting piezoelectric spherical shell, or, It includes an insulating support solid sphere and a piezoelectric polymer layer disposed on the surface of the insulating support solid sphere.

[0009] According to the present invention, a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes is provided, wherein the spherical piezoelectric functional body is a continuously integrally formed piezoelectric structure, or a quasi-radial polarized structure composed of multiple pre-polarized piezoelectric elements. According to the present invention, a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes is provided. Among the six spherical cap-shaped electrode blocks, three of the spherical cap-shaped electrode blocks form a geometrically non-external electrode region at the intersection vertex. By breaking the area symmetry of the three coordinate axes through the geometrically non-external electrode region, the effective conductive area of ​​each pair of positive and negative spherical cap-shaped electrode blocks along the three coordinate axes is not equal, thereby breaking the central symmetry of the three coordinate axes.

[0010] According to the present invention, a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes is provided, wherein the outer surface radius of the spherical piezoelectric functional body is . R The equivalent radius of the geometrically non-external electrode region is r ,but r Greater than or equal to R The first multiple of the value and less than or equal to R The second multiple of the value. The first multiple is 0.2, and the second multiple is 0.4.

[0011] According to the present invention, a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes is provided, wherein an insulating gap is provided between adjacent spherical cap-shaped electrode blocks, and the outer surface radius of the spherical piezoelectric functional body is given as... R The width of the insulation gap is w ,but w Less than or equal to R The third multiple of the value. The third multiple is 0.05. In a second aspect, the present invention provides a stress inversion method for a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes, comprising the following steps: The charge response of the transverse and longitudinal wave separated piezoelectric sensor under calibration conditions is obtained, and the relationship matrix between the six-dimensional charge vector and the six-dimensional full tensor stress vector is constructed to obtain the calibration matrix. Calculate the inverse of the calibration matrix; The charge signals output by the six spherical cap-shaped electrode blocks of the transverse and longitudinal wave separation piezoelectric sensor in the test environment are acquired in real time to form a real-time charge vector; By multiplying the inverse matrix with the real-time charge vector, the normal stress components and shear stress components of the three coordinate axes of the three-dimensional orthogonal coordinate system are obtained.

[0012] According to a stress inversion method provided by the present invention, the charge response of a transverse and longitudinal wave separated piezoelectric sensor under calibration conditions is obtained, and a relationship matrix between a six-dimensional charge vector and a six-dimensional full tensor stress vector is constructed to obtain a calibration matrix, including: Six sets of orthogonal unit stress loads were independently applied to the surface of the transverse and longitudinal wave separation piezoelectric sensor. The first three sets of unit stress loads were uniaxial normal stress loads, and the last three sets of unit stress loads were uniaxial shear stress loads. The induced charge of the six spherical cap-shaped electrode blocks under each group of unit stress loads is extracted sequentially and combined into a full-rank calibration matrix.

[0013] The stress inversion method provided by the present invention further includes: The calibration matrix is ​​denoised, and the specific process is as follows: Set a numerical noise floor threshold, and force the geometric integral residues in the calibration matrix whose absolute values ​​are less than the numerical noise floor threshold to be zero.

[0014] The stress inversion method provided by the present invention further includes: Based on the time-domain characteristics of the normal stress component, the longitudinal wave component in the excitation of the environment under test is extracted; Based on the time-domain characteristics of the shear stress components, the transverse wave components in the excitation of the environment under test are extracted. The spatial azimuth angle of the incident wave signal is calculated based on the vector synthesis of the three normal stress components.

[0015] This invention has at least the following beneficial effects: This invention utilizes the structural characteristics of spherical symmetrical and asymmetrical partitioned external electrode groups to achieve direct decoupling of three-dimensional full tensor stress at the scale of a single spherical piezoelectric sensor. By introducing an asymmetrical region spanning the intersection of multiple axes into the spherical electrode distribution, the linear correlation of charge response under symmetrical structures is broken, transforming the charge-stress mapping relationship from a degenerate structure to a full-rank structure, thereby achieving independent inversion of six-dimensional stress components. Based on the calibration matrix construction and inversion process, a real-time mapping relationship between charge signals and full tensor stress is established, enabling synchronous reconstruction of normal stress components and shear stress components in complex wave fields. Combining the physical meaning of stress components, direct separation of longitudinal waves (P-waves) and transverse waves (S-waves) at the sensor end and inversion calculation of their propagation directions are achieved. This invention fully utilizes the geometric features of asymmetric electrodes that break area symmetry, enabling a single sensor to acquire complete three-dimensional stress information. By constructing a linear mapping relationship based on a calibration matrix, it avoids the error accumulation and ill-posedness problems caused by relying on complex wavefield decomposition algorithms, significantly improving the stability and noise resistance of the inversion results. Simultaneously, this structure achieves wave pattern separation and direction sensing without requiring a multi-sensor array, reducing system complexity and enhancing applicability in complex stress environments and confined spaces. In summary, this invention reconstructs the acquisition method of elastic wave information at the sensor geometry level and realizes direct monitoring of three-axis transverse and longitudinal waves at the hardware level, providing a reliable hardware foundation and methodological support for high-precision stress inversion, wave pattern identification, and source location under complex wavefield conditions in tunnel engineering. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] In the attached diagram: Figure 1 This is a schematic diagram of the structure of a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to a specific embodiment of the present invention; Figure 2 This is a cross-sectional schematic diagram of a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to a specific embodiment of the present invention; Figure 3 This is a flowchart of the stress inversion method of the transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to the present invention; Figure 4 This is a schematic diagram of six working conditions used in calculating the calibration matrix C in a specific embodiment of the present invention; Figure 5 This is a schematic diagram of the stress field and electric potential field under a certain working condition in a specific embodiment of the present invention; Figure 6 This is a waveform diagram of the received signal from the six-sided electric field in a specific embodiment of the present invention; Figure 7 This is a specific embodiment of the present invention showing the applied load and the inverted load carrier waveform. Figure 8 This is a schematic diagram of the full tensor stress inversion verification of the present invention; Figure 9 This is a waveform diagram of the six-sided electric field received signal during the full tensor stress inversion verification of this invention; Figure 10 This is the applied load and inversion load curve diagram during the full tensor stress inversion verification of this invention.

[0018] Reference numerals: 1-Sensor, 1.1-Internal insulating support sphere, 1.2-Piezoelectric layer, 1.3-Common inner electrode, 1.4-Outer electrode, 1.4.1-Complete electrode region, 1.4.2-Asymmetric electrode region, 1.4.3-Missing region, 1.5-Insulating gap. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] The following detailed description of some embodiments of the present invention will be provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0021] This invention provides a piezoelectric sensor based on asymmetric electrodes for separating transverse and longitudinal waves, and a stress inversion method, which can solve the problem that existing sensors cannot directly monitor three-dimensional transverse and longitudinal wave stress. Please refer to... Figure 1 The transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes provided by the present invention includes the following structure: (1) A spherical piezoelectric functional body with radial polarization distribution; (2) A common internal electrode located inside the spherical piezoelectric functional body; (3) An asymmetric partitioned external electrode group is set on the outer surface of the spherical piezoelectric functional body. The asymmetric partitioned external electrode group includes six mutually insulated spherical cap-shaped electrode blocks, which are distributed along the positive and negative directions of the three coordinate axes of the three-dimensional orthogonal coordinate system, and the two spherical cap-shaped electrode blocks along the positive and negative directions of the same coordinate axis are arranged asymmetrically.

[0022] Specifically, the spherical piezoelectric functional body is a self-supporting piezoelectric spherical shell, or... It includes an insulating support solid sphere and a piezoelectric polymer layer disposed on the surface of the insulating support solid sphere.

[0023] Specifically, the spherical piezoelectric functional body is a continuous, integrally formed piezoelectric structure, or a quasi-radial polarized structure composed of multiple pre-polarized piezoelectric elements spliced ​​together.

[0024] Specifically, among the six spherical cap-shaped electrode blocks, three of them form a geometrically non-external electrode region at their intersection vertices. By simultaneously disrupting the area symmetry along the three coordinate axes through this geometrically non-external electrode region, the effective conductive area of ​​each pair of positive and negative spherical cap-shaped electrode blocks along the three coordinate axes is not equal. This disrupts the central symmetry along the three coordinate axes, breaks the linear correlation of the charge response matrix, and achieves independent decoupling of the full tensor stress.

[0025] Specifically, let the outer surface radius of the spherical piezoelectric functional body be... R The equivalent radius of the geometrically electrodeless region is r, and the two should satisfy the dimensional relationship: 0.2 R ≤ r ≤0.4 R .

[0026] Specifically, an insulating gap is provided between adjacent spherical electrode blocks, and the width of the insulating gap is [missing information]. w And satisfy w ≤0.05 R This is to maximize the effective stress sensing area of ​​the spherical cap electrode blocks while ensuring electrical insulation between adjacent spherical cap electrode blocks.

[0027] It should be noted that the theoretical basis of this invention is the long-wavelength approximation, and the source wavelength should satisfy the wavelength requirement. l Much larger than the sensor diameter D (For example l >10D, preferred l >20D), when the vibration wavelength l ≈10 D At this time, the stress field inside the sensor is no longer uniform, making it impossible to accurately decouple the stress. However, in current tunnel detection based on seismic wave methods, the source frequency is usually no more than 1000Hz, and the sensor can meet the engineering requirements.

[0028] The following is a specific embodiment of the present invention, which performs sensor calibration and theoretical decoupling verification.

[0029] like Figure 1 , Figure 2 As shown, the transverse and longitudinal wave separation piezoelectric sensor 1 based on asymmetric electrodes provided in this embodiment mainly includes the following structure: (1) Internal insulating support ball 1.1: It is a high-rigidity solid ball (made of epoxy resin or acrylic) as the mechanical skeleton of the sensor, which is used to bear the main stress transmitted by the external environment such as the stratum; (2) Piezoelectric layer 1.2: Covers the outside of the inner insulating support ball 1.1. In this embodiment, it is preferably made of vinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)), which is radially polarized. It can be a continuous integral film structure or a quasi-radial polarized structure composed of multiple pre-polarized piezoelectric elements. (3) Common inner electrode 1.3: formed by copper plating on the inner surface of the piezoelectric layer 1.2, serving as the electrical grounding reference terminal of the sensor; (4) External electrode 1.4: formed by silver plating on the outer surface of piezoelectric layer 1.2.

[0030] Specifically, the outer electrode 1.4 includes six spherical cap-shaped electrode blocks, each positioned along one of the three coordinate axes of a three-dimensional orthogonal coordinate system. x , y , z The positive and negative directions are distributed, and adjacent spherical cap-shaped electrode blocks are separated by an insulating gap of 1.5.

[0031] Since the integrands are all even functions, if the electrodes are perfectly symmetrical, then the corresponding positive and negative poles (e.g.) and The integral areas of all ) are exactly equal, resulting in the following on the plane of symmetry, such as the plane of symmetry. x +、 x The signals on the electrodes are the same, which leads to only three of the six electrode signals being linearly independent, and the determinant of the calibration matrix C, det(C), is 0.

[0032] This invention establishes asymmetric electrode regions, specifically two spherical cap-shaped electrode blocks arranged asymmetrically along the positive and negative directions of the same coordinate axis. This asymmetric arrangement is achieved by using a circular missing region 1.4.3 at the vertex where the three electrode blocks intersect to disrupt the symmetry of the electrode blocks, resulting in three asymmetric electrode regions 1.4.2. This single missing region simultaneously disrupts the area symmetry of the three axes, ensuring that the effective conductive areas of each pair of positive and negative electrode blocks in the three axes of the three-dimensional orthogonal coordinate system are unequal. Consequently, the asymmetric electrode regions 1.4.2 and the complete electrode region 1.4.1 produce different electrical signal responses under load. This difference fundamentally breaks the linear correlation of the charge response matrix, providing the necessary mathematical conditions for achieving independent decoupling of the full tensor stress.

[0033] By setting an asymmetric electrode region, Similarly, this ensures that det(C) ≠ 0. At this point, the matrix is ​​full rank and invertible, and its six components can be solved as follows:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] in, s xx , s yy , s zz Represents the normal stress component. t xy , t xz , t yz Represents the components of shear stress (or simply shear stress); M ij It is a submatrix of the calibration matrix C, det(M) ij ) is the cofactor of the calibration matrix C. i =1,2,3,4,5,6 j =1,2,3,4,5,6.

[0040] For the first three columns (normal stress term, j =1, 2, 3):

[0041] For the last three columns (shear stress term, j =4, 5, 6):

[0042] in Corresponding to the six partitioned electrode blocks A x+ A x- A y+ A y- A z+ A z- ; a , b These represent the direction cosine components of the two orthogonal axes corresponding to the shear stress components, such as... j When =4, the corresponding t yz ,but n a n b =n y n z .

[0043] In this embodiment, R =5 mm, r =1 mm, w =0.05 mm.

[0044] like Figure 3 As shown, another embodiment of the present invention provides a stress inversion method for a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes as described in the foregoing embodiments, comprising the following steps: S1: Obtain the charge response of the transverse and longitudinal wave separated piezoelectric sensor under calibration conditions, construct the relationship matrix between the six-dimensional charge vector and the six-dimensional full tensor stress vector, and obtain the calibration matrix; Specifically, under the action of external full-tensile stress, the induced charge generated on the surface of any spherical cap-shaped electrode block (hereinafter referred to as electrode) A in the spherical piezoelectric functional body is... Q (A) Satisfies the following analytical formula for area:

[0045] In the formula, d 33 and d 31 The piezoelectric constant is... n x , n y , n z The cosine of the outward normal direction of the spherical cap-shaped electrode block surface.

[0046] Each term in the formula represents a term in the stress tensor that generates a charge on the spherical cap electrode block A. For example, for , It is a signal generated in the vertical polarization direction. It is a signal generated by the polarization direction.

[0047] In some embodiments, S1 further includes: S1.1: Establish six sets of orthogonal unit stress load conditions.

[0048] Six spherical electrode blocks ( x +, y +, z +, x -, y -, z The charge output combination of -) is represented by the column vector Q, and the external stress combination is represented by the column vector σ= Then a 6×6 calibration matrix C can be established:

[0049] According to the above formula, if and only if the first... i When one component equals 1 and the other five components equal 0, the equation degenerates into: Therefore, it can be done as follows: Figure 4 As shown, perform the following steps respectively: S1.1.1: Along x , y , z A unit uniaxial normal stress load is applied to each shaft. s xx , s yy , s zz ; S1.1.2: In yz , xz , xyz Apply unit shear stress load to the plane respectively t yz , t xz , t xy The calibration matrix C can be obtained from the experiments under the six working conditions shown in Table 1.

[0050] Table 1 Experimental conditions for obtaining calibration matrix C

[0051] S1.2: Extracting electrode charge response under various operating conditions In this embodiment, finite element software is used to simulate the above-mentioned working conditions. For example, the stress and potential field conditions obtained under working condition 6 are as follows: Figure 5 As shown. S1.2 specifically includes: S1.2.1: For each set of operating conditions, record data simultaneously using six electrodes ( x +, x -, y +, y -, z +, z -) the amount of induced charge; S1.2.2: Calculation of the cosine integral contribution of the electrode normal: Due to the presence of the missing region, the cosine integral contribution of each electrode normal changes, resulting in a difference in the induced charge between the porous and non-porous surfaces. The output results for the six operating conditions are shown in Table 2: Table 2 Electrode Induced Charge under Various Operating Conditions

[0052] S1.3: Assemble the 6×6 calibration matrix C: Extract and combine the charge output of the six spherical cap electrode blocks under six operating conditions to construct the original full-rank calibration matrix C.

[0053] S2. Real-time inversion of full tensor stress: Calculate the inverse matrix of the calibration matrix; acquire the charge signals output by the six spherical cap-shaped electrode blocks of the transverse and longitudinal wave separation piezoelectric sensor in the test environment in real time to form a real-time charge vector; multiply the inverse matrix with the real-time charge vector to obtain the normal stress components and shear stress components of the three coordinate axes of the three-dimensional orthogonal coordinate system.

[0054] Specifically, after obtaining the full-rank calibration matrix C, a numerical noise floor threshold is set, and the geometric integral residuals with extremely small absolute values ​​in the calibration matrix C are forced to zero to complete the noise reduction process. Then, the inverse matrix C is obtained by performing an inversion operation on it. -1 According to Cramer's rule, the inverse matrix C... -1 Each element in the matrix is ​​determined by the cofactor M of the calibration matrix C. ij It consists of the determinant det(C).

[0055] In actual detection, the charge signals output by the six spherical cap-shaped electrode blocks of the sensor are acquired in real time, forming a real-time charge vector Q( t )=[Q1( t ), Q2( t ), Q3( t ), Q4( t ), Q5 t ), Q6 ( t )] T Through the inverse matrix C -1 With real-time charge vector Q( t ) matrix multiplication operations, reconstructing arbitrary t The three-dimensional full tensor stress column vector σ( t Its inversion equation is:

[0056] Therefore, the three time-varying normal stress components can be independently obtained through the cofactor weighting calculation in six dimensions. s xx , s yy , s zz and three shear stress components t xy , t xz , t yz .

[0057] In some embodiments, S2 specifically includes: S2.1: Numerical optimization of the calibration matrix and solution of the inverse matrix.

[0058] S2.1.1: Set a numerical noise floor threshold for noise reduction to reduce crosstalk interference.

[0059] In this embodiment, the coordinate axes pass through the center of each surface. This allows the normal stress to be solved first using three complete surfaces, and then the shear stress to be solved using three incomplete surfaces. The calibration matrix C then simplifies to:

[0060] The nine terms whose positions are consistent with the original matrix are omitted, and only those terms that are modified to be 0 are corrected. After obtaining the full-rank calibration matrix C, according to the theoretical calculation of the above formula, it can be seen that nine terms should be 0. As can also be seen from Table 3, nine terms have an order of magnitude of 10. -21 ~10 -20 The induced charge is much smaller than that of the other electrodes, indicating a good correspondence between the simulation results and theoretical calculations. The reason for the inaccurate zero value is crosstalk between the electrodes. Therefore, by setting a numerical noise floor threshold and forcing the geometric integral residuals with extremely small absolute values ​​in the calibration matrix C to zero, the calibration matrix C can be obtained as follows:

[0061] S2.1.2: Verify and invert the matrix when it is full rank.

[0062] After obtaining the simplified full-rank calibration matrix C, inverting it yields the inverse matrix C. -1 As shown in Table 3. According to Cramer's rule, the inverse matrix C -1 Each element in the matrix is ​​determined by the cofactor M of the calibration matrix C. ij It consists of the determinant det(C).

[0063] Table 3 Inverse Matrix C -1

[0064] S2.2: Charge signal extraction and real-time stress reconstruction S2.2.1: Apply a load to the sensor It also collects the charge signals output by the six electrodes of the sensor in real time, forming a real-time charge vector Q( t )=[Q1( t ), Q2( t ), Q3( t ), Q4( t ), Q5 t ), Q6 ( t )] T .

[0065] In this embodiment 1, the applied multiaxial coupled sinusoidal load is as follows:

[0066] Right now: x-axis:

[0067] y-axis:

[0068] z-axis: 0 Pick =1MPa, resulting in the following: Figure 6 The Q( shown) t )curve.

[0069] S2.2.2: By Q( t ) and C -1 Calculate stress σ( t ) Through the inverse matrix C -1 With real-time charge vector Q( t The matrix multiplication operation of ) reconstructs in real time the three-dimensional full tensor stress column vector σ( ) inside the medium at time t. t Its inversion equation is:

[0070] Therefore, the three time-varying normal stress components can be independently obtained through the cofactor weighting calculation in six dimensions. s xx , s yy , s zz and three shear stress components t xy , t xz , t yz .like Figure 7 As shown, the dashed line represents the applied load, and the solid line represents the inversion load. It can be seen that the inversion results are basically accurate.

[0071] In some embodiments, the method further includes: S3, separation of transverse and longitudinal waves and calculation of the spatial azimuth angle of the wave source.

[0072] Based on the dynamic characteristics of seismic wave propagation, longitudinal waves (P-waves) cause volume compression and expansion of the medium, and their energy is mainly manifested as work done by normal stress; transverse waves (S-waves) cause shape distortion of the medium, and their energy is mainly manifested as work done by shear stress. Therefore, the three normal stress components obtained from the above inversion can be directly extracted ( s xx , s yy, s zz The time-domain characteristic curve of the signal is used as the longitudinal wave (P-wave) signal; three shear stress components are directly extracted. t xy , t xz , t yz The time-domain characteristic curve of the P-wave is used as the transverse wave (S-wave) signal. This method achieves precise separation of the P-wave and S-wave from a physical perspective, effectively eliminating signal crosstalk caused by waveform conversion.

[0073] Since the particle vibration direction of a longitudinal wave (P-wave) is strictly parallel to the direction of the wave propagation ray, the spatial vector of the incident wave can be determined by vector synthesis using the instantaneous amplitudes of the three separated normal stress components. Let the horizontal azimuth angle of the wave source be... i (exist x - y in plane and x (angle between axes), perpendicular space angle is (and z If the angle between the axes is 0, then the formula for calculating the azimuth angle in the propagation space is:

[0074]

[0075] By calculating the spatial azimuth characteristics of the incident wave signal based on the above formula, it is possible to accurately locate and detect underground rupture sources, seismic sources, or microseismic events in three-dimensional space.

[0076] To further verify the environmental adaptability and reliability of the sensor of the present invention in practical engineering applications, a full tensor stress inversion verification was conducted under a geological burial environment. Based on the aforementioned specific embodiments, the detection conditions of sensor 1 being buried in the surrounding rock of a real tunnel were simulated.

[0077] like Figure 8 As shown, a cubic enclosure with a side length of 10R (i.e., 50 mm) is constructed outside sensor 1 to simulate the surrounding rock medium. The material of this enclosure is set to granite with a Young's modulus of 70 GPa, a Poisson's ratio of 0.25, and a density of 2700 kg / m³. 3 The outer surface of sensor 1 is set to be in a completely continuous constraint with the contact surface with the surrounding rock to simulate the pre-embedded state of tight coupling inside the stratum.

[0078] Due to the modulus difference between the concrete (30 GPa) and the internal insulating support sphere 1.1 (3.2 GPa), a significant stress shielding effect occurs during the transmission of stress waves from the surrounding rock to the interior. To eliminate the systematic error caused by medium coupling, step S1 is repeated, but during loading, the unit load is... It is applied to the six outer surfaces of the cubic surrounding rock, rather than directly to the sensor surface. =1 MPa, the applied multiaxial coupled sinusoidal load is as follows:

[0079] Right now: x-axis:

[0080] y-axis:

[0081] z-axis:

[0082] At this point, the coupling calibration matrix can still be constructed using step S2.1. and its inverse matrix Among them, the inverse matrix of the coupling calibration matrix of the buried environment As shown in Table 4.

[0083]

[0084] Table 4. Inverse matrix of the coupling calibration matrix for the buried environment

[0085]

[0086] By monitoring real-time charge, such as Figure 9 As shown, and using the decoupling model mentioned in steps S2.2 and S3 above for inversion, the calculation equation is adjusted to:

[0087] The results obtained are as follows Figure 10 As shown, even under complex medium stiffness mismatch and severe signal attenuation, the inverted stress curve (solid line) still highly coincides with the original load (dashed line) applied externally to the surrounding rock, and the transverse and longitudinal wave components are accurately separated. This indicates that the sensor of this invention has the ability to directly reconstruct the far-field full tensor stress of the strata, thereby providing real surrounding rock dynamic parameters for tunnel advance detection.

[0088] In summary, this invention utilizes the structural characteristics of spherical symmetrical and asymmetrical partitioned external electrode groups to fundamentally solve the technical challenge of traditional sensors being unable to directly monitor transverse and longitudinal wave signals. By introducing an asymmetrical partitioned external electrode group structure with a geometrically non-external electrode region, it breaks the linear correlation of the charge response matrix, achieving independent decoupling of the three-dimensional full tensor stress. Furthermore, by constructing the inverse matrix of the calibration matrix and introducing a numerical noise floor threshold denoising mechanism, it suppresses error amplification and crosstalk during stress inversion, improving the purity of longitudinal and transverse wave separation and the tracking accuracy of the wave source's spatial orientation. Therefore, this invention can achieve direct separation and monitoring of elastic waves at the hardware level, providing high-resolution physical parameter support for identifying adverse geological formations ahead during tunnel construction.

[0089] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes, characterized in that, include: A spherical piezoelectric functional body with radial polarization distribution. The common internal electrode is located inside the spherical piezoelectric functional body. And, an asymmetric partitioned external electrode group disposed on the outer surface of the spherical piezoelectric functional body; the asymmetric partitioned external electrode group includes six mutually insulated spherical cap-shaped electrode blocks, which are distributed along the positive and negative directions of the three coordinate axes of the three-dimensional orthogonal coordinate system, and the two spherical cap-shaped electrode blocks along the positive and negative directions of the same coordinate axis are arranged asymmetrically. Among the six spherical cap-shaped electrode blocks, three of them form a geometrically non-external electrode region at their intersection vertices. This geometrically non-external electrode region simultaneously disrupts the area symmetry along the three coordinate axes, making the effective conductive area of ​​each pair of positive and negative spherical cap-shaped electrode blocks along the three coordinate axes unequal, thereby disrupting the central symmetry along the three coordinate axes.

2. The transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to claim 1, characterized in that, The spherical piezoelectric functional body is a self-supporting piezoelectric spherical shell, or... It includes an insulating support solid sphere and a piezoelectric polymer layer disposed on the surface of the insulating support solid sphere.

3. The transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to claim 1, characterized in that, The spherical piezoelectric functional body is a continuous, integrally formed piezoelectric structure, or a quasi-radial polarized structure composed of multiple pre-polarized piezoelectric elements spliced ​​together.

4. The transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to claim 1, characterized in that, ... The outer surface radius of the spherical piezoelectric functional body is R The equivalent radius of the geometrically non-external electrode region is r ,but r Greater than or equal to R The first multiple of the value and less than or equal to R The second-highest value.

5. The transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes according to claim 1, characterized in that, An insulating gap is provided between adjacent spherical cap-shaped electrode blocks, and the outer surface radius of the spherical piezoelectric functional body is given as... R The width of the insulating gap is w ,but w Less than or equal to R The third value.

6. A stress inversion method for a transverse and longitudinal wave separation piezoelectric sensor based on asymmetric electrodes as described in any one of claims 1-5, characterized in that, Includes the following steps: The charge response of the transverse and longitudinal wave separated piezoelectric sensor under calibration conditions is obtained, and the relationship matrix between the six-dimensional charge vector and the six-dimensional full tensor stress vector is constructed to obtain the calibration matrix. Calculate the inverse of the calibration matrix; The charge signals output by the six spherical cap-shaped electrode blocks of the transverse and longitudinal wave separation piezoelectric sensor in the test environment are collected in real time to form a real-time charge vector; By multiplying the inverse matrix with the real-time charge vector, the normal stress components and shear stress components of the three coordinate axes of the three-dimensional orthogonal coordinate system are calculated.

7. The stress inversion method according to claim 6, characterized in that, The charge response of the transverse and longitudinal wave separated piezoelectric sensor under calibration conditions is obtained, and the relationship matrix between the six-dimensional charge vector and the six-dimensional full tensor stress vector is constructed to obtain the calibration matrix, including: Six sets of orthogonal unit stress loads were independently applied to the surface of the transverse and longitudinal wave separation piezoelectric sensor. The first three sets of unit stress loads were uniaxial normal stress loads, and the last three sets of unit stress loads were uniaxial shear stress loads. The induced charge of the six spherical cap-shaped electrode blocks under each group of unit stress loads is extracted sequentially and combined into a full-rank calibration matrix.

8. The stress inversion method according to claim 6, characterized in that, Also includes: The calibration matrix is ​​denoised, and the specific process is as follows: Set a numerical noise floor threshold, and force the geometric integral residuals in the calibration matrix whose absolute values ​​are less than the numerical noise floor threshold to be zero.

9. The stress inversion method according to claim 6, characterized in that, Also includes: Based on the time-domain characteristics of the normal stress component, the longitudinal wave component in the excitation of the environment under test is extracted; Based on the time-domain characteristics of the shear stress components, the transverse wave components in the excitation of the environment under test are extracted. The spatial azimuth angle of the incident wave signal is calculated based on the vector synthesis of the three normal stress components.

Images