A Low-Frequency Passive RFID Positioning Method and Device for Underground Cable Detection

Abstract

The present invention belongs to the technical field related to positioning, and discloses a low-frequency passive RFID positioning method and device for underground cable detection, including the following steps: (1) Power the low-frequency passive RFID tag by the electromagnetic wave energy of the RFID reader-writer, and derive the minimum induced voltage required for the RFID tag to work according to the inductive coupling equivalent circuit between the RFID reader-writer and the RFID tag, so as to construct a quantitative mapping relationship between the minimum working current of the RFID reader-writer antenna required for the RFID tag to work and the tag depth, and further obtain a ranging model based on the working current; (2) Measure the data required for parameter estimation of the ranging model in the soil medium, and use the Gauss-Newton method to process the obtained data to estimate the optimal solution of the minimum working current of the ranging model, and then input it into the ranging model to calculate the RFID tag depth. The present invention can provide precise positioning services in most medium environments.

Description

Technical Field

[0001] The present invention belongs to the technical field related to positioning, and more specifically, relates to a low-frequency passive RFID positioning method and device for underground cable detection. Background Art

[0002] At present, the construction of modern urban power grids is inseparable from the application of power cables. Their advantages such as high reliability, space saving, and urban beautification have led to an increasing cable rate. At the same time, the reduction in cost has also greatly increased the utilization rate of power cables in urban distribution network systems. The urban power supply method has gradually shifted from overhead lines to underground laying of power cables. As the most important infrastructure of the power system, underground cables have increasingly become the lifeline to ensure the normal operation of the city. Due to the high concealment of underground cables themselves, the loss of cable channel drawings and materials, and the problem of untimely updates, tracing the cable path brings great difficulties to the operation and maintenance of the distribution network. Therefore, there is an urgent need for an underground cable positioning technology.

[0003] Due to the influence of the formation and foundation, common metal detection devices are difficult to achieve precise positioning of underground cables. RFID (Radio Frequency Identification) that wirelessly identifies cables through electronic tags is expected to provide a new way for the rapid, accurate, and convenient detection of underground cables. For example, in CN202110098873.0, it uses the radio frequency communication between a ground RFID reader and a buried RFID tag to obtain information such as the type and historical maintenance records of the cable, which can effectively overcome the limitations of traditional metal detection devices affected by geological conditions and other factors. However, there is still a problem that the depth information of underground cables cannot be accurately obtained. Ultra-high frequency RFID positioning technology has now been widely studied and applied, but the penetration ability of RFID signals with ultra-high frequency and microwave frequencies is too weak to be applied to underground environment positioning. For passive low-frequency RFID technology suitable for underground environments, the available positioning information is mainly the received signal strength (RSSI). However, the RSSI value is relatively sensitive to environmental interference, and it is difficult to further improve the accuracy. Applying it to near-field underground passive RFID positioning will have the problem of low positioning accuracy.

[0004] Through the above analysis, the problems and defects existing in the prior art are as follows:

[0005] (1) Due to the influence of the formation and foundation, common metal detection devices are difficult to achieve precise positioning of underground cables;

[0006] (2) The existing underground RFID identification methods have the problem that the depth information of underground cables cannot be accurately obtained;

[0007] (3) Passive low-frequency RFID technology, the available positioning information of which is mainly the received signal strength (RSSI). However, the RSSI value is sensitive to environmental interference and it is difficult to further improve the accuracy. Applying it to near-field underground passive RFID positioning will have the problem of low positioning accuracy. Summary of the Invention

[0008] In view of the above defects or improvement requirements of the prior art, the present invention provides a low-frequency passive RFID positioning method and device for underground cable detection, which is an effective underground cable precise positioning model, with simple structure, low cost, convenient deployment, capable of realizing real-time positioning, and can provide precise positioning services in most medium environments.

[0009] To achieve the above object, according to one aspect of the present invention, a low-frequency passive RFID positioning method for underground cable detection is provided. The method mainly includes the following steps:

[0010] (1) Use the electromagnetic wave energy of the RFID reader to power the low-frequency passive RFID tag, and deduce the minimum induced voltage V required for the RFID tag to work according to the inductive coupling equivalent circuit between the RFID reader and the RFID tag, so as to construct a quantitative mapping relationship between the minimum working current of the RFID reader antenna required for the RFID tag to work and the tag depth, and then obtain a ranging model based on the working current; the expression of the ranging model is: actmin , and regard the minimum working current I of the reader antenna and the tag depth Z as variables;

[0011]

[0012] In the formula, N is the number of turns of the tag coil, r is the radius of the tag coil, f is the working frequency of the underground RFID system, μ is the vacuum permeability, ε s is the relative dielectric constant of the signal passing through the medium, c is the speed of light in vacuum, R is the radius of the reader antenna, the minimum working current I min and the tag depth Z are regarded as variables;

[0013] (2) Measure the data required for parameter estimation of the ranging model in the soil medium, and use the Gauss-Newton method to process the obtained data to estimate the optimal solution of the minimum working current of the ranging model, and then input the estimated optimal solution of the minimum working current into the ranging model to calculate the RFID tag depth and realize the low-frequency passive RFID positioning of the underground cable.

[0014] Further, when the induced voltage V act generated when the tag receives the signal reaches a threshold V min , the tag is activated and returns information to the reader; the minimum induced voltage V required for the tag to workactmin ≈V min 。

[0015] Furthermore, for a given antenna, if the distance Z between the reader antenna and the tag antenna is changed, the minimum current I of the reader antenna required to activate the RFID tag min should also change accordingly.

[0016] Furthermore, different distances are selected in the soil medium, and the minimum operating current of the reader antenna when the tag signal is on the verge of disappearing is measured to obtain M sets of experimental data; then, the data is screened using the outlier removal method based on the Gaussian model, and the screened data is corrected using the statistical mean model; finally, the optimal solution of the ranging model parameters is obtained using the Gauss-Newton method.

[0017] Furthermore, first, if there are still m sets of data after the experimental data is preprocessed, then the residuals of these m sets of data are r i = Z i - Z(I imin ; V actmin ; ε s ), then the objective function is:

[0018]

[0019] where i ∈ [1, m];

[0020] After that, the average value of the calculated parameters is used as the initial value V imin ; V actmin ; ε s ) of the coefficient set to be estimated for the Gauss-Newton method iteration V (0) (I imin (0) ; V actmin (0) ; ε s (0) );

[0021] Next, the nonlinear regression model is linearized to obtain:

[0022] Z(I imin ; V actmin ; ε s ) = Z(I imin (0) ; V actmin (0) ; ε s (0) ) + J(I imin (0) ; V actmin (0) ; ε s (0) )V＝V(0) (V - V (0) )

[0023] Next, the least squares method is used to estimate and correct H (k) , then ΔV (k) =(J (k)T J (k) ) -1 J (k)T L i (k) . Let V(0) be the first iteration value, then V (k+1) =V (k) +ΔV (k) ;

[0024] After that, when the number of iterations reaches m times, the correction factor is ΔV (m) =(J (m)T J (m) ) -1 J (m)T L i (m) ; When ΔV (m) <ε, stop the iterative repetition, otherwise continue to update; the (m + 1)-th iteration value is V (m+1) =V (m) +ΔV (m) ; Thus, the optimal solution obtained after iteration is the optimal solution of the ranging model parameters.

[0025] Furthermore, in step (2), the reader antenna and the tag antenna are aligned in the axial direction; N fixed different distances are selected in the soil medium, and the minimum operating current of the reader antenna when the tag signal is about to disappear is measured.

[0026] The present invention also provides a computer storage medium, which stores a computer program. When the computer program is executed by a processor, the processor is caused to execute the low-frequency passive RFID positioning method for underground cable detection as described above.

[0027] The present invention also provides a device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor is caused to execute the low-frequency passive RFID positioning method for underground cable detection as described above.

[0028] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the low-frequency passive RFID positioning method and device for underground cable detection provided by the present invention mainly have the following beneficial effects:

[0029] 1. The present invention takes into account the influence of media such as soil, establishes a ranging model based on the working current in the underground environment, and uses the working current of the reader antenna, avoiding the large depth estimation error easily caused by using the RSSI value returned by the tag.

[0030] 2. The present invention uses the experimental data obtained from actual tests, and estimates the parameters that are difficult to directly measure in practice through a certain method, transforms the problem of solving the model parameters into a least-squares problem, and uses the Gauss-Newton method to solve the model parameters.

[0031] 3. The present invention provides an effective precise positioning model for underground cables, which has a simple structure, low cost, convenient deployment, can achieve real-time positioning, can provide precise positioning services in most media environments, and also has the advantages of long life, non-contact, reusable, and no external power supply, etc., and has great commercial value.

[0032] 4. The present invention uses a ranging model based on the working current considering the influence of media such as soil to achieve positioning, making up for the gap in the low positioning accuracy of the current industry technology; underground cables, as the most important infrastructure of the power system, are the lifelines to ensure the normal operation of the city. Due to the high concealment of underground cables themselves, the loss of cable channel drawings and materials, and the problem of untimely update, etc., cable path tracing brings great difficulties to the distribution network operation and maintenance. And the present invention proposes a new positioning method based on the working current ranging model for the underground passive low-frequency RFID positioning system, overcoming the technical problem of low real-time positioning accuracy.

[0033] 5. For the passive low-frequency RFID technology applicable to the underground environment, the available positioning information is mainly the received signal strength (RSSI). However, the RSSI value is sensitive to environmental interference and it is difficult to further improve the accuracy. Applying it to the near-field underground passive RFID positioning will have the problem of low positioning accuracy. And the present invention uses a ranging model based on the working current considering the influence of media such as soil to achieve positioning, using the working current of the reader itself, and can achieve real-time precise positioning, breaking through the traditional technical prejudice and greatly improving the practical value of the present invention. Description of the Drawings

[0034] Figure 1 is a schematic flow chart of a low-frequency passive RFID positioning method for underground cable detection provided by the present invention;

[0035] Figure 2 In (a) and (b) of [figure reference], they are respectively schematic diagrams of the positioning principle provided by the embodiments of the present invention;

[0036] Figure 3 is a schematic diagram of the comparison between the model prediction and the actual data provided by the embodiments of the present invention;

[0037] Figure 4 It is a schematic diagram of error cumulative distribution provided by an embodiment of the present invention. Specific embodiments

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Please refer to Figure 1 and Figure 2 , the present invention provides a low-frequency passive RFID positioning method for underground cable detection. The positioning method mainly includes the following steps:

[0040] S101, power the low-frequency passive RFID tag with the electromagnetic wave energy of the RFID reader, and deduce the minimum induced voltage V required for the RFID tag to work according to the inductive coupling equivalent circuit between the RFID reader and the RFID tag actmin , to construct a quantitative mapping relationship between the minimum working current of the RFID reader antenna required for the RFID tag to work and the tag depth, and then obtain a ranging model based on the working current; the expression of the ranging model is:

[0041]

[0042] In the formula, N is the number of turns of the tag coil, r is the radius of the tag coil, f is the operating frequency of the underground RFID system, μ is the magnetic permeability of vacuum, ε s is the relative dielectric constant of the signal passing through the medium, c is the speed of light in vacuum, R is the radius of the reader antenna, and the minimum working current I of the reader antenna min and the tag depth Z are regarded as variables.

[0043] Since the low-frequency RFID tags buried in the soil cannot be replaced with batteries, the underground RFID system has to use passive tags, and the tags are powered by the electromagnetic wave energy of the reader signal. For passive tags, the reader emits a radio frequency signal of a certain frequency through the transmitting antenna. When the tag receives the signal, an induced voltage is generated, and the tag obtains energy and is activated and returns information to the reader.

[0044] When the low-frequency RFID system works, in a dielectric or conductive medium, such as wet soil, the electromagnetic propagation is different from that in air. In particular, the penetration depth in the medium decreases with the increase of the signal frequency, and the electromagnetic properties of the soil will change significantly with the change of humidity. Using the RFID tag induced voltage model in the air environment in this case will lead to a large depth estimation error. In order to minimize the error and improve the accuracy of tag depth estimation under wet soil conditions, a more complex RFID tag induced voltage model considering the signal frequency and the characteristics of the soil medium is considered for estimating the tag depth in the case of highly conductive media such as wet soil. Since the induced voltage V is generated only when the tag receives the signal act reaches a threshold V min after which the tag is activated and returns information to the reader, that is, the minimum induced voltage V required for the tag to work actmin ≈V min where the V actmin is a constant value, which is only related to the structure and characteristics of the tag's own antenna and can be regarded as a constant unknown parameter. According to the inductive coupling equivalent circuit between the RFID reader and the tag, the minimum induced voltage V required for the RFID tag to work is derived actmin that is, the quantitative mapping relationship between the minimum working current I min of the reader antenna loop and the tag depth Z is:

[0045]

[0046] where N is the number of turns of the tag coil, r is the radius of the tag coil, f is the operating frequency of the underground RFID system, 134.2 KHz, μ is the permeability of free space, ε s is the relative dielectric constant of the signal passing through the medium, c is the speed of light in vacuum, R is the radius of the reader antenna, and the minimum working current I min of the reader antenna and the tag depth Z are regarded as variables.

[0047] For a given antenna, if the distance Z between the reader antenna and the tag antenna is changed at this time, then the minimum current I min required for the reader antenna to activate the RFID tag should also change accordingly. Therefore, after aligning the centers of the antennas, for each tag depth Z, based on the ranging model, the depth of the tag antenna can be estimated by measuring the minimum working current I min of the reader antenna when the tag signal is about to disappear, and the ranging is completed.

[0048] The tag depth is estimated through the ranging model based on the working current of the reader antenna and is used in the complex underground environment of highly conductive media, where the highly conductive media includes wet soil.

[0049] S102. Measure the data required for estimating the ranging model parameters in the soil medium, and use the Gauss-Newton method to process the obtained data to estimate the optimal solution of the minimum operating current of the ranging model.

[0050] Since it is difficult to directly measure some environmental and system hardware parameters in practice, the parameter estimation of the ranging model can be obtained by using the experimental data of actual tests and solving the model through a certain method;

[0051] First, select different distances in the soil medium, measure the minimum operating current of the reader antenna when the tag signal is about to disappear, and obtain M groups of experimental data;

[0052] Then, use the outlier elimination method based on the Gaussian model to screen out the data with smaller errors, use the statistical mean model to correct the data, and preprocess the experimental data;

[0053] Finally, after preprocessing, use the Gauss-Newton method to obtain the optimal solution of the ranging model parameters.

[0054] The specific steps of the Gauss-Newton method include:

[0055] (1.1) Construct the objective function. After preprocessing, there are still m groups of data in the experimental data. Then the residuals of these m groups of data are r i = Z i - Z(I imin ; V actmin ; ε s ). Then the objective function is:

[0056]

[0057] where i ∈ [1, m];

[0058] (1.2) Given the initial value, take the average value of the calculated parameters as the initial value V imin ; V actmin ; ε s ) of the coefficient set to be estimated in the iteration of the Gauss-Newton method V (0) (I imin (0) ; V actmin (0) ; ε s (0) );

[0059] (1.3) Linearize the non-linear regression model to obtain:

[0060]

[0061] (1.4) Use the least squares method to calculate H(k) For estimation correction, then ΔV (k) =(J (k)T J (k) ) -1 J (k)T L i (k) , let V(0) be the first iteration value, then V (k+1) =V (k) +ΔV (k) ;

[0062] (1.5) When the number of iterations reaches m times, the correction factor is ΔV (m) =(J (m)T J (m) ) -1 J (m)T L i (m) ; When ΔV (m) <ε, stop repeating the iteration, otherwise continue to update; The (m + 1)-th iteration value is V (m+1) =V (m) +ΔV (m) ; Thus, the optimal solution obtained after iteration is the optimal solution of the ranging model parameters.

[0063] In the determination of the tag depth, in the vertical direction, the RFID reader antenna is located on the surface of the medium, and the RFID tag is in the assumed uniform soil medium. The determination of the tag depth includes:

[0064] (2.1) Align the reader antenna and the tag antenna in the axial direction; Select N fixed different distances in the soil medium, measure the minimum operating current of the reader antenna when the tag signal is about to disappear, measure 5 times at each distance, and a total of 5N groups of experimental data are obtained. Then, preprocess these groups of data through methods such as the outlier removal method based on the Gaussian model and the statistical mean model method.

[0065] (2.2) Establish a ranging model based on the operating current, and use the Gauss-Newton method to estimate the parameters of the ranging model, and then substitute the estimated parameters into the model.

[0066] (2.3) For an unknown tag, measure the minimum operating current of the reader antenna when its signal is about to disappear, and substitute it into the ranging model to obtain the estimated tag depth, realizing the precise positioning of underground cables.

[0067] S103, Input the optimal solution of the estimated minimum operating current into the ranging model to calculate the RFID tag depth and realize the low-frequency passive RFID positioning of underground cables.

[0068] The low-frequency passive RFID positioning system for underground cable detection provided by the embodiment of the present invention includes:

[0069] A model establishment module, configured to establish a ranging model based on the working current, and construct a quantitative mapping relationship between the minimum working current of the RFID reader antenna required for the tag to work and the tag depth.

[0070] A parameter estimation module, configured to perform parameter estimation on the ranging model based on the working current by using the Gauss-Newton method.

[0071] A positioning module, configured to measure the tag depth and achieve precise positioning of the underground cable.

[0072] The low-frequency passive RFID positioning method for underground cable detection provided by the application embodiment of the present invention is applied to a computer device, the computer device includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the low-frequency passive RFID positioning method for underground cable detection.

[0073] The low-frequency passive RFID positioning method for underground cable detection provided by the application embodiment of the present invention is applied to a computer-readable storage medium, stores a computer program, and when the computer program is executed by a processor, the processor executes the low-frequency passive RFID positioning method for underground cable detection.

[0074] The low-frequency passive RFID positioning method for underground cable detection provided by the application embodiment of the present invention is applied to an information data processing terminal, and the information data processing terminal is used to implement the low-frequency passive RFID positioning system for underground cable detection.

[0075] It should be noted that the embodiments of the present invention can be implemented through hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated designed hardware. Those of ordinary skill in the art can understand that the above devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code is provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits of programmable hardware devices such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable logic devices such as field programmable gate arrays, or can be implemented by software executed by various types of processors, or can be implemented by a combination of the above hardware circuits and software, such as firmware.

[0076] Through the positioning experiment test of the tag depth, the comparison chart between the model prediction and the actual data is as shown in Figure 3 the figure. In the soil medium, the predicted result is very close to the actual measured distance.

[0077] According to the model prediction data and the actual data, the error cumulative distribution chart is as shown in Figure 4 the figure. As can be seen from Figure 4 the figure: in the soil medium, 90% of the model prediction tag depth errors are less than 0.35 cm; in addition, the maximum error of this test does not exceed 0.45 cm. Generally speaking, the positioning prediction error of the ranging model based on the working current is small, the model is reliable, and the effect is good.

[0078] Those skilled in the art can easily understand that the above is only a preferred embodiment of the present invention, and is not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-frequency passive RFID positioning method for underground cable detection, characterized in that, The method comprises the following steps: (1) Power the low-frequency passive RFID tag with the electromagnetic wave energy of the RFID reader, and deduce the minimum induced voltage V required for the RFID tag to work according to the inductive coupling equivalent circuit between the RFID reader and the RFID tag actmin , to construct a quantitative mapping relationship between the minimum working current of the RFID reader antenna required for the RFID tag to work and the tag depth, and then obtain a ranging model based on the working current; the expression of the ranging model is: where N is the number of turns of the tag coil, r is the radius of the tag coil, f is the operating frequency of the underground RFID system, μ is the permeability of free space, ε s is the relative permittivity of the medium through which the signal passes, c is the speed of light in a vacuum, R is the radius of the reader antenna, and the minimum operating current I min of the reader antenna and the tag depth Z are regarded as variables; (2) Measuring the data required for estimating the ranging model parameters in the soil medium, processing the obtained data by using the Gauss-Newton method to estimate the optimal solution of the minimum working current of the ranging model, and then inputting the estimated optimal solution of the minimum working current into the ranging model to calculate the RFID tag depth, so as to realize the low-frequency passive RFID positioning of the underground cable; Selecting different distances in the soil medium, measuring the minimum working current of the reader antenna when the tag signal is about to disappear, and obtaining M groups of experimental data; then, screening out the data by using the outlier elimination method based on the Gaussian model, and correcting the screened data by using the statistical mean model; finally, obtaining the optimal solution of the ranging model parameters by using the Gauss-Newton method; First, after preprocessing the experimental data, there are still m groups of data. Then the residuals of these m groups of data are r i = Z i - Z(I imin ; V actmin ; ε s ), then the objective function is: wherein, i ∈ [1, m]; After that, the average value of the calculated parameters is used as the initial value V(I imin ; V actmin ; ε s ) of the coefficient set V to be estimated in the Gauss-Newton method iteration (0) (I imin (0) ; V actmin (0) ; ε s (0) ); Next, the nonlinear regression model is linearized to obtain: Z(I imin ; V actmin ; ε s ) = Z(I imin (0) ; V actmin (0) ; ε s (0) ) + J(I imin (0) ; V actmin (0) ; ε s (0) )(V - V (0) ) Next, the least squares method is used to estimate and correct V (k) to obtain ΔV (k) =(J (k)T J (k) ) -1 J (k)T r (k) . Let V (0) be the first iteration value. Then V (k+1) =V (k) +ΔV (k) ; After that, when the number of iterations reaches n times, the correction factor is ΔV (n) =(J (n)T J (n) ) -1 J (n)T r (n) ; Stop repeating the iteration when ΔV (m) < ε, otherwise continue to update; The value of the (n + 1) - th iteration is V (n+1) = V (n) + ΔV (n) ; Thus, the optimal solution obtained after iteration is the optimal solution of the ranging model parameters.

2. The low-frequency passive RFID positioning method for underground cable detection according to claim 1, wherein: The induced voltage V generated when the tag receives a signal act reaches a threshold V min after which the tag is activated and returns information to the reader; the minimum induced voltage V required for the tag to operate actmin ≈V min .

3. The low-frequency passive RFID positioning method for underground cable detection according to claim 1, characterized in that: For a given antenna, if the distance Z between the reader antenna and the tag antenna is changed, the minimum current I of the reader antenna required to activate the RFID tag min should also change accordingly.

4. The low-frequency passive RFID positioning method for underground cable detection according to claim 1, characterized in that: In step (2), the reader antenna and the tag antenna are aligned in the axial direction; N different fixed distances are selected in the soil medium, and the minimum working current of the reader antenna when the tag signal is about to disappear is measured.

5. A computer storage medium, characterized in that: The computer storage medium stores a computer program, and when the computer program is executed by a processor, the processor executes the low-frequency passive RFID positioning method for underground cable detection according to any one of claims 1-4.

6. A computer device, characterized in that: The device comprises a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the low-frequency passive RFID positioning method for underground cable detection according to any one of claims 1-4.

Images