CN107766906A - Steel corrosion detecting system and detection method based on high frequency passive RFID label tag - Google Patents
Steel corrosion detecting system and detection method based on high frequency passive RFID label tag Download PDFInfo
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Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K17/00—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
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- G—PHYSICS
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- G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
- G06K19/0723—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
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- G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
- G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
- G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
- G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
- G06K19/077—Constructional details, e.g. mounting of circuits in the carrier
- G06K19/07749—Constructional details, e.g. mounting of circuits in the carrier the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
- G06K19/07773—Antenna details
- G06K19/07777—Antenna details the antenna being of the inductive type
- G06K19/07779—Antenna details the antenna being of the inductive type the inductive antenna being a coil
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- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
- G06K7/10336—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers the antenna being of the near field type, inductive coil
Abstract
The present invention relates to the steel corrosion detecting system based on high frequency passive RFID label tag, including RFID label tag and read write line；The RFID label tag is arranged at object to be detected surface, and RFID label tag includes tag coil and tag microchip, and read write line is arranged in RFID label tag working range, and read write line includes reader circuitry and read write line coil；The reader circuitry is powered to the RFID label tag by read write line coil and wirelessly received and sent messages, and object to be detected and tag coil inductively and produce vortex；When RFID label tag sends modulated response signal 5, eddy current effect is in tag coil, and the impedance that will change RFID label tag；Vortex makes RFID label tag produce feedback signal；Read write line end receives the impedance of RFID label tag and feedback signal carries out feature-extraction analysis, and the feature of the object to be detected of extraction is analyzed and is sent to host computer by the read write line coil by reader circuitry compared with reference signal.
Description
Technical Field
The invention relates to a corrosion detection system and a detection method thereof, in particular to a steel corrosion detection system and a detection method based on a high-frequency passive RFID (radio frequency identification) tag, and belongs to the technical field of nondestructive detection and corrosion detection.
Background
Non-destructive testing of steel corrosion has long been a technical challenge, since failure of coatings is a long term gradual process that often does not match inspection and maintenance cycles of the protected steel and its components. This is likely to occur when the coating is intact at some stage or during visual inspection of the joint, and in fact, corrosion of the steel under the coating occurs, with the attendant risk of corrosion damage and other implication. For this reason, it is necessary to perform safety production inspection of the corrosion of steel at different stages of use of the steel using related detection techniques. Meanwhile, the research on the service performance and failure mechanism of key steel parts and components thereof has important practical significance on the safety evaluation of the whole life of the offshore wind power plant. The steel corrosion needs to pass through three stages of initiation, expansion and damage, and the steel can be converted into an oxidation state, so that the mechanical properties of the steel, such as strength, toughness and the like, are obviously reduced, the geometric shape of a steel component is damaged, the service life of the steel is greatly shortened, and disastrous accidents, such as fire, explosion and the like, can be caused. Typically, steel corrosion reaches a certain size, which can be detected by conventional visual inspection, such as with an endoscope. In addition, optical techniques such as fiber optic sensing have been used for structural health monitoring in a variety of situations, including corrosion monitoring, because of their ability to operate in extremely harsh environments. However, since the optical fiber needs to be attached to the object to be monitored, the construction difficulty is increased, and the application range of optical fiber detection is limited finally.
Because the essence of steel corrosion is an electrochemical process, the electrochemical detection technology is a main method for detecting metal corrosion under a coating at home and abroad at present. Among them, electrochemical Impedance Spectroscopy (EIS), stray current (Straycurrent), electrochemical Noise (EN), and other technologies have been widely applied to steel corrosion detection research, and numerous technologies and methods capable of rapidly and accurately measuring coating performance and steel corrosion conditions in different environments have been proposed. However, these electrochemical measurement methods are difficult to be speeded up, automated and visualized, and require high data processing capability of the operator and use of expensive measurement equipment. Ultrasonic detection is based on the fact that the propagation velocity and intensity attenuation of ultrasonic waves in an object are dependent on the density and elasticity of the object. Thus, ultrasonic testing is well suited for describing changes in physical properties of materials. It has been widely used for the detection of metal corrosion. However, ultrasonic testing requires couplants and some surface pretreatment, and is limited by the scanning range of the ultrasonic probe. The ray detection technology such as X-ray realizes the imaging detection of the object by measuring the attenuation intensity of each part when penetrating the object, and finally utilizes the manual work to judge the metal corrosion area. However, the high equipment investment and radiation protection problems limit the daily use and development of the radiation protection device. Eddy current testing has been used to describe surface and subsurface corrosion of magnetic metals. The depth of detection of eddy currents is limited due to their skin effect.
Magnetic leakage detection (MFL) measures the leakage flux with a magnetic field sensor, such as a hall element, and may use a computer for further processing, analysis, and quantitative evaluation. At present, magnetic flux leakage detection is adopted for most of pipeline defect and corrosion detection. However, the magnetic flux leakage detection can be applied only to the detection of a magnetic metal material, and cannot be remote from the surface of an object to be detected. In addition, due to a plurality of magnetic flux leakage influence factors, only qualitative evaluation can hardly achieve quantitative evaluation, and summary and intensive research are needed on the basis of a large number of experiments. The infrared thermal imaging method has a good detection effect on corrosion damage under a coating, can be used for estimating the thickness of the coating and realizing quantitative identification of the size and the position of the corrosion damage, such as Panmonspring of national defense science and technology university and Hunan university He/36191, applies an infrared thermal imaging phase method to steel corrosion detection and successfully positions the steel corrosion position. However, the infrared thermography test results are greatly affected by the uniformity of the material surface. Furthermore, the high price of thermal imagers is an important factor that is not negligible for detection using thermal imaging. The corrosion imaging method based on microwave nondestructive detection attracts great attention due to its advantages in metal corrosion detection and quantitative analysis under the non-metal coating. Zhang Macro utilizes matrix decomposition technology, such as Principal Component Analysis (PCA) and non-negative matrix decomposition (NMF), to process and analyze the whole waveguide frequency band to obtain spatial mode characteristics for positioning steel corrosion in a microwave image, successfully improves the spatial resolution of the microwave detection image, quantifies steel corrosion size and depth information, and successfully solves the problem of artificially selecting frequency and characteristic values. However, the expensive equipment investment and the characteristic that microwave signals are easily absorbed by water limit the application of corrosion detection in marine environments.
In conclusion, researchers at home and abroad research and apply methods such as optics, electrochemistry, ultrasonic detection, eddy current detection, magnetic flux leakage detection, infrared thermal imaging, microwave detection and the like to obtain a plurality of important achievements on steel corrosion research, but the quantitative research on steel corrosion behavior and mechanism research, especially corrosion layer microstructure evolution, is still immature. Aiming at the problems existing in the health monitoring of the steel structure under the coating and the defects of the existing nondestructive detection technology, the invention introduces the high-frequency RFID label detection technology to the steel corrosion detection and finally realizes the real-time monitoring of the steel corrosion through the label sensing array.
The western developed countries are the first to develop related researches based on the RFID label detection technology and obtain some research achievements. Due to the significant advantages in volume and life time, passive RFID tags have been developed into various detection systems, such as temperature, humidity, stress, food quality control, and chemical monitoring. In 2012, mohammed, n.k.k.university, used the time domain signature of passive low frequency RFID tags to conduct preliminary studies on corrosion detection of carbon steel (millisteel). The characteristics of the conductivity and permeability changes of different corrosion stages are realized by the aid of the Ali through optimizing impedance matching and working frequency and extracting static and transient characteristics, wireless power transmission is realized through magnetic coupling resonance, and the communication distance between the reader-writer and the tag is increased. Mohammed, N.C. university successfully realizes the detection of thermal barrier steel corrosion by using a passive low-frequency RFID tag detection system. The applicant researches a steel corrosion detection system based on a high-frequency passive RFID tag, extracts the complex impedance of a tag antenna by using a vector network analyzer, and successfully extracts a characteristic value which is not influenced by the thickness of a coating by a principal component analysis method. ZhangJun provides a steel corrosion detection system based on an ultrahigh frequency RFID sensor, and a 3D antenna is installed on the surface of a steel test piece, so that the thickness change monitoring of steel corrosion within a range of 1 meter is realized. In addition, rania redesigns the RFID tag antenna by using antenna optimization, and realizes the detection of steel corrosion within the range of 2 meters.
Domestic RFID label monitoring research aiming at steel corrosion detection is still in a budding state. From the research of documents, scholars of the university of Nantong researched the RFID tag detection for the low-speed impact of the shape memory alloy reinforced composite structure and the wireless distribution monitoring of the SMA reinforced composite material laminated plate, and also researched the RFID tag detection for the health monitoring of the spindle thermal error, the bending strain and the motor vehicle speed wireless structure. The students of the Guizhou university study a power transmission model of a passive ultrahigh frequency RFID tag for wireless monitoring of tire pressure. Scholars at Tianjin university have studied locatable vital signs monitoring systems based on RFID tags. The RFID tags are researched by students of the university of fertilizer industry and the university of science and technology in Huazhong for wireless monitoring of the state of electrical equipment and information acquisition.
The patent document of the invention discloses an industrial pipeline and tank corrosion detection device, which comprises a detection lead, a wafer and a detection instrument, wherein the detection lead is provided with a detection circuit, and the detection instrument comprises: the detection wire is an iron wire loop which is electrically connected with a chip; the chip comprises a transmitting circuit, the transmitting signal circuit is electrically connected with a battery through a detection wire, and the battery provides power required by the transmitting signal circuit, so that the chip can transmit signals through the transmitting signal circuit; the detection instrument further comprises a receiving signal circuit which can receive the signal transmitted by the wafer.
When the industrial pipeline and tank corrosion detection device operates, whether water vapor permeates into the heat insulation cotton layers of the industrial pipeline and the tank can only be detected, different corrosion degrees of steel pipes in the industrial pipeline cannot be reflected, automatic steel corrosion identification and positioning cannot be realized, and development evolution of the steel corrosion detection device can be predicted.
Disclosure of Invention
In order to overcome the problems in the prior art, the invention provides a steel corrosion detection system based on a high-frequency passive RFID tag, which utilizes self-adaptive sparse control to realize automatic identification and positioning of steel corrosion, predicts the development evolution of the steel corrosion, improves and enhances the service life performance of steel and components thereof, reduces the operation and maintenance cost, improves the operation reliability and safety of equipment, and realizes efficient and safe production.
Another object of the present invention is to provide a method for detecting steel corrosion based on a high frequency passive RFID tag.
The technical scheme of the invention is as follows:
scheme one
The steel corrosion detection system based on the high-frequency passive RFID tag comprises the RFID tag and a reader-writer; the RFID tag is arranged on the surface of the detected object, the RFID tag comprises a tag coil and a tag microchip, the reader-writer is arranged in the working range of the RFID tag, and the reader-writer comprises a reader-writer circuit and a reader-writer coil; the reader-writer circuit supplies power to the RFID tag through the reader-writer coil and wirelessly receives and sends information, and the detected object is inductively coupled with the tag coil to generate eddy current; when the RFID tag sends the modulated response signal, the eddy current acts on the tag coil and changes the impedance of the RFID tag; the eddy current causes the RFID tag to generate a feedback signal; and the reader-writer end receives the impedance of the RFID label and the feedback signal to perform characteristic extraction and analysis, and the reader-writer circuit compares the extracted characteristic of the detected object with the reference signal and sends the characteristic to the upper computer through the reader-writer coil.
The reader-writer circuit comprises a matching circuit and a loop switch circuit matched with the matching circuit, the matching circuit is matched with the reader-writer coil, and the loop switch circuit controls the on-off of the matching circuit.
Scheme two
The steel corrosion detection method based on the high-frequency passive RFID tag adopts the steel corrosion detection system based on the high-frequency passive RFID tag in the scheme I, and the detection method comprises the following steps:
s1: the RFID label is placed on the surface of the detected object, the reader-writer is placed in the working range of the RFID label, and then the label coil generates a magnetic field and generates inductance; inductance generation voltage U of label coil i After rectification, voltage U i Powering the label microchip; the RFID label starts to work, and the object to be detected and the label coil generate inductive coupling and eddy current;
s2: the reader-writer coil is connected with the capacitor Cr in parallel, the capacitor Cr and the inductance of the reader-writer coil form a certain resonant frequency, and the resonant frequency corresponds to the working frequency f of the RFID tag detection system; when the RFID tag begins to transmit its modulated response signal, the eddy currents change the impedance of the RFID tag;
s3: controlling the magnetic field intensity by adjusting the number of turns and the current intensity of a coil of the reader-writer, wherein eddy current generates an inductive load effect on the RFID label and distorts a feedback signal of the RFID label; finally, energy is transmitted and the RFID label is remotely operated;
s4: the reader-writer performs characteristic extraction analysis on the impedance and the feedback signal of the received RFID tag, and extracts the characteristics of the detected object;
s5: the reader-writer compares and analyzes the extracted detected object characteristics with the reference signal;
s6: and the reader-writer circuit sends the comparison and analysis result to the upper computer through the reader-writer coil.
The characteristic of the detected object extracted by the reader-writer 2 in the step S4 is coil inductance L, the reference signal in the step S5 is a theoretical value of the coil inductance L calculated according to the working frequency f of the RFID tag 1, the change of the steel magnetic conductivity is calculated, and the corrosion degree of the steel obtained through the change of the steel magnetic conductivity is sent to an upper computer through the coil of the reader-writer in the step S6;
wherein the operating frequency f of the RFID tag detection system is obtained by the following equation:
where L is the coil inductance and C is the capacitance of the coil.
Wherein, the theoretical value of the coil inductance L is obtained by the following equation:
wherein N is the number of coil turns, mu 0 R is the coil radius and d is the radius of the wire, which is the permeability of free space.
The characteristic of the detected object extracted by the reader-writer 2 in the step S4 is a coil mutual inductance M, the reference signal in the step S5 is a theoretical value of the coil mutual inductance M obtained through calculation, the steel corrosion depth is calculated, and the obtained steel corrosion depth is sent to an upper computer through the reader-writer coil in the step S6;
the theoretical value of the coil mutual inductance M is obtained by the following equation:
wherein, mu 0 Is the permeability of free space, N 1 Number of coil turns, N, of reader-writer 2 Is the number of coil turns, R, of the RFID tag 1 Radius of coil wire of reader-writer, R 2 Being a lead of a tag coilRadius, x is the distance of the reader from the tag.
Wherein the characteristic of the detected object extracted by the reader/writer 2 in step S4 is the RFID tag response signal voltage, and the reference signal in step S5 is the theoretical value u of the calculated RFID tag response signal voltage 2 Calculating the dielectric constant generated by corrosion, and sending the obtained dielectric constant generated by corrosion to an upper computer through the reader-writer coil 22 in the step S6;
theoretical value u of label voltage 2 This is obtained from the following equation:
wherein L is 1 Inductance, R, of the induction coil of the reader/writer 2 Is the impedance of the tag coil, L 2 Inductance of induction coil of label, load resistance R L Representing the current consumption, R, of the tag chip 2 Is the radius of the coil wire of the tag, and x is the distance between the reader and the tag; c 2 Capacitance, ω is the carrier frequency; wherein, C 2 ＝C′ 2 +C p From parallel capacitors C' 2 And parasitic capacitance C of the actual circuit p And (4) forming.
In step S4, the characteristic of the detected object extracted by the reader/writer 2 is a complex impedance of the RFID tag, in step S5, the reference signal is a theoretical value of the calculated voltage of the response signal of the RFID tag, and the dielectric constant generated by corrosion is calculated, and in step S6, the obtained dielectric constant generated by corrosion is transmitted to the upper computer through the reader/writer coil 22;
the theoretical value of the complex impedance of the RFID tag is given by the following equation:
wherein Z is R Is the inherent impedance of the coil of the reader/writer, Z T To be the inherent impedance of the RFID tag coil, ω is the carrier frequency and M is the mutual inductance coupling coefficient.
The invention has the following beneficial effects:
unlike traditional detection techniques such as ultrasound, X-ray, etc. which detect steel from the coating surface manually or robotically, the method integrates the advantages of passive RFID tags and electromagnetic detection: 1) The RFID label has small volume, can be placed under the coating and directly contacts with a monitored object, and has high sensitivity; 2) The reader-writer performs energy and information transmission through radio frequency, so that the penetration capability is strong and the reader-writer is insensitive to the change of the coating thickness; 3) The electromagnetic characteristic change is more obvious than other physical characteristic changes when the steel is corroded, and the RFID label steel corrosion monitoring is based on the electromagnetic coupling mechanism of the RFID label and the monitored steel; 4) Due to the fact that the RFID tags are low in price, an offshore wind plant steel corrosion intelligent monitoring network can be formed by using a large number of passive RFID tags, the steel corrosion distribution state can be acquired and reconstructed in real time for a long time (the service life can reach 20 years), steel corrosion information is mined and extracted, separation and quantification of steel corrosion are achieved by processing distribution images, and the mapping relation between electromagnetic characteristic changes of steel corrosion in different stages and steel structure damage is achieved.
The invention has very important scientific and engineering significance: 1) The problem of monitoring the steel corrosion in real time is solved, and the research range of nondestructive testing and the Internet of things is expanded; 2) The steel corrosion blind source separation processing method based on the self-adaptive sparse matrix control is adopted to replace full data, so that the calculated amount is reduced to the maximum extent, and the accuracy is improved; 3) The RFID tag array is used for realizing the networking of steel corrosion monitoring and realizing the real-time monitoring of the health of a steel structure; 4) The self-adaptive sparse control is utilized to realize automatic identification and positioning of marine steel corrosion, the development evolution of the marine steel corrosion is predicted, the service life performance of the steel and the components thereof is improved and enhanced, the operation and maintenance cost is reduced, the operation reliability and safety of equipment are improved, and efficient and safe production is realized.
Drawings
FIG. 1 is a schematic structural diagram of a high-frequency passive RFID tag-based steel corrosion detection system of the invention.
Fig. 2 is a circuit diagram of a reader-writer of the high-frequency passive RFID tag-based steel corrosion detection system of the present invention.
FIG. 3 is an equivalent circuit diagram of the reader-writer and the tag coil coupling of the high-frequency passive RFID tag-based steel corrosion detection system of the present invention.
The reference numbers in the figures are:
1. RFID label, 2, reader-writer, 11, label coil, 12, label microchip, 21, reader-writer circuit, 22, reader-writer coil, 23, matching circuit, 24, loop switch circuit.
Detailed Description
The invention is described in detail below with reference to the figures and the specific embodiments.
As shown in fig. 1, the steel corrosion detection system based on the high-frequency passive RFID tag comprises an RFID tag 1 and a reader-writer 2; the RFID tag 1 is arranged on the surface of an object to be detected, the RFID tag 1 comprises a tag coil 11 and a tag microchip 12, the reader-writer 2 is arranged in the working range of the RFID tag 1, and the reader-writer 2 comprises a reader-writer circuit 21 and a reader-writer coil 22; the reader-writer circuit 21 supplies power to the RFID tag 1 through the reader-writer coil 22 and wirelessly receives and transmits information, and the detected object is inductively coupled with the tag coil 11 to generate eddy current; when the RFID tag 1 sends a modulated response signal, eddy currents act on the tag coil 11 and will change the impedance of the RFID tag 1; the eddy current causes the RFID tag 1 to generate a feedback signal; the reader-writer end receives the impedance of the RFID label 1 and the feedback signal to perform characteristic extraction analysis, and the reader-writer circuit 21 compares the extracted characteristic of the detected object with a reference signal for analysis and sends the characteristic to an upper computer through the reader-writer coil 22.
As shown in fig. 2, the reader/writer circuit 21 includes a matching circuit 23 and a loop switch circuit 24 cooperating with the matching circuit 23, the matching circuit 23 is matched with the reader/writer coil 22, and the loop switch circuit 24 controls switching of the matching circuit 23.
The working principle is as follows: the high-frequency RFID monitoring system consists of two parts: tags (Tag) and readers/writers (Reader). The RFID tag detection may be classified into LF (low frequency), HF (high frequency), UHF (ultra high frequency), and the like according to the operating frequency. In addition, the label may be classified into: active and passive. Because the passive RFID tag does not need to be provided with an energy component, the volume, the use cost and the monitoring service life (at least 20 years) of the passive RFID tag have great advantages, and the corrosion monitoring system developed based on the passive RFID tag is adopted.
The steel corrosion detection method based on the high-frequency passive RFID tag adopts the steel corrosion detection system based on the high-frequency passive RFID tag, and comprises the following steps:
s1: the RFID label 1 is placed on the surface of an object to be detected, the reader-writer 2 is placed in the working range of the RFID label 1, and then the label coil 11 generates a magnetic field and generates inductance; the inductance of the tag coil 11 generates a voltage Ui, and the voltage Ui supplies power to the tag microchip 12 after rectification; the RFID label 1 starts to work, and the object to be detected and the label coil 11 generate inductive coupling and eddy current;
s2: the reader-writer coil 22 is connected in parallel with the capacitor Cr, and the capacitor Cr and the inductance of the reader-writer coil 22 form a certain resonant frequency, which corresponds to the working frequency f of the RFID tag detection system; when the RFID tag 1 starts to transmit its modulated response signal, the eddy current changes the impedance of the RFID tag 1;
s3: the magnetic field intensity is controlled by adjusting the number of turns and the current intensity of the coil 22 of the reader-writer, the eddy current generates an inductive load effect on the RFID tag 1, and a feedback signal of the RFID tag 1 is distorted; finally, energy is transmitted and the RFID tag 1 is remotely operated;
s4: the reader-writer 2 performs characteristic extraction analysis on the impedance and the feedback signal of the received RFID tag 1, and extracts the characteristics of the detected object;
s5: the reader-writer 2 compares and analyzes the extracted detected object characteristics with the reference signal;
s6: the reader circuit 21 sends the result of the comparative analysis to the upper computer through the reader coil 22.
The coupling mechanism of the RFID label multi-physical field and the abnormal electromagnetic signal generation mechanism are the theoretical basis of steel corrosion detection separation and quantification. The physical process of monitoring steel corrosion by passive RFID tag detection is shown in figure 1: 1) The reader-writer coil 22 supplies energy to the RFID tag 1 through a certain distance, and then the tag coil 11 generates a magnetic field and generates inductance; 2) The inductance of the tag coil 11 generates a voltage Ui, and the voltage Ui supplies power to the tag microchip 12 after rectification; 3) The reader-writer coil 22 is connected in parallel with the capacitor Cr, and the capacitor Cr and the inductance of the reader-writer coil 22 form a certain resonant frequency, which corresponds to the working frequency f of the RFID tag detection system; 4) The magnetic field intensity is controlled by adjusting the number of turns and the current intensity of the reader/writer coil 22, and finally the energy is transmitted and the RFID tag 1 is remotely operated.
The passive RFID tag monitoring working principle is as follows:
(1) principle for detecting change of magnetic permeability of steel by using RFID system working frequency
For an RFID tag detection system, the RFID operating frequency (also called resonant frequency) can be obtained from the following thomson equation:
in equation (1), f is the operating frequency of the RFID system, L is the inductance of the coil, and C is the capacitance of the coil. As the operating frequency f increases, the inductance of the required tag coil decreases. Thus, the number of coil windings is reduced (about 100-1000 windings at 135kHz, reduced to 3-10 windings at 13.56 MHz). Since the operating frequency f of the tag is directly proportional to the induced voltage, the reduction in the number of windings results in a higher efficiency in the power transfer in the higher frequency range. This is one of the reasons for using high frequency, ultra high frequency RFID in this study. The coil inductance L is the ratio of the magnetic flux ψ and the coil current I, and its variation can be obtained by the following equation:
in equation (2), N is the number of turns of the coil, μ is the permeability, H is the magnetic field strength, a is the coil area, and I is the current strength. Obviously, when the coil properties, current and material permeability parameters are unchanged, the inductance L change and the magnetic field strength H are linearly related. For a rectangular RFID coil of size a × b, the magnetic field strength H at a distance x from it can be obtained by the following equation:
when the radius d of the wire is much smaller than the radius R of the coil (d/R < 0.0001), equation (2) can be reduced to:
in equation (4), N is the number of coil turns, μ 0 ＝4π×10 -7 V.s/(A.m) is the magnetic permeability of free space, R is the coil radius, and d is the radius of the wire. Thus, when the monitored steel corrodes, its magnetic permeability is inversely proportional to the operating frequency of the RFID tag.
(2) Principle for detecting corrosion depth of steel by RFID (radio frequency identification) tag
As shown in fig. 2, the mutual inductance M is used to describe the coupling of the RFID system through a magnetic field, and has the same units as the inductance. The following equation can be used to calculate the mutual inductance M:
μ in equation (5) 0 Is the magnetic permeability of free space, N1 is the number of turns of the coil of the reader/writer, N2 is the number of turns of the coil of the RFID tag, R1 is the radius of the coil wire of the reader/writer, R2 is the radius of the coil wire of the tag, and x is the distance between the reader/writer and the tag. It can be seen that the mutual inductance M generated is inversely proportional to the depth x and the radius of the tag coil wire under the condition that the induced current and the induced current frequency are stableThe square root of (a) is inversely proportional. However, in practice, there are problems with energy transfer and losses, so the method must be calibrated to minimize measurement errors.
(3) RFID tag response signal voltage
Fig. 3 shows an equivalent circuit diagram of the RFID coil coupling. In this magnetically coupled RFID system, the reader inductive coil is denoted as L1. R2 is the impedance of the tag coil, the sense coil of the tag is L2, and the load resistance RL represents the current consumption of the tag chip. The operating frequency (resonant frequency) of the tag is determined by the tag induction coil L2 and the capacitor C2 connected in parallel. The tag voltage u2 is as follows:
in equation (6), C 2 ＝C′ 2 +C p From parallel capacitors C' 2 And parasitic capacitance C of the actual circuit p And (4) forming. Briefly, the dielectric constant resulting from corrosion will be detected in the steel material in the form of parasitic capacitance.
(4) RFID tag complex impedance
The mutual inductive coupling between the reader and the tag may be used to transmit measured complex impedance data from the RFID tag in addition to transmitting energy. The measured complex impedance of the RFID tag is related to the following formula:
wherein Z is R Is the inherent impedance of the coil of the reader/writer, Z T Omega is the carrier frequency and M is the mutual inductance coupling coefficient, which is the inherent impedance of the RFID tag coil. Briefly, the measured complex impedance is proportional to the square of the mutual inductance coupling coefficient M. In fact, when the RFID tag is used for steel corrosion detection, the RFID tag also relates to the surface state (including surface radian, roughness and surface impurities) of the RFID tag.
As is clear from the above analysis, the detection signal of the RFID tag is closely related to the electrical property, the medium property, the magnetic property, and the like of the material to be detected.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (7)
1. Steel corrosion detecting system based on high frequency passive RFID label, its characterized in that: the RFID tag comprises an RFID tag (1) and a reader-writer (2); the RFID tag (1) is arranged on the surface of an object to be detected, the RFID tag (1) comprises a tag coil (11) and a tag microchip (12), the reader-writer (2) is arranged in the working range of the RFID tag (1), and the reader-writer (2) comprises a reader-writer circuit (21) and a reader-writer coil (22); the reader-writer circuit (21) supplies power to the RFID tag (1) through the reader-writer coil (22) and wirelessly receives and transmits information, and an object to be detected is inductively coupled with the tag coil (11) to generate eddy current; when the RFID tag (1) sends the modulated response signal, the eddy current acts on the tag coil (11) and changes the impedance of the RFID tag (1); the eddy current causes the RFID tag (1) to generate a feedback signal; the reader-writer end receives the impedance of the RFID label (1) and the feedback signal to carry out feature extraction and analysis, and the reader-writer circuit (21) compares the extracted feature of the detected object with the reference signal to carry out comparison and analysis and sends the feature to an upper computer through the reader-writer coil (22).
2. The high frequency passive RFID tag-based steel corrosion detection system of claim 1, wherein: the reader-writer circuit (21) comprises a matching circuit (23) and a loop switch circuit (24) matched with the matching circuit (23), the matching circuit (23) is matched with the reader-writer coil (22), and the loop switch circuit (24) controls the on-off of the matching circuit (23).
3. The steel corrosion detection method based on the high-frequency passive RFID tag is characterized by comprising the following steps: the steel corrosion detection system based on the high-frequency passive RFID tag of claim 1 is adopted, and the detection method comprises the following steps:
s1: the RFID tag (1) is placed on the surface of an object to be detected, the reader-writer (2) is placed in the working range of the RFID tag (1), and then the tag coil (11) generates a magnetic field and generates inductance; the inductance of the tag coil (11) generates a voltage U i After rectification, voltage U i Powering the tag microchip (12); the RFID label (1) starts to work, and the object to be detected and the label coil (11) can generate inductive coupling and eddy current;
s2: the reader-writer coil (22) is connected with the capacitor Cr in parallel, the capacitor Cr and the inductance of the reader-writer coil (22) form a certain resonant frequency, and the resonant frequency corresponds to the working frequency f of the RFID label detection system; when the RFID tag (1) starts to transmit its modulated response signal, the eddy current changes the impedance of the RFID tag (1);
s3: the magnetic field intensity is controlled by adjusting the number of turns and the current intensity of a coil (22) of the reader-writer, eddy current generates an inductive load effect on the RFID label (1), and a feedback signal of the RFID label (1) is distorted; finally transmitting energy and remotely operating the RFID tag (1);
s4: the reader-writer (2) performs characteristic extraction analysis on the impedance and the feedback signal of the received RFID tag (1) and extracts the characteristics of the detected object;
s5: the reader (2) compares and analyzes the extracted detected object characteristics with the reference signal;
s6: the reader-writer circuit (21) sends the result of the comparative analysis to the upper computer through the reader-writer coil (22).
4. The high-frequency passive RFID tag-based steel corrosion detection method of claim 2, wherein:
the characteristic of the detected object extracted by the reader-writer 2 in the step S4 is coil inductance L, the reference signal in the step S5 is a theoretical value of the coil inductance L calculated according to the working frequency f of the RFID tag 1, the change of the steel permeability is calculated, and the corrosion degree of the steel obtained through the change of the steel permeability is sent to an upper computer through the reader-writer coil (22) in the step S6;
wherein the operating frequency f of the RFID tag detection system is obtained by the following equation:
where L is the coil inductance and C is the capacitance of the coil.
Wherein, the theoretical value of the coil inductance L is obtained by the following equation:
wherein N is the number of coil turns, mu 0 The permeability of free space, R is the coil radius, and d is the radius of the wire.
5. The high-frequency passive RFID tag-based steel corrosion detection method of claim 3, wherein:
in the step S4, the characteristic of the detected object extracted by the reader-writer 2 is a coil mutual inductance M, in the step S5, the reference signal is a theoretical value of the calculated coil mutual inductance M, the steel corrosion depth is calculated, and in the step S6, the obtained steel corrosion depth is sent to an upper computer through the reader-writer coil (22);
the theoretical value of the coil mutual inductance M is obtained by the following equation:
wherein, mu 0 Is the permeability of free space, N 1 Number of turns of coil, N, of reader-writer 2 Is the number of coil turns, R, of the RFID tag 1 Radius of coil wire of reader-writer, R 2 Is the radius of the tag coil wire and x is the distance between the reader and the tag.
6. The high-frequency passive RFID tag-based steel corrosion detection method of claim 3, wherein:
the characteristic of the detected object extracted by the reader/writer 2 in step S4 is the RFID tag response signal voltage, and the reference signal in step S5 is the theoretical value u of the calculated RFID tag response signal voltage 2 Calculating the dielectric constant generated by corrosion, and sending the obtained dielectric constant generated by corrosion to an upper computer through the reader-writer coil 22 in the step S6;
theoretical value u of the tag voltage 2 This is obtained from the following equation:
wherein L is 1 Inductance, R, of the induction coil of the reader/writer 2 Is the impedance of the tag coil, L 2 Inductance of induction coil of tag, load resistance R L Represents the current consumption, R, of the tag chip 2 Is the radius of the coil wire of the tag, and x is the distance between the reader and the tag; c 2 Capacitance, ω is the carrier frequency; wherein, C 2 ＝C′ 2 +C p From a parallel capacitor C' 2 And parasitic capacitance C of the actual circuit p And (4) forming.
7. The high frequency passive RFID tag-based steel corrosion detection method of claim 3, wherein:
in the step S4, the characteristic of the detected object extracted by the reader/writer 2 is a detection value of the complex impedance of the RFID tag, in the step S5, the reference signal is a theoretical value of the complex impedance of the RFID tag obtained by estimation, and in the step S6, the obtained theoretical value and the detection value are transmitted to the upper computer through the reader/writer coil 22;
the theoretical value of the complex impedance of the RFID tag is obtained by the following equation:
wherein Z is R Is the inherent impedance of the coil of the reader/writer, Z T Omega is the carrier frequency and M is the mutual inductance coupling coefficient, which is the inherent impedance of the RFID tag coil.
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