Sensor for detecting cracks of metal structure by adopting passive radio frequency identification technology

Abstract

The utility model discloses a sensor for detecting cracks of a metal structure by adopting a passive radio frequency identification technology, and aims to meet the requirements of low cost, high precision and long-term detection on large-scale building groups. The sensor comprises a dielectric substrate and a resonator etched on the dielectric substrate, the resonator adopts an arc and square ring combined structure, the core of the resonator is a square ring structure, and four arcs extend outwards from the central positions of four sides of the square ring to form a central symmetry structure. The sensor is attached to a to-be-detected metal structure, and based on a passive chipless radio frequency identification technology, the sensor can detect surface cracks at different angles and different positions of the metal structure in real time by using RCS amplitude change as a crack characterization characteristic. The crack sensor provided by the utility model has the characteristics of flexible deployment, low cost, high sensitivity and high detection precision.

Description

TECHNICAL FIELD

[0001] The utility model relates to structural health detection technical field, concretely relates to a sensor of adopting passive radio frequency identification technology to detect metal structure crack. BACKGROUND

[0002] With metal structure being widely used in aviation, machinery, building and multiple fields, the structural failure caused by metal fatigue crack becomes the problem to be solved at present. The metal structure is easy to produce fatigue crack in the long-term use process under the influence of extreme load and bad environment, and the initiation and expansion of these cracks will significantly reduce the structural strength, and even cause catastrophic accidents, cause huge personnel casualty and economic loss. Therefore, monitoring the initiation and growth of crack in real time has important significance for guaranteeing the structure safety and preventing accidents.

[0003] In recent years, passive radio frequency identification technology is suitable for the structural health monitoring field of low manufacturing cost and long-term measurement because of its non-contact identification, strong adaptability to bad environment and high cost-effectiveness. Especially, the chipless radio frequency identification metal crack sensor disclosed in the patent with the announcement number CN117030749A realizes the crack length and width detection based on the resonance frequency shift through the candy-shaped topology resonator design composed of square and circular resonators, and effectively separates the mutual influence between width and depth.

[0004] Although the above-mentioned technology has made progress in crack size identification, it does not consider the influence of crack position on resonance frequency, and does not study the optimal detection range of the sensor, resulting in blind area in the monitoring process, which is difficult to realize the all-round and instant monitoring of the crack, has certain limitation, so the innovation is needed on this technology. SUMMARY

[0005] In order to overcome the above-mentioned deficiencies of prior art, the purpose of the utility model is to provide a sensor of adopting passive radio frequency identification technology to detect metal structure crack, which aims at realizing the blind area-free, full-range, high-sensitivity and high-precision detection of metal structure crack, improving the detection efficiency and realizing the early warning of metal structure health.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the utility model is:

[0007] The application discloses a sensor for detecting cracks in metal structures by using passive radio frequency identification technology, comprising a dielectric substrate and a resonator etched on the dielectric substrate; the resonator is designed by combining a circular arc and a square ring, the core of the resonator is a square ring structure, four circular arcs are extended outward from the center of four sides of the square ring, and a center-symmetrical structure is formed; when cracks in a metal structure are detected, the sensor is attached to the surface of the metal structure to be detected, a reader cooperates with the sensor, the passive chipless radio frequency identification technology is used, the amplitude change of a radar scattering cross section is used as a crack characteristic, and cracks on the surface of the metal structure at different angles and different positions are detected.

[0008] The radius of the four circular arc structures is 1.1mm-4.6mm, and the central angle is 180°; under a specific frequency band, the electric length of the circular arc in the size range is optimized, the resonance effect of the resonator is enhanced, and the sensitivity and identification precision of the sensor are improved; meanwhile, the 180° central angle design optimizes the symmetry of the circular arc structure, reduces the frequency deviation caused by external interference, and improves the frequency stability of the sensor.

[0009] The side length of the square ring is 7.4mm-10.4mm, which can provide sufficient inductive area, optimize impedance matching, reduce the reflection coefficient, and ensure high-precision and effective detection of cracks in the metal structure; in addition, the square ring structure in the size range can be effectively combined with the circular arc structure and reduce electromagnetic interference, and the resonator can generate multiple resonance wave peaks, further widening the detection range of the sensor.

[0010] The center of the dielectric substrate and the center of the resonator are located on the same vertical axis, ensuring the accurate alignment between the resonator and the dielectric substrate, thereby optimizing the transmission and coupling efficiency of electromagnetic waves between the resonator and the dielectric substrate; meanwhile, the alignment mode also helps to reduce signal loss and frequency deviation caused by improper installation, and improves the overall performance and stability of the sensor. The resonator is made of copper, which has excellent electrical conductivity and mechanical strength, can effectively reduce energy loss, and ensure stable signal transmission. The dielectric substrate is made of polyimide resin with a dielectric constant of 3.8-4.1, which has excellent heat resistance and chemical stability, can maintain stable dielectric properties in a wide temperature range and at a high frequency band, and ensures the accuracy and long-term stability of the sensor in harsh environments. The thickness of the dielectric substrate is 1.4mm-1.8mm, which can optimize the propagation path of electromagnetic waves in the dielectric substrate, reduce signal loss, and improve the overall performance of the sensor.

[0011] When detecting the crack of the metal structure, the sensor is attached to the surface of the metal to be detected, and the reader is placed horizontally at a distance of 30 cm from the sensor and faces the sensor. The reader emits electromagnetic waves of a specific frequency band to excite the resonator on the surface of the sensor. The resonator surface generates an induced current, and the induced current causes an induced magnetic field to backscatter the signal with sensing information back to the reader. The difference between the response of the metal structure to be detected and the response of the structure without cracks is analyzed and compared by using the RCS amplitude change as the crack characterization characteristic, so that the crack is detected in real time.

[0012] The sensor of the utility model aims at meeting the low-cost, high-precision and long-term detection needs of large-scale building groups. Compared with the prior art, it has the following advantages:

[0013] 1) No blind area: compared with the existing candy-shaped topological structure resonator, the resonator of the sensor of the utility model adopts a combined design structure of circular arc and square ring, so that the radiation surface is centrally symmetric, which can provide omnidirectional radiation characteristics, thereby covering the entire detection area, and the state of the metal structure to be detected can be obtained by processing the collected backscattering signals. No matter where the crack appears and how the direction is, the sensor of the utility model can monitor in real time, avoiding the existence of blind area during detection of the existing sensor.

[0014] 2) High sensitivity and high precision: the square ring in the resonator of the sensor of the utility model can reduce cross-polarization components and optimize impedance matching, thereby reducing the reflection coefficient, so that very fine cracks of various types can be detected, the small position change of the crack can be accurately measured, and the detection accuracy is improved. The circular ring in the resonator has a high quality factor value and good frequency stability, and has high anti-interference degree to external environmental changes. The resonator of the utility model has the performance of circular ring and square ring at the same time through the size parameter fusion ratio, which effectively improves the sensitivity and precision of the sensor crack detection.

[0015] 3) Real-time monitoring: the sensor of the utility model has the characteristics of wireless and passive, and is convenient to install, which is suitable for metal structures of various shapes and sizes, and can monitor the state of the metal structure to be detected in real time, and can quickly detect the initiation of the crack, thereby improving the detection efficiency.

[0016] 4) The sensor of the utility model does not contain a silicon chip and can be printed as a whole, which is suitable for harsh environments, and only a reader is needed for detection to collect metal structure data, thereby greatly reducing the detection cost. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The utility model discloses a crack detection system block diagram for applying the sensor of the utility model;

[0018] Figure 2In (a) and (b) are respectively the top view and side view of the structure of the sensor of the present utility model and the placement position of the metal to be measured.

[0019] In the figure, 1 - metal plate to be measured; 2 - sensor; 3 - reader; 4 - resonator; 5 - dielectric substrate; 6 - crack to be detected. Specific implementation manner

[0020] The present utility model will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0021] As Figure 1 shown, it is a block diagram of a crack detection system applying the sensor of the present utility model. This crack detection system includes a sensor 2 installed on the metal plate 1 to be measured and a reader 3 communicating with it. As Figure 2 shown, attach the sensor 2 to the surface of the metal plate 1 to be measured, ensuring that the sensor is closely attached to the metal plate 1 to be measured without gaps. Place the reader 3 facing the sensor 2 horizontally at a distance of 30 cm from the sensor. Turn on the reader 3 and set it to emit electromagnetic waves of a specific frequency band to excite the sensor 2. An induced current is generated on the surface of the resonator 4 of the sensor 2, and the induced current causes an induced magnetic field to backscatter the signal carrying the information of the metal plate 1 to be measured back to the reader. Before detection, attach the sensor 2 to a healthy metal structure, use the reader 3 to excite the sensor 2 and collect its backscattered signal, and mark and store this signal as the response of the healthy structure. When detecting cracks, just attach the sensor 2 to the metal plate 1 to be measured, the reader 3 excites the sensor 2 and collects its backscattered signal, and the sensor 2 completes information exchange through the reader 3. Through the radar cross-section analysis method, convert the signal received by the reader 3 into a single-station RCS (radar cross-section) spectrum signal and a surface current signal, extract the change in the amplitude of the RCS (radar cross-section) as the characteristic of the crack, and analyze and compare the difference between the response of the metal plate 1 to be measured and the response of the healthy structure to achieve real-time detection of the crack 6 to be detected. The sensor 2 of the present utility model can also receive electromagnetic waves from the reader 3 and convert the received radio frequency energy into electrical energy for its own operation.

[0022] As Figure 2The utility model discloses sensor structure plan and side view as shown in (a) and (b), the utility model sensor includes resonator 4 and dielectric substrate 5. Among them, resonator 4 adopts the design of combination of circle arc and square ring, and the resonator core is square ring structure, and four circle arcs are extended outward to the center position of four edges of square ring, form the central symmetry structure. Select copper as material to ensure good conductivity and mechanical strength, and dielectric substrate 5 is made of polyimide resin. According to design, draw the pattern of resonator 4 on the polyimide resin board, and the pattern includes the combined design of circle arc and square ring. Use high-precision etching technology to etch resonator pattern on dielectric substrate 5, clean and dry etched dielectric substrate 5, ensure that the surface is free from impurities, and then combine to form sensor 2. Because of the central symmetry structure of resonator 4, after the excitation of reader 3, the radiation surface of resonator 4 is central symmetry, and the whole radiation field completely covers the metal plate 1 to be measured, so that each corner of the metal plate 1 to be measured is radiated, and the induced current is formed. Because any defect in the sensor area can change the formation of surface current of the metal plate 1 to be measured and resonator 4, and reconstruct the radar scattering cross section parameter, therefore, through the detection of the resonant amplitude change of resonator 4, the generation or change of the crack 6 to be detected can be effectively and accurately identified. Therefore, no matter where the crack appears, how the direction is and how the size is, the crack information will be taken as the carrier of the backscattering signal and be collected by the reader 3. After signal conversion into single-station RCS spectrum signal and surface current signal, compared with the pre-stored healthy structure signal, accurate and effective crack detection is realized. In the subsequent long-term monitoring demand, only need to go to the area to be detected regularly to read the data information of the sensor 2 in the area, and compare it with the pre-stored healthy structure response, and compare its RCS amplitude, long-term, efficient and low-cost crack monitoring can be realized.

Claims

1. A sensor for detecting cracks in metal structures using passive radio frequency identification technology, characterized in that: The sensor (2) comprises a medium substrate (5) and a resonator (4) etched on the medium substrate (5), the resonator (4) adopts a structure combining a circular arc and a square ring, the resonator core is a square ring structure, four circular arcs are extended outward from the center positions of four sides of the square ring to form a central symmetric structure.

2. The sensor for detecting a crack in a metal structure using passive radio frequency identification technology according to claim 1, wherein: The material of the resonator (4) is copper, the material of the medium substrate (5) is a polyimide resin with a dielectric constant of 3.8-4.1, and the thickness of the medium substrate is 1.4mm-1.8mm.

3. The sensor for detecting cracks in a metal structure using passive radio frequency identification technology according to claim 1, wherein: The radius of the four circular arc structures is 1.1mm-4.6mm, and the central angle is 180°, and the side length of the square ring is 7.4mm-10.4mm.

4. The sensor for detecting a crack in a metal structure using passive radio frequency identification technology according to claim 1, wherein: The center of the medium substrate (5) and the center of the resonator (4) are located on the same vertical axis.

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