A structural health monitoring system and method

Abstract

This invention discloses a structural health monitoring system and method. The system includes: at least one passive wireless strain sensing tag attached to the surface of the structure under test. The tag includes a dielectric substrate, a metal ground plane disposed on one side of the dielectric substrate, and at least one metal open-loop resonant unit disposed on the other side of the dielectric substrate. The open-loop resonant unit has an opening gap, and a strain amplification structure is disposed near the opening gap. A transceiver is used to transmit broadband electromagnetic signals and receive electromagnetic response signals reflected or backscattered by the tag. A signal processing unit is used to extract resonant characteristic parameters from the electromagnetic response signals and determine the strain state of the structure under test based on their changes. This invention uses a strain amplification structure to concentrate minute structural strains into changes in the opening gap size, thereby altering the resonant characteristics. This achieves high-sensitivity strain monitoring without batteries or chips, and supports quasi-distributed measurement through arrayed arrangement.

Description

Technical Field

[0001] This invention relates to the field of structural health monitoring technology, and specifically to a structural health monitoring system and method. Background Technology

[0002] Structural health monitoring is a crucial means of ensuring the safe operation of critical infrastructure. Strain, as one of the fundamental physical quantities characterizing the stress state of a structure, crack initiation, connection degradation, and localized damage, is essential for accurately measuring structural safety.

[0003] Traditional manual inspections rely on experience and periodic visual checks, making it difficult to promptly capture early, minute strain changes caused by load, temperature variations, material aging, crack propagation, or loose connections during structural service. As infrastructure scales up and service life increases, the need for continuous online monitoring becomes increasingly urgent, requiring a large number of sensors to be permanently attached to or embedded in critical structural locations. Therefore, the cost, power supply method, maintenance frequency, environmental adaptability, and ease of installation of sensors become key factors for achieving large-scale deployment.

[0004] Currently, common structural strain monitoring solutions mainly include resistance strain gauges, vibrating wire strain gauges, fiber Bragg grating sensors, and active wireless sensing nodes. Resistance strain gauges are simple in structure and low in cost, but they typically require wires, bridge circuits, acquisition units, and a stable power supply, resulting in high wiring and maintenance costs. Furthermore, they are prone to zero-point drift and fatigue failure after long-term service. Fiber Bragg grating sensors offer strong resistance to electromagnetic interference and high accuracy, but demodulation equipment is expensive, and fiber optic splicing and repair processes are demanding, making construction and maintenance difficult. Active wireless sensing nodes integrate strain-sensitive elements, acquisition circuits, processing chips, wireless communication modules, and power modules. They can transmit strain information to gateways or cloud platforms via Bluetooth, ZigBee, LoRa, 4G / 5G, etc. While reducing some wiring, the node hardware cost is high. Each measurement point requires a sensing chip, RF front-end, and power management unit. With large-scale deployment, the overall cost increases rapidly with the number of measurement points. The nodes also require batteries or external power to operate, leading to power attenuation and replacement issues after long-term operation. Maintenance is extremely difficult in hard-to-reach locations such as bridges, tunnels, and high-rise buildings. In addition, active nodes also suffer from problems such as battery failure, package aging, sensor drift, communication interruption or equipment upgrades during long-term service, requiring regular inspection, calibration and replacement, resulting in high life cycle costs. Summary of the Invention

[0005] The purpose of this invention is to provide a structural health monitoring system and method to achieve low-cost, high-sensitivity, battery-free, and long-term stable structural strain monitoring.

[0006] In a first aspect, embodiments of the present invention provide a structural health monitoring system, comprising: At least one passive wireless strain sensing tag is attached to the surface of the structure to be measured. The sensing tag includes a dielectric substrate, a metal ground disposed on one side of the dielectric substrate, and at least one metal open-ring resonant unit disposed on the other side of the dielectric substrate. The open-ring resonant unit has an opening gap, and a strain amplification structure is provided on the dielectric substrate or between the metal arms near the opening gap. A transceiver is used to transmit broadband electromagnetic signals covering the resonant frequency band of the sensor tag and to receive electromagnetic response signals reflected or backscattered by the sensor tag. A signal processing unit, connected to the transceiver device, is used to extract resonant characteristic parameters from the electromagnetic response signal and determine the strain state of the structure under test based on the changes in the resonant characteristic parameters.

[0007] Furthermore, the strain amplification structure is a through or non-through groove, slit, thinning zone, flexible bridge, or partially hollowed-out structure disposed on the medium substrate and located directly below, on both sides, or around the opening gap, used to concentrate the minute strain on the surface of the structure to be measured into the size change of the opening gap.

[0008] Furthermore, the change in the opening gap size of the open-ring resonant unit causes a change in its equivalent capacitance or equivalent inductance, thereby changing the resonant frequency, absorption peak depth, Q value, bandwidth, or phase parameter in the electromagnetic response signal; the signal processing unit determines the strain state of the structure under test by monitoring at least one of the parameters.

[0009] Furthermore, multiple metal open-ring resonant units are arrayed on the dielectric substrate of the sensing tag to form a metamaterial reflective array, thereby enhancing the equivalent reflection cross-section of the target frequency band. The multiple metal open-ring resonant units have the same structural dimensions and resonant frequency points to synergistically enhance the reflection characteristics of the same frequency band.

[0010] Furthermore, the array arrangement is divided into multiple partitions, and the metal open-ring resonant units in different partitions have different resonant frequencies, structural dimensions, opening gap directions, or strain amplification structures; the transceiver device performs quasi-distributed strain measurement at multiple points, in multiple directions, or in multiple ranges by scanning and identifying the frequency response or polarization response of different partitions.

[0011] Furthermore, the transceiver equipment is installed on a fixed base station, mobile inspection vehicle, robot, drone, or handheld device; the transmitted broadband electromagnetic signal is a multi-carrier signal, a continuous sweep frequency signal, a linear frequency modulation signal, a broadband pulse signal, or a broadband communication signal.

[0012] Furthermore, the signal processing unit pre-stores the reference resonance characteristics of the sensing tag under no abnormal strain conditions; the signal processing unit compares the real-time extracted resonance characteristic parameters with the reference resonance characteristics to determine whether the structure under test has undergone strain changes and the degree of such changes.

[0013] Furthermore, the metal open-ring resonant unit is a square open-ring, rectangular open-ring, circular open-ring, C-shaped open-ring, complementary open-ring, zigzag open-ring, or serpentine open-ring; the open-ring resonant structure has a single opening or multiple openings for responding to tensile, compressive, or strain in different directions respectively.

[0014] Furthermore, the system includes multiple sensor tags, which are respectively attached to different positions of the structure under test; the multiple sensor tags are configured to have different initial resonant frequencies or polarization directions, and the transceiver device scans and distinguishes different frequency responses or polarization responses to perform quasi-distributed strain identification and localization at multiple positions of the structure under test.

[0015] In a second aspect, embodiments of the present invention provide a structural health monitoring method, implemented based on the structural health monitoring system described in the first aspect, the method comprising: At least one passive wireless strain sensor tag is attached to the surface of the structure to be tested. The transceiver device transmits a broadband electromagnetic signal covering its resonant frequency band to the sensor tag; Receive the reflected or backscattered electromagnetic response signal generated by the sensing tag under the excitation of the broadband electromagnetic signal; The signal processing unit extracts the resonant characteristic parameters from the received electromagnetic response signal; The extracted resonance characteristic parameters are compared with the reference resonance characteristics to obtain the change in the resonance characteristic parameters; The strain state of the structure under test at the location where the sensor tag is attached is determined based on the amount of change.

[0016] The structural health monitoring system provided by this invention includes at least one passive wireless strain sensing tag attached to the surface of the structure under test. The tag includes a dielectric substrate, a metal ground plane disposed on one side of the dielectric substrate, and at least one metal open-loop resonant unit disposed on the other side of the dielectric substrate. The open-loop resonant unit has an opening gap, and a strain amplification structure is disposed near the opening gap. A transceiver is used to transmit broadband electromagnetic signals and receive electromagnetic response signals reflected or backscattered by the tag. A signal processing unit is used to extract resonant characteristic parameters from the electromagnetic response signals and determine the strain state of the structure under test based on their changes. This invention concentrates minute structural strains into changes in the opening gap size through a strain amplification structure, thereby altering the resonant characteristics. This achieves high-sensitivity strain monitoring without batteries or chips, and supports quasi-distributed measurement through arrayed arrangement. It is suitable for long-term structural health monitoring of infrastructure such as bridges, tunnels, and buildings. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A structural schematic diagram of a structural health monitoring system provided in an embodiment of the present invention is shown; Figure 2 A schematic diagram of the structure of the passive wireless strain sensing tag provided in an embodiment of the present invention is shown; Figure 3 A schematic diagram of the structure of the metal open-ring resonator provided in an embodiment of the present invention is shown; Figure 4 A schematic diagram illustrating the principle that strain causes changes in the opening gap, leading to a shift in the reflection spectrum peaks / valleys; Figure 5 A flowchart of a structural health monitoring method provided by the present invention is shown. Detailed Implementation

[0018] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0019] The accompanying drawings illustrate various structural schematics according to embodiments of the present invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0020] In the context of this invention, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0021] Figure 1 A schematic diagram of a structural health monitoring system provided in an embodiment of the present invention is shown.

[0022] like Figure 1 As shown, the system includes at least one passive wireless strain sensing tag 10, a transceiver device 20, and a signal processing unit 30.

[0023] The passive wireless strain sensor tag 10 (hereinafter referred to as sensor tag 10) is attached to the surface of the structure to be tested. In this embodiment, the structure to be tested can be the bottom surface of a box girder of a highway bridge.

[0024] Figure 2 A schematic diagram of the structure of the passive wireless strain sensing tag provided in an embodiment of the present invention is shown. Figure 3 A schematic diagram of the structure of the metal open-ring resonator provided in an embodiment of the present invention is shown.

[0025] like Figure 2 As shown, the sensor tag 10 includes a dielectric substrate 11, a metal ground 12 disposed on the bottom surface of the dielectric substrate 11, and a plurality of metal open-ring resonant units 13 disposed on the top surface of the dielectric substrate 11. The metal open-ring resonant units 13 can be made of copper, aluminum, silver, gold, conductive ink, conductive film, or other conductive materials; the dielectric substrate 11 can be made of FR-4 glass fiber epoxy resin copper-clad laminate, polyethylene terephthalate (PET), polyimide PI, polydimethylsiloxane (PDMS), glass fiber resin board, flexible copper-clad laminate, or other dielectric materials suitable for attachment to structural surfaces. The sensor tag can be manufactured using PCB etching, flexible circuit board technology, printed electronics technology, laser etching, screen printing, inkjet printing, or roll-to-roll technology.

[0026] Specifically, the dielectric substrate 11 is made of FR-4 glass fiber epoxy resin copper clad laminate with a thickness of 1.52 mm and a relative permittivity of approximately 4.4. The metal open-ring resonant unit 13 is a square open-ring structure, formed on the copper foil layer on the top surface of the dielectric substrate 11 by PCB etching process, and the copper foil thickness is 35 μm.

[0027] like Figure 3 As shown, the outer side length of a single square open-ring resonant unit 13 l It is 22.2mm in diameter, and the metal line width is... w The opening gap is 2.0mm. d It is 1.0mm. t The thickness is the substrate thickness. Multiple open-ring resonant units 13 are periodically arranged on the dielectric substrate 11. p =30.0mm arranged in a 10×10 two-dimensional array to form a metamaterial reflective array, enhancing the equivalent reflection cross-section of the target resonant frequency band. The target resonant frequency band of this array is designed to be between 5.5GHz and 6.0GHz.

[0028] It is worth mentioning that the multiple metal open-ring resonant units in the metamaterial reflective array have the same structural dimensions and resonant frequency points to synergistically enhance the reflection characteristics of the same frequency band.

[0029] The opening gap d The metal arms on both sides, together with the dielectric substrate 11, constitute the equivalent capacitance, and the metal path of the open-ring constitutes the equivalent inductance. The entire open-ring resonant unit 13 can be equivalent to an LC resonant circuit, whose resonant frequency is determined by the equivalent inductance L and the equivalent capacitance C, satisfying the following conditions: .

[0030] In the opening gap d Directly below, a slit 14 (i.e., a strain amplification structure) penetrating the dielectric substrate 11 is formed on the dielectric substrate. The slit 14 has a width of 0.5 mm and a length equal to the opening gap. d The length of each slit is consistent and 18mm. The function of slit 14 is to create an opening gap. d The substrate regions on both sides form relatively deformable local flexible connection areas. When the structure under test 40 undergoes tensile strain, the strain is transferred to the substrate 11 through the adhesive layer on the bottom surface of the label. Due to the presence of the slit 14, the strain energy is concentrated in the opening gap. d Nearby, making the opening gap d The width change Δd is much greater than the relative change in the overall length of the label, thus achieving a strain amplification effect.

[0031] Opening gap d The change in width causes a change in the equivalent capacitance C, which in turn causes a shift in the resonant frequency Δ. f 0. When the opening gapd When the value increases, the equivalent capacitance C decreases, and the resonant frequency... f 0 increases; conversely, when the opening gap decreases... d When the capacitance C decreases, the equivalent capacitance C increases, and the resonant frequency... f 0 decreases. Therefore, the tensile or compressive strain on the structural surface is converted into a shift in the resonant frequency. For example... Figure 4 The diagram shows the principle that strain causes changes in the opening gap and leads to shifts in the reflection spectrum peaks / valleys. When the strain changes from 0 to 3000με, the reflection amplitude changes significantly at different frequencies, proving that the tag can indeed convert strain into wirelessly readable electromagnetic response changes.

[0032] The transceiver 20 can be installed on a fixed base station, mobile inspection vehicle, robot, drone, or handheld device. The broadband electromagnetic signal transmitted by the transceiver 20 can be a multi-carrier signal, a continuous sweep frequency signal, a linear frequency modulated signal, a broadband pulse signal, or a broadband communication signal. For example, the transceiver 20 can be a handheld vector network analyzer equipped with a broadband omnidirectional antenna. The transceiver 20 transmits a continuous sweep frequency signal covering the 5.0 GHz to 6.5 GHz frequency band, which illuminates the sensor tag 10. The open-loop resonant unit 13 of the sensor tag 10 generates a frequency-selective backscattering response in the 5.5~6.0 GHz frequency band. The transceiver 20 receives the electromagnetic response signal reflected / backscattered by the tag and transmits the signal to the signal processing unit 30.

[0033] The signal processing unit 30 can be a portable computer equipped with signal processing software. The signal processing unit 30 extracts resonance characteristic parameters from the received electromagnetic response signal; in this embodiment, the extracted resonance characteristic parameter is the resonant frequency. f 0. The signal processing unit 30 pre-stores the reference resonant frequency of the sensing tag under strain-free conditions. f 00 =5.78GHz. During the monitoring process, the signal processing unit 30 extracts the resonant frequency in real time. f 0 and reference frequency f 00 Compare and calculate the frequency offset Δ f = f 0- f 00 Based on a pre-calibrated frequency offset-strain relationship curve (e.g., Δ... f / Δε=1.2kHz / με), to Δ f Converted to strain value Δε.

[0034] When Δε exceeds a preset threshold (e.g., 200με), the signal processing unit 30 issues a warning signal, indicating that there is abnormal strain accumulation on the bottom surface of the bridge box girder, which may be caused by overload or structural damage.

[0035] In this embodiment, the sensing tag 10 does not contain any battery, microcontroller, RF modulation circuit, or active amplification element, and operates entirely by passive reflection. The tags are mass-produced using PCB technology, resulting in low cost per tag and allowing for large-area deployment on critical load-bearing parts of bridges.

[0036] The strain amplification structure described in the embodiments of the present invention has several alternative solutions, all of which can achieve the technical effect of concentrating minute strains into changes in the size of the opening gap.

[0037] Implementation method A: Non-through slot structure In this implementation, the substrate thickness of the sensor tag can be 1.0 mm, using a flexible polyimide (PI) copper-clad laminate. A non-penetrating rectangular groove is formed on the top surface of the substrate directly below the opening gap. The groove is 0.7 mm deep (retaining a 0.3 mm bottom bonding layer), 0.4 mm wide, and 1.2 times the length of the opening gap. This non-penetrating groove can also create a localized thinning area in the substrate, causing strain to preferentially concentrate near the opening gap. Compared to the through-groove solution, the non-penetrating groove preserves the integrity of the substrate's bottom surface, which is beneficial for maintaining the tag's structural strength and resistance to environmental corrosion, making it suitable for high humidity or corrosive environments.

[0038] Implementation method B: Symmetrical slit structure on both sides In this implementation, the strain amplification structure is not located directly below the opening gap, but rather two slits are formed on either side of the opening gap. The two slits are parallel to the direction of the opening gap, located 0.5 mm to the left and right of the opening gap respectively, with a slit width of 0.3 mm and a length 1.5 times the length of the opening gap. This symmetrical slit structure allows the metal arms on both sides of the opening gap to form independent cantilever beam structures. When the base is stretched, the cantilever beams open outwards, further amplifying the change in the width of the opening gap. The strain amplification factor of this structure can reach 3 to 5 times.

[0039] Implementation method C: Flexible bridge structure In this implementation, the open region of the open-ring resonator does not have a dielectric groove; instead, a flexible conductive bridge connects the metal arms on both sides of the opening gap. This flexible conductive bridge is composed of a serpentine metal pattern and has low mechanical stiffness. When the substrate experiences strain, the flexible conductive bridge deforms preferentially, concentrating the strain at the opening gap. The advantage of this approach is that it does not compromise the integrity of the dielectric substrate, thus maintaining the substrate's mechanical homogeneity and protective performance.

[0040] Implementation method D: Combination structure of metal clearance zone and hollow structure In this implementation, the metal pattern surrounding the opening gap is designed with an arc-shaped clearance zone, and an elliptical perforation is formed at the corresponding position on the dielectric substrate. The metal clearance zone and the dielectric perforation together form a strain concentration region, enabling in-plane strain in any direction to be efficiently converted into changes in the opening gap. This solution is suitable for applications where the strain direction is uncertain or the principal strain direction changes over time.

[0041] All four implementation methods can achieve the technical effect of concentrating the minute strain on the surface of the structure under test into changes in the size of the opening gap. The specific structural parameters (groove depth, groove width, slit spacing, hollow shape, etc.) can be optimized and selected according to the target strain sensitivity, the mechanical properties of the substrate, and the processing technology.

[0042] In some embodiments, changes in the opening gap size of the open-ring resonant unit 13 cause changes in its equivalent capacitance or equivalent inductance, thereby altering the resonant frequency, absorption peak depth, Q value, bandwidth, or phase parameters in the electromagnetic response signal; the signal processing unit 30 determines the strain state of the structure under test by monitoring at least one of the above parameters.

[0043] Specifically, the signal processing unit 30 can simultaneously monitor multiple resonant characteristic parameters and comprehensively determine the strain state to improve the reliability and anti-interference capability of the measurement. During strain monitoring, factors such as changes in ambient temperature, humidity, and distance between the transceiver and the tag may interfere with individual resonant characteristic parameters. To improve measurement robustness, this embodiment employs a multi-parameter comprehensive determination method.

[0044] The signal processing unit 30 simultaneously extracts the following four resonant characteristic parameters from the electromagnetic response signal: (1) Resonant frequency f 0: Most sensitive to changes in opening gap, it is the main strain indicator parameter; (2) Absorption peak depth A: It is greatly affected by the coupling distance between the tag and the read antenna, but it can be used as an auxiliary verification of frequency offset; (3) Q value: reflects the loss characteristics of the resonant unit. When the adhesive layer between the label and the structure degrades, the Q value will decrease significantly and can be used to diagnose the label's adhesion quality. (4) Resonant bandwidth BW: It is the reciprocal of Q value. A widening of the bandwidth usually means increased loss or uneven deformation of the structure.

[0045] The signal processing unit 30 compares the four parameters extracted in real time with their respective reference values ​​and calculates the change vector V=[Δ f 0, ΔA, ΔQ, ΔBW].

[0046] The determination logic is as follows: When |Δ f 0|> f _threshold (frequency threshold), and |ΔA|<A_threshold (the variation of absorption depth is less than the threshold), it is determined as a true strain change, and the strain value is calculated mainly based on Δ f 0; When |Δ f 0|>f_threshold, |ΔA|>A_threshold, and the variations of ΔQ and ΔBW are not significant, it is determined that the coupling condition change possibly caused by the reading distance change exists, and recalibration or repeated measurement is required; When |ΔQ|>Q_threshold (the drop of Q value exceeds the threshold) and ΔBW is significantly broadened, it is determined that the adhesive layer between the tag and the structure may have aging, falling off or damage, and the system issues a maintenance prompt of abnormal tag pasting quality; When all parameters have no significant change, it is determined that the structural state is normal.

[0047] Through the above multi-parameter comprehensive determination method, the present invention can effectively distinguish structural strain changes from factors such as environmental interference, reading condition changes, and tag self-health state changes, so as to provide more reliable monitoring results.

[0048] In some embodiments, the above metamaterial reflection array can be divided into a plurality of sub-regions, and the metal split-ring resonant units in different sub-regions have different resonant frequency points, structural dimensions, split gap directions or strain amplification structures; the transceiver device 20 performs quasi-distributed strain measurement at multiple points, in multiple directions or in multiple ranges by scanning and identifying the frequency response or polarization response of different sub-regions.

[0049] Specifically, this embodiment provides a structural health monitoring system with multi-point and multi-direction quasi-distributed measurement capability. A total of 64 metal split-ring resonant units arranged in 8×8 are disposed on the dielectric substrate of the sensing tag, these units are divided into 4 sub-regions, and each sub-region contains 16 units arranged in 4×4: Sub-region A (upper left area): the unit dimension has an outer side length l =22.2mm, the line width w =2.0mm, the split gap d =0.8mm, and the target resonant frequency is 5.5GHz. The split gap direction is along the horizontal direction (0°), which is used for monitoring the tensile / compressive strain in the horizontal direction.

[0050] Sub-region B (upper right area): the unit dimension has an outer side length l =21.0mm, the line width w =1.8mm, the split gap d=1.0mm, target resonant frequency is 5.8GHz. The opening gap direction is vertical (90°) to monitor the tensile / compressive strain in the vertical direction.

[0051] Partition C (bottom left region): Unit size is the outer side length l =20.0mm, line width w =2.2mm, opening gap d =1.2mm, target resonant frequency is 6.1GHz. The opening gap direction is along the +45° direction, used to monitor shear strain in the 45° direction.

[0052] Partition D (bottom right region): Unit size is the outer side length l =19.0mm, line width w =1.6mm, opening gap d =0.6mm, target resonant frequency is 6.4GHz. The opening gap direction is along the -45° direction, used to monitor shear strain in the -45° direction.

[0053] The units in the four zones are spatially interspersed but their frequency responses are clearly separated. The resonant frequency intervals of each zone are approximately 0.3 GHz, which is sufficient to make them clearly distinguishable in the spectrum.

[0054] The transceiver 20 is a broadband linear frequency modulated continuous wave radar mounted on a UAV, operating in the frequency band from 5.0 GHz to 7.0 GHz. The UAV flies along a preset route to the vicinity of the structure under test (approximately 5-10 meters away), transmits broadband linear frequency modulated signals to the sensor tag, and receives the backscattered signals from the tag.

[0055] The signal processing unit 30 performs time-frequency analysis on the received signal, separating the reflection spectra corresponding to four frequency bands (5.4~5.6GHz, 5.7~5.9GHz, 6.0~6.2GHz, and 6.3~6.5GHz). By detecting the resonant frequency shift of each of the four bands, the signal processing unit 30 can simultaneously obtain the following information: (1) The change in the resonant frequency of partition A reflects the strain state of the structure in the horizontal direction; (2) The change in the resonant frequency of partition B reflects the strain state of the structure in the vertical direction; (3) The change in the resonant frequency of partition C reflects the strain state of the structure in the +45° direction; (4) The change in the resonant frequency of partition D reflects the strain state of the structure in the -45° direction.

[0056] Using the strain data from the above four directions, the signal processing unit 30 can further calculate the magnitude and direction of the principal strain in the monitored area, providing more complete mechanical information for structural safety assessment.

[0057] In this embodiment, the two-dimensional strain tensor information of the monitoring area can be obtained by a single sensor tag and a single frequency sweep measurement. Compared with the traditional single-point, single-direction sensor, which requires multiple sensors to obtain the same amount of information, the system integration and monitoring efficiency of the present invention are significantly improved.

[0058] In some embodiments, the aforementioned metal open-ring resonant units have different topologies, all of which can realize the technical solution of the present invention, and each has different applicable scenarios. For example, the metal open-ring resonant unit can be a square open-ring, a rectangular open-ring, a circular open-ring, a C-shaped open-ring, a complementary open-ring, a zigzag open-ring, or a serpentine open-ring; the open-ring resonant structure has a single opening or multiple openings, used to respond to tensile, compressive, or strain in different directions respectively.

[0059] In some embodiments, the above-described structural health monitoring system may include multiple sensor tags, which are respectively attached to different locations of the structure under test; the multiple sensor tags are configured to have different initial resonant frequencies or polarization directions, and the transceiver device scans and distinguishes different frequency responses or polarization responses to perform quasi-distributed strain identification and localization at multiple locations of the structure under test.

[0060] For example, ten passive wireless strain sensor tags are attached to different key locations on the structure under test (such as a tunnel lining approximately 50 meters long), including the arch crown, left arch midsection, right arch midsection, left arch foot, right arch foot, and invert. The ten tags have different initial resonant frequencies: 5.10 GHz, 5.15 GHz, 5.20 GHz, 5.25 GHz, 5.30 GHz, 5.35 GHz, 5.40 GHz, 5.45 GHz, 5.50 GHz, and 5.55 GHz, with a frequency interval of 50 MHz, making them clearly distinguishable in the spectrum.

[0061] Each tag consists of an array of 32 (8×4) open-loop resonant units operating at the same frequency to ensure that each tag has sufficient reflected signal strength. The frequency spacing between tags (50MHz) is greater than the resonant bandwidth of each tag (approximately 20MHz) to ensure that the reflection peaks of different tags do not overlap in the spectrum.

[0062] The transceiver is a broadband sweeper fixed to the tunnel sidewall, with a directional antenna facing the tunnel lining surface. The transceiver transmits a sweep signal covering 5.0 GHz to 5.7 GHz at a preset period (e.g., once per hour) and receives the backscatter responses of all 10 tags.

[0063] The signal processing unit identifies 10 reflection peaks from the received composite spectrum, each corresponding to one of the 10 tags. By tracking the frequency offset of each reflection peak, the signal processing unit can obtain strain data at 10 different locations. When the strain value at a certain location exceeds the warning threshold, the system can accurately pinpoint the specific location of the abnormal strain (e.g., excessive strain at the arch crown), achieving spatial localization of strain anomalies.

[0064] The advantages of this embodiment are as follows: 10 tags share the same transceiver device and the same spectrum resource, eliminating the need to configure an independent reader / writer for each tag, thus significantly reducing system hardware costs; each tag uses a different initial resonant frequency to achieve frequency division multiple access, without interfering with each other, and can be monitored simultaneously; the number of tags can be flexibly expanded according to actual monitoring needs, and the frequency interval can be optimized according to the Q value of the tag, achieving efficient utilization of spectrum resources.

[0065] This invention also provides a structural health monitoring method, implemented based on the structural health monitoring system described in the above embodiments. For example... Figure 5 As shown, the method includes the following steps: S101. Attach at least one passive wireless strain sensor tag to the surface of the structure to be tested; S102. The transceiver transmits a broadband electromagnetic signal covering the resonant frequency band to the sensor tag; and receives the reflected or backscattered electromagnetic response signal generated by the sensor tag under the excitation of the broadband electromagnetic signal. S103. The signal processing unit extracts resonance characteristic parameters from the received electromagnetic response signal; compares the extracted resonance characteristic parameters with the reference resonance characteristic to obtain the change in the resonance characteristic parameters; and determines the strain state of the structure under test at the attachment position of the sensing tag based on the change.

[0066] Compared with the prior art, the present invention has the following advantages: (1) The present invention uses a passive metamaterial strain sensing tag. The tag itself does not contain a battery, microcontroller, radio frequency modulation circuit or active amplifier circuit. It works entirely by passive reflection / backscattering, which can fundamentally avoid the power supply attenuation of active nodes and battery replacement problems, significantly reducing the hardware complexity and manufacturing cost of a single measuring point. It is particularly suitable for long-term deployment in difficult-to-maintain scenarios such as bridges and tunnels.

[0067] (2) By setting up strain amplification structures such as grooves, slits, thinning areas or hollows near the opening gap, the present invention can concentrate the small strain on the surface of the structure into the size change of the opening gap. Compared with the traditional scheme that only relies on the overall deformation of the resonant unit, the strain sensitivity can be increased by several times to tens of times, and can effectively sense the structural deformation at the micro-strain level.

[0068] (3) By arranging multiple strain-sensitive units in an array to form a metamaterial reflective array, the present invention can significantly enhance the equivalent reflection cross section and signal-to-noise ratio of the target frequency band, improve the robustness of long-distance reading and measurement in complex environments, and at the same time, a single tag can cover a large area of ​​the structural surface, which is conducive to achieving high-density monitoring.

[0069] To achieve the same structure, those skilled in the art can also devise methods that are not entirely identical to those described above. Furthermore, although various embodiments have been described separately above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.

[0070] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0071] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A structural health monitoring system, characterized in that, include: At least one passive wireless strain sensing tag is attached to the surface of the structure to be measured. The sensing tag includes a dielectric substrate, a metal ground disposed on one side of the dielectric substrate, and at least one metal open-ring resonant unit disposed on the other side of the dielectric substrate. The open-ring resonant unit has an opening gap, and a strain amplification structure is provided on the dielectric substrate or between the metal arms near the opening gap. A transceiver is used to transmit broadband electromagnetic signals covering the resonant frequency band of the sensor tag and to receive electromagnetic response signals reflected or backscattered by the sensor tag. A signal processing unit, connected to the transceiver device, is used to extract resonant characteristic parameters from the electromagnetic response signal and determine the strain state of the structure under test based on the changes in the resonant characteristic parameters.

2. The structural health monitoring system according to claim 1, characterized in that, The strain amplification structure is a through or non-through groove, slit, thinning zone, flexible bridge, or partially hollowed-out structure disposed on the medium substrate and located directly below, on both sides, or around the opening gap, used to concentrate the minute strain on the surface of the structure to be measured into the size change of the opening gap.

3. The structural health monitoring system according to claim 2, characterized in that, The change in the opening gap size of the open-ring resonant unit causes a change in its equivalent capacitance or equivalent inductance, thereby changing the resonant frequency, absorption peak depth, Q value, bandwidth or phase parameters in the electromagnetic response signal. The signal processing unit determines the strain state of the structure under test by monitoring at least one of the parameters.

4. The structural health monitoring system according to claim 1, characterized in that, The sensing tag has multiple metal open-ring resonant units arranged in an array on its dielectric substrate to form a metamaterial reflective array, thereby enhancing the equivalent reflection cross section of the target resonant frequency band. The multiple metal open-ring resonant units have the same structural dimensions and resonant frequency to synergistically enhance the reflection characteristics of the same frequency band.

5. The structural health monitoring system according to claim 4, characterized in that, The array arrangement is divided into multiple partitions, and the metal open ring resonant units in different partitions have different resonant frequencies, structural dimensions, opening gap directions or strain amplification structures. The transceiver device performs quasi-distributed strain measurements at multiple points, in multiple directions, or across multiple ranges by scanning and identifying the frequency response or polarization response of different zones.

6. The structural health monitoring system according to claim 1, characterized in that, The transceiver equipment is installed on a fixed base station, a mobile inspection vehicle, a robot, a drone, or a handheld device; The transmitted broadband electromagnetic signal is a multi-carrier signal, a continuous frequency sweep signal, a linear frequency modulation signal, a broadband pulse signal, or a broadband communication signal.

7. The structural health monitoring system according to claim 1, characterized in that, The signal processing unit pre-stores the reference resonance characteristics of the sensing tag under a state of no abnormal strain. The signal processing unit determines whether the structure under test has undergone strain changes and the degree of those changes by comparing the real-time extracted resonance characteristic parameters with the reference resonance characteristics.

8. The structural health monitoring system according to any one of claims 1 to 7, characterized in that, The metal open-ring resonant unit is a square open-ring, a rectangular open-ring, a circular open-ring, a C-shaped open-ring, a complementary open-ring, a zigzag open-ring, or a serpentine open-ring; The open-ring resonant structure has a single opening or multiple openings for responding to tensile, compressive, or strain in different directions, respectively.

9. The structural health monitoring system according to any one of claims 1 to 7, characterized in that, The system includes multiple sensor tags, which are respectively attached to different positions of the structure under test; Multiple sensor tags are configured with different initial resonant frequencies or polarization directions. The transceiver device scans and distinguishes different frequency responses or polarization responses to perform quasi-distributed strain identification and localization at multiple locations of the structure under test.

10. A method for monitoring structural health, characterized in that, The method, implemented based on the structural health monitoring system according to any one of claims 1 to 10, comprises: At least one passive wireless strain sensor tag is attached to the surface of the structure to be tested. The transceiver transmits a broadband electromagnetic signal covering the resonant frequency band to the sensor tag; and receives the reflected or backscattered electromagnetic response signal generated by the sensor tag under the excitation of the broadband electromagnetic signal. The signal processing unit extracts resonance characteristic parameters from the received electromagnetic response signal; compares the extracted resonance characteristic parameters with the reference resonance characteristic to obtain the change in the resonance characteristic parameters; and determines the strain state of the structure under test at the attachment position of the sensing tag based on the change.

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