An antenna strain sensor, temperature compensation method and detection method

Abstract

This invention belongs to the field of strain measurement technology, specifically an antenna strain sensor, a temperature compensation method, and a detection method. This invention obtains the resonant frequencies of the antenna strain sensor in the width and length directions under initial and operating conditions, respectively. f 10 and f 01 The frequency offset Δf is obtained by measuring the difference between the resonant frequencies of the operating state and the initial state. 10 With Δf 01 Then, based on the offset and sensitivity coefficient, the temperature-induced offset of the two frequencies is calculated, and the resonant frequency of the operating state is determined. f 10 and f 01 Subtracting and from each, we obtain the temperature-compensated resonant frequency. f 10 and f 01 This invention establishes a temperature compensation mechanism for strain sensing in graphene patch antennas, reducing the impact of ambient temperature on the strain measurement results of the patch antenna sensor, effectively improving the strain measurement accuracy of the antenna, and demonstrating significant advantages and broad application prospects in structural health monitoring.

Description

Technical Field

[0001] This invention belongs to the field of strain measurement technology, specifically relating to an antenna strain sensor, a temperature compensation method, and a detection method. Background Technology

[0002] Structural health monitoring is crucial for ensuring the safety and durability of infrastructure in fields such as civil engineering and aerospace. Strain measurement is one of the core methods for assessing the stress state and damage of structures. Traditional sensors such as resistance strain gauges suffer from drawbacks such as susceptibility to electromagnetic interference, poor durability, and high costs associated with distributed measurement.

[0003] In recent years, antenna strain sensors have attracted widespread attention due to their ability to convert mechanical strain into wirelessly readable electromagnetic signals (such as resonant frequencies). However, these sensors face a key challenge in practical applications: their resonant frequencies are sensitive not only to mechanical strain but also to changes in ambient temperature. Temperature variations cause thermal expansion and contraction of the antenna structure and changes in the dielectric constant of the dielectric material, leading to a drift in the resonant frequency. This temperature drift couples with the frequency changes caused by strain, severely interfering with the accuracy of strain measurements and resulting in false alarms or missed alarms.

[0004] Currently, although some temperature compensation techniques exist, most solutions require the integration of additional temperature sensors (such as thermistors), which not only increases the complexity, cost, and size of the system but may also introduce new sources of error. Therefore, developing a high-precision antenna strain sensor capable of self-compensating for temperature effects and requiring no external temperature sensing element has become a pressing technical problem in this field. Summary of the Invention

[0005] The purpose of this invention is to provide an antenna strain sensor, a temperature compensation method, and a detection method. By establishing and solving the coupling equations between the dual resonant frequency and temperature and strain, the cross-influence between the two is decoupled in principle, thereby achieving temperature compensation for strain measurement. To achieve the above objectives, the present invention provides a temperature compensation method for an antenna strain sensor, comprising the following steps: S1. Obtain the resonant frequencies of the antenna strain sensor in the width and length directions in the initial and operating states, respectively. f 10 and f 01 The frequency offset Δf is obtained by measuring the difference between the resonant frequencies of the operating state and the initial state. 10 With Δf 01 ; S2. The temperature-induced shifts in the two frequencies are obtained using the following formulas:

[0006]

[0007] This represents the temperature-induced shift in the resonant frequency f10. This represents the temperature-induced shift in the resonant frequency f01. k 1 represents the sensitivity coefficient of the resonant frequency f01 to temperature. k 2 represents the sensitivity coefficient of the resonant frequency f01 to strain. k 3 is the resonant frequency f 10 Sensitivity coefficient to temperature k 4 is the resonant frequency f 10 Sensitivity coefficient to strain; S3, the resonant frequency of the operating state. f 10 and f 01 Subtract respectively and That is, to obtain the resonant frequency after temperature compensation. f 10 and f 01 .

[0008] Furthermore, the initial state is 20°C and no strain is applied.

[0009] Furthermore, k 1. k 2. k 3. k 4 are obtained by calculation using the following formulas:

[0010]

[0011]

[0012]

[0013] Where c is the speed of electromagnetic wave propagation in a vacuum, with units of m / s. The coefficient of thermal expansion of the dielectric substrate in the width direction is expressed in ppm / ℃, i.e., 10. -6 / ℃, This represents the temperature coefficient of dielectric constant for the substrate material, expressed in ppm / ℃. The relative permittivity is dimensionless. This represents the initial width of the radiating patch, in meters (m). The coefficient of thermal expansion of the dielectric substrate along its length is expressed in ppm / ℃. This represents the initial length of the radiating patch, in meters (m). ρ is the Poisson's ratio of the dielectric substrate, which is dimensionless.

[0014] The present invention also provides an antenna strain sensor, comprising: Antenna strain sensing module unit is used to sense strain and convert it into antenna electromagnetic signals; A signal transmission unit is used to transmit excitation signals to the antenna strain sensing module unit and to transmit the antenna electromagnetic signals. The signal excitation unit is used to output a frequency sweep excitation signal and transmit it to the antenna strain sensing module unit through the signal transmission unit. A temperature compensation unit is used to perform temperature compensation on the electromagnetic signal of the antenna using any of the above-described temperature compensation methods. The signal processing unit is used to process the temperature-compensated antenna electromagnetic signal to obtain the strain magnitude and direction.

[0015] Furthermore, the antenna strain sensing module unit includes a dielectric substrate and a radiating patch formed on one side of the dielectric substrate; the signal transmission unit includes a microstrip feed line connected to the edge of the radiating patch.

[0016] Furthermore, the connection point between the microstrip feed line and the radiating patch is not at the center point of the edge of the radiating patch, in order to form a bias structure to excite the two radiation modes TM10 and TM01 of the antenna strain sensor.

[0017] Furthermore, the radiating patch is a graphene patch; a ground plane is provided on the side of the dielectric substrate opposite to the radiating patch; and / or, the dielectric substrate is made of PET.

[0018] Furthermore, a quarter-wavelength impedance transformer is provided at the connection end between the microstrip feed line and the radiating patch to achieve impedance matching; The antenna strain sensor is also provided with a packaging unit for packaging the antenna strain sensing module unit and the signal transmission unit.

[0019] The present invention also provides a detection method for an antenna strain sensor, comprising the following steps: S1. Fix the antenna strain sensing module unit onto the surface of the device to be tested; S2. The signal excitation unit transmits a sweep frequency excitation signal to the antenna strain sensing module unit through the signal transmission unit, and receives the antenna electromagnetic signal radiated by the antenna strain sensing module unit. S3. Perform temperature compensation on the antenna electromagnetic signal using the temperature compensation method described above; S4. Process the temperature-compensated antenna electromagnetic signal to obtain the strain magnitude and direction of the device under test.

[0020] Furthermore, the frequency sweep excitation signal includes two frequency bands: 3.45-3.55 GHz and 5.45-5.55 GHz.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: (1) The temperature compensation method for the antenna strain sensor provided by this invention cleverly combines the physical characteristics of two resonant frequencies with mechanical principles: by establishing that "lateral strain mainly affects f 10 Longitudinal strain mainly affects f 01 The invention utilizes a unique response mechanism to achieve synchronous and intuitive characterization of strain magnitude and direction on a single sensor. It profoundly reveals the intrinsic relationship between dual resonant frequencies and strain and temperature fields. By constructing a precise set of two-element linear coupling equations, the complex problem of cross-influence of physical fields is transformed into a computable mathematical problem. Using the different sensitivity coefficient matrices of the two frequencies to temperature and strain, mathematical decoupling and online compensation for temperature effects are achieved, fundamentally solving the temperature drift problem and significantly improving the accuracy, reliability, and long-term stability of strain measurement under complex thermal environments.

[0022] (2) This invention breaks the structural symmetry of traditional patch antennas by setting the feeding position of the microstrip feed line at the edge of the graphene radiating patch width as an asymmetric bias structure, thereby stably exciting two basic radiation modes, TM10 and TM01, and generating two independent and deformation-sensitive dual resonant frequency points. Existing patch antenna sensors can usually only obtain a single resonant mode, resulting in insufficient sensing dimensions. They cannot distinguish the strain direction, and their single sensing signal is difficult to eliminate the ubiquitous temperature interference.

[0023] (3) The temperature compensation method of this invention is not a simple "black box" fitting, but a transparent model with a solid theoretical foundation and clear physical meaning. Its core sensitivity coefficients (k1, k2, k3, k4) can be directly calculated and predetermined by transmission line theory model and closely combined with the specific material properties of the sensor (such as the anisotropic thermal expansion coefficient, dielectric constant temperature coefficient, and Poisson's ratio of the dielectric substrate) and the initial structural dimensions (such as the initial length L0 and width W0 of the patch). This feature greatly reduces the reliance on a large number of repetitive experimental calibrations, pushing the sensor from "experimental screening" to a new stage of "model-guided design". This not only shortens the development cycle, but also enhances the universality, predictability and scientific nature of the method, providing a powerful theoretical tool and design freedom for the design and optimization of high-performance, customized sensors for different application scenarios.

[0024] (4) The dual-function sensing and efficient temperature compensation achieved in this invention are accomplished without introducing any additional hardware structures (such as independent temperature sensors, complex reference circuits, or multi-layer composite structures). This allows for a significant improvement in the core performance of the sensor (including multi-parameter sensing and anti-interference capabilities) while perfectly maintaining the inherent advantages of the sensor itself, such as simple structure, low cost, good flexibility, and ease of integration. This cost-effective technical solution greatly reduces the technical threshold and implementation cost of long-term, large-scale, distributed health monitoring on large engineering structures (such as bridges, buildings, and aircraft skins), giving it excellent engineering applicability and broad commercial application prospects.

[0025] In summary, while maintaining the advantages of simple sensor structure and low cost, this invention improves sensing performance through mechanism and model innovation, providing a more effective solution for structural health monitoring. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a dual-resonant patch antenna sensor based on graphene material, as an example of the present invention.

[0027] Figure 2 This is a schematic diagram of the parameters of a dual-resonant patch antenna sensor based on graphene material, as an example of the present invention.

[0028] Figure 3 This is a diagram of the electromagnetic simulation model in ANSYS HFSS software in an embodiment of the present invention.

[0029] Figure 4 The diagram shows the return loss results of the antenna in the model simulation experiment of this invention.

[0030] Figure 5 The diagram shows the results of the antenna model's resonant frequency corresponding to the temperature change in the simulation experiment of the model in this embodiment of the invention.

[0031] Figure 6 The diagram shows the results of the resonant frequency shift in the length and width directions of the ambient temperature under different strain conditions in the simulation experiment of the model of this invention.

[0032] Figure 7 The figure shows the changes in the resonant frequency of the patch antenna before and after temperature compensation in the model and simulation experiments of this invention under two conditions: no strain and 1% strain.

[0033] Figure 8 This is a diagram of the temperature control experimental device according to an embodiment of the present invention.

[0034] Figure 9The figure shows the results of the antenna temperature control experiment in an embodiment of the present invention, showing the change of the resonant frequency of the antenna in the length and width directions as a function of temperature. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] This invention provides a temperature compensation method for an antenna strain sensor, comprising the following steps: S1. Obtain the resonant frequencies of the antenna strain sensor in the width and length directions in the initial and operating states, respectively. f 10 and f 01 The frequency offset Δf is obtained by measuring the difference between the resonant frequencies of the operating state and the initial state. 10 With Δf 01 ; S2. The temperature-induced shifts in the two frequencies are obtained using the following formulas:

[0037]

[0038] This represents the temperature-induced shift in the resonant frequency f10. This represents the temperature-induced shift in the resonant frequency f01. k 1 represents the sensitivity coefficient of the resonant frequency f01 to temperature. k 2 represents the sensitivity coefficient of the resonant frequency f01 to strain. k 3 is the resonant frequency f 10 Sensitivity coefficient to temperature k 4 is the resonant frequency f 10 Sensitivity coefficient to strain; S3, the resonant frequency of the operating state. f 10 and f 01 Subtract respectively and That is, to obtain the resonant frequency after temperature compensation. f 10 and f 01 .

[0039] The derivation of the formula in step S2 is as follows: Based on the change in the two resonant frequencies (Δ) f 01 , Δ f 10 ), constructing a system based on the change in ambient temperature (ΔT) and the structural strain value ( ε A system of two linear equations with variables ) as variables:

[0040]

[0041] This refers to the dimensional change in the width direction of the radiation patch caused by temperature. The dimensional change in the width direction of the radiation patch caused by strain. The dimensional changes along the length of the radiation patch caused by temperature. Δεr represents the dimensional change in the width direction of the radiating patch caused by strain, and Δεr represents the change in the relative permittivity of the antenna dielectric substrate caused by temperature changes.

[0042] The coefficients corresponding to ΔT and ε are the corresponding sensitivity coefficients. k 1, k 2, k 3, k 4.

[0043] This model quantifies the linear superposition relationship between temperature and strain acting on the double resonant frequency.

[0044] Solving the system of two equations decouples the resonant frequency shift caused by changes in ambient temperature and structural strain, thereby enabling accurate measurement of strain and temperature compensation.

[0045] The change in ambient temperature (ΔT) and the structural strain (ε) are obtained by solving the system of two equations, and the solution formula is expressed as follows:

[0046]

[0047] Sensitivity coefficient k 1, k 2, k 3, k 4 is determined by the material properties and initial structural dimensions of the patch antenna sensor.

[0048] The material properties include the coefficients of thermal expansion of the dielectric substrate in the width and length directions. α d,w , α d,l The temperature coefficient of dielectric constant of the dielectric substrate (α ε The Poisson's ratio (μ) of the dielectric substrate and the relative permittivity of the dielectric substrate (μ) ε r ).

[0049] The initial structural dimensions include the initial length (L0) and initial width (W0) of the radiating patch, such as... Figure 2 .

[0050] The sensitivity coefficient is obtained by substituting the material properties and initial structural dimensions into the theoretical expression for the resonant frequency, which comprehensively considers the thermal expansion and dielectric constant temperature drift effects, and then performing differential derivation. k 1. k 2. k 3. k 4 are obtained by calculation using the following formulas:

[0051]

[0052]

[0053]

[0054] Where c is the speed of electromagnetic wave propagation in a vacuum, with units of m / s. The coefficient of thermal expansion of the dielectric substrate in the width direction is expressed in ppm / ℃. This represents the temperature coefficient of dielectric constant for the substrate material, expressed in ppm / ℃. The relative permittivity is dimensionless. This represents the initial width of the radiating patch, in meters (m). The coefficient of thermal expansion of the dielectric substrate along its length is expressed in ppm / ℃. This represents the initial length of the radiating patch, in meters (m). ρ is the Poisson's ratio of the dielectric substrate, which is dimensionless.

[0055] Furthermore, the initial state is 20°C and no strain is applied.

[0056] Please see Figure 1 and 2 The present invention also provides an antenna strain sensor, comprising: Antenna strain sensing module unit is used to sense strain and convert it into antenna electromagnetic signals; A signal transmission unit is used to transmit excitation signals to the antenna strain sensing module unit and to transmit the antenna electromagnetic signals. The signal excitation unit is used to output a frequency sweep excitation signal and transmit it to the antenna strain sensing module unit through the signal transmission unit. A temperature compensation unit is used to perform temperature compensation on the electromagnetic signal of the antenna using any of the above-described temperature compensation methods. The signal processing unit is used to process the temperature-compensated antenna electromagnetic signal to obtain the strain magnitude and direction.

[0057] The antenna strain sensing module includes a dielectric substrate and a radiating patch formed on one side of the dielectric substrate; the signal transmission unit includes a microstrip feed line connected to the edge of the radiating patch.

[0058] The connection point between the microstrip feed line and the radiating patch is not at the center of the edge of the radiating patch, and is used to form a bias structure to excite the two radiation modes TM10 and TM01 of the antenna strain sensor, thereby generating two independent resonant frequencies (f). 10 , f 01 It is used to simultaneously sense the magnitude and direction of structural strain; the microstrip feed line is preferably located at three-quarters of the edge of the radiating patch.

[0059] The microstrip feed line is configured as a bias structure at the feed position along the width edge of the graphene radiating patch. This unique asymmetric design disrupts the antenna's symmetry, enabling the excitation of the patch antenna's two fundamental radiation modes, TM10 and TM01, thereby generating two independent resonant frequencies (TM10 and TM01). f 10 , f 01 The two resonant frequencies exhibit specific responses to strain in different directions: among them, transverse strain primarily affects the resonant frequency. f 10 (TM10 mode) produces a shift, while f 01 The overall value remains basically unchanged; longitudinal strain mainly affects the resonant frequency. f 01 (TM01 mode) produces a shift, while f 10 The values ​​remain essentially unchanged. By monitoring the shift modes at two frequencies, both the magnitude and direction of the strain can be characterized simultaneously.

[0060] Two independent resonant frequencies f 10 and f 01 They were set at around 3.5 GHz and 5.5 GHz respectively to obtain higher strain sensing sensitivity.

[0061] Preferably, the radiating patch is a graphene patch; a ground plane is provided on the side of the dielectric substrate opposite to the radiating patch; after optimization by three-dimensional electromagnetic simulation software (such as HFSS), the specific dimensional parameters of the graphene patch antenna sensor are determined, so that its simulated resonant frequency is highly consistent with the design target, and good impedance matching is achieved at both resonant points. The dielectric substrate is preferably made of PET, with a dielectric constant of... ε r The value is 3, and the thickness is 0.35 mm.

[0062] A quarter-wavelength impedance converter is provided at the connection point between the microstrip feed line and the radiating patch. Figure 1 The matching line in the antenna (with a characteristic impedance of 50 ohms) matches the input impedance of the antenna at the resonant frequency with that of the coaxial transmission line, thereby significantly reducing signal transmission loss, ensuring a prominent peak in the return loss curve, and making the resonant frequency data easy to read. The sensor excites dual resonant modes through a bias-fed structure, which can simultaneously sense strain and temperature, and achieves good impedance matching through a quarter-wavelength impedance transformer, ensuring that the resonant frequency is effectively excited and the signal transmission loss is minimized.

[0063] In some alternative implementations, the initial length (L0) of the radiating patch is 20-30 mm, the initial width (W0) is 10-20 mm, and the length of the dielectric substrate is... l The width of the microstrip feed line is 35-45mm, and the width w is 25-36mm. This refers to the width of the end of the microstrip feed line furthest from the radiating patch. l 2 is 1-3mm, and the length w2 is 3-8mm, which is the length of the matching line near the end of the radiating patch. l 1 is 1-2mm, and the width w1 is 2-3mm.

[0064] The antenna strain sensor is also provided with a packaging unit for packaging the antenna strain sensing module unit and the signal transmission unit.

[0065] This invention relates to a sensor designed with a dual resonant frequency mode, capable of simultaneously sensing changes in structural bidirectional strain and ambient temperature. The use of graphene film as the antenna material enhances the antenna's flexibility and corrosion resistance, broadening its application range in structural health monitoring. For patch antenna sensors, ambient temperature alters the dielectric constant of the substrate and causes thermal expansion of the radiating patch, both of which contribute to a shift in the sensor's resonant frequency. Based on this, this invention derives a quantitative relationship between the patch antenna's resonant frequency change and structural strain and ambient temperature. Based on the difference in sensitivity of the antenna's resonant frequency to temperature and bidirectional strain, a temperature compensation mechanism for graphene patch antenna strain sensing is established. This reduces the impact of ambient temperature on the patch antenna sensor's strain measurement results, effectively improving the antenna's strain measurement accuracy and demonstrating significant advantages and broad application prospects in structural health monitoring.

[0066] Example 1 Please see Figure 1 This is a schematic diagram of the structural layers of a flexible graphene patch antenna sensor provided by the present invention. It adopts a layered structure, and the sensor, from top to bottom, includes a radiating patch made of flexible graphene film, a PET dielectric substrate, and a ground plane. The dielectric substrate has a specific relative permittivity (...). ε r = 3) and a defined thickness (0.35 mm), its function is to provide flexible support and ensure an effective electromagnetic structure between the radiating patch and the ground plane. As the core radiating unit, the precise physical dimensions of the radiating patch were determined through theoretical estimation using a transmission line model and optimization using HFSS electromagnetic simulation. Specific optimized dimensional parameters are shown in Table 1 and... Figure 2 .

[0067] Table 1 Optimized graphene antenna sensor size parameters

[0068] Specifically, Figure 1 The antenna sensor employs an off-center feeding structure. This unique feeding method aims to effectively excite the dual-resonance characteristics of the patch antenna, enabling it to operate simultaneously in both TM10 and TM01 dominant modes, corresponding to two different resonant frequencies (f). 10 with f 01 Near the feed point, the structure of the radiating patch was further optimized to form a specific matching line. The dimensions of this matching line were optimized through simulation, and its core function is to achieve impedance matching between the input impedance of the patch antenna and the coaxial transmission line with a characteristic impedance of 50 ohms. This ensures signal transmission efficiency and makes the resonant frequency exhibit a sharp peak on the return loss curve, facilitating accurate monitoring.

[0069] To verify the radiation characteristics and sensing performance of the flexible graphene patch antenna sensor designed in this invention, a three-dimensional finite element electromagnetic simulation was performed using ANSYS HFSS software. The finite element simulation model is as follows: Figure 3 As shown, the main components include a graphene patch antenna sensor (the core analysis object), an air cavity for simulating the free-space radiation environment, and a port for feeding electromagnetic excitation. The graphene patch antenna sensor consists of three parts: a radiating patch, a dielectric substrate, and a ground plane. The radiating patch is made of a material with a conductivity of 1.1 × 10⁻⁶. 6 A graphene film with a thickness of 0.35 mm and a relative permittivity of S / m is used as the dielectric substrate. ε r The material is PET with a dielectric loss tangent of tanδ of 0.008; the ground plane serves as the bottom surface of the sensor and is set as an ideal conductor in the model through the property definition module.

[0070] To accurately simulate the electromagnetic radiation performance of the antenna in three-dimensional space, the entire air cavity surrounding the sensor is defined as the radiation boundary using a property definition module. The size of this air cavity is carefully considered to ensure it is large enough to prevent simulation errors due to insufficient radiation space. After the model is built, a feed port is set to input electromagnetic excitation to the patch antenna sensor, thereby exciting its resonant mode. This simulation selects the waveport mode, placing the waveport at the end of the patch antenna feed line and setting its characteristic impedance to 50Ω to accurately simulate the real-world situation of feeding the antenna sensor via a coaxial transmission line in practical applications.

[0071] Once the finite element simulation model is fully established, the electromagnetic parameters of the graphene patch antenna sensor under electrical signal excitation at different frequencies can be obtained by setting the frequency scanning range. This simulation process effectively analyzes and studies key sensing performance indicators such as return loss, input impedance, and resonant frequency of the antenna, providing a reliable theoretical basis for evaluating its feasibility as a strain sensor. The simulation results are as follows: Figure 4 As shown, the antenna structure exhibits good resonance characteristics and impedance matching at the set frequency point, verifying the correctness and effectiveness of its design.

[0072] based on Figure 1 The graphene patch antenna sensor structure shown in this invention provides a temperature compensation method, comprising the following steps: S1: Obtain the graphene patch antenna sensor in its initial and operating states, along its width direction (corresponding to f). 01 ) and length direction (corresponding to f) 10 Find the two resonant frequencies of and calculate their offset (Δf). 01 , Δf 10Specifically, the return loss-frequency curve of the patch antenna sensor is measured using a vector network analyzer, and the pre-resonant frequency f is extracted. 10 With the resonant frequency f 01 The frequency offset Δf 10 With Δf 01 It is calculated by the difference between the current resonant frequency value and the initial resonant frequency value.

[0073] S2: Based on the change in the two resonant frequencies (Δf) 01 , Δf 10 Construct a system of two linear equations with the change in ambient temperature (ΔT) and the structural strain value (ε) as variables:

[0074]

[0075] This model quantifies the linear superposition relationship between temperature and strain acting on the double resonant frequency.

[0076] S3: Solve the system of two linear equations described in step S2 to decouple the resonant frequency shift caused by changes in ambient temperature and structural strain, thereby enabling strain measurement and temperature compensation.

[0077] In the design concept of this invention, since the response characteristics of the dual resonant frequencies of the patch antenna sensor to ambient temperature and structural strain are different, by establishing a quantitative relationship model between the dual resonant frequencies and temperature and strain, the synchronous measurement and decoupling of temperature and strain can be realized.

[0078] In step S3 of the present invention, the change in ambient temperature (ΔT) and the structural strain value (ε) are obtained by solving the system of two equations, and the solution formula is expressed as follows:

[0079]

[0080] in, k 1, k 2, k 3, k 4 represents the sensitivity coefficients of the two resonant frequencies to temperature and strain, respectively.

[0081] In step S3 of the present invention, the sensitivity coefficient k 1, k 2, k 3, k 4. The material properties and initial structural dimensions of the patch antenna sensor are determined by the material properties of the substrate and the length direction. The material properties include the coefficients of thermal expansion of the dielectric substrate in the width and length directions.α d,w , α d,l The temperature coefficient of dielectric constant of the dielectric substrate ( α ε The Poisson's ratio (μ) of the dielectric substrate and the relative permittivity of the dielectric substrate (μ) ε r The initial structural dimensions include the initial length (L0) and initial width (W0) of the radiating patch.

[0082] In the design concept of this invention, the sensitivity coefficient is obtained by substituting the material properties and initial structural dimensions into the theoretical expression for the resonant frequency that comprehensively considers the thermal expansion and dielectric constant temperature drift effects, and then performing differential derivation:

[0083]

[0084]

[0085]

[0086] Based on the derived formula, by substituting the various dimensional parameters and material electromagnetic parameters of the patch antenna sensor, the sensing sensitivity of the patch antenna sensor to structural strain and ambient temperature can be obtained.

[0087] In step S3 of this invention, the ambient temperature change ΔT and the structural strain value ε are obtained by solving the system of two linear equations. The measured frequency offset Δf is then used. 10 With Δf 01 By substituting into the equations and performing matrix operations, the changes in ambient temperature and the structural strain can be calculated simultaneously. This eliminates the error introduced by temperature changes in strain measurement and achieves accurate temperature compensation. Specifically, k1, k2, k3, and k4 are first calculated, and then the frequency offset Δf is substituted into the equations. 10 With Δf 01 This allows us to obtain the temperature change. Since the effect of temperature on frequency offset is linear, we can calculate the frequency value affected by temperature. By subtracting the temperature-affected portion from the overall frequency offset, we can obtain the frequency offset affected only by strain, thus obtaining an accurate strain value.

[0088] This invention systematically verifies the temperature compensation method by combining finite element simulation and experimental testing. In the simulation verification phase, a three-dimensional electromagnetic model of the flexible graphene patch antenna sensor was first established in ANSYS HFSS software. The patch antenna is fed by an eccentric microstrip transmission line to excite its dual resonant modes. The thermal expansion coefficients of the dielectric substrate material along the lateral and longitudinal directions were set to 75 ppm / ℃ and 60 ppm / ℃, respectively, and its dielectric constant temperature coefficient was set to 80 ppm / ℃. The simulation frequency scan range covered two frequency bands: 3.45–3.55 GHz and 5.45–5.55 GHz, with a frequency resolution set to 0.02 MHz to ensure accurate capture of resonant characteristics. Within a temperature range of 20℃ to 50℃, parameter scanning was performed in 3℃ increments. Return loss curves at each temperature point were obtained through full-wave simulation, and resonant frequency data were accurately extracted.

[0089] Simulation results are as follows Figure 5 As shown, the dual resonant frequencies of the patch antenna are significantly affected by changes in ambient temperature, and both exhibit a good linear decreasing trend with increasing temperature. Through linear fitting, the temperature sensing sensitivities of the two resonant frequencies obtained from the finite element simulation are respectively... 0.0994 MHz / ℃ and The result of 0.1206 MHz / ℃ is highly consistent with the theoretical calculation results (i.e., the calculation formulas for k1 and k3), verifying the accuracy of the simulation model.

[0090] Building upon the study of the effects of temperature alone, a simulation analysis of the temperature-strain coupled field was further conducted. While maintaining the aforementioned parameter settings, the material parameters of the dielectric substrate were set as temperature-dependent variables, and the sensor structural dimensions were dynamically adjusted based on the strain values. The initial dielectric constant of the substrate was set to 3, the temperature range to 20-50℃, and the strain range to 0-5%. A parameter scanning strategy was employed, with each 5℃ increase in temperature and each 1% increase in strain, to systematically study the sensor response characteristics in the coupled field.

[0091] By extracting the resonant points of the return loss curves under different operating conditions, the initial resonant frequency f was obtained. 10 and the resonant frequency f 01 Variation patterns in a temperature-strain coupled field. Figure 6 The table shows the resonant frequency shifts in the length and width directions caused by an increase in ambient temperature from 20℃ to 50℃ under different strain conditions (i.e., the difference between the resonant frequencies measured at 20℃ and 50℃ under the same strain). It can be seen that the frequency shifts in the two directions are basically consistent under different strain conditions. Table 2 shows the resonant frequencies f measured under strain conditions ranging from 0% to 5%. 10 with f 01The temperature sensitivity coefficients were measured. Both frequencies exhibited stable temperature sensitivity, with standard deviations of 0.0040 and 0.0057, respectively. These characteristics clearly demonstrate that the resonant frequency shift of the patch antenna caused by ambient temperature is unaffected by structural strain.

[0092] Table 2 Temperature sensitivity coefficients under different strain conditions

[0093] Based on the above findings, the effects of temperature and strain on the resonant frequency exhibit good independence, providing a theoretical basis for dual-parameter synchronous sensing. By establishing coupling equations between the dual resonant frequencies and temperature and strain, temperature compensation for structural strain was achieved. To verify the compensation effect, the simulation data underwent systematic processing. Figure 7 (a) and Figure 7 Figure (b) shows the changes in the resonant frequency of the patch antenna before and after temperature compensation under two conditions: no strain and 1% strain. Under no strain, the slope of the temperature-frequency fitting line decreases from 0.1206 MHz / ℃ to 7.143 kHz / ℃; under 1% strain, the slope decreases from 0.115 MHz / ℃ to 5.857 kHz / ℃. These data fully demonstrate that the temperature compensation method proposed in this invention can effectively eliminate the influence of temperature changes on strain measurement, significantly improving the measurement accuracy and reliability of the sensor in variable temperature environments. This compensation method provides an effective technical means for achieving high-precision wireless strain monitoring.

[0094] For experimental verification, a temperature control experiment was conducted on the prepared graphene patch antenna sensor. The antenna sensor was placed in a temperature-controlled experimental chamber (e.g., Figure 8 As shown in the figure, the vector network analyzer (R&S ZNLE18 model) was connected to the outside of the enclosure via a coaxial cable passing through the top opening of the enclosure. The experimental temperature range was set to 20℃ to 50℃, with a temperature increment of 3℃. The actual ambient temperature inside the enclosure was accurately measured by temperature and humidity sensors. The scanning frequency range of the vector network analyzer was set to 3.45GHz to 3.55GHz and 5.45GHz to 5.55GHz, for a total of 5001 scan points, with a frequency interval of 0.02 MHz. After the data stabilized, temperature data and antenna return loss data were recorded. Each set of measurements was repeated ten times to obtain the average value. The experimental results are as follows. Figure 9 As shown, when the ambient temperature rises, both resonant frequencies of the patch antenna sensor decrease accordingly, but the two resonant frequencies exhibit different sensitivities to the same ambient temperature change. Specific test data shows: the initial resonant frequency f... 10 The temperature sensitivity is 0.1016 MHz / °C (corresponding to k3), and the correlation coefficient is 0.9887; the resonant frequency f 01The temperature sensitivity was 0.1127 MHz / °C (corresponding to k1), and the correlation coefficient was 0.9905. As shown in Table 3, the experimentally obtained temperature sensitivity is close to the theoretical calculations and finite element simulation results, proving the accuracy of the theoretical results.

[0095] Table 3. Theoretical calculations, simulations, and experimental results of temperature sensitivity.

[0096] This important discovery confirms the feasibility of compensation based on the temperature response difference of dual resonant frequencies. By substituting the experimentally obtained sensitivity coefficients into the aforementioned binary equations, effective decoupling of temperature and strain effects is achieved, providing a reliable technical solution for improving the measurement accuracy of sensors in variable temperature environments.

[0097] Through the above Figures 1 to 9 The graphene-based dual-resonant patch antenna sensor and its temperature compensation method in the illustrated embodiment combine an eccentric feeding structure with dual-resonant characteristics to establish a mathematical model of the strain-temperature coupling relationship, achieving synchronous sensing and temperature compensation of the structural strain magnitude and direction. Through theoretical analysis, finite element simulation, and experimental verification, the effectiveness of the temperature compensation method has been demonstrated, significantly reducing the temperature sensitivity of strain measurement by approximately one order of magnitude and solving the problem of low strain measurement accuracy of patch antenna sensors under varying temperature environments. This method features a clear model, simple calculations, and high accuracy, improving measurement reliability without increasing hardware complexity, and possesses strong engineering applicability.

[0098] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. For example, reasonable adjustments can be made to the selection of the dielectric substrate material, the specific shape and size of the radiating patch, or the specific implementation of the temperature compensation algorithm. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0099] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature compensation method for an antenna strain sensor, characterized in that, Includes the following steps: S1. Obtain the resonant frequencies of the antenna strain sensor in the width and length directions in the initial and operating states, respectively. f 10 and f 01 The frequency offset Δf is obtained by measuring the difference between the resonant frequencies of the operating state and the initial state. 10 With Δf 01 ; S2. The temperature-induced shifts in the two frequencies are obtained using the following formulas: This represents the temperature-induced shift in the resonant frequency f10. This represents the temperature-induced shift in the resonant frequency f01. k 1 represents the sensitivity coefficient of the resonant frequency f01 to temperature. k 2 represents the sensitivity coefficient of the resonant frequency f01 to strain. k 3 is the resonant frequency f 10 Sensitivity coefficient to temperature k 4 is the resonant frequency f 10 Sensitivity coefficient to strain; S3, the resonant frequency of the operating state. f 10 and f 01 Subtract respectively and That is, to obtain the resonant frequency after temperature compensation. f 10 and f 01 .

2. The temperature compensation method for the antenna strain sensor according to claim 1, characterized in that, The initial state is 20°C and no strain is applied.

3. The temperature compensation method for the antenna strain sensor according to claim 1, characterized in that, k 1. k 2. k 3. k 4 are obtained by calculation using the following formulas: Where c is the speed of electromagnetic wave propagation in a vacuum, with units of m / s. The coefficient of thermal expansion of the dielectric substrate in the width direction is expressed in ppm / ℃. This represents the temperature coefficient of dielectric constant for the substrate material, expressed in ppm / ℃. The relative permittivity is dimensionless. This represents the initial width of the radiating patch, in meters (m). The coefficient of thermal expansion of the dielectric substrate along its length is expressed in ppm / ℃. This represents the initial length of the radiating patch, in meters (m). ρ is the Poisson's ratio of the dielectric substrate, which is dimensionless.

4. An antenna strain sensor, characterized in that, include: Antenna strain sensing module unit is used to sense strain and convert it into antenna electromagnetic signals; A signal transmission unit is used to transmit excitation signals to the antenna strain sensing module unit and to transmit the antenna electromagnetic signals. The signal excitation unit is used to output a frequency sweep excitation signal and transmit it to the antenna strain sensing module unit through the signal transmission unit. A temperature compensation unit is used to perform temperature compensation on the electromagnetic signal of the antenna using the temperature compensation method according to any one of claims 1-3; The signal processing unit is used to process the temperature-compensated antenna electromagnetic signal to obtain the strain magnitude and direction.

5. The antenna strain sensor according to claim 4, characterized in that, The antenna strain sensing module unit includes a dielectric substrate and a radiating patch formed on one side of the dielectric substrate. The signal transmission unit includes a microstrip feed line connected to the edge of the radiating patch.

6. The antenna strain sensor according to claim 5, characterized in that, The connection point between the microstrip feed line and the radiating patch is not at the center point of the edge of the radiating patch, and is used to form a bias structure to excite the two radiation modes TM10 and TM01 of the antenna strain sensor.

7. The antenna strain sensor according to claim 5, characterized in that, The radiating patch is a graphene patch; a ground plane is provided on the side of the dielectric substrate opposite to the radiating patch; And / or, the dielectric substrate is made of PET.

8. The antenna strain sensor according to claim 4, characterized in that, A quarter-wavelength impedance transformer is provided at the connection end between the microstrip feed line and the radiating patch to achieve impedance matching. The antenna strain sensor is also provided with a packaging unit for packaging the antenna strain sensing module unit and the signal transmission unit.

9. A detection method for an antenna strain sensor according to any one of claims 4-8, characterized in that, Includes the following steps: S1. Fix the antenna strain sensing module unit onto the surface of the device to be tested; S2. The signal excitation unit transmits a sweep frequency excitation signal to the antenna strain sensing module unit through the signal transmission unit, and receives the antenna electromagnetic signal radiated by the antenna strain sensing module unit. S3. Perform temperature compensation on the electromagnetic signal of the antenna using the temperature compensation method described in any one of claims 1-3; S4. Process the temperature-compensated antenna electromagnetic signal to obtain the strain magnitude and direction of the device under test.

10. The detection method of the antenna strain sensor according to claim 9, characterized in that, The frequency sweep excitation signal includes two frequency bands: 3.45-3.55 GHz and 5.45-5.55 GHz.

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