Precise calibration device and calibration method for FBG intraocular pressure sensor

Abstract

The invention provides a precise calibration device and calibration method for an FBG intraocular pressure sensor, and belongs to the technical field of medical detection instruments and optical fiber sensing. Comprising a fluid coupling base, and a three-dimensional micro-channel network is integrated in the fluid coupling base; the bionic eyeballs and the three-dimensional micro-channel network are communicated with each other to form a simulated aqueous humor chamber; the to-be-calibrated intraocular pressure sensing unit is arranged on the outer surface, away from the fluid coupling base, of the bionic eyeball and used for acquiring the pressure of the bionic eyeball; the fluid driving unit is used for providing fluid for the simulated aqueous humor chamber; the pressure detection unit is used for monitoring the internal pressure of the fluid coupling base; the FBG temperature sensing unit is used for extending into the intersection of each flow channel in the three-dimensional micro-flow channel network to obtain the temperature of fluid in the simulated aqueous humor chamber; and the control and processing terminal is used for acquiring the output of the intraocular pressure sensing unit, the FBG temperature sensing unit and the pressure detection unit and carrying out calibration through a built-in all-optical temperature compensation algorithm.

Description

Technical Field

[0001] This invention relates to the fields of medical device testing and fiber optic sensing technology, and in particular to a precision calibration device and calibration method for FBG intraocular pressure sensors. Background Technology

[0002] Glaucoma, one of the leading causes of blindness worldwide, relies heavily on the monitoring of intraocular pressure (IOP) fluctuations for diagnosis and treatment. Traditional IOP measurement primarily depends on large, desktop hospital equipment, such as applanation tonometers, which struggle to capture peak IOP levels during nighttime or daily activities. Therefore, continuous intraocular pressure monitoring solutions based on smart wearable technology have emerged. Compared to wireless IOP sensors based on inductive coupling, FBG-based smart contact lens solutions have become a research hotspot in this field due to their passive nature, strong resistance to electromagnetic interference, good biocompatibility, and high sensitivity.

[0003] The working principle of FBG sensors is to inversely correlate intraocular pressure (IOP) changes by detecting minute shifts in the Bragg wavelength. Therefore, establishing an accurate and reliable wavelength-IOP calibration curve before clinical application is a prerequisite for ensuring the accuracy of sensor measurements. However, existing IOP sensor calibration technologies face several significant technical bottlenecks in practical applications, mainly in the following three dimensions: First, distortion in the reproduction of the biomechanical environment. Existing calibration devices mostly use rigid stainless steel pressure chambers or simple planar thin-film devices, which cannot realistically reproduce the complex curvature characteristics of the human cornea and the viscoelastic properties of biological tissues. When smart contact lenses are worn on a soft cornea with a specific Young's modulus, the resulting contact stress distribution is drastically different from that on a rigid substrate. If this "lens-eye" contact mechanical coupling mechanism cannot be accurately simulated during the calibration stage, it will lead to a significant deviation between the calibrated sensitivity coefficient and the actual wearing condition of the human eye, directly affecting the reliability of diagnostic data. Some existing technologies propose using PDMS material to fabricate bionic eyeballs, but these often lack precise matching of contact surface roughness and material modulus, making it difficult to completely eliminate measurement errors caused by substrate hardness mismatch. Secondly, there is the compliance error in the fluid control system. Regarding fluid control and structural integration, existing bionic calibration devices mostly use discrete flexible tubes with multi-connectors to build flow path systems. This non-integrated connection method has significant drawbacks: on the one hand, flexible tubes exhibit a "volume compliance" effect under micro-pressure changes, meaning that the micro-expansion of the tubes themselves absorbs some pressure transmission, leading to hysteresis and nonlinearity in pressure loading; on the other hand, multiple connectors increase the system's dead volume and leakage risk, and the connection between the flexible eyeball and the rigid tubes is prone to creep or displacement during pressurization, making it difficult to construct a long-term stable, sealed, high-rigidity precision test field. Thirdly, there is a lack of decoupling for temperature-stress cross-sensitivity. This is a core challenge unique to FBG sensors. The center wavelength drift of FBG is the result of the combined effects of intraocular pressure-induced strain and temperature. Existing calibration devices are mostly designed for inductively coupled sensors and often lack high-precision temperature decoupling mechanisms, often performing simple pressure tests in an open room temperature environment. Because FBG is extremely sensitive to temperature, even small temperature fluctuations in the experimental environment can cause significant wavelength drift. This thermally induced error is easily misinterpreted as changes in intraocular pressure, leading to severe distortion of the calibration curve.

[0004] Therefore, it is essential to provide a precision calibration device and method for FBG intraocular pressure sensors that can highly replicate the mechanical environment of the human eye, use a rigid integrated flow path to eliminate compliance errors, have micro-pressure precision control capabilities, and achieve temperature compensation during demodulation to eliminate measurement errors. Summary of the Invention

[0005] In view of this, the present invention proposes a precision calibration device and calibration method for FBG intraocular pressure sensors by constructing a high-fidelity biomimetic eyeball mechanical environment and an integrated fluid coupling system, combined with an all-optical temperature compensation algorithm, to achieve precise micro-pressure loading and high-precision passive calibration of the smart contact lens intraocular pressure sensor, thereby eliminating measurement errors caused by environmental temperature fluctuations and contact stress mismatch.

[0006] On one hand, the present invention provides a precision calibration device for an FBG intraocular pressure sensor, comprising: The fluid coupling base integrates a three-dimensional microchannel network. Different surfaces of the fluid coupling base are equipped with injection ports, pressure measurement ports, temperature measurement ports, and hemispherical mounting platforms that are interconnected with the three-dimensional microchannel network. The bionic eyeball is sealed and installed on the hemispherical mounting platform of the fluid coupling base. The internal cavity of the bionic eyeball is interconnected with the three-dimensional microfluidic network to form a simulated aqueous humor chamber. The intraocular pressure sensing unit to be calibrated is set on the outer surface of the bionic eyeball away from the fluid coupling base, and is used to obtain the pressure of the bionic eyeball. The fluid drive unit, which is sealed to the injection interface, is used to supply fluid to the simulated aqueous humor chamber; The pressure detection unit, which is sealed to the pressure measurement interface, is used to monitor the internal pressure of the fluid coupling base; The FBG temperature sensing unit, which is sealed to the temperature measurement interface, is used to extend into the intersection of various channels inside the three-dimensional microfluidic network to obtain the fluid temperature in the simulated aqueous humor chamber. The fiber optic demodulator is connected to the intraocular pressure sensing unit and the FBG temperature sensing unit to be calibrated, respectively, and is used to demodulate the optical signal and output the electrical signal. The control and processing terminal is connected to the output signals of the fiber optic demodulator and the pressure detection unit. It calibrates the intraocular pressure sensing unit to be calibrated through the built-in all-optical temperature compensation algorithm.

[0007] Based on the above technical solution, preferably, the intraocular pressure sensing unit to be calibrated is equipped with a main measurement grating, the FBG temperature sensing unit is equipped with a reference grating, the main measurement grating and the reference grating are respectively connected to different optical paths of the fiber optic demodulator, and the fiber optic demodulator synchronously acquires the wavelength signals of the main measurement grating and the reference grating.

[0008] Based on the above technical solutions, preferably, the fluid coupling base is made of pressure-resistant photosensitive resin additive manufacturing, and the fluid coupling base does not expand or deform under pressure; a simulated aqueous humor chamber simulating the human cornea is arranged at the center of the top of the fluid coupling base.

[0009] Preferably, the bionic eyeball is made of medical-grade silicone with a two-component addition structure of silicone matrix and curing agent. The ratio of silicone matrix to curing agent is 20:1-10:1. The mixture is then vacuum degassed, heated and cured, and cast into an aluminum alloy mold. The elastic modulus of the bionic eyeball is controlled to be 0.3MPa±0.05Mpa.

[0010] Based on the above technical solutions, preferably, the fluid driving unit is a microfluidic injection pump, which is used to provide nanoliter-level fluid to the simulated aqueous humor chamber to simulate smooth intraocular pressure changes with a resolution greater than 0.1 mmHg.

[0011] On the other hand, the present invention also provides a method for precise calibration of an FBG intraocular pressure sensor, comprising the following steps: S1: The above-mentioned precision calibration device for FBG intraocular pressure sensor is configured, and the intraocular pressure sensing unit to be calibrated forms a corneal contact lens-eyeball coupling structure at the bionic eyeball. S2: Initialization and venting: Start the fluid drive unit to inject fluid into the simulated aqueous humor chamber at a low flow rate until the fluid fills the bionic eyeball and removes all tiny air bubbles, establish the preset basic pre-tightening pressure, allow the bionic eyeball to expand to the standard geometric shape and maintain a stable preset duration, and eliminate initial creep. S3: Under the basic preload pressure, adjust the fluid temperature, use the reference grating to analyze the change in ambient temperature, and combine the substrate thermal induced strain theory to accurately determine the temperature response correlation characteristics between the main measurement grating and the reference grating; S4: Pressure calibration cycle: The fluid drive unit performs a pressure increase-decrease cycle within the pressure setting range. The pressure increase or decrease step is 1 mmHg. After adjusting one pressure step, the pressure is kept constant for a period of time to eliminate the dynamic hysteresis effect of the bionic eyeball. After the pressure stabilizes, the sampling data corresponding to the center wavelength of the main measurement grating, the center wavelength of the reference grating, the current temperature, and the current pressure are recorded. S5: Data Decoupling and Performance Evaluation: Based on the data recorded in step S4, a rheological model is introduced to eliminate creep error in dynamic measurement, taking into account the inherent viscoelastic characteristics of the bionic eyeball and corneal contact lens substrate material. A dynamic equation for wavelength drift in the step pressure stabilization stage is constructed, and the dynamic equation is solved to obtain pressure response data that eliminates the influence of creep. A high-confidence intraocular pressure sensitivity coefficient that eliminates the influence of viscoelastic hysteresis is obtained by fitting with the least squares method.

[0012] Preferably, step S3 involves defining the center wavelength of the main measurement grating of the intraocular pressure sensing unit to be calibrated as... l 1. Define the center wavelength of the reference grating of the FBG temperature sensing unit as... l 2. Based on the sensing characteristics of the FBG grating, the wavelength shift is linearly related to the pressure and temperature changes. The proposed response equations are as follows: ,in The main grating is subject to relative wavelength shift. The reference grating is shifted relative to the wavelength; P e The optical-elastic coefficient of the optical fiber; e lens ( p ) represents the strain of the lens substrate in a bionic eyeball; α f The coefficient of thermal expansion of optical fiber; x f The optical fiber thermo-optic coefficient; △T This refers to the change in temperature. or The structural coupling factor characterizes the efficiency of transmitting the deformation of the simulated eyeball surface to the main measurement grating. The thermally induced strain coefficient of the substrate is determined by the substrate modulus, substrate cross-sectional area, and fiber thermal expansion coefficient; the response equations are solved to obtain the temperature response correlation characteristics between the main measurement grating and the reference grating.

[0013] Preferably, the introduction of a rheological model in step S5 to eliminate creep errors in dynamic measurements and construct the dynamic equation for wavelength drift during the step pressure stabilization stage is used to obtain the time-domain response curve of the center wavelength of the main measurement grating during the pressure stabilization stage. This causes the center wavelength of the main measurement grating to drift during the pressure holding phase. It obeys the following dynamic equations. ,in, This represents the true pressure response component under ideal elastic conditions. β The creep characteristic coefficient, t The time constant is the hysteresis. t For the duration to which the pressure is kept constant.

[0014] Further preferably, the solution to the kinetic equation in step S5 to obtain pressure response data that eliminates the influence of creep involves performing an iterative calculation based on the Levenberg-Marquardt damped least squares method: constructing an objective function and collecting time windows for maintaining constant pressure. t Data from N sampling points within ( t i , y i ), y i for t i Based on the observed center wavelength of the master measurement grating at time step, construct the objective function of residual sum of squares. S ( i ), The parameter vector to be estimated Then, iterative optimization is performed, utilizing the Jacobian matrix. J And the approximate form of the Hessian matrix, ,in m The damping factor, r For the residual vector, the subscripts are... k +1 and k Representing the next iteration and the current iteration number, update the parameter vector until the objective function is reached. S ( i Convergence; when the iterative process converges, the optimal solution is obtained. Based on the model properties, the steady-state wavelength shift after the material is fully relaxed is obtained. , .

[0015] Preferably, the pressure calibration cycle described in step S4 is a given pressure range of 10 mmHg to 50 mmHg, where the pressure is kept constant for 15 seconds after each step.

[0016] The present invention provides a precision calibration device and calibration method for FBG intraocular pressure sensors, which has the following advantages compared with the prior art: 1. This invention uses an integrated 3D printed base to replace the traditional "hose + multi-connector" connection method, effectively eliminating the volume compliance effect of flexible pipelines and the dead volume at the joints, significantly improving the system's dynamic response capability and control rigidity to minute pressure changes, and ensuring a strict linear relationship between micro-liter fluid injection and intraocular pressure changes.

[0017] 2. This invention innovatively introduces a reference FBG into the fluid inside the base, realizing co-source, synchronous, and in-situ monitoring of the thermal environment. Combined with the differential algorithm, the system can output pure pressure response data even in non-constant temperature experimental environments, completely solving the problem of temperature cross-sensitivity that is difficult for FBG sensors to overcome.

[0018] 3. The introduction of silicone eyeballs and their optimized encapsulation with rigid bases successfully reproduced the complex contact mechanical coupling mechanism between the corneal contact lens and the eyeball, avoiding calibration errors caused by the rigid base and improving calibration accuracy.

[0019] 4. The method provided by this invention can not only obtain sensitivity, but also automatically quantify key industrial indicators such as linearity, hysteresis and repeatability of the sensor, providing a standardized quality testing method for the clinical translation of smart contact lenses. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a structural block diagram of a device for precise calibration of an FBG intraocular pressure sensor and a calibration method according to the present invention. Figure 2 This is a schematic diagram of the fluid coupling base and bionic eyeball combined in the present invention, which is a precision calibration device and calibration method for FBG intraocular pressure sensors. Figure 3 This invention relates to the relationship between the accuracy and precision of a precision calibration device and method for FBG intraocular pressure sensors.

[0022] Reference numerals: 1. Fluid drive unit; 2. Fluid coupling base; 3. Pressure detection unit; 4. Intraocular pressure sensing unit to be calibrated; 5. FBG temperature sensing unit; 6. Fiber optic demodulator; 7. Control and processing terminal; 8. Bionic eyeball; 9. Simulated aqueous humor chamber; a. Liquid injection interface; b. Pressure measurement interface; c. Temperature measurement interface. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Existing intraocular pressure sensor calibration technologies suffer from issues such as biomechanical simulation distortion, severe temperature cross-sensitivity interference, and insufficient fluid control precision. Therefore, if... Figure 1 As shown, in one aspect, the present invention provides a precision calibration device for an FBG intraocular pressure sensor, comprising:

[0025] The fluid coupling base 2 integrates a three-dimensional microchannel network inside. Different surfaces of the fluid coupling base 2 are equipped with a liquid injection interface a, a pressure measurement interface b, a temperature measurement interface c, and a hemispherical mounting platform that are interconnected with the three-dimensional microchannel network. The bionic eyeball 8 is sealed and installed on the hemispherical mounting platform of the fluid coupling base 2. The internal cavity of the bionic eyeball 8 is interconnected with the three-dimensional microfluidic network to form a simulated aqueous humor chamber 9. The intraocular pressure sensing unit 4 to be calibrated is set on the outer surface of the bionic eyeball 8 away from the fluid coupling base 2, and is used to obtain the pressure of the bionic eyeball 8. The fluid drive unit 1 is sealed to the injection interface a and is used to supply fluid to the simulated aqueous humor chamber 9. Pressure detection unit 3 is sealed to pressure measurement interface b and is used to monitor the internal pressure of fluid coupling base 2; The FBG temperature sensing unit 5 is sealed to the temperature measurement interface c and is used to extend into the intersection of each channel inside the three-dimensional microfluidic network to obtain the fluid temperature inside the simulated aqueous humor chamber 9. The fiber optic demodulator 6 is connected to the intraocular pressure sensing unit 4 and the FBG temperature sensing unit 5 to be calibrated, respectively, and is used to demodulate the optical signal and output the electrical signal. The control and processing terminal 7 is connected to the output signals of the fiber optic demodulator 6 and the pressure detection unit 3. It calibrates the intraocular pressure sensing unit 4 to be calibrated through the built-in all-optical temperature compensation algorithm.

[0026] In this embodiment, the fluid coupling base 2, serving as the core of fluid interaction, is manufactured using high-precision additive manufacturing technology, specifically stereolithography 3D printing. The material chosen is a high-pressure resistant photosensitive resin with a Young's modulus greater than 2 GPa, ensuring that the base itself does not expand or deform under microfluidic pressurization. The internal three-dimensional microchannel network has optimized channel dimensions, with a preferred diameter of 1.5 mm to minimize flow resistance while controlling dead volume. A hemispherical mounting platform adapted to the physiological characteristics of the human eye is located at the top, serving as the space for placing the simulated eyeball 8. The simulated eyeball 8 is interconnected with the three-dimensional microchannel network to form a simulated aqueous humor chamber 9. In this embodiment, the radius of curvature of the simulated aqueous humor chamber is selected as 7.8 mm to simulate the corneal parameters of a standard adult eye. Figure 2 As shown, the fluid coupling base 2 has three different sides equipped with a liquid injection port a, a pressure measurement port b, and a temperature measurement port c, respectively. The ports are preferably designed with Luer tapered joints, but threaded ports, flange ports, or barbed hose ports can also be used according to actual needs.

[0027] The fabrication of the bionic eyeball 8 is crucial in this embodiment. The bionic eyeball 8 is made of a two-component addition-curing medical-grade silicone matrix and curing agent. The ratio of the silicone matrix to the curing agent is 20:1-10:1, mixed and vacuum-degassed, then cured by heating and cast using an aluminum alloy mold. The surface roughness of the aluminum alloy mold cavity is strictly controlled to approximately Ra 0.02μm. The elastic modulus of the bionic eyeball 8 is controlled to 0.3MPa±0.05MPa, thus highly replicating the hardness of a real eyeball in biomechanical terms. The bottom of the silicone eyeball and the hemispherical mounting platform at the top of the 3D-printed fluid coupling base 2 are both treated with oxygen plasma surface activation, then coated with a thin layer of biocompatible silicone adhesive, and cured under pressure. This allows the internal cavity of the silicone bionic eyeball 8 to form a completely connected, dead-volume-free, and highly airtight simulated aqueous humor chamber 9 with the three-dimensional microfluidic network inside the fluid coupling base 2.

[0028] Regarding the fluid circuit, this embodiment constructs a highly rigid fluid circuit. The first lateral interface of the fluid coupling base 2, namely the injection interface a, is connected to the fluid drive unit 1 via a rigid PTFE conduit with an inner diameter of 0.5 mm. In this embodiment, the fluid drive unit 1 is preferably a microfluidic injection pump equipped with a precision micro-injection component driven by a stepper motor. In this embodiment, a 500 μL glass injector is preferred, capable of injecting or extracting degassed distilled water into the cavity with flow accuracy at the microliter or even nanoliter level. Specifically, in this embodiment, the accuracy can reach 0.1 μL / min and nanoliter ultra-micro-step volume, thereby achieving pulsation-free, highly linear pressure loading, providing nanoliter-level fluid to the simulated aqueous humor chamber 9, and simulating smooth intraocular pressure changes with a resolution greater than 0.1 mmHg. The second lateral interface of the fluid coupling base 2, namely the pressure measurement interface b, is connected to a pressure monitoring unit 3 with an accuracy better than 1 Pa. As a preferred embodiment, this unit uses a high-precision digital pressure sensor as the calibration "true value" data. The third lateral interface of the fluid coupling base 2, namely the temperature measurement interface c, is used to install the FBG temperature sensing unit 5. A fiber optic probe encapsulated with a reference grating is inserted through a customized sealed connector, so that its sensing end is directly immersed in the fluid channel convergence point inside the fluid coupling base 2, ensuring that the temperature measured by the reference grating is completely consistent with the fluid temperature in the simulated aqueous humor chamber 9. The intraocular pressure sensor 4 to be calibrated is worn on the anterior surface of the bionic eyeball 8. The main measuring grating of the intraocular pressure sensor 4 to be calibrated and the reference grating of the FBG temperature sensor 5 in the fluid coupling base 2 are respectively connected to different channels of the same multi-channel fiber optic demodulator 6 via fiber optic patch cords. The fiber optic demodulator 6 synchronously acquires the wavelength signals of the main measuring grating and the reference grating.

[0029] In addition, the fluid drive unit 1, pressure detection unit 3, and fiber optic demodulator 6 all establish communication connections with the control and processing terminal 7 through a standard data communication interface. In this embodiment, to balance transmission rate and versatility, the communication interface preferably uses a USB interface. However, in other implementation scenarios, RS485 industrial bus, Ethernet, GPIB interface, or wireless Bluetooth communication module can also be selected depending on the device spacing and anti-interference requirements. The control and processing terminal 7 has built-in automatic calibration software based on a professional measurement and control development platform, preferably written in LabVIEW or Python. It can read pressure feedback and run a PID algorithm to control the fluid drive unit 1, achieving closed-loop pressure locking.

[0030] In addition, the present invention also provides a method for precise calibration of FBG intraocular pressure sensors, comprising the following steps: S1: The above-mentioned precision calibration device for FBG intraocular pressure sensor is configured, and the intraocular pressure sensing unit 4 to be calibrated forms a corneal contact lens-eyeball coupling structure at the bionic eyeball 8.

[0031] S2: Initialization and venting: Start the fluid drive unit 1 and inject fluid into the simulated aqueous humor chamber 9 at a low flow rate until the fluid fills the bionic eyeball 8 and removes all tiny air bubbles, establish a preset base pre-tightening pressure, such as 10 mmHg, so that the bionic eyeball 8 expands to a standard geometric shape and remains stable for a preset time, which is 5 minutes, to eliminate initial creep.

[0032] S3: Under the preload pressure, the fluid temperature is adjusted, and the ambient temperature change is analyzed using a reference grating. Combined with the thermal induced strain theory of the substrate, the temperature response correlation characteristics between the main measurement grating and the reference grating are accurately determined.

[0033] Step S3 involves defining the center wavelength of the main measurement grating of the intraocular pressure sensing unit 4 to be calibrated as... l 1. Define the center wavelength of the reference grating of the FBG temperature sensing unit 5 as... l 2. Based on the sensing characteristics of the FBG grating, the wavelength shift is linearly related to the pressure and temperature changes. The proposed response equations are as follows: ,in The main grating is subject to relative wavelength shift. The reference grating is shifted relative to the wavelength; P e The optical-elastic coefficient of the optical fiber; e lens ( p ) represents the strain of the lens substrate of the bionic eyeball 8; α f The coefficient of thermal expansion of optical fiber; x f The optical fiber thermo-optic coefficient;△T This refers to the change in temperature. or The structural coupling factor characterizes the efficiency of transmitting the deformation of the simulated eyeball surface to the main measurement grating. The thermally induced strain coefficient of the substrate. Through the base modulus E s , base cross-sectional area A s thermal expansion coefficient of the substrate α s and the thermal expansion coefficient of optical fiber α f Determine the solution; solve the response equations to obtain the temperature response correlation characteristics between the master measurement grating and the reference grating. The introduction of the substrate thermally induced strain coefficient effectively corrects the temperature-stress cross-sensitivity residual caused by substrate thermal expansion mismatch in traditional calibration.

[0034] S4: Pressure calibration cycle: The fluid drive unit 1 executes a pressure increase-decrease cycle within the pressure setting range. The pressure increase or decrease step is 1 mmHg. After adjusting the pressure step, the pressure is kept constant for a period of time to eliminate the dynamic hysteresis effect of the bionic eyeball 8. After the pressure stabilizes, the sampling data corresponding to the center wavelength of the main measurement grating, the center wavelength of the reference grating, the current temperature, and the current pressure are recorded.

[0035] The pressure calibration cycle described in step S4 is to maintain a constant pressure for 15 seconds after each step of movement, given a pressure range of 10 mmHg to 50 mmHg.

[0036] S5: Data Decoupling and Performance Evaluation: Based on the inherent viscoelastic characteristics of the bionic eyeball 8 and the corneal contact lens substrate material, and using the data recorded in step S4, a rheological model is introduced to eliminate creep errors in dynamic measurements. A dynamic equation for wavelength drift during the step pressure stabilization phase is constructed, and the dynamic equation is solved to obtain pressure response data that eliminates the influence of creep. A high-confidence intraocular pressure sensitivity coefficient that eliminates the influence of viscoelastic hysteresis is obtained by fitting using the least squares method.

[0037] The introduction of a rheological model in step S5 to eliminate creep errors in dynamic measurements and to construct the dynamic equation for wavelength drift during the step pressure stabilization stage is used to obtain the time-domain response curve of the center wavelength of the main measurement grating during the pressure stabilization stage. This causes the center wavelength of the main measurement grating to drift during the pressure holding phase. It obeys the following dynamic equations. ,in, This represents the true pressure response component under ideal elastic conditions. β The creep characteristic coefficient, t The time constant is the hysteresis. tFor the duration to which the pressure is kept constant.

[0038] This invention introduces the Kelvin-Voigt rheological model to eliminate creep errors in dynamic measurements. During each constant pressure phase of the calibration process (15 seconds in this embodiment), the device not only acquires a single final data point, but also records the time-domain response curve of the main measurement grating at a high sampling rate, such as 100Hz, for the corresponding wavelength within that time period.

[0039] Solving the kinetic equations to obtain pressure response data that eliminates the effects of creep involves performing iterative calculations based on the Levenberg-Marquardt damped least squares method: constructing the objective function and collecting time windows for maintaining constant pressure. t within N Data from sampling points ( t i , y i ), y i for t i Based on the observed center wavelength of the master measurement grating at time step, construct the objective function of residual sum of squares. S ( i ), The parameter vector to be estimated Then, iterative optimization is performed, utilizing the Jacobian matrix. J And the approximate form of the Hessian matrix, ,in m The damping factor, r For the residual vector, the subscripts are... k +1 and k Representing the next iteration and the current iteration number, update the parameter vector until the objective function is reached. S ( i Convergence; when the iterative process converges, the optimal solution is obtained. Based on the model properties, the steady-state wavelength shift after the material is fully relaxed is obtained. , Time window t The corresponding length is [0, 15] seconds. Through this dynamic compensation algorithm, this method can accurately predict the true response value of the material in a fully relaxed state within a finite time of maintaining constant pressure, thereby completely eliminating the dynamic hysteresis error introduced by different pressurization rates or insufficient holding time.

[0040] To better evaluate the performance of the intraocular pressure sensing unit 4 to be calibrated, it was also evaluated from aspects such as hysteresis, repeatability, and accuracy.

[0041] 1. Hysteresis Hysteresis abbreviated as H Due to the elastic aftereffect and elastic hysteresis of elastic materials, elastic elements do not immediately return to their initial state after the applied force is removed. This causes a back-and-forth difference in multiple measurements by the instrument, also known as hysteresis error. The absolute value Δ of the maximum difference between the average forward and reverse stroke wavelength values ​​during the pressure cycle test of the intraocular pressure sensing unit is calculated. H max Then divide by the full-scale output value. l ES The hysteresis error can then be calculated. e H : .

[0042] 2. Repeatability Repeatability Repeatability error refers to the difference between repeated measurements under the same testing environment, including testing procedures, personnel, and natural conditions. It is primarily calculated using Bessel's formula. First, the subsample standard deviation during loading and unloading is obtained. Then calculate the standard deviation of the sensor subsamples. The repeatability error of the sensor can be obtained from the subsample standard deviation. :

[0043] , , , ,in i =1,2,…, N This indicates the number of test points during loading and testing. and The first two steps in the loading and unloading process, respectively. i Point 1 j The wavelength value of the second time. , These are the average values ​​for the loading and unloading processes, respectively. n The number of load / unload loops. or The inclusion factor, typically taken as 2-3 according to the range method; the denominator It is the maximum range of change in the sensor's output wavelength.

[0044] 3. Measurement accuracy Accuracy of MeasurementWhen evaluating sensor performance, a key performance indicator is measurement accuracy. Generally, measurement accuracy includes precision and accuracy. From a measurement perspective, precision characterizes the difference between multiple measurements of the same point, i.e., the random error of the measured value; accuracy, on the other hand, characterizes the difference between the measured value and the true or specified value, i.e., the systematic error of the measured value. In metrology, accuracy grades are used to approximate the degree of measurement accuracy, comprehensively reflecting both precision and accuracy. The relationship between them is as follows: Figure 3 As shown.

[0045] In engineering, accuracy levels are generally expressed as a series of percentage values. Under specific measurement conditions, the data measured by the pressure sensor under test is compared with that of a standard pressure sensor, or the pressure sensor under test is used to measure a known standard pressure. The maximum absolute error between the measured value and the standard value is determined. , and full-scale output value The ratio between them is the sensor's maximum reference error. This error is a fundamental error of the measurement system. Based on this error, the accuracy level of the overall measurement system can be obtained. .

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A precision calibration device for FBG intraocular pressure sensors, characterized in that, include: The fluid coupling base integrates a three-dimensional microchannel network. Different surfaces of the fluid coupling base are equipped with injection ports, pressure measurement ports, temperature measurement ports, and hemispherical mounting platforms that are interconnected with the three-dimensional microchannel network. The bionic eyeball is sealed and installed on the hemispherical mounting platform of the fluid coupling base. The internal cavity of the bionic eyeball is interconnected with the three-dimensional microfluidic network to form a simulated aqueous humor chamber. The intraocular pressure sensing unit to be calibrated is set on the outer surface of the bionic eyeball away from the fluid coupling base, and is used to obtain the pressure of the bionic eyeball. The fluid drive unit, which is sealed to the injection interface, is used to supply fluid to the simulated aqueous humor chamber; The pressure detection unit, which is sealed to the pressure measurement interface, is used to monitor the internal pressure of the fluid coupling base; The FBG temperature sensing unit, which is sealed to the temperature measurement interface, is used to extend into the intersection of various channels inside the three-dimensional microfluidic network to obtain the fluid temperature in the simulated aqueous humor chamber. The fiber optic demodulator is connected to the intraocular pressure sensing unit and the FBG temperature sensing unit to be calibrated, respectively, and is used to demodulate the optical signal and output the electrical signal. The control and processing terminal is connected to the output signals of the fiber optic demodulator and the pressure detection unit. It calibrates the intraocular pressure sensing unit to be calibrated through the built-in all-optical temperature compensation algorithm.

2. The precision calibration device for an FBG intraocular pressure sensor according to claim 1, characterized in that, The intraocular pressure sensing unit to be calibrated is equipped with a main measurement grating, and the FBG temperature sensing unit is equipped with a reference grating. The main measurement grating and the reference grating are respectively connected to different optical paths of the fiber optic demodulator. The fiber optic demodulator synchronously acquires the wavelength signals of the main measurement grating and the reference grating.

3. The precision calibration device for an FBG intraocular pressure sensor according to claim 1, characterized in that, The fluid coupling base is made of pressure-resistant photosensitive resin additive manufacturing. The fluid coupling base does not expand in volume or deform under pressure. A simulated aqueous humor chamber, simulating the human cornea, is arranged at the center of the top of the fluid coupling base.

4. The precision calibration device for an FBG intraocular pressure sensor according to claim 3, characterized in that, The bionic eyeball is made of medical-grade silicone with a two-component addition structure of silicone matrix and curing agent. The ratio of silicone matrix to curing agent is 20:1-10:

1. The mixture is then vacuum degassed and cured by heating before being cast into an aluminum alloy mold. The elastic modulus of the bionic eyeball is controlled to be 0.3MPa±0.05Mpa.

5. The precision calibration device for an FBG intraocular pressure sensor according to claim 1, characterized in that, The fluid drive unit is a microfluidic injection pump used to provide nanoliter-level fluid to the simulated aqueous humor chamber, simulating smooth intraocular pressure changes with a resolution greater than 0.1 mmHg.

6. A precision calibration device and calibration method for FBG intraocular pressure sensors, characterized in that, Includes the following steps: S1: Configure the precision calibration device for FBG intraocular pressure sensor as described in any one of claims 2-5, wherein the intraocular pressure sensing unit to be calibrated forms a corneal contact lens-eyeball coupling structure at the bionic eyeball. S2: Initialization and venting: Start the fluid drive unit to inject fluid into the simulated aqueous humor chamber at a low flow rate until the fluid fills the bionic eyeball and removes all tiny air bubbles, establish the preset basic pre-tightening pressure, allow the bionic eyeball to expand to the standard geometric shape and maintain a stable preset duration, and eliminate initial creep. S3: Under the basic preload pressure, adjust the fluid temperature, use the reference grating to analyze the change in ambient temperature, and combine the substrate thermal induced strain theory to accurately determine the temperature response correlation characteristics between the main measurement grating and the reference grating; S4: Pressure calibration cycle: The fluid drive unit performs a pressure increase-decrease cycle within the pressure setting range. The pressure increase or decrease step is 1 mmHg. After adjusting one pressure step, the pressure is kept constant for a period of time to eliminate the dynamic hysteresis effect of the bionic eyeball. After the pressure stabilizes, the sampling data corresponding to the center wavelength of the main measurement grating, the center wavelength of the reference grating, the current temperature, and the current pressure are recorded. S5: Data Decoupling and Performance Evaluation: Based on the data recorded in step S4, a rheological model is introduced to eliminate creep error in dynamic measurement, taking into account the inherent viscoelastic characteristics of the bionic eyeball and corneal contact lens substrate material. A dynamic equation for wavelength drift in the step pressure stabilization stage is constructed, and the dynamic equation is solved to obtain pressure response data that eliminates the influence of creep. A high-confidence intraocular pressure sensitivity coefficient that eliminates the influence of viscoelastic hysteresis is obtained by fitting with the least squares method.

7. The precision calibration device and calibration method for an FBG intraocular pressure sensor according to claim 6, characterized in that, Step S3 involves defining the center wavelength of the main measurement grating of the intraocular pressure sensing unit to be calibrated as... λ 1. Define the center wavelength of the reference grating of the FBG temperature sensing unit as... λ 2. Based on the sensing characteristics of the FBG grating, the wavelength drift is linearly related to the pressure change and temperature change. The response equations of the main grating relative to the wavelength drift and the reference grating relative to the temperature change are proposed. The response equations are solved to obtain the temperature response correlation characteristics of the main measurement grating and the reference grating.

8. The precision calibration device and calibration method for an FBG intraocular pressure sensor according to claim 6, characterized in that, The introduction of a rheological model in step S5 to eliminate creep errors in dynamic measurements and to construct the dynamic equation for wavelength drift during the step pressure stabilization stage is used to obtain the time-domain response curve of the center wavelength of the main measurement grating during the pressure stabilization stage. The center wavelength drift of the master measurement grating during the pressure holding stage The dynamic equations are derived, and by solving them, the true pressure response components under ideal elastic conditions are obtained. creep characteristic coefficient β Hysteresis time constant τ Pressure response data after removing the effects of creep for three unknowns.

9. A precision calibration device and calibration method for an FBG intraocular pressure sensor according to claim 8, characterized in that, The step S5 involves solving the dynamic equation to obtain pressure response data that eliminates the influence of creep. This is achieved by performing an iterative calculation based on the Levenberg-Marquardt damped least squares method. Once the iterative process converges, the steady-state wavelength shift corresponding to the optimal solution after the material is fully relaxed is obtained.

10. A precision calibration device and calibration method for an FBG intraocular pressure sensor according to claim 6, characterized in that, The pressure calibration cycle described in step S4 is to maintain a constant pressure for 15 seconds after each step of movement, given a pressure range of 10 mmHg to 50 mmHg.

Images