Dual-frequency csrr blood glucose detection sensor and non-invasive blood glucose detection method thereof

Abstract

This invention belongs to the field of biomedical detection equipment and sensor technology, and proposes a dual-frequency CSRR sensor with both high resonance depth detection sensitivity and high resonance frequency detection sensitivity, along with a non-invasive blood glucose detection method. The dual-frequency CSRR blood glucose detection sensor and its non-invasive blood glucose detection method include an open-circuit / combiner microstrip line, a substrate, and complementary open-loop resonator units, wherein: the open-circuit / combiner microstrip line is etched on a copper layer on the top of the substrate; two double-ring circular dual-frequency complementary open-loop resonator CSRR units and two single-ring circular dual-frequency complementary open-loop resonator CSRR units are etched on a copper layer on the bottom of the substrate; the symmetry line of the four CSRR units is perpendicular to the axis of the open-circuit / combiner microstrip line; blood glucose is tested using the above sensor. It is mainly applied in the design and manufacturing of blood glucose monitoring devices.

Description

Technical Field

[0001] This invention belongs to the field of biomedical detection and sensor technology, and relates to a dual-frequency complementary open-loop resonant ring (CSRR) sensor with both amplitude and frequency detection sensitivity and a non-invasive blood glucose detection method thereof. Background Technology

[0002] Diabetes mellitus is a metabolic disease characterized by high blood sugar and accompanied by various complications. Monitoring blood glucose levels can effectively help diabetic patients manage their condition. Currently, invasive blood glucose monitoring methods are commonly used, but these methods pose risks of pain and infection to diabetic patients. Furthermore, frequent invasive blood glucose testing can lead to decreased adherence to medical advice, reduced self-management, and ultimately, a worsening of the condition.

[0003] Non-invasive blood glucose testing methods overcome the drawbacks of invasive methods, causing no pain or discomfort during measurement and making the process safer and more comfortable for diabetic patients. Based on their working principles, non-invasive blood glucose testing methods can be divided into electrochemical and electromagnetic methods.

[0004] 1. Electrochemical-based non-invasive blood glucose detection methods. Electrochemical-based non-invasive blood glucose detection methods measure the blood glucose concentration in the human body using easily obtainable external bodily fluids such as saliva, tissue fluid, tears, and sweat.

[0005] 2. Electromagnetic-based non-invasive blood glucose detection methods. Electromagnetic-based non-invasive blood glucose detection methods utilize the reflection, absorption, and scattering properties of electromagnetic waves to measure the blood glucose concentration in the human body. Typical detection methods include near-infrared spectroscopy, microwave detection, and impedance spectroscopy.

[0006] Among the aforementioned detection methods, electrochemical-based non-invasive blood glucose detection methods exhibit a certain time delay between the measured glucose concentration and the actual blood glucose concentration. The overlap of absorption peaks of other interfering substances in the human body and glucose in the near-infrared spectral range can introduce errors into near-infrared spectroscopy measurements. The impedance of human tissues is affected by various factors, such as temperature, sweat, skin thickness, and humidity. Furthermore, relative movement between the skin and the electrode can alter the measurement impedance and may cause allergic reactions. Compared to other detection methods, microwave detection methods demonstrate considerable performance and lower manufacturing costs. Microwave sensors are also small in size, making them suitable for integration into wearable glucose sensing systems. Among microwave sensors, metamaterial-based microwave sensors have attracted widespread attention due to their high sensitivity and small electrical size. These sensors detect blood glucose concentration primarily through changes in the sensor's resonant frequency and depth. Blood glucose concentration detection based on resonant frequency changes has high accuracy in predicting low glucose concentrations, while blood glucose concentration detection based on resonant depth changes has high accuracy in predicting high glucose concentrations. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies and address their deficiencies, as well as the latest industry demands, this invention aims to propose a dual-frequency CSRR sensor and its non-invasive blood glucose detection method that simultaneously possesses high resonance depth detection sensitivity and high resonance frequency detection sensitivity. The dual-frequency CSRR blood glucose detection sensor includes an open-circuit / combiner microstrip line, a substrate, and complementary open-circuit resonant ring units, wherein:

[0008] (1) The open circuit microstrip line / combiner microstrip line is etched on the copper layer on the top of the substrate. The open circuit / combiner microstrip line consists of two combiner microstrip lines and two open circuit microstrip lines.

[0009] (2) The substrate material can be selected from FR4, Rogers RO4003, Rogers RO3003, Rogers RO4350 and Rogers RO5880 models;

[0010] (3) Two double-ring circular dual-frequency complementary open-ring resonant ring CSRR units and two single-ring circular dual-frequency complementary open-ring resonant ring CSRR units are etched on the copper layer at the bottom of the substrate. The double-ring CSRR unit is composed of two circular concentric grooves with symmetrical openings, and the single-ring CSRR unit is composed of a circular opening groove.

[0011] (4) When a microwave signal is applied to the microstrip line, if the symmetry line of the CSRR unit is perpendicular to the axis of the microstrip line, the microstrip line provides electric field excitation to the CSRR unit; if the symmetry line of the CSRR unit is parallel to the axis of the microstrip line, the microstrip line provides both electric field excitation and magnetic field excitation to the CSRR unit; the symmetry lines of the four CSRR units are perpendicular to the axis of the open circuit / combiner microstrip line.

[0012] (5) Apply a microwave signal to the microstrip line of the sensor to measure the sensor's transmission coefficient S. 21 The transmission coefficient S 21 Two transmission zeros are displayed, which are named Resonance Mode 1 and Resonance Mode 2. The highest electric field strength of the sensor at resonance can be regarded as a manifestation of high resonant frequency detection sensitivity. Compared with Resonance Mode 1, the sensor has a higher maximum electric field strength in Resonance Mode 2. The resonance depth of the sensor under no-load conditions is regarded as a manifestation of high resonance depth detection sensitivity. Compared with Resonance Mode 2, the sensor has a larger resonance depth in Resonance Mode 1. These phenomena indicate that the sensor has high resonant frequency detection sensitivity in the first resonant mode and high resonance depth detection sensitivity in the second resonant mode.

[0013] The characteristic impedance of the combiner microstrip line of the sensor is 50Ω, and the characteristic impedance of the opener microstrip line of the sensor is 100Ω. The characteristic impedance of the width microstrip lines of the combiner and opener microstrip lines is calculated by the following formula:

[0014]

[0015] Where, ε e The expression is as follows:

[0016]

[0017] Among them, W Line ε is the width of the microstrip line, h is the thickness of the substrate, and ε e ε is the effective dielectric constant of the microstrip line. r is the dielectric constant of the sensor substrate.

[0018] If the sensor is modeled as a circuit, then: L1 is the inductance of the combiner microstrip line above the dual-loop CSRR unit; L2 is the inductance of the open-circuit microstrip line above the single-loop CSRR unit; C1 is the coupling capacitance between the combiner microstrip line and the dual-loop CSRR unit; C2 is the coupling capacitance between the open-circuit microstrip line and the single-loop CSRR unit; the gap capacitance, metal wire inductance, and loss of the dual-loop CSRR unit are determined by C... C1 L C1 R1 represents the gap capacitance, metal wire inductance, and loss of a single-ring CSRR unit, which are determined by C.C2 L C2 R2 represents the microstrip line above the CSRR unit, which is characterized by the characteristic impedance Z. i and electrical length θ i (i = 1, 2) indicates that the two double-ring CSRR units are far apart, so the coupling between them can be ignored. The electrical distance between the two single-ring CSRR units is very close, so the mutual coupling between them cannot be ignored. The coupling between the two single-ring CSRR units is represented by capacitor C. m The circuit model's ABCD matrix is ​​shown below:

[0019]

[0020] The parameters ABCD in the matrix are shown below:

[0021]

[0022] The expressions for Z1, Z2, Z3, Z4, Z5, and Z6 are as follows:

[0023]

[0024] By setting the parallel impedance to zero, the resonant frequency of the sensor can be obtained. The parallel impedance of the sensor is shown below:

[0025]

[0026] Since the sensor's resistance and the microstrip line above the CSRR have no effect on the sensor's resonant frequency, they are ignored in the resonant frequency calculation. The expression for the sensor's resonant frequency is:

[0027]

[0028] The sensor's S 21 The parameters can also be obtained from the ABCD matrix, and the sensor's S... 21 The parameters are as follows:

[0029]

[0030] A non-invasive blood glucose detection method, implemented using the aforementioned sensor, comprises the following steps:

[0031] (1) Solder two coaxial connectors onto the microstrip line of the opener / combiner. Connect the sensor to ports 1 and 2 of the vector network analyzer via the coaxial line, and measure and record the sensor transmission coefficient S. 21 The resonant frequencies and resonant depths of the two resonant modes above;

[0032] (2) Place your finger on the four CSRR units. The dual-frequency CSRR sensor is equivalent to a resonant circuit composed of capacitor, inductor and resistor. At a fixed frequency, the real part and imaginary part of the relative complex permittivity of blood decrease with the increase of blood glucose concentration. The change in the dielectric properties of blood will be reflected in the resonant frequency and resonant depth of the sensor by perturbing the effective capacitance and effective resistance of the sensor.

[0033] (3) Measure the resonant frequency and resonant depth of the two resonant modes of the dual-frequency CSRR sensor under different blood glucose concentrations, and perform data fitting based on the measurement data to construct a blood glucose concentration prediction model.

[0034] (4) Place your finger on the dual-frequency CSRR sensor for non-invasive blood glucose detection and measure the sensor's transmission coefficient S. 21 The resonant frequencies and resonant depths of the two resonant modes are determined. Using the resonant depth of mode 1 and the resonant frequency of mode 2 as features, a multiple linear regression equation is trained. This equation is then used to predict blood glucose concentration. The expression for the multiple linear regression equation is shown below:

[0035]

[0036] Where y is the blood glucose concentration These correspond to the resonance depth of sensor resonance mode 1 and the resonance frequency of resonance mode 2, respectively, where w0 is a constant to be fitted. These are the weights corresponding to each independent variable.

[0037] The features and beneficial effects of this invention are:

[0038] (1) The present invention provides a dual-frequency CSRR sensor for non-invasive blood glucose detection with two resonance modes. In resonance mode 1 and resonance mode 2, it has high resonance depth detection sensitivity and high resonance frequency detection sensitivity, respectively. Blood glucose concentration is predicted by using resonance depth and resonance frequency, which improves the accuracy of blood glucose concentration measurement.

[0039] (2) The dual-frequency CSRR sensor for non-invasive blood glucose detection provided by the present invention adopts a planar design and the sensing area is the same size as a human finger, which makes it easy to integrate into a portable blood glucose measurement system.

[0040] (3) This invention measures the S of a dual-frequency CSRR sensor. 21 The parameters are used to predict blood glucose concentration. The measurement algorithm is simple and is less susceptible to interference. Attached image description:

[0041] Figure 1The schematic diagrams of the dual-frequency CSRR sensor for non-invasive blood glucose detection provided by the present invention are as follows: (a) top-level structure; (b) bottom-level structure.

[0042] Figure 2 Equivalent circuit model of a dual-frequency CSRR sensor

[0043] Figure 3 For the S-wave simulation of the dual-frequency CSRR sensor under no-load condition in full-wave simulation 21 parameter

[0044] Figure 4 The electric field distribution on the surface of the dual-frequency CSRR sensor under no-load conditions in full-wave simulation is shown in (a) resonant mode 1 and (b) resonant mode 2.

[0045] Figure 5 This invention provides a dual-frequency CSRR sensor for non-invasive blood glucose detection, which is used in full-wave simulations, to demonstrate the S-wave characteristics of blood glucose concentration changes. 21 Parameters (a) Resonance mode 1; (b) Resonance mode 2.

[0046] Figure 6 This is a physical image of a dual-frequency CSRR sensor for non-invasive blood glucose detection provided by the present invention.

[0047] Figure 7 The following are examples of changes in blood glucose concentration and sensor resonance characteristics obtained using a dual-frequency CSRR sensor for non-invasive blood glucose detection provided by this invention. (a) Comparison of resonance depth and blood glucose concentration in resonance mode 1; (b) Comparison of resonance depth and blood glucose concentration in resonance mode 2; (c) Comparison of resonance frequency and blood glucose concentration in resonance mode 1; (d) Comparison of resonance frequency and blood glucose concentration in resonance mode 2. Detailed Implementation

[0048] A dual-frequency CSRR sensor for non-invasive blood glucose detection includes an open / combiner microstrip line, a substrate, and complementary open-loop resonant ring units, wherein:

[0049] (1) The open-circuit / combiner microstrip line is etched onto the copper layer on top of the substrate. The open-circuit / combiner microstrip line consists of two combiner microstrip lines and two open-circuit microstrip lines. The characteristic impedance of the combiner microstrip line in the sensor is 50Ω, and the characteristic impedance of the open-circuit microstrip line is 100Ω. The characteristic impedance of the width microstrip lines of the combiner and open-circuit microstrip lines is calculated using the following formula:

[0050]

[0051] Where, ε e The expression is as follows:

[0052]

[0053] Among them, W Line ε is the width of the microstrip line, h is the thickness of the substrate, and ε e ε is the effective dielectric constant of the microstrip line. r is the dielectric constant of the sensor substrate.

[0054] (2) The substrate material can be selected from FR4, Rogers RO4003, Rogers RO3003, Rogers RO4350 and Rogers RO5880 models;

[0055] (3) Two double-ring circular dual-frequency complementary open-circuit resonator (CSRR) units and two single-ring circular dual-frequency complementary open-circuit resonator (CSRR) units are etched on the copper layer at the bottom of the substrate. The double-ring CSRR unit consists of two concentric circular grooves with symmetrical openings, and the single-ring CSRR unit consists of a single circular opening groove; wherein:

[0056] If the sensor is modeled as a circuit, then: L1 is the inductance of the combiner microstrip line above the dual-loop CSRR unit; L2 is the inductance of the open-circuit microstrip line above the single-loop CSRR unit; C1 is the coupling capacitance between the combiner microstrip line and the dual-loop CSRR unit; C2 is the coupling capacitance between the open-circuit microstrip line and the single-loop CSRR unit; the gap capacitance, metal wire inductance, and loss of the dual-loop CSRR unit are determined by C... C1 L C1 R1 represents the gap capacitance, metal wire inductance, and loss of a single-ring CSRR unit, which are determined by C. C2 L C2 R2 represents the microstrip line above the CSRR unit, which is characterized by the characteristic impedance Z. i and electrical length θ i (i = 1, 2) indicates that the two double-ring CSRR units are far apart, so the coupling between them can be ignored. The electrical distance between the two single-ring CSRR units is very close, so the mutual coupling between them cannot be ignored. The coupling between the two single-ring CSRR units is represented by capacitor C. m The circuit model's ABCD matrix is ​​shown below:

[0057]

[0058] The parameters ABCD in the matrix are shown below:

[0059]

[0060] The expressions for Z1, Z2, Z3, Z4, Z5, and Z6 are as follows:

[0061]

[0062] By setting the parallel impedance to zero, the resonant frequency of the sensor can be obtained. The parallel impedance of the sensor is shown below:

[0063]

[0064] Since the sensor's resistance and the microstrip line above the CSRR have no effect on the sensor's resonant frequency, they are ignored in the resonant frequency calculation. The expression for the sensor's resonant frequency is:

[0065]

[0066] The sensor's S 21 The parameters can also be obtained from the ABCD matrix, and the sensor's S... 21 The parameters are as follows:

[0067]

[0068] (4) The sensitivity of the sensor is related to the excitation method of the CSRR unit. When a microwave signal is applied to the microstrip line, if the symmetry line of the CSRR unit is perpendicular to the axis of the microstrip line, the microstrip line provides electric field excitation for the CSRR unit. If the symmetry line of the CSRR unit is parallel to the axis of the microstrip line, the microstrip line provides both electric and magnetic field excitation for the CSRR unit. The sensor has better sensitivity when the symmetry line of the CSRR unit is perpendicular to the microstrip line. Therefore, in this design, the symmetry lines of the four CSRR units are perpendicular to the axis of the open / combiner microstrip line.

[0069] (5) Apply a microwave signal to the microstrip line of the sensor to measure the sensor's transmission coefficient, and the sensor's S... 21 The parameters show two transmission zeros, which are named Resonance Mode 1 and Resonance Mode 2. The highest electric field strength of the sensor at resonance can be considered a manifestation of high resonant frequency detection sensitivity; compared to Resonance Mode 1, the sensor has a higher maximum electric field strength in Resonance Mode 2. The resonance depth of the sensor under no-load conditions is considered a manifestation of high resonance depth detection sensitivity; compared to Resonance Mode 2, the sensor has a greater resonance depth in Resonance Mode 1. These phenomena indicate that the sensor has high resonant frequency detection sensitivity in the first resonant mode and high resonance depth detection sensitivity in the second resonant mode.

[0070] A dual-frequency CSRR sensor detection method for non-invasive blood glucose monitoring is implemented using the aforementioned sensor, and the steps are as follows:

[0071] (1) Solder two coaxial connectors onto the microstrip line of the opener / combiner. Connect the sensor to ports 1 and 2 of a vector network analyzer (VNA) via the coaxial line, and measure and record the sensor transmission coefficient (S). 21 The resonant frequencies and resonant depths of the two resonant modes on the parameter (parameter).

[0072] (2) Place your finger on the four CSRR units. The dual-frequency CSRR sensor is equivalent to a resonant circuit composed of capacitor, inductor and resistor. At a fixed frequency, the real part and imaginary part of the relative complex permittivity of blood decrease with the increase of blood glucose concentration. The change in the dielectric properties of blood will be reflected in the resonant frequency and resonant depth of the sensor by perturbing the effective capacitance and effective resistance of the sensor.

[0073] (3) Measure the resonant frequency and resonant depth of the two resonant modes of the dual-frequency CSRR sensor under different blood glucose concentrations, and perform data fitting based on the measurement data to construct a blood glucose concentration prediction model.

[0074] (4) Place your finger on the dual-frequency CSRR sensor for non-invasive blood glucose detection and measure the sensor S. 21 The resonant frequencies and resonant depths of the two resonant modes are used as parameters. The resonant depth of mode 1 and the resonant frequency of mode 2 are used as features to train a multiple linear regression equation. This equation is then used to predict blood glucose concentration. The expression of the multiple linear regression equation is shown below:

[0075]

[0076] Where y is the blood glucose concentration x s1 x f2 These correspond to the resonance depth of sensor resonance mode 1 and the resonance frequency of resonance mode 2, respectively. w0 is the constant to be fitted, and w s1 w f2 These are the weights corresponding to each independent variable.

[0077] To make the objectives, technical solutions, and advantages of this invention clearer, specific examples are provided below to illustrate the embodiments of this invention. It should be understood that this invention can also be implemented or applied through other different specific embodiments and is not intended to limit the invention. A specific technical solution for a dual-frequency complementary open-circuit resonant ring (CSRR) sensor with both amplitude and frequency detection sensitivity and its non-invasive blood glucose detection method is as follows:

[0078] (1) The structure of the dual-frequency CSRR sensor is as follows: Figure 1As shown in the diagram, gray represents metal, and white represents the etched portion. FR4 was selected as the sensor substrate, which is 40mm long, 20mm wide, and 0.8mm thick. The open / close microstrip line is etched onto a copper layer on top of the 35μm thick substrate, consisting of two W-width lines. C The combiner microstrip line and two W-width... S The circuit consists of microstrip lines for opening circuits. In this example, the width of the microstrip line for the combiner is 1.5 mm, and the width of the microstrip line for the splitter is 0.3 mm.

[0079] (2) Two double-ring CSRR cells and two single-ring CSRR cells are etched onto a copper layer at the bottom of a 35 μm thick substrate. The horizontal distance between the two circular double-ring CSRR cells is b, and the vertical distance between the two circular single-ring CSRR cells is c. The circular double-ring CSRR cell consists of two concentric circular grooves with symmetrical openings spaced t apart. The diameter of the outer ring is a1, the width of the opening is g, and the width of the groove between the inner and outer metals is s. The circular single-ring CSRR cell consists of a single circular groove with an opening. The diameter of the outer ring is a2, the width of the opening is g, and the width of the groove between the inner and outer metals is s.

[0080] (3) The equivalent circuit model of the dual-frequency CSRR sensor is as follows: Figure 2 As shown in the figure, L1 is the inductance of the combiner microstrip line above the dual-loop CSRR unit; L2 is the inductance of the open-circuit microstrip line above the single-loop CSRR unit; C1 is the coupling capacitance between the combiner microstrip line and the dual-loop CSRR unit; C2 is the coupling capacitance between the open-circuit microstrip line and the single-loop CSRR unit; the gap capacitance, metal wire inductance, and loss of the dual-loop CSRR unit are determined by C... C1 L C1 R1 represents the gap capacitance, metal wire inductance, and loss of a single-ring CSRR unit, which are determined by C. C2 L C2 R2 represents the microstrip line above the CSRR unit, which is characterized by the characteristic impedance Z. i and electrical length θ i (i = 1, 2) indicates that the two double-ring CSRR units are far apart, so the coupling between them can be ignored. The electrical distance between the two single-ring CSRR units is very close, so the mutual coupling between them cannot be ignored. The coupling between the two single-ring CSRR units is represented by capacitor C. m The circuit model's ABCD matrix is ​​shown below:

[0081]

[0082] The parameters ABCD in the matrix are shown below:

[0083]

[0084] The expressions for Z1, Z2, Z3, Z4, Z5, and Z6 are as follows:

[0085]

[0086] By setting the parallel impedance to zero, the resonant frequency of the sensor can be obtained. The parallel impedance of the sensor is shown below:

[0087]

[0088] Since the sensor's resistance and the microstrip line above the CSRR have no effect on the sensor's resonant frequency, they are ignored in the resonant frequency calculation. The expression for the sensor's resonant frequency is:

[0089]

[0090] The sensor's S 21 The parameters can also be obtained from the ABCD matrix, and the sensor's S... 21 The parameters are as follows:

[0091]

[0092] (4) Sensor S under no-load condition 21 Parameters such as Figure 3 As shown in the figure, the sensor displays two transmission zeros, which is consistent with the analysis results of the sensor's equivalent circuit. These two transmission zeros are named Resonance Mode 1 and Resonance Mode 2. The resonant frequency and resonance depth of Resonance Mode 1 are 4.51 GHz and 34.3 dB, respectively, while the resonant frequency and resonance depth of Resonance Mode 2 are 6.35 GHz and 20.1 dB, respectively. Compared with Resonance Mode 2, Resonance Mode 1 has a larger resonance depth.

[0093] (5) When a microwave signal is applied to the microstrip line, the electric field generated by the microstrip line will excite the CSRR unit, and a highly concentrated ring electric field will appear around the CSRR unit. The electric field distribution on the surface of the dual-frequency complementary open-loop resonant sensor at resonance is as follows: Figure 4 As shown, when the sensor is in resonant mode 1, the maximum electric field strength of the sensor is 2.45 × 10⁻⁶. 4 V / m, the maximum electric field strength of the sensor is 6.76 × 10⁻⁶ when the sensor is in resonant mode 2. 4 V / m, compared with resonant mode 1, resonant mode 2 has a higher maximum electric field strength.

[0094] (6) Si of dual-frequency CSRR sensor resonant mode 1 and resonant mode 2 at different blood glucose concentrations21 Parameters such as Figure 5 As shown, S at different blood glucose concentrations 21 The parameter curves are easily distinguishable from each other. Simulation results show that the dual-frequency CSRR sensor has high resonance depth detection sensitivity and high resonance frequency detection sensitivity in resonance mode 1 and resonance mode 2, respectively. In resonance mode 1, the resonance depth detection sensitivity of the dual-frequency complementary open-loop resonator sensor is 2.2 × 10⁻⁶. -6 The resonant frequency detection sensitivity of the dual-frequency complementary open-loop resonant sensor is 4.6 × 10 dB / (mg / dL). -3 MHz / (mg / dL).

[0095] (6) Measurement systems for human experiments, such as Figure 6 As shown, the measurement system consists of a vector network analyzer, a coaxial cable, and a sensor. The sensor is connected to ports 1 and 2 of the VNA via the coaxial cable, which is secured with tape to prevent movement during measurement and thus avoid experimental errors. A piece of pearl cotton foam cut into the shape of a finger is attached to the sensor; volunteers place their index fingers in the gaps of the foam to reduce measurement errors caused by finger movement. The changes in blood glucose concentration and sensor resonance characteristics within 30 minutes after the volunteers eat are shown below. Figure 7 As shown, experimental results indicate that the sensor's resonance depth detection sensitivity in resonance mode 1 is 4.4 × 10⁻⁶. -3 dB / (mg / dL), the resonant frequency detection sensitivity in resonant mode 2 is 7.4×10 dB / (mg / dL). -1 MHz / (mg / dL).

[0096] (7) Using the resonance depth of mode 1 and the resonance frequency of mode 2 of the dual-frequency CSRR sensor as inputs to the mathematical model, a multiple linear regression model was established to predict the blood glucose concentration of volunteer subjects. The formula for predicting blood glucose concentration is as follows: Where y represents blood glucose concentration, in mg / dL. and These correspond to the resonance depth of sensor resonance mode 1 and the resonance frequency of resonance mode 2, respectively. The unit is dB. The unit is GHz.

[0097] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. The present invention is not limited to the above examples. Modifications or equivalent substitutions made within the principles of the technical solutions of the present invention, as long as they meet the requirements of the method of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A dual frequency CSRR blood glucose detection sensor, characterized in that, It comprises open / close microstrip line, substrate, complementary open resonant ring unit, wherein: (1) the open / close microstrip line is etched on the copper layer on the top of the substrate, and the open / close microstrip line is composed of two close microstrip lines and two open microstrip lines; (2) the material of the substrate is one of FR4, Rogers RO4003, Rogers RO3003, Rogers RO4350 and Rogers RO5880; (3) two double-ring circular double-frequency complementary open resonant ring CSRR units and two single-ring circular double-frequency complementary open resonant ring CSRR units are etched on the copper layer on the bottom of the substrate, the double-ring CSRR unit is composed of two circular concentric grooves with symmetrical openings, the single-ring CSRR unit is composed of one circular open groove, and the two double-ring CSRR units and the two single-ring CSRR units are symmetrically and spacedly arranged; (4) when the microwave signal is applied to the microstrip line, if the symmetry line of the CSRR unit is perpendicular to the axis of the microstrip line, the microstrip line provides the CSRR unit with electric field excitation; if the symmetry line of the CSRR unit is parallel to the axis of the microstrip line, the microstrip line provides the CSRR unit with electric field excitation and magnetic field excitation; the symmetry lines of the four CSRR units are perpendicular to the axis of the open / close microstrip line; (5) applying a microwave signal to the microstrip line of the sensor to measure the transmission coefficient S of the sensor 21 , the transmission coefficient S 21 shows two transmission zeros, which are named as resonance mode 1 and resonance mode 2; the highest electric field intensity of the sensor at resonance can be considered as a kind of performance of high resonance frequency detection sensitivity, and the sensor has higher maximum electric field intensity at resonance mode 2 than at resonance mode 1; the resonance depth of the sensor in the unloaded state is considered as a kind of performance of high resonance depth detection sensitivity, and the sensor has greater resonance depth at resonance mode 1 than at resonance mode 2; the above phenomena show that the d sensor has high resonance frequency detection sensitivity at resonance mode 1 and high resonance depth detection sensitivity at resonance mode 2.

2. The dual frequency CSRR blood glucose measurement sensor of claim 1, wherein the first and second CSRRs are configured to operate at a first frequency of 1.5 GHz and a second frequency of 3.5 GHz, respectively. The characteristic impedance of the close microstrip line of the sensor is 50 Ω, the characteristic impedance of the open microstrip line of the sensor is 100 Ω, and the width of the microstrip line is calculated by the following formula: wherein The expression of the above formula is shown as follows: wherein, is the width of the microstrip line, h is the thickness of the substrate, is the effective dielectric constant of the microstrip line, is the dielectric constant of the sensor substrate.

3. The dual frequency CSRR blood glucose measurement sensor of claim 1, wherein the first and second CSRRs are configured to operate at a first frequency of 1.5 GHz and a second frequency of 3.5 GHz, respectively. When the sensor is equivalent to a circuit model, L1 is the inductance of the microstrip line above the combining port of the double-ring CSRR unit; L2 is the inductance of the microstrip line above the open port of the single-ring CSRR unit; C1 is the coupling capacitance between the microstrip line of the combining port and the double-ring CSRR unit; C2 is the coupling capacitance between the microstrip line of the open port and the single-ring CSRR unit; the gap capacitance, metal wire inductance and loss of the double-ring CSRR unit are represented by C C1 , L C1 and R1; the gap capacitance, metal wire inductance and loss of the single-ring CSRR unit are represented by C C2 , L C2 and R2; the microstrip line above the CSRR unit is represented by characteristic impedance Z i and electrical length θ i (i = 1, 2); the coupling between the two single-ring CSRR units is represented by capacitance C m , and the ABCD matrix of the circuit model is as follows: Wherein, the ABCD parameters in the matrix are as follows: Wherein, the expressions of Z1, Z2, Z3, Z4, Z5 and Z6 are as follows: Let the parallel impedance be zero, the resonant frequency of the sensor is obtained, and the parallel impedance of the sensor is as follows: Because the resistance of the sensor and the microstrip line above the CSRR have no effect on the resonant frequency of the sensor, the resistance and the microstrip line above the CSRR are ignored in the calculation of the resonant frequency, and the resonant frequency expression of the sensor is: Sensors S 21 The parameters can also be obtained from the ABCD matrix, Sensors S 21 The parameters are as follows: 。 4. A non-invasive blood glucose measurement method, characterized by, The sensor of claim 1 is used to realize detection, and the detection steps are as follows: (1) two coaxial connectors are welded on the open / close microstrip line, the sensor is connected with the 1, 2 ports of the vector network analyzer through the coaxial line, and the resonant frequency and the resonant depth of the two resonant modes of the transmission coefficient S21 of the sensor are measured and recorded; (2) the fingers are placed on the four CSRR units, the double-frequency CSRR sensor is equivalent to a resonant circuit composed of capacitance, inductance and resistance, the real part and the imaginary part of the relative complex permittivity of blood decrease with the increase of blood glucose concentration at a fixed frequency, and the change of the dielectric properties of blood is reflected on the resonant frequency and the resonant depth of the sensor through the disturbance of the effective capacitance and the effective resistance of the sensor; (3) the resonant frequency and the resonant depth of the two resonant modes of the double-frequency CSRR sensor under different blood glucose concentrations are measured, data fitting is carried out according to the measured data, and a blood glucose concentration prediction model is constructed; (4) Place the finger on the dual-frequency CSRR sensor for non-invasive blood glucose detection, measure the transmission coefficient S 21 Resonant frequency and resonant depth of the above two resonant modes; the resonant depth of resonant mode 1 and the resonant frequency of resonant mode 2 are used as features to train a multiple linear regression equation, which is used to predict the blood glucose concentration; the expression of the multiple linear regression equation is as follows: where y is the blood glucose concentration x s1 , x f2 correspond to the resonance depth of the sensor resonance mode 1, the resonance frequency of the resonance mode 2, respectively, w0is a constant to be fitted, w s1 , w f2 is the weight value corresponding to each independent variable.

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