Microwave sensing system for noninvasive blood glucose detection

Abstract

The invention discloses a microwave sensing system for noninvasive blood glucose detection, and relates to the technical field of blood glucose detection, and the microwave sensing system comprises a voltage-controlled oscillator used for generating a frequency-adjustable radio frequency signal; the radio-frequency amplifier is used for improving radio-frequency signal power; the double-resonance unit differential detection structure comprises a test channel and a reference channel which are the same in structure and each comprise a split ring interdigital resonator and an envelope detector. The power divider / directional coupler is used for distributing the output signal of the radio frequency amplifier to the test channel and the reference channel according to the proportion of 1: 1; the test channel is used for outputting a direct-current voltage Vtest; the reference channel outputs direct-current voltage Vref; the differential processing module comprises a subtractor and is used for calculating the voltage difference delta V = Vtest-Vref in real time and eliminating common-mode interference. The method does not depend on a vector network analyzer, and the cost is reduced; the common-mode interference of environmental noise is effectively suppressed; the system volume is reduced and the power consumption is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of blood glucose detection, and in particular to a microwave sensing system for non-invasive blood glucose detection. Background Art

[0002] Currently, most diabetic patients use blood glucose test strips and blood glucose meters to measure blood glucose by pricking their fingers. Patients have to endure the risks of pain and infection every day to monitor their blood glucose levels. The electrochemical method is usually the main method of commercial blood glucose monitoring technology, which uses the catalytic reaction of glucose oxidase for detection. It is welcomed because of its high accuracy and high stability, but it still requires blood sampling and belongs to an invasive method.

[0003] Some non-invasive blood glucose monitoring technologies have also emerged in the prior art, mainly focusing on the following methods: a. Infrared spectroscopy: The concentration is measured by analyzing the absorption characteristics of infrared light in glucose molecules. However, it is greatly affected by environmental factors and has insufficient sensitivity and accuracy; b. Microwave technology: Combining technologies such as microwave and radio frequency for blood glucose monitoring, which has the advantages of non-invasiveness and rapid detection. However, the microwave detection technology faces a core challenge: Traditional microwave sensors rely on large and costly vector network analyzers (VNAs), which seriously restricts portability and clinical applications. CN119375256A discloses a microwave sensing system for non-invasive blood glucose detection, which improves the sensitivity through the coupling design of substrate integrated waveguide (SIW) and split ring resonator (SRR). However, it still relies on an external vector network analyzer (VNA) for frequency domain analysis and has limited anti-interference ability. Summary of the Invention

[0004] To solve the deficiencies of the prior art, the present invention provides a microwave sensing system for non-invasive blood glucose detection, which does not rely on a vector network analyzer, reduces costs, and shrinks the volume.

[0005] To achieve the purpose of the present invention, the following scheme is proposed: A microwave sensing system for non-invasive blood glucose detection includes a voltage-controlled oscillator, a radio frequency amplifier, a power splitter / directional coupler, a dual-resonator unit differential detection structure, and a differential processing module connected in sequence.

[0006] The voltage-controlled oscillator is used to generate an adjustable-frequency radio frequency signal; The radio frequency amplifier is used to increase the power of the radio frequency signal; The dual-resonator unit differential detection structure includes a test channel and a reference channel, both of which have the same structure and each includes a split ring interdigital resonator and an envelope detector connected in sequence; The split-ring interdigital resonator includes a split-ring resonator and an interdigital structure disposed therein. The split-ring resonator is configured as a rectangular ring structure, including two horizontal segments and two vertical segments. A notch is provided at the middle position of the horizontal segments. An input segment and an output segment are respectively and perpendicularly connected to the outer sides of the two vertical segments. The interdigital structure includes a rectangular frame and a plurality of interdigital fingers disposed therein. The plurality of interdigital fingers are respectively and perpendicularly connected to two opposite inner walls of the rectangular frame and are arranged in a staggered manner. The interdigital fingers are parallel to the horizontal segments. The power splitter / directional coupler is used to distribute the output signal of the RF amplifier to the test channel and the reference channel in a 1:1 ratio. In the test channel, the split-ring interdigital resonator is used to input the acquired solution information into the envelope detector, and the envelope detector is used to output a DC voltage V_test. In the reference channel, the split-ring interdigital resonator is used to input the acquired interference information into the envelope detector. The interference information includes ambient temperature, ambient humidity, and electromagnetic noise. The envelope detector is used to output a DC voltage V_ref. The differential processing module includes a subtractor for calculating the voltage difference ΔV = V_test - V_ref in real time to eliminate common-mode interference.

[0007] Further, the output power of the voltage-controlled oscillator is 7 dBm.

[0008] Further, the power splitter / directional coupler adopts a high-isolation Wilkinson power splitter / directional coupler.

[0009] Further, the length of the interdigital finger is 5 mm, the width is 0.34 mm, the inner spacing between two adjacent interdigital fingers is 0.31 mm, the width of the side of the rectangular frame perpendicular to the interdigital fingers is 0.6 mm, and the width of the side of the rectangular frame parallel to the interdigital fingers is 0.575 mm.

[0010] Further, the length of the input segment is 6 mm, the width is 1.5 mm, the length of the horizontal segment is 8 mm, the width is 0.5 mm, the length of the vertical segment is 11 mm, and the width is 0.6 mm.

[0011] Further, the split-ring interdigital resonator adopts Rogers RO4350 board material, with a size of 20 mm × 20 mm and a thickness of 0.762 mm. The bottom is a copper-clad area.

[0012] The beneficial effects of the present invention are as follows: 1. By adopting an improved split-ring interdigital resonator, combining the split-ring resonator and the interdigital structure, the sensor area is effectively reduced, and the electric field intensity is significantly enhanced.

[0013] 2. Solve the dependence on the vector network analyzer in the existing method, and greatly reduce the cost.

[0014] 3. The differential structure is adopted to effectively suppress the common-mode interference of environmental noises (temperature and humidity, electromagnetic noises), featuring strong anti-interference ability and self-compensation for temperature drift.

[0015] 4. System miniaturization and low power consumption: The self-contained radio frequency link (integrating voltage-controlled oscillator, radio frequency amplifier, and envelope detector) replaces the traditional VNA, reducing the system volume and greatly lowering the power consumption, meeting the integration requirements of wearable devices.

[0016] 5. Non-invasive and high comfort: Based on the microwave sensing principle, it eliminates the need for blood sampling or skin puncture. The detection process is painless and risk-free of infection, significantly improving patient compliance. Description of the Drawings

[0017] Figure 1 Shows the connection diagram of the microwave sensing system; Figure 2 Shows the schematic diagram of the split-ring interdigital resonator structure; Figure 3 Shows the electric field distribution diagram of the split-ring interdigital resonator; Figure 4 Shows the simulation and measured result diagram of the split-ring interdigital resonator; Figure 5 Shows the S21 parameter diagram of different glucose solution concentrations in the frequency range of 2.35 GHz to 2.55 GHz; Figure 6 Shows the S21 parameter diagram of different glucose solution concentrations in the frequency range of 2.40 GHz to 2.70 GHz; Figure 7 Shows the circuit diagram of the subtractor; Figure 8 Shows the relationship diagram between glucose concentration and output voltage; Figure 9 Shows the schematic diagram of another split-ring interdigital resonator structure; Figure 10 Shows the electric field distribution diagram of another split-ring interdigital resonator; Reference Signs: Split-ring resonator - 1, Horizontal segment - 11, Vertical segment - 12, Notch - 13, Interdigital structure - 2, Rectangular frame - 21, Interdigital fingers - 22, Input segment - 31, Output segment - 32. Detailed Embodiments

[0018] As Figure 1 shown, this embodiment provides a microwave sensing system for non-invasive blood glucose detection, including a voltage-controlled oscillator, a radio frequency amplifier, a power divider / directional coupler, a dual-resonator unit differential detection structure, and a differential processing module connected in sequence.

[0019] Specifically, the voltage-controlled oscillator is used to generate a tunable radio frequency signal with an output power of 7 dBm.

[0020] Specifically, the radio frequency amplifier is used to boost the power of the radio frequency signal and also to drive the differential detection structure of the dual resonator unit.

[0021] Specifically, the differential detection structure of the dual resonator unit includes a test channel and a reference channel, both having the same structure, each including a split-ring interdigital resonator and an envelope detector connected in sequence.

[0022] Specifically, the power splitter / directional coupler uses a high-isolation Wilkinson power splitter / directional coupler to distribute the output signal of the radio frequency amplifier to the test channel and the reference channel in a 1:1 ratio.

[0023] Specifically, in the test channel, the split-ring interdigital resonator is used to input the acquired solution information into the envelope detector, and the envelope detector is used to output a DC voltage V_test. In the reference channel, the split-ring interdigital resonator is used to input the acquired interference information into the envelope detector, where the interference information includes environmental temperature, environmental humidity, electromagnetic noise, etc., and the envelope detector is used to output a DC voltage V_ref.

[0024] Specifically, the differential processing module includes a subtractor for calculating the voltage difference ΔV = V_test - V_ref in real time to eliminate common-mode interference.

[0025] More specifically, as Figure 2 shown, the split-ring interdigital resonator includes a split-ring resonator 1 and an interdigital structure 2 disposed therein. The split-ring resonator 1 includes two horizontal segments 11 and two vertical segments 12, forming a rectangular ring structure. A notch 13 is provided at the middle position of the horizontal segment 11. An input segment 31 and an output segment 32 are respectively and vertically connected to the outer sides of the two vertical segments 12. The interdigital structure 2 includes a rectangular frame 21 and ten interdigital fingers 22 disposed therein. The ten interdigital fingers 22 are respectively and vertically connected to the opposite inner walls of the rectangular frame 21 and are arranged in an interleaved manner. The interdigital fingers 22 are parallel to the horizontal segment 11.

[0026] Among them, the split-ring interdigital resonator uses Rogers RO4350 board material, with a size of 20 mm × 20 mm and a thickness of 0.762 mm. The bottom is a copper-clad area, and the size of the split-ring interdigital resonator is reduced by 86%.

[0027] Among them, the length of the interdigital finger 22 is 5 mm, the width is 0.34 mm, the inner spacing between two adjacent interdigital fingers 22 is 0.31 mm, the width of the side of the rectangular frame 21 perpendicular to the interdigital finger 22 is 0.6 mm, the width of the side of the rectangular frame 21 parallel to the interdigital finger 22 is 0.575 mm, and the length of this side is 6.5 mm.

[0028] Among them, the input segment 31 has a length of 6 mm and a width of 1.5 mm, the horizontal segment 11 has a length of 8 mm and a width of 0.5 mm, and the vertical segment 12 has a length of 11 mm and a width of 0.6 mm.

[0029] As Figure 3 shown, the maximum electric field strength of the split-ring interdigital resonator provided in this embodiment can be increased by 2.9 times, and the simulation results are as Figure 4 shown.

[0030] As Figure 9 shown, it is a split-ring interdigital resonator of another structure, and its electric field distribution diagram is as Figure 10 shown. It can be seen that its electric field strength is not as good as that of the split-ring interdigital resonator in this embodiment.

[0031] To evaluate the response of the split-ring interdigital resonator to solutions with different complex permittivities, a vector network analyzer (VNA) is used to measure the S-parameters of the split-ring interdigital resonator. The full name of the S-parameters is Scatter parameters, that is, scattering parameters. Connect the two ports of the split-ring interdigital resonator to the vector network analyzer (VNA), inject the solution to be measured into the container, place the container on the split-ring interdigital resonator, and use the vector network analyzer to measure the forward transmission coefficient S21 of the split-ring interdigital resonator. The measurement results are as Figure 5 、 Figure 6 shown. The experimental results show that as the solution concentration increases, the resonance frequency of the split-ring interdigital resonator increases.

[0032] As Figure 7As shown in the figure, the subtractor circuit includes RF connector U2, RF connector U3, operational amplifier U1, resistor R1, resistor R2, resistor R3, resistor R4, pin header H1, pin header H2, capacitor C1, capacitor C2, capacitor C3 and capacitor C4. The models of both RF connector U2 and RF connector U3 are SMA-KHD9, the model of operational amplifier U1 is OPA627, the resistance values of resistor R1 and resistor R4 are 28 kΩ, the resistance values of resistor R2 and resistor R3 are 10 kΩ, the values of capacitor C1 and capacitor C3 are both 10 uF, and the values of capacitor C2 and capacitor C4 are both 100 nF. The output end of RF connector U3 is connected to the input end of resistor R3, the output end of resistor R3 is connected to the non-inverting input end of operational amplifier U1, the input end of resistor R4 is connected to the non-inverting input end of operational amplifier U1, the output end of resistor R4 is grounded, the output end of operational amplifier U1 is connected to the input end of pin header H1, the output end of RF connector U2 is connected to the input end of resistor R2, the output end of resistor R2 is connected to the inverting input end of operational amplifier U1, the input end of resistor R1 is connected to the inverting input end of operational amplifier U1, the output end of resistor R1 is connected to the output end of operational amplifier U1. The positive power supply VCC of operational amplifier U1 is grounded after being connected to capacitor C1, the negative power supply VEE of operational amplifier U1 is grounded after being connected to capacitor C3, the positive power supply VCC of pin header H2 is grounded after being connected to capacitor C2, and the negative power supply VEE of pin header H2 is grounded after being connected to capacitor C4.

[0033] The signal of the experimental group is input from RF connector U3 and input into operational amplifier U1 after passing through resistor R3. The signal of the control group is input from RF connector U2 and input into operational amplifier U1 after passing through resistor R2. Operational amplifier U1 calculates the difference between the two signals and outputs ΔV. The subtractor circuit provided in this embodiment adopts a high-precision resistor network to construct a differential amplifier circuit with a gain of 2.8. Combining with the low-noise characteristics of OPA627, it can achieve efficient common-mode rejection of V_test and V_ref.

[0034] Circuit test: Adjust the output signal frequency of the voltage-controlled oscillator to 2.55 GHz. From Figure 5 and Figure 6 it can be known that S21 increases with the increase of glucose concentration at 2.55 GHz. Connect the envelope detector of the experimental group to the non-inverting input end of the operational amplifier, and connect the envelope detector of the control group to the inverting input end of the operational amplifier. Measure the output voltage of the subtractor through a voltmeter as shown in Figure 8 . x corresponds to the glucose concentration on the horizontal axis, y corresponds to the output voltage on the vertical axis, and the correlation coefficient R 2 = 0.99. It can be seen that as the glucose concentration increases, the output voltage of the subtractor increases.

[0035] The above embodiments are only used to illustrate the technical idea and features of the present invention, and do not represent that it is the only one or a limitation to the present invention. Those skilled in the art should understand that without departing from the scope of the present invention, various changes or equivalent substitutions made to the present invention all fall within the scope of protection of the present invention.

Claims

1. A microwave sensing system for non-invasive blood glucose detection, characterized in that, It includes a voltage-controlled oscillator, a radio-frequency amplifier, a power splitter / directional coupler, a dual-resonator unit differential detection structure, and a differential processing module connected in sequence; The voltage-controlled oscillator is used to generate a tunable radio-frequency signal; The radio-frequency amplifier is used to boost the power of the radio-frequency signal; The dual-resonator unit differential detection structure includes a test channel and a reference channel, which have the same structure and both include a split-ring interdigital resonator and an envelope detector connected in sequence; The split-ring interdigital resonator includes a split-ring resonator (1) and an interdigital structure (2) disposed therein. The split-ring resonator (1) is configured as a rectangular-ring structure, including two horizontal segments (11) and two vertical segments (12). A notch (13) is provided at the middle position of the horizontal segment (11). An input segment (31) and an output segment (32) are respectively and perpendicularly connected to the outer sides of the two vertical segments (12). The interdigital structure (2) includes a rectangular frame (21) and a plurality of interdigital fingers (22) disposed therein. The plurality of interdigital fingers (22) are respectively and perpendicularly connected to the opposite inner walls of the rectangular frame (21) and are arranged in a staggered manner. The interdigital fingers (22) are parallel to the horizontal segment (11); The power splitter / directional coupler is used to distribute the output signal of the radio-frequency amplifier to the test channel and the reference channel in a 1:1 ratio; In the test channel, the split-ring interdigital resonator is used to input the acquired solution information into the envelope detector, and the envelope detector is used to output a DC voltage V_test; In the reference channel, the split-ring interdigital resonator is used to input the acquired interference information into the envelope detector. The interference information includes ambient temperature, ambient humidity, and electromagnetic noise, and the envelope detector is used to output a DC voltage V_ref; The differential processing module includes a subtractor, which is used to calculate the voltage difference ΔV = V_test - V_ref in real time to eliminate common-mode interference.

2. The microwave sensing system for non-invasive blood glucose detection according to claim 1, wherein The output power of the voltage-controlled oscillator is 7 dBm.

3. The microwave sensing system for non-invasive blood glucose detection according to claim 1, characterized in that The power splitter / directional coupler adopts a high-isolation Wilkinson power splitter / directional coupler.

4. The microwave sensing system for non-invasive blood glucose detection according to claim 1, wherein, The length of the interdigital finger (22) is 5 mm, the width is 0.34 mm, the inner spacing between two adjacent interdigital fingers (22) is 0.31 mm, the side width of the rectangular frame (21) perpendicular to the interdigital finger (22) is 0.6 mm, and the side width of the rectangular frame (21) parallel to the interdigital finger (22) is 0.575 mm.

5. The microwave sensing system for non-invasive blood glucose detection according to claim 1, characterized in that, The length of the input segment (31) is 6 mm, the width is 1.5 mm, the length of the horizontal segment (11) is 8 mm, the width is 0.5 mm, and the length of the vertical segment (12) is 11 mm, the width is 0.6 mm.

6. The microwave sensing system for non-invasive blood glucose detection according to claim 4, wherein The split-ring interdigital resonator adopts Rogers RO4350 board material, with a size of 20 mm × 20 mm and a thickness of 0.762 mm, and the bottom is a copper-clad area.

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