Research And Design Of Non-invasive Blood Glucose Measuring System Based On Microwave

Diabetes is a common disease and it is characterized by hyperglycemia.Its Common symptoms include sudden blindness,postprandial hypoglycemia,polyuria,hyperphagia and wasting.Long-term high blood sugar will lead damage to many organs in the body,which has a great impact on people's health and life.The number of people with diabetes has been on the rise in recent years.For the prevention and control of diabetes,patients not only need to keep a positive attitude and live a regular life,but also need a safe and convenient blood glucose detection device.However,all blood glucose meters on the market now require invasive blood collection,which not only brings physical and mental pain to patients,but also puts them at risk of skin infection.Therefore,this thesis studies the design of a non-invasive blood glucose testing system based on microwave method.The research contents of this paper are as follows:1.By analyzing the relationship between the complex dielectric constant of glucose solution and blood concentration with frequency,it can be concluded that the higher operating frequency can make the sensor more sensitive to the change of solution concentration.At the same time,through information research we can find that when the frequency is greater than 100MHz,the charging effect of the cell membrane will slow down rapidly,and the relative dielectric constant of the tissue will no longer depend on the membrane structure.In addition,by analyzing the penetration depth of electromagnetic wave to human tissues,it can be seen that the penetration depth becomes shallower with the increase of frequency.To sum up,the working frequency of the sensor is selected about1GHz,and the sensing area is selected to be human fingers with relatively more blood vessels.At the same time,by comparing several common types of sensor structure,the sensor type in this thesis is selected to be microstrip.2.Microwave sensor is designed from two aspects of improving sensitivity and miniaturization.The basic operation principle of the sensor is that the resonant frequency varies with the concentration of the solution.Firstly,the most basic microstrip square ring resonator was simulated,and it was found that the electric field was mainly distributed near the two coupling gaps,and the overall size of the resonator is too large to be completely covered.By bending the metal strip,the overall size of the resonator can be reduced by more than half,and the sensitivity is not high when the measured object is covered in the gap of the resonator.However,the full coverage will generate multiple resonances,which will affect the performance of the sensor.In order to solve the above disadvantages,SRR is adopted as the sensor and the high-impedance microstrip feeder is used to enhance the electromagnetic coupling.This structure has the advantages of concentrated electric field distribution and small size,and the measured object is placed near its open gap.The simulation shows that compared with the bent closed-loop resonator,its sensitivity is improved to a certain extent and the overall size is smaller.Since the solution under test will affect the equivalent capacitance at the opening of the resonator,in order to further improve the sensitivity of the sensor,the intersecting capacitance is used to replace the open capacitance of SRR,and ICLLR is used as the sensor.Simulation results show that ICLLR has higher sensitivity and greatly reduced size,which is only 2.2mm×2.2mm×0.8mm?0.0338₀?×0.0338?₀×0.0123₀??.Therefore,ICLLR was selected as the sensor to simulate glucose solution and blood.The simulation results show that the resonant frequency of the resonator is approximately linear with the concentration,and it is feasible to use the sensor to measure the concentration.3.Design the overall scheme of the system,complete the design of signal source and detector and briefly introduce the software design process of the system.We select ADF4351as the signal source of this system.ADIsimPLL is used to design the loop filter,and then the peripheral circuit of the signal source and its PCB layout are designed.We next introduce the characteristics of the detection chip AD8313 briefly and the schematic diagram and PCB layout are designed.Finally,the design process is briefly introduced and it includes DSP control sweep signal source,AD sampling design and display design.