In this paper, a multi-resonance sensor using multipole expansion for microwave frequency region is proposed. A folded loop shape was proposed to fabricate it, it was deformed into a shape that could work on FR4 substrate, and optimization was performed to work in a body environment with a high dielectric constant. Glucose concentrations were continuously measured by resonant frequency of reflection coefficient in water/rat environments similar to those in vivo, comparing the blood glucose concentration with the trend of resonant frequency transition in rats.
It was verified that the resonance frequency changed similarly from 2.34 GHz to 2.26 GHz while the blood sugar changed from 500 mg/dL to 250 mg/dL.
INTRODUCTION
Until recently, the strip sensor shown in Figure 1.2 (a) was the mainstream of blood glucose sensors. It measures the electrochemical reaction between the enzyme from the strip and the blood glucose collected from the fingertips[4]. However, if the blood glucose reading is wrong, a new reading is required and a reading is required at least six times a day.
Using the property of glucose that diffuses into the interstitial fluid from blood vessels, a thin needle is inserted into abdominal subcutaneous fat and measurement is performed. This shows high accuracy, but requires correction twice a day, and has a problem of high cost and eczema due to plaster. To prevent eczema caused by patches and to have high accuracy and sensitivity at the same time, an invivo sensor that measures blood sugar by being transplanted every six months or more is becoming mainstream in the next generation.
The EM characteristics (propagation speed, signal absorption and phase shift) depend on the electromagnetic parameters of the medium through which the wave propagates. The impedance is changed according to the change in the dielectric constant of the external medium, and the transition of the reflection coefficient can be measured. In addition, Figure 1.4(b) indicates the measurement of the dielectric constant according to the glucose concentration of plasma.[6] As the blood sugar level increased from 0 mg/dl to 2000 mg/dl, the dielectric constant was found to decrease from 53.92 to 52.2 at 10 GHz.
When these characteristics are applied to the blood glucose sensor, the change in dielectric constant according to the change in glucose appears as a reflection/transmission coefficient transition. Ideally, a non-destructive/non-invasive measurement method is possible by predicting changes in blood sugar by measuring changes in dielectric constant through electromagnetic penetration using in vitro sensors. Since the wavelength is inversely proportional to the magnitude of the frequency, it is easy to fabricate ultra-small sensors and easy to mass-produce using general-purpose circuits, and it has semi-permanent properties because it does not use an amount of limited. amount of material.
Bioimpedance spectroscopy, shown in Figure 1.5 (a), can use the method of detecting the concentration of glucose in the blood through the impedance spectrum according to the change in the membrane potential of red blood cells. In the case of the resonator-based sensor shown in Figure 1.5(b), the glucose level is measured by passing through the resonance frequency of the reflection coefficient. However, previous studies have limited the detection of ultrafine dielectric constant changes through resonance frequency transitions due to the low Q factor.
PROSPOSED STRUCTURE
- Operating pinriciples
- Multipole Expansion and Sub-radiative mode…
- Q factor Improvement using by sub-radiative mode…
- Comparison between electric dipole and magnetic dipole
- Proposed Design
- Optimization in In-vivo environment
- Balun for Symmetric current distribution…
- Reflection Coefficient by Permittivity…
- Low Q factor by Loss tangent
- Fabrication and measurement
It is defined as the ratio of the initial energy stored in the resonator to the energy lost in one radian cycle of oscillation. In the case of loss resistance, as it is a resistance based on material characteristics such as final conductivity, dielectric loss. As shown in Figure 2.4 (c), when operating as an actual sensor, a high Q factor has advantages in detecting the transition of the reflection coefficient within a limited frequency interval.
As a result of comparing the reflection coefficients of the three forms, it was confirmed that the Q factor was the highest in the case of the folded loop. When a rapid change in the imaginary part of the impedance occurs, a rapid change in the reflection coefficient occurs, resulting in a high Q factor. a). As a result, from the unfolded form it can be seen that only magnetic dipoles remain in the middle layer through which the current flows in the same direction. a) Reflection coefficient of single feeder structure, (b) multipole broadening, (c) current distribution at each resonance.
When analyzing a current change in each resonance, schematically only the electric dipole in the y direction remains in resonance I, III, and only a middle layer current with a current in the same direction remains to form a magnetic dipole resonance II to shape. In the case of PCB substrates and coaxial cables used for manufacturing, asymmetry occurs due to the difference in charge amount of the conductors. In Figure 2.12, a balun is an electrical device that brings balanced and unbalanced lines into contact without disturbing the impedance placement of the two lines.[13]
For this purpose, it is necessary to adjust the impedance by increasing the thickness of the patch so that charges can actively flow. As shown in Figure 2.16, the symmetry of the current distribution can be improved while the thickness of the patch is adjusted. However, when the loss tangent is large (>> 0), such as water or body tissue, electric polarization occurs in the dielectric and cannot respond quickly to the external electric field.
Recently, there is a trend to minimize losses by using polyimide with low dielectric loss on the surface of the PCB substrate. Additionally, the variables for each parameter of the sensor were optimized to compensate for the asymmetry of the dielectric conductor and shield of the coaxial cable. For this purpose, the size and dielectric properties of the conventional coaxial cable (SR 085) were reflected, and in the case of the Via hole, it is set to the radius of 0.2 mm, which is the smallest size that can be manufactured.
In the simulation results of the fabrication, it was verified that the reflection coefficient was efficient with multiple resonance with a high Q factor. As a result of current distribution control in magnetic dipole resonance, the electric dipole in the upper and lower layers is displaced, and the magnetic dipole in the intermediate layer remains as a principal moment, as illustrated in Figure 2.21. In the case of the upper surface of the upper plate, Balun was applied by increasing the thickness of the ground part feed line to minimize the unbalanced condition due to the imbalance of the axial cable.
The resonance frequency transition performance according to the change in the dielectric constant outside the sensor was verified by using the dielectric constant reduction property according to the increase in the temperature of water.
CONCLUSION
Joseph, Review of the long-term implantable Senseonics continuous glucose monitoring system and other continuous glucose monitoring systems, J. Moreland, "Glucose-dependent dielectric properties of blood plasma," in General Assembly and Scientific Symposium URSI, Istanbul, 2011. This work was supported by Material Component Technology Development Program Development of Sustained Precision Semi-Permanent and Low Time Delay 3rd Generation CGMS for Diabetes Patients Without Blood Sampling in Glucose Monitoring) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea)' and Basic Science Research Program through the National Research Foundation of Korea (NRF ) funded by the Ministry of Education (2018R1C1B 5041286).
Gangil Byun is a consultant who gained me a lot of experience and knowledge and developed my research skills while I participated in research and tasks related to antenna engineering and RF engineering with strong motivation during my research. Jae-Gon Lee for impressing many insights and intuition on RF engineering and antenna engineering conferences and meetings. I thank my fellow researchers, Jong-won Yoon, Yen, Jin-myung Heo, Tae-ho Yu, Sion You, Duyen, for their valuable assistance.
I also thank my colleagues Jin-sol Choi, Sun-hye Shin, Kaeul Lim, Hoon-yeop Jeong, Won-ju Jin, Young-soo Ahn, Je-hoon Lee, Woo-seok Kim, Hoi-chang Jeong, Woo- Young Jang, Sung-hyuk Park, Hyung joon Byun, and Eun-hye Kim for helping me on my research journey. Finally, I was able to endure the Master's period because of the endless love and trust of my family.
