Diabetes has become a serious public health problem in Asia. According to statistics, there are currently about 30 million diabetic patients in Southeast Asia, and this number is expected to rise to nearly 80 million by 2025. Traditional blood glucose monitoring methods usually require blood drawing, which is not only painful but also a significant psychological burden for patients. Therefore, non-invasive blood glucose monitoring technology has always been a research focus in the medical and engineering fields.

In 2008, Yoshio Nikawa and T. Michiyama from Kokushikan University in Japan published a paper at the Asia-Pacific Microwave Conference, proposing a non-invasive blood glucose monitoring method based on millimeter wave reflection coefficients, offering new hope for diabetic patients.

Why Use Microwaves?

The complex permittivity of blood is very sensitive to glucose concentration in the microwave frequency band. This means that, in theory, by measuring the reflection characteristics of human tissues to microwaves, the glucose level in the blood can be deduced.

However, the high loss characteristics of human tissues to microwaves make it very difficult to detect these subtle changes from outside the body. To address this, the researchers designed a resonant metal fiber sensor placed between the waveguide and the fingertip, significantly improving detection sensitivity.

Experimental Design and Key Findings

The research team first measured the complex permittivity of glucose solutions at different concentrations using an open-ended coaxial probe. They found that changes in glucose concentration cause significant changes in the complex permittivity. Specifically, for every 1% increase in glucose concentration, the real and imaginary parts of the permittivity change by approximately 0.386 and -0.325, respectively.

Subsequently, they designed a patch-type resonator applied directly to a volunteer's fingertip. By measuring the change in the reflection coefficient at the resonant frequency, they estimated the blood glucose level. The experimental results showed:

• Higher blood glucose concentrations lead to lower resonant frequencies;

• The change in the reflection coefficient has a linear relationship with the blood glucose concentration, with a sensitivity of about 0.011 dB/(mg/dl).

Although this change is small, it is detectable by modern vector network analyzers, proving the feasibility of the method.

Significance and Future Prospects

This research demonstrates the great potential of microwave technology in medical diagnostics. Non-invasive and painless blood glucose monitoring can not only improve patients' quality of life but also pave the way for future home-based, continuous blood glucose monitoring devices.

Although this technology is still in the laboratory stage and some distance away from commercialization, it undoubtedly points to a new technical direction for non-invasive blood glucose monitoring.

References
Y. Nikawa and T. Michiyama, "Blood-Sugar Monitoring by Reflection of Millimeter Wave," Asia-Pacific Microwave Conference, 2007.