Real-Time Noninvasive Measurement of Glucose Concentration Using a Modified Hilbert Shaped Microwave Sensor.

We developed a microwave glucose sensor based on the modified first-order Hilbert curve design and measured glucose concentration in aqueous solutions by using a real-time microwave near-field electromagnetic interaction technique. We observed S21 transmission parameters of the sensor at resonant frequencies depend on the glucose concentration. We could determine the glucose concentration in the 0-250 mg/dL concentration range at an operating frequency of near 6 GHz. The measured minimum detectable signal was 0.0156 dB/(mg/dL) and the measured minimum detectable concentration was 1.92 mg/dL. The simulation result for the minimum detectable signal and the minimum detectable concentration was 0.0182 dB/(mg/dL) and 1.65 mg/dL, respectively. The temperature instability of the sensor for human glycemia in situ measurement range (27-34 °C for fingers and 36-40 °C for body temperature ranges) can be improved by the integration of the temperature sensor in the microwave stripline platform and the obtained data can be corrected during signal processing. The microwave signal-temperature dependence is almost linear with the same slope for a glucose concentration range of 50-150 mg/dL. The temperature correlation coefficient is 0.05 dB/°C and 0.15 dB/°C in 27-34 °C and 36-40 °C temperature range, respectively. The presented system has a cheap, easy fabrication process and has great potential for non-invasive glucose monitoring.

Noninvasive in vitro measurement of pig-blood d-glucose by using a microwave cavity sensor.

We have developed an electromagnetic microwave cavity sensor based on the resonant frequency shift for real time measurement of the glycemia in pig blood. We could determine the concentration of d-glucose in pig blood in the range of 150-550mg/dl at the resonance frequency near 4.75GHz with a bandwidth of 300MHz. The change in the d-glucose concentration in blood brings microwave reflection coefficient S(11) changes of about 6.26dB and resonance frequency shifts of about 11.25MHz due to the electromagnetic interaction between the cavity resonator and the blood filled plastic tube inserted into the cavity. This proposed system provides a unique approach for real time noninvasive and contactless glucose monitoring.

Non-invasive in vitro sensing of D-glucose in pig blood.

We have developed an electromagnetic resonant spiral sensor and have measured the glycemia in pig blood and the concentration of D-glucose in aqueous solution by using a real-time electromagnetic interaction phenomenon between the microwave sensor and the liquid. We could determine the concentration of glucose with a minimal resolution of 5 mg/dl in the 100-600 mg/dl concentration range at operating frequencies of about 7.65 GHz (for the glucose aqueous solution) and 7.77 GHz (for the pig blood sample). The change in the glucose concentration brings the changes of the microwave reflection coefficient due to the electromagnetic interaction between the resonator and the glucose solution. The in vitro results show the measured signal-to-noise ratio of about 34 dB, and the minimum detectible signal level of about 0.022 dB/(mg/dl). Our proposed system provides a unique approach for non-invasive and non-contact glucose monitoring, and it may serve as a bloodless glucometer.

Visualization of magnetic domains by near-field scanning microwave microscope.

A near-field scanning microwave microscope (NSMM) system was used for the investigation of magnetic properties of a hard disk (HD) under an external magnetic field. To demonstrate local microwave characterization of magnetic domains by NSMM, we scanned the HD surface by measuring the microwave reflection coefficient S(11) of the NSMM at an operating frequency near 4.4GHz. The NSMM offers a reliable means for quantitative measurement of magnetic domains with high spatial resolution and sensitivity.

Investigation of photoconductivity of silicon solar cells by a near-field scanning microwave microscope.

The photovoltaic effect in silicon solar cells were investigated by using a near-field scanning microwave microscope (NSMM) technique by measuring the microwave reflection coefficient at an operating frequency near 4GHz. As the photoconductivity in the solar cells was varied due to the incident light intensities and the wavelength, we could observe the photoconductivity changes at heterojunction interfaces inside the solar cells by measuring the change of reflection coefficient S(11) of the NSMM. By measuring the change of reflection coefficient, we also directly imaged the photoconductivity changes at heterojunction interfaces inside the solar cells.