Abstract
We present a sensing system operating at millimetre (mm) waves in transmission mode that can measure glucose level changes based on the complex permittivity changes across the signal path. The permittivity of a sample can change significantly as the concentration of one of its substances varies: for example, blood permittivity depends on the blood glucose levels. The proposed sensing system uses two facing microstrip patch antennas operating at 60 GHz, which are placed across interrogated samples. The measured transmission coefficient depends on the permittivity change along the signal path, which can be correlated to the change in concentration of a substance. Along with theoretical estimations, we experimentally demonstrate the sensing performance of the system using controlled laboratory samples, such as water-based glucose-loaded liquid samples. We also present results of successful glucose spike detection in humans during an in-vivo Intravenous Glucose Tolerance Test (IVGTT). The system could eventually be developed into a non-invasive glucose monitor for continuous monitoring of glucose levels for people living with diabetes, as it can detect as small as 1.33 mmol/l (0.025 wt%) glucose concentrations in the controlled water-based samples satisfactorily, which is well below the typical human glucose levels of 4 mmol/l.
Highlights
Quasi-optical setups have been used recently for dielectric measurements to detect the water contents of rocks and oils[1]
Mm-wave spectroscopy in reflection mode has been used for non-invasive glucose sensing through human skin[7]
Since we utilize glucose dissolved in water-based samples, its concentration can be measured as a percent w/w in water, or through the weight of glucose per 1 l of water
Summary
Shimul Saha[1], Helena Cano-Garcia[1,2], Ioannis Sotiriou[1], Oliver Lipscombe[1,2], Ioannis Gouzouasis[1,2], Maria Koutsoupidou[2], George Palikaras[1], Richard Mackenzie[3], Thomas Reeve[3], Panagiotis Kosmas2 & Efthymios Kallos[1]. We present a sensing system operating at millimetre (mm) waves in transmission mode that can measure glucose level changes based on the complex permittivity changes across the signal path. In addition to material characterization, mm-wave spectroscopy in reflection mode has been used to detect sugar or glucose levels in water or blood, in the frequency spectrum of 33–95 GHz4. To take advantage of transmission data, a sensor operating at K band (27–40 GHz) has been developed to detect glucose level in blood non-invasively[8]. A pair of patch antennas tuned to operate around 60 GHz has been designed and fabricated to replace the earlier-used waveguide structures These antennas are mounted on an experimental setup for measuring transmission across an acrylic tank filled with controlled water-based glucose solutions using micro-positioners and 3D-printed sample holders. The in-vivo results show that despite the signal uncertainty introduced by the human tissue, glucose spikes can be adequately detected with the present sensing system
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