A Glucose Sensing System Based on Transmission Measurements at Millimetre Waves using Micro strip Patch Antennas

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.

Millimeter-Wave Sensing of Diabetes-Relevant Glucose Concentration Changes in Pigs

“…Hence, the expected additional concentration of blood glucose in the animal soon after injection is approximately Δg = 55/ 1.43 l = 38.5 mmol/l. For a d = 3 mm thick tissue sample such as the ear, the sensitivity value was calculated in [21] as S = 5.4 × 10 −3 dB/((mmol/l)/mm), which yields an expected transmission coefficient change equal to ΔS 21 = S*Δg*d = 0.62 dB. We note that an analytical time-dependent estimation of the change in glucose levels is not possible at this stage, as there are too many processes involved in affecting the glucose level concentration, such as the injection of insulin by the pancreas and the circulation of blood and glucose around the vessels of the body.…”

“…A more detailed description of the system can be found in [21]. Here, we summarize the key system aspects that are important to this animal study.…”

“…Another version of the system was tested in a proof-of-concept in vivo investigation in humans, showing promising initial results [21], but no consistent clean detection of glucose level changes. This is because several uncertainties were introduced when testing with live humans, such as uncontrolled skin and ambient temperatures and unwanted motion of the tissue being sampled due to the reactions of the subjects.…”

“…In our earlier work, a strong correlation between RF signal transmission and glucose concentration was demonstrated for saline laboratory samples loaded with glucose [17][18][19][20][21]. The system comprised two opposing patch antennas operating around 60 GHz, connected to a Network Analyzer (VNA).…”

Study and Suppression of Multipath Signals in a Non-Invasive Millimeter Wave Transmission Glucose-Sensing System

“…Based on these considerations, a non-invasive biomedical system for blood glucose sensing is currently under development by MediWise Ltd, which combines mmwaves with transmission-based sensing [7], [8]. Water absorption is maximized in the mm-wave range for normal body temperatures [9].…”