Feasibility of a non-invasive wireless blood glucose monitor

Blood glucose monitors are critical to diabetes management. Many new noninvasive measurement techniques are being investigated. The present work focuses on the possibility of a monitor that non-invasively measures blood glucose levels using electromagnetic waves. The technique is based on relating a monitoring antenna\u27s resonant frequency to the permittivity and conductivity of blood which in turn is related to the glucose levels. At first a realistic data base for the dielectric properties of blood has been established through in-vitro measurements performed on blood samples obtained from 20 patients with glucose levels ranging from normal (87 mg/dl) to hyperglycemic (330 mg/dl). Using the Agilent 85070E dielectric probe and an Agilent 8720B network analyzer the dielectric permittivity and conductivity of the blood samples have been measured over a frequency range of 1GHz - 10GHz. The Cole-Cole model has been modified through curve fitting to in-vitro data that includes a factor representing glucose levels. Two antennas (wideband and narrowband) have been designed, constructed and tested in free space. A simulation model of layered tissue and blood together with an antenna has been created to study the effect of changing glucose levels. It is noted that the antenna\u27s resonant frequency increases with increase in glucose levels. An analytical model for the antenna has been developed, which has been validated with simulations. The model consists of a lumped-element antenna that represents a narrowband radiator. The resonant frequency of the radiator is dictated by a resonant LCR circuit, which is a function of the materials within the antenna\u27s near-field. A measurement system has been developed to measure the resonant frequency of the antenna. A frequency synthesizer generates an RF signal over the desired frequency range. This signal is sent to the antenna through a directional coupler that generates forward and reflected signals. These voltages are measured and the reflection coefficient is calculated with a microprocessor. As an experimental verification, two antennas were strapped one on each leg of a patient with one antenna connected to the PNA and the other to the measurement system. As the patient ingested fast acting glucose tablets, the blood glucose level was measured by a traditional glucose meter. At the same time, a comparison of the resonant frequency of the antenna measured by the PNA and by the measurement system showed good agreement. Further, it is seen that the antenna resonant frequency increases as the glucose level increases, which is consistent with the simulation model