32 nd URSI GASS, Montreal, 19-26 August 2017 A Comparative Study for Development of Microwave Glucose Sensors Tuba Yilmaz*, Tugce Ozturk, and Saul Joof Department of Electronics and Communication Engineering, Istanbul Technical University, Maslak, Istanbul, 34469 Turkey. Abstract This paper presents a comparative study in an attempt to identify the best frequency of operation for a potential microwave glucose sensor. Two patch antennas operating at 2.45 GHz and 5.8 GHz are designed to radiate towards high permittivity and high loss de-ionized water medium. Antennas are covered with superstrates to limit the contact with the liquid and mounted at the bottom of containers. From the measured S 11 response of the antennas with changing glucose levels, it was concluded that the antenna operating at the higher frequency is more sensitive to the changes in the glucose levels. 1. Introduction Proper management of chronic diseases can only be possible with life style adoptions and appropriate medical care enabled with the collected vital signs information [1]. One of the vital signs is blood glucose levels that should be regulated to prevent the complications of diabetes disease. Diabetes patients are monitoring the blood glucose levels with chemical means where a drop of blood needs to be withdrawn, usually from the fingertips of the patient. Current monitoring technique is unable to meet the need to collect the continuous blood glucose levels data for effective management of the disease. Another drawback of the current monitoring technique is the invasive nature of the application, discouraging the patient from collection of frequent measurements. Therefore, there is a need for a continuous and non-invasive technique to monitor the blood glucose levels. Within the last decade, microwave sensing has been increasingly studied as a candidate technique for continuous and non-invasive blood glucose monitoring. A microwave cavity resonator is investigated in [2] detect the dependence of the Q factor and S 21 magnitude to the variations in blood glucose concentrations. Other than cavity resonators, split ring resonators (SRR) have been investigated in the literature [3]. An open-ended microstrip spiral transmission line is proposed in [4]. Forward transfer function (S 21 ) variation resulting from the changes in the permittivity of the test material is measured with the spiral antenna over the frequency range from 100 MHz to 5 GHz. The spiral resonator is then used in another study to retrieve the relative permittivity of phantoms with varying sugar contents [5]. In [6], an ultra wide band monopole antenna is modified to operate at lower frequencies. The antenna is then simulated in HFSS, for three different glucose concentrations: hypoglycemia, normoglycemia, and hyperglycemia. In [7], a patch resonator operating at 2.46 GHz is proposed. Change in input impedance of the resonator was measured. The literature suggests that the glucose dependent dielectric property changes alters the response of the microwave resonators. However, a significant permittivity change can only be possible with high levels of glucose [8]. Considering the realistic glucose changes in the human body, the realistic permittivity change is very limited. Thus, there is a need for a comprehensive study investigating the best possible sensor design and operation frequency to realize a microwave noninvasive glucose sensor. In this study, to identify the best frequency of operation, two patch antennas designed to operate at two different ISM bands are investigated with glucose solutions. Section 2 gives the antenna designs, experimental set-up is given in Section 3, Section 4 shows the results, and finally Section 5 presents the conclusion. 2. Design of Antennas Two patch antennas operating at 2.45 GHz and 5.8 GHz ISM bands are optimized to function in a high permittivity and high loss de-ionized water environment. Both of the antennas are fabricated on an FR4 substrate with the relative permittivity of 4.4 and dissipation factor of 0.021 at 10 GHz. Antennas are also covered with two FR4 superstrates. The superstrate prevents the direct contact between the radiating parts of the antennas and the liquids. Due to the high permittivity environment surrounding the antennas, two layers of FR4 is stacked together to form a thick layer of superstrate which decreased the effective permittivity of the microstrip antennas. Through this approach is adopted to ease the fabrication of antennas. It should be noted that, a superstrate can be useful to limit the specific absorption rate (SAR) for a practical application. The thickness of the FR4 material is standard (1.6 mm). An iterative approach is used to design the antennas. First the required antenna dimensions are calculated to operate at the air medium, then the layers are added and the antenna is optimized with the trial-and-error method. Final