Tuba Yilmaz

Detecting Vital Signs with Wearable Wireless Sensors

The emergence of wireless technologies and advancements in on-body sensor design can enable change in the conventional health-care system, replacing it with wearable health-care systems, centred on the individual. Wearable monitoring systems can provide continuous physiological data, as well as better information regarding the general health of individuals. Thus, such vital-sign monitoring systems will reduce health-care costs by disease prevention and enhance the quality of life with disease management. In this paper, recent progress in non-invasive monitoring technologies for chronic disease management is reviewed. In particular, devices and techniques for monitoring blood pressure, blood glucose levels, cardiac activity and respiratory activity are discussed; in addition, on-body propagation issues for multiple sensors are presented.

Broadband Tissue Mimicking Phantoms and a Patch Resonator for Evaluating Noninvasive Monitoring of Blood Glucose Levels

Tissue mimicking phantoms (TMPs) replicating the dielectric properties of wet skin, fat, blood, and muscle tissues for the 0.3 to 20 GHz frequency range are presented in this paper. The TMPs reflect the dielectric properties with maximum deviations of 7.7 units and 3.9 S/m for relative dielectric constant and conductivity, respectively, for the whole band. The dielectric properties of the blood mimicking material are further investigated by adding realistic glucose amounts and a Cole-Cole model used to compare the behavior with respect to changing glucose levels. In addition, a patch resonator was fabricated and tested with the four-layered physical phantom developed in house. It was observed that the input impedance of the resonator is sensitive to the changes in the dielectric properties and, hence, to the realistic glucose level changes in the blood layer.

Towards Accurate Dielectric Property Retrieval of Biological Tissues for Blood Glucose Monitoring

An analytical formulation for relative dielectric constant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and effective relative dielectric constant of a lossy superstrate, such as biological tissue. To do so, an analytical equation is modified by constructing functions for the two unknowns, the filling factor A and effective length leff of the resonator. This is done by simulating the resonator with digital phantoms of varying permittivity. The values of A and leff are determined for each phantom from the resulting S-parameter response, using particle swarm optimization. Multiple nonlinear regression is applied to produce equations for A and leff, expressed as a function of frequency and the phantoms relative dielectric constant. These equations are combined to form a new nonlinear analytical equation, which is then solved using the Newton-Raphson iterative method, for both simulations and measurements of physical phantoms. To verify the reconstructed dielectric constant, the dielectric properties of the physical phantoms are determined with commercial high temperature open-ended coaxial probe. The dielectric properties are reconstructed by the described method, with less than 3.67% error with respect to the measurements.

Wearable wireless sensors for healthcare applications

Recent activities at Queen Mary, University of London, relating to wearable wireless sensors research for healthcare applications are reviewed in this paper. The monitoring of blood glucose levels using non-invasive radio-based sensors is discussed. The analysis of on-body radio propagation channels is then presented, with an emphasis on variations related to activity.

Patch resonator for non-invasive detection of dielectric property changes in biological tissues

In this study, a patch resonator with two ports is proposed for retrieving the dielectric properties of biological tissues. The resonator is designed to operate in the 2.45 GHz Industrial, Scientific, and Medical band when placed on the tissue. CST Microwave Studio was used to simulate the structure with five layers of tissue above. Two via pins are used to tune the resonance frequency and to miniaturize the patch resonator. Rogers R03010 is used as a substrate. The configuration of the resonator and the simulation results are given. This paper also presents recipes of tissue-mimicking materials, along with dielectric property measurement results of fabricated physical tissue phantoms.

Compact Resonators for Permittivity Reconstruction of Biological Tissues

In this paper, a patch resonator is proposed for non-invasive measurement of dielectric properties of biological tissues. Resonator is operating at 2.4 GHz when placed on tissue. The patch resonator is simulated in HFSS with four layered tissue mimicking material (skin, fat, blood, muscle) placed on top. The electrical properties of blood layer is decreased and the change in S parameters is tracked. Effective dielectric properties of the tissue is reconstructed from simulated S parameter response of the resonator.

Multi-objective particle swarm optimization applied to the design of Wireless Power Transfer systems

This paper proposes a stochastic method - particle swarm optimization (PSO) and Pareto front technique, to conduct a multivariable optimization and design an inductively coupled power transfer system. Previously, design methods have been proposed which require designer experience; they are not only computationally challenging, but also frequently result in suboptimum solutions. The algorithm proposed in this paper models all losses and inductance matrix analytically. We study four common compensation structures, and select a series-parallel topology to design a 200 W experimental prototype optimized with respect to transfer efficiency and VA rating. Experiments and numerical simulations are employed to verify the optimization algorithm.

Sensing of dielectric property alterations in biological tissues at microwave frequencies

In this paper, testing of an open ended spiral resonator for electrical property retrieval of biological tissues is presented. A spiral open ended resonator operating at 630 MHz when placed on human skin is tested with high water content phantoms. Phantoms are prepared by mixing water and flour and adding 5%, 10%, 15%, 20%, 25%, 30% sugar to the mixture. To collect reference data, electrical properties of the phantoms are measured in advance with Agilent 85070 high temperature dielectric probe kit. Response of the structure is collected by placing the phantoms on top. Trough the S-parameter measurements the electrical properties of the phantoms are retrieved and the results are compared with the collected reference data.