An RCL sensor for measuring dielectrically lossy materials in the MHz frequency range: 1. Comparison of hydrogel model simulation with actual hydrogel impedance measurements

There is a requirement for the development of non-invasive continuous blood glucose monitoring devices to meet the clinical demands of the rapidly increasing number of people currently developing diabetes mellitus. Impedance Spectroscopy is a technology that meets the requirements of such devices. An NI CGMD is being developed as a device that couples a sensor to the skin to form an RCL sensor. The reliability of such an RCL sensor model has been investigated by comparing electrodynamical simulations to in-vitro measurements of dielectrically 'lossy' materials. The sensor has been modeled and simulated in FEMLAB (Finite Element Modeling Laboratory). In-vitro measurements are performed on hydrogels, representing the lossy material, by the aid of a Rohde & Schwarz VNA (vector network analyzer). From the quantitative agreement of the results we conclude, that the proposed qualitative model is appropriate for the characterization of the RCL sensor and suggests that more detailed models can be used to elucidate the behavior of human skin tissue. Index Terms--Equivalent circuits, circuit simulation, transducers, dielectric measurements, dielectric materials, skin, medical diagnosis.