Accurate dielectric characterisation of biological tissues in the microwave range using the open-ended coaxial probe technique
La Gioia, Alessandra
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Accurate knowledge of the dielectric properties of biological tissue samples is fundamental in the design of novel electromagnetic-based medical devices. Biological tissue samples are typically characterised dielectrically using the open-ended coaxial probe technique, which is based on the assumption that the investigated sample is homogeneous. Thus, in order to associate the acquired dielectric properties with the different tissue types within heterogeneous samples, the sample can undergo post-measurement histological analysis. Specifically, histological analysis needs to be conducted on the region of sample consisting of the tissues that may have contributed to the measured dielectric properties. To this extent, it is fundamental to define the sensing volume of the measurement probe, which is delineated by the sensing radius and sensing depth. Recent research studies have investigated the impact of the sensing depth definition and calculation on the dielectric characterisation of a number of layered material samples, thus demonstrating how this parameter may be a source of error in the interpretation of dielectric data acquired from heterogeneous samples. However, few studies have investigated the sensing radius, and only for a limited number of probes and material samples. For this reason, in this thesis, the sensing radius is investigated through both dielectric measurements and numerical simulations conducted on radially heterogeneous tissue-mimicking and biological samples, with different dielectric properties and contrasts. Thus, this thesis provides a basis for consistent identification of the sensing radius and accurate interpretation of the dielectric properties acquired from radially heterogeneous tissue samples, with the aim of supporting the design of electromagnetic medical devices.