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Several reports over the last few decades have shown that the dielectric properties of healthy and malignant tissues of the same body organ usually show different values. However, no intensive dielectric studies of human colon tissue have been performed, despite colon cancer's being one of the most common types of cancer in the world. In order to provide information regarding this matter, a dielectric characterization of healthy and malignant colon tissues is presented. Measurements are performed on ex vivo surgery samples obtained from 20 patients, using an open-ended coaxial probe in the 0.5-18 GHz frequency band. Results show that the dielectric constant of colon cancerous tissue is 8.8% higher than that of healthy tissues (p  =  0.002). Besides, conductivity is about 10.6% higher, but in this case measurements do not have statistical significance (p  =  0.038). Performing an analysis per patient, the differences in dielectric constant between healthy and malignant tissues appear systematically. Particularized results for specific frequencies (500 MHz, 900 MHz, 2.45 GHz, 5 GHz, 8.5 GHz and 15 GHz) are also reported. The findings have potential application in early-stage cancer detection and diagnosis, and can be useful in developing new tools for hyperthermia treatments as well as creating electromagnetic models of healthy and cancerous tissues.

In-body sensor networks are those networks where at least one of the sensors is located inside the human body. Such wireless in-body sensors are mainly used for medical applications, collecting and monitoring important parameters for health and diseases treatment. The IEEE Standard 802.15.6-2012 for Wireless Body Area Networks (WBAN) considers in-body communications in the Medical Implant Communication Service (MICS) band. Nevertheless, high data rate communications are not feasible at the MICS band due to its narrow occupied bandwidth. In this framework, Ultra-Wideband (UWB) systems have emerged as a potential solution for in-body high data rate communications, due to its miniaturization capabilities or low power consumption. In the last years, some open issues have determined the research about in-body propagation. Firstly, the propagation medium, i.e., the human body tissues, is frequencydependent and exhibits a large attenuation at UWB frequencies. Secondly, the behavior of the in-body antennas is highly dominated by the surrounding tissues. Thus, the in-body channel characterization in UWB depends not only on the channel behavior itself, but also on the methodology of characterization. This paper intends to outline the research performed in the field of UWB in-body radio channel characterization considering the propagation medium, as well as the methodology of analysissoftware simulations, phantom measurements, in vivo measurements-. Thus, authors provide an overall perspective of the current state of the art, limitations for the analysis of in-body propagation, and future perspectives for UWB in-body channel analysis.

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