This article deals with the theory and performance of a sensor for measuring thermal conductivity. The sensor, in the form of a small ball, generates heat and simultaneously measures its temperature response. An ideal model of the hollow sphere in an infinite medium furnishes a working equation of the hot-ball method. A constant heat flux through the surface of the ball generates the temperature field. The thermal conductivity of the surrounding medium is to be determined by the stabilized value of the temperature response, i.e., when the steady-state regime is attained. Error components of the sensor are discussed due to analysis of the deviations of the real hot-ball construction from the ideal model. The functionality of a set of hot balls has been tested, and the calibration for a limited range of thermal conductivities was performed. A working range of thermal conductivities of tested materials has been estimated to be from 0.06 W · m −1 · K −1 up to 1 W · m −1 · K −1 .

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In this paper, the dependence of radio-frequency (RF) field absorption on human body dimensions is investigated. The resonance properties of an ellipsoidal homogeneous human model have been investigated in frequency range from 10 MHz to 500 MHz with assistance of CST Microwave Studio program environment. In the article, the simulation of RF field absorption in the ellipsoidal body model has been performed for three various body heights, as well as three widths for a given body height.