In this paper, we present a new method for evaluating heat transfer materials. When electronic devices are mounted on a metallic heat sink, a heat-transfer material is required to handle the thermal flow from the devices while maintaining electrical insulation. The concept proposed in this paper is to measure the thermal characteristics of a heat-transfer material placed on an aluminum plate that is machine-milled to form precise grooves, which represent the surface roughness of the heat sink. By varying the shape of the grooves and the amount of applied pressure, the contact conditions can be precisely controlled. In order to verify the effectiveness of the proposed method, an evaluation system was constructed, in which the temperature was controlled using flowing water. Tests were then carried out on two types of heat-transfer materials, one with a hardness of C10 and the other with a hardness of C60, as determined using an Asker C type hardness meter.

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Human body communication, which utilizes our body as part of the transmission medium, is expected to be a new transmission method for networks between wearable devices such as a body area network (BAN). Wearable devices demand a long battery operating life, small size, and light weight. Therefore, it is important to achieve impedance matching and improve transmissions between devices without any additional parts such as transformers or stubs. In this study, the input impedance characteristics of transmitter electrodes were investigated through a three-dimensional electromagnetic field analysis for improving transmission characteristics between devices by impedance matching. Simulation using a detailed human body model showed that the input impedance characteristic is different from that obtained when using a homogenous cylinder model. Furthermore, input impedance characteristics were analyzed by substituting the electrical properties of body tissues with those of other body tissues and air. This analysis has revealed that skin, fat and muscle are the main body tissues that determine the input impedance characteristics of electrodes. Moreover, we compared the electric field distribution and transmission characteristic of various models and found that skin, fat and muscle were also the dominant body tissues that determine these characteristics. In the transmitter configuration assumed in this study, the SAR (Specific Absorption Rate) values inside the body were within safety standards.

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