Wearable technology has been rapidly evolving. Many functions beyond current smartphone capabilities must be realized in wearables that are smaller than smartphones. Heat generation due to power consumption may cause both circuit malfunctions and lowtemperature burns. This letter presents thermal design methods to promote heat dissipation of wrist wearables. First, the thermal model to easily obtain each part temperature is described. Next, belt heat dissipation effects are clarified by simulations with the model. The results indicate that each technique using the belt width, thickness, length, covering rubber, or heatsink has a high effect on heat dissipation. In addition, by combining these techniques, temperature rises of the display, bottom of device body, and belt can be reduced by 30.5%, 52.4%, and 52.7%.

This letter proposes a novel method to promote the heat dissipation of watch-type smart devices by using receiver coils for wireless charging. It is achieved by embedding a spiral coil inside the belt. The heat dissipation effects of the proposed method on temperatures at key hot spots are clarified. The power transfer efficiency is also clarified. In watch-type smart devices, the most critical part for temperature is the underside surface of the belt, since this is the part that touches the skin for a long time. The analysis results show that the proposed method can reduce the increase in ambient temperature at the belt's underside surface by 59.7% and that its power transfer efficiency is more than 90%.