Development and Performance of a Battery-Free Disaster Prevention Radio “HOOPRA” Using the Energy Harvested from Radio Waves

抄録

A battery-free radio receiver, HOOPRA (hoop type radio), is proposed for acquiring information using middle wave AM radio broadcasting during unexpected power failures or disasters, with emphasis on wide coverage, immediate information acquisition, and energy saving. The HOOPRA utilizes middle waves for energy harvesting. As this radio is intended for use during disasters, the protection methods, receiving performance, and the applications of energy harvesting are reported in this paper. The HOOPRA is ring-shaped with a diameter of 20 cm when retracted, for portability and 60 cm when expanded, for usage and is lightweight (180 g). The HOOPRA works on the principle of a crystal radio but has an adequate receiving performance without an external antenna that is generally necessary for crystal radios and is portable. It could receive a radio broadcast within an area of radius 15 km from a transmitting station of the NHK Fukui Daiichi Broadcasting (JOFG, 5 kW). Further, the energy harvested from the middle waves utilizing the high sensitivity of the HOOPRA was found to light-up a white LED. In a field test with the HOOPRA, it was found that the receiving sensitivity was particularly enhanced near a tall building, probably owing to the diffraction effect of the radio waves. Use of this effect for enhancing the sensitivity of the battery-free radio is also explained.