부산대학교 도서관

There is a need for economical monitoring of fragile goods that are sensitive to temperature, tilt or vibrations during transit. The mishandling of these goods could permanently alter or damage them. Existing methods rely on electronic devices that need a continuous power source for sensing and data logging. This article introduces a simple battery-free economical solution for recording a singular event of temperature crossing or a tilt activity using liquid metal, namely eutectic gallium indium (EGaIn) coupled to a Radio-Frequency Identification (RFID) tag. The crossing of a threshold of either temperature or tilting angle results in EGaIn flow, which activates or deactivates the RFID tag permanently. This change is irreversible; thus, the sensor memorizes the specific temperature or tilt event. This built-in memory function and wireless communication of the RFID sensor enables economical monitoring of temperature and motion-sensitive goods during transport without the need for a battery. In this paper, we have further reduced cost by fabricating these temperature and tilt sensors on paper substrates.