Light-Energy-Harvested Flexible Wireless Temperature-Sensing Patch for Food Cold Storage

The conventional rigid and energy-limited battery-powered wireless sensor network (WSN) needs to be improved for continuously sensing temperature and guaranteeing food quality and safety in cold storage. This paper aims to propose and develop a light-energy-harvested flexible wireless temperature-sensing patch (LTSP) for food cold storage. The LTSP could provide sustainable light-energy-powered battery-free applications in low-light conditions. The flexible circuit of LTSP was fabricated by the photosensitive etching method with a polyimide (PI) film as the flexible substrate and copper (Cu) as the circuit. The light energy was harvested by two pieces of amorphous silicon solar cells and stored in a micro-supercapacitor by the power-management module. The LTSP is flexible and can be bent. The micro-supercapacitor of 1 mF was rapidly charged from 0 to 3 V after only about 47 s and the micro-supercapacitor of 10 mF took about 465 s under the light intensity of 2100 lux by the light-energy-harvesting module. The temperature of the packaged food was sensed and acquired by a wireless module. The temperature-sensing data and voltage status of the micro-supercapacitor could be displayed on a liquid crystal display (LCD) in real time or read by radiofrequency identification (RFID) or near-field communication (NFC) reader such as NFC-enabled smart phone or device via a frequency of 13.56 MHz. The LTSP worked well under a light intensity of 2100 lux. The temperature fluctuation could be acquired under the table grapes storage temperature of 0 °C. The proposed LTSP has potential applications in food cold storage in supermarkets with light-energy reuse and could provide insights into the development of sustainable food quality and safety.