Passive UHF RFID Tag for Heat Sensing Applications

A possible method of utilizing paraffin wax as a substrate material in developing a threshold heat sensing radio frequency identification (RFID) tag is discussed. A small narrow band passive UHF RFID tag is made on top of a multilayer substrate. Paraffin wax acts as the main heat sensitive layer of the substrate. The properties and characteristics of the paraffin layer change due to heat. The narrow band tag on top of the substrate is designed to be sensitive enough to detect any structural and physical changes of the substrate material. The changes in the properties of the substrate material will cause a shift in the operating frequency of the tag. This frequency shift will reduce the performance of the narrow band RFID sensor tag. The change in the properties of paraffin wax after being exposed to heat is irreversible under normal conditions and therefore, the proposed RFID tag can be referred to as a threshold heat sensing device. Such a low-cost solution can be useful in detecting heat exposures in various supply chains and transportation mishandling of heat sensitive items.