Development of a nanoparticle time-temperature sensor for passive and active RFID

We have developed a thermally activated Time-Temperature Indicator (TTI) suitable for use in passive and active RFID applications. In general, this type of indicator can be used in the cold chain to monitor the thermal age of foods and pharmaceuticals as well as provide more accurate estimates of shelf life. In this manuscript we have sought to design an indicator with a time-temperature profile similar to that of milk. The sensor is composed of a dc resistance measurement of Cobalt/Antimony (Co/Sb) multilayer films. Upon deposition and processing, the Co self-assembles into single domain magnetic nanoparticles approximately 20 nm in-plane and 4 nm perpendicular to the plane resembling nano-pancakes embedded within the Sb matrix. At ambient temperatures the Co nanoparticles ensemble magnetization decreases. This is a thermally activated process that follows an Arrhenius like behavior. As the sample magnetization decreases, the resistivity of the material also decreases following the same thermally activated behavior as the magnetization.