Monitoring of freezing processes in liquid nitrogen by means of passive RFID through container walls

Medical and biological cooling processes as well as many industrial processes operated at low temperatures utilize liquid nitrogen as a coolant. In order to monitor the cooling process (i.e. the freezing state of the sample), contacting temperature sensors could be attached to the probe. However, this requires cabling both to supply the sensors and to transmit the measurement signal to the exterior of the cooling tank. The RFID based sensor proposed in this paper provides a measurement of the object's freezing state and can be operated without any cabling or on-sensor power supply directly inside the liquid nitrogen vessel.