Assessing the dynamic behavior of WSN motes and RFID semi-passive tags for temperature monitoring

• RFID and WSN are used for monitoring cold chain, fast temperature changes may occur.
• There is no previous studies of the dynamic behavior of the devices.
• This study proves that the dynamic response is influenced by the sensor housing.
• 180 s is the time response difference in aerial mount vs to motherboard soldering.
• Some of these devices are not able to track temperature changes faster than 308 s.

Wireless Sensor Networks (WSN) and Radio Frequency Identification (RFID) are two wireless technologies that are being used for cold chain monitoring and tracking. Several applications in this field have been reported in the last few years. However, there are no studies about the the dynamic behavior of this hardware and how this affects the measurements. Therefore the purpose of this study is to evaluate the dynamic behavior of the sensors. A series of trials were designed and performed, covering temperature steps between cold chamber (5 °C), room temperature (23 °C) and heated environment (35 °C). Three WSN motes, with different sensor configurations, and four RFID tags (with and without housing), were compared. In order to assess the dynamic behavior two alternative methods have been applied for adjusting experimental data to a first order dynamic response that allows extracting the time response (τ) and corresponding determination coefficient (r2). The shortest response time (10.4 s) is found for one of the RFID semi-passive tags. Its encapsulated version provides a significantly higher response (60.0 s), both times are obtained with the same method. The longest τ corresponds to one of the sensors embedded in a WSN mote (308.2 s). We found that the dynamic response of temperature sensors within wireless and RFID nodes is dramatically influenced by the way they are housed (to protect them from the environment); its characterization is basically to allow monitoring of high rate temperature changes and to certify the cold chain.