In this paper, a wireless interrogable sensor device based on an ultra low -
power microcontroller for data collection and a radio frequency identification
(RFID) interface for data transmission is presented. Wireless sensor systems
utilizing RFID transponders offer a new and exciting means of measurement
and identification suitable for many biomedical applications.
For the majority of these applications, small, inexpensive radio request sensor
systems are desirable. In this paper, an ultra-low -power and low -cost wireless
temperature data logger system is presented with its application in observing
dental retainer use.
For this purpose, the retainer's ambient temperature is measured by an
integrated sensor and recorded using a microcontroller which acts like a
temperature data logger storing the thermal history of several months.
For a self powered wireless data transmission from the sensor to the
interrogation unit a RFID transponder, operating in the 13.56 MHz ISM band, is
used. The presented sensor system includes hard- and software power saving
modes reducing the sensor idle current consumption to 1 muA.
This allows a battery powered operation of the device for up to two years. For
dental and biomedical applications, the device is hermetically sealed using a
biocompatible polymeric encapsulation. Results of the first clinical trials
observing the patient's dental retainer usage by a set of retainers equipped
with the RFID temperature sensor/data logger device are presented.
The stored temperature values are analyzed and a clear temperature
characteristic indicating the retainer usage was found.
