Temperature Sensing System With Short-Range Wireless Sensor Based on Inductive Coupling

This paper presents the theory, development, and results for a temperature sensing system that employs a wireless sensor with powering and communications based on inductive coupling. The theory of inductive coupling is presented along with a methodology that has been developed to determine the system elements in order to fulfill communication range and bandwidth requirements in a certain class of applications. A miniaturized wireless sensor was built (volume 3.2
${\rm cm} ^{3}$
), and the whole system was validated by means of an experiment where the sensor was immersed in a water bath, in which the temperature was varied during 69 h in a cycle covering a span of 30
$\ ^{\circ}\hbox{C}$
. Measurements had a high correlation with an accurate reference thermometer. It is shown that the interruption of the radio frequency (RF) field during the measurements is a useful method to improving the measurement quality. In the course of the validation experiment, this method reduced the standard deviation of the measures up 0.01
$\ ^{\circ}\hbox{C}$
.