Higher-order harmonics of a magnetically soft sensor: Application to remote query temperature measurement

This letter describes the application of magnetically soft ribbons for remote query temperature monitoring based upon amplitude changes in the higher-order harmonics emitted by the sensor in response to a magnetic interrogation signal. The harmonic-based temperature sensor is placed, or rigidly embedded since there are no moving parts, within the region of interest where it is remotely monitored using a single interrogation and detection coil. Taking the amplitude ratio between two or more different-order harmonics eliminates the effect of relative orientation between the sensor and monitoring coil, enabling wide-area monitoring. Remote query monitoring of temperature from within a concrete block is demonstrated. The wireless and passive nature of the described sensor platform makes it ideally suited for long-term monitoring applications, such as measuring the temperature inside a concrete roadway or building structure.