Magnetic structures for contactless temperature sensor

In this paper, an innovative idea of the use of NiFe alloys as temperature sensor is presented. The NiFe sensor is associated to a remote magnetic transducer and provides a contactless temperature measurement. The measurement is done by magnetic coupling between the sensor and the transducer without any mechanical and electrical contact. At the so-called Curie temperature (Tc), magnetic materials loose their magnetic properties and become paramagnetic. The NiFe alloys used in this study are strongly temperature dependant and could be efficiently used as temperature sensors. Any temperature variation around Tc causes a progressive and reversible variation of the magnetic polarization Js and the relative permeability μr. These alloys have also controlled Tc and could easily be performed for various applications. Three magnetic structures were realized in order to exploit the NiFe magnetic variations to generate a variable output signal with temperature: structure with magnets, structure without magnets and differential structure. A few millimetres contactless measurement was obtained. The experimental set-up used for the tests and some results are also presented and discussed.