تعیین درجه حرارت بدون تماس فازهای مغناطیسی جاسازی شده از پوشش سخت با بهره برداری از پسماند مغناطیسی

A non-contact temperature sensor is described which is based on the temperature dependency of the hysteresis of a magnetic phase embedded in a non-magnetic hard coating. For the measurement principle the technique of frequency mixing is used, with extension toward phase sensitivity as indicator for the temperature. The sensor's capabilities such as selectivity and sensitivity are investigated on TiN–FeCo magnetic multilayers. The sensor has been proven for temperatures up to 500 °C and shows capabilities for higher temperatures.

Measurement of physical parameters based on changes of magnetic properties of a sensor phase has already been applied in areas where established methods cannot be used, e.g. extreme temperature applications or UHV [1]. Characteristic examples are represented by pressure and strain sensors, where magnetostrictive materials are used as sensor phase [2]. More recently, superparamagnetic beads as specific labels for proteins or bacteria are used to measure their concentration [3]. To date, for temperature investigation typically the magnetic properties of a sensor phase, i.e. magnetostriction, permeability, or the Curie temperature have been measured as direct indicators [4] and [5]. More recently, the magnetization curve of superparamagnetic beads and its temperature dependency has been described analytically, enabling their use for temperature measurement in medical applications [6]. In this paper, a new technique based on frequency mixing is proposed. The temperature is indirectly determined by related changes of the magnetic hysteresis of a sensor phase. The performance of the method is tested for temperatures up to 500 °C in the case of TiN-based hard coatings, where the in-situ non-contact measurement of the temperature of the coating would be a valuable quantity for process optimization.

In this paper, a non-contact sensor concept is introduced to measure the temperature of soft magnetic materials. The novelty of the principle based on frequency mixing technique is that the phase of the demodulated frequency mixing signal is used to gain information about the magnetic properties, e.g. hysteresis, and implicitly on the related physical properties, e.g. temperature. The prospects and limitations of the technique were tested using TiN–FeCo multilayers as model samples. To complement the experimental analysis, a theoretical model based on measured magnetization curves by a standard technique (VSM) has been developed. Results from measurement and simulation have shown good qualitative agreement. Even more, by introducing an empirical factor for the system's calibration, both results have shown quantitative agreement, too. It has been proven that phase fluctuations below 0.015° and temperature noise less than 1 K can be measured if the system parameters are chosen properly. The system has been proven for temperatures up to 500 °C, but simulation and measurements indicated nearly constant rates of up to 0.016°/K from 200 °C, which makes it promising even for higher temperatures. As the measurement and evaluation of the phase shift is independent from other methods of evaluating frequency mixing signals, phase sensitive detection can be used to gain additional information, or eliminate cross-correlation between different effects. For example, the separation between mechanical stress introduced into the material and temperature-dependent stress due to thermal expansion seems feasible.