Eddy current displacement sensor with LTCC technology

It is indispensable to improve the lifetime and performance of conventional displacement sensors and to transform these sensors to match the requirements of engine health monitoring such as a blade tip sensing systems in turbo-machinery. <br>In this work, first literature and information were collected and compared. An eddy current displacement sensor using the novel LTCC technology was found to match the related measurement conditions such as harsh and high temperature environments, non-magnetic metal blades, etc. Then, according to the structure of the LTCC sensor coil, a set of analytic calculating methods based on fundamental equations of the inductance and the capacitance between two simple thin strips was built. The inductance, resistance, capacitance, quality factor, self-resonant frequency of a complete sensor coil and standard skin depth of eddy current in target blade were considered. Subsequently, the FEM method was used for further calculations. It was found via modal analysis that the position over the sharp end of a blade tip is the optimal mounting position for a sensor. Electromagnetic analysis showed that the sensitivity of the sensor inductance has one principal influence factor, which is the outer size of the sensor coil. Effects on the resistance of the sensor and on the quality factor concerning changes of layers, turns and fill factor were also investigated. In addition, the 3D eddy current distribution and the relations between the impedance of the sensor and the blade displacement in horizontal and vertical directions were obtained. Finally, a complete optimization work flow was proposed based on the methods and conclusions of analytic and FEM analysis as well as LTCC fabrication guideline. The layout was designed for the sensor variation with the optimal parameters, and it was realized by LTCC fabrication. Eight sensors were obtained for further experimental testing. <br>With respect to experimental work, the characteristics of the sensors were measured by LCR meter and impedance analyzer. These testing results were used to check the results of the FEM simulation and analytic calculation. Temperature dependent experiments were carried out to identify the feasibility of the LTCC sensor at high temperature using the eddy current operating mechanism. Finally, a complete displacement sensor system composed of a motor, a rotor with blades, a testing circuit, a data acquisition system, a computer control and signal processing system were built to simulate a blade tip measurement system. The recording rate was up to 24000 blades per minute. The clearance between sensor and blade tip, and the blade change of geometry were measured and proven to reflect the corresponding information correctly. <br>All the results identified that the comprehensive optimization method combined with analytic analysis and FEM simulation is an effective design approach to LTCC planar sensor. FEM simulation comprises modal, electromagnetic and thermal-mechanical analysis. In addition, our LTCC eddy current sensor shows good properties for high temperature environments up to 500 oC and high-speed measurements up to 3000 rpm (24000 bpm). Its feasibility to work for turbomachinery in harsh and high temperature environments was verified under laboratory conditions.

Author dc:creator

• Lai, Yuqing

Contributors dc:contributor

• Wilde, Jürgen

• Wirbelstrom, FEM, Abstand
• Eddy current sensor, LTCC, FEM simulation, displacement measurement

Repository record source_url

https://freidok.uni-freiburg.de/data/1915

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:1915