Interrogation of passive wireless sensors in harsh environments

Hochschulschrift

Zusammenfassung: The automotive, aerospace and all other applications working in severe conditions require sensing solutions to monitor critical parameters in order to increase the systems lifetime or to reduce power consumption. The sensors must be small, robust and exhibit low manufacturing costs. Passive wireless sensors have the advantages that they do not require any battery and they can be interrogated with no physical connection to the reader electronics. This thesis reports the development of different torque and high temperature wireless sensing systems based on sensors initially used for radio frequency signal filtering: Surface Acoustic Wave (SAW) and microwave dielectric resonators. The described coupling methods between the reader antennas and the sensors improve the sensing accuracy, resolution, interrogation distance and immunity to the environmental clutter, currently being the main issues when using these sensors in harsh environments. Based on the piezoelectric effect and the propagated mechanical wave velocity dependence with the environment, SAW resonators are used for passive wireless torque or temperature sensing on rotating machinery. However, the main source of errors comes from the angular variations of the coupling between the coupler elements and the receiving coupler element impedance. This parasitic frequency shift is known as pulling effect and concerns all measurements using resonators. In this work, several wireless coupling solutions for the interrogation of SAW resonators on a clamp system fixed on a small diameter shaft are presented. The maintained solution is a capacitive coupler based on coplanar strip lines. It allows an angular transmission amplitude variation lower than 4 dB and a single 434 MHz resonator angular frequency pulling lower than 200 Hz (0.46 ppm). The RADAR-based interrogation, Finite Element Method (FEM) simulations, coupler parameters and frequency pulling measurement results are presented to demonstrate the performances of the complete sensing system. Dielectric resonators are resilient in harsh environments where SAW sensors suffer from the packaging and the radiating element constraints. In this work, the sensitivity of multi-mode dielectric resonators over temperature is investigated. The resonance frequency shift is due to the material permittivity change and the thermal expansion. Moreover, dielectric resonators are physically connected to metallic surfaces in order to get a sufficient coupling between the reader antenna and the sensor. As for cavity resonators filled with a dielectric material, the ohmic losses degrade the sensor quality factor Q, decreasing the sensing resolution and increasing the sensitivity to the environmental clutter. In this work, a far-field high temperature measurement technique up to 700°C is reported using a monolithic and metalization-free zirconium tin titanate (ZST) resonator working near the 2.45 GHz band. A chamotte stone oven allows the signal back scattering measurement between the reader antenna and the sensor through it. The isolated dielectric resonator external radiation fields were adequate for the far-field coupling without the need to use any conducting part on its surface. This measurement method allows to retain a sufficient quality factor higher than 670, exclusively limited by the dielectric and radiation losses, improving the sensing resolution compared to other electromagnetic sensors. The effect of temperature on the tracked sensor resonance frequency, signal-to-noise ratio (SNR) and Q-factor are presented. The material permittivity, thermal expansion and electrical conductivity measurements are also given. This concept is suitable for applications operating at high temperatures such as aerospace applications, where the use of passive, wireless and metalization-free sensors are mandatory

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Albert-Ludwigs-Universität Freiburg, Dissertation, 2015

Klassifikation und Themen

• Klassifikation: Industrielle und handwerkliche Fertigung

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2015
• Urheber: Boccard, Jean-Michel
• Beteiligte Personen und Organisationen: Reindl, Leonhard M.

Weitere Informationen

• DOI: 10.6094/UNIFR/10349
• URN: urn:nbn:de:bsz:25-freidok-103493
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 14.08.2025, 10:59 MESZ