Chipless Wireless High-Temperature Sensing in Time-Variant Environments

The wireless sensing of various physical quantities is demanded in numerous applications. A usual wireless sensor is based on the functionality of semiconductor Integrated Circuits (ICs), which enable the radio communication. These ICs may limit the application potential of the sensor in certain specific applications. One of these applications stands in the focus of this thesis: the operation in harsh environments, e.g., at high temperatures above 175°C, where most available sensors fail. Chipless wireless sensors are researched to exceed such chip-based limitations. A chipless sensor is setup as an entirely electro-magnetic circuit, and uses passive Radio Frequency (RF) backscatter principles to encode and transmit the measured value. Chipless sensors that target harsh environment operation are facing two important challenges: First, the disturbance by clutter, caused by time-variant reflections of the interrogation signal in the sensor environment and second, the design of suitable measurand transducers. These challenges are addressed in the thesis. To overcome the first challenge, three basic chipless sensor concepts feasible for operation in clutter environments are introduced. The concepts are realized by demonstrator designs of three temperature sensors and are proofed by wireless indoor measurements. A channel estimation method is presented that dynamically estimates and suppresses clutter signals to reduce measurement errors. To overcome the second challenge, measurand-sensitive dielectric materials are used as measurement transducers, and are being characterized by a novel high-temperature microwave dielectric characterization method. Complex permittivity characterization results in temperatures up to 900°C are presented. Finally, in-depth description and discussion of the three chipless concepts is given as well as a performance comparison in wireless indoor measurement scenarios. The first concept is based on polarization separation between the wanted sensor backscatter signal and unwanted clutter. The second concept separates tag and clutter signals in the frequency domain by using harmonic radar. The third concept exploits the slow decay of high-Q resonances in order to achieve the desired separation in time domain. This concept’s realization is based on dielectric resonators and has demon- strated the capability of wirelessly measuring temperatures up to 800°C without requiring an optical line-of-sight. This performance significantly exceeds temperature- and detection-limitations of commercially available sensors at the current state-of-the-art

Wireless Temperature Sensing with BST-Based Chipless Transponder Utilizing a Passive Phase Modulation Scheme

A passive wireless temperature sensor with identification capabilities based on a phase modulation scheme is discussed in this paper. The approach presented utilizes a pulse backscatter technique based on slow wave (metamaterial) transmission lines. The focus of the work are the material engineering for the temperature-sensitive element and the integration of this element into a passive phase modulation circuit and the entire sensor tag. The approach makes use of temperature-sensitive bariumstrontium-titanate thick film capacitances. The discussed principle has been experimentally verified with a prototype

Chipless Wireless Temperature Sensor for Machine Tools Based on a Dielectric Ring Resonator

This paper presents a wireless temperature sensor designed for the monitoring of machine tools, where valuable workpieces are processed and a defective tool can lead to costly damage to the workpiece. Since cutting tools quickly deteriorate at high temperatures, a measurement of the tool’s temperature allows monitoring its state. A wireless measurement is advantageous due to the high angular velocities achieved by the tool. The oil used to cool down the tool and the chips coming out of the workpiece shadow the line-of-sight condition necessary for infrared measurements. In addition, temperatures above 200 ºC are achieved, making the employment of silicon-based chips hardly feasible. In this paper, the temperature is read from the resonance frequency of a dielectric resonator mounted on the tool by means of radio-frequency backscattering techniques. A successful temperature measurement has been performed up to 300 ºC to test the stability of the sensor. Furthermore, system tests have been performed in a real machine tool where the sensor is interrogated from outside the machine tool through its door, with the tool rotating at up to 10,000 rpm. With this sensor, real-time monitoring of the tool temperature becomes feasible without altering the current workflow of the machine tool