Christian Mandel

Metamaterial Inspired Microwave Sensors

Cheap and ubiquitous sensor systems will shape the coming decades. There is an emerging class of small high-performance electronic devices such as mobile phones, electronic toys, home appliances, monitoring and control systems in industrial facilities, and medical diagnosis systems, which are or will be equipped with pill box sized microprocessors or computers as well as sensors. These “smart sensors” with limited power and processing capabilities are often wirelessly interconnected. An assembly of many of them spread throughout the physical world will form sensor networks able to identify, localize, and monitor physical, environmental, and industrial processes, biological and health conditions, goods, vehicles, factories, stores, or even people.

A novel passive phase modulator based on LH delay lines for chipless microwave RFID applications

This paper discusses novel techniques to overcome problems arising when porting the surface acoustic wave approach of building passive radio-frequency identification and measurement systems to the electromagnetic domain without the need of mechanical (acoustical) delay lines. These techniques include the utilization of left-handed artificial delay lines and the increase of information density by using a higher order modulation scheme. The benefit from the porting is a broader field of applications, e. g. RFID tags working at very high temperatures or in other harsh environments become possible.

Phase modulation scheme for chipless RFID- and wireless sensor tags

Inspired by state of the art surface acoustic wave (SAW) technique an approach for the realization of chipless microwave RFID tags based on electrical circuits is proposed. For information coding of the retransmitted signal a passive QPSK coding scheme and for wireless monitoring of physical quantities an analog phase modulation scheme are investigated. Key elements for the realization of tags are lumped element delay lines. Therefore properties of left- and right-handed lines are discussed with the view on the special application. Finally, the proposed principles have been experimentally verified with a prototype.

A wireless passive strain sensor

This paper introduces a wireless passive sensor concept for measurement of one- and two-dimensional strain and bending. An identification opportunity can easily be added to the sensor element to distinguish between different sensor “tags”. The concept is based on the modulation of the frequency domain backscatter signature of a radar target by the measured value. The target itself is realized as a small resonant metamaterial structure which generates an amplitude peak in the radar cross-section at resonance. The modulation is done by a variation of the capacitive element of the resonator by the measured quantity. Benefits of the presented design are the passive chipless buildup allowing a construction for the operation in harsh (e. g. high temperature) environments, the simple standard, low-cost fabrication process, the small footprint, the identification opportunity, the possibility of a FMCW-radar-based readout and the versatility of possible sensor designs.

Metamaterial-inspired passive chipless radio-frequency identification and wireless sensing

The presented paper demonstrates how metamaterials with their unique properties and structures derived from metamaterials can offer solutions to overcome technical limitations of passive and chipless wireless sensor and RFID concepts. Basically, the metamaterial approach allows for miniaturization, higher sensitivity, and an extreme geometric flexibility. Miniaturization is certainly important for both, sensing and identification, while higher sensitivity is primarily applicable to sensors. The geometric flexibility is at first important for sensing since it allows for novel sensor concepts. But at least concerning buildup technology, also RFID concepts can benefit from this advantage. The presented examples of metamaterial-inspired passive chipless RFID and wireless sensing can be assigned to the following three categories: metamaterial resonator approaches, composite right/left-handed lines, and frequency-selective surfaces. In this paper, these different concepts are evaluated and discussed with regard to the metamaterial properties. Furthermore, criteria and figures of merit are given, which allow for a fair comparison of passive, chipless concepts and beyond. Finally, these criteria are applied to the presented sensor and identification concepts.

Wireless high-temperature sensing with a chipless tag based on a dielectric resonator antenna

This paper presents a wireless temperature sensor, which enables high-temperature operation due to its passive and chipless design. The sensor uses radio-frequency backscattering techniques to encode and transmit the measured value: The resonance frequency of a dielectric resonator on the sensor tag is determined as a peak in its radar cross section. The tag is built from a half-split cylindrical ceramic resonator with temperature-dependent permittivity and resonance frequency. It offers wireless reading without need for reference measurements of radar clutter due to the resonators high quality factor and applied time-gating. Wireless indoor measurements have proven the sensor concept. These measurements were performed in a temperature range between 20°C and 370°C, where the resonance frequency of the tag lies around 3GHz with a temperature sensitivity of 307 kHz/K.

Multi-resonant perturbation method for capacitive sensing with composite right/left-handed transmission lines

The possibility to use the left-handed capacitances of a composite right/left-handed (CRLH) transmission line for a capacitive sensor array is demonstrated. The capacitances values are extracted with the presented algorithm that is based on a multi-resonant perturbation technique. The CRLH line structure was chosen since its physical implementation is much better suited to a capacitive sensing transmission line than a right-handed (RH) one. In contrast to other techniques like time domain reflectometry single cell spatial resolution can be achieved with moderate bandwidth demand. Presented numerical and experimental results prove the concept.

Capacitive level monitoring of layered fillings in vessels using composite right/left-handed transmission lines

This paper presents a concept for level monitoring of layered fillings in vessels with partially or completely unknown properties of the filling materials. A key sensor component is a composite right/left-handed transmission line resonator. Based on this element in combination with the multi resonant cavity perturbation theory an algorithm for the sensor signal processing is derived for the extraction of material properties and filling levels. The presented concept is verified with full wave electromagnetic simulations and experiments that had been carried out with a realized demonstrator.

Group-delay modulation with metamaterial-inspired coding particles for passive chipless RFID

Significant progress has happened to the research field of passive chipless RFID since it is beneficial in various applications but in terms of encodable information content it lags far behind the chip-based counterparts. Novel approaches tend to implement higher-order modulation to overcome this situation. This work presents a straight forward approach for implementing a reliable higher-order modulation scheme, thus to increase the information content. It is based on a frequency domain on-off-keying backscatter modulation scheme with extremely small resonators, where additional information, the resonators group delay, is added to the on-states within this novel group-delay modulation scheme. Between different IDs, the group delay is varied by changing the resonators loaded quality factor without introducing additional losses. Beside showing the working principle, prototype measurements proof the concept by realizing a two-symbol wireless identification.

Potential and Practical Limits of Time-Domain Reflectometry Chipless RFID

This paper provides a fundamental analysis of the maximum possible information content and reading range of chipless time-domain reflectometry (TDR) radio frequency identification (RFID). Bits encoded on a tag as well as bits that can be decoded by the reader need to be considered to estimate the information content on a tag. This needs an approach that deals with the entire RFID system. Factors such as insertion loss, reader signal, reading range, and channel properties impact the number of bits that can be decoded by the reader. Taking these parameters into account on their own, we can model the signal properties at the decoder by equations from radar theory such as the Cramer-Rao lower bound. The overall performance of these systems cannot be satisfactorily described by the radar theory, as todays chipless RFID systems use different modulation schemes to increase the information content. Modulation theory can provide a detailed analysis of the modulation schemes depending on the channel and signal properties. This theory influences the tag design and the demodulation algorithms on the decoder, but is not suited to describe the RFID systems as a whole. This paper provides an approach that combines the radar and modulation theories to provide an exhaustive description of chipless TDR RFID communication. The maximum information content obtainable in practice can be estimated with this analysis. The introduced methodology is applied to surface-acoustic wave and ultra-wideband delay-line-based TDR tags. We present the simulations and measurements taken with different tags to show the practical importance of the theoretical findings.