Martin Schussler

Design of compact planar antennas using LH-transmission lines

This contribution demonstrates the possibility to reduce the size of planar antennas by using LH-transmission lines. Two different types of radiators are investigated - a microstrip patch and a slotted cavity. A transmission line model is employed to design and compare these two approaches and their realization with a varying number of L-C loaded unit cells. Three representative antenna configurations have been selected and subsequently optimized with full wave electromagnetic analysis. Return loss and radiation pattern measurements of these antennas proof the developed concept.

Sensor array based on split ring resonators for analysis of organic tissues

A sensor array concept has been developed using microstrip-line-excited split ring resonators (SRR). With the proposed structure it is possible to spatially resolve the dielectric properties of a Material Under Test (MUT). The split rings are designed to have different resonant frequencies and are decoupled from each other to allow a spatial distribution where a frequency shift of one individual resonant peak will indicate the dielectric properties of the MUT and its location within the array. Several prototype sensors have been realized and tested with different MUT such as dielectric bricks and pig lung tissue to prove the concept.

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.

Frequency Multiplexed 2-Dimensional Sensor Array Based on Split-Ring Resonators for Organic Tissue Analysis

A frequency multiplexed 2-dimensional sensor array was developed using microstrip-line-excited split-ring resonators (SRRs). With the proposed structures, it is possible to spatially resolve the relative changes of the dielectric properties of a Material Under Test (MUT) in one and two dimensions. The SRRs are designed to have different resonant frequencies and are decoupled from each other. With these design characteristics, it is possible to track changes on the resonant frequency of individual SRR that will indicate the dielectric properties of the MUT around the ring and therefore its location within the array. The number of pixels of the dielectric image corresponds to the number of SRRs within the sensor. Several prototype sensors have been realized and tested with different MUT such as dielectric bricks, animal tissue and phantoms of human tissue to prove the concept.

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.

Compact tunable periodically LC loaded microstrip line for phase shifting applications

The properties of periodically LC loaded lines with tuneable capacitors are investigated for phase shifting applications. Basic equations are derived describing the losses due to the tuning mismatch and the quality of the tuneable material. The performance of microstrip line phase shifting devices with right- and lefthanded wave propagation is compared and evaluated in terms of a defined figure of merit. As a demonstrator, a phase shifter circuit using the principle of periodically LC reactive loading is realized with varactor diodes. The comparison with other circuit topologies confirms the idea to realize compact devices with this circuit concept.

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.

Performance evaluation of left-handed delay lines for RFID backscatter applications

The operation principle of a passive RFID tag on the basis of delay lines is presented and the performance of left- and right-handed lines for this application is compared. Additionally, limitations due to the dispersion properties of left-handed lines for the maximum number of usable cells are discussed. In conclusion, an expression relating the maximum number of usable bits for the tag impulse response to system parameters like bandwidth, centre frequency etc. is given. A proof of concept is realized with a 100 cell four bit backscatter tag. The set up of the tag is described and the performance analysed.

Artificial transmission lines for high sensitive microwave sensors

Two common and two new unit cells for artificial lines made of four reactive elements are studied concerning their sensitivity to capacitive changes and their applicability as capacitive sensors. It is shown that selection of the unit cell is very important and can highly influence the sensitivity. The shown principle is very powerful and can be scaled up to THz frequencies, only limited by available fabrication technology. A built planar differential microwave sensor based on artificial lines working at 2.3 GHz is presented. It features a simple output power evaluation instead of a classic but more complicated phase difference measurement. With power variation of up to 60 dB in dependence of small environmental dielectric changes it shows a very high sensitivity and dynamic range. Functional layer coatings can be applied easily due to its planarity and open wide application areas for biomedical sensing.

New Microwave Flow Sensor based on a Left-Handed Transmission Line Resonator

This paper presents a new material density sensor for process monitoring applications based on a composite right/left-handed transmission line resonator. Compared to a conventional right-handed line resonator an increased sensitivity could be demonstrated by measurements of a prototype. The presented sensor principle promises the possibility to design precise permittivity sensors with low to moderate costs. The areas of application of such sensors are gas/solids, gas/liquid and liquid/solids flows in various industrial applications.