Bernd Kubina

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.

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.

Compact quasi-chipless harmonic radar sensor with a dielectric resonator antenna

Design and measurement of a quasi-chipless harmonic radar sensor are presented. The sensor is setup as an entirely passive RF circuit. It transduces a temperature measurement value to a spectral signature. For this purpose the sensor consists of a patch antenna, a temperature-sensitive dielectric resonator antenna and an unbiased diode with matching circuit, which is designed in planar microstrip technology. The nonlinear behaviour of the diode generates the harmonic signal at 6.1 GHz. Wireless indoor measurements proof the functionality: A reading range of 3.75 m is achieved with a temperature measurement accuracy of 1.9 K.

Design of a quasi-chipless harmonic radar sensor for ambient temperature sensing

This paper presents a passive wireless tag for ambient temperature sensing. The tag uses harmonic radio-frequency backscattering to encode and transmit the measured value. The harmonic radar approach is taken due to the advantage of a radar clutter-free Rx signal, which increases the applicability of the tag significantly compared to many other chipless sensors. The harmonic tag is fabricated with planar printed circuit board technology and it uses a harmonic generator based on a single unbiased diode. The tag setup and wireless proof-of-concept measurements with a range of more than 3.25m are presented.

Dual Frequency Selective Multiple Access With Quasi-Chipless/Powerless RFID Mixer Tags

A novel concept of quasi-chipless RFID Mixer tags is introduced in this letter, that extends the harmonic radar principle by a multiple access scheme. In this scheme, two RF signals being transmitted by a reader are downconverted in the tag by an unbiased diode mixer after reception only when the interrogation frequencies of both signals do match the filter characteristics of the two narrow-band receiving antennas. Only in this case, the downconverted RF signal is backscattered toward the reader by a third narrow-band antenna. Thus, several tags can be addressed by individual frequency pairs, what allows for the implementation of a multiple access scheme. This scheme is discussed in detail and accompanied by a proof-of-concept implementation. The functionality has been verified by corresponding measurements of different tag combinations and a read range analysis has been performed.

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

Abstract 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.

Readout scheme for resistive chipless wireless sensors

A readout scheme for resistive chipless wireless sensors is derived from a systematic analysis of the signal flow in a generic reader-tag-system. The mathematical model is based on assumptions of tag, reader and channel properties. It is shown, that with a tailored tag antenna design the maximal operation range can be significantly extended since only two of three calibration measurements are necessary and the measurement with the weakest response in signal level can be omitted. With this approach at least a 30% increase in operation range can be expected. Experiment with sensor tags based on patch and PIFA antennas, loaded with temperature dependent resistive sensors, prove the concept.

Screen printed chipless wireless temperature sensor tag based on Barium Strontium Titanate thick film capacitor

The paper describes the development of a demonstrator for a chipless wireless temperature sensor tag operating in the ultra-wideband (UWB) spectrum. For temperature measurement, the backscattered time domain response is analyzed. Specific in this work is, that with the use of an Alumina substrate and screen printing layer deposition, the fabrication technology has been chosen to enable high temperature operation. The development of this demonstrator requires a dedicated RF tag design, particularly for the antenna, and the application of profound knowledge of the Barium Strontium Titanate (BST) material system which is the basis of the transducer. Measurements confirm the tags functionality, but reveal limits of the particular design as well.