Martin Schüßler

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.

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.

Highly sensitive chipless wireless relative humidity sensor based on polyvinyl-alcohol film

This paper presents a chipless, highly sensitive, low profile, low cost and easily fabricated passive wireless relative humidity (RH) sensor. The sensor consists of a narrow band loop antenna loaded with PVA film coated interdigital capacitor (IDC) at 2.85 GHz. The RH sensor generates an amplitude peak at resonance in the radar cross section (RCS), which changes with different RH. The sensor is interrogated remotely by a reader antenna, and the measurement results show a good sensitivity up to 5.35 MHz/%RH above 50% RH.

Calibration scheme for microwave biosensors using exclusively liquid calibration standards

In the growing field of biosensing, the dielectric analysis of liquids and cell suspensions has become an important research topic. This paper suggests a novel calibration scheme for capacitive sensors, which exclusively relies on liquids instead of conventional termination standards. Moreover, the influence of several parameters on the reliability of the measurements is investigated by simulation. Finally, the concept of calibration is proven by measurements obtained using three different sensor prototypes.

A capacitively coupled data transmission system for resistance based sensor arrays for in-situ monitoring of lithium-ion battery cells

The demand for space resolved temperature monitoring and collection of other in-cell data is rising as lithium-ion batteries gain more and more importance, especially for high power applications like power tools or electric vehicles. Safety issues and fast aging are still unresolved problems. To face these, sensor matrices that provide the possibility to collect multiple sensor data at the same time are recently under investigation by various research groups. The problem of data transmission from in-situ sensors to external battery management systems however is yet to be solved, especially when it comes to laminated pouch cells. As a possible solution a method is developed for capacitive coupling in combination with frequency multiplexing to be able to read out multiple sensor data without additional wiring. The presented concept is designed such that it can be minimized and digitized in next steps and therewith fully integrated into the cells during production.

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.

Concept and design of a 40 GHz differential sensor for the analysis of biomedical substances

This paper discusses a low cost coplanar differential sensor at 40 GHz suitable for the lab on chip integration. Its ability to resolve small permittivity differences with a high dynamic range was proved by analytical calculations and full-wave EM simulations and was finally validated with measurements. A sensitivity of τ = 2.5dB/%Δεr>eff was achieved for small permittivity differences. Thereby, a change of 100 % ethanol to 99 % ethanol mixed with 1 % DI water, results in a difference of ΔS21 = 5 dB. In order to further minimize the complexity e.g. for single use purposes, the influence of the absence of the termination resistors of the couplers was investigated.

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.