Zusammenfassung Große zylindrische Stahlprüflinge werden mittels der Methode der finiten Differenzen im Zeitbereich (engl. finite differences in time domain, FDTD) simulativ untersucht. Dabei werden Pitch-Catch-Messanordnungen verwendet. Es werden zwei Bildgebungsansätze vorgestellt: ersterer basiert auf dem Imaging Principle nach Claerbout, letzterer basiert auf gradientenbasierter Optimierung eines Zielfunktionals.

In this paper, an autofocusing radar technique is presented for tip clearance measurements in combustion turbines capable of resolving the edges of a typical blade tip. The clearance is determined by measuring the reflection at the blade tip while passing by the antenna, subsequently focusing the data by means of a matched filter operation and interpreting the phase of the blade edge reflection according to the continuous wave radar principle. For this, an autofocus approach was developed, which minimizes defocusing effects and provides an estimate of the clearance as the first result, which is utilized to overcome the phase ambiguity and, thus, to increase the measurement range. The autofocus algorithm applies a weighted phase gradient of the pointlike blade edge reflection as cost function and sensitive indicator for the focal quality.

Up to now, wireless transmission in a magnetic resonance imaging (MRI) device is not used extensively for sensor networks or data transmission. Wireless sensors measuring physiological parameters like pulse, ECG, blood pressure or temperature would increase patient safety during a measurement. Beside and rather more interesting is the transmission of MRI sensor data. Patients benefit from higher comfort in the magnet and faster preparation for a measurement procedure. The wireless channels in an MRI device are not well studied at present. In this paper we give a first overview of the available antenna configurations for wireless links and summarize published results. As an MRI device is located in a shielded chamber, the frequency range for a transmission can be chosen freely above the resonance frequencies of the nuclei. To get an insight in the MRI channels we studied in a first approach three exemplary channels at the GSM-900 band, the 5 GHz WLAN band and the 24 GHz ISM band in three scenarios: empty, a real patient, a NaCl-filled tube.

This paper at first illustrates implementation aspects and measurement results of a subcomponent for a multistandard RF identification (RFID) transponder. It is intended to be a common reference cell, both for basic UHF requirements and advanced application fields like local positioning and wireless sensing. Different single circuit topologies shown in previous studies or literature and their applicability for that RFID system are evaluated. After that, measurement results of two final circuit configurations, including a newly designed RC oscillator with metal-metal capacitors, are discussed and compared. Layout aspects for reducing the process variations and low power consumption are demonstrated. Simulation results show border conditions for the power supply of the transponder on chip level. Moreover, distance measurements with our first complete transponder compliant to the electronic product code protocol are shown. It includes the newly presented reference cells and other necessary transponder components. All chips are designed based on a 0.13-μm CMOS technology.

This paper evaluates the implementation of a Round-Trip-of-Flight (RToF) technique into a UHF transponder. Different possible transponder architectures are investigated and measurement results for a passive design are shown at circuit level. The chip is designed based on a 0.13 μm CMOS technology.

RFID is used today in many fields of every day life like access control, anti-theft protection or logistics. Within this article a short overview of the basic RFID principles and the EPC protocol flow is given at first. Afterwards new design approaches for RFID systems within the scope of the research project RFID-S are presented.

This article has offered a brief excerpt of the basic requirements and current development trends in (passive) RFID systems in different application areas. Even after reaching a sophisticated state of development, RFID technology is still dependent on sufficient acceptance at the market. Conventional bar code systems lack programmability, have low storage capability, and need a line-of-sight connection to the reader. If the fall in prices for low-cost tags continues, barcodes could be largely replaced in some years. In this case, additional features like positioning or sensing will become even more attractive for commercial and industrial application fields.

In an ever-increasing number of wireless communications applications the measurement of positions of transmitters distributed in space is desired. Demands on low cost and power consumption make solutions that allow positioning with existing communications hardware during the process of data transmission particularly interesting. In this paper we discuss a method for using IEEE 802.15.4 (ZigBee) transmitter nodes with a special frequency-hopping scheme for this purpose and show the insensitivity of this method to transmitter motion mathematically as well as by exemplary simulations and measurements.

This paper describes the theory of distance measurements with passive UHF transponders using the principle of modulated backscattering. The method was evaluated with the analogue frontend of a passive RFID chip for the UHF range. The chip was designed in a 0.14mum CMOS technology.

The addition of positioning capabilities to low-cost communications such as IEEE 802.15.4 compliant (ZigBee) networks can open up interesting markets, in particular if existing hardware and standard communications packets can be used for this purpose. High-precision localization requires large transmission bandwidths and thus the use of multiple frequency-channels. In the presence of oscillator frequency uncertainty the coherent synthesis of individual measurements poses a challenge. This paper proposes a particular frequency-hopping and signal processing scheme by which most transmitter and receiver frequency-errors can be eliminated in signal processing. Measurements show that high precision distance estimation with errors down to a few cm can be achieved.

In modern wireless communications products it is required to incorporate more and more different functions to comply with current market trends. A very attractive function with steadily growing market penetration is local positioning. To add this feature to low-cost mass-market devices without additional power consumption, it is desirable to use commercial communication chips and standards for localization of the wireless units. In this paper we present a concept to measure the distance between two IEEE 802.15.4 (ZigBee) compliant devices. The presented prototype hardware consists of a low- cost 2.45 GHz ZigBee chipset. For localization we use standard communication packets as transmit signals. Thus simultaneous data transmission and transponder localization is feasible. To achieve high positioning accuracy even in multipath environments, a coherent synthesis of measurements in multiple channels and a special signal phase evaluation concept is applied. With this technique the full available ISM bandwidth of 80 MHz is utilized. In first measurements with two different frequency references-a low-cost oscillator and a temperatur-compensated crystal oscillator-a positioning bias error of below 16 cm and 9 cm was obtained. The standard deviation was less than 3 cm and 1 cm, respectively. It is demonstrated that compared to signal correlation in time, the phase processing technique yields an accuracy improvement of roughly an order of magnitude.