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The embedding of microwave devices is treated by applying the finite-difference method to three-dimensional shielded structures. A program package was developed to evaluate electromagnetic fields inside arbitrary transmission-line connecting structures and to compute the scattering matrix. The air bridge, the transition through a wall, and the bond wire are examined as interconnecting structures. Detailed results are given and discussed regarding the fundamental behavior of embedding.
Structures for interconnecting active microwave semiconductor-devices, e.g. FET's and MIC's, with the electrical surrounding or with each other have to be designed more and more carefully when increasing the desired upper frequency limit. Therefore, several connecting structures for device embedding have been examined. Mainly, their applicability for the frequency range from 10 GHz to 100 GHz was considered. Additionally, different equivalent circuits were developed to approximately describe their behaviour for CAD-applications.
It is demonstrated that microwave structures incorporating dielectric resonators (DR) are accurately characterised by means of a 3-dimensional finite-difference CAD package. All major assumptions made so far have been dropped, offering the possibility of a rigorous analysis of the embedding of dielectric resonators into microwave structures. In particular, a finite thickness for the microstrip conductor has been taken into account. The coupling of the DR to a microstrip placed in a metallic housing has been theoretically and experimentally investigated. Theoretical and experimental results are in good agreement and give new insight into DR coupling to microstrip circuits.
The advantages of the coupling-of-modes (COM) formalism and the transmission-matrix approach are combined to create exact and computationally efficient analysis and synthesis CAD tools for the design of SAW-resonator filters. The models for the filter components, especially gratings, interdigital transducers (IDTs). and multistrip couplers (MSCs), are based on the COM approach, which delivers closed-form expressions. In order to determine the relevant COM parameters, the integrated COM differential equations are compared with analytically derived expressions from the transmission-matrix approach. The most important second-order effects such as energy storage, propagation loss and mechanical and electrical loading are fully taken into account. As an example, the authors investigate a two-pole, acoustically coupled resonator filter at 914.5 MHz on AT quartz. Excellent agreement between theory and measurement is found.
The advantages of the coupled-mode (COM) formalism and the transmission-matrix approach are combined in order to create exact and computationally efficient analysis and synthesis tools for the design of coupled surface acoustic wave resonator filters. The models for the filter components, in particular gratings, interdigital transducers (IDTs) and multistrip couplers (MSCs), are based on the COM approach that delivers closed-form expressions. To determine the pertinent COM parameters, the COM differential equations are solved and the solution is compared with analytically derived expressions from the transmission-matrix approach and the Green's function method. The most important second-order effects, such as energy storage, propagation loss, and mechanical and electrical loading, are fully taken into account. As an example, a two-pole, acoustically coupled resonator filter at 914.5 MHz on AT quartz is investigated. Excellent agreement between theory and measurement is found.
An investigation is underway regarding the usefulness of altazimuth-mounting telescopes' incorporation of laser gyros for pointing and fiber gyros with extremely small random-walk coefficient for telescope inertial stabilization during tracking. A star tracker is expected to help stabilize long-term gyro bias. Gyro and telescope specifications have been derived by means of computer simulations and systems analyses.
A polarization mode dispersion measurement set-up based on a Mach-Zehnder Interferometer was realized. Measurements were carried out on short high-birefringent fibers and on long standard telecommunication single-mode fibers. In order to ensure high accurate results, special emphasis was placed on the evaluation of the interference pattern. The procedure will be described in detail and practical measurement results will be presented.
The prototype of an optical gyro encoder (OGE) has been successfully tested on the NTT telescope in September '93. The OGE consists of a ring laser gyro and a fiber optic gyro with their input axis parallel. The gyro outptu signals are compensated for earth rotation and misalignment and are subsequently integrated to get the angles. An adaptive digital control loop locks the fiber optic gyro to the laser gyro data. Thus the combined output has the precision of the laser gyro and the low noise of the fiber optic gyro. Specifically, the bias stability is better than 2 X 10-3 deg/h, the scale factor accuracy better than 1 ppm, the random walk coefficient better than 5 X 10-4 deg/(root)h and the resolution better than 3 X 10-4 arcsec. The OGE has been mounted in the altitude and in the azimuthy axis of the telescope. The data were compared with the telescope disk encoder data. The test data show that the pointing accuracy is about 1 arcsec and the tracking accuracy 0.1 arcsec over a time of 30 seconds. This accuracy is sufficient for the very large telescope, for instance.
This paper treats the Brillouin backscattering in a single mode optical fiber and its implications on the Brillouin Ring Laser Gyroscope (BRLG). The BRLG consists of a fiber ring cavity in which stimulated Brillouin scattering is induced and provides two resonant counterpropagating backscattered waves. If this cavity is rotating around its axis, the backscattered waves get different resonant frequencies because of the Sagnac effect. The frequency difference is proportional to the rotation rate (Omega) by inducing a frequency offset between the counterpropagating waves. Some reported Brillouin spectra exhibit several peaks, which means that one pump wave provides at least two backscattered waves with distinguishable frequencies. In order to understand this multi-backscattering and to take advantage of it for the BRLG, we present results of a simulation of the Brillouin backscattering in a single mode optical fiber.
This paper treats the interaction between acoustic modes and light (Brillouin scattering) in a single mode optical fibre. Different observed spectra of the Brillouin backscattering in several fibres have been already reported. In order to have a clear idea of the process, we made a simulation to be able to `draw' the theoretical Brillouin spectrum of an optical fibre and to identify the origin of the observed backscattered lines.
First, the model and the computation method used in our simulation are described. Second, the experimentally observed spectra of two real fibres are compared with their computed spectra. Real spectra and simulated spectra are in good agreement.
Our work provides an interesting tool to investigate the changes in the Brillouin spectrum when the input parameters (characteristics of an optical fibre) vary. This should give useful indications to people working on systems which use Brillouin backscattering.
Formal verification (FV) is considered by many to be complicated and to require considerable mathematical knowledge for successful application. We have developed a methodology in which we have added formal verification to the verification process without requiring any knowledge of formal verification languages. We use only finite-state machine notation, which is familiar and intuitive to designers. Another problem associated with formal verification is state-space explosion. If that occurs, no result is returned; our method switches to random simulation after one hour without results, and no effort is lost. We have compared FV against random simulation with respect to development time, and our results indicate that FV is at least as fast as random simulation. FV is superior in terms of verification quality, however, because it is exhaustive.
The flow field-flow fractionation (FIFFF) technique is a promising method for separating and analysing particles and large size macromolecules from a few nanometers to approximately 50 μm. A new fractionation channel is described featuring well defined flow conditions even for low channel heights with convenient assembling and operations features. The application of the new flow field-flow fractionation channel is proved by the analysis of pigments and other small particles of technical interest in the submicrometer range. The experimental results including multimodal size distributions are presented and discussed.
The importance of obtaining simultaneous particle size and concentration values has grown up with continuing discussion of the health effects, of internal combustion engine generated particulate emissions and in particular of Diesel soot emissions. In the present work an aerosol measurement system is described that delivers information about particle size and concentration directly from the undiluted exhaust gas.
Using three laser diodes of different wavelengths which form one parallel light beam, each spectral attenuation is analysed by a single detector and the particle diameter and concentration is evaluated by the use of the Mie theory and shown on-line at a frequency of 1 Hz. The system includes an optical long-path-cell (White principle) with an adjustable path length from 2.5 to 15 m, which allows the analysis within a broad concentration range.
On-line measurements of the particulate emissions in the hot, undiluted exhaust of Diesel engines are presented under stationary and transient engine’s load conditions. Mean particle diameters well below 100 nm are detected for modern Diesel engines. The measured particle concentration corresponds excellently with the traditional gravimetrical measurements of the diluted exhaust. Additionally, measurements of particle emissions (mostly condensed hydricarbons) from a two-stroke engine are presented and discussed.
The bandwidth behavior of graded-index multimode fibers (GI-MMFs) for different launching conditions is investigated to understand and characterize the effect of differential mode delay. In order to reduce the launch-power distribution the near field of a single-mode fiber is used to produce a controlled restricted launch. The baseband response is measured by observing the broadening of a narrow input pulse (time-domain measurement). The paper verifies the degradation in bandwidth due to profile distortion by scanning the spot of the single-mode fiber with a transversal offset from the center of the test sample. In addition, the impact of the launch-power distribution tuned by different spot-size diameters is demonstrated. Measurements were taken on ‘older’ 50-μm and 62.5-μm GI-MMFs as well as on laser-performance-optimized fibers more recently developed.
Bluetooth personal area networks (PANs) share the 2.4 GHz ISM spectrum with the IEEE 802.11b wireless local area networks (WLANs). With the popularity of wireless devices, this ISM spectrum is becoming more and more crowded. As a result of this interference between WLANs and PANs, the performance of each network is decreased. Current research has not significantly covered the degrading impact of an 802.11b interferer on Bluetooth voice transmission. Within this project, simulations were carried out to precisely study the impact of an 802.11b interferer on the performance of Bluetooth voice transmission at different ratio levels of Bluetooth power to WLAN power at the receiver side. Furthermore, the impact of SNR on the Bluetooth voice performance and the benefit of using the SCORT packet type was analysed as well. Based on the results presented, network performance can be evaluated at the desired activity level.