Rainer Pietig

Ferrite-loaded waveguides-a perturbation theory approach

We have developed a perturbation theory for ferrite-loaded waveguides. The perturbation operator is chosen as the deviation of the relative permeability matrix from unity. The method allows a systematic calculation of the propagation constant as well as the perturbed modes to any desired order. It can be used for any direction of the bias field and also for inhomogeneous bias fields as long as the translation invariance along the waveguide is kept. We apply our method to ferrite-loaded waveguides with a bias field in the propagation direction. For the completely filled case, first order expressions for the propagation constant are obtained and the coupling behaviour of TE, TM and TEM modes is discussed. Furthermore we study the scattering of TEM modes in partially filled waveguides and obtain the S-matrix for the ferrite coupled line in the first order.

Multiport S-Parameter Measurements of Linear Circuits With Open Ports

A simple technique to measure the S-parameters of a linear multiport with a two-port network analyzer is evaluated. Just two probes and a single specimen are required. All two-port combinations are measured with the other ports left open. Special care was taken to estimate the maximum measurement uncertainties and to identify critical parameter values. Results can be further improved by using a simplified weighting scheme or by correcting for open-port capacitances. The technique is especially suited for wafer probes

Design of Microstrip Ferrite-Coupled Line Devices Using Perturbation Theory

Ferrite perturbation theory is applied to analyze a ferrite-coupled microstrip line (FCL) with longitudinal magnetization. The properties of an FCL structure with a given finite length are discussed. Optimal conditions for the waveguide cross section and the length are derived. Using the results of the perturbation analysis, a circulator and an isolator based on the microstrip line FCL are designed, fabricated, and measured. Agreement between measured and calculated S parameters is obtained. The devices show an insertion loss of 2?3 dB within the frequency range of 6?10 GHz.

Monte Carlo simulation and experimental investigation of x-ray spectra from very thin metal layers on diamond substrates

We used the Monte Carlo code EGSnrc to simulate electron energy loss profiles as well as angle resolved x-ray spectra for metal-layer/substrate combinations in the primary electron energy range of 60-160 keV. We were furthermore able to separate the bremsstrahlung fraction originating in the substrate from that of the metal layer. The simulations were accompanied by experimental investigations. High-energetic electrons of 60-160 keV were directed onto 1-2 μm thin tungsten layers on top of 500 μm diamond substrates. The spectra were recorded by an energy resolved detector positioned in backward direction. We compared the experimental data with the simulation results and found good agreement. An enhanced monochromaticity in backward direction however, as expected from thin film theory, has not been observed due to the influence of the substrate.

A cone beam CT scanner without moving parts

We propose a cone beam CT scanner without moving parts. The proposed scanner has a large number of small, stationary x-ray sources that are aligned along a specially shaped source curve. It also has a stationary detector strip with a large area and a special shaping. The sources are based on carbon nanotube field emitters. The detector is assembled from smaller modules having a flat, rectangular detector area. The special shapings of the source curve and the detector strip make it possible to collect a complete set of cone beam projections of a patient’s volume of interest in a very short time. The proposed scanner appears to be well suited for cardiac CT.