Applications

Tim Herrmann, Johannes Mallow, OvG University Magdeburg Magnetic resonance imaging (MRI) is one of the most important non-invasive examination methods in the modern medicine. To raise up examine possibilities, MRI systems with more powerful magnetic fields are constituted. The standard high-field whole body (1.5T-3T) MRI Systems (Fig. 1) are using a body coil for the excitation. MRI at ultra-high-field (UHF) requires different Tx-coils for excitation of different body parts since the construction of one large body coil, similar to those at lower fields, is to difficult. Moreover, at 7T B1 is inhomogeneous as the RF-wave length within the object is smaller than the object extensions. While in RF-coils the usable B1-field is restricted to dimensions and geometry of the RF-coil itself, with the new travelling wave concept, described by Brunner [1], the usable B1-field is restricted to the dimensions of the waveguide (RF-shield) only. Thus the MR travelling wave concept allows excitation of large volumes depending on the length of the RF-shield. For an antenna with a frequency of 297MHz the approximate wavelength is about 1m. Thus the RF-shield of the gradient coil with a diameter of 64cm can be used as a waveguide, because of the cut-off frequency. The cut-off frequency is the minimum frequency where a wave fits into the waveguide without damping. This study examines the use of the travelling wave concept as an efficient body coil replacement in UHF MRI-System with the support simulations in CST Microwave Studio 2009 and measurements. Therefore two different types of antennas have been simulated and produced. The B1-field distribution of a dipole and a patch antenna where simulated and compared with B1-field measurements in a 7T MRI System. The efficiency compared to a 1.5T body coil was investigated. Further research goals are to create biological models based on anatomical MRI-Dataset for use in field-simulation software with dynamic thermal solver for more realistic SAR calculation. However the remaining problems of exposing sensitive body parts, such as the human head by increased SAR needs to be solved for next generation UHF MRI-Systems. Read full article..

Yael Kaldor, Rafael This work describes the simulation and optimization processes of a small antenna located on a large platform. (The platform size is 13? x 3? x 3?). The required antenna frequency performance is wideband and it is required to perform under severe environmental conditions. The antenna structure was modeled and simulated using CST (MWS) for return Loss and Radiation Pattern performance. The antenna model was parameterized to allow future optimization. The Return Loss specification for the Antenna was -8 dB maximum (VSWR 2.2:1) over a 30% bandwidth. Simulated Return Loss was initially poor over the full frequency range (sufficient performance was obtained over 6% bandwidth only). See Figure 1. The Antenna model was optimized using Mode Frontier for Return Loss performance over the full frequency range. The optimization results are depicted in Figure 2. The Return loss and VSWR performance were highly improved using the optimization process. 34% bandwidth was obtained. Read full article..

Joost ter Laak, JTL Engineering B.V. VBA programming was used to create a fully parametrised design in MWS of a RF module containing matching circuits and antenna for a RF module to be used in a Xbox game controller. The complete module was modelled in MWS and the design trade-offs were investigated by varying different parameters. Using this VBA program it became easy to create different designs and optimize interesting parameters for board size and performance. The design was fabricated and found to behave according to the simulation results, no second spin was needed. The design will be used in mass production. Read full article..

J. Rodnizki, Soreq NRC The SARAF RFQ is a four rod RFQ, operating at a frequency of 176 MHz, designed to bunch and accelerate a 4 mA deuteron/proton beam from 20 keV/nucleon DC up to 1.5 MeV/nucleon CW. The electrodes voltage for accelerating deuterons is 65 kV, a field of 22 MV/m (1.6 Kilpatrick). The RFQ injected power is induced by a loop coupler. The power needed to achieve this voltage is 250 kW, distributed along the 3.80 m RFQ length. This constitutes a power density that is approximately 3 times larger than that achieved in other 4-rod RFQs. The RFQ tank is made of 35 mm thick stainless steel. Its inner surface is electroplated with Copper. At high power, local high surface currents in the RFQ might cause overheating which will lead to out-gassing and in turn to sparking, which will prevent the RFQ from reaching the desired operating power. Therefore, there is a vital need for a detailed RF simulation of the RFQ, in combination with heat transfer simulations, in order to determine a priori the areas that heat up uncontrollably at high power, and aid in the design of further cooling to circumvent these phenomena. These simulations should include the RFQ detailed structure and its water cooling system, which incorporates a total flow of 1000 liter/minute. We used CST MWS to simulate the RF currents and fields in a 3D detailed model of the SARAF RFQ, including its loop coupler. The correct eigenmode was reproduced and both Qe and Qo are consistent with the measured ones. Detailed results reproduced the experimental observation of several overheated regions in the RFQ, including the end flanges and the plungers. Further results predicted overheating at regions around the bottom of several ports in the RFQ tank, as shown in figure 1, which were subsequently measured and are now being fixed by additional cooling. Read full article..

Stefan Prorok, Hamburg University of Technology We present an overview of our current research activities in silicon photonics and thermal barrier coatings. Doing so, we will comment on how CST Microwave Studio can be used to design strip waveguides, micro ring resonators, as well as 2-D and 3-D photonic crystal structures. Particularly we will concentrate on the discussion of photonic crystal micro cavities which can be used as electro-optic modulators. It will be shown that MWS provides all the functionality to optimize and characterize optical micro cavities. The appearance of resonant modes is adjusted through eigenmode calculation of the photonic crystal waveguide modes. Time domain simulation with discrete port excitation is applied to calculate the intrinsic Q-factor of the cavity. Waveguide ports are used to model experimental conditions of excitation with strip waveguide modes. Field monitors help to understand the mechanism of energy loss from the cavity. The simulation results are compared to measurements on fabricated structures. As possible application we will show a hybrid silicon organic hetero structure cavity for GHz electro-optic modulation. Read full article..

Matthias Spang, University Erlangen-Nuremberg In order to carry out near-field scans of printed circuit boards for EMC investigations, knowledge of the electric and magnetic fields above various calibration boards is necessary. CST Microwave Studio’s transient solver is therefore employed to calculate the near-field patterns on a scanning plane above various microstrip structures. After a spatial 2D-Fourier-transformation, the field values and the measured probe output signals are used to determine the field probe’s receiving characteristics. The results of this calibration process are then verified by applying them on further field measurements with the probe above another microstrip structure and comparing the obtained field strengths with respective simulations again. To obtain a high spatial field resolution, roughly 2.5 million meshcells are used. The frequency band of interest extends from 1MHz up to 3GHz so that great importance is attached to sufficient energy decay. Read full article..

Floc’h Jean Marie, IETR The antenna is used with UWB Radar techniques in order to locate buried alive victims. The detection is based on the signature of alive persons by using Doppler analysis of movements and respiration. Detecting victims in this environment is very difficult due to the large dynamic range of signal levels. In fact, the reflected signal caused by the buried alive victim is very low behind other reflected or disturbing signals such as mobile phones, vegetation movements, water, rescuers… A two flares UWB antenna, light weight and easy transportable has been specially design for the research of buried victims beneath building rubble. This paper focuses on antenna design, simulation using CST software and measurement. These measurements have been made by IETR and CEA. The experimental results show a good comparison between measurements and simulations. The goals for the design were: - Frequency band: 300 MHz – 3 GHz - Compact antenna - Gain around 10 dBi at the center frequency - Low back side radiation - Good impulse response - Very light weight antenna Read full article..

Marcello Zolesi, Thales Alenia Space The scope of the present work is to analyze the effective coverage of TT&C subsystem of a LEO satellite at an altitude of 700 kilometres. The antenna assembly is made of two units, Main and Fill-In Antennas, accommodated on opposite sides of the spacecraft. Starting from the free-space radiation performance of each of the two antennas, the problem to predict the global TT&C subsystem radiation pattern in presence of the spacecraft is treated in order to identify potential blind areas or interferences caused by the neighbouring structures. The prediction of electromagnetic field scattered in complex environment is usually a hard task since the solution cannot generally be expressed in a simple and/or closed analytical form. Therefore a variety of numerical methods have been developed in literature. The effectiveness of a single method depends on the type of the electromagnetic environment and the working frequencies. The calculations of the global TT&C subsystem radiation pattern in presence of the main spacecraft structures are carried out by means a full-wave electromagnetic software, CST Microwave Studio Integral Solver. The Integral Solver is ideally suited for electrically large structures respect to the wavelength, when dominated by electrical conductors. This solver uses a combination of an open boundary integral formulation and a Multilevel Fast Multi-Pole Method (MLFMM) exhibiting an optimal complexity in terms of memory and simulation time compared to the traditional Method of Moment (MoM). Key-words: Coverage, EIRP, MLFMM, MoM, TT&C antennas. Read full article..

Hubregt J. Visser, PhD, Holst Centre – IMEC-NL Antennas, when brought into close proximity with RF reflective objects or lossy human tissue, will show a degradation in performance. This degradation is visible in the input impedance as a function of frequency and in the radiation pattern, gain and efficiency. In the presentation we will show two examples of miniature antennas designed for on-body use that exhibit a negligible performance degradation when brought near or onto the human body. One of the examples comprises a miniature, curved microstrip patch antenna for application on the wrist, see Figure 1. Here, the ground plane of the patch antenna has been used to form a shielding between antenna and environment. The other example is a CPW printed monopole antenna, embedded in a low-loss dielectric body to contain the fields and thus minimize reactive tuning, see Figure 2. Furthermore the short ground plane of this antenna has been modified to suppress coaxial cable current radiation. In the designs, the human body has been modeled as a curved, layered medium consisting of skin, fat, muscle, bone and, when appropriate, dura, cerebrospinal fluid and brain tissue. The CSTMWS designs, the realized prototypes and the measurement results will be presented. Figure 1: Curved microstrip patch antenna for use on the wrist. Figure 2: Printed monopole antenna in proximity to the human body. Read full article..

Winfried Krämer, Hirschmann Automation and Control GmbH Hirschmann Automation and Control is one of the leading providers of industrial Ethernet at bitrates up to 10 Gigabit per second. Using CST MWS we have examined signal paths regarding signal quality, crosstalk and EMC related issues and have identified influences of vias, stackup and other parameters affecting the quality of our high speed interfaces. As the measurement of impedance of critical pins in the power delivery system is challenging, a simulation allows us to evaluate the position dependent information. Furthermore, we also succeeded in improving housing design in RF-matters, tag and optimize the “sites of crime”. Using the capabilities of a simulation helps us to fit the “first shot” layout into a demanding environment and also to optimize an existing layout to ensure performance at growing requirements to the designs. Additionally, it gives us a cost and time effective possibility to answer the “what if” – questions and visualize the points of interest helps to generate reliable constrains. Read full article..

Guillermo Vietti, Politecnico di Torino A VBA script has been developed, controlling all CST STUDIO SUITE™ tools to represent all mechanical elements in the space around the tire in a vehicle, incorporating this complex geometry in a parametric way. One of the applications of this script is for the study of EM field propagation inside and outside the tire. The same script is capable of choosing the appropriate mesh parameters to optimize the simulation time, with the radiating element inside the tire. It is capable also to set field monitors at all frequencies and to run the simulation automatically. The tire geometry is mainly designed with azimuthally variable tire sections, taking in account the deformation of the tire. The main advantages of designing a parametric geometry controlled by a VBA script are the possibility of: -> adapting the model to different vehicles and tires. -> studying the EM propagation in the whole 3D space for different orientations of the tire and angular positions of the radiating element, without the need of re-designing the structure. -> changing the deformation of the tire near the ground surface due to the load of the vehicle, taking into account the asymmetries of the model. The EM effect of this deformation on the propagation depends on the position of antenna. -> running many iterative simulations, changing iteration variables simply introducing the VBA script inside a cycle “for … next”. Read full article..

Richard Roberts, Astrium Ltd This presentation describes how CST Microwave Studio (MWS) has been used in conjunction with POS 5 and GRASP 8 to design an X-Band circularly polarised Splashplate Antenna. The antenna essentially consists of a centre fed reflector (17 wavelengths in diameter), the Splashplate feed (~2 wavelengths in diameter), and a septum polariser to allow the Tx and Rx bands to operate in opposite polarisations. A significant factor in the design is that a short circuit had to be assumed at the other port of the septum polariser meaning that the return loss of the Splashplate feed and the reflector were critical to the axial ratio performance. CST MWS enabled this aspect of the design to be modelled and analysed using the T-solver. Comparison of the measured and predicted antenna performance has validated the design process. Although a compliant performance has been achieved, it is evident that some modelling improvements could be sought in order to get a better convergence between prediction and measurement. Read full article..

Fabio Freschi, Politecnico di Torino The work presents a two stage approach to solve a class of nonlinear 3D eddy current problems with high saturation, typical of induction heating processes. The proposed method separates the problem of heavy nonlinearity from the complexity of the geometry, by resorting to a 1D fast nonlinear solver which is coupled with a CST 3D solver. Under certain hypotheses on the geometry, the approach is shown to be effective and accurate. Comparison with the full 3d nonlinear approach obtained with a commercial code will be provided. Read full article..

Christof Thalhammer, Berlin Ultrahigh Field Facility, Max-Delbrueck-Center At the Berlin Ultrahigh Field Facility we explore the advantages and needs of Magnetic Resonance Imaging (MRI) at 7 Tesla. Apart from the magnet and the gradient system, the radio frequency (RF) coils form an essential part of the MR system and are topic of intense research. Ultrahigh field systems are not yet in clinical use and the number of commercial coils for these systems is very limited, hence the coil design is an important part of our facility’s work. Since higher magnetic fields require higher frequencies, one has to deal with stronger interaction of the RF fields with the human tissue. Therefore conventional coil designs established at lower magnetic field strengths cannot be directly applied at 7.0 T which asks for new concepts and developments. To accelerate and streamline the design of new coils, our group recently started to use CST Studio Suite 2010. Together with detailed voxel models of human bodies (the “Virtual Family” by the ITIS Foundation), we use the CST package to simulate the distribution of the magnetic field and the RF power distribution in the patient’s body with the ultimate goal to optimize our coil designs for reasons of B1-homogeneity and local SAR distribution. Some of the first results will be shown to illustrate the application of CST Studio Suite in one of our projects, i.e. the design of a multi channel transmit/receive coil array for cardiovascular MRI at 7.0 Tesla. Read full article..

Sebastian Sczyslo, Gunnar Armbrecht, Holger Thye, Sven Dortmund, Thomas Kaiser, Leibniz Universität Hannover This contribution deals with the accurate determination of the impulse response of Ultra-wideband (UWB) antennas both by simulation and measurement. As can be found in recent literature, knowledge about the impulse response does not only allow for the derivation of further antenna parameters such as gain or group delay, but also to design more efficient receivers and to run more realistic simulations. Here we will exemplarily use the cone antenna as the antenna under test (AUT), as this is a very prominent antenna type in the field of UWB. In the first part CST Microwave Studio (CST MWS) is used to model and simulate the antenna in the transmit case. To extract the radiated E-Field, we developed a new macro based on the transient broadband farfield monitor. Applying this macro is time-saving compared to the conventional method using farfield probes which can be found in many publications. The transmit impulse response is determined by a deconvolution operation. Finally Lorentz reciprocity is used to evaluate the receive impulse response as it is common in literature. In the second part the obtained simulation results from CST MWS will be compared to measurement results. At this we will not only use the conventional two-antenna method but we will also introduce the GTEM method, as a fast and accurate antenna measurement method. We developed this novel method based upon our previous research in the field of GTEM cells and it allows for a direct determination of the receive impulse response using a single antenna only. Read full article..

Thomas-Michael Winkel, Roland Frech, IBM Entwicklungs GmbH Thomas Gneiting, AdMOS GmbH The interface between a multi pin connector and the printed circuit board is a critical part of the signal path in high speed digital systems like mainframe computers. Long range via coupling effects are analysed for connectors with a huge signal count and high speed signals using CST Microwave Studio simulations. A realistic cross section of the printed circuit board with a mixture of ground and voltage layers have been taken into account. It was possible to understand the reason for this behaviour by analyzing the field distributions during the signal propagation inside the printed circuit board. A further important result was the calculation of the magnitude of the distortions to judge their impact on the signal integrity of a complete system. Finally, the long range crosstalk effect was verified with time domain measurements on a specially designed test card system. Read full article..

Ad Reniers, Technical University Eindhoven High-data-rate wireless communications need wide bandwidths. In the Ultra-Wideband (UWB) frequency band from 3.1 GHz to 10.6 GHz, information may be spread over a large bandwidth at low power levels thus creating the possibility to share the spectrum with other users. To prevent interference with existing wireless systems, like IEEE 802.11a WLAN, stop band characteristics are required from 5 GHz to 6 GHz*. The notch filter function is designed in a low-cost circular planar dipole antenna based on the ‘two-penny’ dipole. To achieve the required specifications for this notch function we used first the CST optimizer. After that we optimized systematic the design. In this presentation we want to show the results of both approaches to achieve a maximum result and try to understand the working of this notch and spur function in this compact UWB antenna. * Paper: Low-cost, compact UWB antenna with frequency band-notch function. H.J. Visser. Read full article..

The-Quan Pham, OptiY e.K. Meta-modeling is a process to win the mathematical relationship between design parameters and product characteristics. For each point in the parameter space, there is a corresponding point of the design space. Many model calculations should be performed to show the relationship between outputs and inputs systematically. For a high computing effort of the product model, it is practically infeasible. Adaptive response surface methodology can be used to solve this problem. The mathematical relationship between design parameters and product characteristics presents a new dimension of the simulation results and called meta-model. Based on this meta-model, a virtual optimization or test of the virtual design can be performed very fast to evaluate and to improve the design under real conditions. The meta-model can be exported into C-, Modelica-, or Matlab-code for further using as surrogate model in system simulation as Matlab/Simulink, circuit-simulators. We apply this on a hybrid waveguide junction in CST Studio Suite. Design parameters are geometrical dimensions of the junction. The reflection and transmission at the operating point 8GHz are defined as design goals. Read full article..