Terahertz broadband metal-dielectric near-field antenna

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..

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..

Radio Frequency Identification Systems (RF-ID) are widely used and are thus one of the fastest growing sectors of todays radio industry, allowing advanced solutions for a variety of applications in the area of authentication, ticketing, access control, supply management, etc. One of the most common band allocated to RFID systems is 13.56 MHz. For this application example operating at this particular frequency band we have chosen a transponder inlay which was created using the ACIS based solid modeler of CST MICROWAVE STUDIO® The frequency domain solver of CST MICROWAVE STUDIO® has been applied to accurately predict the input impedance, followed by a lumped element based equivelent circuit derivation to describe the impedance versus frequency. Read full article..

The dichroic filter is an example for setting up simulations of frequency selective surfaces. The simulation is performed with CST MICROWAVE STUDIO® and compared to measurements. Read full article..

In this acticle the simulation of novel interdigital backward wave oscillators with CST PARTICLE STUDIO® is described. The mutual coupling of the charged particle movement and transient electromagnetic fields is taken into account by a sophisticated Particle in Cell algorithm. The resulting output power is in excellent agreement with theoretical values. Results are presented with the courtesy and permission of Teraphysics Corporation, USA. Read full article..