Multiport S-parameter measurements of linear circuits with open ports

\u3cp\u3eA 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.\u3c/p\u3

Spatial selectivity enhancement in magnetic fluid hyperthermia by magnetic flux confinement

Aiming to increase spatial selectivity to enhance the precision in Magnetic Fluid Hyperthermia (MFH) therapy and the spatial resolution in imaging, we propose a strategy to increase the selection field gradient in Magnetic Particle Imaging (MPI). In this study, a solution for an existing MPI system topology was simulated, using an additional soft magnetic material as iron core retrofit at the center of the selection field coil. Due to the core's high magnetic permeability relative to air, the magnetic flux is confined, increasing the selection field gradient. Within this simulation study, the optimal core position is evaluated, whilst its effects on the magnet system are validated. According to our results, this strategy can achieve a 27 % reduction in theranostic field of therapy. We found that this technique increases the magnetic field gradient up to a factor of 1.4 (from 2.5 to 3.4 T/m) in z-direction, without significant loading of the drive field resonance circuit caused by eddy currents in the MPI compatible iron core shielding.   Int. J. Mag. Part. Imag. 7(1), 2021, Article ID: 2103002, DOI: 10.18416/IJMPI.2021.210300

Spatial selectivity enhancement in RF-hyperthermia by magnetic flux confinement

Aiming to increase spatial selectivity which provides the precision in hyperthermia therapy and high resolution in imaging, we propose a strategy to increase field gradient for Magnetic Particle Imaging (MPI) modality. In this study, a solution for an existing MPI system topology was simulated, which uses additional soft magnetic material as iron core retrofit at the center of selection field coil. Due to core property of high magnetic permeability relative to air, magnetic flux gets confined to increase selection field gradient field slope. Within this simulation study, the optimal core position is evaluated whilst its effects on the magnet system is validated. We found that this technique increases the magnetic field gradient up to a factor of 1.4 from 2.5 T/m to 3.4 T/m in z-direction, without significant loading of the drive field resonance circuit due to power losses caused by eddy currents in the MPI compatible iron core shielding.   Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009015, DOI: 10.18416/IJMPI.2020.200901

Validation of spatial selectivity enhancement for magnetic fluid hyperthermia by introducing ferromagnetic cores

Spatial selectivity plays a crucial role in magnetic fluid hyperthermia because it can define the precision of thermal dose localization and spatial resolution. We propose an application of additional ferromagnetic cores, with high magnetic permeability, to confine the magnetic flux of the selection field coil. An increased gradient leads to increasing spatial selectivity in theranostic therapy of MPI-assisted magnetic fluid hyperthermia. This work validates our recent simulation study [1] by actual experiments of iron core prototypes. This study shows that our core prototypes can increase the gradient by a factor of 1.3 which suggests a 21% improvement in thermal localization in hyperthermia therapy.  &nbsp

Material properties and RF applications of high k and ferrite LTCC ceramics

\u3cp\u3eThe continuous trend in modern electronic applications towards smaller size, higher integration density and enhanced functionality requires new materials, which allow embedding passive functions into the substrate. In this paper an LTCC material system with specialized dielectric and magnetic LTCC tapes cofireable in a low-shrinkage process for RF-passive integration is reported. An LTCC dielectric with a dielectric constant of up to 80 is presented. The material is successfully used in a cofired multi-material stack to realize a fully integrated band-pass filter for Bluetooth applications of 1.3 mm\u3csup\u3e3\u3c/sup\u3e volume. A ferroelectric LTCC ceramic with a maximum dielectric constant of 3000 is presented and the reduction of the dielectric constant to a maximum value of 1100 under constrained-sintering is discussed. Magnetic permeabilities of 14 for a NiZnCo-ferrite and 3.5 for a Ba\u3csub\u3e3\u3c/sub\u3eCo \u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e24\u3c/sub\u3eO\u3csub\u3e41\u3c/sub\u3e (Co\u3csub\u3e2\u3c/sub\u3eZ) ferrite have been realized under LTCC processing conditions, with gyromagnetic resonance frequencies above 1 GHz and 3 GHz respectively. The permeability of these materials is determined for constrained and unconstrained sintering conditions. A maximum absorption of 27 dB/cm and 30 dB/cm is measured for an embedded stripline in NiZnCo- and Co\u3csub\u3e2\u3c/sub\u3eZ ferrite respectively. Two-winding planar RF-chokes in different multi-layer stacks are compared. A maximum of 14.3 nH inductance is realized for a 1.8 mm × 2 mm coil in an LTCC research pilot line.\u3c/p\u3