A novel frequency selective surface based on substrate integrated waveguide technology (SIW) is proposed and studied theoretically and experimentally. Its primary function is the selection of a linear polarization of an incident wave and its 90-degree rotation in a given frequency band. The proposed structure is based on an SIW cavity, coupled to the input and output by two orthogonal slots, and is designed using a simulation code based on the method of moments boundary integral-resonant mode expansion method, especially developed for the accurate characterization of FSS structures. Moreover, a complete design procedure for the proposed structure and a parametric study of its performance are presented. Finally, in order to verify the proposed structure, a prototype is designed at an operation frequency of 35 GHz, exhibiting a relative bandwidth of 9.1% and an impedance matching of better than -11 dB with a maximum insertion loss of 0.2 dB in the passband. Its performance is investigated in detail including the analysis of non-orthogonal incidence angles.

A novel class of substrate-integrated waveguides (SIWs) is presented, based on the concept of the classical ridge rectangular waveguide, which permits the design of broadband, compact and low-loss integrated components and interconnects. Two configurations are proposed. The former is the ridge SIW, where the structure is integrated in a dielectric substrate with top and bottom metal layers, and comprises two-sided rows of full-height metal cylinders and a central row of partial-height metal posts connected at their bottom by a metal strip. The latter is the ridge substrate-integrated slab waveguide; this structure presents a geometry similar to the ridge SIW, but includes additional air holes to further enhance the bandwidth. The design and experimental verification of two prototypes, covering the frequency band from 6.8 to 25 GHz and from 7.1 to 30.7 GHz, respectively, are also presented. The proposed structures exhibit a mono-modal bandwidth three times broader than classical rectangular waveguides or SIWs, and their size is half of the SIW with the same cut-off frequency.

A screen-printed pediatric MRI coil yielded diagnostic image quality and a signal-to-noise ratio that was comparable to that of a commercial 32-channel adult coil and had greater flexibility and co... BackgroundScreen-printed MRI coil technology may reduce the need for bulky and heavy housing of coil electronics and may provide a better fit to patient anatomy to improve coil performance.PurposeT...

Magnetic resonance imaging systems rely on signal detection via radiofrequency coil arrays which, ideally, need to provide both bendability and form-fitting stretchability to conform to the imaging volume. However, most commercial coils are rigid and of fixed size with a substantial mean offset distance of the coil from the anatomy, which compromises the spatial resolution and diagnostic image quality as well as patient comfort. Here, we propose a soft and stretchable receive coil concept based on liquid metal and ultra-stretchable polymer that conforms closely to a desired anatomy. Moreover, its smart geometry provides a self-tuning mechanism to maintain a stable resonance frequency over a wide range of elongation levels. Theoretical analysis and numerical simulations were experimentally confirmed and demonstrated that the proposed coil withstood the unwanted frequency detuning typically observed with other stretchable coils (0.4% for the proposed coil as compared to 4% for a comparable control coil). Moreover, the signal-to-noise ratio of the proposed coil increased by more than 60% as compared to a typical, rigid, commercial coil.

Purpose: To accurately analyze vibroacoustics in MR head gradient coils.Theory and Methods: A detailed theoretical model for gradient coil vibroacoustics, including the first description and modeling of Lorentz damping, is introduced and implemented in a multiphysics software package. Numerical finite‐element method simulations were used to establish a highly accurate vibroacoustic model in head gradient coils in detail, including the newly introduced Lorentz damping effect. Vibroacoustic coupling was examined through an additional modal analysis. Thorough experimental studies were used to validate simulations.Results: Average experimental sound pressure levels (SPLs) and accelerations over the 0‐3000 Hz frequency range were 97.6 dB, 98.7 dB, and 95.4 dB, as well as 20.6 g, 8.7 g, and 15.6 g for the X‐, Y‐, and Z‐gradients, respectively. A reasonable agreement between simulations and measurements was achieved. Vibroacoustic coupling showed a coupled resonance at 2300 Hz for the Z‐gradient that is responsible for a sharp peak and the highest SPL value in the acoustic spectrum.Conclusion: We have developed and used more realistic multiphysics simulation methods to gain novel insights into the underlying concepts for vibroacoustics in head gradient coils, which will permit improved analyses of existing gradient coils and novel SPL reduction strategies for future gradient coil designs. Magn Reson Med 78:1635–1645, 2017. © 2016 International Society for Magnetic Resonance in Medicine.