Ultrahigh field imaging of the body and the spine is challenging due to the large field-of-view (FOV) required. It is especially difficult for RF transmission due to its requirement on both the length and the depth of the ${\rm{B}}_{1}^{{\rm + }}$ field. One solution is to use a long dipole to provide continuous current distribution. The drawback is the natural falloff of the ${\rm{B}}_{1}$ field toward the ends of the dipole, therefore the ${\rm{B}}_{1}^{{\rm + }}$ per unit square root of maximum specific absorption rate ${\rm{(B}}_{1}^{{\rm + }}{\rm{/ \surd SAR}}_{{\rm{max}}})$ performance is particularly poor toward the end of the dipole. In this study, a segmented element design using forced-current excitation and a switching circuit is presented. The design provides long FOV when desired and allows flexible FOV switching and power distribution without additional power amplifiers. Different element types and arrangements were explored and a segmented dipole design was chosen as the best design. The segmented dipole was implemented and tested on the bench and with a phantom on a 7T whole body scanner. The switchable mode dipole enabled a large FOV in the long mode and improved ${\rm{B}}_{1}^{{\rm + }}{\rm{/ \surd SAR}}_{{\rm{max}}}$ efficiency in a smaller FOV in the short mode.

This paper reports a novel approach using an inductive loading to reduce the resonant frequency of a mushroom-shaped high impedance surface. The current path is extended on the mushroom-shaped structure's vias and additional traces, which introduces a three-dimensional inductor to the unit cell and leads to an increase in total inductance. As a result, the resonant frequency of the high impedance structure decreases, and a smaller unit cell size can be achieved at the low gigahertz frequency range. Finite element electromagnetic simulation, equivalent circuits modeling, and experimental measurements suggest the feasibility of the proposed approach.

It has been recently discovered that strong magnetoplasmonic effects exist on graphene and may open a new avenue for many novel THz non-reciprocal devices. The magnetoplasmonic response of two-dimensional graphene strongly depends on the electromagnetic properties of the surrounding medium. We develop a modified transmission line analog formulation to investigate the Faraday and Kerr rotation associated with multi-sheet magnetized graphene embedded in the layered medium. The formulation utilizes a junction transformer to model anisotropic conductive sheets at the interfaces and is highly numerically efficient and stable. It is also demonstrated for the first time that a multiple heterojunctions conjugated photonic crystal with graphene embedded at the interfaces will significantly enhance the magneto-optical effect of the system. 15.3° Faraday angle under 0.25 T low static bias magnetic field is achieved at 15 THz with a high transmittance, which enables the design of accessible high-performance non-reciprocal devices in the high THz frequency regime. The proposed formulation and design principle may lay the foundation for future THz graphene-based plasmonic devices.

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