Theory of a high impedance coil (HIC)-a cable loop antenna with a modified shield-is comprehensively discussed for MRI application in both transmitting and receiving regimes. Understanding a weakness of the previously reported HIC in transmitting regime, we suggest another HIC which is advantageous in both transmitting and receiving regimes compared to a conventional loop antenna. In contrast with the claim of previous works that the reported HICs are advantageous in transmission regime, we show only this HIC is a practical transceiver HIC. Using the perturbation approach and adding gaps to both shield and inner wire of the cable, we tune the resonance frequency to be suitable for ultra-high field (UHF) magnetic resonance imaging (MRI). These gaps reduce the quality factor of the enhanced HIC which makes its resonant frequency more stable with respect to different loadings. Our theoretical model and applicability of our HIC for MRI applications are verified by simulations. Using the theoretical model, we have designed and fabricated an array of three HICs operating at 298 MHz. The operation of the array has been experimentally studied in the presence of different phantoms used in ultrahigh field MRI and the results compared with those obtained for a conventional array.

No abstract

No abstract

We present a theoretical and numerical study of a dual-metasurface superlens dedicated to the near-field optical imaging of submicron objects. Compared to the previous studies of dualmetasurface plasmonic superlenses, we suggest a more adequate theoretical model of their operation. The new model allows us to obtain twice better operational characteristics of the re-designed superlens. For the first time, we describe the operation of such the superlens using full-wave numerical simulations, taking into account the interfaces of the host medium slab and proving the nanoimaging for scattering objects instead of radiating sources. We discuss and address both application and fabrication issues for this superlens.

Phased antenna arrays of dipoles are widely used in ultra-high field magnetic resonance imaging for creating the controllable radio-frequency magnetic field distributions in a human body. Due to safety and imaging quality reasons each individual channel of the array should be decoupled-electromagnetically isolated from the others. The required number of channels is large and in some techniques the dipole antennas should be located in the close proximity of the human body. Their ultimately dense arrangement leads to a strong mutual coupling and makes the conventional decoupling structures inefficient. This coupling needs to be suppressed without a significant distortion of radio-frequency fields in the imaged area. In this work, we propose and study a novel decoupling technique for two ultra-high field transceiver on-body dipole antennas. The decoupling is performed by a periodic structure of five parallel resonant wires referred to as a metasurface. In contrast to conventional decoupling with a single resonant wire, the metasurface decoupled by means of excitation of a higher-order coupled mode of the wires, which field is highly confined. The main advantage is a low distortion of the RF-field in the central region of the body.