Synthesis design of artificial magnetic metamaterials using a genetic algorithm.

In this article, we present a genetic algorithm (GA) as one branch of artificial intelligence (AI) for the optimization-design of the artificial magnetic metamaterial whose structure is automatically generated by computer through the filling element methodology. A representative design example, metamaterials with permeability of negative unity, is investigated and the optimized structures found by the GA are presented. It is also demonstrated that our approach is effective for the synthesis of functional magnetic and electric metamaterials with optimal structures. This GA-based optimization-design technique shows great versatility and applicability in the design of functional metamaterials.

In vivo 1H magnetic resonance imaging and spectroscopy of the rat spinal cord using an inductively-coupled chronically implanted RF coil.

An inductively coupled, chronically implanted short-solenoid coil was used to obtain in vivo localized 1H NMR spectra and diffusion-weighted images from a rat spinal cord. A 5 x 8 mm two-turn elliptically shaped solenoid coil was implanted in rats at the site of a T-12 vertebral-level laminectomy. Excitation was achieved solely by a 3 x 3 cm external surface coil, and signal detection was achieved by inductively coupling the external coil to the implanted coil. The image signal-to-noise ratio (SNR) obtained with the inductively-coupled implanted coil was compared with that obtained using a linear or a quadrature external surface coil. The implanted coil provided a gain by over a factor of 3 in SNR. The implanted coil was used to measure localized 1H spectra in vivo at the T13/L1 spinal-cord level within a 1.85 x 1.85 x 4.82 mm (16.5 microL) volume. With 256 averages, a approximately 3-s repetition delay and respiratory gating, a high-quality spectrum was acquired in 13 min. In addition, water translational diffusion was measured in three orthogonal directions using a stimulated-echo imaging sequence, with a short echo time (TE), to produce a quantitative map of diffusion in a rat spinal cord in vivo.