  In this paper we propose, design and test a new dual-nuclei RF-coil inspired
by wire metamaterial structures. The coil operates due to resonant excitation
of hybridized eigenmodes in multimode flat periodic structures comprising
several coupled thin metal strips. It was shown that the field distribution of
the coil (i.e. penetration depth) can be controlled independently at two
different Larmor frequencies by selecting a proper eigenmode in each of two
mutually orthogonal periodic structures. The proposed coil requires no lumped
capacitors for tuning and matching. In order to demonstrate the performance of
the new design, an experimental preclinical coil for $^{19}$F/$^{1}$H imaging
of small animals at 7.05T was engineered and tested on a homogeneous liquid
phantom and in-vivo. The presented results demonstrate that the coil was well
tuned and matched simultaneously at two Larmor frequencies and capable of image
acquisition with both the nuclei reaching large homogeneity area along with a
sufficient signal-to-noise ratio. In an in-vivo experiment it has been shown
that without retuning the setup it was possible to obtain anatomical $^{1}$H
images of a mouse under anesthesia consecutively with $^{19}$F images of a tiny
tube filled with a fluorine-containing liquid and attached to the body of the
mouse.
