  We calculate the light transmission by a subwavelength plasmonic array using
the boundary element method for parallel cylinders with different
cross-sections: circular or elliptic with axes ratio 4:1. We demonstrate that
the plasmonic resonance is sharper for the case of ellipses with a large
horizontal axis. This structure is susceptible to the refractive index
variations of media since the high derivative of reflection and transmission
coefficients are near the angle of total internal reflection. To obtain an
approximate analytical expression, we use the model of a metallic layer. We
explore the "sandwich" structure with an anisotropic film between two
dielectrics and demonstrate its quantitative agreement with numerical results.
