  We design a two-dimensional ultra-thin elastic metasurface consisting of
steel cores coated with elliptical rubbers embedded in epoxy matrix, capable of
manipulating bulk elastic wave modes for reflected waves. The energy exchanges
between the longitudinal and transverse modes are completely controlled by the
inclined angle of rubber. One elastic mode can totally convert into another by
the ultra-thin elastic metasurface. The conversion mechanism based on the
non-degenerate dipolar resonance is a general method and easily extended to
three-dimensional or mechanical systems. A mass-spring model is proposed and
well describe the conversion properties. We further demonstrate that high
conversion rates (more than 95%) can be achieved steadily for one elastic
metasurface working on almost all different solid backgrounds. It will bring
wide potential applications in elastic devices.
