  We are interested in the problem of retrieving information on the refractive
index $n$ of a penetrable inclusion embedded in a reference medium from
farfield data associated with incident plane waves. Our approach relies on the
use of transmission eigenvalues (TEs) that carry information on $n$ and that
can be determined from the knowledge of the farfield operator $F$. In this
note, we explain how to modify $F$ into a farfield operator
$F^{art}=F-\tilde{F}$, where $\tilde{F}$ is computed numerically, corresponding
to well chosen artificial background and for which the associated TEs provide
more accessible information on $n$.
