  The path is explored between one-dimensional scattering through
Dirac-$\delta$ walls and one-dimensional quantum field theories defined on a
finite length interval with Dirichlet boundary conditions. It is found that two
$\delta$'s are related to the Casimir effect whereas two $\delta$'s plus the
first transparent P$\ddot{\rm o}$sch-Teller well arise in the context of the
sine-Gordon kink fluctuations, both phenomena subjected to Dirichlet boundary
conditions. One or two delta wells will be also explored in order to describe
absorbent plates, even though the wells lead to non unitary Quantum Field
Theories.
