  Imposing either Dirichlet or Neumann boundary conditions on the boundary of a
smooth bounded domain $\Omega$, we study the perturbation incurred by the
voltage potential when the conductivity is modified in a set of small measure.
We consider $\left(\gamma_{n}\right)_{n\in\mathbb{N}}$, a sequence of perturbed
conductivity matrices differing from a smooth $\gamma_{0}$ background
conductivity matrix on a measurable set well within the domain, and we assume
$\left(\gamma_{n}-\gamma_{0}\right)\gamma_{n}^{-1}\left(\gamma_{n}-\gamma_{0}\right)\to0$
in $L^{1}(\Omega)$. Adapting the limit measure, we show that the general
representation formula introduced for bounded contrasts in
\citep{capdeboscq-vogelius-03a} can be extended to unbounded sequencesof matrix
valued conductivities.
