  Electrical impedance tomography is an imaging modality for extracting
information on the interior structure of a physical body from boundary
measurements of current and voltage. This work studies a new robust way of
modeling the contact electrodes used for driving current patterns into the
examined object and measuring the resulting voltages. The idea is to not define
the electrodes as strict geometric objects on the measurement boundary, but
only to assume approximate knowledge about their whereabouts and let a boundary
admittivity function determine the actual locations of the current inputs. Such
an approach enables reconstructing the boundary admittivity, i.e. the locations
and strengths of the contacts, at the same time and with analogous methods as
the interior admittivity. The functionality of the new model is verified by
two-dimensional numerical experiments based on water tank data.
