  The probe method gives a general idea to obtain a reconstruction formula of
unknown objects embedded in a known background medium from a mathematical
counterpart (the Dirichlet-to-Neumann map) of the measured data of some
physical quantity on the boundary of the medium. It is based on the sequence of
special solutions of the governing equation for the background medium related
to a singular solution of the equation. In this paper the blowup property of
the sequence is clarified. Moreover a new formulation of the probe method based
on the property is given in some typical inverse boundary value problems.

Analysis of PDEs