High definition impedance imaging (HDII) is applicable, from d.c. upward for electrical, sonic and elasticity signal
excitations. At low frequencies, great depth is achievable in contrast to that provided by radar without HDII. The HDII
solution process results in a very large and sparse matrix system and associated algorithms provide convergence with
few iterations and high image definition. The methodology solves the three-dimensional image solution rather that by
solving in slices. HDII image quality results from the number of linearly independent equations resulting from the
number of electrodes and linearly independent measurements that are obtained. To construct a standoff (i.e. contactless)
system, the three-dimensional vector Helmholtz equation, i.e. the formulation used in antennal analysis, may be
employed. To do this, the same basic HDII imaging algorithm, as used for the contact case, is employed for standoff
imaging. Over determination can permit significantly refined image quality.
The high definition impedance imaging (HDII) Electroscan algorithm casts the error norm problem into the interior of
the region and iteratively minimizes the difference norm calculated between solutions achieved for applied currents (i.e.
the Neumann problem) and the solution achieved for the measured voltages (i.e. the Dirichlet problem) - in the
electrical-excitation case. This results in very sparse matrices instead of densely-packed Jacobian matrices.
Minimization of the error yields a three-dimensional image of the conductivity distribution. The paper presents a rapid,
sparse-matrix methodology for high definition admittivity imaging involving a very large number of voxels. It is a least-square
algorithm, simultaneously involving all excitations, and it is error resilient and well-conditioned. The solution
iterative procedure is accelerated by a variety of means such as: solution of mutually-constrained, three-dimensional
field equations; successive point-iterative overrelaxation; multi-acceleration factors; measurements at a multiplicity of
electrodes; and excitation modification for image enhancement. Laboratory, field, and simulation case studies are
presented. Spatially restricted-region and open-region solutions are compared. Signal-source modeling is not required.
Conductivity and, generally, admittivity values are able to be determined. And so, the imaging process has diagnostic
capability. It is applicable to non-contact standoff excitations, e.g. magnetic fields, microwave/radar, sonic and elasticity