Level-set shape reconstruction of binary permittivity distributions using near-field focusing capacitance measurements
Measurement science and technology
A near-field focusing capacitance sensor consists of an array of long, coplanar electrodes offset by a small interface gap from an identical orthogonal array of electrodes. The sensor may be used to characterize permittivity inhomogeneities in thin dielectric layers. The sensor capacitance measurements represent a tessellated matrix of integral-averaged values describing void content in a series of zones corresponding to the electrode crossing points (junctions) of the sensor. The sensor does
... . The sensor does not lend itself to computed tomography because the individual capacitance measurements do not represent overlapping regions of sensitivity. An evolving level-set algorithm is proposed to reconstruct a binary permittivity distribution. A mathematical construct, based on the physics of inverse-square fields, is used to approximately reconstruct shape features too small to be captured by the raw measurements. The method accommodates the non-uniform areasensitivity of the junction capacitance measurement. Effective use of the algorithm requires active management of the convergence criterion and evolution rate. The algorithm is demonstrated on a series of phantoms as well as measurements of a voided dielectric thermal interface material using a near-field focusing sensor.