Hidden Inclusions Research Articles

Refined stability estimates in electrical impedance tomography with multi-layer structure

<p style='text-indent:20px;'>In this paper we study the inverse problem of determining an electrical inclusion in a multi-layer composite from boundary measurements in 2D. We assume the conductivities in different layers are different and derive a stability estimate for the linearized map with explicit formulae on the conductivity and the thickness of each layer. Intuitively, if an inclusion is surrounded by a highly conductive layer, then, in view of "the principle of the least work", the current will take a path in the highly conductive layer and disregard the existence of the inclusion. Consequently, a worse stability of identifying the hidden inclusion is expected in this case. Our estimates indeed show that the ill-posedness of the problem increases as long as the conductivity of some layer becomes large. This work is an extension of the previous result by Nagayasu-Uhlmann-Wang[<xref ref-type="bibr" rid="b15">15</xref>], where a depth-dependent estimate is derived when an inclusion is deeply hidden in a conductor. Estimates in this work also show the influence of the depth of the inclusion.</p>

Microwave imaging of multilayered structures using ultrawideband noise signals

A microwave ultrawideband (UWB) radar system is developed and used for non-destructive testing (NDT) of multilayered structures. The effectiveness of this approach lies in the choice of critical parameters such as waveform type, operational frequency range, and stand-off distance. Matched filtering of the received waveform with a replica of the transmitted signal is used to locate hidden anomalies or flaws within a multilayered structure, most of which are not apparent through common visual-inspection techniques. Due to the impulse-like autocorrelation properties of white noise, noise waveforms provide the ability to locate material discontinuities as well as, or better than, other common waveforms such as Gaussian-modulated sinusoidal pulses (GMSP) or linearly frequency modulated chirp signals. Experimental data are gathered using a specially developed microwave imaging system which operates in the X-band frequency range. Subsequently, two-dimensional (2-D) and three-dimensional (3-D) images are rendered following a raster scanning approach to reveal internal boundaries, hidden inclusions, and defects due to impact damages or corrosion in fiber-reinforced polymer (FRP) materials and other dielectric materials.

Infrared thermography applied to the quantitative determination of spatial and thermophysical parameters of hidden included objects

In this paper we present a study of case of determination of material properties using information from the surface temperature distribution obtained by infrared thermography. Two samples are used for the study: one in gypsum plaster and another with a hidden included steel cylinder. Both samples are heated to 120 °C and their surface temperature distributions are recorded while they are left to be cooled by natural convection in a 30 °C ambient. A simple numerical model is used in order to simulate the transient phenomenon. The parameters are determined by minimizing the deviation between the numerical and experimental results. First the parameters of the gypsum plasterboard are obtained from the information of the plain gypsum plaster sample and after the parameters of the steel inclusion are obtained from the data from the sample with the hidden inclusion. The following parameters are obtained: thermal conductivity and thermal capacity of the gypsum plaster; thermal capacity, radius, position and height of the steel cylinder. During all the presentation we discuss extensively on the particularities of the method when used in this chosen pair of materials. The last section is devoted to summarize the results and discussions.

Random walk analysis of time-resolved transillumination measurements in optical imaging

Data relating photon migration in human tissue can be obtained from experiments in which laser light is injected into one face of a finite slab of tissue and detected at the opposite face. From the results of such experiments one would like to infer optical properties of the underlying tissue which are related to its biological properties. Random walk theory has been successfully applied to the translation of such data into the physical parameters that characterize properties of the tissue. We here outline a technique based on the theory of random walks for analyzing how well time-resolved transillumination experiments may be expected to perform for detecting hidden inclusions which have a greater absorption than surrounding tissue. We use an asymptotic evaluation of exact results to determine the degree to which detection is possible.

The use of infrared spectroscopy for the determination of the nature of hidden inclusions in mica

The use of infrared spectroscopy for the determination of the nature of hidden inclusions in mica