Let’s suppose that we have a one-parameter naturalization problem so, over the
whole scanning area, all parameters of the object have the same value known to us
except for one, for example, the gap between the tip of the probe and the surface of the
object. Let's suppose also to facilitate understanding of the example put forward, that
scanning is carried out on one straight line only. The signal profile and the surface
profile of the virtual object are shown in Fig. 4.
Figure 4. Surface profile of the investigated object (shaded area) and its
corresponding resonant frequency shift signal (solid line)
To solve this problem, it is necessary to solve the direct measurement problem
many times, obtaining the dependence of the information signal on the measured
parameter in a wide range, including, but not limited to the range of the real change in
the parameter under study. Having such a characteristic it is necessary to carry out its
analytical approximation. Its result should be a function describing the curve to be
approximated. In the presence of such an analytic function, the solution of the inverse
one-parameter problem turns into a solution of an equation with one unknown, which
simplifies the task as much as possible. The result of solving this problem is also
illustrated in Fig. 4 as the line, titled h
z vost
.
The two-parameter problem is complicated by the presence of another parameter
that is variable throughout the scan length. Such a problem is urgent in the
measurements of the water content of solid objects, when an uneven content of free
and/or bound water is added to the unevenness of the surface, reflecting a local change
in the dielectric constant of the sample.
In this situation, the presence of approximate analytical dependencies will lead to
the need to solve a system of linear algebraic equations. For this, at the stage of
scanning the object, two measurements must be made at each point: at the initial height
from the surface of the sample and at a height different from the previous one by a
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