We saw that some of
the involved impedances were very variable. The
electrode with the skin, forms a capacito-resistive
system. The problem to resolve is to find the values
of the components by knowing that : Each
individual is different, the values change according
to the zones and size of electrodes, the stress, the
taken of certain drugs... We believe that this
problem is insoluble and we do not even try hard to
make calculations to have, at least, an order of
idea.
It is true that
calculation is difficult, but per hour of data
processing, there is no more obstacle. Moreover, all
the modern generators microprocessors which have,
moreover embark, one analogique/numeric treatment
unit. These calculating units are capable to render
this service to us. To solve the following formula
is, for these integrated circuits a formality of a
few microseconds.
The advantage of
such an approach, technological, is the
simplification of the implementation of the
treatments. On the other hand, this way of proceeding
does not bring any knowledge, really useful, for the
therapeutist. It makes it possible however to
visualize the variation of impedance, total,
according to the frequency. It is a concept
to be retained.
Moreover, the term w is calculated in the following way;
Unfortunately, it
is possible to calculate them only insofar as the
currents applied are purely sinusoidal (w is single in the formula).
Electrotherapy shows us that this type of current is
used rather little.
As we mentioned
above, we are in presence, of a capacito-resistive
system. This system has a mathematical property good
known of the electronics specialists. By
approximation, this unit is overall derivative
device. The terminal voltage of R1 (Rt) is the
expression of derivative from the function presented
at the terminals of the system. Out, R1 is purely
resistive. One can as conclude from it as the current
I which it cross-piece is an expression of derivative
(except for a constant) from the tension U applied at
the boundaries of the system.
Thus,
By the generalized
law of ohm , one can affirm:
We as know, as the
derivative of a function is the expression of its
slope and even, if we do not have the formula of the
function, we can calculate the slope, in any point,
by the famous formula:
With these elements,
it is possible to affirm that Zep is inversely
proportional to the slope, because well on;
You will have
understood the essential importance of these
relations;
- I is the
derivative of U (except for a constant).
- Z is
conversely proportional with the variation of
U.
