We saw that the taught bases were
insufficient for a perfect comprehension of electrotherapy. We will introduce
the concept of signal. Within the framework of our techniques of treatment, a
signal can represent the current which crosses the zone to be treated, or for
example, the tension delivered by the generator.
All the signals, which we use, are
temporal. They move according to the time which ravels. At every moment t
corresponds, one and only one value of the signal. It is thus possible to
describe the signal, according to a temporal variable t.
The signals which we use are
considered causal. They exist only as from a time t0, beginning of the
application of the treatment.
The great majority of the signals
which we use are periodic. The reason (left useful therapeutic) reproduces with
a regular interval T.
The period T determines the
fundamental frequency F of the signal.
The fundamental frequency of the
signal is the smallest frequency which perhaps contained in the signal.
Any signal can be put in the form
(by knowing F and N integer) of an infinite succession of sinusoidal and cosine
functions of the form:
This formula is universally known.
We owe it to a French mathematician, Joseph Fourier (1768 1830). This tempting
formula has remarkable properties:
- A0 is the average value of the function, it is
the constant part of signal.
- A1 is the amplitude of fundamental frequency
F.
- A2... An are the amplitudes of the harmonics.
- B1 characterize the dephasing of the fundamental
one.
- B2... Bn characterize the dephasing of the
harmonics.
