Low and medium Frequency Electrotherapy - Implox

One method for obtaining amplitude modulation is interferential therapy.
Definition: interferential therapy is the phenomenon that occurs when two or more oscillations simultaneously affect
the same point or series of points in a medium.
When interferential therapy is applied in electrotherapy, use is made of two medium-frequency alternating currents
that interact with each other. One of these alternating currents has a fixed frequency of 4000 Hz, while the frequency
of the other current can be adjusted between 4000 and 4250 Hz. The interference results from the superimposition of
these two currents (Fig. 13’.
At the point where the currents intersect, a new medium-frequency alternating current arises with a modulated
amplitude. The AMF corresponds to the difference in frequency between the two currents.
Fig. 13.
Superimposition of two medium-frequency alternating currents with different frequencies.
In addition to the frequency, the amplitude modulation is also characterized by the modulation dept (M). The
modulation depth is expressed as a percentage, and can lie between 0 and 100%. It will be clear that a modulation
dept of 100% is required to actually interrupt the current (Fig. 14).
Fig. 14.
Different depths of modulation (M) of a medium-frequency alternating current.
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