thank you for your answer, I already saw that article, but the system used in that report is a bipolar radiofrequency used for aesthetic purposes, I don't know if it shares the same mechanism that can be found on monopolar radiofrequency.
There are some questions that I can't answer 1) HOW HUMAN TISSUES RESPOND TO DIFFERENT FREQUENCIES? I found other sources that states that human tissue impendance (a measure of the opposition to electric current in an electric circuit) drops at high frequency (Electrotherapeutic Devices: Principles, Design, and Applications Artech House Author: George D. O'Clock) SOURCE: You can find it on this link, pages 51-55 https://www.aipro.info/wp/wp-content/uploads/2017/08/Electrical_Properties_Response.pdf
On the other hand, we do have the famous skin effect SOURCE: https://en.wikipedia.org/wiki/Skin_effect
that causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller. The problem is that skin effect was studied on conductors, but the human body is not a copper wire, it's a resistor (at least in my point of view) and when electrical current passes through resistor THEORETICALLY This leads to the impedance dropping with increasing frequency. This is called the Boella Effect.
2)Does monopolar radiofrequency produce electrical current inside the body? monopolar radiofrequency is ,electrically speaking, a capacitor so it produces an inducted current inside the body so how does this circuit responds to different frequencies? This should question could be answered with the Capacitive Reactance phenomenon: the behaviour of a capacitor in a variable frequency circuit as being a sort of frequency controlled resistor that has a high capacitive reactance valuet very low frequencies and low capacitive reactance value at very high frequencies SOURCE: https://www.electronics-tutorials.ws/filter/filter_1.html
So my conclusion is that the higher the frequency the deeper you stimulate, but, again this is just my theory, I would like to be proved wrong or right with real evidence
Thanks in advance