meaning of impedance(about imaginary part)

When I measured impedance of the RF system, I discoved decreasing imaginary part(minus value). but!! it is minus value(like -5 -10

-12...) and the real part of impednace was incresed accoding to the increasing power(13.56MHz). finally we find decreasing the impednce

I have a few question

I wondering the deceasing imaginaey part of impedance(minus) whats the meaning? acually RF system is inductively coupled plasma source for plasma processing these are consist of coil, quartz, vacuum. we applied 13.56MHz RF power to the coil(3 of 4 turn) and by using V/I probe which installed between rf matching network and coil.

when i measured the electrical properties of system(current voltage and phase) how to calculate the inductance of coil?

please let me know

I'm not going to answer your homework questions directly. The basics of what "real" and "imaginary" are this:

If you force a sinusoidal voltage (or current) across (or through) a device that is resistive (e.g. a resistor) then the resulting current (or voltage) will be in phase with its source. That is, the peaks of the source (voltage/current) sinusoid will occur at the same position (0 degrees) of each period of the (sinusoidal) response (current/voltage).

If you do the same with a reactive device (e.g. a capacitor or an inductor) then the peaks of the source sinusoid will occur 1/4 period (90 degrees) away from its response.

If you have a combination of devices that are both resistive and reactive, then the resulting response could be something other than exactly 0 degrees or 90 degrees, but the response of each purely resistive or purely reactive device will always be as described above.

The response to a reactive device is different than a resistive device because a device that is "purely reactive" does not dissipate any power. Purely reactive devices are energy storage devices. Resistors dissipate all of the energy applied to them.

Be aware that there is also energy dissipated through radiation, but this part of the energy dissipation must be considered separately.

Bob