i am a 3rd year Mech batch doing my dissertation on developing an inductive sensor to determine wear in brake discs. As you know it works by inducing eddy currents into the disc and the are monitored by measuring the impedance of the coil. i am really struggling with understanding the impedance part of it. I have a device called miniVNA pro which measures the impedance & frequency and gives the output to a laptop/computer when the sensor is connected to it. Before testing the sensor on brake discs i need to calibrate it(change number of turns on the coil, change the diameter, thickness etc) by testing it on other metal specimens like steel/aluminium etc. This is where my problem lies, I need to know how to work out impedance for these metals so that i can compare it with my tested values. Is there a table online with these values or do i have to work it out using a formula? Can you help me with this please?