Great work Zac. One thing which always confused me is that when we says that fields always propogate between ground plane and microstrip trace , then why the surface roughness above the trace matters?
The propagating magnetic field component always induces some surface current in the conductor, and the current then generates the electric and magnetic fields. These waves are reinforcing, which is why you get wave propagation at all. So yes, the fields propagate in the dielectric, but there is also a propagating current in the conductor. The current in the inductor attempts to follow paths of least reactance, which would be along the skin of the conductor and thus it follows physically longer paths when the conductor is rougher, which is why you get more energy lost in the conductor as heat.
Think about it though, it's just whatever the inductance would be when there was no inductive or resistive contribution from the skin effect. Or to think of it another way, if you take the limit as frequency goes to infinity, the inductive portion of the design dominates the numerator in the classic transmission line impedance equation, and the L at infinite frequency is just that inductance in the numerator.
Great work Zac. One thing which always confused me is that when we says that fields always propogate between ground plane and microstrip trace , then why the surface roughness above the trace matters?
The propagating magnetic field component always induces some surface current in the conductor, and the current then generates the electric and magnetic fields. These waves are reinforcing, which is why you get wave propagation at all. So yes, the fields propagate in the dielectric, but there is also a propagating current in the conductor. The current in the inductor attempts to follow paths of least reactance, which would be along the skin of the conductor and thus it follows physically longer paths when the conductor is rougher, which is why you get more energy lost in the conductor as heat.
Bumpy just like my boards before watching these videos
Hmmm - I'm no scientist but L at infinite frequency sounds dodgy to me!
Think about it though, it's just whatever the inductance would be when there was no inductive or resistive contribution from the skin effect. Or to think of it another way, if you take the limit as frequency goes to infinity, the inductive portion of the design dominates the numerator in the classic transmission line impedance equation, and the L at infinite frequency is just that inductance in the numerator.