When using ferrite beads in spice, I often have the impression that they are not lossy enough compared to the real thing. In particular, the conventional model of RLC all in parallel is basically a short at frequencies well above GHz.
I realize that there is interwinding capacitance, and that HF currents therefore can take a shorter path through the component, but they still have to pass beside the ferrite material, which still has a large loss term at GHz (even peaking at the ferromagnetic resonance frequency in case magnetic material is used). So the resistive behavior should still matter when the part is well in its capacitive regime, right ? Not at its full strength but it shouldn't be ignored, I guess.
Below, I compare the standard bead model to a customized one, where the capacitance is divided into smaller capacitors each with a bit of series resistance.
The effect is that the phase stays much closer to 0° beyond the peak impedance and never really drops to -90° as it would for a pure capacitor.
The transient behavior is also much more benign compared to the standard bead model. Here, a 1 Volt step is applied to the bead into a 100 pF capacitor with a small series inductance of 500pH, and capacitor voltage is monitored:
So again, is this modified bead model reasonable or is there some good physical reason to ignore loss in the very high frequency regime?