When the frequency is very low, 2πf ESL < 1/ 2πfC, the whole capacitor behaves capacitively,
When the frequency is very high, 2πf ESL > 1/ 2πfC, the capacitor behaves as inductive at this time, so “capacitor is no longer a capacitor at high frequency”, but appears as an inductance.
At this time, the difference between the capacitive impedance vector and the inductive impedance is 0, and the total impedance of the capacitor is the smallest, showing pure resistance characteristics. This frequency point is the self-resonant frequency of the capacitor. The self-resonant frequency point is the dividing point that distinguishes whether the capacitor is capacitive or inductive. When it is higher than the resonant frequency, “the capacitor is no longer a capacitor”, so the decoupling effect will decrease.