This tool calculates the impedance of an inductor from its inductance value (units: Henry) and frequency of operation (units: Hertz).
- Frequency of operation
- Inductance value (with the appropriate units)
For a pure inductor, the impedance (ZL) can be represented as:
ZL= jωL = j2πfL
The reactance is given by XL= ωL = 2πfL
- ZL is the impedance of the inductor.
- j is the imaginary unit (to denote the 90-degree phase shift between voltage and current in an inductor).
- ω is the angular frequency of the AC signal (measured in radians per second).
- L is the inductance of the inductor (measured in Henry).
In this representation, the magnitude of the impedance ZL is directly proportional to the frequency of the AC signal (ω) and the inductance (L).
Note that the units for reactance are ohm and the impedance is an imaginary quantity with the same absolute value and units.
A 10 µH inductor operating at 120 MHz has an impedance value of 7.54 kohm (kΩ).
The same value of inductor operating at 1 GHz has a higher impedance value of 125.7 kΩ.
The impedance of an inductor is the opposition that it offers to the flow of alternating current (AC). It’s a complex quantity, meaning it has both a magnitude (measured in ohms) and a phase angle (measured in degrees).
At low frequencies (compared to the inductor’s self-resonant frequency), the impedance of the inductor is primarily reactive and increases linearly with frequency. However, at high frequencies, the parasitic capacitance associated with the inductor becomes significant, affecting its impedance characteristics.
The plots below show the change in inductance value with frequency.
The 47 nH inductor for instance, behaves like it’s supposed to below 400 MHz.
In practical circuits it’s important to understand the frequency of operation. As an example the 47 nH inductor will not work as expected if it’s used to design a CLC filter operating at 1.5 GHz.
- Reactance on Wikipedia