Types of Impedance and How They Work

In this article, we are going to talk about the idea of impedance and its properties. This is a very crucial subject topic in electronics, and its concept and mechanism come from the analysis of AC (Alternating Current). We limit our study to inputs to electric circuits that look like a sinusoid, sine, or cosine in AC analysis. Of all the signals that we could have in the entire universe, we are going to limit ourselves to sine waves, and some great amplifications emerge from this. 

What is Impedance?

Electric impedance is the degree of resistance that an electric circuit offers to an electric current when a voltage is applied to it. Impedance extends the idea of resistance to AC (Alternating Current) electric circuits. Impedance consists of both magnitude and phases.

In simple words, impedance is the measure of resistance to the flow of the electric current that is presented by the circuit or the network whenever the voltage signal is applied.

It is denoted by Z = VI

Where Z = Electrical impedance (in ohms)

             V = Voltage (in volts), &

              I = Electric current (in amperes)

How does impedance work?

• Impedance is a more relevant term when the applied input signal is AC sinusoidal signal. And in a way, some properties of impedance are similar to that of the resistance, which also implies the opposition to the flow of current. But the resistance is frequency independent. 
• It means that suppose you have a resistive network or a simple resistor. If you operate this network at, let’s say, DC (Direct Current) voltage or at 100KHz, then the value of the resistance will not change with the frequency. On the other hand, the impedance of the circuit will change with the frequency because it involves reactive elements like the capacitor and the inductor. 
• Now, in the case of this inductor and the capacitor, the resistance that is offered by these elements is known as the reactance, and it is denoted by the symbol of X. So, for the inductive reactance, it is denoted as XL, and for the capacitive reactance, it is denoted as XC. 
• Now, the value of this inductive reactance will be equal to jwL, while the value of this capacitive reactance will be equal to 1/jwC. This reactance is actually the ratio between the voltage and the electric current, which is the voltage that is applied across the inductor or capacitor and the current that is flowing through the conductor. 
• So, if we simply take the ratio of this voltage and current, then we will get the reactance of either the inductor or capacitor. And the unit of this reactance is the ohm. Now, if we only consider the magnitude of this reactance, then for the inductive reactance, it will be equal to wL, and for the capacitive reactance, it will be equal to 1/wC. 

Deriving the expressions

So, as you can observe from the above-mentioned paragraph that these inductive and the capacitive reactances are frequency-dependent, which means that with the frequency, the value of this reactance will change.

Now, suppose your circuit contains the resistive element as well as some reactive element, then the total resistance that is offered by the circuit is known as the impedance. And it is denoted by the symbol of Z. So, the total impedance will be the summation of this resistive element as well as the reactive element. So, here, in this case, the total impedance will be equal to R+jwL. Now, a lot of times, it is also depicted in the polar form. It means that it has some finite magnitude as well as some finite phase. 

Now the magnitude of this impedance can be given by this expression: |Z|=R2+X2 

And the phase of this impedance can be found by this expression = tan-¹(X/R)

Now similar to the resistance, the impedance is also a ratio of voltage and current. So for any particular network or circuit, if the impedance is represented like this, it means that the voltage will lead the current by some phase angle and that the ratio of the voltage and current signal will give the magnitude of the impedance.

Types of impedance

There are two types of impedance. One is an input impedance, and the other is the output impedance.

• Input Impedance: Let’s say we have one circuit, and to this circuit, some voltage source is connected via the input terminals. Now, if we look at the electric circuit from the source perspective, the impedance that is offered by the electric circuit is termed the input impedance. Hence, the input impedance is the type of impedance that is perceived by the voltage source between the two terminals of the electric circuit.
  

• Output Impedance: Let’s say in the circuit, we have connected some load at the output terminal, and the circuit is giving some output voltage. Now, the output voltage should also appear across the two terminals of the load. But from the loading perspective, it will also find some finite resistance in the electric series with the output voltage. So, this finite resistance is referred to as the output impedance of the electric circuit.
  

Conclusion

This article gives an insight into how impedance works. Impedance works with the help of three major elements, namely, inductor, capacitor, and resistor. It also gives an idea about the two types of impedance, i.e., the input impedance and the output impedance, and the types of resistance they provide. It also sets out the difference between the reactance and the impedance with the help of examples.