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**Goal:**

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**Introduction:**

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**How it works (Analogy):**

In a conventional step down transformer the secondary is connected to the AC mains while the primary winding is connected to the device being powered e.g. radio set or television. A transformer works by obeying the principle of electromagnetic coupling in which two coils placed close together induces an emf (electro-motive force) when current is varied in one coil, this is also known as mutual inductance.

## Mutual inductance:

Mutual induction can be defined as the current flowing in one coil that induces a voltage in an adjacent coil. In addition, irrespective of the type of core used either solid (iron) or gas (air) mutual inductance always takes place as far as the two coils are placed close together. Mutual inductance is one of the principle that aid in wireless power transmission. For more information on mutual inductance click here.Where;

L = inductance of the coil.

d = the diameter of coil in inches.

n = number of turns.

l = length of coil in inches.

The formula above can be used to calculate the inductance of a coil but in cases where another coil is brought close the other coil, mutual inductance would take place, this is because the two coils tends to couple. Therefore transmission is based on inductive coupling of the two coil. To know the extent of coupling between the two coils means calculating the coupling coefficient which is a function of mutual inductance which can be given as;

Where;

M = Mutual inductance.

L1 = Inductance of L1

L2 = Inductance of L2

Where;

M = Mutual inductance.

L1 = Inductance of L1

L2 = Inductance of L2

## Coupling Factor or Coupling Coefficient

The coupling Factor K ranges from 0 to 1, when it is equal to 0 it means no mutual inductance. Thus there would be no transmission from L1 to L2, this depict a situation where the coil are kept far apart. When K approaches 1 it means there is mutual inductance to some extent, this could mean the two coils are in range of transmission and reception. Several factors can also affect inductive coupling. Factors like type of coil, number of turns, coil design, core etc.

The equation above can be further expatiated to give the following;

Where;

V2 = voltage on receiving coil.

V1 = Voltage on transmitting coil.

N2 = Number of turns on receiving coil.

N1 = Number of turns on transmitting coil

For information on how the above equation was derived click here.

In conclusion wireless power transmission has been in existence since the time of Nickolas Tesla, this article just concentrates on power transmission through inductive coupling of coils in a close proximity. Since the invention of wireless power transmission in 1904 by Nickolas Tesla there have been invention of newer ways to transfer power wireless e.g. microwave, resonance inductive coupling, light-waves etc. In my next post I will go through the stages of wireless power transfer through inductive coupling.

The equation above can be further expatiated to give the following;

Where;

V2 = voltage on receiving coil.

V1 = Voltage on transmitting coil.

N2 = Number of turns on receiving coil.

N1 = Number of turns on transmitting coil

For information on how the above equation was derived click here.

In conclusion wireless power transmission has been in existence since the time of Nickolas Tesla, this article just concentrates on power transmission through inductive coupling of coils in a close proximity. Since the invention of wireless power transmission in 1904 by Nickolas Tesla there have been invention of newer ways to transfer power wireless e.g. microwave, resonance inductive coupling, light-waves etc. In my next post I will go through the stages of wireless power transfer through inductive coupling.

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