# DC offset in wireless power transfer

#### noelcucu

Joined May 24, 2019
5
why there is a DC offset in a receiver coil of wireless power transfer? what is the theory behind?

#### nsaspook

Joined Aug 27, 2009
7,469

I've seen a DC bias fluxgate used to control power transfer using magnetic shielding material. The normal permeability (μ >>1) of the shield reduces flux until a receiver static magnetic field saturates the shielding material reducing the soft ferrite material permeability (μ ≈ 1 air) allowing for power coupling.

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#### noelcucu

Joined May 24, 2019
5

I've seen a DC bias fluxgate used to control power transfer using magnetic shielding material. The normal permeability (μ >>1) of the shield reduces flux until a receiver static magnetic field saturates the shielding material reducing the soft ferrite material permeability (μ ≈ 1 air) allowing for power coupling.

for example, I will be charging a 9V battery wirelessly when I transmit an AC signal to the receiver coil there is a DC offset? where does the dc component come from if Dc cannot be transferred wirelessly? what is the theory behind?

#### noelcucu

Joined May 24, 2019
5
I will be charging a 9V battery wirelessly when I transmit an AC signal to the receiver coil there is a DC offset? where does the dc component come from if Dc cannot be transferred wirelessly? what is the theory behind?

#### LesJones

Joined Jan 8, 2017
2,687
The output of the receiver coil is AC. As you need DC to charge a battery you need to convert the AC to DC using a rectifier.

Les.

#### noelcucu

Joined May 24, 2019
5
The output of the receiver coil is AC. As you need DC to charge a battery you need to convert the AC to DC using a rectifier.

Les.
yes, you are correct that the output of the receiver coil is AC, but with DC offset. what is the reason why there is a DC component?

#### AlbertHall

Joined Jun 4, 2014
10,226
You need to describe what you mean by 'DC offset' and how you measured it.

#### noelcucu

Joined May 24, 2019
5
the reference voltage in the receiver coil is 15V and I measure it by setting the oscilloscope to DC coupling. the reason why I did that is because it has the same voltage output in the rectifier output.

#### MrChips

Joined Oct 2, 2009
21,639
Is the transmitted signal 50% duty cycle?
If it is not 50% you will get a DC offset.