What is magnetic induction?

We can create an alternating magnetic field by driving alternating current through a loop of wire. If the alternating magnetic field passes through a second loop of wire, an alternating current will then be induced in the second loop of wire. In this way energy can be transmitted from the first loop to the second loop without any physical connection.

Two coils wrapped around a shared ferromagnetic core form a transformer; the shared flux path allows power to flow from the driven coil to the secondary loaded coil.

The Classic Transformer

The quintessential example of magnetic induction is the power transformer, used to step up or step down the voltage of AC transmission lines. In the case of the power transformer nearly the entire flux of the magnetic field generated by the primary coil is forced through the secondary coil by means of a shared steel transformer core. The ferromagnetic steel core acts as a guide for the flux, confining it to the desired path through both the primary and secondary coils of wire.

Two coils in close proximity form an air core transformer; power flow is limited by the amount of shared flux.

The Air-Core Transformer for Wireless Power Transfer

The situation becomes more complicated if we want to have flexible separation between the primary and secondary coils, as is the case in a wireless power transfer system. In this case we can no longer use a shared ferromagnetic core as a magnetic flux guide between the primary and secondary coils. An inductive wireless power transfer system is effectively an air-core transformer, and only a fraction of the flux generated by the primary coil will be shared with the secondary coil, depending on the relative arrangement and proximity of the coils.

As the amount of flux shared between the coils decreases, it becomes harder and harder to transmit power from one to the other, necessitating clever design of the coil driver and receiver electronics to efficiently maintain the flow of power.

Click back to learn more about how Nimbus Integrated is overcoming the classic limitations of wireless power transfer systems.

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