How Wireless Power Works

Inductive Coupling

Inductive coupling uses magnetic fields that are a natural part of current’s movement through­ wire. Any time electrical current moves through a wire, it creates a circular magnetic field around the wire. Bending the wire into a coil amplifies the magnetic field. The more loops the coil makes, the bigger the field will be.
How Wireless Power Works
If you place a second coil of wire in the magnetic field you’ve created, the field can induce a current in the wire. This is essentially how a transformer works, and it’s how an electric toothbrush recharges. It takes three basic steps:

  1. Current from the wall outlet flows through a coil inside the charger, creating a magnetic field. In a transformer, this coil is called the primary winding.
  2. When you place your toothbrush in the charger, the magnetic field induces a current in another coil, or secondary winding, which connects to the battery.
  3. This current recharges the battery.

You can use the same principle to recharge several devices at once. For example, the Splashpower recharging mat and Edison Electric’s Powerdesk both use coils to create a magnetic field. Electronic devices use corresponding built-in or plug-in receivers to recharge while resting on the mat. These receivers contain compatible coils and the circuitry necessary to deliver electricity to devices’ batteries.
A newer theory uses a similar setup to transmit electricity over longer distances. We’ll look at how it works in the next section.

Resonance and Wireless Power

Household devices produce relatively small magnetic fields. For this reason, chargers hold devices at the distance necessary to induce a current, which can only happen if the coils are close together. A larger, stronger field could induce current from farther away, but the process would be extremely inefficient. Since a magnetic field spreads in all directions, making a larger one would waste a lot of energy.
In November 2006, however, researchers at MIT reported that they had discovered an efficient way to transfer power between coils separated by a few meters. The team, led by Marin Soljacic, theorized that they could extend the distance between the coils by adding resonance to the equation.
­ A good way to understand resonance is to think of it in terms of sound. An object’s physical structure — like the size and shape of a trumpet — determines the frequency at which it naturally vibrates. This is its resonant frequency. It’s easy to get objects to vibrate at their resonant frequency and difficult to get them to vibrate at other frequencies. This is why playing a trumpet can cause a nearby trumpet to begin to vibrate. Both trumpets have the same resonant frequency.
Research at MIT indicates that induction can take place a little differently if the electromagnetic fields around the coils resonate at the same frequency. The theory uses a curved coil of wire as an inductor. A capacitance plate, which can hold a charge, attaches to each end of the coil. As electricity travels through this coil, the coil begins to resonate. Its resonant frequency is a product of the inductance of the coil and the capacitance of the plates.

For more detail: How Wireless Power Works


About The Author

Ibrar Ayyub

I am an experienced technical writer with a Master's degree in computer science from BZU Multan University. I have written for various industries, mainly home automation and engineering. My writing style is clear and simple, and I am skilled in using infographics and diagrams. I am a great researcher and am able to present information in a well-organized and logical manner.

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