Wireless charging has been around since the late 19th century, when electricity pioneer Nikola Tesla demonstrated magnetic resonant coupling – the ability to transmit electricity through the air by creating a magnetic field between two circuits, a transmitter and a receiver.
But for about 100 years it was a technology without many practical applications, except, perhaps, for a few electric toothbrush models.
Today, there are nearly a half dozen wireless charging technologies in use, all aimed at cutting cables to everything from smartphones and laptops to kitchen appliances and cars.
There are charging pads that use tightly-coupled electromagnetic inductive or non-radiative charging; charging bowls or through-surface type chargers that use loosely-coupled or radiative electromagnetic resonant charging that can transmit a charge a few centimeters; and uncoupled radio frequency (RF) wireless charging that allows a trickle charging capability at distances of many feet.
Both tightly coupled inductive and loosely-coupled resonant charging operate on the same principle of physics: a time-varying magnetic field induces a current in a closed loop of wire.
A magnetic loop antenna (copper coil) is used to create an oscillating magnetic field, which can create a current in one or more receiver antennas. If the appropriate capacitance is added so that the loops resonate at the same frequency, the amount of induced current in the receivers increases. This is resonant inductive charging or magnetic resonance; it enables power transmission at greater distances between transmitter and receiver and increases efficiency. Coil size also affects the distance of power transfer. The bigger the coil, or the more coils there are, the greater the distance a charge can travel.
In the case of smartphone wireless charging pads, for example, the copper coils are only a few inches in diameter, severely limiting the distance over which power can travel efficiently.
Advantages of wireless charging:
- Safer way to transfer power to your phone.
- Simple to just drop your phone on the charging pad.
- Puts less strain on the charging port of your phone.
Disadvantages of wireless charging:
- Wireless charging is slower, especially for phones with Quick Charge technology – plugging into a wall outlet will be much, much quicker for those devices.
- If you’ve got your phone charging via a cable, you can still hold it and use it as normal. If you take your phone off a wireless charging pad to use it, it stops charging.
- Not all phones have it.
While the standards for wireless charging have been in flux for years, now that most devices either support multiple standards or at least Qi, wireless charging is likely to become a standard part of smartphones in the near future