Tech: Wireless charging and how it works

Would you believe it that wireless charging technology has been around for more than 100 years? 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.

Recently, its inclusion in devices such as Apple's new iPhone line has given it new life and given. For about 100 years it was a technology without many practical applications. currently, 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.

Here's how it works, and why it could soon show up in everything:

Wireless charging is making inroads in the healthcare, automotive and manufacturing industries because it offers the promise of increased mobility and advances that could allow tiny internet of things (IoT) devices to get power many feet away from a charger.

The most popular wireless technologies now in use rely on an electromagnetic field between a two copper coils, which greatly limits the distance between a device and a charging pad. That's the type of charging that smart phones are using today.

There are three types of wireless charging, according to experts. 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.

It works like this:

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.

But when the coils are larger, more energy can be transferred wirelessly.

In 2007, MIT physics professor Marin Soljačić proved he could transfer electricity at a distance of two meters; at the time, the power transfer was only 40% efficient at that distance, meaning 60% of the power was lost in translation. Soljačić started WiTricity later that year to commercialize the technology, and its power-transfer efficiency has greatly increased since then.

Last year, Japan-based robotics manufacturer Daihen Corp. began shipping a wireless power transfer system for automatic guided vehicles (AGVs). AGVs equipped with Daihen's D-Broad wireless charging system can simply pull up to a charging area to power up and then go about their warehouse duties.

In September 2017, Apple finally chose a side after lagging behind other handset manufacturers for years by embracing WPC's Qi standard, the same that Samsung and other Android smartphone makers have been using for at least two years.

The first class of mobile device wireless chargers emerged about 2010. They used tightly coupled or inductive charging, which requires users to place a smartphone in an exact position on a pad for it to charge. This is still the most common kind of wireless charging but experts say this will soon change and one will be able to charge devices without being in close proximity to the charger.