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.

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 Wireless 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 Apple has incorporated into the iPhone 8 and the iPhone X.

How wireless charging works

Broadly speaking, there are three types of wireless charging, according to David Green, a research manager with IHS Markit. 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 Stand 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. That's the tactic WiTricity, a company formed from research at MIT a decade ago, has helped pioneer. It licenses loosely-coupled resonant technology for everything from automobiles and wind turbines to robotics.

Whether you’re an ardent party host or laid-back college student in a shoebox dorm room, a Bluetooth Speaker is a simple way to improve your soundscape. Sometimes you don’t have the want (or funds) to make the leap into the world of high-end stereo or home theater audio systems, but a good Bluetooth speaker can keep you company in and out of the home. This article covers what features to look out for when searching for the best product for your needs. If your summer days consist of hikes, camping, or hours on your bike, get a durable speaker. At the very least, this means a speaker with an IP rating, which indicates water resistance. Anyone who’s particularly clumsy should also get a speaker with some degree of drop protection, even if it only covers one meter.

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