Contrary to popular belief, wireless charging is not new. In fact, even before ‘electronics’ really existed, in a New York City laboratory a scientist by the name of Nikolai Tesla was powering lights wirelessly – in 1894!

Unfortunately, the technology of the day could not benefit from this discovery and Tesla’s work lay dormant for decades. Eventually, after several decades some specialist applications such as body-implanted medical devices (pacemakers, ICDs) and electric toothbrushes used the discovery to provide ultra-safe, non-contact charging.

As we have seen a rise in small portable electronic devices in the past decade or so, there is now a real demand for wireless charging – to allow these devices to charge as conveniently as they send and receive data. So, after approximately 125 years, Tesla’s work is now finding a ‘home’.

Why charge wirelessly?

While charging with cables is effective, there are numerous potential drawbacks. Simply having to carry multiple chargers and differing cables is, in itself, a pain. Worse than this cables fray and break, or simply go missing and connectors wear – all of which create unreliability. Even if the connectors do not fail, they can allow in water or dust and take up space as well as increasing the size of the device and adding to the bill-of-material (BoM) cost.

In general, we are seeing connector disappear from devices as wireless data is perfectly adequate for interacting with devices. They only really remain for charging purposes – and that is definitely changing.

Wireless charging: Science and technology

Charging is usually done with a power adapter that uses magnetic induction via a transformer to isolate and reduce the voltage supplied from the mains to the device, thereby producing a charging voltage.

In essence, wireless charging is very similar except that the transformer is split with the primary in a charging mat and the secondary in the device. When the device to be charged is placed on the mat, the magnetic waves from the primary (mat) energise the secondary (device) and charging power is transferred. As the coupling is now via air, it is significantly less efficient than an adapter, but it works – at least over a short range of around one centimetre or so (provided the device case is of the right material and no more than a few millimetres thick).

Efficiency can be improved by matching the two coils so that they resonate at the same frequency. This not only improves the efficiency of the power being transferred but also increases the effective range to several centimetres and permits several devices to be charged simultaneously. While this at first appears to be a significant leap forward, its origins are found in Tesla’s work.

In fact, much of the current innovation is based on Tesla’s original work. He also looked into the possibility of replacing the coils with the plates of a capacitor. Modern engineers have also followed this path and, while some research continues, this has been largely side-lined in favour of the more ‘mainstream’ inductive approaches.

Where advancement is needed is in applying intelligence to the charging systems to deliver the safety and convenience that consumers demand. The first consideration is that the charger needs to detect the presence (and location) of one or more devices and then direct the charging power accurately to optimise efficiency. Another challenge is the presence of ‘foreign objects’ – other metallic items such as coins or keys. If not detected, these devices can become hot – using exactly the same principle by which an inductive hob heats a pan.

The more sophisticated wireless charging systems are not only able to ‘scan’ their environment so that they can detect devices and use multi-coil technology to direct charging power to where it is needed. In fact, some systems are able to communicate with the devices being charged to optimise the process.

Standards are converging

As with many new technologies, competing standards have emerged, each promoting a different approach to solving the problem. The Wireless Power Consortium (WPC) developed their ‘Qi’ standard (pronounced ‘chee’) and, with the backing of companies such as Qualcomm, Apple, Texas Instruments, Samsung, Bosch, Sony, LG, Philips and others, this is now emerging as the preferred standard for the future. 

This is reinforced by companies such as Ikea offering furniture and accessories such as desk lamps with in-built charging that is Qi-compliant. Carmakers, including German firm Audi, are including Qi-compatible charging technology in their cars. Even Apple, who were once reluctant to include any form of wireless charging have included Qi technology in their latest flagship devices, the iPhone 8 and iPhone X.

Apple’s commitment to Qi is further demonstrated by their own AirPower technology that extends the Qi specification to enable the charging of three devices simultaneously. Apple is now working with the WPC to have these enhancements embedded into the Qi specification.

Other standards which were once prominent include the AirFuel Alliance (AFA) which support both resonant and inductive charging. Originally formed from two earlier organisations – the Alliance for Wireless Power (A4WP) and the Power Matters Alliance (PMA), the AFA seems to be acknowledging the strength of Qi. In fact, Powermat Technologies (a co-founder) recently announced software updates that would make their product offerings Qi compatible. 

Given the variety of devices to be charged, Qi has several power levels, with variants up to 1kW under development. Most of the current activity is at the low-power end (up to 5W) as wireless charging is currently focussed on smaller devices such as smartphones, small tablets, smart watches and other wearable devices. Laptops and other similarly powered devices would be covered by the medium-power specification that provides up to 15W. 

Continuing progress

While great progress has been made in recent years, wireless technology is still in its infancy and there are several areas where progress must happen before maturity is achieved. Efficiency is at the top of this list and will become more important as wireless charging becomes more prevalent- and as people move to charging higher-powered devices. 

The distance that charging can take place over is another area of focus. At the moment devices have to be placed flat on a mat and are therefore relatively hard to operate (when being charged with a cable, a mobile phone could still be used with relative ease). Recent technologies such as beam forming from Pi Inc. are now able to extend the charging range of Qi compatible technologies to 30cm and further enhancements are likely.

Many device manufacturers are welcoming the benefits of wireless technology, most notably the ability to remove large sockets that restrict the form factor of their device, and to have the ability to make a truly waterproof solution. In doing so, they have to consider case design carefully and move away from metal cases to plastics or glass. However, these new materials not only improve the wireless charging but also communications such as wireless data or NFC.

While there remain a few challenges to overcome, wireless charging is moving ahead rapidly and the few remaining issues are likely to be addressed soon. So, after almost 125 years Tesla’s discovery is now having a profound effect on devices that he could never have imagined, even in his wildest dreams!

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