WIRELESS TECHNOLOGY FEATURE
WIRELESS CHARGING - IT’S A GROWING VALUE PROPOSITION
Mark Patrick, Mouser Electronics explores what’s behind wireless changing and its market adoption T
he emergence of small, powerful, always-on mobile devices and items
of wearable electronics are generating serious application demand for wireless charging. As well as the innate convenience of this technology - which dispenses with the need for cables and adaptors, it also has key design advantages, by lowering the price tags of products that employ it and making them more streamlined. Thanks to wireless charging there will no longer be a reliance on bulky external connectors, which have numerous issues associated with them. Among these are, presenting a point of
ingress for dirt, dust and water, being vulnerable to physical damage, taking up valuable board space and impinging on the overall aesthetic qualities of the product, as well as adding to production costs and extending the time needed for testing procedures. At this stage, the majority of wireless
charging technologies are based on magnetic induction. Described in a simple form, this technique puts the wire coil of one side of a transformer inside the device, then the other side of the transformer goes into the charger pad. The charger pad can create a magnetic field if the two coils are brought into close proximity with each other. This induces a current within the coupled device. It has an extremely short practical range however (approximately 1cm) and will fail to penetrate barriers that are more than a few mm thick. Resonant inductive coupling is starting
to become increasingly commonplace. This has substantially enhanced performance, due to the tuning of the coils so that they resonate at the same frequency. It results in greater efficiency figures being derived and extended operational range (several cm). Furthermore, it is better at penetrating blocking materials, as well as offering the possibility to charge multiple devices simultaneously. An alternate technique is capacitive
coupling, but this seems to not be gaining the same sort of attention as the magnetic induction technologies just outlined. In addition, there is ongoing research activity in relation to wireless
/ ELECTRONICS Figure 2:
Wireless charging docking station
use the Qi low-power specification, which provides up to 5W and is suitable for charging mobile phones, smart watches, wearables, etc. Components are also available that comply with the newer 15W Qi medium-power specification - offering faster charging and greater suitability for larger format devices (like laptops). Higher-power variants of Qi are in the pipeline, covering 120W up to 1kW. Competition for Qi’s is mainly via the
Figure 1:
The majority of wireless charging technologies are based on magnetic induction
power delivery using other methods - including radio frequency radiation and even ultrasound. To facilitate efficient wireless charging,
the system must detect when a chargeable device is within range, thus avoiding unnecessary expenditure of energy. Also, the charging system needs to detect any stray metallic objects (jewellery, keys and non-compatible devices) so that power is not delivered to them, because heating and damage could occur. Inductive devices can achieve these goals by regularly scanning the nearby area at lower power, and possibly by using multiple coils for directionality. Modern general-purpose wireless
charging specifications include two-way data transfer to communicate with their client devices, in order to assure optimal charging efficiency and maximise safety. During the past few years, Qi has
established itself as a leading wireless charging standard for mobile devices. Qi is promoted by the Wireless Power Consortium (WPC) - an industry body. The current Qi version is based upon resonant inductive coupling. Most devices
AirFuel Alliance. The organisation’s technologies include the Rezence magnetic resonance charging technology and PMA inductive charging. However, many feel that AirFuel is struggling to gain traction over Qi. While wireless charging has many advantages over wireline based charging there are still significant drawbacks to be aware of. Most notable of these is the lower efficiency of energy transfer when compared to a wireline connection - with losses of between 20% and 40% normally being expected. In addition, current wireless charging technologies are not always that convenient. For example, a phone handset placed flat on a charging pad will prove difficult to operate, while a handset connected to a typical cable can be used more easily under such circumstances. Though taking a wireless approach
allows OEMs to get rid of outdated external sockets, it does bring other issues with it. Mobile phone handsets that support wireless charging typically have glass or plastic backs, as metallic cases impair wireless charging performance. This can have implications in terms of handset cost and robustness. Non-metallic cases do, however, exhibit better performance with short range wireless data transmission technologies, such as NFC. Increasing prevalence of wireless charging infrastructure is certain to push consumer uptake. The remaining technical challenges that it poses are relatively minor and likely to be addressed by higher power levels and other innovations over the coming years.
Mouser Electronics
www.mouser.co.uk T: 01494 427 500
ELECTRONICS | SEPTEMBER 2018 19
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