Communication is key for wireless charging

Mark de Clercq
Product Marketing Group Manager
Communication is key for wireless charging
Wireless charging is fast becoming a major technology, but for it to work properly, communication between the charger and the device is essential

Wireless charging has come a long way in the past five years since practical implementations for mobile-computing devices first appeared on the market.

The core technology could become so pervasive in the future that it could even be laid into roads to charge electric vehicles as they pass over. Trials of stationary systems for public-service vehicles are already underway. But it’s mobile where most attention is focused right now. A key issue today is which of the two leading standards will be adopted.

Standards are key to the success of wireless charging. Consumers do not want to have to plug in multiple charging stations to deal with all their devices. And a key advantage of wireless charging is that it provides a way for hospitality businesses to keep customers happy and in their locations. Knowing that they can make use of the wireless charging tables and desks they have on offer is key to attracting those users in through the door in the first place. Does this mean there is, realistically, only room for one winner? The reality is likely to be more complicated.

Following the decision by the Alliance for Wireless Power (A4WP) and the Power Matters Alliance to join forces, there are now two main choices. The Rezence standard developed by A4WP provides a charging scheme based on magnetic resonance. Qi, promoted by the Wireless Power Consortium, is based on the more widespread concept of electromagnetic induction. Qi has the benefit of being in use for longer, providing manufacturers with more experience of how it works in the field. But Rezence provides more scope for product design as charging does not rely on precise alignment between the transmit and receive coils. The use of resonance at higher frequencies ensures an efficient transfer of power under many more circumstances.

The reduced restrictions over device alignment with Rezence will tend to favour its use in devices where there is no obvious ideal orientation for the device as it sits on the charger. This is likely to suit wearables and similar devices. Qi, on the other hand, naturally suits devices with a large, flat surface area, such as tablets and laptops. The question is how manufacturers can ensure their customers get the widest choice of power delivery. Communication is key.

Qi embeds the signalling between charger and device in the magnetic field fluctuations that it uses to transfer power. If Rezence were to use the same technique, it would be in an entirely different frequency range, rendering the two incompatible. But there is one protocol that can ensure consumers get a consistent experience: Bluetooth. And that is what Rezence already uses.

With its ubiquity across mobile devices, Bluetooth provides a way of extending support for wireless charging in a way that transcends individual standards. And it supports the idea of developing multi-standard charging stations for public locations, with the low-power Bluetooth Smart protocol providing a way for devices to locate a compatible charger. Bluetooth becomes the lingua franca between station and device to ensure that the right power-delivery mechanism is used, no matter what it is.

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