Single Antenna Handles IoT Wireless Charging and Communications New NFC Forum Candidate Specification Available For Comment

By Jürgen Böhler, Chairman and Michael Stark, Vice-Chairman of the NFC Forum’s Technical Committee

Wireless charging is just what it sounds like — a way to charge your phone, tablet or other device without using any wires. Usually the charger itself is connected to a power source, but the device doesn’t have to be physically plugged in to be charged.  Simply place a mobile phone, for example, on a charging pad and the device is wirelessly charged.  When wireless charging is discussed it is usually in relationship to mobile phones and the Wireless Power Consortium’s (WPC) Qi, among other wireless standards.

The NFC Forum’s Wireless Charging Candidate Specification (WLC) puts a new spin on wireless charging, especially for Internet-of-Things (IoT) devices.

Learn more about the Wireless Charging Candidate Specification and Comment

The WLC specification allows the antenna in an NFC-enabled device, like a smartphone, to handle both communications and wireless charging providing an alternative method to charge IoT devices.  This unique solution makes it easier and more convenient to charge low-power IoT devices such as smart watches, fitness trackers, headsets and other consumer devices. For example, a Bluetooth headset that includes NFC technology for pairing could also use the NFC interface for wireless charging.  In this case, the NFC antenna is used to exchange the pairing information and to transfer power.

Once adopted, WLC could become the standard that does for IoT devices what the Qi standard is doing in the handset space.  According to Gartner, there are over 36 billion IoT devices in the world and WLC will let users simply and easily wirelessly charge NFC-enabled devices at a power transfer rate of up to one watt.  This does not compete with the Qi standard which supports a higher power transfer rate.  The WPC is an NFC Forum liaison partner.

Why use NFC for wireless charging of IoT devices?

The benefits of using NFC technology for wireless charging of IoT devices are:

– Users now have another option for charging their IoT devices, either by specific chargers or NFC-enabled smartphones / tablets supporting the new NFC Forum standard for wireless charging.

– With the ability to share the same antenna for communication and power charging, manufacturers can now design smaller and more affordable IoT devices.

Learn more about the Wireless Charging Candidate Specification and Comment

Here’s how it works

Using existing NFC technology, the RF field (using a base frequency of 13.56 MHz) generated for NFC communication already provides enough power to bring NFC Forum Tags without their own power supply into operation. The WLC specification extends this power transfer ability of the RF field and uses the existing communication protocols for NFC Forum Tags exchanging NFC Data Exchange Format messages to control the power transfer.

The NFC Forum Wireless Charging Candidate Specification supports two modes of operation:

  • Static Mode

The static mode targets devices with a very small power budget able to operate with standard RF field strength used for NFC communication. In this static mode, the device receiving the power announces its wireless charging capabilities to the WLC charging device. The WLC charging device provides the RF field according these capabilities.

  • Negotiated Mode

The negotiated mode allows power transfers of up to 1000 mW. There are four different defined power classes including 250, 500, 750 and 1000 mW. For power transfer in negotiated mode, the RF field strength needs to be increased compared to the RF field strength used for NFC communication. To avoid damaging NFC cards or tags as well as for safety reasons, different foreign object detection mechanisms are defined to stop the power transfer once an NFC card or tag or another metallic object is detected in the RF field. The negotiated mode allows the device receiving the power to request the optimum needed power level from the charging device.

Comment now

The WLC was published as a candidate specification allowing the industry to review the document before this specification is validated by the NFC Forum. For more information or to comment on the specification click here. Non-NFC Forum members will be required to purchase the specification to comment but will be entitled to a final version of the specification once it is adopted at no additional charge.

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