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Wirelessly charge your IoT devices with your smartphone

Guest Contributor
Paula Hunter
Paula Hunter
NFC Forum

According to Gartner, there are over 36 million IoT devices in the world, and soon many of them will be able to be wirelessly charged with the near field communication technology found in smartphones, tablets and any NFC-enabled device. Simply hold an IoT device, like a Bluetooth headset for example, near a smartphone and the headset can be recharged wirelessly. This innovation won’t replace device chargers, which charge more powerfully, but if you’re on the road, at the beach or anywhere you don’t have access to a charger, it is a great alternative.

This new spin on wireless charging for IoT devices is the result of the NFC Forum’s recently released Wireless Charging Candidate Specification (WLC). The WLC was published as a candidate specification, allowing the industry to review the document before this specification is officially adopted by the NFC Forum.

Simple, convenient way to recharge consumer devices on the go

The WLC specification allows the antenna in an NFC-enabled device, like a smartphone, to handle both communications and wireless charging. This makes it easier and more convenient to charge low-power IoT devices, such as smartwatches, fitness trackers, headsets and other consumer devices. In this case, the NFC antenna is used to exchange the pairing information and to transfer power to the IoT device.

For example, if your fitness tracker ran out of battery power during your workout, you could recharge it with your phone, tablet or other device. This ability puts an IoT charger in your pocket anywhere you go.

Once adopted, WLC could become the standard that does for IoT devices what the Qi wireless charging standard is doing in the handset space. WLC will let users simply and easily wirelessly charge NFC-enabled devices at a power transfer rate of up to one watt. The WLC will be a great solution for small IoT devices that can benefit from a smaller charge.

Why use NFC-enabled devices to recharge IoT devices

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

  • A second option. Users now have another option for charging their IoT devices, either by specific chargers or NFC-enabled smartphones or tablets supporting the new NFC Forum standard for wireless charging.
  • Shared antenna. With the ability to share the same antenna for communication and power charging, manufacturers can now design smaller and more affordable IoT devices.

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 energy to power NFC Forum tags without their own electrical supply. 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:

  1. Static mode. The static mode targets IoT 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 to these capabilities.
  2. 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.

For more information or to comment on the specification, click here.

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