Microsoft researchers use light beams to charge smartphones

Build indoor solar charger prototype for smartphones

The prototype AutoCharge system uses a Microsoft Kinect camera.

The prototype AutoCharge system uses a Microsoft Kinect camera.

Smartphones are amazing but their battery life is frequently absurd. It's not uncommon for people to charge their smartphones once, twice or even more in the course of a single day. Enter a team from Microsoft Research that wants to stop you from worrying about plugging in your phone.

Yunxin Liu, Zhen Qin and Chunshui Zhao from Microsoft Research's Beijing campus have developed a new system they dub AutoCharge: A prototype automatic charging system for smartphones.

But not only is it designed to charge smartphones automatically, it does so wirelessly.

The researchers' paper (PDF) notes that "wireless power methods have several disadvantages, preventing them from being used in our targeted usage scenarios": "First, the electromagnetic radiation of wireless power is much higher than wireless communications (e.g., Wi-Fi or 3G). Thus, safety to human bodies is a big issue in wireless power. As a result, wireless power is usually used only in extreme scenarios such as in outer space, for military purposes, or in very short ranges...

"Second, as the radio frequencies used in wireless power are much lower than the frequencies of lights, it is hard to emit the radio waves within a straight beam. This causes energy waste if the receiver is not large enough and makes it hard to ensure safety."

The current crop of wireless charging solutions for smartphones typically require special phone cases and 'charging pads', and work using electromagnetic induction. Power is transmitted only over a few centimetres.

The Microsoft Research team instead envisage using solar power techniques to charge smartphones.

However, due to scattering, "indoor surrounding light is usually much weaker (two orders of magnitude weaker or even worse) than the sunlight and thus cannot be used to charge a smartphone".

Instead of relying on the sun, the team built a prototype charger that can be mounted on a ceiling and automatically locate a smartphone lying on a table, then charge it using a directed beam of light.

The light charger has two modes. In the 'detection' mode, it uses a camera (from a Microsoft Kinect) and image recognition software to detect objects with the size and shape of a smartphone lying on a table. The charger will rotate until it detects an object that looks like a smartphone.

The device then enters charging mode and turns on its light. The prototype used an UltraFire CREE XM-L T6 Focusing LED Flashlight. (Potentially, the system could use infrared light for charging, which would reduce the irritation of using a visible beam, the researchers note.)

Source: AutoCharge: Automatically Charge Smartphones Using a Light Beam

To avoid attempting to charge a phone that already has a full battery - or trying to charge a random smartphone-shaped object - the system relies on the smartphone exchanging messages with the charger via an on-phone LED.

For the prototype, along with attaching a solar panel to the test smartphone, the team integrated a microcontroller and an LED that are powered by the photovoltaic panel not by the phone's battery.

When the charger directs the light beam at the smartphone, the microcontroller checks the state of the phone's battery and if it needs charging it will blink a 'ready to charge' message using the LED.

That signal is recognised by the camera used by the charger for image recognition. The LED can also be used to indicate when the battery is fully charged. (For the prototype, the team used a Kinect camera.)

In addition the charger can recognise when an object moves between it and the phone, and automatically shut down the light beam within 50 milliseconds.

Source: AutoCharge: Automatically Charge Smartphones Using a Light Beam

Using a light beam to charge a smartphone could be as quick as many wired chargers, the researchers found, depending on the size of the PV panel.

A big problem with implementing the system is that smartphones do not currently come with PV panels attached. (For the prototype, a panel was hooked up to a smartphone, not integrated.)

However, the paper notes that new generations of smartphones are released every year. Because many people would typically sit their phone face-up on the desk, smartphones could potentially integrate a transparent PV film on the front as well as a panel on the back.

"To take advantage of the AutoCharge approach, we imagine that future smartphones may integrate a PV film/panel on both sides. Therefore, no matter whether the screen of a smartphone faces up or down, the smartphone can always be charged by a light beam," the paper states.

The system could be used to turn tables or even large rooms into charging areas for mobile devices (though the paper notes that implementing the system for a room would involve significant tweaking of the prototype). Another possibility would be a 'charging box'.

The paper concludes that although the prototype "is still far away from a real product and may be further improved in many aspects, we have demonstrated the feasibility and made a significant step towards automatic smartphone (and other mobile devices) charging".

Follow Rohan on Twitter: @rohan_p

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