Wireless charging pads may be more convenient than traditional wired smartphone chargers, but a team from Microsoft Research in China thinks that they're still not convenient enough. According to Yunxin Liu, Zhen Qin and Chunshui Zhao, pads still require users to consciously place their phone in a specific spot, for the express purpose of charging. Instead, they envision a system in which users just toss their phone onto a table, where it's automatically charged using a beam of light. They've already built a working prototype of the system, which is known as AutoCharge.

Here's how the technology works ...

Using an overhead camera (a Kinect, in the case of the current prototype) and object recognition software, AutoCharge continuously scans the table top, looking for smartphone-shaped objects. When it detects one – which it does in less than one second – it shines a beam of focused light onto it. Both the camera and the light can rotate, in order to image and illuminate the target from an optimum angle.

A photovoltaic panel on that phone (which could be a transparent Wysips film) subsequently generates electricity from that light, charging the phone's battery. The researchers said that in tests of the prototype using a phone-sized PV panel, it was found to charge phones approximately as fast as some wired chargers.

In order to keep from continuously lighting up phones that don't need charging, AutoCharge utilizes a system in which the PV panel powers a microcontroller and an LED indicator on the top surface of the phone. When the phone is first illuminated, that LED blinks in a specific pattern, indicating the battery's current charge level. AutoCharge uses its camera to detect that pattern, and only keeps illuminating the phone if it needs juicing up. Once the phone's battery is full, the LED will flash in a different pattern, letting AutoCharge know that it's time to stop.

Likewise, if the object recognition software is fooled by a smartphone-shaped object that isn't actually a phone, its lack of flashing LEDs will keep AutoCharge from trying to charge it – beyond an initial inquiry, that is.

In a recent paper on their research, the team admit that AutoCharge is "still far away from a real product." One of its biggest hurdles is the current scarcity of phones with solar panels ... although there are a few, and more could follow as the technology advances.