Batteries remain by far the weakest point of all mobile devices. No matter how advanced the optimizations in the latest models, sooner or later we have to connect the "cord" and let it charge for a couple of hours. At the University of Washington, they are working to change that pattern, and the first result is a prototype cell phone that consumes just 3.5 microwatts. It obtains its energy from ambient signals and leverages small vibrations caused by the user to encode the voice signal.
When we start removing components from a smartphone, besides simplifying its configuration, we can reduce overall energy consumption. That was one of the goals of Google's Project Ara, "technically suspended" until further notice. The customization we enjoy on desktop PCs seems impossible on smartphones, and its absence condemns us to a constant dependence on bigger batteries, emergency chargers, and outlets in establishments with very overpriced coffee. Now imagine a cell phone that doesn't need batteries. Of course, energy must come from somewhere, and the main candidates are the radio waves already in the air.
Such a mobile phone is not only possible, but the University of Washington has just presented a prototype. According to Bryce Kellogg, one of the research team members, the power obtained from a radio signal or a basic light source ranges from 1 to 10 microwatts. The prototype currently has a total consumption of 3.5 microwatts. As the image reveals, the phone has no screen or anything like it. The buttons are capacitive, and the user hears calls through earphones. A critical aspect in the phone's design is the elimination of the classic analog-to-digital conversion in voice processing. Instead, it uses vibrations caused by the user speaking near the microphone, equipped with a small antenna. That antenna converts movement into changes (encoded patterns) on a standard radio signal emitted by a base station.
As expected, the battery-free phone has a couple of asterisks (caveats). The first is that it depends on Skype to make and receive calls. This is not a bad thing, however, it makes us think more of a VoIP phone than a mobile. The second is that it needs a customized base station, whose technology could be integrated without major difficulties into WiFi routers or conventional cell towers. The phone can work at nine meters from its station if it uses the energy of ambient signals, but if it includes a photodiode, the range extends to fifteen meters.
