Lucas123 writes "Engineers at Duke University say they've constructed a device that can collect stray wireless signals and convert them into energy to charge batteries in devices such as cell phones and tablets. The WiFi collection device, made of cheap copper coils and fiberglass, can even aggregate energy from satellite signals and sound waves (abstract). The researchers created a series of five fiberglass and copper energy conductors on a circuit board, which was able to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power. The device, the researchers say, is as efficient as solar cells with an energy conversion rate of 37%."