You may already heard that there is a way to harvest energy from radio signals which are abundant in our modern world(TV signal, radio, mobile phone cells, etc). But that harvested energy is not enough to emit WiFI signals. The engineers from the University of Washington  have figured out a way to communicate by reflecting those signals, thus enabling power-free communication between devices. “Now, University of Washington engineers have designed a new communication system that uses radio frequency signals as a power source and reuses existing Wi-Fi infrastructure to provide Internet connectivity to these devices. Called Wi-Fi backscatter, this technology is the first that can connect battery-free devices to Wi-Fi infrastructure.” Source: University of Washington