Electronics are becoming so energy-efficient, and radio transmitters so common, that simple electronic devices can run forever just by harvesting ambient radio waves. Here’s a sample of devices already entering the market that run forever just on the free energy transmitted from TV/radio broadcast stations, cellphone towers, and Wi-Fi networks:
- Thermometers that can broadcast their temperature readings every 5 seconds
- Hard hats that beep when the wearer moves too close to dangerous construction equipment
- Wall clocks
- CO2 alarms
- Shelf label displays
One ramification of this trend is with more sensors come more data, and the easy proliferation of sensors will help to quickly make “big data” normal.
The devices that transmit signals use about 50 microwatts on average, while the display-only devices use less than 5 microwatts on average. A radio station transmitter easily produces 50 microwatts of harvestable energy more than 2.5 miles away from the tower.
Not only is processing power doubling every 18 months in relation to dollar cost, it’s also doubling every 18 months in relation to energy usage, and has been for the last 60 years. In other words, energy usage of devices is getting cut in half every 1.5 years for the same processing power. For example, today an office-range gigabit wireless router costs less than $100 and uses 5 watts. Projecting forward, in 10 years the same system could be powered by ambient radio waves and cost less than a buck (5 watts/2^7 = 39 microwatts; $100/2^7 = $0.79), easily making mesh networks freely accessible everywhere.