Cell Phones Powered By Conversations

disco_tracy sent in a story about some fancy new power technology designed to tap energy from sound waves. Although the cell phone concept grabs the headline, they also talk about harvesting noise from traffic.

Comments

Bogus

[dtmos]

This is a bogus story that wanders around every now and then. Cell phones require hundreds of milliwatts of transmit power, an amount of power far beyond what the human voice can achieve -- even at 100% conversion efficiency.

Re:Bogus

[blueg3]

The human voice produces a hell of a lot more power than a cellphone, you can disagree if you want

Well, a human shouting is about 1 mW. A cell phone's antenna outputs in the ballpark of 250 mW.

Some quick back-of-the-envelope calculations suggest that if the entire area of a cell phone could pick up sound energy, the ambient sound level was at the pain threshold of 120 dB (1 W/m^w), and it achieved 100% energy conversion, this would generate about 15 mW. For just the 250 mW antenna, this means about 90 minutes of talk time per 24 hours exposure.

120 dB is very loud, and a far cry from how much sound a phone would normally be exposed to. Note that sound is measured on a logarithmic scale. If the phone was constantly exposed to 60 dB of sound, then it'd only generate 15 nanowatts.