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.

Re:Traffic solution?

[Lotana]

...and remember that things powered by the car driving over a power capturing device is stealing gas from your tank indirectly.

Stealing? Are you trying to troll by attempting to get people outraged that the device powers from the sound generated due to inefficiency of your vehicle?

It is technically true, the energy of the sound does comes from your fuel tank. But remember that your car would still be expanding just as much energy on generating the noise whether or not there is any sound-gathering device around. Driving on the country road in the middle of nowhere will not increase your fuel efficiency.

Really the term "stealing" is completely invalid in this case. Now if the headline was about some fancy road surface that converted traction into energy then you would be absolutely correct, because it would adversely affect the performance of your vehicle, thus increasing its energy expenditure, thus stealing from your fuel tank.

From the Article

[PiAndWhippedCream]

The sound waves produced a mild electrical current of about 50 millivolts. The average cell phone requires a few volts to operate, several times the power this technology can currently produce.

Wrong, so very wrong. Millivolts is not a unit of current, and volts is no unit of power. Nor is power current. I've seen journalists not understanding electrical units before, but never have I seen something quite so wrong as this.