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Talk-Powered Cell Phones Won't Need Batteries

Posted by samzenpus on from the talk-charging dept.

alphadogg writes "It's possible that in the future conversations on your cell phone could generate enough electrical power to run the phone, without batteries. That's one possible outcome of recent work by a team of Texas researchers, who appear to have discovered that by building a certain type of piezoelectric material to a specific thickness (about 21 nanometers, compared to a typical human hair of 100,000 nanometers), you can boost its energy production by 100 percent. And the technology could power not just phones, but a whole range of low-power mobile devices and sensors. The breakthrough is an example of 'energy harvesting' that can convert one kind of energy, such as vibrations or solar rays, into electricity."

3 of 197 comments (clear)

  1. Physics might say otherwise by Anonymous Coward · · Score: 5, Informative

    Lets assume that a minimum channel capacity (bits/s) is required to support a conversation, even if we use the absolute best vocoder that eliminates all redundant information. Shannon's Law then says that for a given noise power (set by the environment) there is a minimum signal power which must be transmitted to get error free transmission. Again we are assuming we have an optimal codec, which achieves Shannon's bound. This sets the absolute minimum power consumption of an ideal radio telephone. A real life phone will use more than this. My guess is that this theoretical minimum power is greater than the power which can be harvested from the human voice.

  2. Re:If you can get the power down by sexconker · · Score: 4, Informative

    ?
    Your math. It is very wrong.

    A typical AAA battery is 1.5v @ about 900 mAH.
    Round that up and you get 1500 mWH.

    1500 mWH / 10 mW = 150 hours.

  3. Re:Do the math, Barbie by goodmanj · · Score: 4, Informative

    A little help for those too lazy to do the math:

    Power per area transmitted by a sound wave:

    F = p^2 / (rho0 c)
    where
    p = rms pressure variations in the sound wave (.01-.05 Pa or so for human voice)
    rho0 = density of air (1.3 kg/m3 typ.)
    c = speed of sound in air (330 m/s)

    I get 1 microwatt per square meter. So for a 20-cm2 cell phone, 2 nanowatts, ignoring the receiver-coupling issues mentioned by the parent post.

    No way, Jose, and by at least three zeros after the "1".

    Let's make that nine.