MadSci Network: Engineering

Re: Sound energy to charge mobile phones?

Date: Sat Jan 12 16:03:43 2008
Posted By: Madhu Siddalingaiah, Physicist, author, consultant
Area of science: Engineering
ID: 1185248163.Eg

Hi Niket,

That's a good question. Your resoning is good, sound is a form of energy
that can be converted to other forms of energy, including electrical energy.

The only problem with this particular application is the available power.
This website lists the power available for given sound levels:

The table shows that loud speech can deliver about 0.001 Watts or 1
milliWatt of power. Normal speech is much less, on the order of 10
microWatts! This is the total available power. If we assume that
you can capture all of it and you are able to efficiently convert all of it
to electrical energy, you will be well below the operating power of a
typical mobile phone.

During operation, a typical mobile phone handset can radiate several watts
of power. Most of the battery power goes to driving the transmitter and
antenna, but some of it will be taken by analog and digital circuitry in
the phone.

At the end of the day, the sound power in speech can at best reduce
the required operating power by 0.1% or so. It can't really charge the
battery as more power is used than produced, but it could increase battery
life *slightly*. In the real world where much less than 100% of the
available sound power can be converted to electrical power, battery life
would not be noticeably increased.

If you had sound power levels on the order of a jack hammer or a machine
gun, you might see a difference, but it is still a significant engineering

I hope that answers your question. -

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