MadSci Network: Engineering

Re: sound energy to electrical energy

Date: Tue May 30 14:51:36 2000
Posted By: Frank Berauer, Technology Transfer Engineer Microelectronics
Area of science: Engineering
ID: 957256377.Eg

Hi Cheng Ka Wing,

I'll try to answer your questions below:

> 1i)How electrical energy be stored?
The usual way to store electrical energy is to convert it into a
chemical energy form first (e.g. in a battery or as H2 after electro-
lysis of water). This way it is stable and can be kept for long time.
Electrical energy can directly be stored in capacitors for a short
while (not more than a few seconds due to internal losses).

>  ii)in a chip
Chips are designed to store or process electrical signals and not
energy. In fact it is aim of chip development to decrease the amount
of energy necessary to store or process signals as much as possible.
I don't think chips could ever store considerable amounts of energy.

> 2ai)Can sound energy be converted into electrical energy?
Certain kinds of microphones convert sound into energy, but at very 
low efficiency, since again it is the signal that interests us, not
the energy. Other kinds of microphones, which modulate a current and
do not produce energy, work just as well for this purpose.
I have not heard of any system developed to convert sound into elec-
trical energy efficiently and I do not think it is worthwhile to de-
velop one, since the amounts of energy available in the form of sound
are rather small, even if it appears very loud to your ears (see

>  ii)if
By moving an electric conductor (e.g. a wire) through a magnetic
field, some of the kinetic energy is converted to electricity and a
voltage is induced in the conductor. Some kinds of microphones use
this effect by having a wire coil excited by sound (waves of moving
air particles) in the field of a build-in magnet. The resulting
voltages are very small and need to be amplified to be usable.

> bi)how to store the converted electrical energy?
It is not worthwhile to store such tiny amounts of energy. Normally
one is only interested in storing the information contained in the
signal (e.g. voice recording), but that costs a lot more energy than
the captured sound originally had.
If you are 20m from the 40kW-speakers of a heavy metal concert, you
easily become deaf. Yet if you have a 1m x 1m device that converts
all incoming sound energy at 100% efficiency, you would get 10W of
electrical power - a tenth of what an ordinary light bulb needs.
Microphones have less than 1% efficiency and are much smaller ...

>  ii)in a chip ?
Chips are not a medium of choice to store energy. See above.

> 3)Is their anything that is very /extremely sensitive to sound?
Microphones, human (and other) ears.

Please let me know if you need further clarifications.

Greetings from Singapore,
        Frank Berauer

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