Charge Your Cell Phone By Shouting At It

The requirement of electrical energy or power is on its peak today! At the same time the conventional methods of producing electrical energy using fossil fuels (coal), water (hydropower) has been raising concerns for quite some time due to limited availability of these resources. This is a reason scientists and engineers are continually trying to harness electrical energy from non-renewable sources which are available in abundance. Moreover most of our portable electronic devices run on low power, and thus there have been efforts by the engineering community to develop power sources for these gadgets that are a) not dependent on conventional power sources, b) are self sufficient, c) automatically charge your device. Like smart solar based battery charger system could automatically charge your mobile phone when it is not in use and is resting on your table or in your pocket (concepts of such technology is available and may soon be available commercially). Some of the other such sources that could be used to generate power are heat, light, pressure etc. Among all these unconventional sources of power one could be sound or noise. Can we convert sound or noise into useful electrical energy? Let us understand.

Conventional Method of Converting Sound into Electrical Signal (Microphone)

The conventional method of converting sound into electrical energy is the use of a microphone in public address systems. As diaphragm of microphone vibrates when sound falls on it and light weight coil attached to the diaphragm moves in the magnetic field. Due to change of magnetic flux across the coil, an EMF induces across it according to Faradays law of electromagnetism. Further this low strength electrical signal from mic is amplified with the help of amplifier and fed to the loudspeaker. So it is possible to convert sound into electrical energy and this is nothing new but can this energy be used to power any electronic device? Let us see.

Charging Mobile Phone using Sound/Noise

Sound waves easily propagate in the air medium and when then strike the piezo-electric material; they could be converted in to electric charge. A prototype of such system is being developed at Queen Mary University of London (QMUL) in collaboration with Microsoft, which could convert 100dB sound into 50 mV voltage. Such small amount of volts may not be sufficient to charge a cell phone but a adequate voltage can be obtained by altering the composition and structure of the piezoelectric material used for the same. Researchers in London have created a device which is about the size of a cell phone and uses Zinc oxide wires as piezoelectric material between two electrodes. When sound waves hit on the electrodes, it tends to compress and elongate the zinc oxides strands which induces charge on the electrodes and produces the voltage. It is a property of the zinc oxide that when it is compressed or stretched it produces voltage, thus motion is converted into electrical energy. The final device designed by researchers at University of London and Nokia is the same size as that of Nokia Lumia 925 which generates five volts, enough to charge a phone.

It is a very good example where an unwanted energy or pollution (noise) is channelizes to generate a useful electrical energy which could be a boon for our cell phone. It may mean that we will never have to charge our cell phones ever, they will be charged when we talk on cell phone or listen to the music etc.

By - Harpreet Kaur - Asst. Professor, ECE, Chitkara University H.P.