Yoshizen's Blog

MEMS Microphne

I guess, the most of the readers may not understand what

this title means.  —– yet most of the people are using it

only without knowing = it is a microphone inside of

Mob-phone or Smart-phone.

= If you ever disassemble or happened to see inside of a broken

phone might have noticed a component which got a hole, right

behind of a hole on the phone’s outer shell. ——————————————- (Photo  Knowle’s MEMS Microphone )

—– In the past 10 years, the microphone has changed their round shape into square and the

principle how it works has completely changed.

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When I was in my junior school, I was a member of the Radio Club and we were in charge with the preparation

for a morning assembly or any event which use the PA system, and the control of the PA system as well.

(and often to repair them as long as we, together with the supervising teacher can manage )

Among the old disused equipment, I have seen Carbon Microphone and many

Crystal Microphones.  But the main Microphone on that time was the Dynamic Microphone.  

Then the teacher showed us latest procurement of Ribbon Microphone which can produce

much better sound quality.

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The granules of Carbon changes its conductivity under the pressure = hence put them

under a vibrating membrane can work as a microphone which needs no amplification hence

it is a cheapest kind in an audio system. ( Connect a carbon mic directory to a battery and a

magnetic head-phone in series and make a loop = it makes an audio communication system !

—– though, sound quality is not good at all, yet there wasn’t

anything else but Carbon-Mic even in a recording industry then.

—– The carbon granules absorb moisture, and a singer blows her breath to the mic, a recorded sound

deteriorates with its use !   So that, the top singer wanted to have a morning session, not in the afternoon 😀

(It’s from “History of Recording” kind of a book I read long time ago )

Carbon-Mic has been used in the Telephone system well into 60th and I bought some of them in a second-hand

market (to see the inside and experiment with them 😀 )

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If you are a musician or dealing with sound systems must be familiar with Dynamic Microphone.

They are technically the same as an ordinary Speaker. = a coil was attached to a vibrating membrane or

speaker corn. —– the coil is placed between the magnet, so that, if it moves, with Electro-magnetic effect

= the changing electric signal will be created = this is a microphone.

But when electric signal was applied to the coil, it will be either attracted or repelled from the magnet hence

moves the corn according to the signal = this is a speaker.

—– So that, in my secondary school, once I connected the cables which goes to a speaker of a room of which

the teachers meeting was held, to a Microphone input and able to over-heard all the conversation.

( I didn’t disclose what I’ve heard and this is the first time me to revile the story 😀 )

(There is the matters in Impedance matching etc, but it worked and most of the case it works 😀 )

[]

In the old days, there was a Condenser Microphone in a Mob-phone. —– in any small devices, the Mic was

almost all ways a Condenser-Mic (commonly called Electoret Mic)  = Condenser Microphone was made of

a metal coated thin plastic film and the insulated metal base.   Two conductive plates facing each other having

an electric charge between them hence it was called Condenser. —– This electric charge changes if the

membrane vibrates with a sound, and this changing charge was amplified and used as a sound signal.

They are simple and small hence cheap therefore they were used everywhere despite of the sound quality is

not necessary good.

But since 2002 it was replaced by the MEMS Microphone made by Knowls (Google please)

( I saw a news, that their sale of Microphone reached to the 300 millions, since 2002. = Oh, Gosh ! )

= microscopic whisker suspended above base conductor, vibrates with sound wave, and this vibration was

converted into the electronic signal.  The cavity inside of Microphone should be designed to resonates with

the sound hence it works as a microphone.  If its whisker was made sensitive to magnetism, MEMS act as

a Compass, or when it detects the gravity it tells whether the device is upright or horizontal, like iPad does.

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Once the basic technology was established, MEMS devices infiltrated everywhere in the past 10 years or so.

Microscopic moving part was made by electro-etching (chemically dissolve and removes the material and

make a metal parts in a wanted shape ) or even carved by a Laser beam.

And the minute movement of this part (whisker) hence its change of the capacitive charge was detected and

converted into an electronic signal.

—– Can you imagine, in a so-called Motion Sensor such as in a Wii controller, microscopic whisker moves

with the movements and its movement was converted into an electronic signal to control the game.

Microns long whisker which was made of,  may be few thousands of atoms lined up, would be bent with its

flexibility, hence the electronic charge may change accordingly, and this change would be amplified,

—– but amplified to how many million times without noise. —– as they are commonly used everywhere

now, it mast be just reliable or even better than old technology though, still it is incredible to me.

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So, having an old rusted brain, I rather indulge an old memory, when I saw a small light bulb

connected straight to a Telephone’s Carbon-Microphone and battery, changed its brightness

when I pressed the center of the Microphone.  = It was a delightful amazing moment for a child !

How sweet and peaceful, in our old days were 😀 😀

___/\___

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2 Responses

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  1. Lemony (Gr)Egghead said, on June 5, 2012 at 19:37

    🙂

    • yoshizen said, on June 5, 2012 at 20:59

      Thank you Lemony to endure reading this one. 🙂


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