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ECE5320 Mechatronics
Assignment#01: Literature Survey on Sensors and Actuators
Topic: Microphones
Prepared by: Cameron Chidester
Dept. of Electrical and Computer Engineering
Utah State University
E: ; T: (435)797-; F: (435)797-3054 (ECE Dept.)
W: http://
3/9/2012
Slide-2
Outline
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Reference list
Major applications
Basic working principle
Types
Major specifications
Limitations
How to choose
Cost
Where to Buy
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-3
Reference list
1. http://en.wikipedia.org/wiki/Microphone
2. http://electronics.howstuffworks.com/gadgets/au
dio-music/question309.htm
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-4
Major applications
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Telephones
Motion picture production
Radio and television broadcasting
Live or recorded performances (ie. Concerts,
music albums, etc.)
• Voice recognition
• Knock sensors
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-5
Basic Working Principle
• Microphones use electromagnetic induction,
capacitance change, piezoelectric generation, or
light modulation to produce an electrical voltage
signal from a mechanical vibration.
• Most use a diaphragm (usually a thin metal foil)
to pick up the vibrations caused by sound waves
and then converts them to a signal.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-6
Types – Liquid Microphones
• Consisted of a metal cup filled with water and
sulfuric acid.
• A diaphragm with a needle on the receiving side
was placed over the cup.
• Sound waves would cause the needle to move in
the water and a small electrical current ran to the
needle, which was modulated by sound
vibrations2.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-7
Types – Carbon Microphones
• Consisted of a thin metal or plastic diaphragm
with carbon dust on one side.
• Sound waves hitting the diaphragm would
compress the carbon dust, which changes its
resistance.
• A signal was created by sending a current
through the carbon and as the resistance changed,
so would current2.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-8
Types – Fiber Optic Microphones
• Changes acoustic waves into electrical signals by
sensing changes in light intensity.
• Light from a laser source travels through the
optical fiber and illuminates on the surface of a
reflective diaphragm.
• Sound vibrations on the diaphragm modulate the
intensity of light reflecting off the diaphragm.
• The modulated light is transmitted over a second
optical fiber to a photo detector1.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-9
Fiber Optic Microphones (cont.)
• Extremely small
• Can be used in electrically
sensitive environments2.
• Resistant to environmental
changes such as heat and
moisture.
• Used a lot in medical
applications1.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-10
Types – Dynamic Microphones
• A diaphragm is connected to a small movable
induction coil positioned in the magnetic field of
a permanent magnet.
• Sounds vibrates the diaphragm which moves the
coil in the magnetic field which produces a
current in the coil through electromagnetic
induction1.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-11
Types – Condenser Microphone
• A diaphragm acts as one plate of a capacitor and
the vibrations from sound produce changes in the
distance between the plates.
• This movement causes changes in the capacitance
of the capacitor, which amplified to create a
signal.
• Usually needs a small battery to provide a voltage
across the capictor2.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-12
Types – Electret Microphone
• The externally applied charge of a condenser
microphones is replaced by a permanent charge in
an electret material.
• An electret is a ferroelectric material that has
been permanently polarize1.
• Most widely used microphones (over a billion
produced each year). Used in cell phones,
computers, PDAs, and hands-free headsets2.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-13
Types – Ribbon Microphones
• A thin ribbon, usually
aluminum, is suspended in a
magnetic field.
• Sound waves move the
ribbon, which changes the
current flow through it.
• Sound can be picked up from
both sides of the mic1.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-14
Types – Laser Microphones
• A laser beam is pointed at a plane, such as a
window, and reflects back to a photo detector.
• Sound vibrations cause the windowpane to bend,
which causes the laser beam to bend, which can
be translated to sound using a photocell2.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-15
Types – Crystal Microphones
• A diaphragm is attached
to a crystal.
• Because crystals change
their electrical properties
as they change shape, the
crystal will create a
signal when sound waves
hit the diaphragm2.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-16
Types – MEMS Microphones
• A pressure-sensitive diaphragm is etched directly
into a silicon chip by MEMS techniques.
• Most are variants of the condenser microphone
design.
• Usually accompanied with an integrated
preamplifier and often have built in analog-todigital converter circuits on the same CMOS chip,
making the chip a digital microphone and so more
readily integrated with modern digital products1.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-17
Types – Speakers
• Since a conventional speaker is constructed much
like a dynamic microphone, speakers can work
“in reverse” as microphones.
• A speaker has poor quality, limited frequency
response, and poor sensitivity when used as a
microphone, therefore only used as such in
applications where these qualities are not needed,
such as intercoms, walkie-talkies, or video game
voice chat peripherals1.
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-18
Limitations
• Dependent on type, most tend to have a narrow
application range, however, the most common
limitations seem to be:
– Distance from sound source
– Environmental conditions
– Polar patterns
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-19
How to Choose
• The microphone you use is completely dependent
on the application. You must consider the
following:
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Size limitations
Polar pattern
Environment of use
Useful range
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-20
Cost
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Dynamic cardioid microphone - $50 to $100
Computer/cell phone microphone - $10 to $30
Laser microphone - $60 to $80
Fiber optic microphones - $50 to $1000
Electret microphones - $50 to $300
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Slide-21
Where to Buy
• www.amazon.com
• Musicians Friend
• Performance Audio
(www.performanceaudio.com)
• Walmart
• Best Buy
• Sears
• www.opticalheadsets.com
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ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators