Slide đa phương tiện chương 4 multimedia devices

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Multimedia Devices

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Tien Pham Van, Dr. rer. nat.
Hanoi University of Science and
Technology

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Agenda

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• Capturing/recording/Sensing
devices
• Rendering/Recontruction/Actuator
devices

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Microphones

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• Microphones are sound sensors (really - transient
pressure sensors)
• Speakers are sound actuators
• The first microphones and speakers (or
earphones) were devised and patented for use in
telephones.
• Alexander Graham Bell patented the first variable
resistance microphone in 1876

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Bell’s Microphone

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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The carbon microphone (Edison)

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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The carbon microphone

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group

Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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The magnetic microphone

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Dynamic microphone

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Capacitive microphones

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Also called “condenser” microphones

Idea is trivially simple:
Allow sound to move a plate in a capacitor
Sense the change in capacitance

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

Email:
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The electret microphone

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• The electret microphone is a capacitive microphone
• Made of two conducting plates with a layer of an
electret material under the upper plate

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

Email:
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Piezoelectric devices

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Qx = d11 Fx

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• A piezoelectric device is built as a
simple capacitor, (capacitance C)
• Assuming force is applied on the xaxis in this figure, the charge
generated by force is:

d = thickness
A = area

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Voltage developed across it is:

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Qx d11 Fx d11 Fx d
V=
=
=
C
C
εA

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

Email:
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Acoustic actuators

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• Among these we shall discuss two:
• The classical loudspeaker used in audio
work.
• Piezoelectric actuators for the purpose of
sound generation will be introduced.

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– Audible devices referred to as buzzers
– Mechanical actuation will be discussed
separately later in this chapter.

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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• The basic structure of a
loudspeaker
• The force is given by the
Lorenz force, NBIL.
• Magnetic field supplies
by permanent magnets

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Acoustic actuators

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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A titanium diaphragm speaker

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Loudspeakers

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• Directional response indicates the relative power
density in different directions in space.
• Indicates where in space one can expect larger or
lower power densities and the general coverage.
• Note that the power density behind the speaker is
lower than in front of it as expected.

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Directional response

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Small loudspeakers

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Low frequency loudspeaker

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Low frequency loudspeaker (side)

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Magnetic buzzers

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Piezoelectric earphones and buzzers

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• Piezoelectric earpiece:
• A piezoelectric disk is physically bonded to a diaphragm
• Connection to a voltage source will cause a mechanical motion in the
disk.
• When an ac source due to sound is applied, motion of the disk
reproduces the sound.
• An earphone of this type is shown in Figure below together with its

piezoelectric element.
• Properties - same as the piezoelectric microphone

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Piezoelectric buzzer

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Digital Camera

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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How does a camera work?

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• Light is converted to electrical charge.
• Charge is stored in potential wells, these are
the “Pixels” on the camera.
• Energy collected in each pixel is digitized.
• Digital data is transferred to computer.

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Pham Van Tien, Dr. rer. nat. , Embedded Networking Research Group
Faculty of Elec. and Telecom, Hanoi University of Science and Technology

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Digital Camera

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Image Formation

Film

The Eye
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