What is a smart dust?
'Smart dust' — sensor-laden networked computer
nodes that are just cubic millimetres in volume. The smart dust project
envisions a complete sensor network node, including power supply, processor,
sensor and communications mechanisms, in a single cubic millimetre. .Smart dust motes could run for years , given
that a cubic millimetre battery can store 1J and could be backed up with a
solar cell or vibrational energy source.
The goal of the Smart Dust project is to build a
millimeter-scale sensing and communication platform for a massively distributed
sensor network. This device will be
around the size of a grain of sand and will contain sensors, computational
ability, bi-directional wireless communications, and a power supply. Smart dust
consists of series of circuit and micro-electro-mechanical systems (MEMS)
designs to cast those functions into custom silicon. Microelectromechanical
systems (MEMS) consist of extremely tiny mechanical elements, often integrated
together with electronic circuitry.
Core Functionality Specification
Choose the case of
military base monitoring wherein on the order of a thousand Smart Dust motes
are deployed outside a base by a micro air vehicle to monitor vehicle movement.
The motes can be used to determine when vehicles were moving, what type of
vehicle it was, and possibly how fast it was travelling. The motes may contain
sensors for vibration, sound, light, IR, temperature, and magnetization. CCRs
will be used for transmission, so communication will only be between a base
station and the motes, not between motes. A typical operation for this scenario
would be to acquire data, store it for a day or two, then upload the data after
being interrogated with a laser. However, to really see what functionality the
architecture needed to provide and how much reconfigurability would be
necessary, an exhaustive list of the potential activities in this scenario was
made.
Listening To A Dust Field
Many Smart Dust
applications rely on direct optical communication from an entire field of dust
motes to one or more base stations. These base stations must therefore be able
to receive a volume of simultaneous optical transmissions. Further,
communication must be possible outdoors in bright sunlight which has an
intensity of approximately 1 kilowatt per square meter, although the dust motes
each transmit information with a few milliwatts of power.
Abstract
Advances in hardware technology have enabled very compact,
autonomous and mobile nodes each having one or more sensors, computation and
communication capabilities, and a power supply.
The Smart Dust project is exploring whether an autonomous sensing,
computing, and communication system can be packed into a cubic-millimeter mote
to form the basis of integrated, massively distributed sensor networks. It
focuses on reduction of power consumption, size and cost.
Passive Reflective Systems
The passive reflective
communication is obtained by a special device called CCR (Corner cube retro
reflector) consists of three mutually orthogonal mirrors. Light enters the CCR,
bounces off each of the three mirrors, and is reflected back parallel to the
direction it entered. In the MEMS version, the device has one mirror mounted on
a spring at an angle slightly askew from perpendicularity to the other mirrors.
Communicating From A Grain Of Sand
Smart Dust’s full
potential can only be attained when the sensor nodes communicate with one
another or with a central base station. Wireless communication facilitates
simultaneous data collection from thousands of sensors. There are several
options for communicating to and from a cubic-millimeter computer. Radio-frequency and optical communications
each have their strengths and weaknesses. Radio-frequency communication is well
under-stood, but currently requires minimum power levels in the multiple
milliwatt range due to analog mixers, filters, and oscillators. If whisker-thin
antennas of centimeter length can be accepted as a part of a dust mote, then
reasonably efficient antennas can be made for radio-frequency communication.
While the smallest complete radios are still on the order of a few hundred
cubic millimeters, there is active work in the industry to produce
cubic-millimeter radios.
Summary
Smart dust is made up
of thousands of sand-grain-sized sensors that can measure ambient light and
temperature. The sensors -- each one is called a "mote" -- have
wireless communications devices attached to them, and if you put a bunch of
them near each other, they'll network themselves automatically. These sensors,
which would cost pennies each if mass-produced, could be plastered all over
office buildings and homes. Each room in an office building might have a
hundred or even a thousand light- and temperature-sensing motes, all of which
would tie into a central computer that regulates energy usage in the building.
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