An overview of how Wireless Sensor Networks are being extended to a system which has tremendous capabilities. The future is all about Smart Dust. Trillions of sensors may be planted across the world to improve the ecosystem as well as the lives of human beings. Although the aim of reducing the volume to orders of micrometer has not yet been fulfilled, considerable developments have been made to build motes that combine sensing, computing, wireless communication capabilities and autonomous power supply within volume of only few millimeters and that too at low cost.

1. Smart Dust
Soumyajit Pal
Department of Computer Science
St. Xavier's College
Kolkata, India
palsoumyajit7@gmail.com
Abstract: This seminar document gives a detailed study of smart
dust technology by focusing on the transformation of sensor
nodes to the size of tiny dust with tremendous computation
capabilities. Although the aim of reducing the volume to orders
of micrometer has not yet been fulfilled, considerable
developments have been made to build motes that combine
sensing, computing, wireless communication capabilities and
autonomous power supply within volume of only few
millimeters andthat too at low cost.
Keywords: sensor, wireless network, autonomous power source,
size reduction.
I. Introduction
Smart Dust is a system of interconnected wireless
sensor nodes that can sense changes in light, temperature,
vibration, magnetism, humidity or chemicals, through RFID
(Radio Frequency Identification), take necessary steps
against these changes and communicate with its surroundings
wirelessly at minimal cost. The name "smart dust" comes
from the fact that the sensor nodes making up the wireless
system are comparable to the size of dust particles, thereby
allowing them to be sprinkled into the atmosphere like fine
grains of rice. The term was coined by Kristofer Pister, who
along with Joe Kahn and Bernhard Boser presented a
research proposal to build wireless sensor nodes with a
volume of 1 mm3 to the Defense Advanced Research Projects
Agency (DARPA) of the United States. The proposal was
given the go-ahead by DARPA in 1998 and it had two major
outcomes. Firstly, the project led to a working mote smaller
than a grain of rice. Also, it allowed the construction of
"COTS (Commercial Off-The-Shelf) Dust" devices which
further kicked off the TinyOS effort at Berkeley, University
of California. A more general view is to consider Smart Dust
as a system of multiple tiny microelectromechanical systems
(MEMS) such as sensors,robots orother related devices.
II. Literature Survey
A. Wireless Sensor Networks (WSN)
The domain of Wireless Sensor Networks merges
sensing, computation and communication into a single tiny
device known as sensor. These devices that make up a WSN
or WSAN (Wireless Sensor and Actuator Networks) as it is
sometimes called, tend to be autonomous in terms of
computational abilities as well as power supply. They are
distributed over a given area to monitor physical or
environmental conditions such as sound, humidity, pressure,
temperature, etc., and to cooperatively pass their data through
the network to a main location. Size of sensor nodes vary
from a shoebox to that of a rice grain. Likewise, cost of
sensor nodes varies depending on its complexity. Size and
cost constraints on sensor nodes result in corresponding
constraints on resources such as energy, memory,
computational speed and communications bandwidth.
The architecture of a sensor node is shown in Figure
1. The primary components are transceiver, controller,
external memory, power source and one or more sensors. An
ADC (Analog to Digital Converter) is used to convert the
continuously-sensed data using sensors into digital form for
carrying out necessary computations.

2. Figure 1. Architecture ofa Sensor Node
1) Controller : The controller performs computations on the
data and controls the functionality of other components in the
sensor node. Due to major advantages of low power
consumption and minimal cost, microcontroller is the most
preferred controller for driving a network sensor node.
However, desktop microprocessors as well as digital signal
processors may also be used.
2) Transceiver : This module combines the functionality of
both transmitter and receiver into a single device. The
operational states of a transceiver are transmit, receive, idle,
and sleep. Current generation transceivers have built-in state
machines that perform some operations automatically. Most
transceivers operating in idle mode have a power
consumption almost equal to the power consumed in receive
mode. In order to save power, it is advisable to completely
shut down a transceiver when not in use. Also, an appreciable
amount of power is consumed by the node when the
transceiver switches from sleep mode to transmit mode. The
possible choices of wireless transmission media are radio
frequency (RF), optical communication (laser) and infrared
transmission. Lasers require less energy, but need line-of-
sight for communication and are sensitive to atmospheric
disturbances; same is the case with infrared. Radio
frequency-based communication is the most relevant that fits
most of the WSN applications.
3) External Memory : From the perspective of energy
consumption, the most relevant kinds of memory are the on-
chip memory of a microcontroller and Flash Memory. Flash
memories are used due to their low cost and high storage
capacity. Memory requirements are very much application
dependent. Two categories of memory based on the purpose
of storage are: user memory for storing application related
data and program memory for programming the device.
Program memory also contains identification data of the
device if present.
4) Power Source : One of the primary reasons for using a
wireless sensor node is the difficulty faced in providing a
mains supply to the mote. However, since the sensor node is
often deployed in harsh environmental conditions which are
hard-to-reach, changing the battery regularly can be costly
and inconvenient. An important aspect in the development of
a wireless sensor node is ensuring that there is always
adequate energy available to power the system. The sensor
node consumes power for sensing, communicating and data
processing. Maximum energy is required for data
communication purposes. Power is stored either in batteries
(chargeable and non-chargeable) or capacitors. Current
sensors are able to renew their energy from the solar power
emitted by solar sources.
5) Sensors : These are used by the nodes to capture data from
the environment in which they are deployed. Sensors are
hardware devices that produce a measurable response to a
change in a physical condition like temperature, pressure or
humidity. The continual analog signal produced by the
sensors is digitized by an ADC and sent to the
microcontroller for further processing. Most sensor nodes are
small in size, consume little energy, operate in high
volumetric densities, are autonomous and operate unattended
and are able to adapt to the environment in which they are
setup. Since wireless sensor nodes are typically very small
electronic devices, they can only be equipped with a limited
power source of 0.5-2 ampere-hour and 1.2-3.7 volts. Sensors
are classified into three categories: passive, Omni-directional
sensors; passive, narrow-beam sensors; and active sensors.
Passive sensors sense the data without actually manipulating
the environment. They are self powered; i.e., energy is
needed only to amplify their analog signal. Active sensors
actively probe the environment, for example, a sonar or radar
sensor, and they require continuous energy from a power
source. Narrow-beam sensors have a well-defined notion of
direction of measurement, similar to a camera. Omni-
directional sensors have no notion of direction involved in
their measurements.
The real power of a wireless sensor network lies in
its ability to deploy large numbers of nodes, very small in
size, which intelligently adapt to the surrounding conditions
and connect among themselves to form a network of motes.
Usage scenarios for these systems range from real-time
tracking, to monitoring environmental conditions, to
ubiquitous computing environments. The network could be
incrementally extended by simply adding more sensor nodes
- no rework or complex configuration. WSNs not only reduce
installation costs but also have the ability to adapt to
changing environments. Adaptation mechanisms can respond
to changes in network topologies or can cause the network to
shift between drastically different modes of operation. For
Power
Source
Transceiver
Controller
External
Memory
Sensor1
ADC
Sensor2

3. example, the same embedded network performing leak
monitoring in a chemical factory might be reconfigured into a
network designed to localize the source of a leak and track
the diffusion of poisonous gases. The network could then
direct the workers to the safest path for emergency
evacuation.
B. Smart Dust Technology
Fig.2 Structural Components of a Smart Dust Mote
Smart dust takes Wireless Sensor Nodes to the next level. Its
goal is to build a Smart Dust mote, illustrated in Fig. 2.
Integrated into a single package are MEMS sensors, a
semiconductor laser diode and MEMS beam-steering mirror
for active optical transmission, a MEMS corner-cube
retroreflector for passive optical transmission, an optical
receiver, signal processing and control circuitry, and a power
source based on thick-film batteries and solar cells. This
package has the ability to sense the environment and
communicate and be self-powered. A major challenge is to
incorporate all these functions while maintaining very low
power consumption, thereby maximizing operating life given
the limited volume available for energy storage. To meet the
design goal of a cubic millimeter volume, the best battery
technology is used, resulting in the total stored energy to be
of the order of 1 J. If this energy is consumed continuously
over a day, the dust mote power consumption cannot exceed
roughly 10 µW. The functionality envisioned for Smart Dust
can be achieved only if the total power consumption of a dust
mote is limited to microwatt levels, and if careful power
management strategies are utilized (i.e., the various parts of
the dust mote are powered on only when necessary). To
enable dust motes to function over the span of days, solar
cells could be employed to scavenge as much energy as
possible when the sun shines (roughly 1 J per day) or when
room lights are turned on (about 1 mJ per day).
C. Applications ofSmart Dust
Smart dust has tremendous applications in all domains of
science, technology and human resource. Some of these are
enlisted below:
1) Ability to scatter hundreds of tiny sensors around a
building to monitor temperature or humidity.
2) Deploying, like pixie dust, a network of minuscule, remote
sensor chips to track enemy movements in a military
operation.
3) Catching manufacturing defects by sensing out-of-range
vibrations in industrial equipments.
4) Tracking patient movements in a hospital room.
5) Traffic sensors in congested urban areas.
6) Monitoring power consumption of household appliances to
determine whether they are operating at peak efficiency.
7) Cosmetics companies uses wireless sensors to gauge
humidity levels in its warehouses for moisture-sensitive
producst.
D. Future Scope
Recent reviews have talked about taking smart dust
beyond mm dimensions to the µm level. The sheer number
of sensors in the network is what truly makes a smart dust
project different from other efforts to record data about the
world. Smart dust researchers tend to talk in millions, billions
and even trillions. However, sensors have to be designed for
specific purposes and spread out on the land intentionally -
not scattered in the wind as smart dust was originally pitched.
Despite these differences, the original smart dust theory -
monitoring everything will benefit humanity - essentially
remains unchanged. There are a number of real-world
projects that, in one way or another, seek to use wireless
sensors to take the Earth's vital signs. In all of these cases, the
sensor networks are deployed for specific purpose. Hewlett
Packard's proposal Central Nervous System for the Earth
plans to deploy trillion sensors all over the planet. The
wireless devices would check to see if ecosystems are
healthy, detect earthquakes more rapidly, predict traffic

4. patterns and monitor energy use. The idea is that accidents
could be prevented and energy could be saved if people knew
more about the world in real-time, instead of when workers
check on these issues only occasionally.
E. Conclusion
Although concerns have been raised by many
groups regarding the privacy violations that come along with
Smart dust, it is a reality that one has to accept. The benefits
that come along with real-time monitoring of smart dust
technology outweigh the negativities that people often talk
about. Some researchers are looking to make mobile phones
into sensors. In this scenario, the billions of people roaming
the earth with cell phones become the smart dust.
Undoubtedly a novel concept, if implemented, would benefit
the human race by leaps and bounds.
References
[1] Emerging Challenges: Mobile Network for Smart Dust. Joseph M. Kahn,
Randy HowardKatz, Kristofer S.J. Pister.
[2] Neural Dust: An Ultrasonic, Low Power Solution for Chronic Brain-
Machine Interfaces. Dongjin Seo, Jose M. Carmena , Jan M. Rabaey,
Elad Alon, and Michel M. Maharbiz
[3] System Architecture for Wireless Sensor Networks, Jason Lester Hill.
[4] SMART DUST, KristoferS.J. Pister
[5] Smart Dust Mote Core Architecture: Brett Warneke, Sunil Bhave