The Hindu Business Line : Leave that dust alone

I should have known better. With a quarter of my scalp turned into a solar reflector and the remaining of what little (hair) is left either graying or falling, I sure should have known better. It was a simple request from my second daughter.

“Dad, give me an example of an oxymoron”. I blurted what came to my mind first (something I had read about a few hours ago) and that was ‘Smart Dust.’

“You are joking, dad. Despite my stomach pain, I am studying for my test and you are making fun of me”. She burst into tears.

Consolation, pacification, placation, and apology — nothing worked. ….. Yes, I should have known better to give an example that she could have appreciated.

I am sorry, dear. But, Smart Dust is an oxymoron and is also a scientific term.

Smart Dust (also known as mote) is a sensor that has a tiny microcomputer and a transreceiver for communication. Intel defines it as “a tiny, self-contained, battery-powered computer with radio links that enable it to communicate with other motes/devices”. A mote is of the size of a few millimetres. Eventually it is expected to be very small and hence named ‘smart dust’.

Sensors, computers, wireless transmission, and network of computers are not new. These fields were independently evolving. But the advances in miniaturisation and integration have brought them together to yield unprecedented and unimaginable value from these new sensors in diverse fields — medicine, defence, ecology, etc.

CONSTITUENTS OF A MOTE

Motes are made by a process similar to the manufacturing of integrated chips — involving processes at the nanometer level (far smaller than the width of a strand of human hair). A tiny sensor senses the signal to be detected/monitored. A microcomputer is the heart of the mote. It controls the tasks performed by the mote and the power supplied to the various components. A radio is used for transmitting the data up to a range of 100-200 ft.

The microcomputer processes, stores and transmits the signals it periodically receives from the sensor to other motes or to the base station (central computer). It also periodically checks for any other incoming data. This can be a message from another mote requesting an action/response or it can be a command from the base station. The mote is powered by batteries. Research is under way to use solar and other sources of energy. To conserve power, the microcomputer keeps most of the components in sleep mode except during the times when the signals are processed or transmitted.

The microcomputer needs an operating system. Researchers at university of California, Berkeley, have developed an operating system called “TinyOS” to meet the special needs. It is written in nesC, a programming language for embedded systems. It has a library of sensor drivers and network protocols. A program is needed to collect the data from individual motes, process it, and then forward it to the base station/computer. Typically, this is a difficult and cumbersome task. A GUI-based query processing system called TinyDB has been developed for this purpose. TinyDB also includes triggers i.e., queries that trigger actions when certain events occur or conditions are met. Both TinyOS and TinyDB are open source software.

A group of motes can form an “ad-hoc wireless sensor network” and communicate with each other. If one mote is not responding or has been taken out of the network, then the remaining can automatically regroup to form a new network and continue to function. This is a big advantage for the effective functioning is not disturbed by the absence of an intermediate mote.

WHAT IS SO GREAT ABOUT MOTES?

More than two thousand years ago, balances (weight sensors) have been in use. Temperature sensors were developed by Galileo in the sixteenth century. So what is so great about these sensors?. Well, in a way motes are the result of advances in manufacturing, miniaturisation, integration, communication and software. But producing such a tiny device and creating a network of them is fraught with challenges and constraints.

Size: A mote has to be as small as possible for it to be used in a variety of environments. The smaller it is, the more are the places it can be used.

Maintenance: Motes are deployed once and are not meant to be monitored daily or periodically. Hence, the power consumed by a mote should be small so that the need for changing batteries arises only after a long time.

Power: Computation consumes less power than transmission of data. The energy needed to transmit a single bit is approximately equal to that needed to execute 1,000 instructions. To conserve power, a mote is in sleep mode for about 90 p er cent of the time.

Impromptu: Motes must be ‘self-reprogrammable’ to changing conditions and needs. The extent of reprogramming can vary from changing a few parameters to uploading new software — all to a microcomputer that is not physi cally reachable (and often difficult to locate). In certain cases, the motes are deployed in areas accessing which will disturb the environment.

Bandwidth: The bandwidth for transmission is limited. Hence, the code is broken into small chunks. The rate of calculation and production of data is much higher than the rate at which it can be communicated. This requires special techn iques to aggregate and route data.

Environment: Motes also have to withstand harsh environments — such as sunshine, winds, rain, snow, ice, heat, and vibrations. They have to be tiny, inexpensive and be mass-produced economically. The communications are restricte d by distance, available power and made worse by noise.

Memory and Storage: The motes have limited memory and storage capacity.

Performance: As the number of motes increases in a network, the performance can degrade. This is contrary to expectation that more computers mean more power and higher performance.

Mobility: A mote may be attached to a vehicle, animal, bird or any object that moves frequently. This implies that the network coverage and topography continually change — something similar to four people sitting in separate vehi cles moving in different directions and participating in a conference call.

TYPICAL APPLICATIONS OF MOTES

There are many applications for motes. They include the mundane such as sensing vibrations of machinery, bridges and other structures, to the seemingly inane such as studying the ecosystems in mountains, forests, and even arcane such as comprehending Alzheimer’s disease. The motes can sense a variety of stimulus (pressure, temperature, humidity, vibration, sound, dust, magnetic field etc), record conditions, detect events and even trigger actions. They can collect behavioural and biological, environmental and etiological, and physical or chemical data.

The famous Golden Gate Bridge in San Francisco is littered with 200 motes that form an ad hoc sensor network. These measure the stresses on the bridge and also how much the bridge swings/sways (During strong winds, these sways can b e several feet).

Scientists at the California Institute of Technology, popularly called Cal Tech, have developed an ‘electronic nose’ capable of ‘sensing smells’. In general, each chemical produces a unique ‘smell spectrum’ — the signature produced by various sensors that respond differently to the chemical. Using pattern recognition algorithms, these spectra signals are compared with known spectra. And thus an ‘artificial nose’ can sniff trace quantities of a variety of chemicals. This has immense value and use in confined areas such as space shuttle where a leakage (of ammonia for example) has to be detected very early. Electronic noses can sense as low levels as 1ppm.

An interesting project is under way in Wayne State University. Researchers are implanting retinal prosthetics to people (suffering from diseases such as retinitis pigmentosa, macular degeneration) whose eyes’ sensors are dead but the retina is good. In this case, the sensors cannot have batteries (inside an eye??) and hence energy is supplied over a radio link along with video data.

Great Duck Island off the coast of Maine is a breeding ground for seabirds called Leach’s storm petrels. Here, ornithologists have placed motes in burrows that send data in near real-time to a laboratory in Berkeley.

British Petroleum (BP) placed motes in an oil tanker in the North Sea. The wireless sensor network was subjected to extreme conditions — high temperature, large vibrations, and significant RF (radiofrequency) noise. The network operated successfully.

Biosensors are used to study the binding of protein and other molecules which will help in early detection of Alzheimer’s disease. Implantable sensors are being investigated for early detection of heart attacks, and epileptic seizures.

WIRELESS SENSORS AND INTERNET

There are many sensors that have been developed for specific applications. But making them interoperable is a formidable task. The ZigBee Alliance has more than 150 companies as its members and is working on developing a universal standard for interoperability.

The data from sensors can also be transmitted to a computer connected to the Internet and made available to anyone. This means that people can see and hear what is happening across the globe via Internet in real time.

May be one day from my office, I will be able to see (on my laptop) what my wife is cooking for dinner and decide whether to pick up pizza on the way or not.

The author is Consultant, Satyam Computer Services Ltd, and can be reached at chellaiah_s@satyam.com

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