Twenty four hours a day, year-in, year-out, doctor Flemming wants to monitor the heart rate and blood oxygen of a patient working in a factory at minimum cost in real time. Scientist Galvin was given the task of monitoring in real time two dozen variables in a very hostile environ around the clock over wide area in all three dimensions. This hostile environ could be a battle field scenario or uninhabited glacier of Himalayas. There are myriad such vexed complex problems, given a chance, which scientists wants to explore ceaselessly. It is endless list of problems like ecosystems, habitat of animals/birds, soil-biodiversity, nutrient cycling, climatology, flooding, traffic control, pollution and so on. We cannot solve complex problems with limited data. To illustrate, soil is the most complex layer in the chain of ecosystem, but it is poorly understood due to limited data collected by technicians through selective sampling for analysis in the laboratory. Is there a methodology to monitor such global phenomena ? Thanks to our scientists, the solution is in sight.
Today, we have tiny computers packed in a box size of just few millimeters called 'motes' or 'smart dust'. They have the ability to monitor data continuously in real time of the physical world on a large scale over large sample-population over large geography. Some call this tiny stuff 'motes', others call it 'smart dust'. Basically motes are building-blocks of wireless sensor network. Why 'Smart dust'? The name smart dust was coined by Pister, University of California, Berkely to describe his version of sensors joined in network in 1000's or even millions to comprehend a physical scenario as though it is observed by a human brain.
The core of a mote is a small low cost low power computer.
A typical mote uses an 8-bit micro-computer that has 512 Kbytes of on board flash memory running at 4 MHz. The CPU usually matches with 8088 CPU of IBM PC with 10 bits A to D converter. It is designed to consume just 8 milli amp in working and 15 micro amp while in sleep. It can have operation life of nearly 150 hrs with two AA batteries. To consume power, it is made to sleep for 10 secs and wake up and give status for few microsecond before going to sleep again. A programmer writes software to control the mote and make it perform a certain way.Deployment:
The motes are usually required to be deployed in 100's to millions with embedded sensors forming a self-organising sensor network despite limited processing power, storage, energy and bandwidth. There is no limit on type of sensors. Imagine any type of sensor from temperature, light, sound, position, acceleration, vibration, stress, weight, pressure and so on. The computer in the mote connects to the outside world with a radio link with transmitting range of about 5-100 m. Motes are packed in tiny size boxes of size not exceeding 5 mm. Current cost of the motes on average is about 25 US $ and likely to fall down with time.
Challenges:
Design, development and deployment include network discovery, control routing, information processing, querying and security, creating a sensor web for scientific applications requires extensive customization, new standards, dedicated operating system, programming and user friendly web tools. To cut down costs one needs to look into commercial adoption and networking on a larger scale, which is slowing the speed by several years.
The future:
Wireless sensor network have been identified as one of the most important upcoming technologies in the 21st Century. Wireless sensor network is going to revolutionize many physical field scenarios by making large scale measurements possible at temporal and spatial dimensions. There are myriad ways that motes might be used and as people appreciate the concept, the application scope will be even more. It is opening up a fascinating new field of distributed sensing which is far beyond the scope of present day knowledge. The diverse application in the future include agricultural management, complex structures and earth quake monitoring, industrial controls, military applications, transportation, shipping, fire-fighting and home-automation and many more - all at global scale.
Author is Director, Naval Science and Technological Laboratory, DRDO, Visakhapatnam 530027, India.
