Smart Dust

Contributor:Saritha Mary Zachariah

Picture being able to scatter hundreds of tiny sensors around a building to monitor temperature or humidity. Or deploying, like pixie dust, a network of minuscule, remote sensor chips to track enemy movements in a military operation.

"Smart dust" devices are tiny wireless microelectromechanical sensors (MEMS) that can detect everything from light to vibrations. Thanks to recent breakthroughs in silicon and fabrication techniques, these "motes" could eventually be the size of a grain of sand, though each would contain sensors, computing circuits, bidirectional wireless communications technology and a power supply. Motes would gather scads of data, run computations and communicate that information using two-way band radio between motes at distances approaching 1,000 feet.

Smartdust is a term used to describe groups of very small robots which may be used for monitoring and detection. Currently, the scale of smartdust is rather small, with single sensors the size of a deck of playing cards, but the hope is to eventually have robots as small as a speck of dust. Individual sensors of smartdust are often referred to as motes because of their small size. These devices are also known as MEMS.

MEMS stands for Micro Electro-Mechanical Systems, referring to functional machine systems with components measured in micrometers. MEMS is often viewed as a stepping stone between conventional macroscale machinery and futuristic nanomachinery. MEMS-precursors have been around for a while in the form of microelectronics, but these systems are purely electronic, incapable of processing or outputting anything but a series of electrical impulses. However, modern MEMS-fabrication techniques are largely based upon the same technology used to manufacture integrated circuits, that is, film-deposition techniques which employ photolithography.

Largely considered an enabling technology rather than an end in itself, the fabrication of MEMS is seen by engineers and technologists as another welcome advance in our ability to synthesize a wider range of physical structures designed to perform useful tasks. Most often mentioned in conjunction with MEMS is the idea of a "lab-on-a-chip," a device that processes tiny samples of a chemical and returns useful results. This could prove quite revolutionary in the area of medical diagnosis, where lab analysis results in added costs for medical coverage, delays in diagnosis and inconvenient paperwork.

Brief description of the operation of the mote:

The Smart Dust mote is run by a microcontroller that not only determines the tasks performed by the mote, but controls power to the various components of the system to conserve energy. Periodically the microcontroller gets a reading from one of the sensors, which measure one of a number of physical or chemical stimuli such as temperature, ambient light, vibration, acceleration, or air pressure, processes the data, and stores it in memory. It also occasionally turns on the optical receiver to see if anyone is trying to communicate with it. This communication may include new programs or messages from other motes. In response to a message or upon its own initiative the microcontroller will use the corner cube retroreflector or laser to transmit sensor data or a message to a base station or another mote.

Longer description of the operation of the mote:

The primary constraint in the design of the Smart Dust motes is volume, which in turn puts a severe constraint on energy since we do not have much room for batteries or large solar cells. Thus, the motes must operate efficiently and conserve energy whenever possible. Most of the time, the majority of the mote is powered off with only a clock and a few timers running. When a timer expires, it powers up a part of the mote to carry out a job, then powers off. A few of the timers control the sensors that measure one of a number of physical or chemical stimuli such as temperature, ambient light, vibration, acceleration, or air pressure. When one of these timers expires, it powers up the corresponding sensor, takes a sample, and converts it to a digital word. If the data is interesting, it may either be stored directly in the SRAM or the microcontroller is powered up to perform more complex operations with it. When this task is complete, everything is again powered down and the timer begins counting again.

Another timer controls the receiver. When that timer expires, the receiver powers up and looks for an incoming packet. If it doesn't see one after a certain length of time, it is powered down again. The mote can receive several types of packets, including ones that are new program code that is stored in the program memory. This allows the user to change the behavior of the mote remotely. Packets may also include messages from the base station or other motes. When one of these is received, the microcontroller is powered up and used to interpret the contents of the message. The message may tell the mote to do something in particular, or it may be a message that is just being passed from one mote to another on its way to a particular destination. In response to a message or to another timer expiring, the microcontroller will assemble a packet containing sensor data or a message and transmit it using either the corner cube retroreflector or the laser diode, depending on which it has. The corner cube retroreflector transmits information just by moving a mirror and thus changing the reflection of a laser beam from the base station. This technique is substantially more energy efficient than actually generating some radiation. With the laser diode and a set of beam scanning mirrors, we can transmit data in any direction desired, allowing the mote to communicate with other Smart Dust motes.

Smartdust has theoretical applications in virtually every field of science and industry. Research in the technologies is well-funded and sturdily based, and it is generally accepted that it is simply a matter of time before smartdust exists in a functional manner.

The Defense Advanced Research Projects Agency (DARPA) has been funding smartdust research heavily since the late 1990s, seeing virtually limitless applications in the sphere of modern warfare. So far the research has been promising, with prototype smartdust sensors as small as 5mm. Costs have been dropping rapidly with technological innovations, bringing individual motes down to as little as $50 each, with hopes of dropping below $1 per mote in the near future.

Applications

• Defense-related sensor networks

• battlefield surveillance, treaty monitoring, transportation monitoring, scud hunting, ...
• Virtual keyboard
• Glue a dust mote on each of your fingernails. Accelerometers will sense the orientation and motion of each of your fingertips, and talk to the computer in your watch. QWERTY is the first step to proving the concept, but you can imagine much more useful and creative ways to interface to your computer if it knows where your fingers are: sculpt 3D shapes in virtual clay, play the piano, gesture in sign language and have to computer translate, ...
• Combined with a MEMS augmented-reality heads-up display, your entire computer I/O would be invisible to the people around you. Couple that with wireless access and you need never be bored in a meeting again! Surf the web while the boss rambles on and on.
• Inventory Control
• The carton talks to the box, the box talks to the palette, the palette talks to the truck, and the truck talks to the warehouse, and the truck and the warehouse talk to the internet. Know where your products are and what shape they're in any time, anywhere. Sort of like FedEx tracking on steroids for all products in your production stream from raw materials to delivered goods.
• Product quality monitoring
• temperature, humidity monitoring of meat, produce, dairy products
• impact, vibration, temp monitoring of consumer electronics
• failure analysis and diagnostic information, e.g. monitoring vibration of bearings for frequency signatures indicating imminent failure (back up that hard drive now!)

• Smart office spaces

• The Center for the Built Environment has fabulous plans for the office of the future in which environmental conditions are tailored to the desires of every individual. Maybe soon we'll all be wearing temperature, humidity, and environmental comfort sensors sewn into our clothes, continuously talking to our workspaces which will deliver conditions tailored to our needs. No more fighting with your office mates over the thermostat.

Energy use is a major area of research in the field of smartdust. With devices so small, batteries present a massive addition of weight. It is therefore important to use absolutely minimal amounts of energy in communicating the data they collect to central hubs where it can be accessed by humans.

Development of smartdust continues at a breakneck speed, and it will no doubt soon be commonplace to have a vast army of thousands or millions of nearly invisible sensors monitoring our environment to ensure our safety and the efficiency of the machines around us.

REFERENCES

1. www.computerworld.com

2. www.robotics.eecs.berkeley.edu

3. www.bsac.eecs.berkeley.edu

4. www.nanotech-now.com

5. www.wikipedia.org