21-01-2010, 08:03 PM
[attachment=1289]
ABSTRACT
The ËœSmart Dustâ„¢ project is aiming to build an autonomous sensing, computing, and communication system packed into a cubic-millimeter mote, to form the basis of integrated, massively distributed sensor networks. So, this device will be around the size of a grain of sand and will contain sensors, computational ability, bidirectional wireless communications, and power supply, while being inexpensive enough to deploy by the hundreds. Smart Dust requires evolutionary and revolutionary advances in integration, miniaturization and energy management.
If the project is successful, clouds of smart dust could one day be used in an astonishing array of application, from following enemy troop movements and hunting send missiles to detecting toxic chemicals in the environment and monitoring weather patters around the globe.
INTRODUCTION
The current ultramodern technologies are focusing on automation and miniaturization. The decreasing computing device size, increased connectivity and enhanced interaction with the physical world have characterized computingâ„¢s history. Recently, the popularity of small computing devices, such as hand held computers and cell phones; rapidly flourishing internet group and the diminishing size and cost of sensors and especially transistors have accelerated these strengths. The emergence of small computing elements, with sporadic connectivity and increased interaction with the environment, provides enriched opportunities to reshape interactions between people and computers and spur ubiquitous computing researches.
Smart dust is tiny electronic devices designed to capture mountains of information about their surroundings while literally floating on air. Nowadays, sensors, computers and communicators are shrinking down to ridiculously small sizes. If all of these are packed into a single tiny device, it can open up new dimensions in the field of communications.
The idea behind Ëœsmart dustâ„¢ is to pack sophisticated sensors, tiny computers and wireless communicators in to a cubic-millimeter mote to form the basis of integrated, massively distributed sensor networks. They will be light enough to remain suspended in air for hours. As the motes drift on wind, they can monitor the environment for light, sound, temperature, chemical composition and a wide range of other information, and beam that data back to the base station, miles away.
MAJOR COMPONENTS AND REQUIREMENTS OF SMART DUST
Smart Dust requires both evolutionary and revolutionary advances in miniaturization, integration, and energy management. Designers can use microelectromechanical systems to build small sensors, optical communication components, and power supplies, whereas microelectronics provides increasing functionality in smaller areas, with lower energy consumption. The power system consists of a thick-film battery, a solar cell with a charge-integrating capacitor for periods of darkness, or both. Depending on its objective, the design integrates various sensors, including light, temperature, vibration, magnetic field, acoustic, and wind shear, onto the mote. An integrated circuit provides sensor-signal processing, communication, control, data storage, and energy management. A photodiode allows optical data reception. There are presently two transmission schemes: passive transmission using a corner-cube retro reflector, and active transmission using a laser diode and steerable mirrors.
The moteâ„¢s minuscule size makes energy management a key component. The integrated circuit will contain sensor signal conditioning circuits, a temperature sensor, and A/D converter, microprocessor, SRAM, communications circuits, and power control circuits. The IC, together with the sensors, will operate from a power source integrated with the platform.
The MEMS industry has major markets in automotive pressure sensors and accelerometers, medical sensors, and process control sensors. Recent advances in technology have put many of these sensor processes on
exponentially decreasing size, power, and cost curves. In addition, variations of MEMS sensor technology are used to build micro motors.
Figure 1: Components of smart dust
DESCRIPTION OF WORKING OF SMART DUST
The smart dust mote is run by a microcontroller that not only determines the task performed by the mote, but consists of the power to the various components of the system to conserve energy. Periodically the micro controller 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, process the data, and store it in memory. It also turns on 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 retro reflector or laser to transmit sensor data or a message to a base station or another 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 look for an incoming packet. If it doesnâ„¢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 retro reflector or the laser diode, depending on which it has. The corner cube retro reflector 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.
COMPUTING AT THE MILLIMETER SCALE
Computing in an autonomous cubic-millimeter package must focus on minimizing a given taskâ„¢s energy consumption. Smaller, faster transistors have reduced parasitic capacitance, thereby resulting in diminished dynamic power consumption. Constant electric field scaling has reduced supply voltages, producing dramatic power reductions for both high-performance and low-energy computing because dynamic power has a quadratic dependence on supply voltage. However, constant electric field scaling also calls for a reduction in the threshold voltage. This will result in larger leakage currents, which are already a concern in the high-performance processors to be released in 2001 that will leak amps of current. The process engineers need to keep leakage currents low, which will also benefit low-energy designers. In millimeter-scale computing, the shrinking transistorâ„¢s size lets designerâ„¢s compact significant computing power into this small area
Low-energy computation
Besides advanced micro fabrication technology processes, using other techniques at every level achieves low-energy computation. First, because we use a high-performance process but operate at low speeds, we can drop the supply voltage to the minimum level at which the devices still function; theoretically this is 0.1 volt, 6 but for 0.5- to 0.2-micron processes it is more realistically 0.2 to 0.3 volt. To minimize current leakage, which can cause significant power consumption at the low clock rates and duty cycles that these low-energy architectures use, we can increase the channel-to-source junctionâ„¢s reverse bias, thus increasing the threshold voltage. Initially, adding two extra supply voltages in this package may seem onerous; however, if the mote scavenges solar power, placing two small photodiodes on the integrated circuit provides the few atto-amps per device necessary to bias these junctions. The Smart Dust moteâ„¢s tasks closely relate to the physical realm, where the fastest sampling is 10 to 20 kHz for vibration and acoustic sensors so the amount of data is small enough that we can use low data transmition rates. Therefore we can use clock rates in the 1 to 180 kHz range to decrease dynamic power consumption. Despite these low clock rates, the circuits perform all their transitions during a small portion of the cycle; then they remain idle. Thus, powering down blocks for even a few clock cycles saves energy.
Remote programmability
Remote programmability plays an important role in millimeter-scale computing. Given their small size and large numbers, we prefer to program these devices in masses, without direct connections. Remote programmability also avoids the costs of recollecting and reprogramming devices after we deploy them.
MODE OF COMMUNICATION
Smart Dustâ„¢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 understood, but currently requires minimum power levels in the multiple milliwatts 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.
Semiconductor lasers and diode receivers are intrinsically small, and the corresponding transmission and detection circuitry for on/off keyed optical communication is more amenable to low-power operation than most radio schema. Most important, optical power can be collimated in tight beams even from small apertures. Diffraction enforces a fundamental limit on the divergence of a beam, whether it comes from an antenna or a lens. Laser pointers are cheap examples of milliradian collimation from a millimeter aperture. To get similar collimation for a 1-GHz radiofrequency signal would require an antenna 100 meters across, due to the difference in wavelength of the two transmissions. As a result, optical transmitters of millimeter size can get antenna gains of one million or more, while similarly sized radio frequency antennas are doomed by physics to be mostly isotropic.
Collimated optical communication has two major drawbacks. Line of sight is required for all but the shortest distances, and narrow beams imply the need for accurate pointing.
Further optical communication is explored in some depth due to the potential for extreme low-power communication.
Figure 2: Comparison of communication modules
OPTICAL COMMUNICATIONS
Two approaches to optical communication are explored: Passive reflective systems and active steered laser systems. In a passive communication system, the dust mote does not require an onboard light source. Instead, a special configuration of mirrors can either reflect or not reflect light to a remote source.
Passive-reflective systems
The passive reflective device 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 MEMS version, the device has one mirror mounted on a spring at an angle slightly askew from perpendicularity to the other mirrors. The mirrorâ„¢s low mass allows the CCR to switch between 0 and 1 states up to a thousand times per seconds, using less than a nanojoule per 0-1 transition. A 1-0 transition on the other hand is practically free because damping the charge stored in the electrode to the ground requires almost no energy.
Passive communication system suffers several limitations. Unable to communicate with each other, motes rely on a central station equipped with a light source to send and receive data from other motes. Also, because CCR reflects only a small fraction of the light emitted from a base station, the systems range cannot easily extend beyond 1 km.
Active- steered laser systems
For mote- to “ mote communication, an active steered laser communication system uses an onboard light source to send a tightly collimated light beam towards an intended receiver. Steered laser communication has the advantage of high power density. This system allows communication over enormous distances using millwatts of power.
Here, a laser emits an infrared beam that is collimated with a lens. This lens directs the narrow laser beam into a beam steering mirror, aiming the beam towards the intended receiver.
LISTENING TO A DUST FIELD
Many smart dust applications rely on direct optical communication from an entire field of dust motes to one more base stations. These base stations must therefore be able to receive a volume of simultaneous optical transmissions. Communication must be possible outdoors in bright sunlight. Using a narrow band optical filter to eliminate all sunlight, except the portion near the light frequency used for communication can only partly solve this problem.
Imaging receivers
Imaging receivers can overcome both the above challenges. Light from a large field of view can be focused ino an image, as in our eyes or in a camera. Imaging receivers utilize this to analyze different portions of the image separately to process simultaneous transmissions from different angles. This method of distinguishing transmissions based on their originating location is referred to as space division multiple access (SDMA). In contrast, most radio- frequency antennas receives all incidents radio power in a single signal, which requires using additional tactics, such as frequency tuning or code division multiple access (CDMA), to separate simultaneous transmissions.
Video camera
A video camera is a straight forward implementation of an imaging receiver. If each member in a colony of smart dust motes flashes its own signal at a rate of a few bits per seconds, then each transmitter will appear in the video stream at a different location in the image.
Using a high speed camera and a dedicated digital signal processor to process the video signal achieves higher data rates. With modern cameras and DSPs, processing video at about 1000 frames per second should be feasible. This allow communication at a few hundred bits per seconds, which is acceptable for many applications. An alternative receiver architecture provides a more elegant solution at much higher data rates, avoiding the need for computationally intense video processing and very high speed cameras.
Smart Pixel Imaging Receivers
This is a fully integrated CMOS imaging device that receives data upto a few megabits per second. The receiver leverages the power of shrinking integrated circuits and recent developments in CMOS ËœSmart pixelâ„¢ sensors to create a microchip similar to a digital camera sensor, but with a complete asynchronous receiver circuit integrated into every pixel in the imaging array.
During the receivers operations, each pixel autonomously monitors its own signal, looks for a transmission, decodes it, and transmits the data off chip when it receives a valid data packet. Each pixel in the imager requires a photosensor and circuits to perform analog signal processing and amplification, analog-to-digital conversion and an asynchronous serial receiver. Such a receiver should be able to receive transmissions of only a few milliwatts in strength up to a few megabytes per second over a distance of several kilometers.
Figure 3: Imaging receiver concept
Figure 4: Basic components of a smart pixel in an integrated imaging receiver
CURRENT ADVANCEMENTS
MICROBOTICS
Add legs or wings to smart dust and we get micro robots. Like smart dust, these synthetic insects will sense, think, and communicate. In addition they will have the ability to move about and interact physically with their environment. Micro machining can be used to build micro actuators and micro mechanisms, forming legs and wings, which are integrated with other smart dust components.
The crawling microbot consume only tens of micro watts of power; the motors can lift more than 130 times the robotâ„¢s own weight. The flying microbot have a wing span of 10-25 mm and will sustain autonomous flight. Developers folded 50 micron thick stainless steel into desired shape to create the wings and exoskeleton. Piezoelectric motors attached to the exoskeleton actuate the wings. These legged and winged microbots will consume a total power of less than 10 milliwatts, provided by onboard solar cells.
Figure 5: Crawling microbot Figure 6: Flying microbot
COTS DUST
They are large scale bodies for models for smart dust and they are devices that incorporate communications, processing, sensors and batteries into a package about a cubic inch in size.
COTS dust was designed with the intention of testing out communication and sensing capabilities of large number of nodes. Potential applications are limitless! They can range from fire detectors to espionage, from earthquake monitoring to people tracking.
The basic structure of COTS dust consists of an Atmel microcontroller with sensors and communication unit. The communication unit is one of the following: an RF transceiver, a laser module, a corner cube reflector. Devices can have one or all of the following sensors: temperature, light, humidity, pressure, 3axis magnetometer, 3axis accelerometers.
GOLEM DUST
This consists of a CMOS IC that contains an integrated optical receiver, an analog to digital converter, and a custom controller. This IC is designed to interface with a MEMS chip consisting of a solar cell array for powering the system, a corner cube retro reflector and a capacitor accelerometer which will be read by ADC. The entire system will be 6.6 mm3.
Figure 7: Golem dust-system
Figure 8: Golem dust- CMOS ASIC
LIMITATIONS
¢ A major challenge is to incorporate all functions while maintaining very low power consumption, thereby maximizing operating life; given the limited volume available for energy storage. The functionality envisioned for smart dust can be achieved only if total power consumption of a dust mote is limited to microwatt levels, and if careful power management strategies are utilized.
¢ Privacy issues “ Though smart dust can be used as a total surveillance device, abuse of such technology can cost us our privacy.
ADVANTAGES
Miniaturization effort could help solve one of the most pressing economic problems of the day: run away energy costs. Once attached to buildingâ„¢s walls, the sensors would form a network relaying data about each roomâ„¢s temperature, light and humidity to central computer that would regulate energy usage for a fraction of the cost of current climate control systems. The emerging smart energy technologies potentially could save nations on electricity costs, as buildings drain away more than a third of the total energy supply.
APPLICATIONS OF SMART DUST
¢ Chemical or biological sensors.
¢ Weapons stockpile monitoring.
¢ Defense related sensor networks.
¢ Inventory controls.
¢ Land or space communication networks.
¢ Monitoring environmental conditions that affect crops and livestock.
¢ Building virtual keyboards.
¢ Providing interfaces for the disabled.
¢ Product quality monitoring.
¢ Internal space craft monitoring.
CONCLUSION
Research in the wireless sensor network area is growing rapidly in both academia and industry. Most major universities and many companies now have sensor networking projects, and some products are appearing on the market. Innovative research includes short-range micro power radio, energy scavenging from thermal gradients and vibration, operating systems, networking and signal processing algorithms, and applications. While the raw power of future computing environments will enable more massive and amazing hardware and software networks, a growing community will be pushing the limits on the lower end, building smaller hardware and writing terser code.
REFERENCES
1. Brett Warneke, Matt Last, Brian Leibowitz, Kristofer S.J Pister, Smart Dust-Communicating with a cubic millimeter computer IEEE Journal- Computer. January 2001. Pages 2-9.
2. bsac.eecs.berkely.edu
3. robotics.eecs.berkely.edu
ACKNOWLEDGEMENT
I extend my sincere gratitude towards Prof . P.Sukumaran Head of Department for giving us his invaluable knowledge and wonderful technical guidance
I express my thanks to Mr. Muhammed kutty our group tutor and also to our staff advisor Ms. Biji Paul for their kind co-operation and guidance for preparing and presenting this seminars.
I also thank all the other faculty members of AEI department and my friends for their help and support.
CONTENTS
1. INTRODUCTION 1
2. MAJOR COMPONENTS AND REQUIREMENTS OF SMART DUST 2
3. DESCRIPTION OF WORKING 3
4. MODE OF COMMUNICATION 7
5. OPTICAL COMMUNICATIONS 9
6. LISTENING TO A DUST FIELD 11
7. CURRENT ADVANCEMENTS 14
8. LIMITATIONS 17
9. ADVANTAGES 18
10. APPLICATIONS OF SMART DUST 19
11. CONCLUSION 20
12. REFERENCES 21
