31-12-2010, 02:53 PM
Submitted by:
Shruti Srivastava
INTRODUCTION
Smart dust is a tiny dust size device with extra-ordinary capabilities. Smart dust combines sensing, computing, wireless communication capabilities and autonomous power supply within volume of only few millimeters and that too at low cost. These devices are proposed to be so small and light in weight that they can remain suspended in the environment like an ordinary dust particle. These properties of Smart Dust will render it useful in monitoring real world phenomenon without disturbing the original process to an observable extends. Presently the achievable size of Smart Dust is about 5mm cube, but we hope that it will eventually be as small as a speck of dust. Individual sensors of smart dust are often referred to as motes because of their small size. These devices are also known as MEMS, which stands for micro electro-mechanical sensors.
Background:
The Defense Advanced Research Projects Agency (DARPA) has been funding Smart Dust 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 smart dust sensors as small as 5mm.But further scaling down needs advance technological changes. 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.
Smart Dust Structure:
A smart dust particle is often called motes (Fig. 1). One single mote has a Micro Electro Mechanical System (MEMS), a semiconductor laser diode, MEMS beam steering mirror for active optical transmission, a MEMS corner cube retro-reflector for passive optical transmission, an optical receiver, a signal processing and control circuitry, and a power source based on thick-film batteries and solar cells.
A major challenge is to incorporate all these functions while maintaining very low power consumption and optimizing the operating life of the mote. The structure of a single moat is shown in Figure 2. Smart dust motes consist of a passive optical transmitter with a micro fabricated corner- Cube Retro-reflector (CCR). This CCR contains three mutually perpendicular mirror fabricated of gold- coated poly-silicon (fig. 3). The CCR reflects any ray of light within a certain range of angles centered about the cube diagonal back to the source.
The power system consists of a thick-film battery or a solar cell, or both with a charge-integrating capacitor (power capacitor). The thick film battery of sol or gel V2O3 provides as a backup in darkness, while solar cells generate energy from sunlight. Depending on its objective, the design integrates various sensors, including light, temperature, vibration, magnetic field, acoustic, and wind shear, onto the mote. Active transmitters make possible peer-to-peer communication between dust motes, provided there exists a line-of-sight path between them.
Corner Cube Retro-Reflector (CCR):
CCR comprises three mutually perpendicular mirrors of gold-coated polysilicon. The CCR has the property that any incident ray of light is reflected back to the source (provided that it is incident within a certain range of angles centered about the cube’s body diagonal). If one of the mirrors is misaligned, this retro-reflection property is spoiled. The micro-fabricated CCR includes an electrostatic actuator that can deflect one of the mirrors at kilohertz rates. It has been demonstrated that a CCR illuminated by an external light source can transmit back a modulated signal at kilobits per second. Since the dust mote itself does not emit light, the passive transmitter consumes little power. Using a micro-fabricated CCR, we can achieve data transmission at a bit rate up to 1 kilobit per second, and over a range up to 150 meters, using a 5milliwatt illuminating laser.
One should note that CCR-based passive optical links require an uninterrupted line-of-sight path. Moreover, a CCR-based passive transmitter is inherently directional; a CCR can transmit to the BTS only when the CCR body diagonal happens to point directly toward the BTS, within a few tens of degrees.
A passive transmitter can be made more omni-directional by employing several CCRs oriented in different directions, at the expense of increased dust mote size. If a dust mote employs only one or a few CCRs, the lack of omni-directional transmission has important consequence on feasible network routing strategies.
Challenges:
The hardware design has to face many challenges due to the small size of the Smart Dust. First of all, it is hardly possible to fit current radio communication technology into Smart Dust both size wise and energy wise. The present radio communication has large antennas and thus requires larger space. The energy requirements are also high. So, a more size and power efficient passive laser based communication schemes have to be adopted. But it also has its share of disadvantages.
Another factor of concern is the energy consumption by the Smart Dust. 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 the central hubs, where humans can access it.
Submitted by:
Shruti Srivastava
[attachment=7804]
INTRODUCTION
Smart dust is a tiny dust size device with extra-ordinary capabilities. Smart dust combines sensing, computing, wireless communication capabilities and autonomous power supply within volume of only few millimeters and that too at low cost. These devices are proposed to be so small and light in weight that they can remain suspended in the environment like an ordinary dust particle. These properties of Smart Dust will render it useful in monitoring real world phenomenon without disturbing the original process to an observable extends. Presently the achievable size of Smart Dust is about 5mm cube, but we hope that it will eventually be as small as a speck of dust. Individual sensors of smart dust are often referred to as motes because of their small size. These devices are also known as MEMS, which stands for micro electro-mechanical sensors.
Background:
The Defense Advanced Research Projects Agency (DARPA) has been funding Smart Dust 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 smart dust sensors as small as 5mm.But further scaling down needs advance technological changes. 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.
Smart Dust Structure:
A smart dust particle is often called motes (Fig. 1). One single mote has a Micro Electro Mechanical System (MEMS), a semiconductor laser diode, MEMS beam steering mirror for active optical transmission, a MEMS corner cube retro-reflector for passive optical transmission, an optical receiver, a signal processing and control circuitry, and a power source based on thick-film batteries and solar cells.
A major challenge is to incorporate all these functions while maintaining very low power consumption and optimizing the operating life of the mote. The structure of a single moat is shown in Figure 2. Smart dust motes consist of a passive optical transmitter with a micro fabricated corner- Cube Retro-reflector (CCR). This CCR contains three mutually perpendicular mirror fabricated of gold- coated poly-silicon (fig. 3). The CCR reflects any ray of light within a certain range of angles centered about the cube diagonal back to the source.
The power system consists of a thick-film battery or a solar cell, or both with a charge-integrating capacitor (power capacitor). The thick film battery of sol or gel V2O3 provides as a backup in darkness, while solar cells generate energy from sunlight. Depending on its objective, the design integrates various sensors, including light, temperature, vibration, magnetic field, acoustic, and wind shear, onto the mote. Active transmitters make possible peer-to-peer communication between dust motes, provided there exists a line-of-sight path between them.
Corner Cube Retro-Reflector (CCR):
CCR comprises three mutually perpendicular mirrors of gold-coated polysilicon. The CCR has the property that any incident ray of light is reflected back to the source (provided that it is incident within a certain range of angles centered about the cube’s body diagonal). If one of the mirrors is misaligned, this retro-reflection property is spoiled. The micro-fabricated CCR includes an electrostatic actuator that can deflect one of the mirrors at kilohertz rates. It has been demonstrated that a CCR illuminated by an external light source can transmit back a modulated signal at kilobits per second. Since the dust mote itself does not emit light, the passive transmitter consumes little power. Using a micro-fabricated CCR, we can achieve data transmission at a bit rate up to 1 kilobit per second, and over a range up to 150 meters, using a 5milliwatt illuminating laser.
One should note that CCR-based passive optical links require an uninterrupted line-of-sight path. Moreover, a CCR-based passive transmitter is inherently directional; a CCR can transmit to the BTS only when the CCR body diagonal happens to point directly toward the BTS, within a few tens of degrees.
A passive transmitter can be made more omni-directional by employing several CCRs oriented in different directions, at the expense of increased dust mote size. If a dust mote employs only one or a few CCRs, the lack of omni-directional transmission has important consequence on feasible network routing strategies.
Challenges:
The hardware design has to face many challenges due to the small size of the Smart Dust. First of all, it is hardly possible to fit current radio communication technology into Smart Dust both size wise and energy wise. The present radio communication has large antennas and thus requires larger space. The energy requirements are also high. So, a more size and power efficient passive laser based communication schemes have to be adopted. But it also has its share of disadvantages.
Another factor of concern is the energy consumption by the Smart Dust. 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 the central hubs, where humans can access it.
