27-02-2013, 11:34 AM
Motes
[attachment=52030]
Introduction:
Motes is a tiny dust size device with extra-ordinary capabilities. It 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 motes will render it useful in monitoring real world phenomenon without disturbing the original process to an observable extends. Presently the achievable size of Motes is about 5mm cube, but we hope that it will eventually be as small as a speck of dust.Motes are also called as smart 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 Motes 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.
Motes 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).
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 Motes. First of all, it is hardly possible to fit current radio communication technology into Motes 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 Motes. 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.
Radio Frequency transmission:
It is based on the generation, propagation and detection of electromagnetic waves with a frequency range from tens of kHz to hundreds of GHz. It could be used to function as both the uplink and the downlink. Since RF transceiver typically consists of relatively complex circuitry, it is impossible to achieve the required low power operation using such an approach in a smart dust system. When large numbers of motes are involved in smart dust, RF links may employ alternative multiplexing techniques: time, frequency or code-division multiplexing. Their use leads to modulation, bandpass filtering, demodulation circuitry, and additional circuitry, all of which needs to be considered based on power consumption. RF communication can be used for smart dust communication but it poses following problems:
a) Size of the antenna: Since the size of the antenna should be ¼ of the carrier wavelength, if we reduce the size of the antenna (which is very difficult to achieve) the wavelength of the carrier wave will decrease, thus requiring high frequency transmission. This system will no longer comply with low power consumption requirement of the small dust.
b) RF communication can only be achieved by using time, frequency or code division.
c) Multiplexing (TDMA, FDMA, or CDMA) each having their own complications. For TDMA mote should transfer at high bit rate (as high as aggregate uplink capacity) in absence of other transmission. Beside this, mote should coordinate their transmission with other mote. In FDMA, the accurate control of oscillator frequency is required. Since CDMA operates for a relatively extended time interval, it requires high-speed digital circuitry and it consumes excessive power. Both FDMA and CDMA should avoid coordination between dust motes and they require dust motes to be preprogrammed with unique frequencies or codes in order to prevent such coordination.
Conclusion:
There are many ongoing researches on Motes, the main purpose of these researches is to make Smart Dust mote as small as possible and to make it available at as low price as possible. Soon we will see Motes being used in varied application from all spans of life.
[attachment=52030]
Introduction:
Motes is a tiny dust size device with extra-ordinary capabilities. It 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 motes will render it useful in monitoring real world phenomenon without disturbing the original process to an observable extends. Presently the achievable size of Motes is about 5mm cube, but we hope that it will eventually be as small as a speck of dust.Motes are also called as smart 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 Motes 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.
Motes 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).
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 Motes. First of all, it is hardly possible to fit current radio communication technology into Motes 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 Motes. 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.
Radio Frequency transmission:
It is based on the generation, propagation and detection of electromagnetic waves with a frequency range from tens of kHz to hundreds of GHz. It could be used to function as both the uplink and the downlink. Since RF transceiver typically consists of relatively complex circuitry, it is impossible to achieve the required low power operation using such an approach in a smart dust system. When large numbers of motes are involved in smart dust, RF links may employ alternative multiplexing techniques: time, frequency or code-division multiplexing. Their use leads to modulation, bandpass filtering, demodulation circuitry, and additional circuitry, all of which needs to be considered based on power consumption. RF communication can be used for smart dust communication but it poses following problems:
a) Size of the antenna: Since the size of the antenna should be ¼ of the carrier wavelength, if we reduce the size of the antenna (which is very difficult to achieve) the wavelength of the carrier wave will decrease, thus requiring high frequency transmission. This system will no longer comply with low power consumption requirement of the small dust.
b) RF communication can only be achieved by using time, frequency or code division.
c) Multiplexing (TDMA, FDMA, or CDMA) each having their own complications. For TDMA mote should transfer at high bit rate (as high as aggregate uplink capacity) in absence of other transmission. Beside this, mote should coordinate their transmission with other mote. In FDMA, the accurate control of oscillator frequency is required. Since CDMA operates for a relatively extended time interval, it requires high-speed digital circuitry and it consumes excessive power. Both FDMA and CDMA should avoid coordination between dust motes and they require dust motes to be preprogrammed with unique frequencies or codes in order to prevent such coordination.
Conclusion:
There are many ongoing researches on Motes, the main purpose of these researches is to make Smart Dust mote as small as possible and to make it available at as low price as possible. Soon we will see Motes being used in varied application from all spans of life.