Role of MEMS in Sensors - MEMS _ Microsystems _ USF

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Role of MEMS in Sensors - MEMS _ Microsystems _ USF Powered By Docstoc
					Shekhar Bhansali
First things first, what is a Sensor ?

A device used to measure a physical quantity such
as temperature and convert it into an electronic
signal of some kind (e.g a voltage), without
modifying the environment.

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         Sensors in our body
•   Mechanoreceptors (feel)
•   Auditory system
•   Visual System
•   Olfactory System (Nose)

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      What can be sensed?
Almost Everything!!!
Commonly sensed parameters are :
• Pressure
• Temperature
• Flow rate
• Radiation
• Chemicals
• Pathogens

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              What is MEMS ?

• MEMS or Micro Electro Mechanical Systems is a
  technique of combining Electrical and Mechanical
  components together on a chip, to produce a system
  of miniature dimensions ..
• By miniature, we mean dimensions less than the
  thickness of human hair !!!!

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                    The wonder called
• Nanotechnology is the technology of arranging atoms and
  molecules in a material.
• This allows to alter the properties of a material and build
  structures of desired features.
• A nanometer is one-billionth of a meter.
• Nanotechnology makes it possible to manufacture devices
  80,000 times smaller than the thickness of human hair !!

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               A simple analogy..
•   The atoms in an object can be
    compared to the blocks in a
    building game.

•   In a building game, the blocks
    can be arranged to create
    different looking structures.

•   Similarly, atoms can be
    arranged differently to produce
    a multitude of devices. This
    forms the basis of

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 Same game, different names
• Europe – Microsystem technology
• Japan - Micromachines

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       But why mems for sensors?
Sensors made using MEMS are better than
their conventional counterparts because they are :

•   Smaller in size
•   Have lower power consumption
•   More sensitive to input variations
•   Cheaper due to mass production
•   Less invasive than larger devices

           So good things do come in small
                    packages !!!!

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Projected MEMS Market Share 2006

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MEMS Revenue

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       Market for Sensors
• Auto Industry
• Medical industry
• Department of Defense

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          Types of Sensors
•   Mechanical Sensors
•   Optical Sensors
•   Thermal Sensors
•   Chemical and Biological Sensors

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     Mechanical Micro sensors
•   Strain Gauges
•   Accelerometers
•   Gyroscopes (Rotation rate)
•   Pressure Sensors
•   Microphones
•   Tactile Sensors (sensory feedback)
•   Biological Sensors (cochlear implants)
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Used in deploying airbags, navigation,
activity detection for pacemakers

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Sensors in automobiles

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     Size is important in
     automotive industry



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Comparison between conventional
 and MEMS based inertial sensor

        Conventional                              MEMS based
Mass      1587.5 gm                                 10 gm
Size      15x8x5 cm                                 2x2x0.5 cm
Power     35 W                                      ~1mW
Cost      $20,000                                   $500

            Adapted from :
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MEMS based cochlear implant

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            Optical Sensors
• Direct Sensors
 (Light → Electronic Signal)
  – Photoemissive
  – Photoconductive
• Indirect Sensors
 (Light → Intermediate energy → Electronic signal)
  – Pyroelectric detectors
  – Bolometers
• Biological Light Sensors

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        Sight for the blind
MEMS based array that may be inserted in
the retina of a blind person to provide partial


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          Thermal Sensors
•   Thermo mechanical (dimension)
•   Thermo resistive (resistance)
•   Acoustic (sound)
•   Biological

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    Features of MEMS thermal
•   Waterproof
•   Contact free (wireless)
•   Find use in household appliances (iron)
•   Can be used in tight ends

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         Chem Bio Sensors
• Electronic nose can
  sense a large
  number of gases


• Electronic tongue
  can sense a variety
  of liquids

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Chemical lab on a chip
Used to detect chemicals in gas, liquids and

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       Medical and homeland
        security applications
•   Biocavity laser
•   Decontamination foam
•   Smart pill
•   Sensors for missile systems

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          Biocavity laser
This device distinguishes cancerous from non
cancerous cells thus aiding the surgeons in


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           Decontamination foam
• It can neutralize both chemical and
  biological agents (anthrax) and help in
  homeland security
• Not harmful to people, hence can be
  dispensed freely
 Source : Sandia Labs

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             Smart PILL
• Implanted in the body
• Automatic drug delivery (on demand)


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MEMS and Marine

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        Need for sensors in marine
Sensing in marine environment maybe done for various
reasons :

 Oil exploration and related applications

 Global weather predictions

 Monitor water quality for any contamination

 Measure parameters detrimental to the “health” of
  structures in the sea ( like oil rigs and ships )

 Study of aquatic plants and animals

 In military operations

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    Parameters monitored in marine
                                  Dissolved gases
pressure, light
                                  (like oxygen),
                                  pH, metals,
tidal and current

Plant pigments
                                  Seismic signal
plankton cells

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 Why measure these quantities after all ?

Water temperature – effects a lot of processes
 directly viz.

• Solubility of substances in water

• Feeding and reproduction of aquatic organisms

• Also, water’s ability to hold dissolved oxygen
  decreases as water temperature increases….
  Now, this is really crucial for aquatic life !!

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       Importance of measuring light
• Indicates algal growth

• Indicates presence of silt in estuaries (confluence of
  river and the sea).

• Sediments if present in water in large amounts
   – May block sunlight to submerged plants
   – Can carry pesticides and other pollutants through the
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    Where are these mems devices
             attached ?
The MEMS devices, in marine
sensing maybe attached to:
• Ships
• Floating devices (buoys) in
  the sea
• Fixed sea structures (like
  oil rigs)
• Sea bed using links
• AUVs

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   AUV ( Autonomous underwater vehicle )
• AUVs are unmanned
  underwater vehicles for real
  time monitoring in the oceans.

• AUVs can be equipped with
  “Lab on a Chip”, a set of
  sensors developed on a single

  chip, using MEMS.
                                                    “ Lab on a Chip”

• These “Lab on a Chip” devices
  can sense a large number of
  chemical pollutants


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  Mems in oil exploration and related applications

                                                               • To find potential oil reserves
                                                               • To detect oil leakage from
                                                               • In cases of unfortunate oil
                                                                   – MEMS sensors can help to
                                                                     sense information about the
                                                                     ocean currents.
                                                                   – Using this it is possible to
                                                                     predict how far the oil slick will         be transported.
                                                                   – This information can aid in
                                                                     clean up.

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    Finding potential oil and gas reserves
•   MEMS geophones and accelerometers can                         MEMS Accelerometer
    sense the vibrations sent up from the earth’s

•   An array of MEMS geophones are planted over a
    wide area on the seabed.

•   Vibrations are intentionally produced on the
    ground surface using some techniques.

•   The MEMS devices measure the reflection of
    these waves from different layers in the earth’s

•   These readings are then used to create a
    geological map, which indicates the size and
    location of the oil/gas reservoir.

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    Role of mems in coastal weather monitoring

≈ MEMS sensors can provide vital information about wave
  pressure, temperature, tidal and current velocity (using
  devices like the MEMS Doppler current profiler).

≈ The information obtained can be used to develop maps
  indicating the distribution of these parameters throughout
  the ocean.

≈ These maps can provide accurate data, regarding any
  imminent sea storms, tsunamis (large sea waves caused
  due to large scale movements inside the earth’s

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                     Hydrophones                         ))))

• Just as microphones collect sounds in air, hydrophones are small
  devices that detect sounds in water.

• The sources of sounds in water maybe ships, earthquakes, waves or
  marine animals.

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           Digital mammal tags
• These are tiny devices attached
  to animals like whales, sharks,
  dolphins etc..
• Provides vital data about the
  animal and its surroundings
• A tag houses
   – Pressure sensor(s)
   – Temperature sensor(s)
   – Hydrophone (sound sensor)
   – Radio transmitter for data
      collection at remote
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        MEMS in marine military operations

•   An array of MEMS sensors spread on the ocean floor could detect the
    presence of enemy submarines.

•   MEMS sensors (pressure sensors, accelerometers etc.) are being used in
    anti-torpedo weapons on submarines and ships.

•   MEMS sensors in torpedoes are responsible for
     – Detonating the torpedo at the right time
     – Hitting the target in a crowded environment
     – Prevent any premature explosion

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    Challenges for MEMS sensors in
          marine environment
• Complex nature of marine environment

• Fouling of sensor surfaces

• Selecting one out of several species

• Should be able to detect extremely low levels of
  chemical concentrations

• Resist drifting along with the currents

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         Future of mems in marine
• MEMS promises to be an effective technique of producing
  marine sensors of high quality, at lower costs.

• The use of fiber optics in marine science offers several
  avenues in fabrication and packaging of sensors.

• The use of sensor dust in the oceans in the coming years,
  would be the best that this technology could offer.

                                    Shekhar Bhansali
        The BIG question
“ Is MEMS really necessary?”
 – Still in nascent stage to be applied
 – Research in this area is important, as it
   probably is the future

                          Shekhar Bhansali
This effort is based upon work partially supported by
the National Science Foundation under Grant No.
0239262 and The Florida Hi-Tech Corridor Workforce
Training grant
Any opinions, findings, and conclusions or
recommendations expressed in this material are
those of the author(s) and do not necessarily reflect
the views of the National Science Foundation or the
Florida HiTech Corridor Workforce Training Grant.

                            Shekhar Bhansali
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