National Science Foundation IndustryUniversity Cooperative Research Center IUCRC

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National Science Foundation Industry/University
Cooperative Research Center (I/UCRC)
Autonomous Sensing VT-2 Site Director
Principal Investigator Prof. Rakesh K.
Kapania Prof. Dan Inman rkapania_at_vt.edu dinma
n_at_vt.edu Ph. 540-231-4881 Ph.540-231-4709
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• Primary Industry Partners
• Automotive
• Aircraft
• Civil structure owners
• Power plants
• Research Thrust Areas
• Applications of Structural health monitoring for
• Lose bolts, delaminations, corrosion, cracking
• Applications to remote wireless sensing

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What is Autonomous Sensing and how does it differ
from wireless sensing

• Autonomous sensing is wireless but also includes
• Self power
• Computing
• Decision making
• Adaptability
• Transmission
• Self diagnostics

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Most Structural Health Monitoring Require Known
Inputs As Well As Measured Responses

• This requires the transduction sensor to also
  have an actuation component
• This energy of excitation must be considered in
  designing an autonomous sensor system
• A nice fit to these requirements is the
  electrical impedance method

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The Properties of the impedance method making it
suitable for autonomous sensing are

• Not model based
• Qualitative approach to damage detection
• Uses small PZTs as co-located actuators and
  sensors
• Can be remotely controlled and automated
• High frequency excitation provides
• Detection of incipient structural faults, such as
  cracks or loose bolts
• Localized sensing area
• Insensitivity to changes in boundary conditions,
  loading, or operational vibrations
• Low excitation forces produce low power
  requirements

There are many other good methods in the
literature
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Impedance Based Methods Have a History of
Successes
Blades
Thermal Protection Tiles
Large Bolted Structures
Rail Track
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What is needed to make such systems autonomous?

• Harvested Energy
• Computing
• Wireless transmission
• Transducers
• And most importantly a synergy between these
  elements

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State of the Art Here is where we are now in
researching this idea.

• The basic building block has been developed
  around the impedance based structural health
  monitoring algorithm, reduced to a board and
  tested on laboratory structures under self
  powered operation.

NASA SBIR Phase II Extreme Diagnostics, Inc
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In order to reduce the required energy to levels
available from harvesting, the impedance method
is emulated with less power hungry computation

• The measuring path passes through the
• piezoelectric, an Opamp, and a comparator
• Differences between the paths are represented in
• terms of a variation count of the number of
• differences between the received reference path
• sequence and measuring path sequence at each
• frequency component
• An ensemble average of variation counts
• produces a signature
• The damage metric is calculated as a sum of
• absolute differences between the baseline and a
• signature through the frequency components

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By decreasing the core clock frequency, the power
is greatly reduced
A LED is used as a damage indicator if the
absolute sum of differences exceeds a set
threshold level The LED increases power
dissipation by 105 mW when lit At the lowest
core clock frequency, the prototype operates at
under 1 W
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Autonomous SHM hardware via a battery and
thermoelectric power harvesting

• A Powerizer 3.7 V, 170 mAh lithium ion cell
• (Li-ion) is used to operate the TMS320F2812
• 32-bit fixed point DSP evaluation board from TI
  
• With a fully charged cell, the prototype ran for
  57 minutes
• Four 3 x 3 x 0.36 cm Melcor R high temperature
  thermoelectric coolers with cooling fins are
  placed on a hot plate
• At a temperature gradient of 80 C, the battery
  is recharged in just over an hour, and could
  operate the prototype for about five minutes

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Milestones for the first year of the proposed
research

• Determine and implement a sensor failure
  diagnostic
• Determine a multiple sensor networking scheme and
  demonstrate this
• Clarify the sensing scales for available
  transducers in preparation of multiple scale
  structural monitoring

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The Vision for Future Years

• Adapt the autonomous sensor concept to a partner
  need
• Develop a multiple scale autonomous sensor system
• Develop a reconfigurable sensor system
• Develop a multiple physics sensor system
  (temperature, strain, flow)

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Other ongoing projects at CIMSS

• Energy Harvesting (AFOSR 06 MURI, U. Washington)
• Structural Health Monitoring (AFOSR 06 MURI,
  Arizona State)
• Structural Mechanics for Adaptive Optics
  (AFOSR/NA)
• Active Sensing (NSF, Extreme Diagnostics, Inc)
• Smart Control Sticks (ARL,Stirling Dynamics, Inc)
• Morphing Aircraft (AFR, AVID, Inc, Barron
  Associates)

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Autonomic Structures The way forward

• Autonomic structures and materials formed the
  topic of a recent workshop sponsored by the
  European Science Foundation, and the US funding
  agencies (NSF, AFOSR, ARO, ONR)
• While no clear definition emerged the following
  idea evolved
• An Autonomic Structure is a load bearing
  composite, multifunctional material structure
  capable of (i) sensing and diagnosis of threats,
  (ii) penetration prevention, (iii) load capacity
  preservation, and (iv) functionality restoration.
• Integrated systems that become more then sensing
  and monitoring and include
• Decision making
• The ability to react
• The ability to change physical configuration
• Our proposed research is a step in this direction