Group 9 Energy Harvesting

1
Group 9 Energy Harvesting
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Week 4 Agenda

• Project History
• Gantt Chart
• Upcoming Plans
• Technical Brief
• Piezoelectric Transducer Circuit Overview
• Testing Methodology and Results
• Energy Storage Device Selection

3
Tasks Accomplished

• Goal Design a non-solar energy harvesting system
  for use with wireless mesh network motes
• Received 20 piezoelectric transducers from MSI
• Created energy harvesting circuit utilizing all
  20 transducers in parallel
• Added voltage rectification to the circuit
• Tested energy harvesting circuit on a shaker
  table
• Conducted geophone testing on shaker table and in
  environmental conditions

4
Gantt Chart
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Energy Harvesting Block Diagram
Designed Testing Piezoelectric Board
AC Rectifier Currently being Designed
Charge Controller Voltage Regulator
Capacitor vs. Li-Ion
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Energy Harvesting Circuit Design
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Shaker Table Testing

• Single Axis Vibration Table
• Designed for Quality Assurance Testing of
  components
• Powered by HP Function Generator inline with
  power amplifier
• Vibration Amplitude and Frequency tunable
• Used Geophone and Labview to display vibration
  waveform

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Testing Methodology

• Oriented piezoelectric circuit to maximize
• output
• Bolted circuit to vibration table to
• minimize damping
• Adjusted frequency and vibration
• amplitude using
• function generator
• Used DMM to measure
• output voltage
• Geophone used to
• measure vibration
• amplitude

9
Test Results

• Charge Generation via Vibration Table
• Approx .4 - .5 V output, 1 uA of current
• Only AC magnitude could be measured
• Initial complications
• Transducers did not sway as much as initially
  estimated (will be changed by adding weights)
• Voltage too low to overcome Vt of rectifier
  diodes
• AC output too weak to hook up to the Geophones
  A/D Converter (amplifier circuit needed)

10
Vibration Table Testing

• 10 Sets of Data Collected
• Calculated relationship between force and
  increasing frequency (decaying exponential)
• Regressed formula for ratio of input voltage to
  force (quadratic)
• Can be used in tandem to calculate the force
  being applied to the transducers on the table
• Best waveforms existed between 20 and 50 Hz, with
  frequencies above 60 Hz showing marked beating
• Highest force recorded of approximately .05 Gs
• Mide Transducers operate optimally at .25 Gs

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Geophone Testing
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Geophone Testing
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Energy Storage Solution

• Battery storage control IC is impractical
• 300 mW power dissipation!
• Initial 200 uA system would not power this device
• Li-Ion Battery requires too much charge for the
  vibration transducers
• Capacitor storage system chosen for
  implementation
• 50 mA for 5 Seconds _at_ 3.3 V
• gt 100 mF required for initial cycling conditions
• Passive switch and regulating diode required for
  charge control

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Next Week

• Continue testing of piezoelectric circuit
• Make modifications to Transducers Rectifier
• Continue testing environmental locales
• Implement capacitor storage system with voltage
  regulator and charge control switch
• Order more MSI piezoelectric transducers, and
  charge storage components
• Continue documentation