Use of Piezoelectrics to Create a SelfPowered Occupancy Sensor

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Use of Piezoelectrics to Create a Self-Powered
Occupancy Sensor

• Andrew Thornburg
• Advisor Dr. William Clark
• MSI Undergraduate Research Project Symposium
• August 2, 2007

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What is piezoelectric material?

• Transform mechanical strain into electrical
  charge1
• PZT used to convert energy from beam vibration
  into electric current

1 Sodano, Henry A., Daniel J. Inman, and Gyuhae
Park. "A Review of Power Harvesting From
Vibration Using Piezoelectric Materials." The
Shock and Vibration Digest 36 (2004).
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Research Conducted
Ultra Low Power Motion Sensor
Efficient Piezoelectric Harvester
Self-Contained Occupancy Sensor
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Harvester Design

• Use hinge rotation and gears to rotate mechanism
  for multiple beam excitations per opening

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Why is it important?

• Wasted energy!!
• Copper wiring installation and material costs
• Maintenance costs
• Could provide a cheap, easily installed waste
  reducer

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Previous Work

• Piezoelectric power generation2
• Use of rechargeable battery as storage
• Ultra low power motion detection3
• 9.37 ?A current possible _at_ 3.0 V
• 31 versus 33 poling4
• Use of mechanical advantage provides higher output

2 Sodano, Henry A., Elizabeth A. Magiula,
Gyuhae Park, and Daniel J. Inman. "Electric Power
Generation Using Piezoelectric Devices." Center
for Inteligent Materials and Structures.
3 Albus, Zach. "Ultra Low Power Motion
Detection Using the MSP430F2013." MSP430
Applications (2005).
4 Clark, W. and Ramsay, M. J., 2000. Smart
Material Transducers as Power Sources for MEMS
Devices. International Symposium on Smart
Structures and Microsystems, Hong Kong.
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Problems Encountered

• Sensor power requirements
• Microcontroller control via code/algorithm
• Low energy harvesting

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Energy Harvesting
Power requirements3
Power budget at 3 V for 1 hour
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Method

• Measured angular velocity of the door closing
  automatically
• Used a linear potentiometer and LabView to
  capture data

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Red - Potentiometer Voltage Blue - ? Voltage
Voltage (V)
Time (sec)
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Data

• Door takes 3.045s to close
• Avg ? of 0.516 rad/s (4.93 RPM)
• Max ? of 0.747 rad/s (7.13 RPM)

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Initial Testing

• Used a 4-armed slapper rotating at 24 RPM
• Connected to a DC rectifier circuit
• Measured voltage across a resistive load

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PZT
Aluminum
Four armed slapper
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Capacitor, 0.22 ?F
Resistor, varies
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Maximum Energy _at_ 3.3k ?
Energy (J)
Resistance (10k ?)
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Power (W)
Time (secs)
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• Inadequate power generation
• 78 door open/close per hour throughout an 8 hour
  day
• Increase frequency dramatically
• Increased excitation possible because of rapid
  decay of vibration

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Power (W)
Time (secs)

• Produced 0.0575 J per opening
• 6 openings per hour per work day

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How the sensor works
Microcontroller Analog/Digital converter
Outputs Voltage
Powered PIR sensor
If motion is detected
Trigger Lights
Compare digital conversion
Else
Wait for next conversion
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Sensor Voltage Offset, hand motion 9 above
sensor
Voltage (V)
Time (secs)
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Texas Instruments Microcontroller

• MSP430F2012
• 600 nA standby current
• Two separate clocks for low power designs

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eZ430-F2013 Development Tool

• USB interfaced tool
• Included target boards for implementation

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Analog/Digital Converter
Where Vin 0.400 V Vpos 1.5 V Vneg 0 V
(ground)
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Conclusion

• Application is feasible
• Use array or stack of PZT to generate necessary
  power
• Size of components can provide discrete wireless
  control

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Is it worth it?

• 75 savings per year per 1000ft2 5
• 11-15 annual savings 6
• Device as cheap as 10

5 "Automatic Lighting Control for Energy
Savings." Electric Ideas Clearinghouse (1992).
6 Atif, M R., and A D. Galasiu. "Energy
Performance of Daylight-Linked Automatic Lighting
Control Systems in Large Atrium Spaces Report on
Two Field-Monitored Case Studies." Energy and
Buildings 35 (2003) 441-461.
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Future Work

• Implement transceiver to control lighting
• Nordic nRF24AP1
• Additional current drain 2 ?A
• More robust application
• Dimming
• Task specific light settings
• With known average power generation of 10s of
  milliwatts, other applications can be tried

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Special Thanks

• Dr. Clark
• MSI
• Vibration and Control Lab Staff