Low Power Energy Harvesting

1
Low Power Energy Harvesting An Enabling
Technology for Maintenance-Free Wireless
Devices J. Choi, A. Dolgov, E. Falkenstein, T.
Paing, R. Zane, Z. Popovic Colorado Power
Electronics Center, Electrical and Computer
Engineering Department University of Colorado at
Boulder, USA
System Overview
Wireless Power Sources
RF Power
Other Sources
Wireless PowerSources

• Thermogenerator
• Devices by Micropelt provide 27 µW of power with
  temperature gradients as low as 12 oC. This is
  equivalent to the difference between core body
  temperature and room temperature.
• Similar to the RFrectenna, the themo-generator
  achievespeak-power with aconstant resistive
  load.

• RF Rectifying antenna (Rectenna)
• Power is delivered bylow-power multipath radio
  waves in the farfield.
• This power is received by an antenna integrated
  witha rectifier to provide DCpower to a load.

Radio Frequency
Piezoelectric
Thermogenerator
Solar

• The antenna designs vary in size and shape with
  desired input power level and radio wave
  frequency.
• Rectenna powercharacteristics indicate that a
  constant resistive load is optimal for peak-power
  harvesting.

• Power Management Unit
• Power Converter/Buffer
• Microcontroller

EnergyStorage

• Piezoelectric and Others
• Piezoelectric generators use vibrations to
  generate electrical power that can be harvested
  by a power management system.
• Inductive coupling also removes wires to power
  devices. Companies such as Splashpower,
  ConvenientPower LTD and MIT WiTricity design
  charging padsbased on this technology.

Thin-filmBattery
Ultra-Capacitor
Power Management
Applications
Resistor Emulation
Energy Harvester IC

• Power Converter
• Switching power converter provides maximum energy
  harvesting from wireless input source and
  delivers power to an energy storage element.
• The converter emulates a positive resistive load
  to the input source by operating in pulsed
  discontinuous conduction mode.

• Objective
• Efficiently harvest energy from input power
  levels below 10 µW.

Possible Applications
Sensor Prototype

• Motivation
• Wireless maintenance-free power is convenient and
  sometimes essential for many applications.
• Sensors in hazardous environments and low access
  areas benefit from the reduced maintenance
  requirement.
• Portable sensors and devices can be mademore
  lightweight and miniaturized withoutthe need for
  a battery pack.

• Onboard Sensors
• Motion from 3-axis accelerometer.
• Skin resistance from GSR sensor.
• Body temperature sensor.
• All three sensors controlled viaTexas
  Instruments MSP430microcontroller optimized
  forultra-low power operation.
• Average power consumption 5 µW.

Implanted neural sensor
CAD to Fabrication

• Converter control parameters (Q1 on-time t1,
  duty-cycle D1, low-frequency pulse rate k, and
  inductance L) are selected to optimize converter
  efficiency for a desired emulated resistance,
  Rem.
• Desired/optimal Rem for maximum energy harvesting
  may change with varying environment conditions.
  Thus an ultra-low power MSP430 microcontroller
  periodically adjusts converter control parameters
  and Rem accordingly.

Wearable sensor built into fabric (Textronics
Inc.)
Engine Wing Integrity Sensor
This work is co-sponsored by the National
Institute on Disability and Rehabilitation
Research (NIDRR) under U.S. Department of
Education grant H133E040019and the Coleman
Institute for Cognitive Disabilities.