Energy Harvesting for Mobile Computing
Joe Paradiso
Responsive Environments Group, MIT Media Lab
http://www.media.mit.edu/resenv
DCU 6/05
Source Material…
Chapter 45 in “Low Power Electronics Design,”
Christian Piguet, editor – CRC Press, Fall 2004
IEEE Pervasive Computing Magazine, February 2005
Systems for Human-Powered Mobile Computing J.A. Paradiso
To appear in Proc. IEEE Design Automation Conference (DAC), July 2006
Smart Sensors and HCI
• Electronics are cheaper, smaller, more capable, lower power...
– Intelligence, sensing, communication, processing…
• Move off desktop into "things” & environments
• Entirely different “input devices” & modalities enabled
Shift toward fine-grained, distributed interfaces
• Ubiquitous Computing (PARC/Weiser)
• Things That Think (ML)
• Disappearing Computer (EU)
• Invisible Computing (Microsoft)
• Pervasive Computing (IBM)
Sensing, communications, power management, context (AI) are key
Batteries
Batteries improve relatively slowly
• Can exploit other chemical reactions
–Fuel Cells
–Microengines
• Clever power management and
circuit design can reduce power
requirements
– Low voltage, clock scaling, large
feature size, adiabatic computing,
analog processing, keep everything off
Energy harvesting may become practical…
4/04
JAP
Solar Cells
iSun – 2 Watts
Media Lab’s Locust Position Beacon
Franhofer ISE Freiberg
1 Watt under halogen
20% eff.
• 10-20% efficiency for commercial modules
• Common polycrystalline Si modules are ~16-17% (mass produced,
cheap process, a few 1$'s a Watt total)
• Monocrystalline Si are a little closer to 20%.
• IC grade Si and fab processes, ~24% is possible but expensive.
• Stacked multi-junction cells, and cells using other materials and
structures get over 30% but are very expensive or still in the lab
– 10-100 mW/cm2 in bright sun
– 10-100 μW/cm2 in an office
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MIT-ML
An option if the light and area are there
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The Hat is an apt location…
Mainly Chillers
Ambient RF
• Power density ~ E2/Z0
Flashing Antenna Top
– (Field strength)2 over 377 Ohms
– Would like to see fields of 10 V/m at antenna
• 26 μW/cm2
– Not seen in typical urban environments
• Except close to cell phone transmitters
• AM Crystal radios yield under 1 mW (typically 20 μW) w. large
antenna and good ground.
Need large collection area and/or need to be very close to transmitter
Mickle et al (US Patent 6,856,291) - U. Pittsburgh - highly resonant regenerative
antenna with an effective cross section that is much larger than its geometric area
(perhaps by a factor of 1000 or more)
Beaming Power
Wireless humidity sensor
Bill Brown
Martinez, 2002
Microwave-powered helicopter, 1964
• Beaming power has a long history (Tesla, etc)
• Rectannas can approach 80-90+% efficiency
• Low power apps common in everyday environments
– RFID (chips use 1 to 100 μW)
• RF-powered sensors coming off the horizon
– Passive LC and SAW devices, sensor chips
– Wireless tire pressure and tire friction sensors
– Implantable sensors for monitoring in vivo blood pressure
RFID Tags
4/04
Human Energy Expenditure
JAP
People dissipate
between 1001000 Watts
Perhaps one can
steal Watt or
two?
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Where to Tap the Power
Caution: Thad’s
numbers tend to be
optimistic!
Watt-level available
Thad Starner, Human-Powered Wearable Computing, IBM Systems Journal 35, pp. 618-629 (1996).
In Vivo Fuel Cells
Adam Heller, UT Austin
• Extrapolating from electrochemical
detection of glucose (TheraSense)
– Adapt techniques for more power
– Make a sugar-burning bio fuel cell
• Composite electrodes and conductive gels
– Biologically transparent system
– Build into a vascular stent
– Generate electricity from glucose and O2 in
blood
• 1 cm long x 4 mm wide
• Can (theoretically) produce up to 1 mW
– 1-3 weeks of power from equal-size battery
• 1-2 μW for 1 week at a 0.5 V demonstrated in
2002 (in a grape)
• US Patent 6,531,239
• In-vitro low power or low duty-cycle
medical systems
– Low-bandwidth biosensors
– Valve for the incontinent
4/04
Thermal Powered Systems
JAP
• Carnot Efficiency for human body at 20° C
– 5.5% (drops to 3.2% at 27° C)
• Today’s thermopiles have <1% efficiency
for T of 5-20° C
• Body restricts blood flow to limit heat loss
at cold points on the skin
• A thermopile skullcap could make on the
order of hundreds of mW.
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Seiko SII Thermic® Heat-Powered Watch
1.7mm
2.14mm
1.27mm
2.14mm
2.36mm
Thermoelectric module
Thermoelectric unit
Thermal energy watch
Watch movement
Heat flow
Battery
Booster IC
arm
Adiabatic
case
Thermoelectric (Photo)
• Uses 10 Thermoelectric modules and a booster IC
• Runs off body heat
Low T, limited surface area, low efficiency -> Microwatts...
Thermo Life Generator
• Thermo Life Energy Corporation
– Applied Digital Solutions (Dr.Ingo Stark)
– Dense array of Bi2Te3 thermopiles deposited onto thin film
• Most efficient at temperatures of 0 to 100 degrees Celsius
• 10 μA or more @ 3 volts (6 V OC) when in contact with
the body (5°C T)
• 60 μW/cm2
• Thin film battery charging
– Front Edge’s NanoEnergy
• Medical monitor powering, biosensors
The ETA Autoquartz Self-Winding Electric Watch
The Swatch Group (SMH)
4/04
The ETA Autoquartz Mechanism
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MIT-ML
Proof Mass winds spring, which pulses generator
JAP
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The Autoquartz Generator Performance
Generator always run at
optimum rate (10-15K RPM)
Power stored on spring until
threshold is exceeded
Generator pulsed for 50 msec
Yields 6 mA at >16 Volts
~100 mW peak power!
Current integrated onto
capacitor
Seiko AGS System
KINETIC outline
diagram Oscillating weight
Oblique view
Oscillating
weight
Charge control
circuit
Oscillating
weight gear
Secondary
power supply
Gear train
Transmission gear
Drive circuit
Rotor
Stator
Coil
Stator
Rotor
Coil
• Proof mass oscillation directly cranks generator
– Little intervening mechanics
– Charge accumulated on capacitor
• Power Output:
– 5 μW average when the watch is worn
– 1 mW or more when the watch is forcibly shaken
4/04
JAP
Seiko Experimental AGS for Marine Mammals
• Uses watch AGS components
– Power Output is 5 to 10 mW
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Magnetic and Electrostatic Microgenerators
• Many, many devices in current literature
– Chandrakasan, Roundy/Wright, Mitcheson, El-Hamadi, James,Yates, Li,
Taishiro, Ching, Miyazaki, Goerge…
• Powers range 10’s-100’s of μW
• Most employ spring return
– Mechanically resonant, 10’s of Hz – several kHz
• Others use bistable action return w/o spring
– Mitcheson 2004 – broadband
• Magnetic generators can approach 1 mW
– 100-500 Hz, 25-200 μm motion, ~1 cm3
(court. Mitchenson)
• Electrostatic generators tend to produce 100 μW
– Simple to integrate onto MEMS
– Need bootstrap supply
– Constant charge (sliding) and constant voltage (pressing) modes
36 mW @ 12.6 kHz
Beeby et al
Southampton
6 μW @ 6 Hz
Miao et al
Imperial College
MEMs Driven Condensor Power Supply
84
mg
• MEMs motor in reverse…
–
–
–
–
–
Special power-control electronics designed & fabbed
8 μW indicated @ 2.5 kHz, 500 μm motion
Could tile for more power
Provides power for their sub μW “picoJoule DSP”
Vision of power, sensing, and processing on one chip
Anantha Chandrakasan, Jeff Lang - MIT MTL
Inertial Microgenerators (piezo)
• Ho, 1961
– Claimed 150 μW when
coupled to 80 Hz heartbeats
• Roundy & Wright, 2003
– PZT bimorph
– 100 μW when shaken at
resonance
– Building MEMs structure w.
80 μW per cm3 (@ 800 Hz)
– Berkeley group also making
tunable cantilevers
4/04
Microgenerator Performance
JAP
1 cm3 devices
•For human body motion (Hz-level excitation)
–Few μW/cm3
•For machine excitation (kHz-level excitation)
–Hundreds of μW/cm3
Tends to go as w3 and y02
Personal comm, Paul Mitcheson, Imperial College UK
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4/04
Shake-Driven Flashlights
JAP
Weighs150 grams and produces 200 mW with a steady shake at its
mechanical resonance (roughly 3.3 Hz) - 2 mW/cm3
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MIT-ML
Dual microgenerator in AAA form factor - 28 μW @ 70 Hz
Yuen et al, CU Hong Kong, 2005 (note that AAA battery would last 15 years)
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4/04
Commercial Microgenerators
JAP
The PMG7 is designed to resonate at mains
frequency (50 or 60Hz) with a bandwidth of
0.2Hz giving excellent performance on any
AC synchronous motor powered equipment.
Output is from 0.1mW to several mW power
depending on the level of vibration (eg up to
5mW at 100mg or 400μW at 25mg).
FerroSolutions, Cambridge MA
Perpetuum, Southampton UK
Both Magnetic
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4/04
Power Backpacks
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MIT-ML
Larry Rome, University of Pennsylvania, 2005
5 cm up-down hip movement from walking reacting
with 20-38 kg inertial load generated up to 7 Watts
JAP
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4/04
JAP
Heel Strike
120
Heel Strike
Toe Off
100%
Body Weight
Reaction Force (% of body weight)
100
80
60
40
20
0
0
0.1
0.2
0.3
0.4
0.5
Time (seconds)
0.6
0.7
0.8
0.9
• Force at heel strike and toe off exceeds 100%
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– Heel can compress by 1 cm – Watts possible?
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Power Harvesting Insoles - 1998
PVDF Stave
Molded into sole
Energy from bend
Ppeak 10 mW
<P> 1 mW
“Thunder” PZT
Clamshell Unimorph
Under insole
Pressed by heel
Ppeak 50 mW
<P> 10 mW
Raw Power
circa 1% efficient
Unnoticable
Responsive Environments Group
MIT Media Lab
1998 IEEE Wearable Computing Conference
Application: Batteryless RF Tag
• Use Piezo-shoes to charge up capacitor after several steps
• When voltage surpasses 14 volts, activate 5 V regulator
– Send 12-bit ID 6-7 times with 310 MHz ASK transmitter
• After 3-6 steps, we provide 3 mA for 0.5 sec
– Capacitor back in charge mode after dropping below output
Responsive Environments Group - MIT Media Lab
4/04
JAP
Rotary Magnetic Generator Retrofit
Responsive Environments Group - MIT Media Lab - 1998
• Attaches lever-driven flywheel/generator to shoe
- 3 cm deflection, bulky
- Suboptimal (e.g., better integration, hydraulics...)
• Produces a quarter watt average ( 1 W peak), but very obtrusive!
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Better Generator Integration
Jeff Hayashida’s BS thesis - 1999
• Mechanical generators entirely in insole
• Produces about 60 mW average power
• Use of a spring to store energy between footfalls can bring a Watt
• Mechanically complex and fragile…
Mechanical Boot Generators…
Barbieri, 1925
Chin, 1996
Lakic, 1989
Mainly foot warming
applications
Lakic, 1986
Landry, 2001
Trevor Baylis’
Electric Shoe
Company
• Piezoelectric “crystal” struck with each footfall
• Claims to generate 100-150 mW
• Used in walk across Namibian Desert, summer 2000
– Cellphone battery partially (e.g., <half) charged after 5 days of
walking
4/04
JAP
Passive Hydraulic Chopping to Excite PZT at Resonance
• Antaki, et al., 1995
– Passive hydraulic resonant excitation of
piezoceramic stack during heel compression
– Big, kludgy shoe
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MIT-ML
• Developed to power artifical organs
• Developed order of 0.2 – 0.7 Watt average power
• 2 Watts from simulated “jogging”
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4/04
JAP
Active Hydraulic Chopping at Heel Strike
• Heel compresses Hydraulic bladder by 8 mm
– μ-hydraulic transducers hammer PZT stack
– Many charge-pump cycles per footstep
– Piezo driven at resonance frequency (20 kHz)
• PZT generators occupy 1-cm cube
– Each produces a watt
• 40% efficiency
8 mm
– 3 per shoe gives 3 watts total
• Components Tested
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MIT-ML
– Fully integrated?
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4/04
Dielectric Elastomers under the heel
JAP
2-4 mm
• Electrostatic generator with silicone rubber or flex
acrylic elastomer between the plates
–
–
–
–
–
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MIT-ML
Placed under heel
2-4 mm of squeeze gives 50-100% area strain
4 kV across them!
Saw 0.8 Watt per shoe (2 Hz pace, 3 mm deflection)
Estimate that 1 Watt is possible with more deflection
Ron Pelrine, Roy Kornbluh - SRI International
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Commercial Active Power Generation
Cranking and Shaking
• 60 turns (1 min) stores 0.6 Watt-hr
• 40% efficient
• Today’s laptop supply roughly 30-50 W-hr
• 1 hour of more of winding (w. heavy spring!)
150 g, 200 mW, 2 Hz
Freeplay (Baygen)
• Innovative Technologies Sidewinder
• 80 g, 2 mins cranking gives >6 mins cellphone talk
4/04
Windup Flashlights in History
VanDeventer, 1916
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MIT-ML
Mining applications…
Luzy, 1922
JAP
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4/04
Nissho Engineering (AladdinPower)
AladdinPower
Squeeze
1.6 W, 1.5 Hz
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MIT-ML
Tug Power
Pull ring to spin flywheel & generator
80 g, 2.5 W
JAP
Step Charger
6 Watts
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$100 Laptop (OLPC Foundation)
Computing for every child on the planet
Power & networking are main technical challenges
New display, efficient electronics and software aim at ~1 Watt
Cheap environmental power needed as infrastructure is unreliable
Originally crank, now pedal doubling as power xformer or dual pulchain, etc.
4/04
The Electric Bolo
JAP
• Saul Griffith (MIT Media Lab)
• 100-200 g proof mass, .3-.5 meter radius, 1-2 Hz rate
• Claims approx. 3-5 Watts...
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Self-Powered Buttons
Johnson, et al., Transmitter Circuit,
US Patent No. 3,796,958, March 12, 1974.
Zenith ‘Space Command”
Crisan, A. (Compaq), Typing Power,
US Patent No. 5,911,529, June 15, 1999
Pipi "Kodomo No Omocha" pager toy
4/04
JAP
Self-powered buttons
Strike Occurrence
14
Tank Capacitor Voltage
12
Voltage (V)
10
3 Volt Regulator Output
8
Spring 2001
6
Serial ID Code
4
2
434
412
390
368
346
324
302
280
258
236
214
192
170
148
126
104
82.4
60.4
38.4
16.4
-2
-5.6
0
Time (msec)
• ~0.5 mJ at 3 Volts per push
• Sends 12-bit RFID 12 x throughout floor (50 ft.)
• No need for battery, wire…
Mark Feldmeier
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4/04
JAP
Cleaner Prototypes
CES Show - 2004
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EnOcean device
uses bistable PZT
bimorph cantilever
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4/04
Power Harvesting – Wireless, Batteryless Window Switch
with ALPS Automotive
JAP
• Command window up-stop-down
• No battery, no wire
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MIT-ML
– Power harvested from single push
– Eliminate need for complex wire harness
Mark Feldmeier
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AES Roadmap
“
Mobility in Sensor Networks
• Forefront research where sensor nets meet robotics
and control
• Sensor clusters move to places to optimally:
–
–
–
–
Measure dynamic phenomena
Position relays to repair or patch broken network
Dump information at access points (portals)
Get recovered or recharged
What does power harvesting
mean in a mobile system?
Energy cost of moving atoms is much
higher than moving bits…
Parasitic Mobility in Sensor Networks
Implications
- Sensor clusters hitch rides to places
where they need to be to optimally:
- Measure relevant phenomena
- Relay information peer-peer
- Dump information into portals
- Get recovered or recharged
- Rapid diffusion of sensors across an environment
- System self-organizes to auto-dispatch nodes to desired regions
Innovations and Architecture
- Interpretation of Energy Harvesting in mobile networks
- Two flavors:
- The Tick (e.g., jumps onto a car, attaches magnetically, then disengages)
- The Bur (e.g., sticks to passing object, then shakes off)
- Contains GPS, RF, basic sensor suite
Phoresis
Paradiso & Laibowitz
4/04
Parasitic Mobility Research (ParaMoR)
•
•
•
•
JAP
Paramor Hardware – small nodes
with sensor suite (light, microphone,
inertial, proximity, temperature,
heat), GPS, RF communication,
rechargeable power source, and
minimal actuation for
attachment/detachment
Active nodes (ticks)
Passive nodes (burs)
Value-added nodes (pens)
Active Node
• ParaSim – Software
simulator to study behavior
and evaluate control
algorithms for parasitically
mobile sensor nodes
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MIT-ML
Passive Node
Mat Laibowitz
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4/04
JAP
Symbiotic Node Tests
Node 7
Only
Light
Accls
Zone #
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4/04
Power Harvesting Summary
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JAP
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4/04
JAP
Summary
•
•
•
•
•
•
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MIT-ML
Human-Powered Systems
Environmental energy μw-W
Biofuel cells μw
Thermal conversion μw
Inertial energy harvesting μw - mW
Heel strike generators mW-W
Deliberately Powered Systems W
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4/04
Humanity’s Destiny?
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JAP
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4/04
JAP
Resting Humans are dim bulbs (100 W)
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MIT-ML
They will use us in more creative ways...
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