motion energy harvesting: myths & opportunities seminar, sept 24, 2007 motion energy harvesting:...

NPL Seminar, Sept 24, 2007

Motion Energy Harvesting: Myths & Opportunities

Eric M. Yeatman

Department of Electronic & Electrical EngineeringImperial College London

Energy Scavenging

• Collecting energy available in the environment, wirelessly

• Wireless means freedom, mobility, simplicity• Wireless doesn’t just mean data!

Let’s get rid of this:

And this:

How Much Power?

Power station 100 megawatts

House 10 kilowatts

Person, lightbulb 100 watts

Laptop, heart 10 watts

Cellphone 1 watt

Wristwatch, sensor node 1 microwatt

Cellphone signal 1 nanowatt

Main Application Area: Wireless Sensor Nodes• self-contained and self-powered, mm-scale• large numbers of nodes, must be low maintenance

Biomedical Application: Body Sensor Networks• low data rates, short transmission range• on body or implanted

1 cc wireless sensor node, IMEC

Sensor Node Power Requirements:

• Sensing Element

• Signal Conditioning Electronics

• Data Transmission

Sensing Element

Simple signals - temperature, pressure, motion – require electrical power above thermal noise limit.

NT ≈ 10-20 W/Hz

For most applications, this is negligible.

For some, e.g. video, power is very high.

Signal Conditioning

Likely principal function: A/D Converter

Recent results: Sauerbrey et al., Infineon (’03)

Power < 1 μW possible for low sample rates!

16 bits/min.1 / min.16 bitsBlood oxygen

16 bits/min.1 / min.16 bitsTemperature

32 bits/min.1 / min.16 bitsBlood pressure

80 bits/min.10 / min.8 bitsHeart rate

Data RateRateDepthSignal

Data Transmission: Required Rates

Conclusion: average rates at or below 1 bit/s sufficient for many sensor types.

Data Transmission: Required Power

Conclusions:

Power independent of bit-rate for low bit-rate

-40 dBm (0.1 μW) feasible for body-scale transmission range

1000100101

Range (m)

Ideal free-space propagation

Typical indoorLoss exponent(3.5)

Figure: F. Martin, Motorola

Estimated Total Power Needs

• Peak power 1 – 100 uW

• Average power can be below 1 uW

Batteries: Present Capability

• 1 μW⋅yr for 0.1 cm3 battery feasible

• Not easy to beat!

• Useful energy reservoir for energy scavenging

Fuel-Based Power Sources

• Energy density much higher than for batteries, ≈ 10 kJ/ cm3

• Technology immature, fuel cells most promising

Micro fuel cell, Yen et al.Fraunhofer Inst.

Magnetic (induction)Piezoelectric Electrostatic

KineticVolume flow (liquids or gases)Movement and vibration

Magnetic induction (induction loop)Antennas

Magnetic and Electro-magnetic Electro-magnetic waves

Thermoelectric or Heat EngineThermal Temperature gradients

Solar CellsLight Ambient light, such as sunlight

Conversion MechanismEnergy Source

Energy Scavenging : Sources

Solar Cells

• highly developed

• suited to integration

• high power density possible:

100 mW/cm2 (strong sunlight)

• but not common:

100 μW/cm2 (office)

• Need to be exposed, and oriented correctly

Solar cell for Berkeley Pico-Radio

Heliomotes, UCLA

Thermo-Electric

• need reasonable temperature difference (5 – 10°C) in short distance

• ADS device ≈ 10 μW for 5°C

• even small ΔT hard to achieve

Heat engine, Whalen et al,

Applied Digital Solutions

US Dept of Energy

Seiko Thermic

Ambient Electromagnetic Radiation

Graph: Mantiply et al.

≈ 10 V/m needed for reasonable power: not generally available

Body Sensor Nodes : Power Scavenging

• Light not generally available

• Temperature differences small

• Motion sources attractive

• Body motion or organ motion (heart, lungs)

• Inertial scavenging safest method

Motion Energy Scavenging

• Direct force devices

• Inertial devices

Direct Force: Heel Strike

Heel strike generator: Paradiso et al, MIT

Body Motion Power Sources

• Low and varying frequency (1 – 10 Hz)

• Large variation in amplitude

Body Sensor Size Limits

• Below 1 cc desirable

• Less for implanted nodes

y = Y cos( t)o ω

damper implements energy conversion

Available Power from Inertial Scavengersassume:• source motion amplitude Yo and frequency ω• Proof mass m, max internal displacement zo

y = Y cos( t)o ω

damper implements energy conversion

Available Power from Inertial Scavengers

• Peak force on proof mass F = ma = mω2Yo

• Damper force < F or no movement

• Maximum work per transit W = Fzo = mω2Yozo

• Maximum power P = 2W/T = mω3Yozo/π

1 10 100frequency (Hz)

How much power is this?

Plot assumes:

• Si proof mass (higher densities possible)

• max source acceleration 1g (determines Yo for any f)

10 x 10 x 2 mm

3 x 3 x 0.6 mm

Performance Trends – progress with time

1996 1998 2000 2002 2004 2006

electromagnetic electrostatic piezo

1996 1998 2000 2002 2004 2006

Imperial

UC Berkeley

1996 1998 2000 2002 2004 2006

electromagnetic electrostatic piezo • There is an upward trend

• No particular correlation of performance with transducer type

• All of the normalised power values are low – there is room for improvement

Performance Trends – as a function of volume

0.01 0.1 1 10

volume (cc)

• There is an upward trend – easier to make a large device than a small device

• No particular correlation of device volume with transducer type

Performance Trends – as a function of frequency

1 10 100 1000

frequency (Hz)

electromagnetic electrostatic piezo • Downward trend –parasitic damping becomes more dominant with increased frequency

• No particular correlation of transducer type with operating frequency

How does this compare to applications?

Plot assumes:

• proof mass 10 g/cc

• source acceleration 1g

100000

0.01 0.1 1 10 100 1000

volume (cc)

f = 1 Hzf = 10 Hz

How does this compare to applications?

Plot assumes:

• proof mass 10 g/cc

• source acceleration 1g

100000

0.01 0.1 1 10 100 1000

volume (cc)

f = 1 Hzf = 10 Hz

Sensor node

cellphone

laptop

Implementation Issues: Resonance

Why use resonant device?• Allows use of full internal range for low Yo

Why not use resonant device?• For body sensor application, Yo > zo likely • Low resonant frequency hard to achieve for small device• Varying source frequency bad for resonant devices

Response Comparison: Harmonic Drive

Resonant devices better for large generators / small displacements, but only if operated near resonance

Non-resonant good for high displacements, wide input frequency ranges

Response Comparison: True Body Motion

• Non-resonant device wins for small generators

• Data obtained in collaboration with ETH Zurich (T. von Buren)

Implementation Issues: Mechanism

Piezoelectric?• Difficult integration of piezo material• Possible leakage time issues for low frequency use

Electromagnetic?• Needs high dφ/dt to get damper force (φ = flux)• dφ/dt = (dφ/dz )(dz/dt )• Low frequency (low dz/dt) needs very high flux gradient• Efficiency issues (coil current)

Typical Inertial Generators

Piezoelectric

Ferro solutionsWright et al, Berkeley

Typical Inertial Generators

Magnetic

Southampton U. CUHK

Implementation Issues: Mechanism

Electrostatic?• Simple implementation, no field gradient problem• Damping force can be varied via applied voltage• But needs priming voltage (or electret)

Chosen Approach: Constant Charge

Input phase Output phase

inputinputVCQ = outputoutputVCQ =

inputoutput

inputouput V

outputoutputinputinputouputoutput VCVCVCE ≈−=Δ

inputoutput VV >>

Electro-mechanical Design

Top plate (silicon)

Base plate (quartz)

Input phase

Output phase

Polyimide suspension

Buck converter

Assembled generator Detail of deep-etched moving plate

Prototype MEMS Device

Device Operation

trajectory of moving plate

t2 t3t1

voltage on moving plate

upperlimit

lower limit

moving plate/ proof mass

fixed plate

discharge contact

charging contact

Output > 2 μW

Power Conditioning Circuit: Challenges

Power convertorefficiency is highly sensitive to parasitics!

Other Options: Rotating Mass

Example #1: traditional self-winding watch

Example #2: Seiko Kinetic

Large Inertial Generators

Backpack: U Penn

• 7 watts!

Large Scavenging Applications

East Japan Railway Co.

• Energy scavenging ticket gates

How else can rotating motion be used in inertial generation?

Proposal: Gyroscopic power generation

Gyroscopic power generationCan also be implemented in silicon!

Georgia Tech / u Mich

Motion Energy Harvesting for Sustainability• Power levels modest – energy saving not key motivator

• Human powered – mW levels likely practical limit

• Battery elimination: yes, except need local storage

• Pervasive sensing: major possibilities for efficient buildings, machines, processes

Motion Energy Harvesting for Sustainability• Power levels modest – energy saving not key motivator

• Human powered – mW levels likely practical limit

• Battery elimination: yes, except need local storage

• Pervasive sensing: major possibilities for efficient buildings, machines, processes

• [ plug: Imperial College Centre for Pervasive Sensing ]

Interaction with Energy Source• Typical energy scavenging implies no significant effect on

source

• i.e. effectively infinite source, power limited only by scavenger

• Otherwise not really “scavenging”

• In practice, loading of source at least power level extracted

• Alternative: collecting wasted power

• Key example: combined heat and power (CHP)

Conclusions• Power levels in the microwatt range are enough for many

wireless sensor nodes

• Inertial devices driven by body motion can achieve these levels

• Nonlinear devices are suitable for low and variable input frequencies, and for high displacement to device size ratios

• Prototype devices have been demonstrated at useful power levels

• Future challenges include associated power electronics

Thanks to:

at Imperial:Andrew Holmes, Paul Mitcheson, Tim Green

others:Joe Paradiso, MIT

Paul Wright, UC BerkeleyThomas von Büren, ETH Zurich

Contact me:e.yeatman@imperial.ac.uk

www.imperial.ac.uk/ee

motion energy harvesting: myths & opportunities seminar, sept 24, 2007 motion energy harvesting:...

Documents

verification 2015-2016 betty yeatman mississippi state...

what is rainwater harvesting? rainwater harvesting for ......

cei william yeatman, darin bartram, justin schwab: comments...

rainwater harvesting regulations -...

energy harvesting with polymers, ferroelectrets and ... ·...

anishinaabe mino-bimaadiziwin - cultural myths, cultures...

“myths misconceptions” -...

yeatman square historic district

pan-gaean flood myths: gondwana myths -- and beyond

ted yeatman: tennessee wild west: 7thcalvary at nashville...

embedding legal research skills - sarah crofts and lucy...

cotswold renewable seminar 2010 owen yeatman. biogas-nord uk

ted yeatman: tennessee wild west: 7th cavalry at nashville...

acne dr josephine yeatman 154 grimshaw street greensborough...

yeatman thesis

rainwater harvesting and utilisation rainwater harvesting...

anaerobic digestion for profitable farming and environmental...

w[1].c. sellar and r.j. yeatman - 1066 and all that - v1.0

aa intermediate unit 3 extended brief 2010/11 ·...

teaching research skills to law students: a case study from...