VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD

VTT Technical Research Centre of Finland Ltd

Energy harversting andtransfer

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ENERGY HARVESTING

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Why energy harvesting?

Why not batteries?Batteries are always empty, when needed.Batteries are un-reliable, on extra point-of-failure.In large installations battery management grows into an enormousburden.Batteries function poorly in gold environments.

Why not accumulators?They must be charged.They self-discharge, they are empty, if they are left for a longerperiod without charging.Their life-time is limited.

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Energy harvesting

Sources of energy that can be harvested:LightMovement (rotation, vibration …)Temperature differenceHydraulicsPneumaticsRadio-frequencies (rf)

Justification for implementation:Removing signal-cables is useless when power-cables stay!

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Energy harvesting, Light

Light is very usefulsource for energy-harvesting, especially indirect sun-shineIndoors other sourceshas to be usedBy cloudy weather,darkness or artificial lightpower density dropsdrasticallyDepends heavily onoperating environment ofa systemTable: Power densities of two solar cells in various environments.

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Energy harvesting, Temperature gradient

Theoretically even severalmilliwatts/cm2 can beachieved with temperature-difference of 10°CThis is the case in practice,too: 15-20°C temperaturedifference produced2mW/cm2 !Low voltage requires activerectificationHighly dependent onenvironment and usage ofthe harvester where it isinstalled in

Graph: Electrical power versus temperaturedifference using a Peltier-element.

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VTT Example: Energy harvesting from hotwater pipe

Modular design for scalablegenerators200mW output for 60 °Ctemperature differenceBulk element

New solutions with thin filmelements

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www.marlow.com

www.micropelt.com

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Energy harvesting, Vibration

Theoretically an idealenergy-source e.g. in avehicleDevelopment inpiezoelectric deviceseasies harvesting fromvibrationDepends mainly on theusage of a vehicle, not somuch on environmentused in

Graph: Acceleration versus time in two vehicles.

Graph: Acceleration versus frequency in two vehicles.

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VTT example: Narrow band vibration energyharvesting

Vibrating mass spring systemResonant structureMoving magnet type generatorControl and conversionelectronicsMax 10mW output on 50HzvibrationCharges internal battery+3.0V DC output voltageController power consumption:60uW

Magnets

Control and conversionelectronics

Coils

Figure: Narrowband vibrational energy harvester

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Sensors

PowerGenerator

Transmitter

Receiver

Fx

Fz

Generating supplypower with piezo filmMeasuring tyre strainwith the same filmFor energy efficiencyonly strain pulse widthand height are sentonce every rotation tocar receiver.Wheel load can beestimated by using thisinformation

Strain versus wheel load (20km/h)

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in(%

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VTT Example: Energy harvesting in a car tyre

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VTT Example: Wide band vibration energyharvester

Machine and automotive applications, P>1mW

Linear to rotation vibration converting harvesterFor wide band vibrationDemonstrator: P=30mW at 15 Hz, >10 mmpp

vibration.Converts 1D or 2D vibration to rotationCombined

energy harvestingenergy storageenergy managementbattery monitoringvoltage conversion

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Figure: Basic idea

Figure: VTT implementation

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Energy harvesting, radiofrequency/inductionEnergy can be harvested fromexisting sources (cellularnetworks etc.) but availableenergy is very lowEnergy can be transmitted usingradiofrequencies or inductionDoes not depend on the status ofthe vehicle(running/idling/stopped) nor onenvironment used inRF-levels needed for transmittingenough energy need probablyspecial licenses

Figure: RFID tag for longer distances.

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Energy harvesting, hydraulic/pneumaticpressure

Hydraulic motor and rotatinggenerator is the most obvioussolution for generating energyin a working machine of heavyvehicleEnergy is always availablewhen there is hydraulicpressure available (the engineis running)The amount of energy isadequateWell designed mechanicalconstruct lasts the wholelifetime of the working machine

Figure: Hydraulic motor and generator, schematic.

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VTT Example: Hydraulic harvester prototype

Figures: A prototype of a rotating, hydraulic generator for a forest harvester made by VTT.

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VTT Example: Energy harvesting forhydraulics

Converts pressure fluctuations to electricpower.Energy source for low power wireless sensorsin hydraulic systemNo fluid through flowPiezo generator with self powering SECEconverterPat. pend. ”Energy harvester”, #20116277 -Finland

0 10 20 30 40 50 60 70112

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0 10 20 30 40 50 60 700

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Pow

er(W

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Average power output, Pave = 1.1mW.

Pres

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Prototype15

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Energy Harvesting: Pros and cons+No power cabling!

+ No production breaks because ofdamaged cables

+ True WSN’s (Wireless Sensor Network)achievable

+No need for batteries!+ No battery replacement or charging!

+Less maintenance!+ Energy harvesters last through the whole

machine lifetime without maintenance- There is no universal solution

- Harvesting of the energy needs to bedesigned case-by-case

Figure: Ponsse Ergo forest harvester.

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WIRELESS ENERGYTRANSFER

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Wireless battery charging, standardization

Wireless Power Consortium WPChttp://www.wirelesspowerconsortium.com/charging power up to 5 W (=> 15W) with "Qi Low Power" specification already released,the main target application being mobile handsets

a lot of commercial products already availablecharging power up to 120 W with "Qi Medium Power" specification under preparation, themain target application being laptop computers

Alliance for Wireless Power A4WPhttp://www.a4wp.org/

Power Matters Alliance PMAhttp://www.powermatters.org/

NFC Forumhttp://www.nfc-forum.org/more information on the next slides

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Wireless battery charging over NFCA forthcoming add-on to NFC (Near Field Communication, see http://www.nfc-forum.org/) forcharging power transmission and charging power reception

Standardization activities started at NFC Forum Wireless Charging Task Force in February 2012.

Applicable to mobile phones and devices with lower charging power (see the figures below)

Main benefits over other wireless charging technologies:more compact and cost-efficient charging interface in portable devicesmore pervasive charger infrastructure with reduced costspossibility to integrate NFC-based services into charging applications

More information:Strömmer et al. "NFC-enabled wireless charging". Proceedings of NFC 2012. IEEE, ss. 36-41.4th International Research Workshop on Near Field Communication, NFC 2012, Helsinki, 13March 2012.Strömmer et al. "NFC-enabled wireless charging". Presentation at WIMA 2012 NFC conference,Monaco, 11 April 2012.Strömmer et al. "Novel wireless charging technology utilises existing NFC antennas and circuits".In: Uniting the physical and virtual - ICT solutions for open smart spaces. Ailisto, Heikki & Belloni,Kaisa (Eds.). VTT Research Highlights 7. VTT, ss. 35 - 40

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The relatively high (13.56 MHz) operating frequency of NFC (compared to theWPC Qi 110 - 205 kHz) favors use cases with relatively low charging power level.Still, charging power levels over 1 W are possible with close proximity between theantennas even within the RF field strength limit of the current NFC specification.Wireless charging over NFC will be rather a completing than a competing technology toWPC Qi specification.

NFC-compatibility won't increase the power level or improve the power efficiency.NFC-compatibility will improve the compactness and cost-efficiency of the entireimplementation (more detailed lists of benefits after examples of potential use cases).

VTT Example: Concept study & performance analysis ofwireless charging over NFC (2010 - 2011) – conclusions

Maximum charging power0.1 W 1 W 10 W

NFC Charging WPC Charging

100 W

"NFC low power" "NFC high power""Qi low power" "Qi medium power"

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Wireless charging of small NFC-enableddevices

Wireless battery charging over NFC– Use caseexamples

Delaying out of battery status &overnight charging of mobile handsets

Using NFC-enabled devices(e.g. a laptop) as wireless chargers

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Benefits of wireless battery charging over NFC

More compact and cost efficient wireless charging interface for small NFC-enabledportable devices

More pervasive charger infrastructure (based on existing NFC devices) with reduced costs(no dedicated chargers)

Extending battery discharging time of mobile handsets

Convenient overnight charging facility of mobile handsets

Possibility to integrate NFC-based service to charging applications

Benefits of 13.56 MHz over lower operating frequencies typically used in wireless chargingLighter antennasHigher frequency reduces parasitic heating of metallic stray objects (e.g. a coin that is forgottenbetween the charger and the device)

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VTT Example: Reference design & demonstration ofwireless power transfer over NFC

An RF solution integrating efficient wireless power transfer and NFC communicationtogether with a shared antenna.

Application examples:wireless charging of various NFC devices,wireless powering of battery-free sensors with communication and enhanced powersupply via NFC.

Block diagram and demonstrator prototype of the NFC-compatible wireless power transmitter

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Technology demonstration:inductive powering, telemetryand telecommand interface of abatteryless pill sized implantsensor

Powering of the sensorIntegrated data uplink &data downlink modulationMaximum operatingdistance: 10 mm

VTT Example: Wireless powering and datatransceiver of a pill sized implant sensor

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Based on inductive coupling betweenpower transmitter on the wheel supportand power receiver on the wheel

Continuous high efficiency contactlesspower transmission to rotating objects

Power transmission is independent ofrotation speed and works even to astatic wheel at any angle

A batteryless acceleration sensor with2.4 GHz radio communication as acase application

VTT Example: Wireless energytransfer to rotating wheels

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VTT Example: Inductive short distance link ofa ball-end controller

Technology demonstration: ball-end controllerIn a Ball-End handle weimplemented inductive energytransmissionData transmission wasimplemented using ZigBee radioData transmission can also bemade using inductive link

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