elec6076 wireless sensor networks - tan

Tristan Brillet de Cande – [email protected]

Wireless Sensor Net-works:

Energy sources

ELEC6076

2

Issues

• Scaling down in size and cost of CMOS electronics has far outpaced the scaling of energy density in batteries

• Battery are now quite big and expensive• Limits the lifetime of the device• And its versatility

Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks

3

Plan

StoreDistributeScavengeStandards consumptionConclusion


4

Store AvailableIn development


Energy reservoirs: Available• Primary batteries are used in

Wireless networks• Secondary batteries could be

used in 2 cases:• Recharged by a primary

battery => too expensive to use both on each node

• Recharged by scavenging devices (solar cell, wind mill, etc)

Primary battery chemistries

Zinc-air

Lithium

Alkaline

Energy(J/cm3)

3780 2880 1200

Secondary battery chemistries

Lithium

NiMHd

NiCd

Energy(J/cm3)

1080 860 650

5

Store


Energy reservoirs: In development• Micro scale batteries• Micro fuel cells• Ultracapacitors• Microheat engines• Radioactive power sources

Material

U238 Ni63 Si32 Sr90 P32

Energy(J/cm3)

2.23x1010

1.6x108

3.3x108

3.7x108

127x109

• Extremely high energy densities• Serious health hazard• highly political and controversial topic.• Very bad efficiency at the moment (4 X 10-6)

• low cost per joule, high energy density, abundant availability, storability, and ease of transport.

• Long lifetime• Complex• Limited in downsizing• Huge heat rejecting due the low

efficiency (10%).

• Good lifetime• Short charging time• High power density• Energy density still 1 to 2

orders of magnitude lower than batteries

• High energy density• Simple• High temperature required• Difficult to reduce because of temperature

• 2D or 3D structure• Better energy density for 2d but

higher power density for the 3d• Difficult to maintain a

microfabricated structure that contain aqueous electrolyte

• Complex• Non uniformities in the supply

=> bad reliability and cycle life

AvailableIn development

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DistributeElectromagnetic Power DistributionWires, acoustic, light


Electromagnetic Power DistributionCommon but ineffective

𝑃𝑟=¿

𝑃0 𝜆 2

4Π 𝑅2 ¿

“If we take basic datas:R=5m, =1W f=2,4-2,485 GHzThen Pr=50 , which is barely useful”

BUT in indoors, it’s more likely

So not enough to power a dense network of wireless devices

R is the distance between transceiver and receiverP0 is the transmitted power is the wavelengh of the signal (1/f)

𝑃𝑟=¿

𝑃0 𝜆 2

4Π 𝑅4 ¿

7

DistributeElectromagnetic Power DistributionWires, acoustic, light


Wire, acoustic, lightAll of them are inappropriate

“100dB sound wave => only 0.96 W/cm2 power level”

Wired: No wireless sensor network anymore

Acoustic wave: Too low power density.

Light => laser: Too complex and not cost effective

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Scavenge


• Photovoltaic• Temperature

gradients• Human power• Wind• Pressure variations• Vibrations

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Scavenge


• Photovoltaic• Temperature gradients• Human power• Wind• Pressure variations• Vibrations

Photovoltaic

Output voltage we want/Stable DC Voltage/Simple conditioning to the battery

But need to control the charging profile through more electronic => more consumption

Conditions

Best technology

Density of light

Efficiency

Power available

Day light(indoors)

Single crystal silicon solar cells

100 mW/cm3 15% 15 mW/cm2

Artificial light(outdoors)

Thin film amorphous silicon

100 μW/cm2 10% 10 μW/cm2

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Scavenge



Temperature gradientEnergy provided by the difference of temperature of a material.Carnot efficiency

(e.g 3.3% for 10ºC above the reference temperature)

Maximum amount of power

Last research has leaded to a thermoelectric generator which produced 40 μW (=5 ºC, area=0.5cm2 Vout=1V)

k is the thermal conductivity of the materialL is the length of the material

“With ºCK= 140 W/mK

(silicon)L=1 cm

Q‘=7 W/cm2 so 11m W/cm2 with

Carnot efficiency”

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Scavenge



Human power• 10.5 MJ of energy per day

(121 W)• Most energy rich and most

easily exploitable source occurs at the foot during heel strike and in the bending of the ball of the foot

“Watch working with the kinetic

energy a of swinging arm and

the heat flow away from the surface of the

skin”“MIT research has lead to the development of

piezoelectric shoe inserts capable of

producing an average of 330 μW/cm2 while a

person is walking. ”

Impractical and not cost efficient to wind up each node

How to get the power from the

shoe to the wireless sensor network?

12

Scavenge



Windpotential power from moving air

• Power densities from air velocity are quite promising

• Hard to get it small• No work has been done on

it yet

P is the powerρ is the density of air (1.22 kg/m3)A is the cross sectional areav is the air velocity

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Scavenge



Pressure variationsCould work with • a change of atmospheric conditions

• And a change of temperatures

ΔE is the change in energyΔP is the change in pressureV is the volume

m is mass of the gasR is gas constantΔT is the change in temperature

Metric Theoretical power density/day

Difference in atmospheric conditions

7.8 nW/cm3

Difference of temperatures

17 μW/cm3

No work has been done on it yet.

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Scavenge



VibrationsThere are vibrations everywhere from 60 – 200 Hz and 1 – 10 m/s2

P is the power outputm is the oscillating proof massA is the acceleration magnitude of the input vibrationsω is the frequency of the driving vibrationsζm is the mechanical damping ratioζe is an electrically induced damping ratio

Power density vs Vibration amplitude

• Electromagnetic, electrostatic and piezoelectric• Competitive compared to the other power

scavenging sources (100 mW/cm3)• Self tuning generators are necessary if we want to

stick to varying frequency of the input vibration• Needs a significant amount of conditioning =>

more power electronic needed• Still not very stable• Energy reservoir could be a capacitor

“Example:Piezoelectric converter of 1 cm3

P= 200 μWVibration : A= 2.25 m/s2, f=120 Hz”

1. P is proportional to the oscillating mass of the system.

2. P is proportional to the square of the acceleration amplitude of the input vibrations.

3. P is inversely proportional to frequency

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Design consumption


The energy consumption depends on Network topologies:

1. Star topology: consume less2. Hybrid Star-Mesh topology: good compromise3. Mesh topology? consume more for the nodes

implementing the multihop communication

Standards1. IEEE802.15.4 (as ZigBee) 1 mW2. IEEE802.15.1 and .2 (as Bluetooth) 10 mW3. IEEE802.11.x (as Wifi) 100 mW

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Conclusion

Nadège Barrage – ELEC6076 – Wireless Sensor Networks

The widespread development of WSNs in the future depend on the development of small, cheap and long life node power sources

There won’t be one unique alternative power source which will solve all WSN’s power issues, but many attractive and creative solutions do exist that can be considered on an application-by-application basis

Low power systems are absolutely necessary

17

Sources

Internet: http://

microstrain.com/white/Wilson-chapter-22.pdf http://

nesl.ee.ucla.edu/fw/documents/reports/2007/PowerAnalysis.pdf

Nadège Barrage – ELEC6076 – Wireless Sensor Networks

http://microstrain.com/white/Wilson-chapter-22.pdf



http://nesl.ee.ucla.edu/fw/documents/reports/2007/PowerAnalysis.pdf



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Questions?

elec6076 wireless sensor networks - tan

Technology

low power density

ineffective6 tristan

costeffective7 tristan

material10 tristan brillet

versatility2tristan

cycle life5 tristan

scaling of energy density

density of air