elec6076 wireless sensor networks - tan
TRANSCRIPT
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
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
4
Store AvailableIn development
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
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
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
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
6
DistributeElectromagnetic Power DistributionWires, acoustic, light
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
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
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
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
8
Scavenge
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• Photovoltaic• Temperature
gradients• Human power• Wind• Pressure variations• Vibrations
9
Scavenge
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• 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
10
Scavenge
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• Photovoltaic• Temperature gradients• Human power• Wind• Pressure variations• Vibrations
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”
11
Scavenge
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• Photovoltaic• Temperature gradients• Human power• Wind• Pressure variations• Vibrations
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
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• Photovoltaic• Temperature gradients• Human power• Wind• Pressure variations• Vibrations
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
13
Scavenge
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• Photovoltaic• Temperature gradients• Human power• Wind• Pressure variations• Vibrations
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.
14
Scavenge
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
• Photovoltaic• Temperature gradients• Human power• Wind• Pressure variations• Vibrations
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
15
Design consumption
Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
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
16
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
18
Questions?