2. • 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
2 Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
3. Store
Distribute
Scavenge
Standards consumption
Conclusion
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4. Available
In 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 Zinc- Lithium Alkaline Secondary Lithium NiMHd NiCd
battery air battery
chemistries chemistries
Energy 3780 2880 1200 Energy 1080 860 650
(J/cm3) (J/cm3)
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5. Available
In development
Energy reservoirs: In development
• Micro scale batteries
• Micro fuel cells
• Ultracapacitors
• Microheat engines
• Radioactive power sources
•
• loworenergyjoule, highdensities
Extremely high energy energy density,
2D cost per density
Good lifetime
High 3D structure
•
• abundant availability, for 2d but higher
Simpleenergy density storability, and
Short charging time
Better
Serious health hazard
•
• ease of density for the 3d
power transport.
High power density
High temperature required
highly political and controversial topic.
•
• Long bad to reduce because of temperature )
Very lifetime still atatheorders of (4 X 10-6
Energy density
Difficult efficiency 1 tomicrofabricated
maintain 2 moment
• Complex that contain aqueous
magnitude lower than batteries
structure
• Limited in downsizing Material U238
electrolyte Ni63 Si32 Sr90 P32
• Huge heat rejecting due the low 2.23x1 1.6x108
Complex Energy 3.3x108 3.7x108 127x109
• efficiency (10%). in the supply => 010
Non uniformities (J/cm3) bad
reliability and cycle life
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6. Electromagnetic Pow
er Distribution
Wires, acoustic, light
Electromagnetic Power Distribution
Common but ineffective
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7. Electromagnetic Power
Distribution
Wires, acoustic, light
Wire, acoustic, light
All of them are inappropriate
Wired: No wireless sensor network anymore
Acoustic wave: Too low power density.
Light => laser: Too complex and not cost
effective
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8. • Photovoltaic
• Temperature gradients
• Human power
• Wind
• Pressure variations
• Vibrations
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9. • 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 Efficiency Power available
light
Day light Single crystal 100 mW/cm3 15% 15 mW/cm2
(indoors) silicon solar cells
Artificial Thin film 100 μW/cm2 10% 10 μW/cm2
light amorphous silicon
(outdoors)
9 Tristan Brillet de Cande – ELEC6076 – Wireless Sensor Networks
10. • Photovoltaic
• Temperature gradients
• Human power
• Wind
• Pressure variations
• Vibrations
k is the thermal conductivity of the material
L is the length of the material
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11. • Photovoltaic
• Temperature gradients
• Human power
• Wind
• Pressure variations
• Vibrations
Human power “Watch working with
• 10.5 MJ of energy per day (121 W) the kinetic energy a
• Most energy rich and most easily of swinging arm and
exploitable source occurs at the the heat flow away
foot during heel strike and in the from the surface of
bending of the ball of the foot the skin”
“MIT research has
Impractical and not cost efficient lead to the How to get the power
to wind up each node development of from the shoe to the
piezoelectric shoe wireless sensor
inserts capable of network?
producing an average
of 330 μW/cm2 while
a person is walking. ”
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12. • Photovoltaic
• Temperature gradients
• Human power
• Wind
• Pressure variations
• Vibrations
potential power from moving air
Wind
• Power densities from air velocity
are quite promising
• Hard to get it small
• No work has been done on it yet
P is the power
ρ is the density of air (1.22 kg/m3)
A is the cross sectional area
v is the air velocity
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13. • Photovoltaic
• Temperature gradients
• Human power
• Wind
• Pressure variations
• Vibrations
Pressure variations
Could work with
• a change of atmospheric conditions
ΔE is the change in energy Metric Theoretical power
ΔP is the change in pressure density/day
V is the volume Difference in 7.8 nW/cm3
atmospheric
• And a change of temperatures conditions
m is mass of the gas Difference of 17 μW/cm3
R is gas constant temperatures
ΔT is the change in temperature
No work has been done on it yet.
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14. • Photovoltaic
• Temperature gradients
• Human power
• Wind
• Pressure variations
• Vibrations
Vibrations
There are vibrations everywhere from 60 – 200 Hz
and 1 – 10 m/s2
“Example:
Piezoelectric P is the power output 3mass
converter of 1 cm
m is the oscillating proof
P= 200 μW A is the acceleration magnitude of the input vibrations
Vibration : A=m2.25 frequency ofdamping ratio
ω is the m/s2, f=120 driving vibrations
ζ is the mechanical
the Hz”
ζe is an electrically induced damping ratio
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 Power density vs Vibration amplitude
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16. 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
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