9/9/2010 1 Jordi Agustí Batlle Departament d’Enginyeria Electrònica Universitat Autònoma de Barcelona Spain [email protected]RF energy harvester based on MEMS NiPS Summer School 2010 Summer School: Energy Harvesting at micro and nanoscale, August 1‐6, 2010 NiPS Workshop: Noise in dynamical systems at the micro and nanoscale, August 6‐8, 2010 La Tenuta dei Ciclamini, Avigliano Umbro (TR) - Italy 07/08/2010 J. Agustí 2 Outline Jordi Agustí • Introduction to Energy Harvesting • Research background of our group • RF energy harvester based on MEMS RF-MEMSTENNA concept Fabrication process Prototype test methods
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Electrostatic transducers, Piezoelectric transducers, Electromagnetic transducers and Thermoelectric transducers
Thomas, J., M. Qidwai, and J. Kellogg, Energy scavenging for small-scale unmanned systems. Journal of Power Sources, 2006. 159(2): p. 1494-1509.
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Research background of our group
Extracted from G. Murillo STIMESI Workshop talk.
2000 2002 2004 2006 2008 2010Date (years)
Working frequency
SCAVENGINGMEMS
3kHz
300kHz
30MHz
3GHz
30Hz
2012
SENSING MEMS
RF MEMS
Power Managment Circuitry
Energy Storage Element
Sensor ULP Controller
µGenerator
RF Transceiver
Energy
Scavenging
Research
WSN diagram:
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“State of the art” or …
… where did the idea came from?
Jensen, K., et al., Nanotube radio. Nano Lett, 2007. 7(11): p. 3508‐3511.
Pros:
- Broadband RF energy harvester (i.e. from 4.8 to 8 GHz)
- The designed can be tuned to harvest energy from certain bands
between the MHz and GHz range
- Efficiencies up to 90%
- Cheap fabrication process
Cons:
- Dimensions on the order of cm
- Non-integrableHagerty, J., et al., Recycling ambient microwave energy with broad-band rectenna arrays. IEEE Transactions on Microwave Theory and Techniques, 2004.
Rectenna concept:
Rectifier + Antenna = Rectenna → Made to harvest energy from the RF electromagne�c spectrum
Nanotube Radio:
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- The source could be a theoretical free and with unlimited power (we don’t care where
does it come from) or…
… it could be an specific one
What are we looking for?
RF energy harvester based on MEMS
NEW DEVICE!
- Using MEMS or NEMS because they…
… are integrable & cheap
… so they can be used to power present and future micro and nano devices (specially
future Ultra Low Power Wireless Sensing Nodes, ULP-WSN)
- Expecting to harvest an amount of energy between pW and µW
- Harvest energy from the radiofrequency electromagnetic spectrum (3 kHz – 300 GHz), …
… focusing on the bands which have more available power (i.e. ISM bands: TV, radio,
WLAN, GSM…)
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The name accounts for the two concepts involved:
MEMS & anTENNA = MEMSTENNA.
The idea is to have a mechanical structure, such as a cantilever or a bridge, that has a certain
quantity of trapped charge incrusted in a specific part of its movable structure. The structure
would be able to generate electricity through an integrated thin film piezoelectric transducer
due to the interaction of its incrusted charge with an incidence RF electric field.
mm
RF wave+
-
λ/2 dipole
RECTENNA CONCEPT
RF waveqPiezo
μm MEMSTENNA CONCEPT
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RF-MEMSTENNA concept
An array of this devices would be used in order to harvest a reasonable amount of energy.
The solution is like:
• The cantilever as a linear oscillator:
If we consider that the mechanical structure is a 1D
harmonic oscillator without losses:
• Taking into account the losses and the incident electric field:
RF-MEMSTENNA concept
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Now our system is a 1D forced harmonic oscillator, where
the electrostatic force is the excitation source.
In order to enhance the induced movement the incident
wave should have a frequency equal to the resonance
frequency of the mechanical structure
2
2
( )( ) 0eff eff
x tm k x t
t
∂ ⋅ + ⋅ =∂
2
2
( )( ) sin(2 )
2 12eff n
n n nVeff
k t Yx t A f f f
m l
κππ ρ⋅= ⋅ ⋅ ⋅ → = → = ⋅ ⋅⋅ ⋅l
22
0 02
( ) ( )2 ( ) e
e f
x t x tx t F
t tF Q E
ξ ω ω∂ ∂+ ⋅ ⋅ ⋅ + ⋅ =∂ ∂
= ⋅
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Is it feasible to implant a charge in the tip of the cantilever?
Is this charge going to last forever?
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Trapped charge… how?
Microphone ELECTRET concept:
Yu-Chong Tai - A Hig Performance MEMS Thin-Film Teflon Electret Microphone
Achievable stable charge densities 1·10-5 C/m2 to 8·10-4 C/m2
τdecay = 10 ‘s - 100’s years
COMSOL Multiphysics modeling
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We are coupling these physics:
- Structural mechanics - Piezoelectric materials
- Electric currents - Electronic circuits
Using COMSOL Multyphysics we are able to simulate our RF-MEMSTENNA with an
standard interface circuit:
… and much more.
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Fabrication process similar to the one used in the VIBES (Vibration Energy Scavenging)
project. The piezoelectric transducer would be made of Aluminum Nitride.
In order to incrust the trapped charge an electrec fabrication process is proposed:
Fabrication process
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Jacobs, H. and G. Whitesides, Submicrometer patterning of charge in thin-film electrets. Science, 2001. 291(5509): p. 1763.
Marzencki, M., et al. A MEMS piezoelectric vibration energy harvesting device. 2005.
• Optic method
If the prototype does not have the piezoelectric
transducer, an optical characterization of the
RF-MEMSTENNA must be done. With this kind
of setup one would be able to characterize the
mechanical properties of the fabricated device.
• Electric method:
If the prototype has the piezoelectric
thin film transducer, the device could
be tested with an electronic circuitry.
Then we could do an electric
characterization of the sample.
Prototype test methods
Agustí, J., et al., Optical vibrometer for mechanical properties characterization of silicalite-only cantilever based sensors. Microelectronic Engineering, 2009.