RF energy harvester based on MEMS

Transcription

1 9/9/010 NiPS Summer School 010 Summer School: Energy Harvesting at micro and nanoscale, August 1 6, 010 NiPSWorkshop: Noiseindynamicalsystemsat themicro and nanoscale, August6 8, 010 La Tenuta dei Ciclamini, Avigliano Umbro (TR) - Italy RF energy harvester based on MEMS Jordi Agustí Batlle Departament d Enginyeria Electrònica Universitat Autònoma de Barcelona Spain Jordi.Agusti@uab.cat Outline Introduction to Energy Harvesting Research background of our group RF energy harvester based on MEMS RF-MEMSTENNA concept Fabrication process Jordi Agustí Prototype test methods 07/08/010 J. Agustí 1

2 9/9/010 Introduction to Energy Harvesting What does the concept of Energy Harvesting mean? Is the capacity to extract energy from an ambient source and convert it to electrical energy. Thomas, J., M. Qidwai, and J. Kellogg, Energy scavenging for small-scale unmanned systems. Journal of Power Sources, (): p Energy sources: Kinetic (vibrations, random fluctuations, wind, flow, ), Thermal gradients, Electromagnetic sources (solar, RF, beta radiation, ), others Transduction methods: Electrostatic transducers, Piezoelectric transducers, Electromagnetic transducers and Thermoelectric transducers 07/08/010 J. Agustí 3 Research background of our group Working frequency 3GHz RF MEMS 30MHz SENSING MEMS 300kHz SCAVENGING MEMS 3kHz 30Hz Energy Scavenging Research Date (years) WSN diagram: µgenerator Sensor Power Managment Circuitry ULP Controller Energy Storage Element RF Transceiver Extracted from G. Murillo STIMESI Workshop talk. 07/08/010 J. Agustí 4

3 9/9/010 where did the idea came from? State of the art or Nanotube Radio: Jensen, K., et al., Nanotube radio. Nano Lett, (11): p Rectenna concept: Rectifier + Antenna = Rectenna Made to harvest energy from the RF electromagne c spectrum 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 Hagerty, J., et al., Recycling ambient microwave energy with broad-band rectenna arrays. IEEE Transactions on Microwave Theory and Techniques, 004. Cons: - Dimensions on the order of cm - Non-integrable 07/08/010 J. Agustí 5 RF energy harvester based on MEMS What are we looking for? - 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 ) - 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 - 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 NEW DEVICE! 07/08/010 J. Agustí 6 3

4 9/9/010 RF-MEMSTENNA concept 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. λ/ dipole + RF wave Piezo q RF wave - mm RECTENNA CONCEPT μm MEMSTENNA CONCEPT An array of this devices would be used in order to harvest a reasonable amount of energy. 07/08/010 J. Agustí 7 RF-MEMSTENNA concept The cantilever as a linear oscillator: If we consider that the mechanical structure is a 1D harmonic oscillator without losses: x( t) m ( ) 0 eff + keff x t = t The solution is like: keff ( κn l) t Y x( t) = A sin( π fn) fn = fnv = m π l 1 ρ Taking into account the losses and the incident electric field: eff x( t) x( t) + ξ ω + ω x( t) = F 0 0 e t t F = Q E e f 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 07/08/010 J. Agustí 8 4

5 9/9/010 Trapped charge how? Is it feasible to implant a charge in the tip of the cantilever? Is this charge going to last forever? Microphone ELECTRET concept: Yu-Chong Tai - A Hig Performance MEMS Thin-Film Teflon Electret Microphone Achievable stable charge densities C/m to C/m τ decay = 10 s s years 07/08/010 J. Agustí 9 COMSOL Multiphysics modeling 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. 07/08/010 J. Agustí 10 5

6 9/9/010 Fabrication process Fabrication process similar to the one used in the VIBES (Vibration Energy Scavenging) project. The piezoelectric transducer would be made of Aluminum Nitride. Marzencki, M., et al. A MEMS piezoelectric vibration energy harvesting device In order to incrust the trapped charge an electrec fabrication process is proposed: Jacobs, H. and G. Whitesides, Submicrometer patterning of charge in thin-film electrets. Science, (5509): p /08/010 J. Agustí 11 Prototype test methods 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: Agustí, J., et al., Optical vibrometer for mechanical properties characterization of silicalite-only cantilever based sensors. Microelectronic Engineering, 009. 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. 07/08/010 J. Agustí 1 6

7 9/9/010 NiPS Summer School 010 Summer School: Energy Harvesting at micro and nanoscale, August 1 6, 010 NiPSWorkshop: Noiseindynamicalsystemsat themicro and nanoscale, August6 8, 010 La Tenuta dei Ciclamini, Avigliano Umbro (TR) - Italy RF energy harvester based on MEMS Jordi Agustí Batlle Departament d Enginyeria Electrònica Universitat Autònoma de Barcelona Spain Jordi.Agusti@uab.cat 7