1EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 1EE C245 – ME C218Introduction to MEMS DesignFall 2007Prof. Clark T.-C. NguyenDept. of Electrical Engineering & Computer SciencesUniversity of California at BerkeleyBerkeley, CA 94720Lecture 20: Lossless TransducersEE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 2Announcements• Hand back graded midterm today• Midterm Statistics:• Come to my office if you would like to see the details of your Z-score62Median13Standard Deviation62Average101Top Score115Max. Possible Score2EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 3Lecture Outline• Reading: Senturia Chpts. 10, 6• Lecture Topics:ª Project Descriptionª Energy Conserving Transducers( Charge Control( Voltage Control( Linearizing Capacitive ActuatorsEE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 4Project Description3EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 5Go Through the Project HandoutEE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 6Micro-Scale Power Generation4EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 7Micro-Scale Power Generation• Goal: generate power at the micron scale with superior energy density compared to batteries• Motivation: enable standalone micro sensors and micro actuators with wireless communication pursuant to realizing large wireless sensor networksSensorsFuelstorageActuatorsASIC/CPURF/OpticalCommHeat engine/Fuel reformerThermal/Exhaustprocessor1 mmTE Converter/Fuel cell•Approach: harness fuels with higher energy density02468101214Energy Density (kW-hr/kg)PropaneMethaneGasolineDieselEthanolMethanolLi BatteryEE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 8Approach: Fuel Cell• Common elements among fuel cells:ª fuel storage/deliveryª anode and cathode electrodesª catalyst to dissociate fuel (e.g., into H+and e-) at anode and combine products at cathodeª ion exchange medium (i.e., electrolyte)Fuel StorageVoutChemicalEnergyFuelDeliveryChemicalEnergyElectricalEnergyElectrolytePorousAnodeElectrodePorousCathodeElectrodeCatalyst(e.g., platinum)Load+-H+e-H+e-CO2O2H2OElectricalEnergy20–50% eff.5EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 9Metal-Hydride Micro Fuel Cell• Objective: provide 0.5mA @ 3.2V output continuous power with 30mA 100ms pulses for comms for 3 month operation• Specific energy: 0.95 W-hr/g• Water and metal hydride powder fuel kept separate until power is neededª shelf life > 10 years• For 3 month operation:ª need 0.9g of LiAlH4(1.4cc)ª Need 1.6g of H2O (1.6cc)Tiny Fuel CellTiny Fuel CellRegulatingCheck ValveRegulatingCheck ValveLiAlH4FuelLiAlH4FuelPolymerBlockPolymerBlock[Honeywell]EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 10e-O2H2H2OH2H2H2H+H+H+H+H+Vout+-e-Hydrogen Generator/Regulator• LiAlH4+ H2O reaction rate regulated by a pneumatic valveª a completely mechanical feedback system requiring no electrical powerWater ChamberLiAlH4PowderChamberValve DiskSealDiaphram¾ H2here consumed by fuel cell¾ Pressure drops¾ Valve opens again¾ H2here consumed by fuel cell¾ Pressure drops¾ Valve opens againWaterevaporatesWaterevaporatesH2generatedwhen H2OreachesLiAlH4powderH2generatedwhen H2OreachesLiAlH4powder¾ Pressure rises¾ Membrane deflects¾ Valve closes¾ Pressure rises¾ Membrane deflects¾ Valve closesH2O generatedH2O generated6EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 11Metal-Hydride MFC Performance• Right: actual AMPGen hydride fuel cell, including fuel storage• Performance: (as advertised)ª steady hydrogen regulatorª steady 3.2V output voltage under a 0.5mA load-6-4-2024680123Time (days)Vfc (Volts), H2 Pressure (psi)-200-150-100-50050100150200250300Air RH (%), Air T (°C), Valve Position (um)H2over-pressureOutput Volts (Load current 70uA)Air HumidityAir Temperature[Honeywell]Series Connectionof 5 Micro Fuel CellsSeries Connectionof 5 Micro Fuel Cells0.90 W-hr/ccEnergy Density:0.95 W-hr/gSpecific Energy:3.19 W-hrsTotal Energy:3.55 ccTotal Volume:3.36 gTotal Mass:• Compare: CR2430 Li Batteryª 4.6g, 1.3cc, 0.83 W-hrsª 0.65 W-hr/cc, 0.18 W-hr/g• Compare: CR2430 Li Batteryª 4.6g, 1.3cc, 0.83 W-hrsª 0.65 W-hr/cc, 0.18 W-hr/g5X Better!!!5X Better!!!EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 12Metal-Hydride Micro Fuel Cell• Objective: provide 0.5mA @ 3.2V output continuous power with 30mA 100ms pulses for comms for 3 month operation• Specific energy: 0.95 W-hr/g• Water and metal hydride powder fuel kept separate until power is neededª shelf life > 10 years• For 3 month operation:ª need 0.9g of LiAlH4(1.4cc)ª Need 1.6g of H2O (1.6cc)Tiny Fuel CellTiny Fuel CellRegulatingCheck ValveRegulatingCheck ValveLiAlH4FuelLiAlH4FuelPolymerBlockPolymerBlock[Honeywell]7EE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 13e-O2H2H+H+H+H2H2H2Vout+-e-Empty Water Chamber Operation• LiAlH4+ H2O reaction rate regulated by a pneumatic valveª a completely mechanical feedback system requiring no electrical powerWater RemovedLiAlH4PowderChamberValve DiskSealDiaphram¾ get very dry condition on left¾ water diffuses towards left¾ get very dry condition on left¾ water diffuses towards leftH2generatedwhen H2OreachesLiAlH4powderH2generatedwhen H2OreachesLiAlH4powder¾ Pressure rises¾ Membrane deflects¾ Valve closes¾ Pressure rises¾ Membrane deflects¾ Valve closesH2O generatedH2O generatedH2OH2OEE C245: Introduction to MEMS Design Lecture 20 C. Nguyen 11/6/07 14Water-Less Operation Improves AMPGen PerformanceExtracting water from exit fuel air can still yield >0.2mWExtracting water from exit fuel air can still yield >0.2mWSpecific energy × 2.7xLiAlH4 AMPGen Ö 2.6 W-hr/gSpecific energy × 2.7xLiAlH4 AMPGen Ö2.6 W2.6 W--hr/ghr/gVolumetric Energy density × 2.4xLiAlH4 AMPGen Ö 2.1 W-hr/ccVolumetric Energy density × 2.4xLiAlH4 AMPGen Ö2.1 W2.1 W--hr/cchr/cc01234567CR2430 LiBatteryLiAlH4w/ WaterLiBH4w/ WaterLiAlH4No W aterLiBH4No W aterPower Source TypeSpecific Energy [W-hr/g]Water-less Operation of AMPGen prototype with LiAlH4 fuel050100150200250024681012Time (days)Power (uWatts)Water-less operation for 12 days, stepping up power level from 0.05, 0.16, and to 0.21 mWWater-less operation for 12 days, stepping up power level from 0.05, 0.16, and to 0.21 mW5x12x14x35xThis is 14x higher than the CR2430 Li Battery!This is 14x higher than the CR2430 Li
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