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© Siemens AG, Corporate Technology
Fluid-Structure Interaction Modeling for an Optimized Design of a Piezoelectric
Energy Harvesting MEMS Generator I. Kuehne1, A. van der Linden2, J. Seidel 1, M. Schreiter1, L. Fromme2 and A. Frey1
1Siemens AG, Corporate Technology, Otto-Hahn-Ring 6, 81730 Munich, Germany 2COMSOL Multiphysics GmbH, Berliner Straße 4, 37073 Goettingen, Germany
COMSOL Conference, Stuttgart, October 2011
Page 2 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Outline
Introduction MEMS generator concept and design FSI simulations Experimental results Summary
Page 3 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Introduction
Energy autonomous sensor node
Sensor Interface
Micro-Controller
RF-Frontend
Environmental energy
Wireless Communication
Temperature Pressure
Energy Storage Capacitor, Accumulator
Battery-Replacement
Energy Harvester
Sensor
Quantity to be measured Solar Vibration Heat Energy
Management
- Maintenance free - Costs - Environmental friendly
Benefits:
Page 4 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Tire pressure monitor system (TPMS) for automotive applications
Reference: 16SV3336
sponsored by
rim
macroscopic piezoelectric harvester
piezoelectric MEMS harvester
Source: Continental
tire
Page 5 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Requirements
Properties of MEMS harvester to enable tire-based TPMS application
Minimized mass in
the micro gram range
Non-resonant excitation scheme
Decoupling of primary tire forces
Overload protection
CMOS compatible voltage level
Good “aero dynamic” (high Q value)
Design Characteristics
MEMS Generator Concept
What is a suitable geometry of the generator: shape, area, layer thicknesses?
Page 6 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
MEMS generator design
Generator “aero dynamic”
Cantilever shape
Cantilever area
Cantilever thickness
Ambient pressure
COMSOL Multiphysics„ Fluid-Structure Interaction (fsi) Interface is used
to investigate the dependency of the generators Q-value from the
The generator Q-value is a design parameter which critically affects
the power output.
Page 7 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
MEMS generator design
Fluid-Structure Interaction Simulations
Essential model settings include:
Compressible flow (Ma < 0.3); no turbulence settings.
Geometric Nonlinearity included in the Linear Elastic Material definition
Fixed Wall (No slip) to which the deformable solid is attached.
For the remaining external boundaries: Open Boundary with Normal stress condition
Specific manual scaling settings for the dependent variables in order to enable
the efficient solution process for both the stationary and the time-dependent simulation.
Procedure:
Stationary study to simulate the initial deformation of the solid object.
Stationary result serves as of initial values, for a subsequent time-dependent study.
Page 8 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
MEMS generator design
2-D Fluid-Structure Interaction
Simulation setup Results
2D: varied carrier thickness
Time [ms]0.0 0.5 1.0 1.5 2.0 2.5
Can
tilev
er d
efle
ctio
n [µ
m]
-1500
-1000
-500
0
500
1000
1500
tc = 50 µm tc = 95 µm tc = 250 µm
Page 9 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
MEMS generator design
3-D Fluid-Structure Interaction
3D: varied pressure
Time [ms]0.0 0.5 1.0 1.5 2.0 2.5
Can
tilev
er d
efle
ctio
n [µ
m]
-300
-200
-100
0
100
200
300
1 bar 2 bar 3 bar
Simulation setup Results
Page 10 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
MEMS generator design
Fluid-Structure Interaction
Summary of Q-value simulation results:
pressure 2D
(rectangular)
3D
(triangle) 50 µm 95 µm 250 µm 250 µm
1 bar 21.1 62.3 100.2 188.8
2 bar 114.6
3 bar 78.0
Q-value improved for increased carrier thickness triangular shape instead of conventional rectangular
Q-value reduced for increased pressure
How fit the simulations with experimental results?
Page 11 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
MEMS based piezoelectric energy harvesting module
Realization and experimental results
energy-management ASIC
storage capacitors
piezoelectric MEMS harvester
Si 50 µm
REM photo
Measurement result for 250 µm carrier @ 1 bar:
Qmeas = 97 Qsim = 189
1 / Qm = 1 / Qsim + 1 / 199
Q of order 200 has to be included in the simulation.
Page 12 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Summary
Design aspects of a piezoelectric energy harvesting micro generator for an energy autonomous tire pressure monitoring wireless sensor node were discussed. The generator Q-value is identified as a critical design parameter. We used a COMSOL Multiphysics Fluid-Structure Interaction application mode to investigate the impact of the surrounding air to the damping behavior of a MEMS cantilever energy harvester operated in a new kind of pulsed excitation operation mode. The combination of the predefined COMSOL FSI interface with the essential model settings has allowed the successful model development for the simulation of a strongly coupled FSI process including the effective damping of the FSI vibration. …
Page 13 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Thank You!
Page 14 © Siemens AG, Corporate Technology I. Kuehne COMSOL Conference, Stuttgart, October 2011
Motivation
Intelligent MEMS based Tire System: Benefits
Body: Tire pressure monitoring
Tire information
Mileage of runflat tires
Driver assist functions
Tire maintenance
Chassis & Safety:
ABS: shorter braking distance
Improved driving dynamics
Improved rollover protection
Environment:
CO2 information in display
Reduced fuel consumption
Reduced CO2 emissions
Powertrain:
Torque control
Transmission regulation
