examples of comsol magnetostrictive transducer models use of multiphysics models in the design and...
TRANSCRIPT
The Use of Multiphysics Models in the Design and Simulation of Magnetostrictive Transducers
Dr. Julie Slaughter ETREMA Products, Inc
Ames, IA
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Designer and manufacturer of technology driven, high value systems based on electromagnetics.
• Small business • Started in 1990 as a foundry for
TERFENOL-D • Developed engineering capability
in the 90’s to grow the market • Shifted to system approach in
2000’s
ETREMA Products, Inc.
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Today’s Talk • What is magnetostriction? • Magnetostrictive devices • Modeling magnetostriction
• Tools & how they are used • Three examples of using COMSOL in various phases of a
product development • Design example • Validation of modeling tools • Diagnosis of a design flaw
• Future modeling efforts • Summary
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What is magnetostriction? • Inherent property of
ferromagnetic materials where the magnetic and mechanical domains are coupled • Applied magnetic field results
in a change in the mechanical state of the material (Joule)
• Applied stress or strain results in a change in the magnetic state of the material (Villari)
• Magnetostrictive materials • Nickel, iron, transformer steels:
strain <50 µε • Iron-gallium alloys (Galfenol):
strain 150-450 µε • Rare earth-iron alloys (Terfenol-
D): strain >1000 µε 4
Characteristics of magnetostrictive materials
• Nonlinear material behavior
• Material properties are not constant (Young’s modulus, magnetic permeability)
• Response is highly dependent on mechanical and magnetic states
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-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-160 -80 0 80 160
Mag
netic
Flu
x D
ensit
y (
Tesla
)
Magnetic Field (kA/m)
Magnetic Flux Density As A Function Of Applied Stress
7.2 MPa
14.1 MPa
20.9 MPa
27.8 MPa
34.6 MPa
41.4 MPa
48.3 MPa
55.1 MPa
Figure from: R.A. Kellogg , The Delta-E Effect in Terfenol-D and Its Application in a Tunable Mechanical Resonator, M.S. Thesis, 2000. p. 45
Data for Terfenol-D produced by ETREMA
Linear magnetostrictive equations
HdTBHdTsS
Tt
H
µ+=
+=
Field Variable
Description
S Strain (m/m)
T Stress (Pa)
B Magnetic flux density (Tesla)
H Magnetic field (A/m)
Material property
Description
sH Compliance matrix at constant H
d, dt Magnetostrictive coefficients (δB/δT, δS/δH)
µT Magnetic permeability at constant stress
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Magnetostrictive transducers • Used in a wide array of
applications and industries • End application drives the device
design
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AMS – Small Engine Piston Turning
Navy Active SONAR
Standard actuators – DC to 25 kHz
STARS – Law enforcement
What is in a transducer?
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• Magnetostrictive material
• Permanent magnets • Coil • Magnetic flux
carrying components
• Structural components
• Thermal transfer components
Transducer design process
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Definition of performance requirements
Basic sizing and
feasibility
Detailed design
Design validation
Tools: 1D models (equivalent
circuits, equation
based) “Hand”
calculations
Tools: 2D & 3D COMSOL models, single
physics
Tools: 2D & 3D COMSOL
models, fully coupled
Design example • Small SONAR source
• Broad bandwidth • High SPL • Compact
• The intent is to package it with integrated electronics • Stray magnetic flux can interfere with electronics • Heating/cooling of both the transducer and electronics is a concern
• Eventual use is in a close-packed array
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Magnetic models
AC magnetics • Size the coil and other components to
generate the alternating magnetic fields needed to produce the appropriate mechanical output
• Match the transducer electrical requirements with available power amplifiers
• Evaluate losses due to eddy currents
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DC magnetics • Size permanent magnets to appropriately
bias the material at the design prestress • Size additional magnetic circuit
components to carry the magnetic flux - avoid saturation
Mechanical models
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Thermal models
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Magnetostrictive FEA models • Coupled linear
magnetostrictive model • Assumes a
magnetically biased design
• Small signal analysis • Coupled to a water load
to calculate acoustic output
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Model validation • ETREMA Terfenol-D transducer -
CU18A • 18 kHz nominal resonant frequency • 5 um (0-pk) displacement
• Significant amounts of performance data exist for this transducer • 100’s have been built and tested
Terfenol-D Coil
Magnets
Housing
Flexure
Tail mass
Threaded output interface
“washer”
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Z-axis
Magnetic fields and displacements
• Magnetic fields and displacements look quite reasonable • Magnetic fields are confined to the magnetic circuit • Flexure and output interface have the largest deflections for the transducer
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Comparison with actual data
• Models of impedance and displacement were very similar to experimental results
• Two main sources of error • Material properties • Damping
0.0
50.0
100.0
150.0
200.0
250.0
300.0
10000 15000 20000 25000
Abso
lute
val
ue o
f im
peda
nce
(ohm
)
Frequency (Hz)
ExperimentCOMSOL
-20.0
0.0
20.0
40.0
60.0
80.0
100.0
10000 15000 20000 25000
Phas
e of
impe
danc
e (o
hm)
Frequency (Hz)
ExperimentCOMSOL
0.00.51.01.52.02.53.03.54.04.55.0
10000 15000 20000 25000
Disp
lace
men
t (um
)
Frequency (Hz)
ExperimentCOMSOL
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Design diagnosis • SONAR projector
• Three “modes” of operation: omnipole, dipole, quadrupole • One of the three modes, dipole, had very low acoustic output (-20 dB)
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omni- di- quad- Head mass
Driver
Center mass
FEA models • Coupled structural-acoustic models • Single ring plus surrounding water • No magnetostriction – too time
intensive to solve • Revealed a problem in the design
Water
Perfectly Matched Layer
Projector
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Expt FEA
Expt FEA
Expt FEA
Problem resolution • FEA showed the cause of the low
dipole output • The design was modified to
improve the response • Experiments verified that the
improved design operated as expected
20 omni- di- quad- cardioid
Flawed hardware
Corrected hardware
Future modeling efforts • Nonlinear fully-coupled magnetostrictive models
• Some models have already been developed – need verification and additional material properties
• Transducers which are not magnetically biased • Large-signal transducers which include hysteresis • Aid in developing closed-loop controls for specific applications
• Couple thermal effects with magnetostrictive models • Include temperature dependent material properties • Different time scale than magnetostrictive process
• Computer-driven optimization of designs • Optimize the amount of high-cost materials in transducers
(magnetostrictive materials, permanent magnets, flux path materials, coils, etc.)
• Improve performance, decrease cost, improve manufacturability 21
Summary • Fully coupled multiphysics simulation is a powerful tool for
transducer design, evaluation, and optimization • Focus was on magnetostriction but all transducer technologies
have coupled multiphysics (piezoelectric, electrostatic, electromagnetic, etc.)
• Finite element models can be used at different stages of product development • Design development • Existing product evaluation • Troubleshooting performance issues
• Resolving differences between models and experimental data is critical to continuous model improvement
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