Measuring Magnetoelectric
Strain
Joe T. Evans, Jr., Scott Chapman, Bob Howard,
Spencer Smith, Allen Gallegos
Radiant Technologies, Inc.
Energy Harvesting Workshop
7 August 2012
Radiant Technologies, Inc.
In Short
• We think energy may be effectively harvested
from environmental energy sources using
magnetoelectric devices.
• Magnetoelectric devices combine magnetostriction
with remanent polarization, yielding a
magnetically driven piezoelectric energy generator.
• Radiant’s objective is to provide a tool for
measuring the fundamental “striction” and energy
conversion properties of non-linear materials.
Radiant Technologies, Inc.
Magnetoelectric Measurement
Field Coil
H-field
axis
HVA
I 2C
DAC
Current Amplifier
AWFG
Helmholtz
Coil
CHARGE
SENSE
VOLTAGE
SENSE
USB to
host
I2C Port
Ferroelectric Tester
Radiant Technologies, Inc.
Polarization Measurement
AWFG
CHARGE
SENSE
VOLTAGE
SENSE
USB to
host
I2C Port
Ferroelectric Tester
• The AWFG voltage source applies a voltage to the sample capacitor.
The Charge Sense input counts electrons. Neither is connected to the
other.
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Polarization Measurement
H y st e re si s o f a 1 n F C e ra m i c D i sk C a p a c i t o r
0 .0 0 5
0 .0 0 4
C = Q/V
C h a rg e
(µ C )
0 .0 0 3
0 .0 0 2
0 .0 0 1
V1
0 .0 0 0
Q1
- 0 .0 0 1
- 0 .0 0 2
Q2
- 0 .0 0 3
V2
V3
Q3
Linearity means:
- 0 .0 0 4
C1 = C2 = C3
- 0 .0 0 5
-5
-4
-3
-2
-1
0
V o lta g e
1
2
3
4
5
• A linear capacitor is simple: Q = CV is a straight line. The sample
above has a slight amount of loss indicated because it is slightly open.
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Polarization Measurement
H ig h V o lta g e P a ra e le c tric C a p a c ito r
[ 3 .3 n F 6 0 0 0 V R atin g ]
1 0 .0
7 .5
C h a rg e (µ C )
5 .0
2 .5
0 .0
- 2 .5
- 5 .0
- 7 .5
- 1 0 .0
-5000
-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
5000
V o lta g e
• Paraelectric capacitors surround us in every piece of electronics. Two
trillion surface-mount capacitors are sold every year. Above is an offthe-shelf 6000-volt power capacitor made with barium titanate.
Radiant Technologies, Inc.
Polarization Measurement
H y s te re s is M e a s u re m e n t
[ Type A B W hite ]
5
4
3
C h a rg e (n C )
2
1
0
-1
-2
-3
-4
-5
-7.5
-5.0
-2.5
0.0
Volts
2.5
5.0
7.5
• Ferroelectric electric capacitors have uncompensated electric fields
emanating from their lattices, fields which must be cancelled by
remanent electric charge on their plates. It is this remanent charge that
creates piezoelectricity: force changes the lattice spacing.
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Piezoelectricity
The remanent
dipoles exist without
an external force
applied.
An external force
stretching the lattice
stretches the dipoles.
Charge flows onto
the capacitor to
compensate.
F
An external force
compressing the
lattice shrinks the
dipole. Charge
flows off of the
capacitor to
compensate.
F
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Measuring Piezoelectricity
AWFG
CHARGE
SENSE
VOLTAGE
SENSE
USB to
host
I2C Port
Ferroelectric Tester
Radiant Technologies, Inc.
Displacement Measurement
• A Polytec laser vibrometer on a test bench with the sample mounted on
a granite block. The entire bench sits on a granite block. This
arrangement allows the capture of the movement of the surface of a thin
piezoelectric film.
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Displacement Measurement
The target is a 1-thick PZT film
with platinum electrodes covered by
glass.
Radiant Technologies, Inc.
Displacement Measurement
A d v a n c e d P ie z o - 1 u P N Z T
P o la r iz a tio n ( µ C /c m 2 )
[ Type A C W H ITE ]
Proc. H yst
Proc. D isp
50
25
0
A n g s tr o m s
5
0
-5
-10
-20
-15
-10
-5
0
Volts
5
10
15
20
• The film surface moved only 17 Ångstroms. Even though the PZT film
is only 1 thick, it will bend the entire 550-thick silicon wafer at 15V.
Radiant Technologies, Inc.
Magnetoelectric Measurement
Field Coil
H-field
axis
HVA
I 2C
DAC
Current Amplifier
AWFG
Helmholtz
Coil
CHARGE
SENSE
VOLTAGE
SENSE
USB to
host
I2C Port
Ferroelectric Tester
Radiant Technologies, Inc.
Magnetoelectric Measurement
(No DC bias)
H-field
axis
Current Amplifier
AWFG
Helmholtz
Coil
CHARGE
SENSE
VOLTAGE
SENSE
USB to
host
I2C Port
Ferroelectric Tester
Radiant Technologies, Inc.
Magnetoelectric Measurement
(No DC bias)
Sample in Shield Box
Radiant Technologies, Inc.
Magnetoelectric Measurement
Radiant Technologies, Inc.
VT Composite Sample - Unbiased
• This test was executed over a ±45.0 Oe sweep at 1 Hz.
V ir g in ia T e c h C o m p o s it e S a m p le w it h n o B ia s
C o i l C u r r e Pn itc o c o u l o m b s
[ 1 2 .5 m V /c m p e r O e a t 4 6 0 O e b ia s ]
M -E R e s p o n s e D a t a
C o il C u r r e n t
2
1
0
1000
0
-1 0 0 0
-4 0
-3 0
-2 0
-1 0
0
10
F i e ld (O e )
20
30
40
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56 Oe Fixed Bias
• The magnet is at 2.0 cm from sample along the coil field
axis. The DC Magnetic field was measured at 56 Oe using a
Lakeshore 425 Gauss meter.
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VT Composite Sample - ±45.0 Oe Sweep
Fixed Bias (±56 Oe) and Unbiased
Point Under
Consideration
• The magneto-electric coefficient a is the slope of the sample response at
each field point of the composite loop, above.
Radiant Technologies, Inc.
ME Coefficient (mV/cm Oe)
aME Response
12
10
8
Maximum operating
point with DC bias.
6
4
Operating point on
previous pages.
2
0
0
200
400
600
800
1000
DC Bais Field (Oe)
Sample synthesized and characterized by S. C. Yang, Center for Energy Harvesting
Materials and Systems (CEHMS), Virginia Tech. Copyright belongs to CEHMS
Radiant Technologies, Inc.
Thin-PZT-Film Capacitor on Cantilever
M a g n e t o -e le c t r ic R e s p o n s e
C o il C u rre n t
p ic o C o u lo m b s
[ C an tilev er w ith M ag n et]
M -E R e s p o n s e D a t a
C o il C u rre n t
200
100
0
~940mV/cm/Oe
-1 0 0
-2 0 0
1 .0
0 .5
-0 . 0
-0 . 5
-1 . 0
-2 5
-2 0
-1 5
-1 0
-5
0
5
M a g n e t i c F i e l d (O e )
10
15
20
25
• This is a composite sample consisting of a piezoelectric element with a
magnet bonded to the cantilever. Note: this sample generated 250pC
from the H-field but would generate 4,800,000 pC from a voltage.
Radiant Technologies, Inc.
Next Step
Field Coil
H-field
axis
HVA
I 2C
DAC
Current Amplifier
AWFG
Helmholtz
Coil
CHARGE
SENSE
VOLTAGE
SENSE
USB to
host
I2C Port
Ferroelectric Tester
Radiant Technologies, Inc.
Measurement Variations
• Measure the magnetic field generated by switching
ferroelectric polarization.
Small Signal Capacitance (nF)
Capacitance (nF)
• Measure
how
electrical properties
change in a magnetic
field.
0.763
0.762
0.761
0.76
0.759
0.758
0.757
0.756
-60
-40
-20
0
20
40
60
Magnetic Field (Oersteds)
• Piezoelectrically move a magnet in a sensor coil.
• Use test automation to
environmental sensitivity!
measure
reliability
and
Radiant Technologies, Inc.
Acknowledgement
• The authors would like to acknowledge the assistance and
cooperation of:
• Dr. Shashank Priya
• Dr. Chee-Sung Park
• Mr. Shashaank Gupta
• Mr. Su Chul Yang
all at the Center for Energy Harvesting Materials and
Systems of Virginia Tech.
Radiant Technologies, Inc.