Radiant Technologies, Inc.
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
HVA
I2C Port
VOLTAGESENSE
Ferroelectric Tester
AWFG CHARGESENSE
USB to host
HelmholtzCoil
Current AmplifierI 2C DAC
Field CoilLas
er Vibr
omete
r
H-fieldaxis
Radiant Technologies, Inc.
Polarization Measurement
• The AWFG voltage source applies a voltage to the sample capacitor. The Charge Sense input counts electrons. Neither is connected to the other.
I2C Port
VOLTAGESENSE
Ferroelectric Tester
AWFG CHARGESENSE
USB to host
Radiant Technologies, Inc.
Polarization Measurement
• 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.
-0.005
-0.004
-0.003
-0.002
-0.001
0.000
0.001
0.002
0.003
0.004
0.005
-5 -4 -3 -2 -1 0 1 2 3 4 5
H ysteresis o f a 1nF C eram ic D isk C apaci to rC
ha
rge
(µ
C)
Voltage
V3
Q3V2Q2 Linearity means: C1 = C2 = C3
V1
Q1
C = Q/V
Radiant Technologies, Inc.
Polarization Measurement
• Paraelectric capacitors surround us in every piece of electronics. Two trillion surface-mount capacitors are sold every year. Above is an off-the-shelf 6000-volt power capacitor made with barium titanate.
-10.0
-7.5
-5.0
-2.5
0.0
2.5
5.0
7.5
10.0
-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000
High Voltage Paraelectric Capacitor[ 3.3nF 6000V Rating ]
Ch
ar
ge
(µ
C)
Voltage
Radiant Technologies, Inc.
Polarization Measurement
• 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.
-5
-4
-3
-2
-1
0
1
2
3
4
5
-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5
H ysteresis M easurem ent[ Type AB White ]
Ch
ar
ge
(n
C)
Volts
Radiant Technologies, Inc.
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
Radiant Technologies, Inc.
Measuring Piezoelectricity
I2C Port
VOLTAGESENSE
Ferroelectric Tester
AWFG CHARGESENSE
USB to host
Laser
Vibrom
eter
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.
Radiant Technologies, Inc.
Displacement Measurement
The target is a 1-thick PZT film with platinum electrodes covered by glass.
Radiant Technologies, Inc.
Displacement Measurement
• 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.
0
25
50
-10
-5
0
5
-20 -15 -10 -5 0 5 10 15 20
A dvanced P iezo - 1u PN Z T[ Type AC WHITE ]
Po
lari
za
tio
n (
µC
/cm
2)
An
gs
tro
ms
Volts
Proc. Hyst Proc. Disp
Radiant Technologies, Inc.
Magnetoelectric Measurement
HVA
I2C Port
VOLTAGESENSE
Ferroelectric Tester
AWFG CHARGESENSE
USB to host
HelmholtzCoil
Current AmplifierI 2C DAC
Field Coil
H-fieldaxis
Radiant Technologies, Inc.
Magnetoelectric Measurement(No DC bias)
I2C Port
VOLTAGESENSE
Ferroelectric Tester
AWFG CHARGESENSE
USB to host
HelmholtzCoil
Current Amplifier
H-fieldaxis
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.
0
1
2
-1000
0
1000
-40 -30 -20 -10 0 10 20 30 40
V irg in ia T ech C o m po site Sa m ple w ith no B ia s[ 1 2 .5 m V /c m p e r O e a t 4 6 0 O e b ia s ]
Pic
oc
ou
lom
bs
Co
il C
ur
re
nt
Field (Oe)
M-E Response Data Coil Current
Radiant Technologies, Inc.
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.
Radiant Technologies, Inc.
VT Composite Sample - ±45.0 Oe SweepFixed Bias (±56 Oe) and Unbiased
• The magneto-electric coefficient a is the slope of the sample response at each field point of the composite loop, above.
Point Under Consideration
Radiant Technologies, Inc.
aME Response
Sample synthesized and characterized by S. C. Yang, Center for Energy Harvesting Materials and Systems (CEHMS), Virginia Tech. Copyright belongs to CEHMS
0 200 400 600 800 10000
2
4
6
8
10
12
DC Bais Field (Oe)
ME C
oeffi
cien
t (m
V/c
m O
e)
Operating point on previous pages.
Maximum operating point with DC bias.
Radiant Technologies, Inc.
Thin-PZT-Film Capacitor on Cantilever
• 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.
-200
-100
0
100
200
-1.0
-0.5
-0.0
0.5
1.0
-25 -20 -15 -10 -5 0 5 10 15 20 25
M agneto-electric R esponse[ C ant i lever w i th M agnet ]
pic
oC
ou
lom
bs
Co
il C
ur
re
nt
Magnetic Field (Oe)
M-E Response Data Coil Current
~940mV/cm/Oe
Radiant Technologies, Inc.
Next Step
HVA
I2C Port
VOLTAGESENSE
Ferroelectric Tester
AWFG CHARGESENSE
USB to host
HelmholtzCoil
Current AmplifierI 2C DAC
Field CoilLas
er Vibr
omete
r
H-fieldaxis
Radiant Technologies, Inc.
Measurement Variations• Measure the magnetic field generated by switching
ferroelectric polarization.
-60 -40 -20 0 20 40 600.754
0.756
0.758
0.76
0.762
0.764
Small Signal Capacitance (nF)
Magnetic Field (Oersteds)C
apac
itan
ce (n
F)• Measure how
electrical properties change in a magnetic field.
• Piezoelectrically move a magnet in a sensor coil.
• Use test automation to measure reliability and environmental sensitivity!
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.