Measuring Magnetoelectric Strain Joe T. Evans, Jr., Scott Chapman, Bob Howard, Spencer Smith, Allen Gallegos Radiant Technologies, Inc. Energy Harvesting

Radiant Technologies, Inc.

Measuring Magnetoelectric Strain

Joe T. Evans, Jr., Scott Chapman, Bob Howard,

Spencer Smith, Allen Gallegos


Energy Harvesting Workshop

7 August 2012


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.


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


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


AWFG CHARGESENSE

USB to host



• 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



• 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



• 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

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-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


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


Measuring Piezoelectricity

I2C Port

VOLTAGESENSE


AWFG CHARGESENSE

USB to host

Laser

Vibrom

eter


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.



The target is a 1-thick PZT film with platinum electrodes covered by glass.



• 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



HVA

I2C Port

VOLTAGESENSE


AWFG CHARGESENSE

USB to host

HelmholtzCoil


Field Coil

H-fieldaxis


Magnetoelectric Measurement(No DC bias)

I2C Port

VOLTAGESENSE


AWFG CHARGESENSE

USB to host

HelmholtzCoil

Current Amplifier

H-fieldaxis


Magnetoelectric Measurement(No DC bias)

Sample in Shield Box




VT Composite Sample - Unbiased• This test was executed over a ±45.0 Oe sweep at 1 Hz.

0

1

2

-1000

0

1000

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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


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.


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


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.


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.

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-100

0

100

200

-1.0

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-0.0

0.5

1.0

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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


Next Step

HVA

I2C Port

VOLTAGESENSE


AWFG CHARGESENSE

USB to host

HelmholtzCoil


Field CoilLas

er Vibr

omete

r

H-fieldaxis


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!


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.

Documents

Measuring Magnetoelectric Strain Joe T. Evans, Jr., Scott Chapman, Bob Howard, Spencer Smith, Allen Gallegos Radiant Technologies, Inc. Energy Harvesting