1. Measuring Magnetoelectric Strain
Joe T. Evans, Jr., Scott Chapman, Bob Howard,
Spencer Smith, Allen Gallegos
Radiant Technologies, Inc.
Energy Harvesting Workshop
7 August 2012

2. 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.

3. Magnetoelectric Measurement
HVA
I2C Port
VOLTAGE
SENSE
Ferroelectric Tester
AWFG
CHARGE
USB to host
Helmholtz
Coil
Current Amplifier
I 2C DAC
Field Coil
Laser Vibrometer
H-field
axis

4. Polarization Measurement
I2C Port
VOLTAGE
SENSE
Ferroelectric Tester
AWFG
CHARGE
USB to host
The AWFG voltage source applies a voltage to the sample capacitor. The Charge Sense input counts electrons. Neither is connected to the other.

5. Polarization Measurement
V3
Q3
V2
Q2
Linearity means: C1 = C2 = C3
V1
Q1
C = Q/V
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.

6. 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.

7. 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.

8. 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.

9. Measuring Piezoelectricity
I2C Port
VOLTAGE
SENSE
Ferroelectric Tester
AWFG
CHARGE
USB to host
Laser Vibrometer

10. 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.

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

12. 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.

13. Magnetoelectric Measurement
HVA
I2C Port
VOLTAGE
SENSE
Ferroelectric Tester
AWFG
CHARGE
USB to host
Helmholtz
Coil
Current Amplifier
I 2C DAC
Field Coil
H-field
axis

14. Magnetoelectric Measurement (No DC bias)
I2C Port
VOLTAGE
SENSE
Ferroelectric Tester
AWFG
CHARGE
USB to host
Helmholtz
Coil
Current Amplifier
H-field
axis

15. Magnetoelectric Measurement (No DC bias)
Sample in Shield Box

16. Magnetoelectric Measurement

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

18. 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.

19. 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.

20. aME Response
Operating point on previous pages.
Maximum operating point with DC bias.
Sample synthesized and characterized by S. C. Yang, Center for Energy Harvesting Materials and Systems (CEHMS), Virginia Tech. Copyright belongs to CEHMS

21. Thin-PZT-Film Capacitor on Cantilever
~940mV/cm/Oe
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.

22. Next Step Ferroelectric Tester HVA I2C Port VOLTAGE SENSE AWFG CHARGE
USB to host
Helmholtz
Coil
Current Amplifier
I 2C DAC
Field Coil
Laser Vibrometer
H-field
axis

23. Measurement Variations
Measure the magnetic field generated by switching ferroelectric polarization.
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!

24. 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.