Measuring Magnetoelectric Strain Joe T. Evans, Jr., Scott Chapman, Bob Howard, Spencer Smith, Allen Gallegos Radiant Technologies, Inc. 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 VOLTAGE SENSE Ferroelectric Tester AWFG CHARGE USB to host Helmholtz Coil Current Amplifier I 2C DAC Field Coil Laser Vibrometer H-field axis

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.

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.

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.

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.

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.

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

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.

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

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.

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

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

Magnetoelectric Measurement (No DC bias) Sample in Shield Box

Magnetoelectric Measurement

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

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 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.

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

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.

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

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!

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.