2. Smart Sensors Based On Piezoelectric PVDF Dr. Michael Eastman Department of Chemistry The University of Texas at El Paso

3. Individuals Contributing to This Project Guillermo Carbajal-Franco, M. S. Dr. M. P. Eastman Dr. C. V. Ramana Dr. Eric Hagedorn Thursday, August 06, 2015 Colleges of Science and Engineering Consultants: Dr. R. C. Hughes, Dr. T.L. Porter

4. PVDF- Basics Polyvinylidene difluoride (PVDF),is also known under various trade names including _KYNAR (Trade Mark: Elf Atochem North American) SOEF (Trade Mark: Solvay S. A.) PVDF is prepared by the polymerization of 1,1-vinylidene difluoride The structure of the monomer is: The structure of the polymer is:

5. Representations of the molecular structure of the vinylidene difluoride (VD) monomer and of the  and  forms of the PVDF polymer. PVDF-  form PVDF-  form VD-wire VD-space filling

6. With piezoelectric materials have a separation of charge which generates a net dipole in the case the dipoles are aligned (2),(3) below- stressing the material generates a voltage. Materials with unaligned dipoles (1) are not piezoelectric. Examples: Inorganic: barium titanate (BiTiO 3 ) and lithium niobate (LiNbO3); Biological materials: bone, tendons, sugar, dentin. Polymers: PVDF. Piezoelectric Materials http://en.wikipedia.org/wiki/Piezoelectricity http://www.physikinstrumente.com/tutorial/ 4_15.html

7. Important Properties of PVDF PropertyUnitsReported Value MeltingC174 Glass TransitionC~ -30 Densityg/ cm 3 1.8 Heat CapacityJoule/(g K)1.9 Tensile Strengthpsi78000 Serving Temperature Long Term C140 Dielectric Constant (60 Hz) -9 Dielectric StrengthKV/mm160 Volume ResistivityOhm/cm1 x 10 14 Refractive Index1.42

8. PVDF Sensors PVDF is piezoelectric and the voltage induced by bending PVDF films can be measured. The surface of the PVDF is coated with metal to allow electrical measurements. PVDF is pyroelectric and readily absorbs thermal radiation in the range 1000-1200 cm -1. The voltage induced by exposing metalized PVDF films to thermal radiation can be measured. By virtue of its piezoelectric properties PVDF possibly could be fabricated into a surface acoustic wave based sensing system.

9. Commercially available metal coated piezoelectric PVDF sensor elements

10. Smart Sensors We use the term “Smart Sensor” to refer to systems that employ a sensor interfaced to microelectronics. Here we will use piezoelectric/pyroelectric PVDF films as our sensors and a computer will take the place of the microelectronics. The systems described are not engineered to minimize size and power consumption but clearly those would be goals in any widely deployed practical device. A USB data acquisition port will allow measured voltage changes to be easily converted to computerized information for data storage and analysis.

11. Circuits Voltage Follower TL082. Dual OpAmp Dual voltage source: ± 15V Electronics

12. Circuits 1: TL082. Dual OpAmp 1: R 10 MΩ. 10 mega- ohms resistors 1: 0.001 uF. 0.001 micro- farads capacitor. 1 nF or 1 nano-farad Dual voltage source: ± 15V Electronics Electric Charge Measurement

13. Circuits Differential AmplifierElectronics TL082. Dual OpAmp 3: R 10 MΩ. 10 mega- ohms resistors Dual voltage source: ± 15V

14. Deflection Sensor Two PVDF metal coated films mounted on both sides of a flexible material. The response of these films capable of quantifying the magnitude, speed and direction of the flexion movement. Circuit (A) used to follow voltage changes

15. PVDF sensor elements, detection circuit and USB data port

16. PVDF sensors mounted on a solid substrate and interfaced to a detection circuit

17. USB data port interfaced to laptop computer gives system properties of a “smart sensor”.

18. Output PVDF sensors on a ruler undergoing oscillator flexing-Note polarity (green/yellow). Blue represents the combined output signal.

19. Output PVDF sensors on flexed ruler- Note polarity (green/yellow) and combined signal.

20. Plot of ln(Displacement) vs time showing that the motion of the flexible material is described by the equation D=D 0 exp (-t  ); this equation characterizes an under damped oscillator.

21. Pyroelectric Matrix Array PVDF is pyroelectric and readily absorbs radiation around  cm -1. Four sensors in matrix array. Array capable of quantifying the heat intensity and the location of the heat source.

22. Four Panel Thermal Detection

23. Infrared Spectrum of PVDF taken on a Bruker IFS 66v spectrometer, equipped with a DTGS detector and a KBr beamsplitter. Note that the strong absorption around 1000 cm-1

24. Voltage output 4 panel Pyroelectric Sensor when exposed to an asymmetrically located heat source

25. Future Work Mechanical and Thermal stabilization of sensor platform. Detailed analysis of experimental results and development of effective learning strategies based on PVDF sensors Develop and understand mathematical – electrical models Use PVDF SAW devices in a chemical sensor system.

26. Personal Acknowledgements Dr. Tim Porter of the Physics and Astronomy Department at Northern Arizona University helped design a number of our detection circuits. Dr. Robert C. Hughes, Sandia National Laboratories, provided important advice during the early stages of this work.

27. Support Acknowledgement This material is based upon work supported in part by the U. S. Army Research Laboratory and the U.S. Army research Office under Contract W911NF0410052.

28. Thank You for Your Attention