PIEZOELECTRIC PRESSURE SENSORS BASED ON FLEXIBLE PZT THICK-FILM COMPOSITE DEVICE by Rongjie Liang Bachelor of Mechanical Engineering, Wuhan University of Technology, 2012 Submitted to the Graduate Faculty of Swanson School of Engineering in partial fulfillment of the requirements for the degree of Master of Science University of Pittsburgh 2014 UNIVERSITY OF PITTSBURGH SWANSON SCHOOL OF ENGINEERING This thesis was presented by Rongjie Liang It was defended on November 24, 2014 and approved by William S. Slaughter, Ph.D., Associate Professor, Department of Mechanical Engineering and Material Science Patrick Smolinski, Ph.D., Associate Professor, Department of Mechanical Engineering and Material Science Thesis Advisor: Qing-Ming Wang, Ph. D, Professor, Department of Mechanical Engineering and Materials Science ii Copyright © by Rongjie Liang 2014 iii PIEZOELECTRIC PRESSURE SENSORS BASED ON FLEXIBLE PZT THICK-FILM COMPOSITE DEVICE Rongjie Liang, M.S. University of Pittsburgh, 2014 In this thesis, piezoelectric diaphragm pressure sensors have been proposed and developed. The piezoelectric Lead Zirconate Titanate (PZT) thick film was used in this sensor as sensing element due to its good piezoelectric property and mechanical flexibility. This kind of PZT thick film was fabricated recently using a tape-casting processing. By this process the PZT film thickness can be controlled in the range from tens to hundreds microns, making the novel flexible PZT diaphragm sensor realizable. Two structures of pressure sensor were designed and fabricated, and the relationship between generated voltage signals to applied pressures of the electromechanical model has been analyzed theoretically. For sandwiched structure sensor, the properties of the sensor to measure low frequency fluctuating pressures have been investigated experimentally. A test setup was designed and applied to generate pulsing fluid pressure waves and calibrate the sensitivities of sensor samples. The proposed pressure sensor exhibited highly sensitive response to low frequency dynamic pressure loading. The effectiveness of this sensor in human arterial pulse monitoring was studied and reported. For pressure sensor with unimorph structure, a blast wave pressure test was conducted using shock tube setup to study its sensing ability to intensive, transient pressure loading. Different sized sensors were tested and showed almost linear relationship to blast pressure in the given range. iv TABLE OF CONTENTS PREFACE ..................................................................................................................................... X 1.0 INTRODUCTION ........................................................................................................ 1 2.0 BACKGROUND ........................................................................................................... 3 2.1 FUNDAMENTAL BACKGROUND OF PIEZOELECTRICITY AND PRESSURE MEASUREMENT PRINCIPLE .................................................... 3 2.2 ADVANTAGES AND DISADVANTAGES OF PIEZOELECTRIC PRESSURE SENSORS ......................................................................................... 8 2.3 GENERAL STRUCTURES OF PIEZOELECTRIC SENSOR ....................... 9 2.4 DIFFERENT TYPES OF PIEZOELECTRIC SENSING ELEMENT .......... 11 3.0 PROPOSAL AND DESIGN OF PZT THICK FILM PRESSURE SENSOR ...... 15 3.1 FABRICATION PROCESS OF PZT THICK-FILM BY TAPE-CASTING 16 3.2 DESIGN AND CONSTRUCTION OF PRESSURE SENSOR ....................... 18 3.2.1 Unimorph Structure ...................................................................................... 19 3.2.2 Sandwiched Composite Structure ................................................................ 20 3.3 THEORETICAL ANALYSIS ............................................................................ 21 3.3.1 Static Response .............................................................................................. 21 3.3.2 Dynamic Response ......................................................................................... 29 3.4 FABRICATION PROCESS OF SANDWICHED STRUCTURE PRESSURE SENSOR ............................................................................................................... 32 4.0 PULSE PRESSURE MEASUREMENT .................................................................. 35 v 4.1 EXPERIMENTAL SETUP DESIGN ................................................................ 35 4.2 EXPERIMENTAL PROCEDURE AND RESULTS ....................................... 39 4.3 ANALYSIS AND DISCUSSION ........................................................................ 48 5.0 AIR BLAST PRESSURE MEASUREMENT ......................................................... 51 5.1 EXPERIMENT SETUP DESIGN ...................................................................... 51 5.2 SENSOR SAMPLES AND SETUP PREPARATION ..................................... 54 5.3 EXPERIMENT RESULTS ................................................................................. 57 5.3.1 Blast Pressure Waveforms ............................................................................ 57 5.3.2 Theoretical Calculation of Shock Tube Pressure ....................................... 60 5.3.3 Calibration Curves of Sensor Samples ........................................................ 62 5.4 ANALYSIS AND DISCUSSION ........................................................................ 63 6.0 SENSOR RESPONSE TO HUMAN PULSE PRESSURE .................................... 66 6.1 INTRODUCTION ............................................................................................... 66 6.2 EXPERIMENT .................................................................................................... 67 6.2.1 Experimental principle and setup ................................................................ 67 6.2.2 Result and Discussion .................................................................................... 68 6.3 CONCLUSION .................................................................................................... 69 7.0 CONCLUSION AND FUTURE WORK ................................................................. 71 APPENDIX A .............................................................................................................................. 75 APPENDIX B .............................................................................................................................. 81 BIBLIOGRAPHY ....................................................................................................................... 85 vi LIST OF TABLES Table 3-1 Properties of pressure sensor sample ............................................................................ 34 Table 4-1 Pump Speed vs. Center deflection of Disk ................................................................... 39 Table 4-2 output voltage vs. disk deflection under certain pulse frequencies .............................. 45 Table 4-3 Comparison of Experiment and Theoretical Sensitivities ............................................ 48 Table 5-1 Parameters of PZT Samples (source: JCADVANCED CERAMIC LTD., CO) .......... 53 Table 5-2 Membrane Parameters .................................................................................................. 56 Table 5-3 Peak Pressure Data ....................................................................................................... 59 Table 5-4 Time Interval of Each Test ........................................................................................... 60 Table 5-5 Theoretical Peak Pressure of each Test ........................................................................ 61 Table 5-6 Comparison of Experiment and Theoretical Sensitivities ............................................ 64 vii LIST OF FIGURES Figure 2-1.Schematic of piezoelectric effect [7] ............................................................................. 4 Figure 2-2. Poling process (a) before poling (b) applying direct voltage (c) after poling [8] ........ 5 Figure 2-3.Force/Charge relationship on piezoelectric element ;(a) d33 mode; (b)d31 mode [9] . 7 Figure 2-4. Operation modes of piezoelectric sensors [11] .......................................................... 10 Figure 2-5. Typical force, pressure and acceleration sensor [11] ................................................. 10 Figure 2-6. Schematic of a PVDF pressure sensor: left: cross-section right: top view [16]......... 14 Figure 3-1.PZT green sheet fabricated by the tape-casting processing [21] ................................. 17 Figure 3-2. The fabricated PZT thick films [21]........................................................................... 18 Figure 3-3. Unimorph Sensor structure ........................................................................................ 19 Figure 3-4. Sandwiched Structure................................................................................................. 20 Figure 3-5. Mechanical Modeling of Pressure Sensor .................................................................. 21 Figure 3-6. Two-part mechanical modeling for convenience of analysis ..................................... 22 Figure 3-7. Sensitivity performance with different thickness ratios and substrate materials.(b/a=0.6) ..................................................................................................... 28 Figure 3-8. Charge-generating performance with different radius ratios and substrate materials. (hp/hm=1.5) ................................................................................................................