INTRODUCTION Pressure sensing technology has been widely applied in human’s daily life. Among various pressure sensing types, piezoelectric sensor generates charge signal by itself in responding to applied pressure, displaying some advantages such as self-powering, fast response of highly dynamic load, and relatively simple readout circuit [1]. Generally, piezoelectric sensor has a diaphragm structure, which is the most effective design for pressure sensing. And it is ideal for measuring fluctuating input pressure signal. Among various piezoelectric materials, lead zirconium titanate (PZT) has relative high piezoelectric charge constant and electromechanical coupling effect, which is favorable for pressure sensing. However, the brittleness nature of PZT makes it is much harder to be fabricated as a diaphragm structure as compared with other more flexible piezoelectric materials such as PVDF. Recent development in the fabrication of thick-film PZT ceramic with thickness about several tens of micrometers using tape-casting processing [2] makes it possible for the design and fabrication of flexible PZT diaphragm pressure sensor. In this work, a sandwiched PZT thick-film composite sensor was designed and fabricated. The properties of the sensor to measure low frequency fluctuating pressures have been investigated experimentally. A self- designed setup was used to generate pulsing fluid pressure waves and calibrate the sensitivities of sensor samples. The proposed pressure sensor exhibited highly sensitive response to low and quasi-static pressure loading, as well as good flexibility, which is promising in monitoring human blood pressure and respiration. Pulse Pressure Sensor Based On Flexible PZT Thick-Film Composite Device Rongjie Liang, Qing-Ming Wang Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, PA 15261 [email protected] ACKNOWLEDGMENTS B: Design and Fabrication of the Pressure Sensors 2014 IEEE IUS Fig. 1 The fabricated PZT thick films using tap-casting method [2]. The PZT thick-film used in this study is fabricated using tape-casting processing by Lifeng Qin et al (2009) [2]. Fig.1 shows photographs of the PZT films with different thicknesses and shapes. EXPERIMENT September 3-6, 2014 CHICAGO, ILLINOIS USA SAMPLE FABRICATION PROCESS The output signal waveform of PZT sensor matches well with the deflection waveform of metal disk center. The pressure magnitude can be derived according to the disk deflection. Thus the relationship between pressure and voltage can be built as Fig.6. In the range up to 18 kPa, the sensitivities of sensors are about 23- 47mV/kPa, as the variance of sample and effect of frequency. Fig. 4 Experiment Process CONCLUSION In the relatively low frequency range up to 18 kPa, the sensor samples made with 70μm thickness PZT film showed good frequency accuracy and linearity in response to the fluctuated pulse pressure. The sensitivities of sensors are about 23-47mV/kPa, as the variance of sample and effect of frequency. More sensor samples with optimized dimension and modified setup will be tested in the future work to further improve the sensitivity and work stability. Nevertheless, the good piezoelectric property and flexibility of PZT thick film make it very promising as the sensing element of low pressure sensor that can be used in human pulse pressure monitoring. REFERENCES A: Preparation of the PZT thick films Fig. 2 Sandwiched Structure of Pressure Sensor In this study, PZT thick films with 70 μm thickness and 15mm diameter are selected as the sensor sample. The fabrication process includes following main steps: a) Trim Polyimide films with 75μm thickness as desired circular shape. b) Sputter coat golden electrodes onto these polyimide films. c) Uniformly spin coat polyimide resin onto one side of Polyimide films, then carefully sandwich PZT film in the middle of two spin coated polyimide. d) Put sandwich composite in the oven and softbake, ramping temperature up to 140°C. About two hours later, take out the samples out from oven, and cooling slowly. e) Finally, bond the sandwiched laminate on the flexible circular stainless steel layer using epoxy. Fig.6 Characteristic curves of PZT sensor samples. Fig. 3 Fluid Pulse Pressure Measurement Setup. RESULTS AND DISSCUSIONS Fig. 5 The pulse pressure responses comparison between PZT sensor and Metal disk at frequency=8.6 Hz. 1. Tseng, Hong-Jie, Wei-Cheng Tian, and Wen-Jong Wu. "Flexible PZT thin film tactile sensor for biomedical monitoring." Sensors 13, no. 5 (2013): 5478-5492. 2. Qin, Lifeng, et al. "Fabrication and characterization of thick-film piezoelectric lead zirconate titanate ceramic resonators by tape-casting." Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on 59.12 (2012): 2803-2812 The authors would like to thank Dr. Lifeng Qin in the preparation and characterization of PZT thick-film samples.