INTRODUCTIONPressure sensing technology has been widely applied

in human’s daily life. Among various pressure sensingtypes, piezoelectric sensor generates charge signal byitself in responding to applied pressure, displaying someadvantages such as self-powering, fast response of highlydynamic load, and relatively simple readout circuit [1].Generally, piezoelectric sensor has a diaphragmstructure, which is the most effective design for pressuresensing. And it is ideal for measuring fluctuating inputpressure signal.

Among various piezoelectric materials, lead zirconiumtitanate (PZT) has relative high piezoelectric chargeconstant and electromechanical coupling effect, which isfavorable for pressure sensing. However, the brittlenessnature of PZT makes it is much harder to be fabricated asa diaphragm structure as compared with other moreflexible piezoelectric materials such as PVDF. Recentdevelopment in the fabrication of thick-film PZT ceramicwith thickness about several tens of micrometers usingtape-casting processing [2] makes it possible for thedesign and fabrication of flexible PZT diaphragm pressuresensor.In this work, a sandwiched PZT thick-film composite

sensor was designed and fabricated. The properties ofthe sensor to measure low frequency fluctuatingpressures have been investigated experimentally. A self-designed setup was used to generate pulsing fluidpressure waves and calibrate the sensitivities of sensorsamples. The proposed pressure sensor exhibited highlysensitive response to low and quasi-static pressureloading, as well as good flexibility, which is promising inmonitoring human blood pressure and respiration.

Pulse Pressure Sensor Based On Flexible PZT Thick-Film Composite Device

Rongjie Liang, Qing-Ming WangDepartment of Mechanical Engineering and Materials Science, University of Pittsburgh

Pittsburgh, PA 15261qiw4@pitt.edu

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 usingtape-casting processing by Lifeng Qin et al (2009) [2].Fig.1 shows photographs of the PZT films with differentthicknesses and shapes.

EXPERIMENT

September 3-6, 2014CHICAGO, ILLINOIS USA

SAMPLE FABRICATION PROCESSThe output signal waveform of PZT sensor matches

well with the deflection waveform of metal disk center.The pressure magnitude can be derived according tothe disk deflection. Thus the relationship betweenpressure and voltage can be built as Fig.6. In the rangeup to 18 kPa, the sensitivities of sensors are about 23-47mV/kPa, as the variance of sample and effect offrequency.

Fig. 4 Experiment Process

CONCLUSIONIn the relatively low frequency range up to 18 kPa, the sensor samples

made with 70μm thickness PZT film showed good frequency accuracyand linearity in response to the fluctuated pulse pressure. Thesensitivities of sensors are about 23-47mV/kPa, as the variance ofsample and effect of frequency. More sensor samples with optimizeddimension and modified setup will be tested in the future work to furtherimprove the sensitivity and work stability. Nevertheless, the goodpiezoelectric property and flexibility of PZT thick film make it verypromising as the sensing element of low pressure sensor that can beused 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 and15mm diameter are selected as the sensor sample. Thefabrication process includes following main steps:

a) Trim Polyimide films with 75μm thickness as desiredcircular shape.

b) Sputter coat golden electrodes onto these polyimidefilms.

c) Uniformly spin coat polyimide resin onto one side ofPolyimide films, then carefully sandwich PZT film in themiddle 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 flexiblecircular 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 sensorfor biomedical monitoring." Sensors 13, no. 5 (2013): 5478-5492.

2. Qin, Lifeng, et al. "Fabrication and characterization of thick-film piezoelectric lead zirconatetitanate ceramic resonators by tape-casting." Ultrasonics, Ferroelectrics and FrequencyControl, IEEE Transactions on 59.12 (2012): 2803-2812The authors would like to thank Dr. Lifeng Qin in the preparation and

characterization of PZT thick-film samples.