| PVDF is a piezoelectric material of polymer which has flexible property, it could play a important role in the field of biological and medical electronics with its mechanical and electrical properties. For the need of biological and medical sensors with good fit, compatible and sensitive properties with human skin, PVDF thin film with good piezoelectricity has been prepared with Sol-Gel method in this article, a flexible pressure sensor array has been designed and fabricated based on PVDF thin film and the electromechanical coupling property of the sensor has been studied, some issues about flexible pressure sensor such as signal interference has been studied with simulation.The test results show that PVDF thin film prepared with Sol-Gel method under Bipolar Loop voltage shows butterfly style for capacitance-voltage(C-V) curve and the capacitance is about 51.5pF. The capacitance declines dramatically under low frequency and tends to be stable under high frequency, relative dielectric constant is about 5.2 under high frequency. Hysteresis loops shows a complete curve, remanent polarization Pr is 0.88μc/cm2 and coercive field is about 55MV/m. AFM shows the surface morphology of needle-like which is crystallization of β phase and surface undulation is under nanometer lever. The film has a good piezoelectricity indicated by the contrast of PFM phase image.On this basis, a flexible sensor array has been designed based on the PVDF film, the sensor array has a sandwich structure, the middle is piezoelectric layer, the up and the down is electrode array, the sensor has an array of 4×4 units with a size of 1.4mm×1.4mm, every 4 units share one connecting wire and the up electrode array has a 90° angle between the down. The sensor array has been fabricated with etching and packaged with PDMS. The results of electromechanical coupling properties show that the sensor exhibits a high signal to noise ratio for voltage. The test results suggest that the sensor array exhibits a high synchronal property. The results of electromechanical coupling properties show that the sensor has a linear curve and the slope is 12mV/kPa. The process of hold-and-release output response of the sensor was obtained with high frequency signal collection, electrical signal would be output within 2.5 milliseconds when the pressure state of PVDF is changed. The test results indicate that the sensor array could be applied on the revealing the micro pressure of human skin with multi point.At last, some issues such as signal interference about flexible sensor array is studied with simulation for optimizing design. First, 16 array electrodes have been applied on pressure with unequal value at the same time through modeling and simulating, the results shows that the sensor array could work independently. Also found that because of the flexibility of PVDF, the thin film would generate additional strain which could cause potential interference to other electrodes when the PVDF film is under pressure. With two array electrodes as modeling objects, the results show that additional potential interference would increase as the pressure linearly and the slope is 0.028mV/kPa. Simulation with PVDF, Zinc Oxide, Lithium Niobate, PZT, Zinc Sulfide, Quartz as materials for the influence to the sensor, results show that PVDF has a maximum slope of electromechanical coupling properties. Thickness of piezoelectric layer with 20μm, 30μm, 40μm, 50μm are simulated, fitting linear slope of electromechanical coupling properties are 12.49mV/kPa、18.93mV/kPa、25.36 mV/kPa、31.64mV/kPa under 20-60 kPa, results state that electromechanical coupling and potential interference would increase at the same time with the increased thickness. Simulation with four different micro size of electrode(0.5mm2、1.0mm2、1.5mm2、2.0mm2) under low biological pressure and the results show a high electrical signal, also found that the size has little impact on electrical signal. |
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