Investigation On The Self-Powered Humidity Sensing Of NaNbO₃ Piezoelectric Nanofibers

Humidity sensor is used to sense environment humidity changes and convert it to electrical signal that can be acquired and controlled.Humidity sensor has a wide range of application in the fields of industry,environmental protection,bio-medicine,etc.With the rapid development of microelectronics and nanotechnology,the humidity sensors are developed towards miniaturize,intelligent and multi-functional.In addition,the performance parameter of sensors,such as sensitivity,repeatability,stability,service life and integration,has caused extensive attention.In recent years,domestic and abroad scientists conversed mechanical energy into electrical energy by using piezoelectric effect of piezoelectric materials,constructed the sensor without an external electric power supply and created the self-driven system on micro-nano scale,which supplied a feasible way to realize self-powered humidity testing.In this thesis,we combined the piezoelectric effect with the humidity sensitivity to build a self-powered humidity sensor,and the perovskite structure of composite metal oxides NaNbO₃ nanofibers was chosen as the sensing materials.We used the output signal of piezoelectric voltage as humidity characteristic to monitor environment humidity.The main contents and results of this paper are as follows:?1?The NaNbO₃/PVP composite nanofibers were prepared by sol-gel and electro-spinning,and made it crystallization under the high temperature annealing.The results showed that the annealing temperature,environmental humidity,PVP concentration and electro-spinning voltage have significant effects on products phase and morphology.?2?Pt/Ti interdigital electrodes on a clean alumina substrate was prepared by micro-fabrication technology and the NaNbO₃ nanofibers were assembled through an electro-spinning process onto the interdigital electrodes?IDEs?,then the resistance humidity sensor based on NaNbO₃ nanofibers was obtained.When the relatively humidity from 15%RH to 80%RH at room temperature,the resistance of the device changed about five orders of magnitude and the response and recovery time was about 3 s and 20 s,respectively.Moreover,this sensor has a weak response to ethanol,but sensitivity of humidity is about 5 orders of magnitude higher than that to ethanol,which means that the sensor has good response selectivity to humidity.Humidity sensitive behavior of the resistance sensor can be attributed to the movement of proton which comes from the physical adsorption of water molecules of the surface layer under the applied bias voltage.?3?Flexible piezoelectric sensors based on NaNbO₃ nanofibers were successfully prepared by using PDMS transfer technology.Under the periodic external pressure,the piezoelectric output signal enlarged with the increase of the bending amplitude and frequency,and more than 2 V open circuit output voltage can be obtained.Under the certain bending amplitude and frequency,the value of piezoelectric output value decreased from 200 mV to 30 mV when the environment relatively humidity changes from 5%RH to 95%RH,which can be used to implement self-powered supply humidity detection.This self-powered humidity sensitive behavior can be attributed to polarization shielding caused by the movement of the proton in the surface layer of adsorbed water molecules.