A Parallel Plate Capacitive Humidity Sensor Based On PI Film And Numerical Study On Its Characteristics

Humidity measurement and control is increasingly close to social life, industrial and agricultural production, transportation, storage and transportation, medicine and health care,national defense science and technology, weather forecasting and so on. The humidity sensor with excellent humidity-sensitive characteristics is the prerequisite for precise measurement and control. Some areas, such as diagnosis of respiratory system and fuel cell vehicles,require miniature humidity sensors not only with miniaturization and good static humidity-sensitive characteristics, but also with good dynamic characteristics.Because the dynamic characteristics obtained fewer concern, and the factors on the dynamic characteristics are more complexity, the achievement on the dynamic characteristics of micro humidity sensors is less than that of the static characteristics, including:(1) The dynamic response time of the humidity sensors at home and abroad market is not enough short;(2) Due to the reasons such as material cost or complex technology, the marketing of the research achievements of the rapid response humidity sensors is a long road to go;(3) The experiment study on the dynamic characteristics of the micro humidity sensor is difficult because of the more influence factors, and the present experimental-research achievements cannot fully indicate the effect mechanism on the dynamic characteristics of the humidity sensors;(4) The numerical study achievement on the dynamic characteristics of humidity sensor is lack, especially that of porous electrode parallel plate capacitive moisture sensor.Aimed at the problems of humidity measurement and control field mentioned above, first of all, this paper indicated the mechanism and the shortcoming of the dynamic characteristics of the present parallel plate capacitive humidity sensor based on grid upper electrode, design the parallel plate electrode capacitive moisture sensor based on the mesh electrodes, and provided a novel parallel plate electrode capacitive moisture sensor based on aperture upper electrode; Secondly, by using Fluent software and a simulation numerical model based on Fick’s law, Shibata and Looyenga equation, and porosity effects of film, a set of results of numerical study on dynamic characteristics of aperture upper electrode parallel plate electrode capacitive humidity sensor effected by some parameters, such as upper electrode size, film thickness and film effective diffusion coefficient of water, the optical design parameters were obtained; Thirdly, according to the results of numerical simulation, a rapid response parallel plate capacitive humidity sensor based on aperture upper electrode was obtained and its characteristics were tested. Finally, the conclusions were obtained as follow.(1) The orifice upper electrode parallel plate capacitive humidity sensor developed in this paper can effectively overcome the dynamic shortcoming due to the grid upper electrode parallel plate capacitive humidity sensor presented and its dynamic response is superior.(2) The numerical model and method used in this paper is effective and its results are credible.(3) The hole spacing, hole radius, film thickness and effective diffusion coefficient of the orifice upper electrode parallel plate capacitive humidity sensor have great effects on dynamic characteristics. Enlarging the effective diffusion coefficient and decreasing the hole spacing and film thickness could improve humidity sensor dynamic response time; With different upper electrode hole radius, dynamic response curves have a intersection and the response time of full range is smaller when upper electrode hole radiu is small.(4) The test device and the method based on the saturated salt solution method used in this paper are simple, accurate, cheap and convenient application.