| Temperature,Salinity and Depth are the most essential and important physical quantities in marine environmental information.Expendable Temperature,Conductivity and Depth(XCTD)system and underwater fast-moving observation platforms,such as Glider and Autonomous Underwater Vehicle(AUV),have become the research focus in the marine field due to their advantages of low cost,high precision,large time and space span measurements.At present,the depth of XCTD is calculated by a fall-rate equation according to the time elapsed after the probe hitting the water surface.As there is no higher precision depth(pressure)element,the measurement accuracy of depth value is generally ±5 meters or 2%of the full scale,which strongly limits the application of XCTD.Nowadays,the vertical spatial resolutions of pressure elements mounted on Glider,AUV and other underwater fast-moving observation platforms are dissatisfied due to the requirements of maximum measurement depth of various ocean applications.Therefore,it is imperative to design a novel pressure element array with both large range and high vertical resolution.In order to meet the demand of depth measurement of XCTD and underwater fast-moving observation platforms,the multi-range pressure sensing technology based on the piezoresistive property of silicon is innovatively proposed,and the theoretical research and simulation of this technology are studied in this paper.The depth correction method of the underwater fast-moving observation platform is also proposed by using the distributed pressure element and the velocity meter,which corrects the influence of seawater velocity and the platform velocity on the depth measurement results.This method has certain theoretical guidance significance for improving the profile measurement accuracy and expanding the application field of the underwater fast-moving observation platforms.The main contents of this paper are summarized as follows:(1)Evaluation and analysis of three-layer composite plate theory.SOI(Silicon on Insulator)pressure sensitive diaphragms are utilized for simulation in this article.This paper deduced the three-layer composite material plate theory and analyzed the influence of buried layer thickness for five kinds of three-layer composite material diaphragms.Then we evaluated the regularity and effectiveness of three-layer composite diaphragm plate theory,two-layer composite diaphragm plate theory and finite element analysis method on the deflection and stress analysis for composite material diaphragms.The regularity of these three methods is similar,but their effectiveness is slightly different.From high to low,the effectiveness of these three methods are finite element analysis,three-layer composite diaphragm plate theory and two-layer composite diaphragm plate theory in order.After comparison and analysis of the results,we selected the appropriate buried oxygen layer thickness for SOI wafer.(2)Parameter design of 20MPa pressure element.Based on the design principles of piezoresistive pressure sensing element,the theoretical modeling and simulation optimization of pressure sensing element with 20MPa range are carried out by using the finite element analysis software COMSOL,and the deflection and stress distribution of pressure sensitive diaphragm are analyzed.The diaphragm parameters,the size,shape and process parameters of the piezoresistor are designed and optimized.The influence of process error on the output sensitivity of the pressure element is analyzed.(3)Design of stress compensation structure for 6MPa pressure element.The stress compensation structure of convex boss on glass substrate formed by dry etching is designed and optimized in this paper.Through the design of stress compensation structure,the maximum stress on the diaphragm of 6Mpa pressure element is reduced from 1.56GPa to 700MPa at 2000 meters water depth,and the anti-overload ability of pressure element is improved.(4)The overall design of the multi-range piezoresistive pressure element.The 2×2 integrated array packaging structure is selected,and the design parameters of diaphragm and resistance of the multi-range pressure element array are given,and the layout of the 2×2 multi-range pressure element array and the glass substrate stress compensation structure are drawn.On the underwater fast-moving observation platforms,the influence of platform speed and seawater velocity on the depth measurement results based on the pressure sensing technology is corrected by using the distributed pressure element and velocity meter. |
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