Design And Realization Of Micro Force Sensor On Surface Acoustic Wave

Sensor technology, as an important symbol of the advancement ofmodern technology, plays a significant role in the economic developmentand social progress. The sensor technology, as well as computer scienceand communication technology, constitutes the backbone of moderninformation industry. Nowadays, the pressure sensor has a broadapplication in the measurement of many variables, such as the surfaceforce, hydraulic pressure and acceleration. Especially, the micro forcesensor on Surface Acoustic Wave (SAW), as a branch of SAW devices,has attracted more and more attention, due to the high resolution, highaccuracy and strong anti-jamming capability during the work. The mainprinciples of SAW micro force sensor is to realize new functions ofpassive and wireless transmission following the piezoelectric properties of crystal materials and the SAW theory. In this way, the commissioningprocess would be simplified due to the stability the crystal temperature.This article explores the micro force sensor derived from the SAWdelay line technique, in which the basic delay line is composed of theinput and output interdigital transducer (IDT) that corroded on the substrate ofcrystal materials. When the micro force sensor is set up in the feedbackloop of broadband amplifiers, a oscillator with high stability will beformed, where the frequency of the oscillator is in a functionalrelationship with the stress of the sensor. According to the stress varianceon the structure of the substrate, the finite element method (FEM) is usedto analyze the stress on the substrate of the SAW micro force sensor.Finally, a new type of SAW micro force sensors is designed, debuggedand tested with peripheral circuits. The concrete research contents andcontribution are addressed as follows:(1) Studying the theoretical modeling approach of the SAW microforce sensor based on the FEM. According to the problem of thin plates inelastic mechanics, this article analyzes the boundary conditions onsubstrates, makes unit division and confirms the boundary conditions onsubstrates of the SAW micro force sensor. Afterwards, the elastic stiffnessmatrix and the situation of IDT can be calculated and determined with theFEM. (2) Developing a SAW micro force sensor that can accuratelymeasure micro stress in real time. The input and output IDT is developedbased on the cosine square function and wavelet analysis. The substratewith delay line structure has strong immunity from interference. Themicro force range is0-20g with high measuring accuracy. Moreover, thephysical realization problem of the SAW micro force sensor is alsoinvestigated.(3) Constructing the linear regression mathematical model of themicro force sensor and drawing the fitted curve between the frequencyand the stress. The original model in this work is in a form of nonlinearfunction. After linearization of this mathematical model, it can be solvedby the least squares method and matrix method. The fitting polynomial issolved according to the values of the frequency and the stress. Then thelinearity between the frequency difference and the stress is proposed andthe fitting curve is presented in this work.(4) Solving the key problems in the design of the SAW micro forcesensor. The work in this part includes the layout design, process of thecantilever beam structure, determination of the measurement range andthe size of the device, selection of the interlayer materials, design and testof the peripheral circuits and calculation of the IDT values, etc.