| Summary: | 博士 === 國立成功大學 === 電機工程學系 === 88 === The equivalent circuit of an AT-Cut quartz resonator and its application on the sensor are studied in this thesis. Different sizes and thickness of aluminum or gold electrode are deposited on the both side of the surface of the quartz disk plate by vacuum deposition method. After deposition, the quartz resonator is loading with different air pressure or different syrup, the characteristics are investigated utilizing by use HP 4194 Impedance/gain-phase Analyzer.
A quartz resonator can be modified as a series circuit consisting of an inductor (L1), a capacitor (C1), and a resistor (R1) in parallel with a capacitor (C0), which are related to the dimensions, density, elastic constants, dielectric constants, piezoelectric constants of the quartz and the electrode area . From the results of the derivation of equivalent circuit, one can know that when the dimensions of quartz are constant, C1 and C0 are directly proportional to the electrode area, and L1 and R1 are inversely proportional to the electrode area. So one can design and apply quartz resonator simpler and easier by controlling the electrode area.
With a surface mass loading, the resonant frequency of quartz resonator will decrease, this loading effect can be represented by an extra inductor (L3). With contacting fluid, the quartz resonator will generate a compression wave in the fluid and cause acoustic energy to radiate away. This effect will result in both a decreases in the resonant frequency of the resonator and an increases in the damping of the resonance; an extra inductor (L2) and a resistor (R2) series section will appear in the equivalent circuit. The L2 and R2 are related to the density and viscosity of the contacting fluid. So the density and viscosity of the contacting fluid can be measured and calculated by L2 and R2. The experimental results show that, when air pressure changes from 1033.6 to 1g/cm2, the equivalent resistance and the resonant frequency of resonator will show a variation of 5 and 90Hz, respectively. In contact with sucrose-water mixture, when the concentration change from 0 to 23wt%, the density will show a variation of 1 to 1.1 (g/cm3) and viscosity will show a variation of 0.01 to 0.024 (g/cm s), respectively. Which cause the equivalent resistance will show a variation of 79 to 110 , and resonant frequency of the resonator will show a variation of 4500 to 7400 Hz, respectively.
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