電容式近接感測器之分析與設計

Abstract

本文的研究方向在於利用邊際電容（fringe capacitance）作為量測原理的微結構電容式近接感測器之數學理論以及數值模擬分析，探討不同性質待測物對此微結構電容器之量測值的影響，並提出改良的結構設計，以利後續製作成品的可行性及商品化。本文的重點可歸納如下： 1. 電容式近接感測器之數學理論分析 2. 電容式近接感測器之模擬分析 3. 電容式近接感測器之結構改良設計 4. 實際量測實驗與理論之比對 5. 總結與討論 數學理論方面，由最基本的靜電場理論出發，求解滿足靜電場之Laplace Equation的解析解(Analytic Solution)，分成三種待測物情形來討論：1.導體接地（Grounding Conductor）2.導體浮接（Floating Conductor）3.介電質（Dielectric），藉由不同的邊界條件（Boundary Condition）以及唯一性定理，求得三種不同待測物情況下的電容理論值。 模擬分析方面，利用Ansoft EM這套軟體作為工具，就三種不同待測物性質作電場與電容值之數值分析，並與數學理論解做相互的印證。結構改良方面，由數學理論解出發，探討模型中各尺寸參數對電容值產生之效應，並根據結果提出適合的實作模型。 最後，做實際模型感測器的電容量測，比較解析解、模擬以及量測結果，探討電容值的誤差來源。

This thesis describes the modeling and design of a proximity capacitive sensor using the so-called fringe capacitance. The model of the fringe capacitance produced by the varying distance of the target objects of different properties is discussed. Main points of the thesis are as follows: 1.Modeling of a capacitive proximity sensor. 2.Simulation of a capacitive proximity sensor. 3.Improvement of a capacitive proximity sensor’s structure. 4.Compare with measurement, simulation and analytic solution and discussion. Three types of materials are considered, i.e., 1. grounding conductors, 2.floating conductors, 3. dielectric materials. Analytic solutions of capacitance are solved by using Laplace’s equation, according to the different boundary conditions and uniqueness theorem. FEM (Finite Element Method) tool- ANSOFT EM is used to analyze the electrostatic fields surrounding electrodes and object. The simulation results are consistent with the analytic solutions within certain errors. The error caused in the analytic solution is investigated in the thesis. Finally, an experiment is conducted to obtain measurement results, which are also compared with simulation and analytic solution. They show consistent property qualitatively.