應用新型電感於被動式無線應變計的研發

Abstract

本論文研究重點在於研發被動式無線應變計，其操作原理為透過LC共振頻率的感測來間接量測應變計所受之應變，主要目標為增加被動式無線應變計的靈敏度。 設計了一新型被動式無線應變計，主要採取包覆式鋸齒狀螺旋電感設計，搭配電容器形成一LC迴路。施加應變時，會對螺旋電感的分佈長度產生變化，進而造成電感值L的變化；除此之外，由於應變施加於包覆材料上，亦會對包覆材料的截面積造成變化，進而影響螺旋線圈的截面積，這亦會對電感值造成變化。若施以一拉伸應變，便會造成其分佈長度增加，同時包覆材料的截面積亦會縮小而造成螺旋線圈的截面積縮小，兩者皆會造成電感值的減小。而包覆式之概念需搭配鋸齒狀螺旋電感之設計方能有效實現之，主要是因為鋸齒狀螺旋電感擁有較低之徑向剛性，靈敏度經量測可達121.9kHz/0.01ε。 另外一設計，是將包覆式鋸齒狀螺旋電感搭配薄膜梳狀電容使用。施加應變時，除了會對電感分佈長度與結面積造成變化之外，亦未對薄膜梳狀電容產生幾何變形，影響其梳狀間距進而改變電容值，藉此來達到同時利用電感變化與電容變化以增加靈敏度。經模擬估計靈敏度可達167.6kHz/0.01ε。

This study, we present a passive strain sensor which employing LC circuit resonant frequency measuring to measure the strain. Our objective is to enhance the sensitivity. One of our designs to enhance the sensitivity is embedded solenoidal inductor. It works with a capacitor to become a parallel-connect LC tank circuit. When applying a strain to the embedded solenoidal inductor, not only the length of the inductor changed, but also affected the cross-section area of the inductor due to the possion’s ratio of the embedding material. Then the length and cross-section area made the inductance vary. The embedded solenoidal inductor should work with saw-shaped solenoidal inductor because of the low radial rigidity. The sensitivity of the embedded saw-shaped solenoidal inductor is 121.9kHz/0.01ε measured by Agilent Network Analyzer 4395A. Another design to enhance the sensitivity is the embedded saw-shaped solenoidal inductor with a thin-film comb capacitor added on. When applying a strain to the embedded solenoidal inductor with a thin-film comb capacitor added on, the length and cross-section area of the inductor and the gap of the thin-film comb capacitor all changed. Which made more changes to the LC resonant frequency then enhancing the sensitivity. With our model, we predict the sensitivity of the embedded saw-shaped solenoidal inductor with a thin-film comb capacitor added on will be 167.6 kHz/0.01ε.