利用楔形體導波探討表面具有感濕膜層的楔形體在濕度變化下的頻散關係

Dispersion Behaviors of Wedge Wave Propagating in Wedges with Hygroscopic Film in Various Humidities.

董博賢(Po-Hsien Tung)

指導教授 ： 楊哲化

國立臺北科技大學/機電學院/製造科技研究所/碩士(2009年)

摘要

楔型體導波(Wedge wave，WW)是沿著楔型體尖端傳播的一種彈性波，且能量集中在離楔形體頂端大約一個波長的範圍內，而在反對稱模態中的楔形體導波則稱為ASF（Anti-Symmetric Flexural）模態。過去的研究發現，對於楔形體頂端附近具有膜層時，ASF模態的傳播行為會受到膜層表面波波速快慢的影響。並利用感測膜層吸附待感測物所產生的變化，研究其ASF模態的傳播行為，作為開發ASF感測器的物理機制的可能性。在研究中顯示，當膜層具有極低的E值時，在頻段下頻散關係會急遽變化，得知隨膜層單位面積上的質量增加波速下降點之頻率有提早的趨勢。具有膜層之楔形體導波有此質量負載效應，證明易受到周遭環境變化而影響其波傳速度故可推廣至感測器上應用。
本研究將利用楔形體導波受膜層性質影響的物理現象作為感測器基礎原理，期望開發新型的ASF溼度感測器，並利用雷射超音波量測技術與有限元素數值分析來探討具有膜層楔形體之頻散關係。研究內容包括不同材料楔形體(黃銅與鋁)、感測膜層聚乙烯醇以及楔型體幾何結構(30°和40°)，並且模擬感測器上吸附層之材料性質，探討膜層上因質量負載效應所產生的密度變化對WW頻散曲線之影響和對ASF感測器的靈敏度影響進行分析。

關鍵字

楔形體導波 ； 反對稱模態 ； 膜層 ； 頻散關係 ； 有限元素分析

並列摘要

Anti-symmetric flexural (ASF) modes are anti-symmetric type of guided waves propagating along the tip of wedge-shaped waveguides.
This paper describes a combined finite element method (FEM) and laser ultrasound technique (LUT) on the dispersion behaviors of ASF modes propagating along wedge tips with a layer of coating on one of the wedge’s surfaces. In truncation-free wedges, the ASF mode dispersion spectra are dispersion-free. When the wedge is coated with a layer of polyvinyl alcohol (PVA), it is found that phase velocity of an ASF mode for the coated wedge (CW) starts at the ASF mode of the same order for the matrix wedge at lower frequency regime, and gradually influenced by the coating with increasing frequency. Especially, phenomena can be observed for ASF modes in the CW with environment factor. PVA is a hydrophilic material. Various with humidity can alter resonance because of mass loading effect. Dispersion curve is discovered to shift downward when enhance moisture. The numerical results also show the relationship as those from measurements.

並列關鍵字

Wedge wave ； ASF mode ； coating ； dispersion ； finite element analysis

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