頻移式都普勒換能器研析

Abstract

在工業感測控制系統的測量和驗證中，流量計是最關鍵的技術，而非侵入式超音波流量計是不可或缺的應用工具。目前常見的超音波流量計多為時間差超音波流量計，缺點是不太容易設定，準確性受測量距離的影響，需要手動找到特定的距離來發射和接收訊號，且只適用於乾淨的流體。本研究主要設計一種流量計，利用都普勒原理測量懸浮在流體中的運動顆粒或氣泡反射回感測器的訊號，並根據聲波的頻移差計算出流速和流量。所使用的超音波換能器是利用壓電片、波導、背膠層製成的，材料的選用、尺寸關係到聲阻抗匹配、訊號的乾淨程度以及良好的頻寬。以FEA模擬為基礎，研究方面包括換能器角度的變化、波導長度的調整以及換能器的架設位置，背膠層的部分參考文獻，實驗不同配比的背膠層，設計出測量結果更準確穩定的都普勒流量計。

In the measurement and verification of industrial sensor control systems, flow meters are the most critical technology, and non-invasive ultrasonic flow meters are indispensable tools in this application. Currently, the most common ultrasonic flow meters are transit-time ultrasonic flow meters, which have the drawbacks of being difficult to set up, with accuracy affected by the measurement distance. They require manual adjustment to find a specific distance for signal transmission and reception and are only suitable for clean fluids. This research mainly focuses on designing a flow meter that uses the Doppler principle to measure signals reflected by particles or bubbles moving in the fluid, and calculates the flow velocity and flow rate based on the Doppler frequency shift. The ultrasonic transducer used is made of piezoelectric sheets, waveguides, and backing layers. The choice of materials and dimensions is crucial for acoustic impedance matching, signal clarity, and achieving a good bandwidth. Based on FEA simulations, the research includes studying the effects of transducer angle variation, waveguide length adjustment, and transducer installation position. The backing layer references literature, and experiments with different ratios of backing material are conducted to design a Doppler flow meter that provides more accurate and stable measurement results.