封閉式超音波換能器設計及性能改善

Abstract

超音波已有多年的發展歷史，不論是在軍事、工業、醫學、或是生活上皆有廣泛的應用。時至今日，隨著科技蓬勃發展，超音波之應用與我們生活更是密不可分。超音波可傳遞於液體、固體、或空氣介質，其主要原理皆為利用換能器發射及接收超音波，來達到偵測物件之功用，其中包括應用於無人載具（車、船）、工廠產線及手機指紋辨識技術等。從結構而言，傳遞於空氣介質之超音波（空氣超音波），其換能器基本上可區分為開放式及封閉式兩大類型。開放式換能器能與空氣直接接觸，其發射/接收效率較高，構造也相對單純。但基於防水、防塵、或一些特殊環境（酸、鹼、鹽、塵…等）防護之必要，換能器必須封閉式的被保護於一外殼內，此時不但犧牲了部分的能量傳遞效率，也相對的造成結構的複雜性。 以目前市售封閉式車用空氣超音波的應用為例，其有效偵測距離約為4 m左右。但有許多的場合（無人船、大型車、聯結車…）需要更長的偵測距離，卻無從購得此類產品，使用者也沒有能力改變其設計。因此本研究將針對封閉式空氣超音波換能器，進行軟體模擬及實際製作，並比對包含阻抗、模態振型、發射/接收靈敏度及指向性等相互結果，期能建立一換能器完整設計流程及製作方法，以有效提升其偵測距離，並控制發射方向及角度，同時也建立未來（目前尚未問世）之高階陣列式空氣超音波設計能力。

Ultrasound has many years of development history, and it has been widely used in life, medicine, and industry. Today, with the vigorous development of technology, ultrasonic transducer has become inseparable from our lives. Ultrasonic waves can be transmitted to liquid, solid, or air media. The main principle is used transducer to transmit and receive ultrasonic waves to detect objects. The application includes using in unmanned vehicles （cars, boats）, factory production lines, and mobile phone fingerprint recognition technologies. In terms of structure, the air ultrasonic transducer can be basically divided into two types: open and closed. The open transducer can be in direct contact with the air, its transmission / reception efficiency is high, and its structure is relatively simple. However, based on the necessity of protection against water, dust, or some special environments （acid, alkali, salt, dust, etc.）, the transducer must be enclosed and protected in a shell, which not only sacrifices part of the energy transmission efficiency, it also relatively increases the complexity of the structure. Taking the application of vehicle ultrasound as an example, its effective detection distance is about 4 m. However, there are many occasions that require longer detection distances, but such products cannot be purchased, and users have no ability to change their design. Therefore, we will try to design the transducer by simulation and verify the sound characteristics by experiments in this research. We hope that we will build up the complete design process and manufacturing method of the transducer. Finally, we can effectively increase its detection distance and control the directivity angle. At the same time, we also establish the ability of designing the high-order array transducer.