低頻水聽器(200kHz以下)的應用十分廣泛。在水中聲學研究方面，可以應用於水下通訊、測距、水中定位與水下形貌量測等等。掌握水聽器的相關技術與自主研發的能力，對水下聲學研究和其他相關研究與應用具有舉足輕重的關鍵地位。此外市售的水聽器，其價格較為昂貴、功能無法客製化、體積大且不易於整合於其他量測工具。所以本研究之目的在於開發一種價格低、體積小以及感度高且能應用於水下環境之水聽器。在製程中採用壓電陶瓷材料(PZT)做為驅動元件，並加上鋁合金防水結構，最後比較市售水聽器的感度大小。在系統測試方面，以市售水聽器為聲波之激發源進行訊號的發射，將自製水聽器在不同頻率範圍下，進行聲場的量測，求得自製水聽器接收端的感度；透過增加訊號放大電路，提升自製水聽器接收端的感度，其感度比市售8104水聽器高出26.6dB。接著進行發方向性的特性量測，了解自製水聽器在接收時所能應用的範圍。最後整合LM1812超音波驅動電路，進行應用方面的測試。透過自製水聽器的開發，未來可以提供海洋研究及小型水下載具之避碰來使用，未來可進一步在水下做遠距離的通訊傳輸為最終目的。

Low-Frequency-Hydrophone (below 200 kHz) is widely used. In underwater acoustics researching, it can be applied to underwater communications, underwater acoustic positioning system and underwater geological surveying system, etc. Mastering hydrophone technology and capability of independent developing is an important key point on underwater acoustics research and other related research and application. Commercially available hydrophone is not only more expensive in price, but also function is not customized, bulky and not easy to integrate with other measurement tools.
This study is to develop an economical, small size hydrophone with high sensitivity for underwater application. The PZT ceramic piezoelectric material is used throughout the research for sensing and actuating purposes. An aluminum waterproof housing is also designed for underwater testing of the hydrophone. Characteristic comparison with the commercial type hydrophone is also provided.
While performing the system test, sound source is provided by the commercially available transducer. The sensitivity of the proposed hydrophone is calculated based on the comparison calibration method with a B&K 8104 hydrophone. In addition, a small size amplifier is also embedded inside the waterproof housing to improve its sensitivity. Directional character of the hydrophone is also provided.
Finally, the proposed hydrophone is integrated with the LM1812 ultrasound driven circuit, and a complete small size sonar system is thus built. This work can be used in the development of underwater autonomous vehicle as a collision avoiding system, and it possibly provides the basic of an underwater communication system.

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