Introduce the development and characteristic of piezoelectric materials, especially Introduce the history of USM in the world. The characteristic of USM and the general application of USM in other countries. State the meaning and content of this thesis.

• 介绍了压电材料的发展及特点，特grj是论述了国内外USM的发展简史和历史情况，概括出USM的特点和国外USM的应用概况，陈述了论文选题意义及本论文的内容。