关键词：关键字: 超声波发生器，超声波换能器，测距 

英文关键词：Key words: Ultrasonic generator ; Ultrasonic wave transducer ;Range finder 

简  介： 摘要: 由于超声波指向性强，能量消耗缓慢，在介质中传播的距离较远，因而超声波经常用于距离的测量，如测距仪和物位测量仪等都可以通过超声波来实现。本文主要介绍超声波在汽车倒车防撞报警系统中的应用，以AT89C51单片机为核心的低成本、高精度、微型化数字显示超声波测距仪的硬件电路和软件设计方法。 

英文简介：Abstract: ： Because ultrasonic wave direction strong, energy consumption slow, disseminates the distance in the medium to be farther, thus the ultrasonic wave frequently uses in the distance survey, like the distance gauge and the thing position measuring instrument and so on all may realize through the ultrasonic wave. This article main introduction ultrasonic wave guards against in the automobile back-draft hits in the alarm system the application, take AT89C51 monolithic integrated circuit as core low cost, high accuracy, microminiaturized numeral demonstration ultrasonic wave distance gauge hardware electric circuit and software design method