超声的用途是很多读者熟知的。我们知道超声就是每秒振动在20,000次以上的声音。那么,要是超声的频率很高(或是波长很短),它会具有什么新的特性呢? 来历每秒振动在1,000兆周以上的超声有个特别的名字,叫做微波超声。频率这样高的超声怎样得到呢? 产生微波超声的方法比较困难。科学工作者通过辛勤劳动,于1958年找到了这种方法,到目前为止已有两三种方法可以得到微波超声。一种方法是用石英晶体的表面 The use of ultrasound is well known to many readers. We know that ultrasound is a sound that vibrates more than 20,000 times per second. So, if the frequency of ultrasound is very high (or the wavelength is very short), what new features will it have? The ultrasound that originates vibrations at more than 1,000 trillion cycles per second has a special name called microwave ultrasound. How is ultrasound with such a high frequency obtained? The method of producing microwave ultrasound is difficult. Scientific workers found this method in 1958 through hard work. So far, two or three methods have been available for microwave ultrasound. One method is to use the surface of a quartz crystal