超声是频率在20千赫以上的声音。人耳只能听得见频率范围约在20赫到20千赫的声音,所以超声是听不见的。检查身体B超所用超声,频率一般是几兆赫,更听不见了。人们早就设法看到空气中或液体中的声音,而能够比较清晰地看到透明 Ultrasound is the sound of frequencies above 20 kHz. The human ear can only hear sounds in the frequency range of about 20 Hz to 20 kHz, so the ultrasound is inaudible. B ultrasonic ultrasound used to check the body, the frequency is generally a few megahertz, more can not hear. People have long been trying to see the sound in the air or in the liquid, and can see clearly the transparent