什么是超声波？超声波现有的定义是什么？

超声波是一种声音，一般来说，声音是空气的振动。当一个物体振动时，周围的空气也以类似的方式振动。振动像声音一样传播和传播。一个人通过摇动位于喉部的声带来振动空气，从而发出声音。声带发出的声音在喉咙里回响，就发出了声音。据悉，人类声音的频率为300Hz ~ 4kHz，而人类能听到的声音(可听到的声音)的频率范围更广，为20Hz ~ 20kHz。超声波被定义为频率高于20kHz的声音或“人类听不到的声音”。

Ultrasound is a kind of soundGenerally a sound is a vibration of the air. When a thing vibrates, thed surrounding air also vibrates in the similar manner. The vibration spreads and propagates as a sound. A person makes a sound by shaking his/her vocal cords located in the throat to vibrate the air. The sound generated on the vocal cords echoes in the throat to produce a voice. It is reported that human voice has frequencies from 300Hz to 4kHz while the sounds humans can hear (audible sounds) are in a wider range of frequencies, 20Hz to 20kHz. Ultrasound is defined as the sound of higher frequencies than 20kHz or "thed sound human can not hear."

人类能听到的声音范围显示了人类能听到的声音范围。横轴和纵轴分别表示频率和声压，声压以Pa或Pascal为单位。天气预报使用百帕或百帕，气压为101325pa或1013hPa。分贝，空气中的标准值设置为0.00002Pa-20uPa或OdB。在超声使用频率较高的水中，tuPa被作为标准。

The sound range a human can hear shows the sound range a human can hear. The horizontal and vertical axes denote frequency and sound pressure, respectively: the latter uses Pa or Pascal as a unit. Weather forecast uses hPa or hectopascal and the atmospheric pressure is 101,325Pa or 1013hPa. decibel, where the standard value in the air is set to 0.00002Pa-20uPa or OdB. In water, where ultrasound is used more frequently, tuPa is adopted as the standard.

超声有两种定义

•频率高于20kHz的声音

•非听力目的声音

即使是可听见的声音，如果声音不是用来听的，也是超声波。

Two kinds of definitions for ultrasound

•Sound of frequencies higher than 20kHz.

•Sound not for the purpose of hearing.

Even an audible sound is ultrasound if the sound is used for other than for hearing.

超声的特性(与可听到的声音的比较)

•方向性更清晰。

•波长更短。

•衰减更大。

Charactorietics of ultrasound (In comparison with audible sound)

•Directivity is sharper.

•Wavelength is shorter.

•Attenuation is bigger.