Satisfied answer: What is sound wave? Sound wave is the propagation form of mechanical vibration state (or energy) of an object. The so-called vibration refers to the back and forth movement of the particles of a substance near its equilibrium position. For example, after the drum surface is hit, it vibrates up and down. This vibration state propagates in all directions through the air medium. This vibration state is called sound wave (in general, the sound wave that people can hear and feel in the natural environment is called sound wave).
When the vibration frequency is above 20KHz (or above 16Hz), the sound waves that people can't hear or feel in the natural environment are called ultrasonic waves.
People usually call the sound wave whose vibration frequency is less than 16Hz as infrasound, and the sound wave whose vibration frequency is more than 20KHz as ultrasonic wave. References:
physics
Defendant: Xu Zhenji.
SONAR is a transliteration of the English abbreviation "sonar", and its full name in Chinese is: acoustic navigation and ranging. It is an electronic device that uses the propagation characteristics of sound waves under water to complete underwater detection and communication tasks through electroacoustic conversion and information processing. It has two kinds, active and passive, and belongs to the category of acoustic positioning. Sonar is an electronic device that uses underwater sound waves to detect, locate and communicate underwater targets. It is the most widely used and important device in hydroacoustics.
Interestingly, sonar is not a patent of human beings. Many animals have their own "sonar". Bats emit 10-20 ultrasonic pulses per second with their throats and receive echoes with their ears. With this "active sonar", they can detect tiny insects and wire obstacles with a thickness of 0. 1 mm ... moths and other insects also have "passive sonar", which can clearly hear the ultrasonic waves of bats 40 meters away, so they often avoid attacks. But some bats can use high-frequency ultrasound or low-frequency ultrasound that insects can't hear, so the hit rate of catching insects is still very high. It seems that animals are also engaged in "sonar warfare" like humans! Marine mammals such as dolphins and whales have "underwater sonar", which can generate very definite signals to explore food and communicate with each other.
Because low-frequency sound waves (infrasound waves) can also penetrate the strata thousands of meters under the sea and obtain information in the strata. So far, there is no more effective means to measure and observe in water than sound waves. So usually the sound waves used in sonar are infrasound waves.