What is ultrasound?
The human ear can hear the sound frequency ranging between 16Hz to 20,000Hz. Any sound frequency higher than 20,000Hz is defined as the ultrasound, because these sounds we are unable to hear radically. But if lower than 16Hz the sounds frequency is sub-sonic sound frequency. The elephant may send out a sub-sonic sound a few miles away to carry out communication with several outside companions.
Ultrasound can not penetrate the barrier with the directive, if the transmission distance is short and rapid attenuation characteristics.
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