Dolphins emit high frequency sound waves typically $$10^5\space Hz$$ and use the echos for guidance and for hunting. The corresponding wave length in water is $$1.48\space cm$$ with this sonar system they can sense objects as small as (roughly) the wavelength. Ultrasonic imaging is a medical technique that uses exactly the same physical principle, sound waves of very short wavelength (or high frequency) called ultrasound are scanned over the human body the echos from the interior organs are used to create image. Ultrasound is more sensitive than x-rays in distinguishing various kinds of tissues and does not have the radiation hazards associated with the x-rays. Ultra sound is used for the study of heart valve action, detection of tumors and prenatal tests.