Tag: medical imaging

Frequencies higher than 20 kHz are called ultrasonic sound
or ultrasound. Ultrasound is produced by dolphins, bats and porpoises. Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know when a bat is flying nearby, and are able to escape capture. Rats also play games by producing ultrasound.

having a frequency above the human ear's audibility limit of about 20,000 hertz —used of waves and vibrations

Sound below frequency of 20Hz is known as Infrasonic

The sound waves having frequency higher than $20kHz$ is called ultrasonic waves. It has short wavelength.

Answer is B.
The ultrasonic devices achieve high directivity by modulating audible sound onto high frequency ultrasound. The higher frequency sound waves have a shorter wavelength and thus don't spread out as rapidly. For this reason, the resulting directivity of these devices is far higher than physically possible with any loudspeaker system. However, they are reported to have limited low-frequency reproduction abilities. 
High power ultrasound can break up stony deposits or tissue, accelerate the effect of drugs in a targeted area, assist in the measurement of the elastic properties of tissue, and can be used to sort cells or small particles for research.
Hence, the above characteristics make ultrasound to be very useful.

Among the following , only Bats can hear this sound and Bat uses this sound for their hunting.

Answer is A.

Bats send out sound waves using their mouth or nose.  When the sound hits an object an echo comes back. The bat can identify an object by the sound of the echo. They can even tell the size, shape and texture of  a tiny insect from its echo. Most bats use echolocation to navigate in the dark and find food.

Answer is D.

Technique of echocardiography is based on reflection property of ultrasonic waves.
An echocardiogram (also called an echo) is a type of ultrasound test that uses high-pitched sound waves that are sent through a device called a transducer. The device picks up echoes of the sound waves as they bounce off the different parts of our heart. These echoes are turned into moving pictures of our heart that can be seen on a video screen.

Ultrasonic sounds having frequency above 20,000 Hz  cannot be heard by humans. But Bats , deer and dogs have the ability to hear those sounds. 

The frequency $f$ is related with intensity $I$ of wave by ,