what are the physics principals behind ultrasound??

Answer 1

Well ultrasound is ultrasonic waves. Meaning compression waves faster than the speed of sound.

Answer 2

Is ultrasound same as ultrasonics?

In common usage, yes. However, if you want to be more precise, use SONIC to represent those SOUND frequencies which are AUDIBLE TO HUMAN EARS. By common agreement, frequencies between 20 Hz (Hertz) and 20 kHz (kilo Hertz) are designated as SONIC frequencies of sound. Sound waves of frequency less than 20 Hz are Infra-sonic waves and sound waves above 20 kHz frequency are ULTRASONIC waves.

Note: The unit of frequency is cycles/second and was renamed as a Hertz in honor of the Scientist who studied Wave motion, especially the electromagnetic waves called Radio Waves.

The word Ultrasound is more commonly used in medical diagnostics using Ultrasonic Sound Waves. NDT professionals use the word ULTRASONIC TESTING.

Is Ultrasonic same as Supersonic?

No, though you will find the two words used interchangeably (or rather to mean the same thing) in some earlier physics text books and research papers. The Russians were using the word SUPERSONIC to denote ULTRASONIC Sound waves. But SUPERSONIC was also used to denote speeds exceeding the speed of sound in air and thus confusion was being created. Hence by agreement, SUPERSONIC is now reserved for aircraft and other objects moving at speeds greater than the velocity of sound in air at Normal Temperature and Pressure. Mach 1 is the Speed of Sound in air. So speeds greater than Mach I are SUPERSONIC speeds. All speeds less than Mach I are SUB-SONIC.

Earlier SUBSONIC was also used to denote frequencies of less than 20 Hz, but as mentioned, they are called INFRASONIC waves.

Sound waves are MECHANICAL Waves and need a medium (a solid, liquid or gas) to pass through. Sound waves cannot propagate through Vacuum, unlike Light. There are longitudinal waves, transverse waves, surface waves, plate waves etc.

When you clap your hands, or play a drum, you are producing sound. Normal sound may contain a mixture of different frequencies.

Ultrasonic waves are produced by piezoelectric crystals, EMATs and other means.