Question

define ultrasound and infrasound in little detail..

Answer 1

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000 hertz) in healthy young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.Ultrasonic devices are used to detect objects and measure distances. 
Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the "normal" limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body.
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Answer 2

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound devices operate with frequencies from 20 khz upto several gigahertz.

Infrasound is sound which are at low frequency level less than 20 Hz. it is below the lower limit of human audibility