[ul] [li]A use is echolocation[/li] [li]They are high-frequency waves (greater than 20 000 Hz, or 20kHz)[/li] [li]They are outside the human audible range[/li] [li]Less than 20Hz is [b]infrasound[/b], for [b]Humans only[/b][/li] [li]Infrasound and Ultrasound depends on the species, so is relative[/li] [li]All sound, including infrasound and [b]ultrasound[/b], is a [b]longitudinal wave[/b][/li] [li]They make groups of particles undergo [b]compression[/b] and [b]rarefaction[/b][/li] [/ul] [b]Compression = Particles are close together Rarefaction = Particles are further apart[/b] [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1487880092/compression_rarefaction_wt3gof.svg' style='width:35vw'] [h3]Ultrasound Scanner[/h3] [b]Ultrasound Scanners[/b] use a [b]Piezoelectric Crystal[/b] (or other material). [ul] [li]When sound is applied to it, it causes compression and rarefaction within the crystal, which causes potential difference inside. ([b]Potential Difference - Voltage[/b])[/li] [li]Applying P.d causes a deformation in the crystal (squashed or lengthened)[/li] [li]It receives P.d from the Ultrasound, which has reflected off of a substance, and the deformation caused is interpreted by a computer, as an image[/li] [li]The ultrasound traverses through materials, and some is reflected at each substance/new substance barrier, which allows for the production of the image[/li] [li]Therefore the transmission/reflection of Ultrasound occurs on the barrier of 2 materials[/li] [/ul] [h3]Foetus (Fetus) Ultrasound Scanner:[/h3] [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488051785/ultrasound_scanner_by1l4d.svg'] The blue arrows represent the [b]ultrasound[/b] going into the body. The red arrows show the reflected waves of [b]ultrasound[/b]. To get a decent image of the [b]fetus[/b], the machine sends out multiple short bursts of ultrasound, and registers only the anticipated waves. So if it is detecting waves returning from the [b]fetus[/b], it will listen for weaker pulses. [h3]Echo Sounding[/h3] Ships can use echoes to search the depths of the Ocean. [highlight] A ship may send out a wave of ultrasound, and depending on how long it takes to return, it can determine the depth of the ocean beneath it. [b]i.e[/b]: If it takes 1 second for the sound to reflect off of the ocean floor and return, the ocean floor will be approximately 1600 metres away (1600m deep), as the speed of sound is approximately [b]1600m/s in water[/b]. Another example: [code] Time for sound to reflect off of ocean floor = 0.75s Depth of water = 1600 [multiply] 0.75 [u]Depth of water = 1200 metres[/u] [/code] These results are shown on an oscilloscope. [/highlight] This method can be used to detect anything underwater.