• Infrasound refers to extreme bass waves or vibrations, those with a frequency below the audibility range of the human ear (i.e. < 20 Hz).

• Hence, these waves cannot be heard by humans.

• They can be felt and, as studies have shown, they produce a range of effects in some people including anxiety, extreme sorrow, and chills.

• Infrasonic waves can carry over long distances [thousands of kilometres] and are less susceptible to disturbance or interference than waves of higher frequencies.

• Infrasound may be produced by wind, types of earthquakes, ocean waves, and certain things such as avalanches, volcanoes, and meteors etc…

• Infrasound is especially dangerous, due to its strong vibrations, or oscillations. They hug the ground, travel for long distances without losing strength, and are unstoppable. Furthermore, not much amplitude is needed to produce negative effects in the human body. Therefore, even mild infrasound exposure requires several hours, or even days, to reverse the resulting symptoms.

•Waves of infrasound are invisible, but they slam into living tissues and physical structures with great force.The sensation vibrates internal organs and buildings, flattening objects as the sonic wave strikes.At certain pitches, it can explode matter.

EXAMPLES• Natural explosions from volcanoes produce infrasonic waves. When Krakatau exploded, an entire island was lifted 100 miles into the air, and windows were shattered 1,000 miles away from ground zero. The shock waves, affecting both earth and atmosphere, continued for hours.• Explosives, such as atomic weapons, produce infrasound. Zone one is ground zero and its destruction. Zone 2 is a powerful, speeding, sonic wave of reduced air pressure. This concussion blast travels at great distances away from ground zero and few survive its destructive path.

Uses of infrasound:1.Medical: (therapeutic devices) - Several studies conducted in Russia and Europe reported that infrasound has therapeutic effects. - Infrasound peumomassage: At 4 Hz, the progression of myopia in school children can be stabilized. - Infrasound phonophersis in antibacterial drugs: In treatment of patients with bacterial keratitis, it is as effective as local instillations of the same drugs. 2. Monitoring activities of the atmosphere:- Infrasonic waves will be influenced by the atmosphere during its propagation, which is closely related with the distribution of temperature and wind in the atmosphere.- By measuring the propagation properties of infrasonic waves generated by natural sources, one can detect some characteristics and rules of the large scale meteorological motions.

3. Forecasting natural disasters: -Many disasters, such as volcanic eruptions, earthquakes, land-slides and clear-air turbulences, radiate infrasound in advance.- By monitoring the infrasound waves, we can forecast these disasters.

FUN FACTS!

• Elephants have the ability to emit infrasound to communicate at distances of up to 10 miles (12 - 35 Hz.). Even tigers emit infrasound.

•F.Y.I•“Odd sensations that people attribute to ghosts may be caused by infrasonic vibrations” --Psychologist Richard Wiseman of the University of Hertfordshire

• High-frequency sound waves that is above the audibility range of the human ear [approximately 22kHz]

• Wavelength of about 1.5 mm

• Sound ccannot be heard but can be emitted and detected by special machines

• The speed of ultrasound does not depend on its frequency; it depends on what material or tissue it is travelling in. Both the mass and spacing of the molecules and the attracting force between the particles of the material have effects on the speed of the ultrasound as it passes through. • Ultrasound travels faster in dense materials and slower in compressible materials. In soft tissue sound travels at 1500 m/s, in bones about 3400 m/s, and in air 330 m/s.• Travels freely through fluid and soft tissues but is reflected back as 'echoes' when it hits a more solid/dense surface• When the ultrasound 'hits' different structures in the body of different density, it sends back echoes of varying strength

How does ultrasound work and how to produce images of ultrasound?

-Ultrasound waves images are produced by a transducer.

-A transducer is a device that takes power from one source, converts the energy into another form, and delivers the power to another target.

-In this case, the transducer acts as a loudspeaker or a microphone, it converts electrical signals to ultrasound waves, and picks up the reflected waves, converting them back into electrical signals.

-The electrical signals returned to the transducer are used to form pictures on a television screen.

1. Medical:

• sonography:

- Ultrasound waves can be bounced off of tissues using special devices. The echoes are then converted into a picture called a sonogram.

- Ultrasound imaging, or ultrasonography, allows physicians and patients to get an inside view of soft tissues and body cavities, without using invasive techniques.

- Ultrasound is often used to examine a foetus during pregnancy, or a fatal heart.

- Ultrasound usually ranges from one MHz (one million cycles per second) to 20 MHz. This is because tissues absorb higher frequency energy more readily, hence producing fainter images.

Uses of ultrasound:

• Pulse echo visualization:

-The information of objects is obtained by using discrete lines of sight, with the transducer position and orientation which defines the line of sight and the delay of received echoes, which is used to determine the range of the echo-producing object.

- It can be used in a wide range of clinical conditions and is useful in many parts of the body.

- There are 3 modes of the pulse echo visualization (i.e. A-mode, M-mode, and B-mode)

• Doppler effect:

-Ultrasound based diagnostic imaging technique can be enhanced with Doppler measurements, which employ the Doppler effect to assess whether structures (usually blood) are moving towards or away from the probe, and its relative velocity.

- The principal applications of Doppler effect are in cardiac and peripheral vesicular diagnostic specialties. Current qualitative applications involve 2 aspects of blood flow evaluation. Doppler devices are primarily concerned with the detection and evaluation of blood flow disturbances resulting from valves and septal defects.

2. In animals:

• For navigation:

- Bats use ultrasound for navigation. They send out ultrasounds and judges the distance of objects ahead of them, or what the objects are, by the received echoes. This allows them to catch flying insects while flying full speed in pitch darkness.

• Communication:

- Whales make use of ultrasounds for communication purposes. Individual pods of whales have their own distinctive dialect of calls, similar to songbirds.

- Singing whales are usually solitary males who exhibit it in a shallow smooth-bottomed area where sound propagates well. They are interpreted as territorial and mating calls.

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/2.http://www.brooksidepress.org/Products/OBGYN_101/MyDocuments4/Ultrasound/basic_ultrasound.htm3.http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/usound.html4.http://www.slideshare.net/andamooka/ultrasound-scanning5.http://www.rajaram-parantapa.com/AuditoryPaper.pdf