• Infrasound refers to extreme bass waves or vibrations, those with a frequencybelow 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 insome people including anxiety, extreme sorrow, and chills.• Infrasonic waves can carry over long distances [thousands of kilometres] and areless susceptible to disturbance or interference than waves of higher frequencies.• Infrasound may be produced by wind, types of earthquakes, ocean waves, andcertain 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 areunstoppable.Furthermore, not much amplitude is needed to produce negative effects in the humanbody. 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 physicalstructures with great force.The sensation vibrates internal organs and buildings, flattening objects as the sonicwave strikes.At certain pitches, it can explode matter.EXAMPLES• Natural explosions from volcanoes produce infrasonic waves. When Krakatauexploded, an entire island was lifted 100 miles into the air, and windows wereshattered 1,000 miles away from ground zero. The shock waves, affecting both earthand atmosphere, continued for hours.• Explosives, such as atomic weapons, produce infrasound. Zone one is ground zeroand its destruction. Zone 2 is a powerful, speeding, sonic wave of reduced airpressure. This concussion blast travels at great distances away from ground zero andfew survive its destructive path.
Uses of infrasound:2.Medical: (therapeutic devices) - Several studies conducted in Russia and Europe reported that infrasoundhas therapeutic effects. - Infrasound peumomassage: At 4 Hz, the progression of myopia inschool children can be stabilized. - Infrasound phonophersis in antibacterial drugs: In treatment ofpatients with bacterial keratitis, it is as effective as local instillations of thesame drugs.2. Monitoring activities of the atmosphere:- Infrasonic waves will be influenced by the atmosphere during itspropagation, which is closely related with the distribution of temperature andwind in the atmosphere.- By measuring the propagation properties of infrasonic wavesgenerated by natural sources, one can detect some characteristics and rulesof the large scale meteorological motions.3. Forecasting natural disasters:-Many disasters, such as volcanic eruptions, earthquakes, land-slides andclear-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 tocommunicate 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 becaused by infrasonic vibrations”--Psychologist Richard Wiseman of the University ofHertfordshire
• High-frequency sound waves that is above the audibility range of thehuman ear [approximately 22kHz]• Wavelength of about 1.5 mm• Sound ccannot be heard but can be emitted and detected by specialmachines• The speed of ultrasound does not depend on its frequency; it dependson what material or tissue it is travelling in. Both the mass and spacing ofthe molecules and the attracting force between the particles of thematerial have effects on the speed of the ultrasound as it passes through.• Ultrasound travels faster in dense materials and slower in compressiblematerials. 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 asechoes when it hits a more solid/dense surface• When the ultrasound hits different structures in the body of differentdensity, 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 theenergy into another form, and delivers the power to another target.-In this case, the transducer acts as a loudspeaker or a microphone, itconverts electrical signals to ultrasound waves, and picks up thereflected waves, converting them back into electrical signals.-The electrical signals returned to the transducer are used to form pictureson a television screen.
Uses of ultrasound: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.
• Pulse echo visualization:-The information of objects is obtained by using discrete lines of sight, with thetransducer position and orientation which defines the line of sight and thedelay 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 manyparts 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 withDoppler measurements, which employ the Doppler effect to assess whetherstructures (usually blood) are moving towards or away from the probe,and its relative velocity.- The principal applications of Doppler effect are in cardiac and peripheralvesicular diagnostic specialties. Current qualitative applications involve 2aspects of blood flow evaluation. Doppler devices are primarily concerned withthe detection and evaluation of blood flow disturbances resulting from valvesand septal defects.
2. In animals:• For navigation:- Bats use ultrasound for navigation. They send out ultrasounds and judgesthe distance of objects ahead of them, or what the objects are, by the receivedechoes. This allows them to catch flying insects while flying full speed in pitchdarkness.• Communication:- Whales make use of ultrasounds for communication purposes. Individualpods of whales have their own distinctive dialect of calls, similar to songbirds.- Singing whales are usually solitary males who exhibit it in a shallowsmooth-bottomed area where sound propagates well. They are interpreted asterritorial and mating calls.