My Science School

            Sonomicrometry is a technique that makes use of the transmission of ultrasound energy through certain type of crystals and tissues to measure distance.

            It has a variety of applications, including measuring the distance between two fixed points in a soft tissue environment, and, quantifying the function and dynamics of cardiac, skeletal or smooth muscles. Traditionally, this technique has been used to determine cardiac function on large research animals like dogs, sheep, pigs etc. It was first done by Dean Franklin in 1956, and was quickly adopted by other biologists.

            At present, sonomicrometry is the most prevalent method to determine muscle length changes during animal locomotion, feeding and other bio-mechanical functions. Sonomicrometry crystals are usually implanted inside the skeletal or cardiac muscle tissues to track length changes during activities such as heart-beat, chewing etc. However, sonomicrometer devices cannot be used to treat or diagnose medical conditions in animals or humans.

           Animals are always thought to be intelligent enough to sense changes in environment. But a few studies in recent times suggest that some birds too are equally smart. For example, the golden winged warblers.

            In April 2014, a massive thunderstorm caused a series of tornadoes to tear through the Southern and Central United States. But something interesting happened just a day or two before this disaster – large flocks of golden winged warblers fled the area. Scientists say that the birds’ behaviour was caused by their ability to sense infrasound, which was an early warning sign.

            Other species that are sensitive to weather changes are seagulls and African guinea fowls. Apparently, seagulls get to hear low frequency sounds caused by large storms and also, earthquakes. This prompts them to fly inland before these disasters happen. So also is the case with African guinea fowls – they predict weather and change their nature accordingly.

            There are many animals that use infrasound for communication. One of the best examples is the elephant. Research has proved that the vocal communication of these mammals ranges down into lower frequencies. As a result, the sound waves get carried farther, and reach elephant groups that are located very far away.

            Interestingly, tigers also produced infrasound, along with a variety of other sounds. This is said to help them maintain their hunting grounds. Their low frequency sounds at 18 Hz and below, most of which are inaudible to humans, drive away rivals from their territory, and also attract mates. Such sounds not only cover long distances, but also penetrate dense forests.

            In addition to these two, there are many other animals that produce infrasound. Examples of these are giraffes, alligators, hippos, and marine mammals like humpback whales.

 

            Since time immemorial, there have been stories, legends, and reports on the sensitivity of animals towards different kinds of sounds.

            But the most commonly heard reports are on how some animals detect infrasonic sounds before natural disasters. As per one of the latest reports, animals like buffaloes, goats and dogs were found unharmed along the Cuddalore coast of India, where thousands died following the tsunami of 2004. People around the region said that many animals fled the area hours before the incident took place.

            Another group of animals that are said to have the ability to sense disasters are cats. Not just smaller animals, large once like elephants too grow restless prior to dangerous natural occurrences.

            Although many studies have been made, the reason for such strange behaviour in animals is yet to be confirmed.

            Infrasound can be defined as the low-frequency sound that is below 20 Hertz.

            For this reason, it cannot be heard by the human ear. Animals, on the other hand, are sensitive to such sounds. Research has proved that some of them can sense infrasonic sounds from natural events like earthquakes and volcanoes, and act accordingly. They can also use it for communication between each other.

            There are many uses of infrasonic sound. Primarily, it can be used to detect volcanic eruptions. Scientists use infrasound to track the passage of meteors through the atmosphere.

            There are many sources from where infrasound can come. They include large natural events like earthquakes, avalanches, volcanoes, and extreme weather events.

            In addition, man-made events such as explosions, wind turbines, aircraft breaking the sound barrier, and certain speakers too, produce it.

            The special characteristic of infrasound is its ability to cover long distances and get around obstacles with little dissipation.

            In the case of medical scans and non-destructive testing, experts use relatively low strength ultrasound waves. Much stronger waves are used for removing unwanted deposits like painful stones.

            Let us make it clearer. If we have problems caused by stones in kidney, gall bladder, or liver, powerful ultrasound waves are fired from outside our body in order to make the stone vibrate, and disintegrate. For this purpose, doctors now use what is known as an ultrasonic gun, which causes relatively lesser pain. The gun forces out short bursts of high frequency vibrations that cause the stones to resonate. These then smash the stones into pieces.

            A similar technique is used to destroy cancerous tumours and damaged regions of the brain called lesions. Here, ultrasound energy is applied to heat in order to destroy diseased tissues.

             Some of the most important applications of ultrasonics can be seen in the field of medicine. Ultrasonography or ultrasonic scanning is one of it, which uses high frequency sound waves to produce images of internal organs, vessels and tissues. This type of scanning is used to diagnose the condition of organs such as liver, kidneys or gallbladder.

            Then, there is something called obstetric ultrasound. It is a technique used during pregnancy to create images of a baby inside the womb.

 

       

 

 

    Another public health application of ultrasonics is in dental care. It enables the equipment called ‘descalers’ to remove plaque from teeth through a smoother and less painful experience.

            Yet another important use can be seen in the cleaning of equipment. What makes ultrasonic technology so popular in medicine is its effectiveness and affordability.

            Acoustic microscopy is a technology that helps in visualizing tiny structures using high frequency ultra sound waves. The microscopes in this fashion penetrate solid materials and create visible images of internal features, including defects like cracks and voids. For this purpose, they use frequencies up to several gigahertz.

             One of the most advanced types of acoustic microscopy is scanning acoustic microscopy. Here, the internal parts of a sample can be viewed without staining or causing any damage. It relies on a beam to scan the sample while it is in water.

            The difference between a traditional microscope and an acoustic microscope is that the former allows us to see only the surface of a specimen, while the latter obtains images from deeper layers. It also takes accurate measurements at a micro-level, which other microscopes may not be able to obtain.

          Just like humans, all forms of life in the Universe have the ability to hear, or sense things around them. But some of them have exceptional features for hearing, which enable them to survive better than others.

          One such animal is the elephant. Its hearing frequency is somewhere between 16 and 12,000 hertz, as a result of which, it can hear at a frequency 20 times lower than us.

          Another mammal that has a special auditory system is the fennec fox. It is a small species of fox seen in the sandy Sahara. It has large ears that play a vital role in hearing, as well as keeping the animal cool by spreading out during high temperatures. Other than these two, there are many animals that are sensitive to sounds. These include pigeons, owls, dolphins, etc. 

            As a matter of fact, no two species of animals look alike, or behave alike. Similarly, the abilities and senses of animals vary too, from species to species.

            One cannot expect a monkey to have the hearing ability of an elephant, nor can auditory ability between a marine mammal and a terrestrial animal be compared. Generally, it is seen that larger animals hear and use low frequency sounds, while smaller ones have with higher frequencies.

            However, there are always exceptions, as in the case of spade foot toads that can easily pick up low-frequency sounds. These are animals that live in desert habitats and spend their days buried in ground during dry seasons. They come out only when pools are formed after infrequent rains. And that is when their young ones are developed, before the water dries up.

            Similar to animals, birds and insects too have peculiar auditory features that help them adapt to surroundings.

 

          Kangaroo rats are unique animals that live in desert and dry, open areas. They are perfectly adapted to desert life, and can survive without drinking water, as they get moisture from their seed diet.

          But, what makes kangaroo rats special is their exceptional sense of hearing. It helps them detect enemies like owls and snakes, even when they are approaching from a distance.

          Kangaroo rats have large ear-drums and middle ears. However, the oval window between the middle and the inner ears is considerably smaller. This peculiarity helps the auditory system of the animal to magnify low frequency sounds by about 100 times.

          As a result, it can hear the sound of air flowing over the wings of an owl, or the scales of a snake moving across sand. Now, isn’t that a rare gift for an animal?

 

          The barn owl is a raptor that can be spotted on all continents except Antarctica. It is said to have extraordinary abilities that help in catching fast-running animals.

          The most predominant ability is the bird’s sense of hearing, which stands out for its sharpness. It is so superior that the bird can decipher the direction and height from which a sound comes! This is exactly what makes it a sharp hunter.

          Unlike others, the barn owl’s ability to hear is strengthened by its feathers. The heart-shaped facial disc made of stiff feathers helps the owl in picking up noise. It funnels any sound towards the ears, which open on either side of the bird’s head. The ruff of feathers is so important for this owl that without it, the bird cannot catch preys. And with it, even the slightest sound can be detected.

          Interestingly, a large portion of the barn owl’s brain is devoted to building sound maps of places!

          Bats are fascinating animals that have many unique features. One of these is the ability to sense a prey location using sound. Confusing, isn’t? Let’s get to know how they do it.

          Bats use the sound technique known as ‘echolocation’. It means determining the location of something by measuring the time it takes for an echo to return from it.

          As they fly, bats make calls, and listen to the returning echoes to build up a sound map of their surroundings. These sounds are produced by contracting their larynx. Measuring the time it takes for the echo to return, this smart mammal can predict at what distance its prey is!

          Usually, the calls of bats are pitched at such high frequencies that humans fail to hear them naturally. Another interesting fact is that bats can distinguish between obstacles and preys through echolocation, and can thus avoid the obstacles and catch the prey.

          How many of us have seen birds that don’t make sounds? Not many. Birds are in fact, most known for their ability to make sound, be it sweet chirping, or harsh caws.

          While humans and other mammals produce sound from the voice box or larynx, birds have a different organ for sound production - the syrinx. Located near lungs, it is a double voice-box that consists of a resonating chamber, and numerous membranes. As air flows over them, the membranes move back and forth, producing sound.

          There are different frequencies at which bird sounds come out. There are other birds too that can sing in high frequency ranges, like warblers, sparrows, wax-wings, kinglets etc. It is believed that one can never stop a bird from learning its own species’ song.

          Interestingly, many species have at least some mimicked sequences in their most common songs and calls.

               For a long time, it was believed that oceans were silent places. But, as science advanced, it was proved that most of the animals living in waters cannot survive without sounds. 

               We know for a fact that light reaches only till the surface of water. In the case of smell, it fails to spread far from their source, while under water. Contrary to this, sound waves find their ideal medium in water, and travel faster than in air. They move greater distances, and at the surface of water, get reflected back into the depths. That is why even the sound of surf crashing on to a rocky beach travels far into the ocean.

               In general, sounds help most marine animals to sense their surroundings, communicate, locate food, and protect themselves.

               Mammals like whales, for instance, identify objects like food and obstacles using low frequency pulse signals. Dolphins communicate through clicks and whistles. They use the technique of echolocation to detect and characterize objects.