tag:theconversation.com,2011:/au/topics/accoustic-waves-17581/articlesAccoustic waves – The Conversation2016-08-11T23:11:52Ztag:theconversation.com,2011:article/623552016-08-11T23:11:52Z2016-08-11T23:11:52ZJust for you: how to create sounds that only you can hear in a venue<figure><img src="https://images.theconversation.com/files/132560/original/image-20160801-25650-1g7boih.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's possible to create sound in a part of a room that only you can hear, but others elsewhere cannot.</span> <span class="attribution"><span class="source">Shutterstock/Syda Productions</span></span></figcaption></figure><p>Picture your typical busy cafe or restaurant that’s full of people. The diners are usually all forced to listen to the same music that’s pumped into the venue via the speakers.</p>
<p>What if you could create sound that was tailored to each table’s taste so the people there could listen to their own music, sports event, news or just enjoy the silence?</p>
<p>It might sound impossible but it’s closer to becoming a reality than you think. And there are many potential uses for these customised zones of sound.</p>
<p>For example, open plan offices could potentially be quieter as the sounds from watching online videos or conferencing could be custom designed so as not to annoy your co-workers. It could be possible to watch movies at the cinema or at home in different languages by simply sitting in the zone that suits you best.</p>
<p>Personalised advertisement in shopping malls could become a reality, tailored to individuals. Sports stadiums could have various commentary and a quieter field to play on. Maybe art installations and museums could provide audible content in front of exhibits. </p>
<p>The list of possibilities is endless.</p>
<h2>How does it work?</h2>
<p>The sounds you hear every day are <a href="https://theconversation.com/explainer-making-waves-in-science-54555">waves</a> that travel through air, just like the ripples on the surface of a pond. When the waves meet they can either stand on top of each other, cancel each other or combine to make new sounds.</p>
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<p>But by carefully controlling the waves and where they combine, it is possible to have them cancel in some spaces and amplify in other spaces.</p>
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<p>If this idea sounds familiar it might be because you’ve heard of noise cancelling headphones and earphones that perform a <a href="https://www.youtube.com/watch?v=HOdEvhEjO2I">similar trick</a>. They listen to sounds moving towards the ear and produce a wave that cancels that sound. But this only happens in one very small area at the ear.</p>
<p>Now think of extending this to a larger area surrounded by loudspeakers to control the ripples of sound travelling through the space inside. </p>
<h2>In the zone</h2>
<p>Each loudspeaker is tuned carefully. They can now produce <a href="http://users.cecs.anu.edu.au/%7Ewzhang/JP/2015SPM_Personal_Sound_Zones.pdf">zones of sound</a> from standing waves and zones of quiet from cancelling waves.</p>
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<span class="caption">By varying the output of sounds from an array of speakers surrounding a space you can target specific sounds in specific locations. The different sounds here are represented by the different colours.</span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Theoretically, with unlimited power, any size and any number of zones of sound or silence can be created. But it is more practical to create zones no smaller than approximately half a metre wide and separated by about half a metre. This size would comfortably fit a human head and so the need to go smaller is often not necessary.</p>
<p>A difficult obstacle to overcome is the reflections of sound from the walls of a room. Reflections introduce more sound that needs to be controlled. </p>
<p>The same way light reflects off a mirror, sound reflects off a wall. A mirror that is dirty or covered reflects light poorly and the walls of a room can be treated in a similar manner to reduce sound reflections.</p>
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<p>But for walls that can’t be treated, a number of microphones in the room <a href="http://dx.doi.org/10.1109/ICASSP.2016.7471727">may be a solution</a> to reducing the reflections. <a href="http://www.npl.co.uk/news/seeing-sound">Lasers</a> have also been used to measure how sound travels through a space and <a href="http://dx.doi.org/10.1109/ICASSP.2014.6854501">might hold potential</a> in the future to predict room reflections.</p>
<p>Generally, the more loudspeakers used, the better the quality of the zones that can be created. When space is limited, the number of loudspeakers that can fit into a room is reduced. </p>
<p>If too few loudspeakers are used and too many zones created, sounds start to leak between the zones. This can cause issues with privacy but not all leaked sounds can be heard.</p>
<p>One way to <a href="http://dx.doi.org/10.1109/ICASSP.2016.7471687">improve the privacy in the zones</a> is by using a technique called sound masking. We do this by carefully adding zones of subtle <a href="https://www.youtube.com/watch?v=9T978ES0LdQ">noise</a> that acoustically covers up leaked sounds with minimal effect on others.</p>
<p>We can also <a href="http://dx.doi.org/10.1109/APSIPA.2015.7415290">reduce the error when creating the zones</a>. This is done by allowing sounds to leak when people can’t hear them, which saves energy. That saved energy can then be used to improve sounds in other places where people want to hear them.</p>
<h2>Promising research</h2>
<p>Some promising research looks at using mathematical models of how the ear hears and processes sound. </p>
<p>This can provide better quality zones and reduce the number of loudspeakers required. Similar to how popular MP3 audio, MP4 video and JPG picture storage technologies work by using human perception to decrease file sizes.</p>
<p>There are still numerous questions to be answered, such as how do we perceive these zones of sound, <a href="https://www.researchgate.net/publication/275257184_The_Relationship_Between_Target_Quality_and_Interference_in_Sound_Zone">is the quality of the sound any good</a> and can reflections from the room be efficiently compensated for?</p>
<p>But we are still on the path to making them a reality. In the past ten years a lot of theory has been published on this topic. In the past five years some two-zone systems have been shown to work in the real world.</p>
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<p>Researchers have shown it is possible to provide a couple of distinct zones (with about half a metre between them). One zone can contain speech (or music) at a volume equivalent to a regular conversation, the other zone can contain a sound at a volume similar to background air conditioning.</p>
<p>Scale this up and public places will never sound the same again.</p><img src="https://counter.theconversation.com/content/62355/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jacob Donley receives funding from the Department of Education and Training (DET) and the University of Wollongong (UOW).</span></em></p><p class="fine-print"><em><span>Christian Ritz works for the University of Wollongong. He has received funding from the Australian Research Council (ARC) and the Cooperative Research Centres (CRC) Programme.</span></em></p>Your own choice of music in a restaurant, your preferred language in a cinema, and a personal tour in a museum. All are possible if you can control the sound in almost any place.Jacob Donley, PhD Candidate, University of WollongongChristian Ritz, Associate professor, University of WollongongLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/545552016-03-01T19:04:18Z2016-03-01T19:04:18ZExplainer: making waves in science<figure><img src="https://images.theconversation.com/files/111888/original/image-20160218-1243-ky6bkp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Making waves.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/_imax/2644301036/">Flickr/Max Nathan</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>We see them at the beach. They’re behind every sound and light show and the miracle of Wi-Fi. And now, thanks to what’s being called the discovery of the century, they have opened a way of detecting distant black-hole collisions.</p>
<p>I’m talking, of course, about waves.</p>
<p>We wouldn’t have speech or ultrasound imaging without sound waves. Water waves are a surfer’s paradise. Electromagnetic waves make both vision and television possible, as well as Wi-Fi, chest X-rays and microwave ovens.</p>
<p>It is electrical waves, not electrons, that sweep down our wires and power lines at close to the speed of light (the actual electrons drift along behind, <a href="http://sciencequestionswithsurprisinganswers.org/2014/02/19/what-is-the-speed-of-electricity/">at less than a snail’s pace</a>!). </p>
<p>And the recent <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">discovery of gravitational waves</a> will open up a new frontier in astronomy.</p>
<h2>What’s in a wave?</h2>
<p>Waves are very different from particles. Waves have energy, but not mass. They love to diffract or spread out, not stay in fixed lumps.</p>
<p>When two waves meet they don’t bounce off each other: they just add and subtract as they pass through each other, and then carry on their ways as if they’d never met. This is called interference, and it makes waves highly unsuitable for snooker, but it is what lets many people use their mobile phones at the same time.</p>
<p>Water is a good example for thinking about the difference between waves and particles. Water can carry energy in two different ways. </p>
<p>First, it can flow from one place to another, such as from the river to the sea. In such a flow, each water molecule starts upstream and moves downstream. The flow is made up of particles.</p>
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<span class="caption">The ripples are waves in the water.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/scott-s_photos/7904846012/">Flickr/Scott Cresswell</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>But imagine the ripples spreading out from a dropped pebble in a pond, or watching the waves spread out from the bow of a passing boat. These waves also carry energy as, for example, they rock floating sticks and even push them along a little. </p>
<p>But the water molecules that make up the shape of the ripple just after the pebble is dropped are completely different to the ones that make up the ever-spreading ripple five seconds later. Each water molecule stays roughly where it is, barring some jiggling, while the wave moves on. So water waves are not a flow of particles.</p>
<h2>So how do waves move?</h2>
<p>When that pebble is dropped in the pond, it pushes water out of the way. The water has nowhere to go but to the side and up, creating a circular peak around the drop point. This peak falls again, under the forces of gravity and surface tension, pushing the water beneath it out of the way.</p>
<p>On the inside of the circle, this newly pushed water fills the hole left by the pebble passing through. But on the outside, it creates a new circular peak, just a little further out.</p>
<p>So a ripple spreads out from the drop point even though the individual water molecules are mostly just moving up and down in place.</p>
<p>More generally, waves need something to wave in: a medium. Water, air, power lines and the electromagnetic field are all suitable media. Even spacetime itself will do, in the case of gravitational waves.</p>
<p>Waves are simply distortions moving through the medium. These distortions can be started off by many means: a dropped pebble, a shout, a radio transmitter or colliding black holes.</p>
<p>In each case, the medium has some degree of elasticity and responds to a distortion by trying to snap back into shape. But this distorts the neighbouring region, and so on, and so a wave is born. </p>
<p>The strength of the distortions is called the amplitude of the wave, and is closely related to its energy.</p>
<h2>Catching the perfect wave</h2>
<p>All waves, whether in water, air or spacetime, can come either in pulses, such as a sharp sound, or as a collection of ripples, such as at the beach. But no matter what shape and size, any wave can be thought of as made up of many perfect waves added together. </p>
<p>A perfect wave is what we hear when a singer holds a single beautiful note. It is a smooth series of peaks and troughs in the strength of the wave, with successive peaks all separated by the same distance: the wavelength. The number of peaks passing a given point every second is called the frequency.</p>
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<p>Every wave is a combination of interfering perfect waves, and so has a spectrum of different frequencies. Visible light waves, for example, have a spectrum of colours, with each colour corresponding to a different frequency.</p>
<p>They can actually be separated out into their spectrum by a prism, as Isaac Newton famously showed to develop his theory of colours. </p>
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<a href="https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/69610/original/image-20150121-29731-1ciiybx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A prism reveals the many colours of visible light.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/23629083@N03/14200678625">Flickr/final gather</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Different radio and television stations transmit their signals on waves made up of different frequency bands, so that we can tune into the frequency we want. </p>
<p>The distortions of perfect waves, at any given point in the medium, fluctuate up and down in strength either along the same direction the wave is moving (longitudinal waves), or at right angles (transverse waves). These choices depend on the medium, and are called polarisations.</p>
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<span class="caption">Longitudinal and transverse waves.</span>
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<p>Sound waves in air are longitudinally polarised, light and gravitational waves are transversely polarised, while the seismic waves causing earthquakes come in both varieties. As do <a href="https://www.youtube.com/watch?v=ilZj8JUTvy8">slinky waves</a>!</p>
<p>Perfect transverse waves have a further choice of the different directions at right angles to the direction the wave is moving in. Polaroid sunglasses take advantage of this, blocking the glare that comes from horizontal fluctuations, while letting through vertically polarised waves.</p>
<h2>Measuring waves</h2>
<p>Measuring waves is important in many parts of science, whether it gives us information about the source of the waves, or about the medium that they have travelled through.</p>
<p>For example, light waves emitted from the sun give us information about its temperature and composition, while light waves passing through a microscope slide can tell us whether someone needs medical treatment or not.</p>
<p>In all cases, the wave must be detected by some means, such as an eye or a camera. </p>
<p>Significant progress in science is made every time we learn how to generate or control or detect a new type of wave. Electromagnetic waves were only <a href="https://theconversation.com/let-there-be-light-celebrating-the-theory-of-electromagnetism-35723">discovered 150 years ago</a> and look at the use we make of them now, as mentioned before: radio, television and microwaves, to name just a few.</p>
<p>Gravitational wave detection is the most recent example, providing a unique window on those events strong enough to shake space and time themselves.</p>
<h2>A quantum twist</h2>
<p>At atomic scales and smaller, the distinction between waves and particles becomes somewhat blurred.</p>
<p>Sufficiently chilled-out atoms can start behaving as if they are spread out and <a href="https://www.learner.org/courses/physics/visual/visual.html?shortname=route_to_bec">overlapping each other</a>, rather like waves. And if the intensity of a light beam is dialled down enough, it is found to only illuminate <a href="https://www.youtube.com/watch?v=GzbKb59my3U">a single camera pixel at a time</a>, as if the beam was made up of particles.</p>
<p>Quantum mechanics tells us that waves and particles are fundamentally two sides of the same coin: different kinds of distortions in a medium. But the nature of the quantum medium is a profound mystery that drives the research of many scientists around the world (including my own).</p>
<p>It is only with its solution that we will finally understand just what waves are.</p><img src="https://counter.theconversation.com/content/54555/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Hall receives funding from the Australian Research Council and the Foundational Questions Institute.</span></em></p>We find them at the beach, in every sound and light show, the miracle of wi-fi and now in the fabric of space-time itself. But what exactly is a wave?Michael Hall, Senior Research Fellow, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/427802015-06-04T05:20:01Z2015-06-04T05:20:01ZScience facts behind Dr Who sonic screwdriver are even more exciting than fiction<figure><img src="https://images.theconversation.com/files/83817/original/image-20150603-2929-1cnt0zk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Turns out a real sonic screwdriver is more than just a plastic torch.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/c/16640120131">danny_k1m</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>Doctor Who employs his fictional sonic screwdriver in a <a href="http://tardis.wikia.com/wiki/Sonic_screwdriver">vast range of situations</a> that includes opening locks, breaking into computers and cash machines, defusing bombs in addition to rotating screws. However, research suggests that this iconic science fiction device is at least partly based on science fact. </p>
<p>The idea that sound waves carry energy seems intuitively reasonable – think of the physical feeling we humans experience when we get close to powerful loudspeakers with heavy sub-bass found at concerts and clubs. Sound can be felt physically and not just heard. A fantastic demonstration of this phenomenon can be found in <a href="http://mashable.com/2014/01/02/acoustic-levitation-video">acoustic levitation experiments</a>: if the distance between a loud speaker and a reflector is adjusted so that a standing wave is formed, objects can be levitated and held aloft at low-pressure regions known as nodes.</p>
<p>While this looks like spooky action at a distance, it’s purely down to the fact that acoustic waves, like their electromagnetic counterparts, carry momentum. This means they can apply a force, usually called the <a href="http://www.researchgate.net/profile/Alexander_Doinikov/publication/235345891_Acoustic_radiation_forces_Classical_theory_and_recent_advances/links/02bfe51138bda0459b000000.pdf">acoustic radiation force</a>. If the force is stronger than gravity, objects can be levitated. Loudspeakers generally produce linear momentum, so that they can push objects in straight lines. </p>
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<p>This may be of great use for <a href="https://www.youtube.com/watch?v=LTuuATDO5os">repelling Daleks</a>, but useless for turning screws. This is where acoustic vortices come to the rescue: these are acoustic waves with wavefronts shaped in a spiral pattern, called a helix (like one strand of the DNA double helix). This spiral pattern provides acoustic vortices with rotational, rather than linear, momentum. If this momentum can be transferred to an object – such as a screw – the result is a sonic screwdriver.</p>
<p>The first to get close to a real sonic screwdriver was a research team from the University of Dundee who in 2012 created an <a href="http://www.bbc.co.uk/news/uk-scotland-17760077">acoustic vortex with a special medical ultrasound transducer</a> designed for destroying tumours. They used this device to rotate a large disk made from a material which absorbed the rotational momentum of the waves. This was impressive, but it doesn’t replicate many of the sonic screwdriver’s capabilities. We’ve gone a step further by showing that similar devices can be scaled down and <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.214301">used to manipulate microscopic particles</a>.</p>
<p>We created the required swirling sound waves using a number of tiny ultrasonic loudspeakers arranged in a circle. This device, only 10mm in diameter, created acoustic vortices of around 1mm in size. In turn, these tiny acoustic vortices were able to rotate objects measuring between one and 100 microns – about the width of a human hair. If the size of the objects was just right, the acoustic vortex acted like a tiny tornado. </p>
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<a href="https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=315&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=315&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=315&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=396&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=396&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83818/original/image-20150603-2935-18t5n86.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=396&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Accoustic vortex, seen in the experiment (top) and in the theoretical predictions (bottom), showing how mm-scale accoustic vortices spin 0.5 micron tracer particles. Colour indicates the rotational energy of the vortex.</span>
<span class="attribution"><span class="source">Bruce Drinkwater/University of Bristol</span>, <span class="license">Author provided</span></span>
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<p>For example, when a mixture of household flour and water was placed in the device, the flour particles were drawn into the vortex core where they were spun around at high speeds. Conversely smaller particles just moved slowly around in circles and were not attracted to the vortex core at all. This millimetre scale means that we now have what could be described as a watchmaker’s sonic screwdriver, potentially capable of undoing the very smallest screws.</p>
<p>So while it’s great to go some way to grounding the imagination of Doctor Who’s scriptwriters in sound science, do these acoustic vortices have any uses in the real world? The answer is yes, but perhaps not in the ways that that Doctor Who might imagine. For example, they could be used to create microscopic centrifuges for sorting biological cells, or for water purification. What makes these possible is that this latest study has shown how different-sized particles behave differently when exposed to tiny acoustic vortices.</p>
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<a href="https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=769&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=769&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=769&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=966&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=966&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83816/original/image-20150603-2929-5y1h1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=966&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Now with more sonic, and more nanoparticles.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/krupptastic/5469973193/">krupptastic</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>More exciting is the knowledge that the particles’ motion is also extremely sensitive to their material properties, such as stiffness and density. This could lead to new methods for medical diagnostics. If, for example, healthy cells can be distinguished from unhealthy ones (cancerous cells are thought to be softer then healthy cells), these detections could be possible on a very small scale – perfect for medical diagnostics and for forensics.</p>
<p>It’s likely that acoustic vortices will soon join existing methods as a new tool for the controlled manipulation of tiny and microscopic matter. So sometimes science fact is just as interesting as science fiction – now if someone could just reverse-engineer the TARDIS.</p><img src="https://counter.theconversation.com/content/42780/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bruce Drinkwater receives funding from the UK Engineering and Physical Sciences Research Council (EPSRC).</span></em></p>Sound waves can do useful things and move physical objects, so a sonic screwdriver isn’t out of the question.Bruce Drinkwater, Professor of Ultrasonics, University of BristolLicensed as Creative Commons – attribution, no derivatives.