Ultrasounds dance the 'moonwalk' in new metamaterial

Silicone beads embedded in a water-based gel (photograph is ~2 cm across). Credit: © CRPP

Metamaterials have extraordinary properties when it comes to diverting and controlling waves, especially sound and light: for instance, they can make an object invisible, or increase the resolving power of a lens. Now, researchers at the Centre de Recherche Paul Pascal (CNRS) and the Institut de Mécanique et d'Ingénierie de Bordeaux (CNRS/Université de Bordeaux/Bordeaux INP/Arts et Métiers ParisTech) have developed the first three-dimensional metamaterials by combining physico-chemical formulation and microfluidics technology. This is a new generation of soft metamaterials that are easier to shape. In their experiment, the researchers got ultrasonic oscillations to move backwards while the energy carried by the wave moved forwards. Their work opens up new prospects, especially for high-resolution imaging (ultrasonography). It is published on 15 December 2014 in the journal Nature Materials.

Since the 2000s, the international scientific community has seen interest in metamaterials and their extraordinary properties grow exponentially. A metamaterial is a medium in which the phase velocity of light or sound waves can be negative (the material is said to have a negative refractive index).. In such a medium, the phase of the wave (the successive oscillations) and the energy carried by this same wave move in opposite directions. This property is not found in any natural homogeneous medium.

To obtain a metamaterial, it is necessary to make a heterogeneous medium that contains a large number of inclusions (known as microresonators). The usual way is to use micromechanical methods (etching, deposition, etc) to machine solid supports that will have the properties of metamaterials in one or two dimensions. However, this method cannot be used to work with soft matter at the micrometer scales required for ultrasounds, and the materials obtained remain limited to one or two dimensions.

In this study, the researchers developed a new type of metamaterial, in the fluid phase, formed of porous silicone microbeads embedded in a water-based gel. This metafluid is the first three-dimensional metamaterial to work at ultrasonic frequencies. In addition, due to its fluid nature, it can be made using physico-chemical processes and microfluidics technologies, which are much easier to implement than micromechanical methods.

One of the properties of porous media is that sound travels through them at very low speed (a few tens of meters per second) compared to water (1500 meters per second). Due to this sharp contrast, the whole suspension has the properties of a metamaterial provided the bead concentration is sufficient: when the researchers studied the propagation of ultrasonic waves through this medium, they directly measured a negative refractive index. Within such a metafluid, the energy carried by the wave travels from the emitter to the receiver, as expected, whereas the oscillations appear to move backwards in the opposite direction, rather like a dancer doing the 'moonwalk'.

These results open the way to numerous applications ranging from high-resolution ultrasound imaging to sound insulation and stealth in underwater acoustics. In addition, the soft-matter physico-chemical techniques used to make this metamaterial makes it possible to produce fluid or flexible materials with adaptable shapes, potentially at the industrial scale.

Source: CNRS (Délégation Paris Michel-Ange)

High-intensity sound waves may aid regenerative medicine

This is a cross section through a histotripsy lesion created in bovine liver tissue with the liquified cellular contents washed out revealing the remaining extracellular matrix. The scale bar represents 5mm. Credit: T.Khoklova/UW

Researchers at the University of Washington have developed a way to use sound to create cellular scaffolding for tissue engineering, a unique approach that could help overcome one of regenerative medicine's significant obstacles. The researchers will present their technique at the 168th meeting of the Acoustical Society of America (ASA), held October 27-31, 2014, at the Indianapolis Marriott Downtown Hotel.

The development of the new technique started with somewhat of a serendipitous discovery. The University of Washington team had been studying boiling histotripsy -- a technique that uses millisecond-long bursts of high-intensity ultrasound waves to break apart tissue -- as a method to eliminate cancerous tumors by liquefying them with ultrasound waves. After the sound waves destroy the tumors, the body should eliminate them as cellular waste. When the researchers examined these 'decellularized' tissues, however, they were surprised by what the boiling left intact.

"In some of our experiments, we discovered that some of the stromal tissue and vasculature was being left behind," said Yak-Nam Wang, a senior engineer at the University of Washington's Applied Physics Laboratory. "So we had the idea about using this to decellularize tissues for tissue engineering and regenerative medicine."

The structure that remains after decellularizing tissues is known as the extracellular matrix, a fibrous network that provides a scaffold for cells to grow upon. Most other methods for decellularizing tissues and organs involve chemical and enzymatic treatments that can cause damage to the tissues and fibers and takes multiple days. Histrostipsy, on the other hand, offers the possibility of fast decellularization of tissue with minimal damage to the matrix.

"In tissue engineering, one of the holy grails is to develop biomimetic structures so that you can replace tissues with native tissue," Wang said. Stripping away cells from already developed tissue could provide a good candidate for these structures, since the extracellular matrix already acts as the cellular framework for tissue systems, Wang said.

Due to its bare composition, the matrix also induces only a relatively weak immune response from the host. The matrix could then theoretically be fed with stem cells or cells from the same person to effectively re-grow an organ.

"The other thought is that maybe you could just implant the extracellular matrix and then the body itself would self-seed the tissues, if it's just a small patch of tissue that you're replacing," Wang said. "You won't have any immune issues, and because you have this biomimetic scaffold that's closer to the native tissue, healing would be better, and the body would recognize it as normal tissue."

Wang is currently investigating decellularization of kidney and liver tissue from large animals. Future work involves increasing the size of the decellularized tissues and assessing their in-vivo regenerative efficacy.

Source: Acoustical Society of America (ASA)

First study of 'Golden Age' mandolins unlocks secrets of their beauty

Mandolins made by G. Filano 1765 (a), A. Vinaccia 1785 (b), G.B. Fabricatore 1789 (c) and G. Gagliano 1799 (d). Credit: Image courtesy of Springer Science+Business Media

Analyzing varnishes and decorations could provide a new way to identify mandolin "Old Masters."

Some of the most elaborately decorated instruments in history were produced in 18th century Naples. The materials for varnishes and decorations used by individual mandolin masters, honed for wealthy clients in the ancient city's labyrinthine artisan quarter, have been kept secret for over 200 years. Details are disclosed for the first time by Tommaso Rovetta from the Università degli Studi di Pavia and colleagues at the Laboratorio Arvedi Research Group in Springer's journal Applied Physics A -- Materials Science & Processing.

Italian conservation scientists studied ten instruments from some of the most important dynasties of the "Golden Age" of Neapolitan mandolins. Advanced high-resolution imaging techniques shed light on some of the most jealously guarded decorative secrets and could provide a new way to accurately identify mandolins from specific workshops.

The Neapolitan mandolin was set apart by the deeper bowl of its body, producing a more resonant sound heard in works by Beethoven and Verdi. The style was developed by the Vinaccia family and adopted by other leading luthiers such as the Filano, Fabricatore and Gagliano families.

The scientists obtained mandolins from each of these makers courtesy of the National Museum of Musical Instruments in Rome and a private collector. Given their rarity and excellent state of conservation, only microscopic samples could be analysed from already-damaged areas. Nevertheless, the team was able to see that different workshops used different techniques and materials to achieve the same aesthetic effect.

"For mandolins of unknown origin, our results could represent a new way to identify where they were made and therefore their historic and economic value," says Tommaso Rovetta.

In particular, the resin used between patterns of pearl, ivory, bone or possibly horn around the sound hole contain a mixture unique to each workshop. Shellac, a resin from the lac beetle popular today in nail varnish, seems to be the only substance which formed a common base to which pigments and minerals were added. In a 1796 Fabricatore, a mineral found only in the volcanic lavas of Mount Vesuvius was detected. The mixtures in Vinaccia instruments were particularly complex and the scientists were surprised to find the fossilised remains of diatoms, a type of algae.

"We assume there were intense exchanges of technical know-how between masters and their apprentices but, with no written records, this knowledge was taken to the grave," says Rovetta. "We hope the rediscovery of ancient recipes will provide inspiration to today's luthiers."

Source: Springer Science+Business Media

Engineers develop new sensor to detect tiny individual nanoparticles

The image shows arrays of self-referenced and self-heterodyned Whispering-Gallery Raman microlasers for single nanoparticle detection. A "pump" laser generates a single Raman lasing mode inside the silica resonators. Upon landing of a nanoparticle on the resonator, Raman laser circulating inside the resonator undergo mode splitting leading to two new lasing modes in different colors. Monitoring the changes in the color difference (frequency difference) enables detecting and measuring of nanoparticles with single particle resolution. Credit: J. Zhu, B. Peng, S.K. Ozdemir, L. Yang

Nanoparticles, engineered materials about a billionth of a meter in size, are around us every day. Although they are tiny, they can benefit human health, as in some innovative early cancer treatments, but they can also interfere with it through viruses, air pollution, traffic emissions, cosmetics, sunscreen and electronics.

A team of researchers at Washington University in St. Louis, led by Lan Yang, PhD, the Das Family Career Development Associate Professor in Electrical & Systems Engineering, and their collaborators at Tsinghua University in China have developed a new sensor that can detect and count nanoparticles, at sizes as small as 10 nanometers, one at a time. The researchers say the sensor could potentially detect much smaller particles, viruses and small molecules.

The research appears in the Proceedings of the National Academy of Sciences online Early Edition Sept. 1, 2014.

Yang and her colleagues have created the Raman microlaser sensor in a silicon dioxide chip to find individual nanoparticles without the need to "dope" the chip with chemicals called rare-earth ions to provide optical gain for the microlaser. Incorporating additions to the microresonator creates the need for more processing steps and increased costs and invites biocompatibility risks. In addition, the use of rare-earth ions requires specific "pump" lasers matching the energy transitions of the ions to generate optical gain, so for different rare-earth ions, different pump lasers must be used. Using the Raman process loosens the requirement of specific wavelength bands for pump lasers because Raman gain can be obtained using pump at any wavelength band, Yang says.

"This gives us the advantage of using the same dopant-free sensor at different sensing environments by tailoring the lasing frequency for the specific environment, for example, at the band where the environment has minimum absorption, and for the properties of the targeted nanoparticles by just changing the wavelength of the pump laser," says Sahin Kaya Ozdemir, PhD, a research scientist in Yang's group and the first author of the paper.

Yang's team integrated Raman lasing in a silica microcavity with the mode splitting technique pioneered by her group to develop a new, powerful sensor that more readily detects nanoparticles. The technology will benefit the electronics, acoustics, biomedical, plasmonics, security and metamaterials fields.

Yang's microsensor is in a class called whispering gallery mode resonators (WGMRs) because it works similarly to the renowned whispering gallery in London's St. Paul's Cathedral, where a person on one side of the dome can hear a message spoken to the wall by another person on the other side. Yang's device does much the same thing with light frequencies rather than audible ones.

One of the main differences between early resonators and the novel resonator, known as a morphology dependent resonator, was they didn't use mirrors to reflect light. Yang's WGMR is an actual mini-laser that supports "frequency degenerate modes," patterns of excitation inside the mini-laser's doughnut-shaped ring that are of the same frequency. One portion of light beamed by the Raman laser goes counterclockwise, another goes clockwise. When a particle lands on the ring and scatters energy between these modes, the single Raman lasing line splits into two lasing lines with different frequencies.

When a Raman laser beam is generated in the resonator, it likely will encounter a particle, such as a virus nanoparticle, on the circle. When the beam initially sees the particle, the beam splits into two, generating two lasing lines that serve as reference to the other to form a self-referenced sensing technique.

"Our new sensor differs from the earlier whispering gallery sensors in that it relies on Raman gain, which is inherent in silica, thereby eliminating the need for doping the microcavity with gain media, such as rare-earth ions or optical dyes, to boost detection capability," Ozdemir says. "This new sensor retains the biocompatibility of silica and could find widespread use for sensing in biological media."

"It doesn't matter what kind of wavelength is used, once you have the Raman laser circulating inside and there is a molecule sitting on the circle, when the beam sees the particle it will scatter in all kinds of directions," Yang says. "Initially you have a counterclockwise mode, then a clockwise mode, and by analyzing the characterization of the two split modes, we confirm the detection of nanoparticles."

In addition to the demonstration of Raman microlasers for particle sensing, the team says their work shows the possibility of using intrinsic gain mechanisms, such as Raman and parametric gain, instead of optical dyes, rare-earth ions or quantum dots, for loss compensation in optical and plasmonic systems where dissipation hinders progress and limits applications.

Source: Washington University in St. Louis

WHACK! Study measures head blows in girls' lacrosse

Trey Crisco invited lacrosse-playing girls to the lab to measure the impact of their blows as they whacked the head of a laboratory dummy — and to evaluate the performance of protective headgear. Credit: Mike Cohea/Brown University

Lacrosse players swing hard, which is why errant stick blows are the leading cause of concussion in girls' and women's lacrosse. In a new study, researchers measured how much the worst blows accelerate the head and how much different kinds of headgear could reduce those accelerations.

Girls' and women's lacrosse is a different game from the version played by males, said Joseph Crisco, the Henry Frederick Lippitt Professor of Orthopaedic Research in the Alpert Medical School of Brown University and a researcher at Rhode Island Hospital. Females wear far less protective equipment than males do, and injuries -- especially severe head injuries -- are comparatively rare. But recently the debate about whether female players should wear headgear has gained prominence.

Coming to blows

The girls delivered peak performance averaging 60 times the acceleration of Earth's gravity (60g) when they struck the headforms with their lacrosse sticks.

"The goal of our study was to answer the question of what types of head accelerations would you see if you were hit in the head with a stick," said Crisco, who used to coach his daughters in girls lacrosse and also sits on the Sports Science and Safety Committee of US Lacrosse, the national governing body of lacrosse.

To conduct the study, published online in the Journal of Applied Biomechanics, Crisco's team asked seven female lacrosse players aged 12 to 14 to deliver at least 36 whacks each, as hard as they possibly could, to various places on two dummy headforms in the lab.

"The kinds of hits recorded were basically aggressive street fights," Crisco said. "They were really whacking at it, every shaft was broken by the end of the study, which would never happen in a game. The goal was just to give US Lacrosse and the manufacturers some baseline information on the types of accelerations they could expect to see in a worst-case scenario."

They used six different sticks, each outfitted with motion capture markers. The headforms had embedded accelerometers. In a second set of experiments the headforms donned one of four different kinds of protective headgear.

On average across 508 successful blows in the first experiment, the girls swung their sticks about 18 miles an hour, enough to complete two revolutions in less than a second. (One of Crisco's prior studies showed, perhaps not surprisingly, that high school and college players swung their sticks even faster). The peak acceleration the girls delivered to the headforms when they struck them with the shafts of their sticks averaged 60 times the acceleration of Earth's gravity (60g).

That's about three times more force than, say, football players with the kind of celebratory head butt that teammates exchange after a big play, Crisco said.

Headgear dampens blows

The second set of experiments examined what effect headgear might have on the girls' harder whacks (those with speeds around 23 miles an hour). Crisco's team measured the accelerations delivered by 20 whacks from the shaft of each volunteer's stick on both the back and the side of each headform. The headforms wore either nothing, a hard-sided men's lacrosse helmet, a rugby scrum cap, mixed martial arts headgear, or soft headgear designed for girls' and women's field hockey and lacrosse.

The average peak accelerations measured on bare headgear were 81.6g for blows to the side and 150.7g for blows to the back. The men's lacrosse helmet brought the average peak acceleration all the way down to 28.2g on the side and 23.1g on the back. The martial arts and girls lacrosse/field hockey headgear each reduced the accelerations significantly as well, but not nearly as much as the men's helmet. The rugby cap failed to reduce acceleration for blows to the side but dampened blows to the back a little better than the martial arts or lacrosse/field hockey gear.

Headgear, therefore, significantly reduced head accelerations. But Crisco cautioned against a run on headgear at the sporting goods store based on the study.

Generally research has shown that helmets do not protect against concussion -- only against skull fractures and traumatic brain injury. Indeed very little data connects accelerations to concussion risk, and individual susceptibility varies widely. Though some research hints at a figure around 100g, only the hard-sided men's helmet brought accelerations for blows to the back significantly below that figure. And in many game situations, given how little other protective equipment female players wear, Crisco said, a hard-sided helmet could easily cause more injuries that it prevents.

"It could actually make the game more aggressive," Crisco said.

Source: Brown University

CT scans could bolster forensic database to ID unidentified remains

Cranium image reconstructed from CT scans. Credit: North Carolina State University

A study from North Carolina State University finds that data from CT scans can be incorporated into a growing forensic database to help determine the ancestry and sex of unidentified remains. The finding may also have clinical applications for craniofacial surgeons.

"As forensic anthropologists, we can map specific coordinates on a skull and use software that we developed -- called 3D-ID -- to compare those three-dimensional coordinates with a database of biological characteristics," says Dr. Ann Ross, a professor of anthropology at NC State and senior author of a paper describing the work. "That comparison can tell us the ancestry and sex of unidentified remains using only the skull -- which is particularly valuable when dealing with incomplete skeletal remains."

However, the size of the 3D-ID database has been limited by the researchers' access to contemporary skulls that have clearly recorded demographic histories.

To develop a more robust database, Ross and her team launched a study to determine whether it was possible to get good skull coordinate data from living people by examining CT scans.

The University of Pennsylvania Museum's Morton Collection provided the NC State researchers with CT scans of 48 skulls. Researchers mapped the coordinates of the actual skulls manually using a digitizer, or electronic stylus. Then they compared the data from the CT scans with the data from the manual mapping of the skulls.

The researchers found that eight bilateral coordinates on the skull -- those found on either side of the head -- were consistent for both the CT scans and manual mapping.

"This will allow us to significantly expand the 3D-ID database," Ross says. "And these bilateral coordinates give important clues to ancestry, because they include cheekbones and other facial characteristics."

However, the five midline coordinates the researchers tested showed inconsistencies between the CT scans and manual mapping. Midline coordinates are those found along the center of the skull, such as the bridge of the nose.

"More research is needed to determine what causes these inconsistencies, and whether we'll be able to retrieve accurate midline data from CT scans," says Amanda Hale, a former master's student at NC State and lead author of the paper.

This research may also help craniofacial surgeons. "An improved understanding of the flaws in how CT scans map skull features could help surgeons more accurately map landmarks for reconstructive surgery," Hale says.

Source: North Carolina State University

Acoustic levitation made simple

Levitation of expanded polystyrene particles by ultrasonic sound waves. Credit: M. Andrade/University of São Paulo

A team of researchers at the University of São Paulo in Brazil has developed a new levitation device that can hover a tiny object with more control than any instrument that has come before.

Featured on this week's cover of the journal Applied Physics Letters, from AIP Publishing, the device can levitate polystyrene particles by reflecting sound waves from a source above off a concave reflector below. Changing the orientation of the reflector allow the hovering particle to be moved around.

Other researchers have built similar devices in the past, but they always required a precise setup where the sound source and reflector were at fixed "resonant" distances. This made controlling the levitating objects difficult. The new device shows that it is possible to build a 
"non-resonant" levitation device -- one that does not require a fixed separation distance between the source and the reflector.

This breakthrough may be an important step toward building larger devices that could be used to handle hazardous materials, chemically-sensitive materials like pharmaceuticals -- or to provide technology for a new generation of high-tech, gee-whiz children's toys.

"Modern factories have hundreds of robots to move parts from one place to another," said Marco Aurélio Brizzotti Andrade, who led the research. "Why not try to do the same without touching the parts to be transported?"

The device Andrade and his colleagues devised was only able to levitate light particles (they tested it polystyrene blobs about 3 mm across). "The next step is to improve the device to levitate heavier materials," he said.

How the Acoustic Levitation Device Works

In recent years, there has been significant progress in the manipulation of small particles by acoustic levitation methods, Andrade said.

In a typical setup, an upper cylinder will emit high-frequency sound waves that, when they hit the bottom, concave part of the device, are reflected back. The reflected waves interact with newly emitted waves, producing what are known as standing waves, which have minimum acoustic pressure points (or nodes), and if the acoustical pressure at these nodes is strong enough, it can counteract the force of gravity and allow an object to float.

The first successful acoustical levitators could successfully trap small particles in a fixed position, but new advances in the past year or so have allowed researchers not only to trap but also to transport particles through short distances in space.

These were sorely won victories, however. In every levitation device made to date, the distance between the sound emitter and the reflector had to be carefully calibrated to achieve resonance before any levitation could occur. This meant that the separation distance had to be equal to a multiple of the half-wavelength of the sound waves. If this separation distance were changed even slightly, the standing wave pattern would be destroyed and the levitation would be lost.

The new levitation device does not require such a precise separation before operation. In fact, the distance between the sound emitter and the reflector can be continually changed in mid-flight without affecting the levitation performance at all, Andrade said.
"Just turn the levitator on and it is ready," Andrade said.

Source: American Institute of Physics (AIP)

Ancient auditory illusions reflected in prehistoric art?

Here are prehistoric paintings of hoofed animals in a cave with thunderous reverberations located in Bhimbetka, India. Credit: S. Waller

During the 168th Meeting of the Acoustical Society of America (ASA), to be held October 27-31, 2014 at the Indianapolis Marriott Downtown Hotel, Steven J. Waller, of Rock Art Acoustics, will describe several ways virtual sound images and absorbers can appear supernatural.

"Ancient mythology explained echoes from the mouths of caves as replies from spirits, so our ancestors may have made cave paintings in response to these echoes and their belief that echo spirits inhabited rocky places such as caves or canyons," explained Waller.

Just as light reflection gives an illusion of seeing yourself duplicated in a mirror, sound waves reflecting off a surface are mathematically identical to sound waves emanating from a virtual sound source behind a reflecting plane such as a large cliff face. "This can result in an auditory illusion of somebody answering you from within the rock," Waller said.

Echoes of clapping can sound similar to hoof beats, as Waller pointed out, while multiple echoes within a cavern can blur together into a thunderous reverberation that mimics the sound of a herd of stampeding hoofed animals.

"Many ancient cultures attributed thunder in the sky to 'hoofed thunder gods,' so it makes sense that the reverberation within the caves was interpreted as thunder and inspired paintings of those same hoofed thunder gods on cave walls," said Waller. "This theory is supported by acoustic measurements, which show statistically significant correspondence between the rock art sites and locations with the strongest sound reflection."

Other acoustical characteristics may have also been misinterpreted by ancient cultures unaware of sound wave theory. Waller noticed a resemblance between an interference pattern and Stonehenge, so he set up an interference pattern in an open field with just two flutes "droning the same note" to explore what it would sound like.

"The quiet regions of destructive sound wave cancellation, in which the high pressure from one flute cancelled the low pressure from the other flute, gave blindfolded subjects the illusion of a giant ring of rocks or 'pillars' casting acoustic shadows," Waller said.

He traveled to England and demonstrated that Stonehenge does indeed radiate acoustic shadows that recreate the same pattern as interference. "My theory that musical interference patterns served as blueprints for megalithic stone circles -- many of which are called Pipers' Stones -- is supported by ancient legends of two magic pipers who enticed maidens to dance in a circle and turned them all into stones," Waller noted.

There are several important implications of Waller's research. Perhaps most significantly, it demonstrates that acoustical phenomena were culturally significant to early humans -- leading to the immediate conclusion that the natural soundscapes of archaeological sites should be preserved in their natural state for further study and greater appreciation.

"Even today, sensory input can be used to manipulate perception and lead to illusions inconsistent with scientific reality, which could have interesting practical applications for virtual reality and special effects in entertainment media," Waller said. "Objectivity is questionable, because a given set of data can be used to support multiple conclusions."

The history of humanity is full of such misinterpretations, such as the visual illusion that the sun moves around the earth. "Sound, which is invisible and has complex properties, can easily lead to auditory illusions of the supernatural," he added. "This, in turn, leads to the more general question: what other illusions are we living under due to other phenomena that we are currently misinterpreting?"

Presentation #2aAA11, "Virtual sound images and virtual sound absorbers misinterpreted as supernatural objects," by Stephen J. Waller will take place on Tuesday, October 28, 2014. The abstract can be found by searching for the presentation number here: https://asa2014fall.abstractcentral.com/planner.jsp

Source:  Acoustical Society of America (ASA)