Abstract
New metamaterial manipulates sound to improve acoustic imaging
Researchers from North Carolina State University (NC State) and Duke University have developed a metamaterial made of paper and aluminum that can manipulate acoustic waves to more than double the resolution of acoustic imaging, focus acoustic waves, and control the angles at which sound passes through the metamaterial. Acoustic imaging tools are used in both medical diagnostics and in testing the structural integrity of everything from airplanes to bridges.
“This metamaterial is something that we’ve known is theoretically possible, but no one had actually made it before”, says Yun Jing, an Assistant Professor of Mechanical and Aerospace Engineering at NC State and corresponding author of a paper describing the work.
Metamaterials are simply materials that have been engineered to exhibit properties that are not found in nature. In this case, the structural design of the metamaterial gives it qualities that make it a “hyperbolic” metamaterial. This means that it interacts with acoustic waves in two different ways. From one direction, the metamaterial exhibits a positive density and interacts with acoustic waves normally—just like air. But from a perpendicular direction, the metamaterial exhibits a negative density in terms of how it interacts with sound. This effectively makes acoustic waves bend at angles that are the exact opposite of what basic physics would tell you to expect.
The practical effect of this is that the metamaterial has some very useful applications.
For one thing, the metamaterial can be used to improve acoustic imaging. Traditionally, acoustic imaging could not achieve image resolution that was smaller than half of a sound’s wavelength. For example, an acoustic wave of 100 kHz, traveling through air, has a wavelength of 3.4 mm—so it could not achieve image resolution smaller than 1.7 mm.
“But our metamaterial improves on that”, says Chen Shen, a PhD student at NC State and lead author of the paper. “By placing the metamaterial between the imaging device and the object being imaged, we were able to more than double the resolution of the acoustic imaging—from one-half the sound’s wavelength to greater than one-fifth”,
The metamaterial can also focus acoustic waves, which makes it a flexible tool.
“Medical personnel and structural engineers sometimes need to focus sound for imaging or therapeutic purposes”, Jing says. “Our metamaterial can do that, or it can be used to improve resolution. There are few tools out there that can do both.”
Finally, the metamaterial gives researchers more control over the angle at which acoustic waves can pass through it.
“For example, the metamaterial could be designed to block sound from most angles, leaving only a small opening for sound to pass through, which might be useful for microphones”, Shen says. “Or you could leave it wide open—it’s extremely flexible.”
Right now, the prototype metamaterial is approximately 30 cm2 and is effective for sounds between 1 and 2.5 kHz.
“Our next steps are to make the structure much smaller, and to make it operate at higher frequencies”, Jing says.
More info: https://www.sciencedaily.com/releases/2015/12/151216151744.htm
Seeing sound: nonsighted people could acquire a new sensory functionality similar to vision
A busy kitchen is a place where all of the senses are on high alert—your brain is processing the sound of sizzling oil, the aroma of spices, the visual aesthetic of food arranged on a plate, and the feel and taste of taking a bite. While these signals may seem distinct and independent, they actually interact and integrate together within the brain’s network of sensory neurons.
Caltech researchers have now discovered that intrinsic neural connections—called cross-modal mappings—can be used by assistive devices to help the blind detect their environment without requiring intense concentration or hundreds of hours of training. This new multisensory perspective on such aids (called sensory substitution devices) could make tasks that were previously attention-consuming much easier, allowing nonsighted people to acquire a new sensory functionality similar to vision. The work is described in a paper published in the October 22 issue of the journal Scientific Reports.
“Many neuroscience textbooks really only devote a few pages to multisensory interaction”, says Shinsuke Shimojo, the Gertrude Baltimore Professor of Experimental Psychology and principal investigator on the study. “But 99 percent of our daily life depends on multisensory—also called multimodal—processing.” As an example, he says, if you are talking on the phone with someone you know very well, and they are crying, you will not just hear the sound but will visualize their face in tears. “This is an example of the way sensory causality is not unidirectional—vision can influence sound, and sound can influence vision.”
Shimojo and postdoctoral scholar Noelle Stiles have exploited these cross-modal mappings to stimulate the visual cortex with auditory signals that encode information about the environment. They explain that cross-modal mappings are ubiquitous; everyone already has them. Mappings include the intuitive matching of high pitch to elevated locations in space or the matching of noisy sounds with bright lights. Multimodal processing, like these mappings, may be the key to making sensory substitution devices more automatic.
The researchers conducted trials with both sighted and blind people using a sensory substitution device, called a vOICe device, that translates images into sound.
The vOICe device is made up of a small computer connected to a camera that is attached to darkened glasses, allowing it to “see” what a human eye would. A computer algorithm scans each camera image from left to right, and for every column of pixels, generates an associated sound with a frequency and volume that depends on the vertical location and brightness of the pixels. A large number of bright pixels at the top of a column would translate into a loud, high-frequency sound, whereas a large number of lower dark pixels would be a quieter, lower-pitched sound. A blind person wearing this camera on a pair of glasses could then associate different sounds with features of their environment.
In the trials, sighted people with no training or instruction were asked to match images to sounds, while the blind subjects were asked to feel textures and match them to sound. Tactile textures can be related to visual textures (patterns) like a topographic map—bright regions of an image translate to high tactile height relative to a page, while dark regions are flatter. Both groups showed an intuitive ability to identify textures and images from their associated sounds. Surprisingly, the untrained (also called “naive”) group’s performance was significantly above chance and not very different from the trained.
The intuitively identified textures used in the experiments exploited the cross-modal mappings already within the vOICe encoding algorithm. “When we reverse the crossmodal mappings in the vOICe auditory-to-visual translation, the naive performance significantly decreased, showing that the mappings are important to the intuitive interpretation of the sound”, explains Stiles.
“We found that using this device to look at textures—patterns of light and dark—illustrated ‘intuitive’ neural connections between textures and sounds, implying that there is some preexisting crossmodality”, says Shimojo. One common example of cross-modality is a condition called synesthesia, in which the activation of one sense leads to a different involuntary sensory experience, such as seeing a certain color when hearing a specific sound. “Now, we have discovered that crossmodal connections, preexisting in everyone, can be used to make sensory substitution intuitive with no instruction or training.”
The researchers do not exactly know yet what each sensory region of the brain is doing when processing these various signals, but they have a rough idea. Stiles says, Auditory regions are activated upon hearing sound, as are the visual regions, which we think will process the sound for its spatial qualities and elements. The visual part of the brain, when processing images, maps objects to spatial location, fitting them together like a puzzle piece.
To learn more about how the cross-modal processing happens in the brain, the group is currently using functional magnetic resonance imaging (fMRI) data to analyze the cross-modal neural network.
These preexisting neural connections provide an important starting point for training visually impaired people to use devices that will help them see. A sighted person simply has to open their eyes, and the brain automatically processes images and information for seamless interaction with the environment. Current devices for the blind and visually impaired are not so automatic or intuitive to use, generally requiring a user’s full concentration and attention to interpret information about the environment. The Shimojo lab’s new finding on the role of multimodal processing and cross-modal mappings starts to address this issue.
Beyond its practical implications, Shimojo says, the research raises an important philosophical question: What is seeing?
“It seems like such an obvious question, but it gets complicated”, says Shimojo: Is seeing what happens when you open your eyes? No, because opening your eyes is not enough if the retina [the light-sensitive layer of tissue in the eye] is damaged. Is it when your visual cortex is activated? But our research has shown that the visual cortex can be activated by sound, indicating that we don’t really need our eyes to see. It’s very profound—we’re trying to give blind people a visual experience through other senses.
More info: https://www.sciencedaily.com/releases/2015/10/151027095242.htm
Vibration measurement for major operator
ClampOn recently completed a job, measuring vibration on a subsea template at a 330-m water depth.
The operator had to close down production from a subsea well due to suspected vibration and needed urgent assistance to measure and confirm actual vibration level.
ClampOn was contacted and mobilized within 2 days from first contact. During this short time, we were able to test, prepare, and ship a complete vibration measuring system, with two vibration monitors, a specially adapted retrofit clamp, a 500 m reel of cable, an ROV basket, and a PC with ClampOn vibration monitoring software. Two experienced ClampOn Service Engineers were mobilized and met the support vessel at the docks, where all the equipment was loaded.
Once offshore, the ClampOn vibration monitors were deployed and installed by ROV and connected to the ClampOn PC with software topside on-board the vessel. Data were gathered and sent in real time to ClampOn’s file server, from which the operator’s own vibration experts downloaded the data for further processing and analyzing.
The vibration test was completed and the operator received confirmation that vibration on the subsea module was outside acceptable levels.
ClampOn’s Service Department has the equipment, people, and expertise to measure vibration, sand production, and leakages and is ready to mobilize for topside and subsea jobs at short notice.
For vibration jobs, this typically means determining whether or not vibrations are within acceptable levels.
Other typical subsea vibration jobs performed include the following:
Vibration on large subsea flapper valves;
Vibration on subsea flowlines;
Vibration from chemical injections.
More info: http://www.clampon.com/latest-news/vibration-measurement-for-major-operator/
Giant web probes spider’s sense of vibration
Inside a lab in Oregon, United States, a 2-m spider web made of aluminum and rope is beginning to unlock how orb weavers pinpoint struggling prey.
When an unlucky insect lands in a web, it is vibration that brings the spider scuttling from the center of its trap.
How spiders interpret those signals is a mystery—so physicists have built this replica to figure it out.
They unveiled the design and their first results on Friday at a meeting of the American Physical Society (APS).
“We wove the web using two different kinds of rope, the same way as spiders use two different formulations of silk”, said Ross Hatton from Oregon State University.
The radial strands that fan out from the center are made of stiff, nylon parachute cable, while elastic bungee cords make up the “spiral strands”.
The whole thing sits in an octagonal aluminum frame, with a speaker strapped to one corner to deliver some hefty vibrations.
“It’s a big subwoofer, so we can give a fairly good push to the web—there’s quite a bit of force in it”, Dr Hatton told BBC News, at the APS March Meeting in Baltimore.
At the center of the web sits an artificial spider—a simple eight-legged frame, which doesn’t move but detects vibrations in the threads, just like a real spider.
“We went in with the basic hypothesis that if you shake one of the radial lines, then the spider will feel that shaking a lot, and the other lines less”, Dr Hatton explained. “And so you could say, well I just go to wherever the line is shaking the most.”
But this was not what he and his colleagues—including biologist Damian Elias at the University of California Berkeley—discovered.
In fact, the outsized orb web revealed surprisingly complex vibration patterns, with quiet spots in certain parts of the web where the shaking completely disappears.
“At different frequencies, different strands—so different feet—stop vibrating”, Dr Hatton said.
Those different frequencies might reflect, for example, different types of trapped insect.
“So at the very least, the spider is going to need to know how the frequency couples with the web structure … in order to find which is the foot that shouldn’t be shaking—so it doesn’t end up going off at 90° to where it should be going.”
More info: http://www.bbc.com/news/science-environment-35849341
Acoustics Module—software for acoustics and vibration analysis
The Acoustics Module is designed specifically for those who work with devices that produce, measure, and utilize acoustic waves. Application areas include speakers, microphones, hearing aids, and sonar devices, to name a few. Noise control can be addressed in muffler design, sound barriers, buildings, and room acoustics applications.
The Acoustics Module consists of a set of physics interfaces—user interfaces with associated modeling and simulation tools—that enable you to simulate the propagation of sound in fluids and solids. Within the Acoustics Module, these are organized into pressure acoustics, acoustic–structure interaction, aeroacoustics, thermoacoustics, and geometrical acoustics.
Acoustic simulations performed using the physics interfaces for pressure acoustics can easily model classic problems such as scattering, diffraction, emission, radiation, and the transmission of sound. These problems are relevant to muffler design; loudspeaker construction; sound insulation for absorbers and diffusers; the evaluation of directional acoustic patterns, like directivity; noise radiation problems; and much more.
The physics interfaces for acoustic–structure interaction model problems involving the interaction between structural elastic waves and fluid-borne sound. For example, acoustic–structure interaction is considered in detailed muffler design, ultrasound piezo-actuators, sonar technology, and noise and vibration analyses of machinery. Using COMSOL Multiphysics, this capability enables you to analyze and design electroacoustic transducers, including loudspeakers, sensors, microphones, and receivers.
The aeroacoustics physics interfaces are used to model the one-way interaction between an external flow and an acoustic field (fluid-borne noise). Applications range from jet-engine noise analysis to wind sensor simulation.
The physics interfaces for geometrical acoustics include ray tracing and the acoustic diffusion equation interfaces. Both interfaces are applicable for modeling acoustics in rooms and buildings. Ray tracing is also used, for example, in ocean acoustics and atmosphere acoustics.
Thermoacoustic applications are accurately modeled using the provided, appropriate physics interfaces. These are applications that include small geometrical dimensions and where thermal properties need to be considered, for example, cell phones, hearing aids, microelectromechanical system (MEMS) applications, and transducer designs.
More info: https://www.comsol.co.in/acoustics-module