Behold A 3D Display, Thanks To A Speeding Foam Ball

We’ve seen 3D image projection tried in a variety of different ways, but this is a new one to us. This volumetric display by Interact Lab of the University of Sussex creates a 3D image by projecting light onto a tiny foam ball, which zips around in the air fast enough to create a persistence of vision effect. (Video, embedded below.) How is this achieved? With a large array of ultrasonic transducers, performing what researchers call ‘acoustic trapping’.

This is the same principle behind acoustic levitation devices which demonstrate how lightweight objects (like tiny polystyrene foam balls) can be made to defy gravity. But this 3D display is capable of not only moving the object in 3D space, but doing so at a high enough speed and with enough control to produce a persistence of vision effect. The abstract for their (as yet unreleased) paper claims the trapped ball can be moved at speeds of up to several meters per second.

It has a few other tricks up its sleeve, too. The array is capable of simultaneously creating sounds as well as providing a limited form of tactile feedback by letting a user touch areas of high and low air pressure created by the transducers. These areas can’t be the same ones being occupied by the speeding ball, of course, but it’s a neat trick. Check out the video below for a demonstration.
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Hackaday Links: November 10, 2019

In the leafy suburbs of northern Virginia, a place ruled by homeowner’s associations with tremendous power to dictate everything from the color of one’s front door to the length of grass in the lawn, something as heinous as garage doors suddenly failing to open on command is sure to cause a kerfuffle. We’ve seen this sort of thing before, where errant RF emissions cause unintentional interference, and such stories aren’t terribly interesting because the FCC usually steps in and clears things up. But this story is a little spicier given the source of the interference: Warrenton Training Center, a classified US government communications station located adjacent to the afflicted neighborhood. WTC is known to be a CIA signals intelligence station, home to spooks doing spooky stuff, including running high-power numbers stations. The interference isn’t caused by anything as cloak-and-dagger as that, though; rather, it comes from new land-mobile radios that the Department of Defense is deploying. The new radios use the 380-400 MHz band, which is allocated to the Federal Government and unlicensed Part 15 devices, like garage door remotes. But Part 15 rules, which are clearly printed on every device covered by them, state that the devices have to accept unwanted interference, even when it causes a malfunction. So the HOA members who are up in arms and demanding that the government buy them new garage door openers are likely to be disappointed.

Speaking of spooks, if you’re tired of the prying electronic eyes of facial recognition cameras spoiling your illusion of anonymity, have we got a solution for you. The Opt-Out Cap is the low-tech way to instantly change your face for a better one, or at least one that’s tied to someone else. In a move which is sure not to arouse suspicion in public, doffing the baseball cap deploys a three-piece curtain of semi-opaque fabric, upon which is printed the visage of someone who totally doesn’t look creepy or sketchy in any way. Complete instructions are provided if you want to make one before your next trip to the ATM.

It’s always a great day when a new Ken Shirriff post pops up in our feed, and his latest post is no exception. In it, Ken goes into great detail about the history of the 80×24 (or 25) line standard for displays. While that may sound a bit dry, it’s anything but. After dispelling some of the myths and questionable theories of the format’s origin – sorry, it’s not just because punch cards had 80 columns – he discusses the transition from teletypes to CRTs, focusing on the very cool IBM 2260 Display Station. This interesting beast used an acoustic delay line made of 50′ (15 m) of nickel wire. It stored data as a train of sound pulses traveling down the wire, which worked well and was far cheaper than core memory, even if it was susceptible to vibrations from people walking by it and needed a two-hour warm-up period before use. It’s a fascinating bit of retrocomputing history.

A quick mention of a contest we just heard about that might be right up your alley: the Tech To Protect coding challenge is going on now. Focused on applications for public safety and first responders, the online coding challenge addresses ten different areas, such as mapping LTE network coverage to aid first responders or using augmented reality while extricating car crash victims. It’s interesting stuff, but if you’re interested you’ll have to hurry – the deadline is November 15.

And finally, Supercon starts this week! It’s going to be a blast, and the excitement to hack all the badges and see all the talks is building rapidly. We know not everyone can go, and if you’re going to miss it, we feel for you. Don’t forget that you can still participate vicariously through our livestream. We’ll also be tweet-storming and running a continuous chat on Hackaday.io to keep everyone looped in.

Acoustic Lenses Show Sound Can Be Focused Like Light

Acoustic lenses are remarkable devices that just got cooler. A recent presentation at SIGGRAPH 2019 showed that with the help of 3D printing, it is possible to build the acoustic equivalent of optical devices. That is to say, configurations that redirect or focus sound waves. One fascinating demonstration worked like an acoustic prism, able to send different notes from a simple melody in different directions. Another was a device that dynamically varied the distance between two lenses in order to focus sound onto a moving target. In both cases, the sounds originate from an ordinary speaker and are shaped by passing through the acoustic lens or lenses, which are entirely passive devices.

Researchers from the University of Sussex used 3D printing for a modular approach to acoustic lens design. 16 different pre-printed “bricks” (shown here) can be assembled in various combinations to get different results. There are limitations, however. The demonstration lenses only work in a narrow bandwidth, meaning that the sound they work with is limited to about an octave at best. That’s enough for a simple melody, but not nearly enough to cover a human’s full audible range. Download the PDF for a quick read about the details, it’s only two pages but loaded with enough to whet your appetite to know more.

Directional sound can be done in other ways as well, such as using an array of ultrasonic emitters to create a coherent beam of sound. Ultrasonic emitters can even levitate lightweight objects. Ain’t sound neat?

Sounding A Sour Note Can Save People From A Sour Stomach (Or Worse)

We’ve covered construction of novel music instruments on these pages, and we’ve covered many people tearing down scientific instruments. But today we’ve got something that managed to cross over from one world of “instrument” into another: a music instrument modified to measure a liquid’s density by listening to changes in its pitch.

This exploration started with a mbira, a mechanically simple music instrument. Its row of rigid metal tines was replaced with a single small diameter hollow metal tube. Filling the tube with different liquids would result in different sounds. Those sounds are captured by a cell phone and processed by an algorithm to calculate the difference in relative density of those liquids. Once the procedure was worked out, the concept was verified to work on a super simple instrument built out of everyday parts: a tube mounted on a piece of wood.

At this point we have something that would be a great science class demonstration, but the authors went a step further and described how this cheap sensor can be used to solve an actual problem: detecting counterfeit pharmaceuticals. Changing composition of a drug would also change its density, so a cheap way to compare densities between a questionable sample against a known good reference could be a valuable tool in parts of the world where chemistry labs are scarce.

For future development, this team invites the world to join them applying the same basic idea in other ways, making precise measurements for almost no cost. “Any physical, chemical, or biological phenomena that reproducibly alters the pitch-determining properties of a musical instrument could in principle be measured by the instrument.” We are the ideal demographic to devise new variations on this theme. Let us know what you come up with!

If you need to do quick tests before writing analysis software, audio frequency can be measured using the Google Science Journal app. We’ve seen several hacks turning a cell phone’s camera into instruments like a spectrometer or microscope, but hacks using a phone’s microphone is less common and ripe for exploration. And anyone who manages to make cool measurements while simultaneously making cool music will instantly become a serious contender in our Hackaday Prize music instrument challenge!

[via Science News]

Calculating Like It’s 1962

We sometimes forget that the things we think of as trivial today were yesterday’s feats of extreme engineering. Consider the humble pocket calculator, these days so cheap and easy to construct that they’re essentially disposable. But building a simple “four-banger” calculator in 1962 was anything but a simple task, and it’s worth looking at what one of the giants upon whose shoulders we stand today accomplished with practically nothing.

If there’s anything that [Cliff Stoll]’s enthusiasm can’t make interesting, we don’t know what it would be, and he certainly does the job with this teardown and analysis of a vintage electronic calculator. You’ll remember [Cliff] from his book The Cuckoo’s Egg, documenting his mid-80s computer sleuthing that exposed a gang of black-hat hackers working for the KGB. [Cliff] came upon a pair of Friden EC-132 electronic calculators, and with the help of [Bob Ragen], the engineer who designed them in 1962, got one working. With a rack of PC boards, cleverly hinged to save space and stuffed with germanium transistors, a CRT display, and an acoustic delay-line memory, the calculators look ridiculous by today’s standards. But when you take a moment to ponder just how much work went into such a thing, it really makes you wonder how the old timers ever brought a product to market.

As a side note, it’s great to see the [Cliff] is still so energetic after all these years. Watching him jump about with such excitement and passion really gets us charged up.

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Floating Ants And Drops Of Liquid With An Acoustic Levitator

Amuse your friends, amaze your enemies, and perplex ants and other insects, insofar as they are capable of perplexment. Accomplish all this and more with this handy dandy homebrew acoustic levitator.

Before anyone gets to thinking about using this technique to build a hoverboard that actually hovers, it’s best that you scale your expectations way, way down. Still, being able to float drops of liquid and small life forms is no mean feat, and looks like a ton of fun to boot. [Asier Marzo]’s Instructable’s post fulfills a promise he made when he first published results for what the popular press then breathlessly dubbed a “tractor beam,” which we covered back in January. This levitator clearly has roots in the earlier work, what with 3D-printed hemispherical sections bristling with ultrasonic transducers all wired in phase. A second section was added to create standing acoustic waves in the middle of the space, and as the video below shows, just about anything light enough and as least as cooperative as an ant can be manipulated in the Z-axis.

There’s plenty of room to expand on [Asier]’s design, and probably more practical applications than annoying bugs. Surface-mount devices are pretty tiny — perhaps an acoustic pick and place is possible?

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Cerebrum: Mobile Passwords Lifted Acoustically With NASB

 

There are innumerable password hacking methods but recent advances in acoustic and accelerometer sensing have opened up the door to side-channel attacks, where passwords or other sensitive data can be extracted from the acoustic properties of the electronics and human interface to the device. A recent and dramatic example includes the hacking of RSA encryption  simply by listening to the frequencies of sound a processor puts out when crunching the numbers.

Now there is a new long-distance hack on the scene. The Cerebrum system represents a recent innovation in side-channel password attacks leveraging acoustic signatures of mobile and other electronic devices to extract password data at stand-off distances.

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