So what exactly is sonoluminescence? The short answer is as the name suggests: a release of light caused by sound. In [Justin]’s case, he used an ultrasonic transducer to set up a standing wave at the resonant frequency of a flask of water. A drop of water is used to entrain a small air bubble, which is held in a stable position in the flask in much the same way as styrofoam beads are in an acoustic levitator. Turn off the lights and you’ll see that the bubble glows with a ghostly blue light.
What causes the glow? Good question. According to [Justin], we just don’t know for sure what causes it, although the leading theory is that cavitation of the bubble causes the trapped gas to compress and heat violently, turning into a brief bit of plasma. But there are problems with that theory, which is one of the reasons he wanted to show just how easy the process can be – now that he’s shaken out the bugs with five years of effort. It wasn’t easy getting the transducers attached and the driver circuit properly tuned, but with little more than a signal generator, an audio amp, and a spool of magnet wire, you too can make your own “star in a jar.”
Art installations are an interesting business, which more and more often tend to include electronic or mechanical aspects to their creation. Compared to more mainstream engineering, things in this space are often done quite a bit differently. [Jan Enning-Kleinejan] worked on an installation called Prendre la parole, and shared the lessons learned from the experience.
The installation consisted of a series of individual statues, each with an LED light fitted. Additionally, each statue was fitted with a module that was to play a sound when it detected visitors in proximity. Initial designs used mains power, however for this particular install battery power would be required.
Arduinos, USB power banks and ultrasonic rangefinders were all thrown into the mix to get the job done. DFplayer modules were used to run sound, and Grove System parts were used to enable everything to be hooked up quickly and easily. While this would be a strange choice for a production design, it is common for art projects to lean heavily on rapid prototyping tools. They enable inexperienced users to quickly and effectively whip up a project that works well and at low cost.
[Jan] does a great job of explaining some of the pitfalls faced in the project, as well as reporting that the installation functioned near-flawlessly for 6 months, running 8 hours a day. We love to see a good art piece around these parts, and we’ve likely got something to your tastes – whether you’re into harmonicas, fungus, or Markov chains.
You’d think that something called “white fuming nitric acid” would be more than corrosive enough to dissolve just about anything. Heck, it’s rocket fuel – OK, rocket fuel oxidizer – and even so it still it wasn’t enough to pop the top on this vintage Fairchild μL914 integrated circuit, at least not without special measures.
As [John McMaster], part of the team that analyzed the classic dual 2-input NOR gate RTL chip from the 1960s, explains it, decapping modern chips is a straightforward if noxious process. Generally a divot is milled into the epoxy, providing both a reservoir for the WFNA and a roughened surface for it to attack. But the Fairchild chip, chosen for dissection for the Maker Faire Bay Area last week specifically because the features on the die are enormous by modern standards, was housed in an eight-lead TO-99 case with epoxy that proved nigh invulnerable to WFNA. [John] tried every chemical and mechanical trick in the book, going so far as to ablate epoxy with a Nd:YAG laser. He eventually got the die exposed, only to discover that it was covered with silicone rather than the silicon dioxide passivation layer of modern chips. Silicone can be tough stuff to remove, and [John] resorted to using lighter fluid as a solvent and a brush with a single bristle to clean up the die.
We applaud the effort that this took, which only proves that decapping is more art than science sometimes. And the results were fabulous; as Hackaday editor-in-chief [Mike Szczys] notes, the decapping led to his first real “a-ha moment” about how chips really work.
That first glimpse of a child in the womb as a black and white image on a screen is a thrilling moment for any parent-to-be, made possible by several hundred thousand dollars worth of precision medical instrumentation. This ultrasound machine cobbled together from eBay parts and modules is not that machine by a long shot, but it’s still a very cool project that actually gives a peek inside the skin.
The ultrasound transducer used by [stoppi71] in this build has an unusual source: a commercial paint-thickness meter. Cue the jokes about watching paint dry, but coatings measurement is serious stuff. Even so, the meter in question only ran about $40 on eBay, and provided the perfect transducer for the build. The sender needs a 100V pulse at about 5 MHz, so [stoppi71] had some fun with a boost converter and a 74121 Schmitt-trigger one-shot driving a MOSFET to switch the high voltage. On the receive side, the faint echo is sent through a three-stage amp using AD811 op amps before going through an LM7171 op amp acting as a rectifier and peak detector. Echos are sent to an Arduino Due for display on a 320×480 LCD. The resolution isn’t great, but the video below shows that it’s enough to see reflections from the skin of [stoppi71]’s forearm and from the bones within.
The build relies on an astounding number of ultrasonic transducers – 72, in fact. The device operates at 40 kHz to be well above the human range of hearing. 36 each are placed in the top and bottom shells of the device’s 3D printed chassis. Through careful construction, the transducers are placed an integer multiple of half the wavelength apart. This allows the device to create a standing wave, with several low-energy nodes in which small objects can be levitated. In this case, [Julius] uses small scraps of styrofoam, but notes that water droplets can also be used if one is careful to avoid spilling any on the electronics.
The transducers are energised with a square wave generated by an Arduino Nano. This allows the possibility of the frequency and phase of the wave to be altered, which can help tune the device and allow some movement in the vertical axis. Unfortunately, movement in the other axes isn’t possible as the transducers appear to be connected in parallel. However, this could be a good upgrade in a later revision.
This project shows that a device relying on incredibly precise measurement and control can now be constructed at home with a 3D printer and some off the shelf electronics.
We’ve all seen acoustic levitation, it’s one of the scientific novelties of our age and a regular on the circuit of really impressive physical demonstrations of science to the public. The sight of arrays of ultrasonic speakers causing small objects and beads of liquid to float in mid-air without any suspension is magical, captivating people of all ages. Thus a lecture at Hackaday Belgrade on the subject from Asier Marzo, a research scientist with a speciality in the field of ultrasonics at the UK’s University of Bristol, was a particularly fascinating and informative one.
He started by explaining acoustic levitation as a concept, and its mechanism. As an idea it’s one with a long history, he tells us that hundreds of years ago people tried mass ranks of the loudest musical instruments at their disposal to move rocks, all to no avail. The array of musicians of yore lacked the ability to control their individual phase, and of course their combined output would have balked at a pea-sized piece of gravel, let alone a boulder.
The Power of Standing Waves
Given that we can now create standing waves between phased arrays of ultrasonic speakers, he explained the mechanism that allows the levitation. The standing wave creates patterns of high intensity and “quiet” low intensity sound, and the object nestles in one of these quiet areas. There is thus a size limit dictated by the wavelength of the sound in question, which for the ultrasound he’s using is in the order of a few millimetres.
Having explained how it all works, we were then taken into the fields in which it finds an application. This was particularly interesting, because it’s the side we never see in the for-the-kids demos where it’s all about “Look, we can make the water droplet float!”. The number of fields that can find a use for it was a surprise, and formed the next phase of the talk.
Real World Uses for Acoustic Levitation
The first example given was in the field of spectroscopy, when reflecting light from a droplet of liquid on a substrate a certain amount of the reflected light comes from the substrate. If the sample is levitated, all the reflection comes from it and nothing else. Microgravity experiments are another interesting application, where it is possible to replicate some of the work that has previously required the environment of a space craft such as the International Space Station. This was a particularly unexpected twist.
The technique can be used for tiny particles in a liquid medium with a much higher frequency — a demonstration involves moving a single blood cell in a pattern. But Asier has more tricks up his sleeve. This technique can be used in human interactions with computers and with the real world. We saw a display in which the pixels were small plastic balls suspended in a grid, they could even be flipped in colour by being rotated under an electric field. A successive display used the balls not in a grid but as a point cloud in a graph, proving that rasters are not the only means of conveying information. Finally we saw the arrays applied to wearable devices, a handheld tractor beam, and a set of standing wave tweezers. He gave the example of picking up an SMD component, something that we can see would be invaluable.
Levitation is Within Our Grasp
The good news for us is that this is a piece of cutting-edge science that is accessible to us at our level too. He’s made a selection of designs available online through the Acoustic Levitator site. There is an ultrasonic array, an acoustic levitator, and an acoustic tractor beam, and the components are such run-of-the-mill parts as Arduinos and motor driver boards. Even schoolchildren building them from kits, with an experimenter using one for Schlieren photography of the acoustic field. Finally we’re shown Ultraino, an ambitious project providing software and driver hardware for large arrays in which every transducer is individually driven, before a tantalising look at future work in fluid ultrasonics and the promise of an ultrasonic audio speaker project.
Hackaday covers a huge array of projects and topics from all corners of our community. Each one is exciting in its own way, from a simple-looking Arduino project that encapsulates a cool hack to a multi-year labour of love. It’s not often though that we can say we’ve seen a genuinely cutting-edge piece of science, while simultaneously having it explained in terms we understand and being given an accessible version that we can experiment with ourselves. We are really looking forward to the projects that will come from this direction, as acoustic levitation becomes yet another known quantity in the hardware hacker’s armoury.
Ultrasound imaging has been around for decades, but Open Source ultrasound has not. While there are a ton of projects out there attempting to create open ultrasound devices, most of this is concentrated on the image-processing side of things, and not the exceptionally difficult problem of pinging a sensor at millions of times a second, listening for the echo, and running that through a very high speed ADC.
The design of the ultrasound system is based around an iCE40 FPGA, the only FPGA with an Open Source toolchain. Along with this, there are a ton of ADCs, a DAC, pulsers, and a high voltage section to drive the off-the-shelf ultrasound head. If you’re wondering how this ultrasound board interfaces with the outside world, there’s a header for a Raspberry Pi on there, too, so this project has the requisite amount of blog cred.
Already, [kelu] has a working ultrasound device capable of sending pulses out of its head and receiving the echo. Right now it’s just a few pulses, but this is a significant step towards a real, working ultrasound machine built around a reasonably Open Source toolchain that doesn’t cost several arms and legs.