Sonolithography With The Raspberry Pi Pico

You can do some wild things with sound waves, such as annoy your neighbours or convince other road users to move out of your way. Or, if you get into sonolithography like [Oliver Child] has, you can make some wild patterns with ultrasound.

Sonolithography is a method of patterning materials on to a surface using finely-controlled sound waves. To achieve this, [Oliver] created a circular array of sixteen ultrasonic transducers controlled via shift registers and gate driver ICs, under the command of a Raspberry Pi Pico. He then created an app for controlling the transducer array via an attached computer with a GUI interface. It allows the phase and amplitude of each element of the array to be controlled to create different patterns.

Creating a pattern is then a simple matter of placing the array on a surface, firing it up in a given drive mode, and then atomising some kind of dye or other material to visualize the pattern of the acoustic waves.

It could be a useful tool for studying the interactions of ultrasonic waves, or it could just be a way to make neat patterns in ink and dye if that’s what you’re into. [Oliver] notes the techniques of sonolithography could also have implications in biology or fabrication in future, as well. If you found this interesting, you might like to study up on ultrasonic levitation, too!

Skip The Radio With This Software-Defined Ultrasound Data Link

We know what you’re thinking: with so many wireless modules available for just pennies, trying to create a physical data link using ultrasonic transducers like [Damian Bonicatto] did for a short-range, low-bitrate remote monitoring setup seems like a waste of time. And granted, there are a ton of simple RF protocols you can just throw at a job like this. Something like this could be done and dusted for a couple of bucks, right?

Luckily, [Damian] wanted something a little different for his wireless link to a small off-grid solar array, which is why he started playing with ultrasound in an SDR framework. The design for his “Software-Defined Ultrasonics” system, detailed in Part 1, has a pair of links, each with two ultrasonic transducers, one for receiving and one for transmitting. Both connect to audio amplifiers with bandpass filters; the received signal is digitized by the ADC built into an Arduino Nano, while the transmitted signal is converted to analog by an outboard DAC.

The transducers are affixed to 3D printed parabolic reflectors, which are aimed at each other over a path length of about 150′ (46 m). Part 2 of the series details the firmware needed to make all this work. A lot of the firmware design is dictated by the constraints introduced by using Arduinos and the 40-kHz ultrasonic carrier, meaning that the link can only do about 250 baud. That may sound slow, but it’s more than enough for [Damian]’s application.

Perhaps most importantly, this is one of those times where going slower helps you to go faster; pretty much everything about the firmware on this system applies to SDRs, so if you can grok one, the other should be a breeze. But if you still need a little help minding your Is and Qs, check out [Jenny]’s SDR primer.

Tiny Speaker Busts Past Sound Limits With Ultrasound

Conventional speakers work by moving air around to create sound, but tiny speakers that use ultrasonic frequencies to create pressure and generate sound opens some new doors, especially in terms of maximum achievable volume.

A new design boasts being the first 140 dB, full-range MEMS speaker. But that kind of volume potential has less to do with delivering music at an ear-splitting volume and more to do with performing truly effective noise cancellation even in a small device like earbuds. Cancelling out the jackhammers of the world requires parts able to really deliver a punch, especially in low frequencies. That’s something that’s not so easy to do in a tiny form factor. The new device is the Cypress, from MEMS speaker manufacturer xMEMS and samples are aiming to ship in June 2024.

Combining ultrasonic waves to create audible sound is something we’ve seen show up in different ways, like using an array of transducers to focus sound like a laser beam. Another thing ultrasonics can do is cause sensors in complex electronics to become unhinged from reality and report false readings. Neato!

Arduino-Powered Missile System Uses Ultrasound To Aim

In the real world, missile systems use advanced radars, infrared sensors, and other hardware to track and prosecute their targets. [Raspduino Uno] on YouTube has instead used ultrasound for targeting for an altogether simpler desktop fire control solution.

This fun build uses a common off-the-shelf USB “missile launcher” that fires foam darts. To supply targeting data for the launcher, an Arduino Uno uses an ultrasonic sensor pair mounted atop a servo. As the servo rotates, the returns from the ultrasonic sensor are plotted on a screen run by a Raspberry Pi. If an object is detected in the 180-degree field of view of the sweeping sensor, a missile is fired using the dart launcher.

It’s a relatively simple build, but nonetheless would serve as a useful classroom demonstration of radar-like targeting techniques to a young audience. Real military hardware remains altogether more sophisticated. Video after the break.

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Mini Ultrasonic Levitation Kit Is An Exercise In Sound Minimalist Design

For those that haven’t heard, ultrasonic levitation is a process by which two or more ultrasonic transducers are set opposite to each other and excited in such a way as to create a standing wave between them. The sound is, as the name implies, ultrasonic — so outside the range of human hearing — but strong enough so that the small, light objects can be positioned and held fixed in mid-air where there’s a pressure minimum in the standing wave. [Olimex] has created a small ultrasonic levitation kit that exemplifies this phenomena.

The kit itself is made using through-hole components, with an ATTiny85 as the core microcontroller to drive two TCT40-16T ultrasonic speakers, and a MAX232 to provide a USB interface drives the transducers (thanks to the folks in the comments for the correction). Two slotted rectangular PCB pieces that solder connect to the main board, provide a base so that the device stands upright when assembled. The whole device is powered through the USB connection, and the ultrasonic speakers output in the 40KHz range providing enough power to levitate small Styrofoam balls.

The project is, by design, an exercise in minimalism, providing a kit that can be easily assembled, and providing code that can be easily flashed onto the device, examined and modified. All the design files, including the bill of materials, KiCAD schematics, and source code are provided under an open source hardware license to allow for anyone wanting to know how such a project works, or to extend it themselves, ample opportunity. [Olimex] also has the kit for sale for those not wanting to source boards and parts themselves.

We’ve featured ultrasonic levitation devices before, from bare bones system driven by a NE555 to massive phased arrays.

Hackaday Prize 2022: Drying Clothes With Ultrasound

Clothes dryers are great, and a key part of modern life, but they do use a lot of energy. [Mike Rigsby] decided to see if there was a more efficient method of drying clothes that could compete with resistive heating for efficiency. Thus, he started work on an ultrasonic clothes dryer.

In early testing, he found ultrasonic transducers could indeed blast droplets of moisture away from fabric, effectively drying it. However, unlike heat, the ultrasonic field doesn’t effectively permeate through a pile of clothes, nor can it readily be used with a spinning drum to dry many garments at once.

[Mike]’s current experiments are centered around using a basket-type system, with a bed of ultrasonic transducers at the bottom. The idea is that the basket will shake back and forth, agitating the load of clothing and allowing the different garments to effectively contact the transducers. It’s still a work in progress, but it’s an interesting approach to the problem. We’d love to see a comparison of the energy use of a full-scale build versus a regular dryer.

We’ve heard of the ultrasonic drying concept before, too, with the Department of Energy researching the matter. It could just be that we’ll all be using ultrasonic dryers in decades to come!

Remove A Speaker’s Voice From A Recording Using Ultrasound

What if you could effectively prevent someone from recording your voice? This is the focus of a study by Guo et al. (2022) at Michigan State University, in which they use a dynamically calculated audio signal that effectively cancels out one’s voice in a recording device. This relies on an interesting aspect of certain micro-electro-mechanical system (MEMS) microphones, which are commonly used in smartphones and other recording devices.

Pressure sensitivity of a MEMS microphone. (credit: Brian R. Elbing)
Pressure sensitivity of a MEMS microphone. (credit: Brian R. Elbing)

A specially crafted ultrasound signal sent to the same microphone which is recording one’s voice can result in the voice audio signal being gone on the final recording. The approach taken by the authors involves using a neural network that is trained on voice samples of the person (“Bob”) whose voice has to be cancelled. After recording Bob’s voice during a conversation, the creatively named Neurally Enhanced Cancellation (NEC) system determines the ultrasound signal to be sent to the target recording device. Meanwhile the person holding the recording device (“Alice”) will still perceive Bob’s voice normally.

As ultrasound is highly directional, the system can only jam a specific microphone and wouldn’t affect hidden microphones in a room. As noted by the authors, it is possible to do general microphone jamming using other systems, but this is legally problematic, which should not be an issue with their NEC system.

Thanks to [JohnU] for the tip!