Ultrasonic Levitation

We are designing and building an ultrasonic levitator, a device that levitates small objects using sound waves. When two sound waves coming from opposite directions create a standing wave, it turns out that at the zero points of that wave, small objects like balls of styrofoam can be stably levitated. By using two phased arrays to create the standing wave, a high level of control can be achieved, allowing the object to be moved around. Any form of levitation is intriguing, but not many methods have the range and control over movement that the ultrasonic one does. We are doing this firstly because we think it is an interesting and fun project with a really neat end result. We also plan to use it as an outreach demo to show future engineers what can be done with engineering.

Our team is a part of a club at Auburn University called SPARC (the Student Projects and Robotics Club). What we do is each semester, we choose projects that we think are interesting, form teams, and use our makerspace to bring those projects to life. We are a platform for all sorts of unique and experimental projects. Examples of past projects are a competition to build an autonomous robot and a large Tesla coil. We also have a big focus on outreach. We use the projects we make to show future students what's so great about engineering and the many possibilities it leads to. The most important outreach event we're involved in is Auburn's E-Day, where students come from across our state to see what our engineering programs are like.

Once the phased arrays are built, there are a number of interesting applications for them. Multiple objects can be levitated and moved independently. The phased arrays can create directional audio and sensations of touch. It is apparently possible to achieve levitation with a single-sided array, so we'd like to eventually build a small handheld version that acts like a tractor beam. Additionally, the levitator will be capable of rather high accelerations, so if the particle is moved along a closed path many times a second and a bright LED is shone on it, it can establish persistence of vision and create real-life holograms. It becomes a fully 3D display. Further information on ultrasonic levitators and their uses can be found in this paper ("A volumetric display for visual, tactile and audio presentation using acoustic trapping" by Hirayama). An image of an animated butterfly from that paper is shown below.

The PCB we're ordering has a 4x4 array of ultrasonic transducers, along with a small Lattice FPGA that controls the phase of the transducers by driving each one with a square wave. With 18 of these boards, we can make two 12x12 phased arrays. The system is controlled by a Teensy 4.1 microcontroller, which communicates with each transducer board using an SPI-like interface. We chose PCBWay because of its excellent capabilities and good prices, and because it was recommended to us by another student. This board has actually been redesigned twice, since due to the semiconductor shortage, the FPGAs we were going to use have gone out of stock twice. This is why we have an FPGA with a 0.4mm BGA pitch that requires advanced PCB manufacturing techniques. The budget is now far higher than initially envisioned, but a sponsorship from PCBWay would be very helpful in counterbalancing this. We believe this project is well worth doing and will inspire excitement about engineering in anyone who sees it.