As a general rule, the smaller a physical system becomes, the harder it is to design and produce its parts. This is definitely the case in the world of robotics. Tiny robots have a lot of potential to squeeze into places that we could never go, but once they get there, they are very limited. Designing parts like actuators and manipulators at this scale is extremely challenging. However, without these components robots do not have many options for interacting with the world around them.
A group led by researchers at Virginia Tech is hoping to do away with these limitations in the near future. Toward that goal, they have developed a new type of chip that can generate highly specific sound waves. The chip gives the researchers precise control over the form of these sound waves, which allows them to grab and move tiny objects, as if with a pair of invisible hands.
A schematic of a PIM (📷: J. Li et al.)
This work takes advantage of a new class of engineered devices called phased interdigital metamaterials (PIMs). The chips are built from intricately shaped interdigital electrodes—tiny metal fingers patterned on a piezoelectric surface—that encode phase information at resolutions far below the wavelength of the acoustic waves they produce. This means that the researchers can program the shape, direction, and energy profile of the sound waves by sculpting the electrodes themselves. This goes far beyond what traditional interdigital transducers can do, which are typically limited to producing straight or gently focused waves.
With PIMs, almost any surface acoustic wave (SAW) field becomes possible. The chips can tilt or bend the waves, funnel energy into a narrow jet no wider than a single wavelength, or even produce paired twin beams that act like a set of miniature acoustic tweezers. They can also route wave-based information in one direction while blocking it in the other, creating diode-like behavior for sound. This ability to precisely sculpt SAWs has enormous implications for both robotics and the broader field of microsystems engineering.
SAW energy beams were produced by the chip (📷: J. Li et al.)
One potential application of the technology involves manipulating fluids and particles at microscopic scales. By tailoring the wavefronts, the researchers can generate swirling vortices, aligned flow channels, or stable traps that hold micro- and nanoscale objects in place. In tests, the team demonstrated patterned arrangements of microparticles, alignment of carbon nanotubes, and controlled motion of nanoscale materials—all without physical contact. For biomedical work, this could mean more precise handling of cells, blood components, or fragile biomolecules during diagnostics or sample preparation.
PIMs accomplish all of this without relying on bulky microstructures or complicated fabrication steps. The metamaterial behavior emerges entirely from the electrode design, making the technology more scalable and integrable than earlier SAW-based metasurfaces. As researchers continue refining the platform, tiny robots may soon gain the dexterity they’ve been missing.
