For the first time, physicists from the Delft University of Technology have developed a new technology on a microchip by integrating two Nobel Prize-winning approaches. This microchip has the potential to quantify distances in materials at high precision, such as for medical imaging or underwater.
Artists’ impression of the trampoline-shaped sensor. The laser beam that passes through the middle of the trampoline membrane creates overtone vibrations inside the material. Image Credit: Sciencebrush
It is valuable for high-precision position measurements in opaque materials as the technology employs sound vibrations rather than light. The instrument can result in novel approaches to tracking human health and the Earth’s climate. Nature Communications published this research.
Simple and Low-Power Technology
The microchip comprises a thin trampoline-shaped ceramic sheet. This trampoline is designed with holes to improve its contact with lasers. It also comes with a thickness of around 1000 times tinier compared to the thickness of a hair. Being a former Ph.D. candidate in the laboratory of Richard Norte, Matthijs de Jong examined the tiny trampolines to make sense of what would happen if they directed a simple laser beam at them.
The surface of the trampoline began vibrating intensely. By quantifying the reflected laser light from the vibrating surface, the team observed a pattern of vibrations in the comb shape they had never witnessed earlier. They discovered that the comb-like signature of the trampoline acts as a ruler for accurate distance measurements.
This novel technology could measure positions in materials with sound waves. Not requiring any precision hardware makes it unique and simple to produce.
It only requires inserting a laser, and nothing else. There’s no need for complex feedback loops or for tuning certain parameters to get our tech to operate properly. This makes it a very simple and low-power technology, that is much easier to miniaturize on a microchip. Once this happens, we could really put these microchip sensors anywhere, given their small size.
Richard Norte, Delft University of Technology
Unique Combination
The novel technology is founded on two distinct Nobel Prize-winning approaches: frequency combs and optical trapping.
The interesting thing is that both of these concepts are typically related to light, but these fields do not have any real overlap. We have uniquely combined them to create an easy-to-use microchip technology based on sound waves. This ease of use could have significant implications for how we measure the world around us.
Richard Norte, Delft University of Technology
Overtones
When the scientists directed a laser beam at the small trampoline, they understood that the forces that the laser applied on it were producing overtone vibrations in the trampoline membranes.
These forces are called an optical trap, because they can trap particles in one spot using light. This technique won the Nobel Prize in 2018 and it allows us to manipulate even the smallest particles with extreme precision. You can compare the overtones in the trampoline to particular notes of a violin. The note or frequency that the violin produces depends on where you place your finger on the string. If you touch the string only very lightly and play it with a bow, you can create overtones; a series of notes at higher frequencies. In our case, the laser acts as both the soft touch and the bow to induce overtone vibrations in the trampoline membrane.
Richard Norte, Delft University of Technology
Bridging Two Breakthrough Fields
Optical frequency combs are used in labs around the world for very precise measurements of time, and to measure distances. They are so important to measurements in general that their invention was given a Nobel Prize in 2005. We have made an acoustic version of a frequency comb, made out of sound vibrations in the membrane instead of light. Acoustic frequency combs could for instance make position measurements in opaque materials, through which vibrations can propagate better than light waves. This technology could for example be used for precision measurements underwater to monitor the Earth’s climate, for medical imaging and for applications in quantum technologies.
Richard Norte, Delft University of Technology
Journal Reference
de Jong, M. H. J. et al. (2023). Mechanical overtone frequency combs. Nature Communications. doi.org/10.1038/s41467-023-36953-8.