EPFL scientists have created nanomechanical oscillators that can oscillate billions of times before halting. The symmetry of mechanical resonators shaped as regular polygons enables these record-low mechanical losses.
Scanning electron micrograph of a polygon resonator. The inset shows the shape of the perimeter mode. Image Credit: Mohammad J. Bereyhi (EPFL).
The vibrational modes of nanomechanical resonators are equivalent to varied notes on a guitar string and share characteristics like frequency (pitch) and lifetime. The quality factor, which is the number of times the resonator oscillates until its energy is lowered by 70%, characterizes the lifetime.
The quality factor is critical for modern mechanical resonator applications because it determines the quality of thermal noise, which is a restriction for sensing weak forces and observing quantum effects.
EPFL researchers, led by Professor Tobias J. Kippenberg, have demonstrated that a regular polygon suspended at its vertices can assist vibrational modes across its perimeter with great quality factors. This is due to regular polygons’ geometrical symmetry coupled with the elastic constants of structures under tension.
This strategy of loss-engineering has a significant advantage over previous methods in that it allows for the realization of good quality factors in devices with much smaller footprints.
The new perimeter modes not only beat the record for the highest quality factor but are almost 20 times more compact than devices with similar performance.
Nils Engelsen, Study Senior Author, EPFL
“The compactness comes with real practical benefits. In our laboratory, we try to measure and control mechanical vibrations at the quantum level using light, which requires the suspension of mechanical resonators less than one micrometer from a structure that guides light. This feat is much simpler with compact devices,” Engelsen added.
The polygon resonators’ simple design enables the researchers to take the investigation one step further and create a series of attached polygon resonators. A chain of coupled oscillators can behave quite differently than a single resonator. The researchers investigated the unique dynamics of this chain, which result from the arrangement of the resonators.
Precision force sensing is a key application for nanomechanical resonators. The researchers note that by assessing the position fluctuations of a polygon resonator with an optical interferometer, these resonators can quantify force fluctuations as low as 1 attonewton. This level of sensitivity is comparable to that of cutting-edge atomic force microscopes.
We hope that the demonstrated force sensitivity of the polygons combined with their compactness and simplicity will inspire their use in actual force microscopes.
Mohammad Bereyhi, Study Lead, EPFL
“So far, improvements in mechanical quality factors have come at the cost of increased size and increased design complexity, making state-of-the-art devices very difficult to fabricate. With perimeter modes, it is a different story. I believe that the simplicity of this new design greatly expands its potential to find new and promising applications,” Bereyhi concluded.
Journal Reference:
Bereyhi, M. J., et al. (2022) Perimeter Modes of Nanomechanical Resonators Exhibit Quality Factors Exceeding 109 at Room Temperature. Physical Review X. doi.org/10.1103/PhysRevX.12.021036.