ECE Department Seminar - Surface wave trapping in isolated and coupled mechanical resonators
2:00pm - 3:00pm
Room 2463 (via lift 25/26), Academic Complex, HKUST

Phononic crystals waveguides have often been presented as a promising path towards control of surface acoustic wave propagation. Yet, although their applicative potential is unquestionable, experimental demonstrations remain scarce. The development of phononic devices exhibiting Bragg band gap has been hindered by technological issues as it requires micro-machining of piezoelectric materials with high enough aspect ratios to ensure wave confinement at the  surface. Line-defect managed inside locally-resonant phononic crystals can be seen as a way to reduce the propagation loss as guided modes will appear at lower frequency, limiting phase-matching to bulk waves. Here we propose to take this approach a step further by using the intrinsic confinement induced by isolated and coupled resonators to trap the elastic energy at the substrate surface. The interplay between a pair of localised mechanical resonators and travelling surface acoustic waves (SAW), demonstrates the existence of a two-sided interaction. These different states allow the use of SAW to trigger and control the resonator oscillation, and to manipulate the elastic energy distribution on the substrate through resonator coupling. Observation of the vectorial structure of the resonator motion reveals the existence of two coupling regimes, a dipole-dipole-like interaction at small separation distance versus a surface-mediated mechanical coupling at larger separation. These results illustrate the potential of this platform for coherent control of mechanical vibration at a resonator level, and reciprocally for manipulating SAW propagation using sub-wavelength elements.

Event Format
Speakers / Performers:
Professor Abdelkrim Khelif
FEMTO-ST / CNRS, Université de Bourgogne-France-Comté, Besancon, France

Abdelkrim Khelif graduated in 1993 with MSc in fundamental physics from university of Lille, France.  In 1998, he completed a PhD in Material sciences from the same university, devoted to the study of scattering and phonons vibrations in nanostructure materials.  He joined the FEMTO-ST Institute in 2002 as full-time research position at Centre National de la Recherche Scientifique (CNRS) to develop phononic crystals and acoustic metamaterials.  He has extensive experience in design, optimization, and simulation of phononic structures.  He contributes a lot in the experimental demonstration of ultrasonic phononic crystal band gap, cavities mode and waveguide at low frequency.  He is also active to extract the potential application of phononic crystal as a new acoustic device for signal processing, and sensing applications.  Due to his achievements in the field of phononic crystal, he has been involved as the symposium session chair, technical committee member, and invited speaker in several conferences in the last 5 years.  He is also a frequent reviewer in this field for multiple physics and acoustic journals (Physical Review Letter, B, E, applied Physics Letters, Journal of applied physcs, and so on).  He has more than 80 journal papers and several invited, and contributed conference and seminar presentations.  He also has 4 patents in phononic crystal and the recipient of Bronze medal awards from CNRS for his work in phononic crystal in 2007.

Recommended For
Faculty and staff
PG students
UG students
Department of Electronic & Computer Engineering

Prof. Amine Bermak

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