Experimental verification of a quasi-trapped degenerate mode magnetic acoustic resonator

Abstract

This paper presents an elastic resonator exhibiting modal degeneracy and quasi-energy trapping of the displacement field. Electromagnetic acoustic based coupling is employed to excite a pair of degenerate SH dominated modes in an aluminium plate. A circular mesa is machined symmetrically on the plate for the purpose of localising the displacement field. Numerical modelling of the modal properties are compared with experimental measurements. Mapping of the modeshapes using 3D laser vibrometry shows that displacement field to be highly localised to the region defining the mesa in agreement with the numerical model. The numerical model shows that significant out of plane displacement outside the mesa region is expected due to the propagating SV+P waves of the plate. It is expected that design modification will reduce the out of plane contributions thus improving the energy trapping. The high Q-factor of the degenerate trapped resonator has potential applications as a gyroscopic sensor or mass sensor.