[Back]

G. Pfusterschmied, Chr. Weinmann, M. Schneider, D. Platz, N. Shen, J. E. Sader, U. Schmid:
"Sound dissipation from plate-type resonators excited in non-conventional transversal modes in liquids";
Journal of Micromechanics and Microengineering, 30 (2020), 1 - 7.

Vibrational modes of higher order in micromachined resonators exhibit low damping in liquid
environments, which facilitates accurate sensing even in highly viscous liquids. A steady
increment in mode order, however, results in sound dissipation effects at a critical mode number
ncrit, which drastically increases damping in the system. Basic understanding in the emerging of
sound dissipation in micromachined resonators is therefore of utmost importance, when an
application of higher mode orders is targeted. For that reason, we experimentally investigated in
this paper the appearance of sound dissipation in higher order non-conventional vibrational
modes in MEMS plate resonators in liquids. The results are compared to those of an analytical
model and of finite element method analyses. Micromechanical piezoelectric resonators were
fabricated and characterized in sample fluids with a dynamic viscosity μfluid ranging from 1 to
5 mPa s and density values ρfluid ranging from 0.774 up to 0.835 kg l−1. Quality factors up to
333 are obtained for the eighth mode order in model solution with a dynamic viscosity of
1 mPa s. By monitoring the resonance and damping characteristics as a function of mode order,
sound dissipation effects occur, observed by the detection of increased damping, starting at
mode number n = 8, which is in good agreement to the predictions of an analytical model and
to finite element method simulations. At the critical mode number ncrit, a reduction in quality
factor up to 50% is measured. The results show a direct correlation of ncrit and the density of the
fluid, which agrees to theory. The lowest value of 8 for ncrit is obtained in a sample liquid with
the lowest density value of 0.774 kg l−1, followed by ncrit = 9 in a sample liquid with
ρfluid = 0.782 kg l−1 and ncrit = 10 in a sample liquid with ρfluid = 0.835 kg l−1. These findings
are of particular interest for sensing applications in low dense liquids, as sound dissipation
effects emerge even at lower mode numbers.

http://dx.doi.org/10.1088/1361-6439/ab8bc9