Frequency response of edge waves in soft viscoelastic materials

Herein we explore the frequency response of circular standing waves, ascertaining the effect of viscosity and elasticity on resonance. Edge waves were mechanically generated in a circular tank mounted on an electromechanical shaker. The wave field was measured using a camera and collimated light source. Water-glycerin mixtures and agarose gels were investigated for frequencies ranging from 4Hz to 22.9Hz and over a range of viscosity and shear modulus. The results showed that 1) the resonance modes for standing waves on water-glycerin mixtures shift to lower frequencies with increasing viscosity; 2) for fixed viscosity, the resonance modes on gels have a higher frequency than water-glycerin mixtures, i.e. elasticity increases the resonance frequency. A new theory for elastocapillary edge waves in a circular geometry is presented. The resonance frequencies predicted by the theory agree favorably with the experimental data. This work could potentially be used to develop a diagnostic method for measuring the complex modulus of soft materials.