Degree: Doctor of Philosophy Abstract: This thesis presents an investigation of macro-scale (>5mm) multi-wavelength acoustophoresis. This is a technique used for the filtration of micro-particles from the containing suspension. It uses the primary acoustic force generated by an ultrasonic acoustic pressure standing wave. Primary acoustic force is isolated in different multi-wavelength acoustic separator experiments and imaging methods are used to capture the motion of particles separating from the containing fluid. Different investigation methods and models for analyzing the macro-scale acoustic resonators are developed and the experimented acoustic resonators are characterized. A particle tracking velocimetry (PTV) approach for measuring individual particle motion is developed specifically to track particles over the lifetime of their motion as they densify to an acoustic pressure node. The applicability of primary acoustic force theory to the macro-scale acoustic resonators is validated by applying the PTV method to images of densification of mono-disperse size and poly-dispersed size particles. Utilizing the developed validated PTV method, the acoustic energy density, a parameter that can only be derived from experiments is also determined. A probability density function (PDF) modeling the location of particles for determination of acoustic energy density is also developed which is in agreement with the PTV method. The influence of dampening and scattering of the acoustic wave in macro-scale multi-wavelength is studied. This is performed by variation of piezo-electric transducer (PZT) voltage and changing the viscosity of the suspension by using different solutions of glycerol in water. The resulting acoustic energy density dependence on PZT voltage in macro-scale multi-wavelength acoustic resonators is observed to be different from that of micro-scale acoustic resonators. This effect, which is visible in all different experimented suspensions, indicates that macro-scale multi-wavelength acoustic resonators inherently show more dampening effects than micro-scale acoustic resonators.