Devices for separating materials from a host fluid are disclosed. The devices include an acoustic chamber having an inlet and an outlet. An ultrasonic transducer and reflector create a multi-dimensional acoustic standing wave in the acoustic chamber that traps the materials and permits a continuous separation of the materials from the host fluid. The materials and the host fluid can thus be separately collected. Multiple sets of trapping lines are generated by the acoustic standing wave, and the transducer is oriented to minimize cross-sectional area for straight vertical channels between the trapping lines.