A method of separating a particulate from a host fluid, comprising: flowing a mixture of the host fluid and the particulate through an apparatus (124, 190), the apparatus (124, 190) comprising: a flow chamber (30, 128, 193) having at least one inlet and at least one outlet; at least one ultrasonic transducer (40, 81, 110, 112, 120, 122, 130) located on a wall of the flow chamber (30, 128, 193), the at least one transducer (40, 81, 110, 112, 120, 122, 130) including a piezoelectric material and driven by an oscillating, periodic, modulated, or pulsed voltage signal at ultrasonic frequencies so that the piezoelectric material vibrates in a higher order mode shape to create a three-dimensional standing wave in the flow chamber (30, 128, 193); and a reflector (132, 194) located on the wall on the opposite side of the flow chamber (30, 128, 193) from the at least one ultrasonic transducer (40, 81, 120, 122, 130); and sending an oscillating, periodic, modulated, or pulsed voltage signal at ultrasonic frequencies to drive the at least one ultrasonic transducer (40, 81, 110, 112, 120, 122, 130) so that the piezoelectric material vibrates in a higher order mode shape to separate the host fluid from the particulate, wherein the three-dimensional standing wave results in an acoustic radiation force which has an axial force component and a lateral force component that are of the same order of magnitude and which is larger than the combined effects of fluid drag and buoyancy or gravity, and wherein the particulate is Chinese hamster ovary cells, NS0 hybridoma cells, baby hamster kidney cells, or human cells. flowing a mixture of the host fluid and the particulate through an apparatus (124, 190), the apparatus (124, 190) comprising: a flow chamber (30, 128, 193) having at least one inlet and at least one outlet; at least one ultrasonic transducer (40, 81, 110, 112, 120, 122, 130) located on a wall of the flow chamber (30, 128, 193), the at least one transducer (40, 81, 110, 112, 120, 122, 130) including a piezoelectric material and driven by an oscillating, periodic, modulated, or pulsed voltage signal at ultrasonic frequencies so that the piezoelectric material vibrates in a higher order mode shape to create a three-dimensional standing wave in the flow chamber (30, 128, 193); and a reflector (132, 194) located on the wall on the opposite side of the flow chamber (30, 128, 193) from the at least one ultrasonic transducer (40, 81, 120, 122, 130); and a flow chamber (30, 128, 193) having at least one inlet and at least one outlet; at least one ultrasonic transducer (40, 81, 110, 112, 120, 122, 130) located on a wall of the flow chamber (30, 128, 193), the at least one transducer (40, 81, 110, 112, 120, 122, 130) including a piezoelectric material and driven by an oscillating, periodic, modulated, or pulsed voltage signal at ultrasonic frequencies so that the piezoelectric material vibrates in a higher order mode shape to create a three-dimensional standing wave in the flow chamber (30, 128, 193); and a reflector (132, 194) located on the wall on the opposite side of the flow chamber (30, 128, 193) from the at least one ultrasonic transducer (40, 81, 120, 122, 130); and sending an oscillating, periodic, modulated, or pulsed voltage signal at ultrasonic frequencies to drive the at least one ultrasonic transducer (40, 81, 110, 112, 120, 122, 130) so that the piezoelectric material vibrates in a higher order mode shape to separate the host fluid from the particulate, wherein the three-dimensional standing wave results in an acoustic radiation force which has an axial force component and a lateral force component that are of the same order of magnitude and which is larger than the combined effects of fluid drag and buoyancy or gravity, and wherein the particulate is Chinese hamster ovary cells, NS0 hybridoma cells, baby hamster kidney cells, or human cells.