Ultrasound and acoustophoresis for water purification

1. An apparatus comprising:

a flow chamber for housing a mixture of a fluid and a particulate;

at least two ultrasonic transducers coupled to the flow chamber, each ultrasonic transducer including a piezoelectric material, wherein each ultrasonic transducer is configured to be excited to generate a multi-dimensional acoustic standing wave at a different ultrasonic frequency and wherein each ultrasonic frequency is generated for a specific range of particle sizes and each ultrasonic transducer is configured to generate a pressure field that is Bessel function; and

at least one reflector located on an opposite side of the flow chamber from the at least two ultrasonic transducers.

2. The apparatus of claim 1 , wherein the at least two ultrasonic transducers are configured to be excited by a voltage signal that is an oscillating, periodic, or pulsed voltage signal of ultrasonic frequencies.

3. The apparatus of claim 1 , wherein the at least two ultrasonic transducers are located outside a wall of the flow chamber and the thickness of the flow chamber wall is configured to contribute to acoustic energy transfer into the mixture.

4. The apparatus of claim 1 , wherein the at least two ultrasonic transducers are arranged at different distances from an inlet to the flow chamber relative to one another.

5. The apparatus of claim 1 , wherein the ultrasonic frequencies are in the range of 10 kHz to 100 MHz.

6. The apparatus of claim 1 , wherein each ultrasonic transducer is configured to influence a specific range of particles selected from the group consisting of microalgae, yeast, fungi, bacteria, spores, gases or oils, metal oxides, metal particles, clays, dirt, plastics, and any particulate with a non-zero contrast factor.

7. The apparatus of claim 1 , wherein the multi-dimensional acoustic standing waves are transverse to the direction of mean flow in the flow chamber.

8. The apparatus of claim 7 , wherein the multi-dimensional acoustic standing waves have a horizontal orientation or a vertical orientation.

9. The apparatus of claim 7 , wherein the multi-dimensional acoustic standing waves exert an acoustic radiation force on the particulate for which the ultrasonic frequency is generated, such that the particulate is trapped in its corresponding multi-dimensional acoustic standing wave against fluid drag force, and wherein the particulate is concentrated in the multi-dimensional acoustic standing waves over time.

10. The apparatus of claim 9 , wherein concentrated particles are translated along a direction of the multi-dimensional acoustic standing wave to either a transducer face or to a reflector face.

11. The apparatus of claim 9 , further comprising a collection pocket located within the flow chamber, wherein concentrated particles are translated along a direction of the multi-dimensional acoustic standing wave to the collection pocket.

12. The apparatus of claim 11 , wherein the collection pocket is planar, conical, curved, or spherical in shape.

13. The apparatus of claim 1 , wherein a frequency of excitation of each multi-dimensional acoustic standing wave is constant.

14. The apparatus of claim 1 , wherein the ultrasonic frequency of each multi-dimensional acoustic standing wave varies in a sweep or step pattern.

15. The apparatus of claim 1 , wherein the multi-dimensional acoustic standing waves are three-dimensional acoustic standing waves.

16. A method of precipitating dissolved metals in a solution comprising introducing the solution comprising dissolved metals to the apparatus of claim 1 .

17. A method of killing microorganisms in a solution selected from the group consisting of suspended virus particles, bacterial spores, and microorganisms in the size range of 1 micron to 100 micron, the method comprising introducing the solution to the apparatus of claim 1 .