Particle separation

Claim 2

In a method of separating different types of particles in which an ultrasonic standing wave having an axis of propagation, and a series of nodes transverse to the axis is propagated in a liquid medium and there is relative motion between the medium and the standing wave, the different types of particles being differently influenced by the acoustic energy of the standing wave and/or the Stokes or drag forces of the fluid medium, the improvement comprising cyclically varying the energy propagation of said standing wave .Iadd.by moving the standing wave at a cyclically varying rate .Iaddend.so that the different particle types are caused to move at .[.cyclically varying.]. .Iadd.different .Iaddend.rates in the direction of the axis of propagation and thereby progressively separating said different particle types while .[.remaining.]. .Iadd.they remain .Iaddend.suspended in the liquid medium.

Claim 3

A method according to claim 1 wherein substantially instantaneous phase changes are introduced between two acoustic energy outputs which interact to produce the moving standing wave, thereby superimposing additional intermittent movements onto the substantially continuous movement of the standing wave.

Claim 4

A method according to claim 1 wherein the standing wave is subjected to cycles of velocity variation in each of which the velocity is varied unidirectionally between a maximum and a minimum rate of movement for the standing wave.

Claim 5

In a method of separating different types of particles in which an ultrasonic standing wave having an axis of propagation, and a series of nodes transverse to the axis is propagated in a liquid medium and there is relative motion between the medium and the standing wave, the different types of particles being differently influenced by the acoustic energy of the standing wave and/or the Stokes or drag forces of the fluid medium, the improvement comprising cyclically varying the energy propagation by varying the intensity of said standing wave so that the different particle types are caused to move at different rates in the direction of the axis of propagation .Iadd.and thereby progressively separating said .Iaddend.different particle types while .[.remaining.]. .Iadd.they remain .Iaddend.suspended in the liquid medium.

Claim 6

In a method of separating different types of particles in which an ultrasonic standing wave having an axis of propagation, and a series of nodes transverse to the axis is propagated in a liquid medium and there is relative motion between the medium and the standing wave, the different types of particles being differently influenced by the acoustic energy of the standing wave and/or the Stokes or drag forces of the fluid medium, the improvement comprising cyclically varying the energy propagation by varying the intensity of said standing wave so that the different particle types are caused to move at different rates in the direction of the axis of propagation .Iadd.and thereby progressively separating said .Iaddend.different particle types while .[.remaining.]. .Iadd.they remain .Iaddend.suspended in the liquid medium.

Claim 7

A method according to claim 3 wherein the standing wave is periodically suppressed and re-established.

Claim 8

A method according to claim 5 wherein said suppression and re-establishment of the standing wave is performed without disturbing the phase continuity of electrical driving signals producing the acoustic energy. .Iadd.7. In a method of separating different types of particles in which an ultrasonic standing wave having an axis of propagation, and a series of nodes transverse to the axis is propagated in a liquid medium and there is relative motion between the medium and the standing wave, the different types of particles being differently influenced by the acoustic energy of the standing wave and/or the stokes or drag forces of the fluid medium, the improvement comprising cyclically varying the energy propagation of said standing wave so that the different particle types are caused to move at different cyclically varying rates in the direction of the axis of propagation and thereby progressively separating said different particle types while they remain suspended in the liquid medium. .Iaddend. .Iadd.8. A method as in claim 7 whereby said cyclically varying energy propagation step comprises the further step of causing the standing wave to move at a cyclically varying rate. .Iaddend.