Acoustic particle separation

A method for separating particles comprising:

• applying sinusoidal acoustic energy to a chamber, which is resonant to a chamber mode, to establish an acoustic standing wave pattern that forms a force potential well in the chamber;
• positioning a plurality of particles in said chamber within said well, while a nonacoustic force field is also applied to said chamber to urge particles away from the center of said well;
• and
• removing particles from selected positions in said force potential well, so that some particles are removed from other particles according to the positions they assumed in said well;
• said chamber is cylindrical and is oriented with the axis of the cylinder extending perpendicular to the direction of said nonacoustic force;
• and
• said step of applying acoustic energy includes applying acoustic waves of the lowest cylindrical mode, of a wavelength of 3.41 times the radius of the cylinder.

A method for separating particles comprising:

• applying sinusoidal acoustic energy to a chamber, which is resonant to a chamber mode, to establish an acoustic standing wave pattern that forms a force potential well in the chamber;
• positioning a plurality of particles in said chamber within said well, while a nonacoustic force field is also applied to said chamber to urge particles away from the center of said well;
• and
• removing particles from selected positions in said force potential well, so that some particles are removed from other particles according to the positions they assumed in said well;
• said chamber is a sphere;
• said step of applying acoustic energy includes applying acoustic waves of the lowest spherical mode, of a wavelength of 3.02 times the radius of the sphere.

A method for separating particles comprising:

• applying sinusoidal acoustic energy to a chamber, of a frequency which is resonant to the chamber, to establish a standing wave pattern with a location of minimum acoustic force, while a nonacoustic substantially linear second force is applied to said chamber to urge particles in a direction away from said location, to form a levitation region within which particles can be suspended against said second force;
• establishing said group of particles in said levitation region;
• and
• withdrawing particles from a selected location in said levitation region;
• said step of applying acoustic energy includes applying energy of a first intensity, and then reducing the intensity relative to said second force to allow only some of the particles to fall out of said levitation region toward the periphery of the chamber.