Patent ID: 7694826

Claim:
A sieve comprising: a base; a sieve screen frame mounted on the base; a separator screen mounted in the frame; a vibrator arranged to vibrate the frame relative to the base; a resonator secured to or contacting the separator screen, wherein the resonator comprises a rod extending between spaced ends; an ultrasonic transducer at one of said spaced ends to excite the resonator rod at a resonant frequency having a predetermined wavelength along the length of the resonator rod; said resonator rod having at least a portion of its length which bends smoothly in a single direction of curvature through at least 90°, and the rod having a minimum radius of curvature at any point between said spaced ends which is greater than said predetermined wavelength; and wherein said resonator rod is S-shaped, comprising a first monotonically curving portion which bends through at least 90° and is smoothly connected to a second curving portion which also bends monotonically (with curvature of opposite sign to the first curving portion) back through at least 90°.