To better understand the effect of needle design parameters on linear phacoemulsification ultrasound We modified two different needle designs by changing the hub weights and determined the response.
Using an opto-transistor test rig, we measured the linear excursion of the needle tip. The Infinity phaco-handpiece was set with 20% continuous linear power and the needle was resonated in air over the test rig.† Static FEA analysis was used to determine the needle stiffness.† The tip mass was determined for that portion beyond 26mm from the needle base.
Removing mass from the hub increased the tip excursion for the first design The reduction from from 188.8 to 150.2 mg in total weight increased displacement from 13.3_ to 19.1_.The stiffness was reduced from 1386 N/mm to 1286 N/mm by the modification The second needle with a lighter tip mass of 5.32mg (compared with 6.98mg), however, had reduced tip excursion. When the weight reduced from 232.2 to 182.2mg, excursion reduced from 12.8 _ to 7.3 _, despite a slightly bigger reduction of stiffness from 1416 N/m to 1168 N/m.
Seemingly a modification on one needle has an opposite effect on another This may be because the natural frequency of each needle/hand-piece combination falls on different sides of the piezo-crystal excitation frequency.† Further investigation is required to better understand the tuning of the phaco-needle design to each specific phaco-handpiece.
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