(color online) Distribution profiles of column diameters observed under different electric field strengths. Diameter of the microsphere is 0.5 μm and the volume fraction of the ER fluid is 0.15. Red lines are the GaussAmp fit of the diameter distributions. ((a)–(d)) Electrical field strengths for the four graphs are 300, 500, 800, and 1200 V/mm, respectively. (a) When the electrical field strength is 300 V/mm, the diameters are in a range from 18 μm to 261 μm. The number of columns, whose diameters are distributed between 148 μm and 150 μm, is greatest. (b) When the electrical field strength is 500 V/mm. The diameters are in a range from 142 μm to 515 μm. The number of columns, whose diameters are distributed between 320 μm and 330 μm, is greatest. (c) When the electrical field strength is 800 V/mm, the diameters are in a range from 145 μm to 555 μm. The column number, whose diameters are distributed between 396 μm and 403 μm, is greatest. (d) When the electrical field strength is 1200 V/mm, the diameters are in a range from 188 μm to 603 μm. The number of columns, whose diameters are distributed between 446 μm and 453 μm, is greatest.