(color online) Top views of ER suspension at different electrical field strengths with 0.5-μm or 47-μm glass microspheres. The volume fraction is 0.15. ((a) and (b)) Top views of ER suspension with 0.5-μm glass microspheres under 300 V/mm and 1500 V/mm, respectively. Insets are side views corresponding to each case. Two figures have the same scale bar; (a) one microsphere connects to another microsphere, forming a chain. As a result, the column diameter is the same as the diameter of microsphere; (b) D₃ = 492.5 μm. There is more than one microsphere per section; ((c) and (d)) Top views of ER suspension with 0.5-μm glass microspheres under 300 V/mm and 1500 V/mm, respectively. Two figures have the same scale bar, D₁ = 261 μm, D₂ = 484 μm.