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[(a)–(f)] Fabrication procedure of the ABF with InGaAs/GaAs/Cr helical tail. (g) FESEM image of an untethered ABF. The scale bar is .
The experimental setup for the swimming tests of ABF using three-axis electromagnetic coils.
ABF swimming motion controlled by magnetic fields with field strength of 2.0 mT. [(a)–(d)] Schematic of a left-handed ABF swimming forward and backward. With the field continuously rotating perpendicular to the axis of the ABF, a misalignment angle between the field and the thin magnetic head will induce a magnetic torque that attempts to align the ABF head with the field, resulting in rotation and propulsion of the ABF. (e) Optical microscope images of the forward/backward motion of an ABF controlled by magnetic fields. The commanded translation and rotation directions of the ABF are indicated by the arrows. (f) If the field is rotated about the Z axis by an angle with respect to the easy axis of the head, then the ABF is steered as it is propelled, as the easy axis attempts to align with the field. This is the steering principle used during normal operation of the ABF. (g) If the field is rotated about the axis by an angle with respect to the easy axis , the ABF will instantaneously attempt to rotate perpendicular to the helix axis. However, steering using the easy axis is not possible simultaneously with forward/backward propulsion. (h) Optical microscope images of the turning motion of an ABF controlled by magnetic fields. The commanded translation and rotation directions of the ABF are indicated by the arrows.
(a) A series of frames taken from a video showing an ABF driven toward a target in 40 s. The ABF has a long InGaAs/GaAs helical tail with left-handed chirality. The scale bar is for all images. (b) The experimental curves of the distance from the center point of the ABF to the target vs the time. Curve “a” shows the result from the ABF moving toward the target, i.e., (a). The forward velocity is , corresponding to an angular speed of 6.3 rad/s. Curve “b” shows result from the same ABF moving forward at the initial 20 s and backward after that. The forward velocity is and the backward velocity is , corresponding to an angular speed of 6.3 rad/s and 10.5 rad/s, respectively.
(a) Two polystyrene microspheres are rotated 70° by a long InGaAs/GaAs/Cr ABF pushing on one of the microspheres. The optical-microscope image sequence represents 2 s of elapsed time. (b) The microsphere is pushed for a radius length by the ABF within 1 s. The scale bars are .
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