ИСТИНА

The potential of magnetic fluid droplets to be used as miniature reconfigurable soft robots and actuators for a range of biomedical, microfluidic, and lab-on-a-chip applications has been explored by different research groups. The magnetic forces, in combination with the force of surface tension, allow for the magnetic droplet to be manipulated via control of the external magnetic field. Electromagnetic coil systems are usually used to change both position and shape of the droplet either independently or simultaneously. However, such a miniature shapeshifting robot, capable of controlled movement, can also engulf/transport wettable particles or push/manipulate nonwettable particles [1]. Since position and shape control of magnetic fluid droplets by the magnetic field gradient, direction, and magnitude has been well studied, we focus on combined shape control of a droplet and position control of an immersed object (not exclusively wettable or nonwettable) by uniform fields. Thus, realizing that the combination of a uniform magnetic field and magnetic fluid droplet offers wireless and programmable manipulation, we performed experiments and theoretical (both analytical and numerical) studies on how a droplet with an immersed magnetizable body deforms on a horizontal plane under a uniform tilted field (see Figure). A magnetizable ball takes its equilibrium position in the droplet. Spherical shape of the body is chosen for ease of calculating due to a known expression for the magnetic field near the surface of the ball being magnetized in a uniform applied field, but bodies of other shapes were also considered in the experiment. In the noninductive approximation, an analytic expression was obtained for the force exerted by magnetic fluid on the body. We developed a three-dimensional model to predict the deformation of the droplet under uniform magnetic fields of different directions and magnitudes. This research examined the shape control of both immobile and shifting droplets (depending on contact angle), however we focused on the position control of the ball: its levitation height and horizontal displacement. The body position could be controlled by tuning the tilt angle and magnitude of the magnetic field.