Fabrication of Microlens Arrays by Utilizing Magnetic Hydrodynamic Instability of Ferrofluid Droplets

Abstract

This study proposes an actively controllable method for fabrication of polymer microlens arrays. Hexagonal arrays of ferrofluid droplets, which were utilized as the mother-mold masters for microlens molding, were generated by inducing the magnetic hydrodynamic instability under different magnetic fields. To fabricate numerous cavity molds for microlens array molding, we used the field-dependent shapes of the ferrofluid droplets to create different sized molds. For the fabricated microlens arrays, their field-dependent bottom areas, lens height, radii of curvature, and the fill-factor were discussed. Furthermore, performances of the microlenses, including the numerical aperture, focal length, and depth of field, were tested.Index Terms-Ferrofluid droplet, magnetic hydrodynamic instability, microlens array.

Spreading of a ferrofluid core in three-stream micromixer channels

“…These results provide understanding as well as practical guidance for novel wireless technologies for important microfluidic applications, such as micromixers, 24 cytometers or cell sorters, 4,5 biological analysis and catalysis with magnetic beads, 25,26 optofluidics devices, 27 and microlenses. 10,11 …”

“…4,5 Other applications include separation of diamagnetic particles, 6,7 rotating seals, 8 loudspeakers, 9 and microlens arrays. 10,11 Usually, permanent magnets [12][13][14] or electromagnets 15,16 are placed adjacent to LOC devices to produce a magnetic field gradient. Alternatively, micro magnets are directly fabricated and embedded in LOC chips by micro fabrication techniques (e.g., sputter deposition and soft-lithography) to produce magnetic (e.g., Ni) thin films with the required geometry.…”

Magnetowetting dynamics of sessile ferrofluid droplets: a review

“…The current method has the flexibility of generating a plethora of MLAs simply by tuning the strength of the applied magnetic field, thereby exhibiting a four-fold base diameter variation, a two-fold height variation, a five-fold apex curvature variation, and a nine-fold focal-length variation from an initially similar FF liquid volume. 68,69 The process showed an error of less than 4% in the dimensions of the lenses within the field strength 1600–3700 Gauss. Furthermore, the microlenses exhibited high numerical aperture values within the range 0.39–0.54.…”

Droplet Manipulation under a Magnetic Field: A Review

“…Magnetically induced droplet transportation enables reliable sample handling On the basis of magnetic droplet deformation and contact angle shifting in a magnetic field, various applications have been fulfilled, such as microfluidic actuators [52,108] and drive other transparent liquid via communicating vessels for making adaptive liquid microlens, grating, etc. [109]. With an electromagnetic field, the deformation of magnetic sessile droplets would lead to an adjustable droplet microlens by connecting droplets through a channel [110] or cavity [111].…”