Fabrication and Characterization of Polymer-Bonded Flexible Anisotropic Micro-Magnet Arrays

Abstract

Here we present a process for the fabrication of arrays of anisotropic flexible bonded micro-magnets attached to a transparent base. The micro-magnets are based on hard magnetic SmFeN or Sr-ferrite powders mixed with polydimethylsiloxane (PDMS). The size, shape and distribution of the micro-magnets are defined using a Si-mould fabricated by deep reactive ion etching (DRIE). The volume fraction of the magnetic powder was fixed at 30% while the thickness of the micro-magnets ranged from 50-300 μm and their in-plane dimensions from 20-400 µm. Powder alignment was achieved using a bulk NdFeB magnet. Arrays of micro-pillars of height 300 µm and width tapering from 300 µm at their base to 200 µm at their top were characterized using vibrating sample magnetometry (VSM) and Scanning Hall Probe Microscopy (SHPM) and the results of the latter were compared with analytical simulations. The homogeneous magnetic field produced by a 3-axis electromagnet was used to move the micro-pillars in a controlled fashion. The field induced in-plane displacement of the SmFeN-based pillars was more than three times greater than that of the Sr-ferrite-based ones, reaching 13 µm at the maximum applied field value of 100 mT.

Hard magnetics and soft materials—a synergy

“…metamaterials) [364]. Some other applications of hMSMs include flexible magnets [365,366], energy harvesting [367] materials, and PCMs [368,369]. This section discusses some of the important applications of hMSMs with a special focus on soft robotics.…”

Microstructured Magnetoelastic Membrane for Magnetic Bioactuators and Soft Artificial Muscles Applications

“…However, they are generally made of thicker polymer elements (e.g., 1 mm, [10] 167, [13] and 35 μm, [12] ) and loaded with a higher density of magnetic particles. These particles are mostly made of hard magnetic materials (e.g., NdFeB or SmFeN powders), [11,13] dispersed as powder, embedded in the thick PDMS layers requiring larger forces to be actuated. We also reported on our thin (5 μm/100 nm) PDMS/Au membrane, driven by an array of thick (1.25 μm) electrodeposited magnetic particles.…”

“…With: i) OOP magnetization M Z in Equations ( 6) or (7); ii) OOP differential magnetic susceptibility χ = dM Z /dB Z ; iii) field B Z expressed in Equation ( 8) and ( 9); and iv) gradient dB Z /dZ expressed in Equation ( 10) and (11). Figure 6b shows the order of magnitude of the forces at two distances from the magnet (Z = 1 μm and Z = 1.9 mm), in piconewton, along the transverse X-axis, based on the field and field gradient.…”

“…[9,10] Their advantages lie in the potentially long range and efficient remote actuation, high stability, and low power consumption. In particular, polydimethylsiloxane (PDMS) comprising micro-/nanomagnets, [11] for example, in the form of membrane, [12,13] has recently opened the way to artificial muscle applications at macroscale [14] and soft microrobotics. [15,16] In addition, such actuable materials enable the development of bioreactors/bioactuators.…”