Force Sensors Constructed from Ferromagnetic Particles Embedded Within Soft Materials

Abstract

The inclusion of magnetic particles as fillers within soft materials has the potential to drive the development of smart materials with high functionality and structural diversity. Six ferromagnetic fillers (i.e., nickel, carbonyl iron, cobalt, iron oxide, magnetite, and neodymium powder) were incorporated within polydimethylsiloxane at concentrations of 0.01 wt %, 0.1 wt %, and 1 wt %. Defined compression tests determined the ability to detect material deformation and the magnetic field response generated during compression cycles. Utilizing iron oxide at 1 wt %, the compressive response of additional silicones and a two-part polyurethane was also investigated. Compression testing of five of the six ferromagnetic fillers in PDMS, with the exception of carbonyl iron, revealed that 1 wt % was the minimum concentration required to detect compression events via the magnetic field response. The findings of carbonyl iron at 1 wt % were not viable as its magnetic field response was similar to that of the PDMS control samples. The neodymium filler particles produced the strongest magnetic field response. However, settling of the neodymium particles became evident during the curing process, which prompted further theoretical exploration at various particle sizes and viscosities. Our findings suggested that smaller neodymium particle sizes should be explored in future analyses. PDMS displayed the optimal relationship between force and displacement amongst the various polymers with 1 wt % iron oxide. The other materials were either too soft or were too resistive to be considered viable as a durable soft sensor material or were limited by an inability to measure magnetic field strength.