Multimodal magnetoactive elastomers for magnetic and touch sensing with stylus functionality

Magnetoactive elastomers (MAEs), primarily consisting of magnetic particles embedded within elastomeric matrices, exhibit remarkable multimodality, including magnetoresistive, magnetocapacitive, and magnetomechanical, which vary depending on the fillers. The integration of these properties in both isotropic and anisotropic MAEs for interactive electronics without additional circuitry, such as capacitive styluses, has not been thoroughly investigated. This study uniquely illustrates the performance of multimodal isotropic and anisotropic MAEs, which consist of soft silicone elastomer and identical dual fillers (carbon black, 3.6% and cobalt, 33%), for magnetoresistance, magnetocapacitance, magnetomechanical, piezoresistance and capacitive coupling (stylus) features. Magnetoresistance and magnetocapacitance were characterized using impedance spectroscopy at 1 kHz (0–300 mT), and piezoresistivity was investigated at 10 Hz through compression tests. Magnetomechanical sensitivity was quantified by measuring bending angles under magnetic fields (0–150 mT), and the stylus functionality was shown by measuring capacitance between the MAE stylus tip and a commercial touchscreen at 100 kHz under applied forces. Enhanced magnetoresistance and magnetocapacitance responses (with sensitivities of 1.67 T−1 and 6.40 T−1, respectively) of the MAEs are attributed to engineered conductivity and permittivity from the filler networks. Magnetomechanical testing revealed greater bending responses in the anisotropic MAE (58° at 150 mT vs 50° for the isotropic), emphasizing alignment-enhanced responsiveness. The piezoresistivity of isotropic MAE shows consistent 36.25% N−1 sensitivity, and notably, the anisotropic MAE exhibited an efficient stylus performance with sensitivity of 0.35 pF N−1, reliably activating touchscreens at minimal forces (<0.1 N).