Development of a flexible coil based on conductive polymer composite for PDMS-based soft electromagnetic microactuators

Soft electromagnetic microactuators (SEMMAs) have gained significant attention for application as the movable membrane of portable microfluidic systems due to their low drive voltage and high response. Membranes with a rigid permanent magnet or a conductive liquid have impaired flexibility. This paper reports a moving-coil-type SEMMA using a flexible coil comprised of conductive polymer composite (CPC). The flexible CPC-based coil is fabricated by screen printing. The coil can realize high flexibility due to its small thickness and low Young’s modulus and can conduct electricity under large deformations. Therefore, a CPC-based coil can move with the polymer membrane and will therefore not affect the membrane’s flexibility. We adopted an oxygen plasma surface treatment to print an Ag-based CPC onto a PDMS membrane to increase the coverage ratio from 55% to 97%. We achieved printing wires having a resistivity of 2.0 × 10-6 Ω⋅m with a thickness of about 6.8 µm on the surface-treated PDMS substrate of 0.1 mm thickness. The smallest width and the smallest spacing of the printed wires were 100 µm and 50 µm, respectively. Thermal annealing was conducted to restore the resistivity of the coil which was increased by mechanical deformation and load during the fabrication process. The resistivity was observed to return to the ideal value due to the reformation of the conductive network of the CPC filler. Finally, a prototype SEMMA with a 19.5 µm thick spiral CPC-based coil was fabricated on a Φ30 mm × t0.1 mm PDMS substrate. The actuator generated static displacements of 0.711 mm and -0.785 mm at a constant voltage amplitude of 15.1 V and -15.1 V, respectively, due to the dominant thermal deformation. At different sinusoidal voltage inputs with RMS values from 2.9 V to 15.1 V and with the corresponding first mode frequency of around 51.5 Hz, asymmetrical displacements with a range of -0.41∼0.5 mm were generated.