A wireless pressure sensor based on surface trapped ferrofluid plug

We present a new inductive wireless pressure sensor based on the change in the shape of a ferrofluid plug/droplet trapped in a hydrophilic island and sandwiched between two superhydrophobic polymeric membranes one of which contains a flat coil. When external pressure deflects one of the membranes, it squeezes the droplet and changes the distribution of high-permeability ferrite microparticles around the coil. This results in a change in the inductance of the coil which also affects its self-resonant frequency that can be monitored wirelessly. When pressure is released, the ferrofluid plug/droplet regains its original shape due to the superhydrophobic nature of its surrounding surface. The sensor is fabricated using polyethylene terephthalate (PET) film and aerosol based superhydrophobic spray-coating. The sensor has a pill-shape design (thickness = 1.23 mm, diameter = 15 mm) with a sensitivity of 12 kHz/mmHg (0-15 mmHg).