Remoldable inductors based on self-heating fusible alloys

Wirelessly powering sensor systems attached to a curved or non-planar surface requires inductor coils able to conform to an irregular geometry. In this work, a coil is demonstrated based on pulling a low melting point (fusible) metal alloy in liquid form through fluidic channels in soft silicone. Although solid at room temperature, when inductors made of Field´s metal are heated through Joule heating above the melting point (62°C) of the alloy, the traces melt, allowing deformation to conform to a surface. The heating power can then be removed, causing the alloy to solidify and hold the new shape. This recasting is demonstrated by creating a mechanically tunable inductor. The coil is stretched to tune the inductance while liquid, with solidification used as a latching mechanism to hold the inductance with zero static power. During tuning, an applied power of 0.8 W is used to melt the inductor traces. Tuning of 50%, from 96 nH to 147 nH, is demonstrated with a fusible alloy inductor; when the inductor was again re-heated, the inductance returned to the initial value due to the restoring mechanical force of the surrounding silicone.