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.