Liquid metal-based resistive membranes for flow acoustics detection

Abstract

Fluid flow over bodies results in vortex and turbulence-induced vibrations that reflect the boundary layer conditions and lead to drag and noise production. Many platforms would benefit from real-time monitoring of these acoustic signatures, providing feedback for control or increased efficiency. Of particular interest are compliant pressure sensors that can be wrapped around any surface. We present a silicone membrane integrated with a liquid phase gallium-indium coil. As the device deforms under pressure fluctuations, the resistance across the liquid metal can be monitored for real-time detection of flow features. The fabrication process is presented, including a masked spray deposition of gallium-indium coupled with layering of elastomer. The 18 mm-diameter sample demonstrates a point load sensitivity of 0.045 W/mm. To evaluate the performance of the device, it is tested in air with an acoustic tube, and its output is compared to impedance analysis at frequencies up to 10 kHz. Furthermore, the membrane vibrations are tracked with scanning laser Doppler vibrometer. These results are then compared to analytic models and COMSOL simulations. The sensor presented here is well suited to bulk fabrication in functional “skins” of active elements. [Work sponsored by the Office of Naval Research.]