We present the design, fabrication, and testing of stretchable pressure sensing membranes. Two sensing techniques are demonstrated: resistive and capacitive. Both designs are incorporated in 400μm-thick films and are fabricated with thin film application of silicone and stencil/mask deposition of conductive materials. The resistive sensor utilizes room temperature liquid metal while the capacitive sensor utilizes multi-walled carbon nanotubes. Tests are performed with 18mm-diameter samples of each. Point load tests and acoustic response in an impedance tube provide feedback on sensor performance. The resistive sensor demonstrates a sensitivity of 0.045Ω/mm, and the sensor’s response has been characterized for in the 30Hz to 10kHz range with varying degrees of sensitivity. The capacitive sensor has a small point-load-deflection sensitivity ranging from 0.018pF/mm to 0.044pF/mm depending on capacitor diameter. Acoustic response are shown for 5Hz to 40 Hz, limited by external electronics. These devices are progress towards developing sensor networks capable of tracking aqueous turbulence.
We design and acoustically simulate additively manufactured, flat acoustic membranes (also called metasurfaces) which can be reconfigured into 3-dimentional solids. Using finite element simulations, we design frequency selective acoustic ‘window’ membranes. These transmit narrow frequency bands near flexure resonances. The frequency range of coverage was chosen to be in the audible range and spans from 2,500Hz to 10,000Hz with first order resonances only. We demonstrate selective, non-overlapping acoustic transmission through each membrane window in its flat configuration, and directional selectively when the flat metasurface is folded into the truncated-octahedron with an omnidirectional microphone placed on the interior of the solid form. This work was supported by the Office of Naval Research.