Design of Reduced Graphene Oxide Based Piezo-Resistive Type Acoustic Sensor on Flexible Kapton for Underwater Applications

Micro Electro Mechanical Systems (MEMS) vector sensor is a recent advancement in the field of underwater acoustic sensors. The major incentive provided by this acoustic vector sensor is that it provides information about the direction of the incoming acoustic source signal in addition to the measurement of the pressure associated with the acoustic signal. We are reporting a design of a MEMS acoustic vector sensor for underwater applications using piezoresistive film of Reduced Graphine Oxide (RGO), realized on kapton (polyimide) film as the starting material. The sensor is designed and fabricated by deposition of RGO on a kapton, which is a flexible substrate by the method of drop casting making the process simple, low-cost and scalable. The application of the piezoresistive transduction principle and ingenious structure of the vector sensor based on bionic principle improves miniaturization and the low-frequency sensitivity. The fabricated sensor shows a repeatable response in both static and dynamic conditions, to the applied strain due to the acoustic signal in a given direction. The experimental results show that fabricated sensor based on MEMS technology and piezoresistive effect is feasible and it possesses intrinsic two-dimensional directivity. The fabricated device has given good response for the low-frequency acoustic signals due to the effect of piezoresistive transduction principle and the resonance frequency of the device is found to be around 80 Hz with the displacement sensitivity around 3 mV/mm and 2 mV/mm of X and Y axis directions respectively.

Two modes of contact‐time reduction in the impact of particle‐coated droplets on superhydrophobic surfaces

Reducing the contact time during droplet impact is essential for many scientific and industrial applications,such as self‐cleaning,anti‐icing,heat transfer,and condensation.This paper reports contact‐time reduction by coating droplets with micro–nano hydrophobic particles.Such particle‐coated droplets are known as liquid marbles(LM).LM impact on superhydrophobic surfaces reveals two different modes of contact‐time reduction.For lower impact energies,the reduced adhesion of LM with the surface is responsible for a reduction of up to 21%.Contact‐time reduction in this regime is found to be independent of particle size but dependent on the solid fraction of LM.However,a fragmentation‐based contact‐time reduction is observed for larger particle sizes and higher impact energies.Here,the reduction is as high as 65%.Such fragmentation occurs because the spreading LM lamella breaks when its thickness becomes similar to particle dimensions.Our findings reveal the potential of LM as a novel approach to reduce contact time during droplet impact,with implications for various scientific and industrial applications.