DESIGN AND CONSTRUCTION OF ACOUSTIC PARTICLE VELOCITY SENSORS FOR INFRASOUND APPLICATIONS

When studying waves propagation in fluids like air, measuring only sound pressure (p) might not be enough for a complete characterization of the acoustic field. Besides this scalar quantity the acoustic particle velocity (u) is a complement that provides information of the direction of energy propagation. When p and u can be measured, acoustic intensity and impedance can be determined. This work focus on the design and construction of a MEMS sensor sensible to the acoustic particle velocity. Based on flow sensors it uses a thermal principle of two suspended metallic wires heated. When an acoustic wave passes through them one wire is cooled and the other heated by forced convection generating a differential change of temperature (ΔT) and thus electrical resistivity which is proportional to the fluid velocity. Numerical simulations with finite element method were carried out to evaluate the optimal distances between wires and geometrical dimensions that maximize ΔT, and thus the sensitivity of the device for infrasound applications. A MEMS prototype was constructed using microfabrication techniques in clean room. The process involved photolithography on a silicon (Si) wafer and dry etches to release suspended metallic micro-wires. Preliminary measurements were conducted in the constructed devices in terms of their filament electric resistance. The results were compared with simulations and previous literature.