The present work aims to model, simulate and propose a process for manufacturing a MEMS electrostatic device called Capacitive Micromachined Ultrasound Transducer (CMUT). The finite element method was used for modeling the operating conditions of the devices. Static analysis were made for three different materials Si, Cu, and SU-8. For Si and Cu membranes wider than 800µm in diameter, the CMUT collapsed. As for the SU-8, the collapse of CMUT occurred around 400µm in diameter and 10µm in thickness. Electrostatic and modal analysis were performed subsequently. The modal analysis were made to determine the natural mode shapes of the CMUT membrane. Simulation results gave an approximate idea of suitable dimensions of the devices. In this way, two microfabrication methods are proposed, one for Cu membrane and the other for the SU-8 membrane. Preliminary results allowed us to assert that the process for producing SU-8 CMUTs is very promising.
This work consists on the design, fabrication and characterization of a sensor to measure the concentration of a liquid solution with dielectric components. The sensor is of capacitive type, and it is processed using conventional microfabrication techniques. A thick interdigital structure made of nickel was electroplated on an alumina substrate. In this way, the interdigital structure forms the capacitor plates while the liquid solution is the dielectric material. The dielectric constant of the solution has an intermediate value when compared to the respective values of the pure components of the mixture. Such microsensors have been successfully applied to distinguish amongst different types of fuels commonly used in Brazilian automobiles (gasoline and ethanol).
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