Capacitance micromachined ultrasonic transducers (CMUTs) have become an attractive alternative to the piezoelectric transducers, especially in air-coupled nondestructive evaluation (NDE) and ultrasound medical imaging flow metering, micro/nanoelectronics, and industrial cleaning, etc. These are similar to other capacitance transducers as these employ a vibrating membrane to send and receive ultrasound in air and water. This paper describes the theory and design of a circular micromachined ultrasonic transducer which could lead to a CMUT with many advantages, including less loading effect. The software programs (Intellisuite 8.2 and MATLAB 7.0) were used to model a single cell of CMUT. The simulations-based studies of the critical parameters like collapse voltage and snapback voltage, which influence the operation of the CMUTs to a large extent, has been discussed. Small signal equivalent circuit model for the circular CMUT has been discussed and the program (SPICE) has been used for the simulation of the small signal equivalent circuit.
The objective of the paper is to investigate the variation of core thickness of a non-Newtonian fluid in an annular cylinder at the entrance region. It is derived numerically, with no prior assumptions on the form of the Velocity profile. The thickness of the core is examined at each cross section of annuli for various values of Bingham number and aspect ratio by applying mass balance equation. The effect of various parameters on the flow rate are obtained graphically. The examination incorporates Bingham plastic fluids, Casson and Herschel-Bulkley fluid. The administering equations are solved using an iterative procedure by converting non-linear algebraic equation, expressing the variation in pressure in terms of core thickness obtained using the mass balance equation and plug core velocities along the boundary layers. The core thickness is obtained numerically by solving this equation using an iterative procedure. MATLAB programming tool has been employed to get the graphical variation of core thickness for different values of aspect ratio. The comparisons have been made between the obtained results and the results of Casson and Herschel-Bulkley fluids. Also, we find excellent agreement between our numerical results and the results available in literature.
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