Browsing by Subject "Finite element simulations"

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Open Access
An equivalent circuit for collapse operation mode of CMUTs
(IEEE, 2010) Olcum, Selim; Yamaner F.Y.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Collapse mode of operation of the capacitive mi-cromachined ultrasonic transducers (CMUTs) was shown to be a very effective way for achieving high output pressures. However, no accurate model exists for understanding the mechanics and limits of the collapse mode. In this work, we extend the analyses made for CMUTs working in uncollapsed mode to collapsed mode. We have developed an equivalent nonlinear electrical circuit that can accurately simulate the mechanical behavior of a CMUT under any large signal electrical excitation. The static and dynamic deflections of a membrane predicted by the model are compared with the finite element simulations. The equivalent circuit model can estimate the static deflection within 1% and the transient behavior of a CMUT membrane within 3% accuracy. The circuit model is also compared to experimental results of pulse excitation applied to fabricated collapse mode CMUTs. The model is suitable as a powerful design and optimization tool for the collapsed as well as the uncollapsed case of CMUTs. © 2010 IEEE.
Open Access
Finite element modeling of micro-particle separation using ultrasonic standing waves
(ASME, 2014) Büyükkoçak, S.; Çetin, Barbaros; Özer, M. B.
Acoustophoresis which means separation of particles and cells using acoustic waves is becoming an intensive research subject. The method is based on inducing an ultrasonic compression standing wave inside a microchannel. A finite element approach is used to model the acoustic and electro-mechanical behavior of the piezoelectric material, the micro-channel geometry as well as the fluid inside the channel. The choices of silicon and PDMS materials are investigated as the chip materials for the resonator. A separation channel geometry which is commonly used in the literature is implemented in this study and the fluid flow inside the microchannel geometry is simulated using computational fluid dynamics. The acoustic field inside the fluid channel is also be simulated using the finite element method. For the separation process to be successful micro-particles of different diameter groups should end up in different channels of the micro-separator. In order to simulate real life scenarios, each particle size group have a size distribution within themselves. For realistic simulation results the particles will be released into the micro separator from a different starting locations (starting location distribution). The results of this Monte-Carlo based finite element simulation approach will be compared with the reported experimental results.
Open Access
Radiation impedance of an array of circular capacitive micromachined ultrasonic transducers
(IEEE, 2010) Senlik, M. N.; Olcum, S.; Köymen, Hayrettin; Atalar, Abdullah
The radiation impedance of a capacitive micromachined ultrasonic transducer (cMUT) with a circular membrane is calculated analytically using its velocity profile for the frequencies up to its parallel resonance frequency for both the immersion and the airborne applications. The results are verified by finite element simulations. The work is extended to calculate the radiation impedance of an array of cMUT cells positioned in a hexagonal pattern. A higher radiation resistance improves the bandwidth as well as the efficiency of the cMUT. The radiation resistance is determined to be a strong function of the cell spacing. It is shown that a center-to-center cell spacing of 1.25 wavelengths maximizes the radiation resistance, if the membranes are not too thin. It is also found that excitation of nonsymmetric modes may reduce the radiation resistance in immersion applications.