Browsing by Subject "Microtechnology"

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Open Access
An equivalent circuit model for transmitting capacitive micromachined ultrasonic transducers in collapse mode
(IEEE, 2011) Olcum, S.; Yamaner, F. Y.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
The collapse mode of operation of capacitive micromachined ultrasonic transducers (CMUTs) was shown to be a very effective way to achieve high output pressures. However, no accurate analytical or equivalent circuit model exists for understanding the mechanics and limits of the collapse mode. In this work, we develop an equivalent nonlinear electrical circuit that can accurately simulate the mechanical behavior of a CMUT with given dimensions and mechanical parameters under any large or small signal electrical excitation, including the collapse mode. The static and dynamic deflections of a plate predicted from the model are compared with finite element simulations. The equivalent circuit model can estimate the static deflection and transient behavior of a CMUT plate to within 5% accuracy. The circuit model is in good agreement with experimental results of pulse excitation applied to fabricated CMUTs. The model is suitable as a powerful design and optimization tool for collapsed and uncollapsed CMUTs.
Open Access
Multi-temperature zone droplet-based microreactor for increased temperature control in nanoparticle synthesis
(Wiley-VCH Verlag, 2014) Erdem, E. Y.; Cheng, J. C.; Doyle, F. M.; Pisano, A. P.
Microreactors are an emerging technology for the controlled synthesis of nanoparticles. The Multi-Temperature zone Microreactor (MTM) described in this work utilizes thermally isolated heated and cooled regions for the purpose of separating nucleation and growth processes as well as to provide a platform for a systematic study on the effect of reaction conditions on nanoparticle synthesis.
Open Access
Nonlinear modeling of an immersed transmitting capacitive micromachined ultrasonic transducer for harmonic balance analysis
(IEEE, 2010) Oguz, H. K.; Olcum, S.; Senlik, M. N.; Taş, V.; Atalar, Abdullah; Köymen, Hayrettin
Finite element method (FEM) is used for transient dynamic analysis of capacitive micromachined ultrasonic transducers (CMUT) and is particularly useful when the membranes are driven in the nonlinear regime. One major disadvantage of FEM is the excessive time required for simulation. Harmonic balance (HB) analysis, on the other hand, provides an accurate estimate of the steady-state response of nonlinear circuits very quickly. It is common to use Mason's equivalent circuit to model the mechanical section of CMUT. However, it is not appropriate to terminate Mason's mechanical LC section by a rigid piston's radiation impedance, especially for an immersed CMUT. We studied the membrane behavior using a transient FEM analysis and found out that for a wide range of harmonics around the series resonance, the membrane displacement can be modeled as a clamped radiator. We considered the root mean square of the velocity distribution on the membrane surface as the circuit variable rather than the average velocity. With this definition, the kinetic energy of the membrane mass is the same as that in the model. We derived the force and current equations for a clamped radiator and implemented them using a commercial HB simulator. We observed much better agreement between FEM and the proposed equivalent model, compared with the conventional model.