Browsing by Subject "Collapse voltage"

Now showing 1 - 4 of 4

Open Access
Calculation of transformer ratio in mason's equivalent circuit for cMUTs
(IEEE, 2006) Ölçüm, Selim; Atalar, Abdullah; Köymen, Hayrettin; Şenlik, Muhammed Niyazi
We present a new method to calculate the transformer ratio of a cMUT in Mason's Equivalent circuit model. The effect of the spring softening capacitance is also included in the analysis. We use the existing turns ratio calculation methods as a starting point to calculate the force-voltage ratio at the secondary of the transformer and the input port of the circuit. We use this ratio and the capacitances in the Mason's circuit to find the actual turns ratio. Different methods are discussed for the calculation of the equivalent circuit parameters. We show that the transformer ratio has a bounded maximum at collapse voltage. We also investigate the effect of electrode size on the transformer ratio. Transformer ratio decreases with decreasing electrode size.
Open Access
CMUT array element in deep-collapse mode
(IEEE, 2011) Olcum, Semih; Yamaner F.Y.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Collapse and deep-collapse mode of operations have boosted the pressure outputs of capacitive micromachined ultrasonic transducers (CMUTs) considerably. In this work, we demonstrate a CMUT element operating in the deep-collapse mode with 25 V pulse excitation and without the effects of charge trapping. The fabricated CMUT element consists of 4 by 4 circular cells with 20 μm radius and 1 μm thick plates suspended over a 50 nm cavity. The overall size of the element is 0.190 mm by 0.19 mm. The collapse voltage of the plates is measured to be approximately 3V. By driving the CMUTs with 25V pulses in the deep-collapse mode without any bias, we achieved 1.2 MPa peak-to-peak pressure output on the surface of the CMUT element with a center frequency of 9 MHz and 100% fractional bandwidth. We applied 1000 consecutive electrical pulses with alternating polarity to the element and witnessed no change in the transmitted acoustic pulse. © 2011 IEEE.
Open Access
Deep-collapse operation of capacitive micromachined ultrasonic transducers
(IEEE, 2011) Olcum, S.; Yamaner F. Y.; Bozkurt, A.; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (CMUTs) have been introduced as a promising technology for ultrasound imaging and therapeutic ultrasound applications which require high transmitted pressures for increased penetration, high signal-to-noise ratio, and fast heating. However, output power limitation of CMUTs compared with piezoelectrics has been a major drawback. In this work, we show that the output pressure of CMUTs can be significantly increased by deep-collapse operation, which utilizes an electrical pulse excitation much higher than the collapse voltage. We extend the analyses made for CMUTs working in the conventional (uncollapsed) region to the collapsed region and experimentally verify the findings. The static deflection profile of a collapsed membrane is calculated by an analytical approach within 0.6% error when compared with static, electromechanical finite element method (FEM) simulations. The electrical and mechanical restoring forces acting on a collapsed membrane are calculated. It is demonstrated that the stored mechanical energy and the electrical energy increase nonlinearly with increasing pulse amplitude if the membrane has a full-coverage top electrode. Utilizing higher restoring and electrical forces in the deep-collapsed region, we measure 3.5 MPa peak-to-peak pressure centered at 6.8 MHz with a 106% fractional bandwidth at the surface of the transducer with a collapse voltage of 35 V, when the pulse amplitude is 160 V. The experimental results are verified using transient FEM simulations.
Open Access
An improved lumped element nonlinear circuit model for a circular CMUT cell
(IEEE, 2012) Köymen, Hayrettin; Atalar, Abdullah; Aydogdu, E.; Kocabas, C.; Oguz, H. K.; Olcum, S.; Ozgurluk, A.; Unlugedik, A.
This paper describes a correction and an extension in the previously published large signal equivalent circuit model for a circular capacitive micromachined ultrasonic transducer (CMUT) cell. The force model is rederived so that the energy and power is preserved in the equivalent circuit model. The model is able to predict the entire behavior of CMUT until the membrane touches the substrate. Many intrinsic properties of the CMUT cell, such as the collapse condition, collapse voltage, the voltage-displacement interrelation and the force equilibrium before and after collapse voltage in the presence of external static force, are obtained as a direct consequence of the model. The small signal equivalent circuit for any bias condition is obtained from the large signal model. The model can be implemented in circuit simulation tools and model predictions are in excellent agreement with finite element method simulations.