Browsing by Author "Bayram, Can"

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    Bandwidth improvement in a cMUT array with mixed sized elements
    (IEEE, 2005-09) Bayram, Can; Olcum, Selim; Şenlik, Muhammed N.; Atalar, Abdullah
    A capacitive micromachined ultrasonic transducer (cMUT) is typically fabricated by concatenation of several cMUT cells with identical physical dimensions. If the membrane thickness is kept fixed, the radius of the cMUT determines the center frequency of operation. A smaller radius implies a greater center frequency. Therefore, it should be possible to put cMUTs with different sizes in parallel to get a larger bandwidth at the expense of gain. In this study, we investigate the optimization of the bandwidth characteristics of a cMUT by using mixed size cells. We designed two mixed size cMUT arrays with a predicted optimized fractional bandwidth value of about 155% at 5.4 MHz, and 146% at 8.8 MHz. These values are about 55% and 58% better than what can be achieved with a uniform size array at the corresponding center frequencies. There is almost no loss in the gain bandwidth product when two different sized cMUTs are used in parallel. There is about 9% increase in gain bandwidth product when three different sized cMUTs are used in parallel. It is shown, in this study, that gain bandwidth product and bandwidth can be enhanced by use of mixed size cMUT cells. © 2005 IEEE.
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    Design charts to maximize the gain-bandwidth product of capacitive micromachined ultrasonic transducers
    (IEEE, 2005) Ölçüm, Selim; Şenlik, Muhammed Niyazi; Bayram, Can; Atalar, Abdullah
    In this work we define a performance measure for capacitive micromachined ultrasonic transducers (cMUT) in the form of a gain-bandwidth product to investigate the conditions that optimize the gain and bandwidth with respect to device dimensions, electrode size and electrical termination resistance. For the transmit mode, we define the figure of merit as the pressure-bandwidth product. Fully-metallized membranes achieve a higher pressure-bandwidth product compared to partially metallized ones. It is shown that the bandwidth is not affected by the electrode size in the transmit mode. In the receive mode, we define the figure of merit as the gain-bandwidth product. We show in this case that the figure of merit can be maximized by optimizing the electrode radius. We present normalized charts for designing an optimum cMUT cell at the desired frequency with a given bandwidth for transmit or receive modes. The effect of spurious capacitance and liquid loading effect are considered. Design examples are given to clarify the use of these charts.