Browsing by Author "Khuri-Yakub, B. T."

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Open Access
Analytic modeling of loss and cross-coupling in capacitive micromachined ultrasonic transducers
(IEEE, Piscataway, NJ, United States, 1998) Bozkurt, A.; Degertekin, F. L.; Atalar, Abdullah; Khuri-Yakub, B. T.
The structural loss mechanism of capacitive micromachined ultrasonic transducer (cMUT) is investigated using finite element analysis and the normal mode theory. A single micromachined transducer membrane on an infinite silicon substrate is simulated by incorporating absorbing boundary conditions in the finite element method. This enables direct evaluation of the mechanical impedance of the membrane. Furthermore, the field distribution along the thickness of the silicon substrate due to outward radiating wave modes is obtained. The normal mode theory is applied to extract the contributions of different wave modes to the complicated field distributions. It is found that, the lowest order Lamb wave modes are responsible for the loss. Evaluation of absolute and relative power losses due to individual modes indicate that the lowest order anti-symmetric (A0) mode is the dominant radial mode in agreement with experimental measurements. The results of the analysis are used to derive a detailed equivalent circuit model of a cMUT with structural loss.
Open Access
Microfabricated ultrasonic transducers: towards robust models and immersion devices
(IEEE, 1996-11) Ladabaum, I.; Jin, X.; Soh, H. T.; Pierre, F.; Atalar, Abdullah; Khuri-Yakub, B. T.
The successful fabrication of ultrasonic immersion transducers is reported. Transducers are observed to operate from 1 MHz to 20 MHz in water, with the frequency range limited by electronics, not the transducers. Transmission results are included which show that a single pair of transducers is able to operate in water at 4, 6, and 8 MHz with a signal to noise ratio of at least 48 dB. The same transducer pair is shown to operate in air at 6 MHz. A model is introduced which highlights the significant parameters of transducer design. The model enables the design of optimized transducers.
Open Access
Micromachinable leaky wave air transducers
(IEEE, 1997-11) Değertekin, F. L.; Atalar, Abdullah; Khuri-Yakub, B. T.
In this paper, ultrasonic air transducers which use the lowest order antisymmetric (A/sub 0/) mode Lamb waves in a thin plate as a means of efficient coupling of ultrasonic energy to air are discussed. For a silicon plate of 1 /spl mu/m thickness, the energy leak rates can go up to 0.6 dB per wavelength. At MHz frequencies the plate thickness should be in the range of 1-10 /spl mu/m, which requires micromachined structures to be used. The radiation pattern of the transducers can be controlled by the geometry of the transducer, which can also be used for focusing. A theoretical model to calculate the efficiency and optimized transducer dimensions is presented. This model is applied to common micromachining materials such as silicon, silicon nitride and silicon dioxide. The analysis show that, with these transducers it is possible to achieve a conversion loss with a minimum of 8.7 dB and 78% fractional bandwidth. Experimental results on transmission imaging are also presented using an implementation of the transducer operating around 580 kHz.
Open Access
Micromachinable ultrasonic leaky wave air transducers
(A I P Publishing LLC, 1998-08-10) Degertekin, F. L.; Atalar, Abdullah; Khuri-Yakub, B. T.
Ultrasonic air transducers using leaky waves on thin membranes are analyzed using perturbation and normal mode approaches. The transducers utilize the efficient coupling of ultrasonic energy to air through radiation of these leaky wave modes when their phase velocity is close to the sound speed in air. Theoretical results on optimum transducer dimensions and bandwidth estimation show that a minimum conversion loss of 8.7 dB with a 78% fractional bandwidth is possible. Common micromachining materials are shown to be suitable transducer materials and result in feasible devices. This is demonstrated by fabricating a 580 kHz transducer using a silicon membrane bonded to a ring of PZT-5H. With this configuration the transducer is self line focusing. Results of through transmission experiments on silicon and transmission images on paper are reported.
Open Access
Micromachined two-dimensional array piezoelectrically actuated transducers
(A I P Publishing LLC, 1998-03-16) Perçin, G.; Atalar, Abdullah; Degertekin, L.; Khuri-Yakub, B. T.
This letter presents micromachined two-dimensional array flextensional transducers that can be used to generate sound in air or water. Individual array elements consist of a thin piezoelectric ring and a thin, fully supported, circular membrane. We report on an optimum design for an individual array element based on finite element modeling. We manufacture the transducer in two-dimensional arrays using planar silicon micromachining and demonstrate ultrasound transmission in air at 2.85 MHz. Such an array could be combined with on-board driving and an addressing circuitry for different applications.
Open Access
Silicon micromachined ultrasonic immersion transducers
(A I P Publishing LLC, 1996-12-09) Soh, H. T.; Ladabaum, I.; Atalar, Abdullah; Quate, C. F.; Khuri-Yakub, B. T.
Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signal‐to‐noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using siliconsurfacemicromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in high‐temperature environments and that arrays can be fabricated at lower cost.
Open Access
Surface micromachined capacitive ultrasonic transducers
(Institute of Electrical and Electronics Engineers, 1998-05) Ladabaum, I.; Jin, X.; Soh, H. T.; Atalar, Abdullah; Khuri-Yakub, B. T.
The current state of a novel technology, surface microfabricated ultrasonic transducers, is reported. Experiments demonstrating both air and water transmission are presented. Air-coupled longitudinal wave transmission through aluminum is demonstrated, implying a 110 dB dynamic range for transducers at 2.3 MHz in air. Water transmission experiments from 1 to 20 MHz are performed, with a measured 60 dB SNR at 3 MHz. A theoretical model is proposed that agrees well with observed transducer behavior. Most significantly, the model is used to demonstrate that microfabricated ultrasonic transducers constitute an attractive alternative to piezoelectric transducers in many applications.
Open Access
Theory and analysis of electrode size optimization for capacitive microfabricated ultrasonic transducers
(Institute of Electrical and Electronics Engineers, 1999-11) Bozkurt, A.; Ladabaum, I.; Atalar, Abdullah; Khuri-Yakub, B. T.
Theoretical analysis and computer simulations of capacitive microfabricated ultrasonic transducers indicate that device performance can be optimized through judicious patterning of electrodes. The conceptual basis of the analysis is that electrostatic force should be applied only where it is most effective, such as at the center of a circular membrane. If breakdown mechanisms are ignored, an infinitesimally small electrode with an infinite bias voltage results in the optimal transducer, A more realistic design example compares the 3-dB bandwidths of a fully metalized transducer and a partially metalized transducer, each tuned with a lossless Butterworth network. It is found that the bandwidth of the optimally metalized device is twice that of the fully metalized device.