Hayrettin Koymen

Bio: Hayrettin Koymen is an academic researcher from Bilkent University. The author has contributed to research in topics: Capacitive micromachined ultrasonic transducers & Equivalent circuit. The author has an hindex of 19, co-authored 98 publications receiving 1136 citations. Previous affiliations of Hayrettin Koymen include Middle East Technical University.

An improved lumped element nonlinear circuit model for a circular CMUT cell

Abstract: 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

SVD-based on-line exercise ECG signal orthogonalization

Abstract: An orthogonalization method to eliminate unwanted signal components in standard 12-lead exercise electrocardiograms (ECG's) is presented in this work. A singular-value-decomposition-based algorithm is proposed to decompose the signal into two time-orthogonal subspaces; one containing the ECG and the other containing artifacts like baseline wander and electromyogram. The method makes use of redundancy in 12-lead ECG. The same method is also tested for reconstruction of a completely lost channel. The on-line implementation of the method is given. It is observed that the first two decomposed channels with highest energy are sufficient to reconstruct the ST-segment and J-point. The dimension of the signal space, on the other hand, does not exceed three. Data from 23 patients, with duration ranging from 9 to 21 min, are used.

Multichannel ECG data compression by multirate signal processing and transform domain coding techniques

Abstract: A multilead electrocardiography (ECG) data compression method is presented. First, a linear transform is applied to the standard ECG lead signals, which are highly correlated with each other. In this way a set of uncorrelated transform domain signals is obtained. Then, the resulting transform domain signals are compressed using various coding methods, including multirate signal processing and transform domain coding techniques. >

A phase aberration correction method for ultrasound imaging

Abstract: A computationally efficient method for phase aberration correction in ultrasound imaging is presented. The method is based on time delay estimation via minimization of the sum of absolute differences between radio frequency samples of adjacent array elements. Effects of averaging estimated aberration patterns over scan angle and truncation to a single bit wordlength are examined. Phase distortions due to near-field inhomogeneities are simulated using silicone rubber aberrators. Performance of the method is tested using experimental data. Simulation studies addressing different factors affecting efficiency of the method, such as the number of iterations, window length, and the number of scan angles used for averaging, are presented. Images of a standard resolution phantom are reconstructed and used for qualitative testing. >

Equivalent circuit-based analysis of CMUT cell dynamics in arrays

Abstract: Capacitive micromachined ultrasonic transducers (CMUTs) are usually composed of large arrays of closely packed cells. In this work, we use an equivalent circuit model to analyze CMUT arrays with multiple cells. We study the effects of mutual acoustic interactions through the immersion medium caused by the pressure field generated by each cell acting upon the others. To do this, all the cells in the array are coupled through a radiation impedance matrix at their acoustic terminals. An accurate approximation for the mutual radiation impedance is defined between two circular cells, which can be used in large arrays to reduce computational complexity. Hence, a performance analysis of CMUT arrays can be accurately done with a circuit simulator. By using the proposed model, one can very rapidly obtain the linear frequency and nonlinear transient responses of arrays with an arbitrary number of CMUT cells. We performed several finite element method (FEM) simulations for arrays with small numbers of cells and showed that the results are very similar to those obtained by the equivalent circuit model.

Transducer array imaging system

Abstract: The embodiments contemplate methods and devices for communicating an acoustic emission via an array of transducers and wirelessly communicating data via a transceiver, where the transceiver may be in communication with the array of transducers. Embodiments also contemplate providing power for the acoustic emission via a power source and providing information regarding a temperature sensor to the transceiver. The wirelessly communicated data may include the information regarding the temperature sensor. Embodiments also contemplate processing the wirelessly communicated data at a relatively remote location with respect to both the power source and the temperature sensor.

Synthetic aperture imaging for small scale systems

Abstract: Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element transmit subaperture defocused to emulate a single-element spatial response with high acoustic power. Echo signals are recorded independently by individual elements of the receive subaperture. Each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations. Following acquisition, image points are reconstructed using the complete data set with full dynamic focus on both transmit and receive. Various factors affecting image quality have been evaluated and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. Multielement synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance. >