Papers by Abdullah Atalar
In light of globalization in the twenty-first century, businesses are seeking employees with skil... more In light of globalization in the twenty-first century, businesses are seeking employees with skills that would make them more competitive in the international arena.
International Experience in Developing the Financial Resources of Universities
A university endowment is typically composed of assets, stocks and bonds to generate money for su... more A university endowment is typically composed of assets, stocks and bonds to generate money for supporting the university’s mission. Most university endowments in the Western hemisphere are developed by donations and gifts. In the developing countries, where the donation culture does not exist, one needs to resort to alternative methods of generating an endowment. The paper presents an alternative model of university endowment, which could be adopted to develop an endowment for a university.
International Experience in Developing the Financial Resources of Universities
It is widely believed that economic returns of tertiary education to the public are much higher t... more It is widely believed that economic returns of tertiary education to the public are much higher than those in other sectors of the economy. Excellence in education and research, therefore, is an important factor for the welfare of countries. To improve the well-being of their citizens, governments invested heavily in higher education. The number of higher education institutes in the world has reached 18,000, and as a result, a larger fraction of people is getting tertiary education degrees. The expansion of the university system required a corresponding increase in the funding.
IEEE Transactions on Circuits and Systems II: Express Briefs
When quadrature couplers and power dividers are implemented in integrated circuits, accurate isol... more When quadrature couplers and power dividers are implemented in integrated circuits, accurate isolation networks can not be realized due to the nonideal resistors and the process variations. We present an isolation network design technique which cancels the resistor parasitic effects and also increases the tolerance to variations in the resistance values. A Lange coupler and a power divider are designed at Ka-band using the proposed accurate and process-tolerant isolation networks. The improvement is analytically shown and empirically verified with our in-house GaN-based microstrip MMIC process. For the coupler, the measured return losses and isolation are better than 20 dB from DC to 40 GHz. The power divider achieves 20 dB return losses and isolation in a fractional bandwidth of 50%. Both devices maintain 20 dB performance even when the variation in sheet resistance is as high as 30%.
IEEE Transactions on Microwave Theory and Techniques
Resistive terminations cannot preserve high-quality matching at high frequencies due to the paras... more Resistive terminations cannot preserve high-quality matching at high frequencies due to the parasitic effects of the nonideal resistor. Moreover, resistance values of the termination resistors in integrated circuits are subject to process variations. Therefore, it is difficult to obtain accurate and process-tolerant terminations that are crucial for high performance in microwave circuits. We propose a new resistive network that compensates for the high-frequency parasitic effects of the resistors to improve the bandwidth of the termination. In addition to maintaining accuracy, the presented network provides tolerance to variation in the resistor values. The accuracy and tolerance of the proposed structure is analytically shown and experimentally verified by three test structures at the X-band fabricated on a GaN technology. The experimental results show that a small size and wideband 50-load with a return loss better than 25 dB can be obtained, while the resistor value changes ±30%.
IEEE Transactions on Circuits and Systems II: Express Briefs
Noise figure expression of a balanced amplifier built with lossy divider and combiner and two imp... more Noise figure expression of a balanced amplifier built with lossy divider and combiner and two imperfectly noisematched component amplifiers is derived analytically using the method of noise waves in terms of the noise parameters of the amplifiers. We present analytical expressions for the three noise parameters of the balanced amplifier. We show that a low-noise amplifier optimized to be used as a stand-alone amplifier is not the optimum choice for the component amplifiers of a balanced amplifier. The derived expressions can be used to choose or optimize the component amplifiers.
Journal of Microelectromechanical Systems
We certify that we have read this dissertation and that in our opinion it is fully adequate, in s... more We certify that we have read this dissertation and that in our opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of Doctor of Philosophy.
IEEE Transactions on Microwave Theory and Techniques
The multiple mode rectangular cavity structure with square corner cuts is revisited. An attempt t... more The multiple mode rectangular cavity structure with square corner cuts is revisited. An attempt to predict the physical dimensions of the cavity for dual mode second-order and triple mode third-order filters is made. Analytic expressions are formed to be used in the design process. The classical triple mode cavity filter structure is altered to give a finite frequency transmission zero either in the lower or upper sideband of the center frequency. The concept is illustrated with example designs. A novel additive manufacturing technique is used to fabricate a selected filter structure. The experimental results are in agreement with the expectations.
IEEE Microwave and Wireless Components Letters
Balanced amplifiers suffer from the noise figure performance in comparison with a stand-alone amp... more Balanced amplifiers suffer from the noise figure performance in comparison with a stand-alone amplifier even with an ideal input divider. The noise parameters degrade further with an imperfect divider. We present exact and approximate analytical results for the noise figure and noise parameters of the balanced amplifier in divider topology. Measurement results are also presented as a verification.
2016 IEEE International Ultrasonics Symposium (IUS), 2016
Cell placement in an element and structural modifications on the array baffle significantly chang... more Cell placement in an element and structural modifications on the array baffle significantly change the bandwidth, band shape and signal to noise ratio of a CMUT receiver array. In this paper, optimum receiver performance tailoring by means of cell placement, cell size variation and use of dummy cells in the array elements is discussed. The performance of the array is modified acoustically at the acoustic port of the elements.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2017
We introduce the large-signal and small-signal equivalent circuit models for a capacitive microma... more We introduce the large-signal and small-signal equivalent circuit models for a capacitive micromachined ultrasonic transducer (CMUT) cell, which has radiating plates on both sides. We present the diffraction coefficient of baffled and unbaffled CMUT cells. We show that the substrate can be modeled as a very thick radiating plate on one side, which can be readily incorporated in the introduced model. In the limiting case, the reactance of this backing impedance is entirely compliant for substrate materials with a Poisson's ratio less than 1/3. We assess the dependence of the radiation performance of the front plate on the thickness of the back plate by simulating an array of bilateral CMUT cells. We find that the small-signal linear model is sufficiently accurate for large-signal excitation, for the purpose of the determining the fundamental component. To determine harmonic distortion, the large-signal model must be used with harmonic balance analysis. Rayleigh-Bloch waves are ex...
A cantilever with a grating coupler engraved on its tip is used for measuring displacement. The c... more A cantilever with a grating coupler engraved on its tip is used for measuring displacement. The coupled light in the cantilever is guided to a single mode optical waveguide defined at the base of the cantilever. The grating period is 550 nm and is fabricated on a SOI wafer using ...
Ultrasonics, IEEE Symposium, 1998
The structural loss mechanism of capacitive micromachined ultrasonic transducer (cMUT) is investi... more 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
IEEE Transactions on Microwave Theory and Techniques, 2014
We propose an isolation network to simultaneously improve the input return loss, output return lo... more We propose an isolation network to simultaneously improve the input return loss, output return loss and isolation of the Wilkinson power divider in a wide bandwidth. The required even mode and odd mode reflection coefficients of the isolation network are calculated. Constructed even and odd mode circuits are combined to give the desired isolation network. Analytical expressions for the optimal component values for a single-section divider are given. Compared with the single-section Wilkinson divider, the final design can triple the bandwidth for an input-output return loss and isolation of greater than 25 dB. Broadband characteristic is achieved without increasing the number of sections hence extra length and insertion loss are avoided. Wide operation bandwidth of the new divider is verified by experimental results. The proposed method can be applied to a two-section divider, also broadening its bandwidth.
2012 IEEE International Ultrasonics Symposium, 2012
We present a design method for airborne capacitive micromachined ultrasonic transducers (CMVT). W... more We present a design method for airborne capacitive micromachined ultrasonic transducers (CMVT). We use an equivalent lumped element circuit to model both electrical and mechanical properties of CMUT and analyze it in frequency domain using harmonic balance approach. We use this method to design CMUTs for large transmitted power generation at low drive voltage amplitude. We determine the dimensions of an airborne CMUT using the proposed method that works at 30 kHz with 5 rum radius, 240 11m membrane thickness and 11.8 11m effective gap height. The CMUT is designed such that an atmospheric depression of 70% of effective gap height is maintained.
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Papers by Abdullah Atalar