Browsing by Subject "Circuit simulation"

Now showing 1 - 8 of 8

Open Access
Analysis of mutual acoustic coupling in CMUT arrays using an accurate lumped element nonlinear equivalent circuit model
(2012) Oğuz, H.Kağan; Atalar, Abdullah; Köymen, Hayrettin
We use an accurate nonlinear equivalent circuit model to analyze CMUT arrays with multiple cells, where every cell in the array is coupled to other cells at their acoustic terminals through a mutual radiation impedance matrix. We get results comparable to finite element analysis accuracy. Hence, the analysis of a large array becomes a circuit theory problem and can be scrutinized with circuit simulators. We study the mutual acoustic interactions that arise through the immersion medium due to the influence of the generated pressure field by each cell on the others. We compare the performance of different 1D cMUT arrays, where each element is half-wavelength wide and 10 and 20 wavelengths long at the resonance frequency of a single cell. © 2012 IEEE.
Open Access
An electrical circuit theoretical method for time-and frequency-domain solutions of the structural mechanics problems
(John Wiley & Sons Ltd., 1999) Ekinci, A. S.; Atalar, Abdullah
Shrinking device dimensions in integrated circuit technology made integrated circuits with millions of components a reality. As a result of this advance, electrical circuit simulators that can handle very large number of components have emerged. These programs use new circuit simulation techniques and can find solutions accurately and quickly. In this paper, we apply these techniques to structural mechanics problems by adopting electrical circuit equivalents. We first apply finite element formulation to the mechanical problem. The obtained sets of equations are treated as if they are sets of equations of an equivalent electrical circuit which consists of linear circuit elements such as capacitors, inductors and controlled sources. The equivalent circuit is obtained in the form of a circuit netlist and solved using a general purpose electrical circuit simulator. Several examples showing the advantages of the circuit simulation techniques are demonstrated. Asymptotic waveform evaluation technique which is widely used for simulation of large electrical circuits is also studied for the same examples and the speed-up advantage is shown.
Open Access
Electromagnetic scattering solution of conducting strips in layered media using the fast multipole method
(Institute of Electrical and Electronics Engineers, 1996-08) Gürel, Levent; Aksun, M. I.
The fast multipole method (FMM) is applied to the solution of the electromagnetic scattering problems in layered media for the first time. This is achieved by using closed-form expressions for the spatial-domain Green's functions for layered media. Until now, the FMM has been limited to the homogeneous-medium problems. An integral equation based on the two-dimensional scalar Helmholtz equation is solved to compute the electromagnetic scattering from sample geometries of conducting strips in layered media in order to demonstrate the accuracy and the efficiency of the new method.
Open Access
Equivalent circuit-based analysis of CMUT cell dynamics in arrays
(IEEE, 2013) Oğuz, H. K.; Atalar, Abdullah; Köymen, Hayrettin
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.
Open Access
A Miniaturized Patch Antenna by Using a CSRR Loading Plane
(Hindawi Publishing Corporation, 2015) Ramzan, M.; Topalli, K.
This paper presents a design methodology for the implementation of a miniaturized square patch antenna and its circuit model for 5.15 GHz ISM band. The miniaturization is achieved by employing concentric complementary split ring resonator (CSRR) structures in between the patch and ground plane. The results are compared with the traditional square patch antenna in terms of area, bandwidth, and efficiency. The area is reduced with a ratio of 1/4 with respect to the traditional patch. The miniaturized square patch antenna has an efficiency, bandwidth, and reflection coefficient of 78%, 0.4%, and -16 dB, respectively. The measurement and circuit modeling results show a good agreement with the full-wave electromagnetic simulations. © 2015 Mehrab Ramzan and Kagan Topalli.
Open Access
A new method for nonlinear circuit simulation in time domain: NOWE
(Institute of Electrical and Electronics Engineers, 1996-03) Ocalı, O.; Tan, M. A.; Atalar, Abdullah
A new method for the time-domain solution of general nonlinear dynamic circuits is presented. In this method, the solutions of the state variables are computed by using their time derivatives up to some order at the initial time instant. The computation of the higher order derivatives is equivalent to solving the same linear circuit for various sets of dc excitations. Once the time derivatives of the state variables are obtained, an approximation to the solution can be found as a polynomial rational function of time. The time derivatives of the approximation at the initial time instant are matched to those of the exact solution. This method is promising in terms of execution speed, since it can achieve the same accuracy as the trapezoidal approximation with much smaller number of matrix inversions.
Open Access
Nonlinear equivalent circuit model for circular CMUTs in uncollapsed and collapsed mode
(IEEE, 2012) Aydoğdu, Elif; Özgürlük, Alper; Oğuz, H. Kağan; Atalar, Abdullah; Kocabaş, Coşkun; Köymen, Hayrettin
An equivalent electrical circuit model valid for collapsed mode operation of CMUT is described. The across and through variables of the circuit model are chosen to be rms force and rms displacement over the surface of the CMUT membrane. The relation between rms displacement and applied voltage is obtained through analytical calculations utilizing the exact force distribution. The radiation impedance of collapsed mode CMUT is included as a load impedance in the circuit model. The resulting equivalent circuit is merged with uncollapsed mode model, to obtain a simulation tool that covers the whole operation range of CMUT. © 2012 IEEE.
Open Access
PLAWE: A piecewise linear circuit simulator using asymptotic waveform evaluation
(1994) Topçu, Satılmış
A new circuit simulation program, PLAWE, is developed for the transient analysis of VLSI circuits. PLAWE uses Asymptotic Waveform Evaluation (AWE) technique, which is a new method to analyze linear(ized) circuits, and Piecewise Linear (PWL) approach for DC representation of nonlinear elements. AWE employs a form of Pade approximation rather than numerical integration techniques to approximate the response of linear(ized) circuits in either the time or the frequency domain. AWE is typically two or three orders of magnitude faster than traditional simulators in analyzing large linear circuits. However, it can handle only linear(ized) circuits, while the transient analysis problem is generally nonlinear due to the presence of nonlinear devices such as diodes, transistors, etc.. We have applied the AWE technique to the transient simulation of nonlinear circuits by using static PWL models for nonlinear elements. But, finding a good static PWL model which fits well to the actual i — v characteristics of a nonlinear device is not an easy task and in addition, static PWL modelling results in low accuracy. Therefore, we have developed a dynamic PWL modeling technique which uses SPICE models for nonlinear elements to enhance the accuracy of the simulation while preserving the efficiency gain obtained with AWE. Hence, there is no modelling problem and we can adjust the accuracy level by varying some parameters. If the required level of accuracy is increased, more simulation time is needed. Practical examples are given to illustrate the significant improvement in accuracy. For circuits containing especially weakly nonlinear devices, this method is typically at least one order of magnitude faster than HSPICE. A fast and convergent iteration method for piecewise-linear analysis of nonlinear resistive circuits is presented. Most of the existing algorithms are applicable only to a limited class of circuits. In general, they are either not convergent or too slow for large circuits. The new algorithm presented in this thesis is much more efficient than the existing ones and can be applied to any piecewise-linear circuit. It is based on the piecewise-linear version of the Newton-Raphson algorithm. As opposed to the NewtonRaphson method, the new algorithm is globally convergent from an arbitrary starting point. It is simple to understand and it can be easily programmed. Some numerical examples are given in order to demonstrate the effectiveness of the presented algorithm in terms of the amount of computation.