Browsing by Subject "Finite element method"

Now showing 1 - 20 of 51

Open Access
3D modeling of on-chip acoustophoretic particle manipulation in a polymer microfluidic device
(Chemical and Biological Microsystems Society, 2016) Çaǧatay, E.; Özer, M. B.; Çetin, Barbaros
This study focuses on understanding of the sensitivities of the acoustophoretic process on uncertainties/errors in the geometric properties of the chip material and the piezoelectric actuators. The sensitivity of the acoustophoretic process is investigated both numerically and experimentally. For the numerical simulations a three dimensional finite element model is used. In the experimental analysis, a microfluidic chip with two stations is used. The first station has the accurate geometric values of the design and the second station has the introduced error in a geometric parameter so that the effect of this error can be demonstrated on the same chip and the channel.
Open Access
Algebraic reconstraction for 3D magnetic resonance-electrical impedance tomography (MREIT) using one component of magnetic flux density
(Institute of Physics and Engineering in Medicine, 2004) Ider, Y. Z.; Onart, S.
Magnetic resonance-electrical impedance tomography (MREIT) algorithms fall into two categories: those utilizing internal current density and those utilizing only one component of measured magnetic flux density. The latter group of algorithms have the advantage that the object does not have to be rotated in the magnetic resonance imaging (MRI) system. A new algorithm which uses only one component of measured magnetic flux density is developed. In this method, the imaging problem is formulated as the solution of a non-linear matrix equation which is solved iteratively to reconstruct resistivity. Numerical simulations are performed to test the algorithm both for noise-free and noisy cases. The uniqueness of the solution is monitored by looking at the singular value behavior of the matrix and it is shown that at least two current injection profiles are necessary. The method is also modified to handle region-of-interest reconstructions. In particular it is shown that, if the image of a certain xy-slice is sought for, then it suffices to measure the z-component of magnetic flux density up to a distance above and below that slice. The method is robust and has good convergence behavior for the simulation phantoms used.
Open Access
Analysis of the 2D nonconcentric large reflector antenna-in-radome system: H-polarization case
(IEEE, 2004) Oğuzer, Taner
2D nonconcentric reflector antenna-in-radome system is analyzed for H-polarization case. Rigorous formulation is performed depending on the MoR, Green's function and CSP methods. Larger geometries are solved in reasonable cpu times by using the FFT based algorithm in the computation of the Green's function.
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
BaTiO3 based photonic time crystal and momentum stop band
(Taylor & Francis, 2020-04) Özer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
Temporally periodic photonic crystals develop an ω-k dispersion relation with momentum band gaps. While conventional photonic crystals induce forbidden bands in the frequency spectrum of photons, photonic time crystals create forbidden regions in the momentum spectrum of photons. This effect allows for enhanced control over many optical processes that require both photonic energy and momentum conservations such as nonlinear harmonic generation. The simulation results show that more intensive scatter fields can obtained in photonic space time crystal. Also, we investigate topological phase transitions of photonic time crystals systems.
Open Access
Circuit theoretical method for efficient finite element analysis of acoustical problems
(IEEE, 1998) Ekinci, A. Suat; Atalar, Abdullah
In the last decade, there has been an outstanding improvement in the computer aided design tools for VLSI circuits regarding solution times and the circuit complexity. This study proposes formulating the acoustic field analysis problem using FEM, and employing the recent speed-up techniques used in the circuit simulators. In this work, total mass, stiffness and damping matrices are obtained using the FE approach, and piped into a computer program which generates an equivalent SPICE compatible circuit netlist. This approach makes it possible to use the most recent circuit simulation techniques to simulate the acoustical problems. The equivalent electrical circuit is a resistor-inductor-capacitor (RLC) circuit containing controlled sources to handle the couplings. The circuit matrices are 6 times larger but are sparser. We analyze these circuits with a general-purpose circuit simulation program, HSPICE, which provides high accuracy solutions in a short time. We also use an in-house developed circuit simulation program, MAWE, which makes use of asymptotic waveform evaluation (AWE) technique that has been successfully used in circuit simulation for solutions of large sets of equations. The results obtained on several problems, which are solved in time and frequency domains using circuit simulators and the FE analysis program ANSYS, match each other pretty well. Using circuit simulators instead of conventional method improves simulation speed without a significant loss of accuracy.
Open Access
Coherent energetic interfaces accounting for in-plane degradation
(Springer Netherlands, 2016) Esmaeili, A.; Javili, A.; Steinmann, P.
Interfaces can play a dominant role in the overall response of a body. The importance of interfaces is particularly appreciated at small length scales due to large area to volume ratios. From the mechanical point of view, this scale dependent characteristic can be captured by endowing a coherent interface with its own elastic resistance as proposed by the interface elasticity theory. This theory proves to be an extremely powerful tool to explain size effects and to predict the behavior of nano-materials. To date, interface elasticity theory only accounts for the elastic response of coherent interfaces and obviously lacks an explanation for inelastic interface behavior such as damage or plasticity. The objective of this contribution is to extend interface elasticity theory to account for damage of coherent interfaces. To this end, a thermodynamically consistent interface elasticity theory with damage is proposed. A local damage model for the interface is presented and is extended towards a non-local damage model. The non-linear governing equations and the weak forms thereof are derived. The numerical implementation is carried out using the finite element method and consistent tangents are listed. The computational algorithms are given in detail. Finally, a series of numerical examples is studied to provide further insight into the problem and to carefully elucidate key features of the proposed theory. © 2016, Springer Science+Business Media Dordrecht.
Open Access
Comparative evaluation of absorbing boundary conditions using Green's functions for layered media
(IEEE, 1995) Aksun, M. İrşadi; Dural, G.
Absorbing boundary conditions are comparatively studied using the Green's functions of the vector and scalar potentials for multilayer geometries and general sources. The absorbing boundaries are introduced as additional layers with predefined reflection coefficients into the calculation of the Green's functions. The Green's functions are calculated using different reflection coefficients corresponding to different absorbing boundaries and compared to those obtained with no absorbing boundary. This approach provides an absolute measure of the effectiveness of different absorbing boundaries.
Open Access
Coupled thermally general imperfect and mechanically coherent energetic interfaces subject to in-plane degradation
(Mathematical Sciences Publishers, 2017) Esmaeili, A.; Steinmann, P.; Javili, A.
To date, the effects of interface in-plane damage on the thermomechanical response of a thermally general imperfect (GI) and mechanically coherent energetic interface are not taken into account. A thermally GI interface allows for a discontinuity in temperature as well as in the normal heat flux across the interface. A mechanically coherent energetic interface permits a discontinuity in the normal traction but not in the displacement field across the interface. The temperature of a thermally GI interface is a degree of freedom and is computed using a material parameter known as the sensitivity. The current work is the continuation of the model developed by Esmaeili et al. (2016a) where a degrading highly conductive (HC) and mechanically coherent energetic interface is considered. An HC interface only allows for the jump in normal heat flux and not the jump in temperature across the interface. In this contribution, a thermodynamically consistent theory for thermally GI and mechanically coherent energetic interfaces subject to in-plane degradation is developed. A computational framework to model this class of interfaces using the finite element method is established. In particular, the influence of the interface in-plane degradation on the sensitivity is captured. To this end, the equations governing a fully nonlinear transient problem are given. They are solved using the finite element method. The results are illustrated through a series of three-dimensional numerical examples for various interfacial parameters. In particular, a comparison is made between the results of the intact and the degraded thermally GI interface formulation. © 2017 Mathematical Sciences Publishers.
Open Access
Deep-collapse operation of capacitive micromachined ultrasonic transducers
(IEEE, 2011) Olcum, S.; Yamaner F. Y.; Bozkurt, A.; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (CMUTs) have been introduced as a promising technology for ultrasound imaging and therapeutic ultrasound applications which require high transmitted pressures for increased penetration, high signal-to-noise ratio, and fast heating. However, output power limitation of CMUTs compared with piezoelectrics has been a major drawback. In this work, we show that the output pressure of CMUTs can be significantly increased by deep-collapse operation, which utilizes an electrical pulse excitation much higher than the collapse voltage. We extend the analyses made for CMUTs working in the conventional (uncollapsed) region to the collapsed region and experimentally verify the findings. The static deflection profile of a collapsed membrane is calculated by an analytical approach within 0.6% error when compared with static, electromechanical finite element method (FEM) simulations. The electrical and mechanical restoring forces acting on a collapsed membrane are calculated. It is demonstrated that the stored mechanical energy and the electrical energy increase nonlinearly with increasing pulse amplitude if the membrane has a full-coverage top electrode. Utilizing higher restoring and electrical forces in the deep-collapsed region, we measure 3.5 MPa peak-to-peak pressure centered at 6.8 MHz with a 106% fractional bandwidth at the surface of the transducer with a collapse voltage of 35 V, when the pulse amplitude is 160 V. The experimental results are verified using transient FEM simulations.
Open Access
The design of a wideband and widebeam piston transducer in a finite closed circular baffle
(2008-06-07) Şahin, Z.; Köymen, Hayrettin
The design of a high power piezoelectric underwater transducer operating at frequency range 40 kHz-80 kHz with acoustic power capability in excess of 250W is described. The transducer consists of two back-toback elements. Each element is formed by stacked PZT-4 ceramic rings, a matching and a steel backing layer, and placed in a finite rigid circular baffle. We investigate the dependence of bandwidth and beamwidth to the combination of piston and baffle radii, a and b, respectively. With ka of 2.45 (κ is the wave number) at resonance and a b/a ratio of 2, the transducer resonates at 60kHz with 67% bandwidth and has a beamwidth of 60° at each half space. We show that when two transducers are placed at right angles spatially and driven in parallel, we can obtain an omnidirectional beam pattern in the lower frequency band. The beam pattern exhibits two dips in each quadrant at the higher end of the frequency band, which are within 8 dB. We also investigated power handling capability of the transducer from thermal point of view using finite element analysis. The input impedance measurements agree well with the numerical results within the pass band.
Open Access
Design of dual-frequency probe-fed microstrip antennas with genetic optimization algorithm
(IEEE, 2003) Ozgun, O.; Mutlu, S.; Aksun, M. I.; Alatan, L.
Dual-frequency operation of antennas has become a necessity for many applications in recent wireless communication systems, such as GPS, GSM services operating at two different frequency bands, and services of PCS and IMT-2000 applications. Although there are various techniques to achieve dual-band operation from various types of microstrip antennas, there is no efficient design tool that has been incorporated with a suitable optimization algorithm. In this paper, the cavity-model based simulation tool along with the genetic optimization algorithm is presented for the design of dual-band microstrip antennas, using multiple slots in the patch or multiple shorting strips between the patch and the ground plane. Since this approach is based on the cavity model, the multiport approach is efficiently employed to analyze the effects of the slots and shorting strips on the input impedance. Then, the optimization of the positions of slots and shorting strips is performed via a genetic optimization algorithm, to achieve an acceptable antenna operation over the desired frequency bands. The antennas designed by this efficient design procedure were realized experimentally, and the results are compared. In addition, these results are also compared to the results obtained by the commercial electromagnetic simulation tool, the FEM-based software HFSS by ANSOFT.
Open Access
Electrical impedance tomography of translationally uniform cylindrical objects with general cross-sectional boundaries
(Institute of Electrical and Electronics Engineers, 1990) Ider, Y. Z.; Gencer, N. G.; Atalar, Ergin; Tosun, H.
An algorithm is developed for electrical impedance tomography (EIT) of finite cylinders with general cross-sectional boundaries and translationally uniform conductivity distributions. The electrodes for data collection are assumed to be placed around a cross-sectional plane,- therefore the axial variation of the boundary conditions and also the potential field are expanded in Fourier series. For each Fourier component a two-dimensional (2-D) partial differential equation is derived. Thus the 3-D forward problem is solved as a succession of 2-D problems and it is shown that the Fourier series can be truncated to provide substantial saving in computation time. The finite element method is adopted and the accuracy of the boundary potential differences (gradients) thus calculated is assessed by comparison to results obtained using cylindrical harmonic expansions for circular cylinders. A 1016-element and 541-node mesh is found to be optimal. For a given cross-sectional boundary, the ratios of the gradients calculated for both 2-D and 3-D homogeneous objects are formed. The actual measurements from the 3-D object are multiplied by these ratios and thereafter the tomographic image is obtained by the 2-D iterative equipotential lines method. The algorithm is applied to data collected from phantoms, and the errors incurred from the several assumptions of the method are investigated. The method is also applied to humans and satisfactory images are obtained. It is argued that the method finds an “equivalent” translationally uniform object, the calculated gradients for which are the same as the actual measurements collected. In the absence of any other information about the translational variation of conductance this method is especially suitable for body parts with some translational uniformity. © 1990 IEEE
Open Access
An equivalent circuit for collapse operation mode of CMUTs
(IEEE, 2010) Olcum, Selim; Yamaner F.Y.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Collapse mode of operation of the capacitive mi-cromachined ultrasonic transducers (CMUTs) was shown to be a very effective way for achieving high output pressures. However, no accurate model exists for understanding the mechanics and limits of the collapse mode. In this work, we extend the analyses made for CMUTs working in uncollapsed mode to collapsed mode. We have developed an equivalent nonlinear electrical circuit that can accurately simulate the mechanical behavior of a CMUT under any large signal electrical excitation. The static and dynamic deflections of a membrane predicted by the model are compared with the finite element simulations. The equivalent circuit model can estimate the static deflection within 1% and the transient behavior of a CMUT membrane within 3% accuracy. The circuit model is also compared to experimental results of pulse excitation applied to fabricated collapse mode CMUTs. The model is suitable as a powerful design and optimization tool for the collapsed as well as the uncollapsed case of CMUTs. © 2010 IEEE.
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
Experimental and finite element analysis of EDM process and investigation of material removal rate by response surface methodology
(2013) Hosseini Kalajahi, M.; Rash Ahmadi, S.; Nadimi Bavil Oliaei, S.
In this study, thermal modeling and finite element simulation of electrical discharge machining (EDM) has been done, taking into account several important aspects such as temperature-dependent material properties, shape and size of the heated zone (Gaussian heat distribution), energy distribution factor, plasma flushing efficiency, and phase change to predict thermal behavior and material removal mechanism in EDM process. Temperature distribution on the cathode has been calculated using ANSYS finite element code, and the effect of EDM parameters on heat distribution along the radius and depth of the workpiece has been obtained. Temperature profiles have been used to calculate theoretical material removal rate (MRR) from the cathode. Theoretically calculated MRRs are compared with the experimental results, making it possible to precisely determine the portion of energy that enters the cathode for AISI H13 tool steel. Also in this paper, the effect of EDM parameters on MRR has been investigated by using the technique of design of experiments and response surface methodology. Finally, a quadratic polynomial regression model has been proposed for MRR, and the accuracy of this model has been checked by means of analysis of residuals. © 2013 Springer-Verlag London.
Open Access
Ferroelectric based fractal phononic crystals: wave propagation and band structure
(Taylor & Francis, 2020-04) Palaz, S.; Özer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
In this study, the band structure and transmission in multiferroic based Sierpinski carpet phononic crystal are investigated based on finite element simulation. In order to obtain the band structure of the phononic crystal (PnC), the Floquet periodicity conditions were applied to the sides of the unit cell. The square lattice PnC consists of various piezoelectric inclusion in a rubber matrix with square and circular cross section.
Open Access
Ferroelectric based microgyroscope for inertial measurement unit: Modeling and simulation
(IEEE, 2012) Ozer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
This paper present the design and modeling of the micro-electromechanical systems (MEMS) on the ternary ferroelectric compounds (PZT and Ba xSr 1-xTiO 3) based by using finite element model (FEM) simulation. © 2012 IEEE.
Open Access
Finite element modeling of micro-particle separation using ultrasonic standing waves
(ASME, 2014) Büyükkoçak, S.; Çetin, Barbaros; Özer, M. B.
Acoustophoresis which means separation of particles and cells using acoustic waves is becoming an intensive research subject. The method is based on inducing an ultrasonic compression standing wave inside a microchannel. A finite element approach is used to model the acoustic and electro-mechanical behavior of the piezoelectric material, the micro-channel geometry as well as the fluid inside the channel. The choices of silicon and PDMS materials are investigated as the chip materials for the resonator. A separation channel geometry which is commonly used in the literature is implemented in this study and the fluid flow inside the microchannel geometry is simulated using computational fluid dynamics. The acoustic field inside the fluid channel is also be simulated using the finite element method. For the separation process to be successful micro-particles of different diameter groups should end up in different channels of the micro-separator. In order to simulate real life scenarios, each particle size group have a size distribution within themselves. For realistic simulation results the particles will be released into the micro separator from a different starting locations (starting location distribution). The results of this Monte-Carlo based finite element simulation approach will be compared with the reported experimental results.
Open Access
Fracture of femoral neck: Analysis of new implant models with a slit and without a slit by the finite element method
(WHO Office in Azerbaijan, 2017) Jafarov, A. A.; Ozer, Z.; Alizadeh, Ch. A.; Mammadov, A. M.
During fractures of the neck of the femur (PBHB) for the completion of postoperative fusion, there is a need for stable fixation - interfragmental immobility. The stability of used implants in a living person is difficult to calculate. For this purpose, the analysis is carried out using the finite element method (the final analysis of the limited elements). The aim of this study is to study the features of the proposed new hip implant with finite element analysis. Based on the digital geometry of the anatomy of the femur, a 3D model of the femur was developed. Stress and strain, obtained with the help of the computer program ANSYS as a result of loads on the head of the thigh, were investigated by the finite element analysis method. Based on the Pawel classification, 3 groups of femoral neck fracture models were created, corresponding to the fracture angles closer to 30, 50 and 70 degrees (type 1, type 2 and type 3). In each group, the corresponding implants are analyzed in 2 types: without a slit and with a slit. For the spongiform bone, the UTS (Ultimate Tensile Stres) is defined as 20 MPA, and for the cortical bone, 150 MPA. In all analyzes, the force loaded in the vertical direction onto the head of the computer model of the femur was calculated to be 4000 N. Given that the slits on the surface of the implant can cross waves, homogeneously distribute the force and pressure throughout the entire implant, on the basis of this, a decrease in pressure on the surface of the bone tissue was observed. It is believed that this process can increase the stability of the implant and minimize the level of damage to the bone tissue.