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Fulltext The HUKM Spinal Instrumentation System for adolescent idiopathic scoliosis. A biomechanical comparison study using finite element analysis

Azlan AM, Mohammad AR, Ariffin AK

Med J Malaysia, 2005 Jul;60 Suppl C:30-4.
PMID: 16381280 MyJurnal

This finite element analysis is aimed at comparing relative stiffness of three different posterior instrumentation constructs: the Hospital Universiti Kebangsaan Malaysia Spinal Instrumentation System (HUKM-SIS), the Cotrell-Dubousset Instrumentation (CDI) and Harrington Instrumentation System (HIS), used in the treatment of adolescent idiopathic scoliosis (AIS). The constructs were tested under various loads using MSC Patran 2001 r2a. Under increasing flexion loads, there was a linearly corresponding increase in deflection magnitudes for all constructs on the load-deflection curve. The CDI was the stiffest construct under axial, forward flexion and extension loads, followed by the HUKM-SIS and HIS. Under lateral bending loads, the HUKM-SIS construct was the stiffest followed by CDI and HIS. The HUKM-SIS construct was stiffer than HIS under torsional loads. We conclude that multiple pedicle screws increase the stiffness of posterior instrumentation constructs under all loads and inter-segmental spinous processes wiring increase the stiffness against lateral bending.

Matched MeSH terms: Finite Element Analysis
Fulltext Numerical Prediction of Residual Stresses Distribution in Thin-Walled Press-Braked Stainless Steel Sections

Mutafi A, Yidris N, Koloor SSR, Petrů M

Materials (Basel), 2020 Nov 26;13(23).
PMID: 33256257 DOI: 10.3390/ma13235378

Stainless steels are increasingly used in construction today, especially in harsh environments, in which steel corrosion commonly occurs. Cold-formed stainless steel structures are currently increasing in popularity because of its efficiency in load-bearing capacity and its appealing architectural appearance. Cold-rolling and press-braking are the cold-working processes used in the forming of stainless steel sections. Press braking can produce large cross-sections from thin to thick-walled sections compared to cold-rolling. Cold-forming in press-braked sections significantly affect member behaviour and joints; therefore, they have attained great attention from many researchers to initiate investigations on those effects. This paper examines the behaviour of residual stress distribution of stainless steel press-braked sections by implementing three-dimensional finite element (3D-FE) technique. The study proposed a full finite element procedure to predict the residual stresses starting from coiling-uncoiling to press-braking. This work considered material anisotropy to examine its effect on the residual stress distribution. The technique adopted was compared with different finite element techniques in the literature. This study also provided a parametric study for three corner radius-to-thickness ratios looking at the through-thickness residual stress distribution of four stainless steels (i.e., ferritic, austenitic, duplex, lean duplex) in which have their own chemical composition. In conclusion, the comparison showed that the adopted technique provides a detailed prediction of residual stress distribution. The influence of geometrical aspects is more pronounced than the material properties. Neglecting the material anisotropy shows higher shifting in the neutral axis. The parametric study showed that all stainless steel types have the same stress through-thickness distribution. Moreover, R/t ratios' effect is insignificant in all transverse residual stress distributions, but a slight change to R/t ratios can affect the longitudinal residual stress distribution.

Matched MeSH terms: Finite Element Analysis
Fulltext Assessment of Nano-Indentation Method in Mechanical Characterization of Heterogeneous Nanocomposite Materials Using Experimental and Computational Approaches

Karimzadeh A, R Koloor SS, Ayatollahi MR, Bushroa AR, Yahya MY

Sci Rep, 2019 10 31;9(1):15763.
PMID: 31673118 DOI: 10.1038/s41598-019-51904-4

This study investigates the capacity of the nano-indentation method in the mechanical characterization of a heterogeneous dental restorative nanocomposite using experimental and computational approaches. In this respect, Filtek Z350 XT was selected as a nano-particle reinforced polymer nanocomposite with a specific range of the particle size (50 nm to 4 µm), within the range of indenter contact area of the nano-indentation experiment. A Sufficient number of nano-indentation tests were performed in various locations of the nanocomposite to extract the hardness and elastic modulus properties. A hybrid computational-experimental approach was developed to examine the extracted properties by linking the internal behaviour and the global response of the nanocomposite. In the computational part, several representative models of the nanocomposite were created in a finite element environment to simulate the mechanism of elastic-plastic deformation of the nanocomposite under Berkovich indenter. Dispersed values of hardness and elastic modulus were obtained through the experiment with 26.8 and 48.5 percent average errors, respectively, in comparison to the nanocomposite properties, respectively. A disordered shape was predicted for plastic deformation of the equilateral indentation mark, representing the interaction of the particles and matrix, which caused the experiment results reflect the local behaviour of the nanocomposite instead of the real material properties.

Matched MeSH terms: Finite Element Analysis
Numerical Three-dimensional Finite Element Modeling of Cavity Shape and Optimal Material Selection by Analysis of Stress Distribution on Class V Cavities of Mandibular Premolars

Pai S, Bhat V, Patil V, Naik N, Awasthi S, Nayak N

J Int Soc Prev Community Dent, 2020 06 15;10(3):279-285.
PMID: 32802773 DOI: 10.4103/jispcd.JISPCD_75_20

Aim: Adhesive restoration does not depend primarily on the configuration of the shape of the cavity. Under varying loading conditions, it is essential to know the stress concentration and load transfer mechanism for distinct cavity shapes. The aim of this study was to evaluate and compare the biomechanical characteristics of various cavity shapes, namely oval, elliptical, trapezoidal, and rectangular shapes of class V cavities on mandibular premolars restored with amalgam, glass ionomer cement, and Cention N using three-dimensional (3D) finite element analysis.
Materials and Methods: A 3D prototype of a mandibular premolar was generated by Digital Imaging and Communications in Medicine (DICOM) images obtained from the cone beam computed tomography and imported to 3D modeling software tool, SpaceClaim. The four distinct load magnitudes of 100, 150, 200, and 250N were applied as a pressure load perpendicular to the lingual plane of the lingual cusp of the occlusal surface (normal load) and at 45° to same (oblique load). The stress distribution patterns and the maximum von Mises stresses were analyzed and compared.
Results: The occlusal stresses were distributed from the force loading point in an approximate actinomorphic pattern, and when the force load was close to the margin, the stress was much greater.
Conclusion: Ovoid cavity showed lesser stress concentration and deformation for each of the tested restorative material.

Matched MeSH terms: Finite Element Analysis
Fulltext A Theoretical Study of Surface Mode Propagation with a Guiding Layer of GaN/Sapphire Hetero-Structure in Liquid Medium

Mohd Razip Wee MF, Jaafar MM, Faiz MS, Dee CF, Yeop Majlis B

Biosensors (Basel), 2018 Dec 05;8(4).
PMID: 30563159 DOI: 10.3390/bios8040124

Gallium Nitride (GaN) is considered as the second most popular semiconductor material in industry after silicon. This is due to its wide applications encompassing Light Emitting Diode (LED) and power electronics. In addition, its piezoelectric properties are fascinating to be explored as electromechanical material for the development of diverse microelectromechanical systems (MEMS) application. In this article, we conducted a theoretical study concerning surface mode propagation, especially Rayleigh and Sezawa mode in the layered GaN/sapphire structure with the presence of various guiding layers. It is demonstrated that the increase in thickness of guiding layer will decrease the phase velocities of surface mode depending on the material properties of the layer. In addition, the Q-factor value indicating the resonance properties of surface mode appeared to be affected with the presence of fluid domain, particularly in the Rayleigh mode. Meanwhile, the peak for Sezawa mode shows the highest Q factor and is not altered by the presence of fluid. Based on these theoretical results using the finite element method, it could contribute to the development of a GaN-based device to generate surface acoustic wave, especially in Sezawa mode which could be useful in acoustophoresis, lab on-chip and microfluidics applications.

Matched MeSH terms: Finite Element Analysis
Fulltext Thermal Delamination Modelling and Evaluation of Aluminium-Glass Fibre-Reinforced Polymer Hybrid

Chow ZP, Ahmad Z, Wong KJ, Koloor SSR, Petrů M

Polymers (Basel), 2021 Feb 04;13(4).
PMID: 33557350 DOI: 10.3390/polym13040492

This paper aims to propose a temperature-dependent cohesive model to predict the delamination of dissimilar metal-composite material hybrid under Mode-I and Mode-II delamination. Commercial nonlinear finite element (FE) code LS-DYNA was used to simulate the material and cohesive model of hybrid aluminium-glass fibre-reinforced polymer (GFRP) laminate. For an accurate representation of the Mode-I and Mode-II delamination between aluminium and GFRP laminates, cohesive zone modelling with bilinear traction separation law was implemented. Cohesive zone properties at different temperatures were obtained by applying trends of experimental results from double cantilever beam and end notched flexural tests. Results from experimental tests were compared with simulation results at 30, 70 and 110 °C to verify the validity of the model. Mode-I and Mode-II FE models compared to experimental tests show a good correlation of 5.73% and 7.26% discrepancy, respectively. Crack front stress distribution at 30 °C is characterised by a smooth gradual decrease in Mode-I stress from the centre to the edge of the specimen. At 70 °C, the entire crack front reaches the maximum Mode-I stress with the exception of much lower stress build-up at the specimen's edge. On the other hand, the Mode-II stress increases progressively from the centre to the edge at 30 °C. At 70 °C, uniform low stress is built up along the crack front with the exception of significantly higher stress concentrated only at the free edge. At 110 °C, the stress distribution for both modes transforms back to the similar profile, as observed in the 30 °C case.

Matched MeSH terms: Finite Element Analysis
Fulltext A Finite Element Model for Dynamic Analysis of Triple-Layer Composite Plates with Layers Connected by Shear Connectors Subjected to Moving Load

Nguyen HN, Nguyen TY, Tran KV, Tran TT, Nguyen TT, Phan VD, et al.

Materials (Basel), 2019 Feb 16;12(4).
PMID: 30781542 DOI: 10.3390/ma12040598

Triple-layered composite plates are created by joining three composite layers using shear connectors. These layers, which are assumed to be always in contact and able to move relatively to each other during deformation, could be the same or different in geometric dimensions and material. They are applied in various engineering fields such as ship-building, aircraft wing manufacturing, etc. However, there are only a few publications regarding the calculation of this kind of plate. This paper proposes novel equations, which utilize Mindlin's theory and finite element modelling to simulate the forced vibration of triple-layered composite plates with layers connected by shear connectors subjected to a moving load. Moreover, a Matlab computation program is introduced to verify the reliability of the proposed equations, as well as the influence of some parameters, such as boundary conditions, the rigidity of the shear connector, thickness-to-length ratio, and the moving load velocity on the dynamic response of the composite plate.

Matched MeSH terms: Finite Element Analysis
Fulltext Surface-Mounted Bare and Packaged Fiber Bragg Grating Sensors for Measuring Rock Strain in Uniaxial Testing

Isah BW, Mohamad H

Sensors (Basel), 2021 Apr 22;21(9).
PMID: 33922008 DOI: 10.3390/s21092926

The paper explores the possibility of using high-resolution fiber Bragg grating (FBG) sensing technology for on-specimen strain measurement in the laboratory. The approach provides a means to assess the surface deformation of the specimen, both the axial and radial, through a chain of FBG sensor (C-FBG), in a basic setup of a uniaxial compression test. The method is cost-effective, straightforward and can be commercialized. Two C-FBG; one was applied directly to the sample (FBGBare), and the other was packaged (FBGPack) for ease of application. The approach measures the local strain with high-resolution and accuracy levels that match up to the existing local strain measuring sensors. The approach enables the evaluation of small-strain properties of the specimen intelligently. The finite element model analysis deployed has proven the adaptability of the technique for measuring material deformation. The adhesive thickness and packaging technique have been shown to influence the sensitivity of the FBG sensors. Owing to the relative ease and low-cost of instrumentation, the suggested method has a great potential to be routinely applied for elemental testing in the laboratory.

Matched MeSH terms: Finite Element Analysis
Effect of different implant configurations on biomechanical behavior of full-arch implant-supported mandibular monolithic zirconia fixed prostheses

Zhong J, Guazzato M, Chen J, Zhang Z, Sun G, Huo X, et al.

J Mech Behav Biomed Mater, 2020 02;102:103490.
PMID: 31877512 DOI: 10.1016/j.jmbbm.2019.103490

Mechanical failure of zirconia-based full-arch implant-supported fixed dental prostheses (FAFDPs) remains a critical issue in prosthetic dentistry. The option of full-arch implant treatment and the biomechanical behaviour within a sophisticated screw-retained prosthetic structure have stimulated considerable interest in fundamental and clinical research. This study aimed to analyse the biomechanical responses of zirconia-based FAFDPs with different implant configurations (numbers and distributions), thereby predicting the possible failure sites and the optimum configuration from biomechanical aspect by using finite element method (FEM). Five 3D finite element (FE) models were constructed with patient-specific heterogeneous material properties of mandibular bone. The results were reported using volume-averaged von-Mises stresses (σVMVA) to eliminate numerical singularities. It was found that wider placement of multi-unit copings was preferred as it reduces the cantilever effect on denture. Within the limited areas of implant insertion, the adoption of angled multi-unit abutments allowed the insertion of oblique implants in the bone and wider distribution of the multi-unit copings in the prosthesis, leading to lower stress concentration on both mandibular bone and prosthetic components. Increasing the number of supporting implants in a FAFDPs reduced loading on each implant, although it may not necessarily reduce the stress concentration in the most posterior locations significantly. Overall, the 6-implant configuration was a preferable configuration as it provided the most balanced mechanical performance in this patient-specific case.

Matched MeSH terms: Finite Element Analysis
Fulltext Non-linear analysis of water thrust on Bakun concrete faced rockfill dam

Ahmad, M.H., Norzaie, J., Al Qbadi, F., Daniel, B.D.

ASM Science Journal, 2009;3(1):17-26.
MyJurnal

The functions of dams are for water supply, flood control and hydroelectric power generation. A concrete faced rockfill dam (CFRD) is preferred by dam consultants due to its many advantages. It is designed to withstand all applied loads, namely gravity load due to its massive weight and hydrostatic load due to water thrust from the reservoir. The structural response of the Bakun CFRD which is the second highest dam in the world after the Shuibuya Dam, was analyzed using finite element method. A two-dimensional plane strain finite element analysis of the non-linear Duncan-Chang hyperbolic model was used in the study of the dam in respect to the deformation and stresses of the main dam of Bakun CFRD project. The Dead-Birth-Ghost element technique was used to simulate sequences of the construction of the dam. The comparison of rigid and flexible foundation on the behaviour of the dam is discussed in this study. In the finite element modeling, the concrete slab on the upstream was represented through a six-noded element, while the interface characteristic between the dam body and the concrete slab was modeled using an interface element. The maximum settlement and stresses of the cross-section were found and their distribution was discussed and tabulated in the form of contours. The effect of reservoir filling loading had a gradual effect on the dam response behaviour. Comparisons with no water impoundment in the dam were also discussed.

Matched MeSH terms: Finite Element Analysis
Fulltext Modeling and simulation of artificial hair cell sensor for underwater applications

M.N.M. Nawi, A.A. Manaf, M.R. Arshad

ASM Science Journal, 2013;7(2):144-151.
MyJurnal

This article uses finite volume and finite element methods for optimization of the artificial hair cell sensor. The performance of the sensor was investigated for different materials such as sicon and polysilicon and by varying hair cell dimensions including width and length. The silicon material which has low young modulus was proposed based on the simulation performance. The performance of the hair cell sensor was achieved by increasing the hair cell length while increasing the width did not significantly influence the performance. The
performance of the sensor was studied for its viscous force, deflection, von mises stress and sensitivity. From the simulation, the hair cell with a length of 1600 µm and 80 µm width was suggested for the subsequent analysis. Another way to improve the performance was by modifying the hair cell geometry and it was proved that the modified hair cell was more sensitive, based on the deflection. The angle of flow that hit the hair cell also affected the deflection of the sensor where the zero angle flow which was parallel to the substrate was the most effective angle. The limitations of the performance of hair cell for various fluid velocity were also discussed in this paper.

Matched MeSH terms: Finite Element Analysis
Fulltext Simulating bio-composite cycling helmet performance through FEA and CFD approaches

Mohd Naim Abdullah, Mustapha, F., Muda, M.K.H., Arrifin, M.K.A., Rafie, A.S.M., Shamsudin, M.A.

Movement Health & Exercise, 2015;4(1):77-91.
MyJurnal

Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) analysis were performed in this work in order to obtain the best design for safety and aerodynamic performance of the bicycle cycling helmet. FEA analysis was computed on two different helmet designs to determine the critical area subjected to impact. A pressure load was applied on the helmets’ outer surface to simulate oblique loading. The critical areas of the helmets were then highlighted and identified, enabling design improvements to be made on both designs. CFD analysis was then executed in order to obtain the lowest drag coefficient number in reducing the air resistance induced by both of the helmet designs, inherently increasing cyclist performance and ensuring competition success.

Matched MeSH terms: Finite Element Analysis
Fulltext Modeling of a viscoelastic damper and its application in structural control

Mehrabi MH, Suhatril M, Ibrahim Z, Ghodsi SS, Khatibi H

PLoS One, 2017;12(6):e0176480.
PMID: 28570657 DOI: 10.1371/journal.pone.0176480

Conventional seismic rehabilitation methods may not be suitable for some buildings owing to their high cost and time-consuming foundation work. In recent years, viscoelastic dampers (VEDs) have been widely used in many mid- and high-rise buildings. This study introduces a viscoelastic passive control system called rotary rubber braced damper (RRBD). The RRBD is an economical, lightweight, and easy-to-assemble device. A finite element model considering nonlinearity, large deformation, and material damage is developed to conduct a parametric study on different damper sizes under pushover cyclic loading. The fundamental characteristics of this VED system are clarified by analyzing building structures under cyclic loading. The result show excellent energy absorption and stable hysteresis loops in all specimens. Additionally, by using a sinusoidal shaking table test, the effectiveness of the RRBD to manage the response displacement and acceleration of steel frames is considered. The RRBD functioned at early stages of lateral displacement, indicating that the system is effective for all levels of vibration. Moreover, the proposed damper shows significantly better performance in terms of the column compression force resulting from the brace action compared to chevron bracing (CB).

Matched MeSH terms: Finite Element Analysis
Fulltext Systematic mechanical evaluation of electrospun gelatin meshes

Butcher AL, Koh CT, Oyen ML

J Mech Behav Biomed Mater, 2017 May;69:412-419.
PMID: 28208112 DOI: 10.1016/j.jmbbm.2017.02.007

Electrospinning is a simple and efficient process for producing sub-micron fibres. However, the process has many variables, and their effects on the non-woven mesh of fibres is complex. In particular, the effects on the mechanical properties of the fibre meshes are poorly understood. This paper conducts a parametric study, where the concentration and bloom strength of the gelatin solutions are varied, while all electrospinning process parameters are held constant. The effects on the fibrous meshes are monitored using scanning electron microscopy and mechanical testing under uniaxial tension. Mesh mechanical properties are relatively consistent, despite changes to the solutions, demonstrating the robustness of electrospinning. The gel strength of the solution is shown to have a statistically significant effect on the morphology, stiffness and strength of the meshes, while the fibre diameter has surprisingly little influence on the stiffness of the meshes. This experimental finding is supported by finite element analysis, demonstrating that the stiffness of the meshes is controlled by the volume fraction, rather than fibre diameter. Our results demonstrate the importance of understanding how electrospinning parameters influence the pore size of the meshes, as controlling fibre diameter alone is insufficient for consistent mechanical properties.

Matched MeSH terms: Finite Element Analysis
Fulltext Demonstration of comparison between goat skin and x-ray film membranes on traditional musical instrument Kompang

Siswanto, W.A., Syiddiq, M.

Pertanika Journal of Science & Technology, 2018;26(2):585-598.
MyJurnal

This paper presents a mathematical model of the traditional musical instrument, the kompang. In this study, a mathematical model of the kompang membrane is developed to simulate the vibration of the kompang membrane in polar coordinates by implementing the Fourier-Bessel wave function. The wave equation in polar direction is applied to provide the vibration modes of the membrane with the corresponding natural frequencies of the circular membrane. The initial and boundary conditions are determined to allow the development of numerical equation based on kompang membrane attachment. The mathematical model is coded in Smath for the numerical analysis as well as the plotting tool. Two kompang membrane cases with different membrane materials i.e. goat-skin and x-ray film are tried to test the model. The Finite Element Method (FEM) programme, Mecway, shows that the natural frequencies and the corresponding mode shapes are comparable with those from the developed model.

Matched MeSH terms: Finite Element Analysis
Fulltext Stress analysis of engine camshaft from light metal

Sharuddin Mohd Dahuri, Nor Hakimah Ahmad Subri, Norashady Mohd Noor

Journal of Engineering and Science Research, 2018;2(1):37-44.
MyJurnal

his paper presents the structure and static model of engine camshaft analysis. For the purposes of this analysis, the finite element method is used. Camshaft is one of the critical components for effective and precise work of internal combustion engines. This camshaft rotates at high speed causing pressure and vibration in the system. Camshafts are also subject to varying fatigue burden due to cam plunger contact. These precise values are required to be determined to prevent failure in the camshaft. The objective of the project is to model and to perform pressure analysis on the camshaft machine. In this project the standard engine cam shafts are modeled and analyzed using the CATIA V5R21 software respectively. This model is created by the basic requirements of the engine. It is done with an existing background, such as the power of acting on cam by means of a valve while running at maxi mum speed. Here the approach becomes fully CAE based. CAE - based approaches enrich Research and limit the time span. A study was conducted to predict the behavior of the different camshafts structure of the material using the finite three - dimensional pressure of the element. Four types of materials such as Steel, Titanium, Aluminum and Magnesium are taken into account. FEA Stress and maximum displacement decisions are calculated and compared to all of the above materials. The conclusion is to focus on the material suitable for the camshaft to reduce the maximum displacement and weight. Titanium materials become the best material for camshaft manufacturing based on analysis.

Matched MeSH terms: Finite Element Analysis
Fulltext Thermo-mechanical contact problems and elastic behaviour of single and double sides functionally graded brake disks with temperature-dependent material properties

Bayat M, Alarifi IM, Khalili AA, El-Bagory TMAA, Nguyen HM, Asadi A

Sci Rep, 2019 Oct 25;9(1):15317.
PMID: 31653877 DOI: 10.1038/s41598-019-51450-z

A thermo-elastic contact problem of functionally graded materials (FGMs) rotating brake disk with different pure brake pad areas under temperature dependent material properties is solved by Finite Element Method (FEM). The properties of brake disk change gradually from metal to ceramic by power-law distribution along the radial direction from the inner to the outer surface. Areas of the pure pad are changing while the vertical force is constant. The ratio of brake pad thickness to FGMs brake disk thickness is assumed 0.66. Two sources of thermal loads are considered: (1) Heat generation between the pad and brake disk due to contact friction, and (2) External thermal load due to a constant temperature at inner and outer surfaces. Mechanical responses of FGMs disk are compared with several pad contact areas. The results for temperature-dependent and temperature-independent material properties are investigated and presented. The results show that the absolute value of the shear stress in temperature-dependent material can be greater than that for temperature-independent material. The radial stress for some specific grading index (n = 1.5) is compressive near the inner surface for double contact while it is tensile for a single contact. It is concluded that the radial strain for some specific value of grading index (n = 1) is lower than other FGMs and pure double side contact brake disks.

Matched MeSH terms: Finite Element Analysis
Fulltext Dataset on microstructural characteristics and mechanical performance of homogeneous and functionally graded fibrous scaffolds

Khoo W, Chung SM, Lim SC, Low CY, Shapiro JM, Koh CT

Data Brief, 2019 Dec;27:104718.
PMID: 31763388 DOI: 10.1016/j.dib.2019.104718

Data in this article are supplementary to the corresponding research article [1]. Morphological features of homogeneous and graded nanofibrous electrospun gelatin scaffolds were observed using scanning electron microscopy. Microstructural properties including fiber diameter and pore size were determined via image analysis, using ImageJ. Uniaxial tensile and fracture tests were performed on both homogeneous and graded scaffolds using a universal testing machine. Stress-strain curves of all scaffolds are presented. Computing software, MATLAB, was used to design fibrous networks with thickness-dependent density and alignment gradients (DAG). Finite element analysis software, Abaqus, was used to determine the effect of the number of layers on the fracture properties of DAG multilayer scaffolds.

Matched MeSH terms: Finite Element Analysis
Fulltext Enhancement of Complex Permittivity and Attenuation Properties of Recycled Hematite (α-Fe2O3) Using Nanoparticles Prepared via Ball Milling Technique

Mensah EE, Abbas Z, Azis RS, Khamis AM

Materials (Basel), 2019 May 24;12(10).
PMID: 31137736 DOI: 10.3390/ma12101696

The purpose of this study was to synthesize high-quality recycled α-Fe2O3 to improve its complex permittivity properties by reducing the particles to nanosize through high energy ball milling. Complex permittivity and permeability characterizations of the particles were performed using open-ended coaxial and rectangular waveguide techniques and a vector network analyzer. The attenuation characteristics of the particles were analyzed with finite element method (FEM) simulations of the transmission coefficients and electric field distributions using microstrip model geometry. All measurements and simulations were conducted in the 8-12 GHz range. The average nanoparticle sizes obtained after 8, 10 and 12 h of milling were 21.5, 18, and 16.2 nm, respectively, from an initial particle size of 1.73 µm. The real and imaginary parts of permittivity increased with reduced particle size and reached maximum values of 12.111 and 0.467 at 8 GHz, from initial values of 7.617 and 0.175, respectively, when the particle sizes were reduced from 1.73 µm to 16.2 nm. Complex permeability increased with reduced particle size while the enhanced absorption properties exhibited by the nanoparticles in the simulations confirmed their ability to attenuate microwaves in the X-band frequency range.

Matched MeSH terms: Finite Element Analysis
Shape-shifting thermal coagulation zone during saline-infused radiofrequency ablation: A computational study on the effects of different infusion location

Kho ASK, Foo JJ, Ooi ET, Ooi EH

Comput Methods Programs Biomed, 2020 Feb;184:105289.
PMID: 31891903 DOI: 10.1016/j.cmpb.2019.105289

BACKGROUND AND OBJECTIVE: The majority of the studies on radiofrequency ablation (RFA) have focused on enlarging the size of the coagulation zone. An aspect that is crucial but often overlooked is the shape of the coagulation zone. The shape is crucial because the majority of tumours are irregularly-shaped. In this paper, the ability to manipulate the shape of the coagulation zone following saline-infused RFA by altering the location of saline infusion is explored.
METHODS: A 3D model of the liver tissue was developed. Saline infusion was described using the dual porosity model, while RFA was described using the electrostatic and bioheat transfer equations. Three infusion locations were investigated, namely at the proximal end, the middle and the distal end of the electrode. Investigations were carried out numerically using the finite element method.
RESULTS: Results indicated that greater thermal coagulation was found in the region of tissue occupied by the saline bolus. Infusion at the middle of the electrode led to the largest coagulation volume followed by infusion at the proximal and distal ends. It was also found that the ability to delay roll-off, as commonly associated with saline-infused RFA, was true only for the case when infusion is carried out at the middle. When infused at the proximal and distal ends, the occurrence of roll-off was advanced. This may be due to the rapid and more intense heating experienced by the tissue when infusion is carried out at the electrode ends where Joule heating is dominant.
CONCLUSION: Altering the location of saline infusion can influence the shape of the coagulation zone following saline-infused RFA. The ability to 'shift' the coagulation zone to a desired location opens up great opportunities for the development of more precise saline-infused RFA treatment that targets specific regions within the tissue.

Matched MeSH terms: Finite Element Analysis

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