Modelling of Ring-Shaped Compound Ultrasonic Waveguides by Means of Finite Elements Method

The paper describes a technique for modelling and optimization of ring-shaped compound ultrasonic waveguides consisting of two sequentially joined segments of different materials by means of finite elements method. The possibility of using such waveguides for amplifying vibrations in amplitude has been justified in the paper. The advantage of the developed technique consists in possibility of its realization by means of standard engineering software, particularly COMSOL Multiphysics. The correctness and efficiency of the technique is proved by comparing the numerical data with the simulation results by means of transfer matrix method using equations of vibration of Euler – Bernoulli and Timoshenko type. It is shown that in compound ring-shaped waveguides two kinds of vibration modes are possible – variable-sign and constant-sign, moreover only constant-sign modes are of practical interest for amplification of vibration amplitude. Recommendations for selection of optimal geometric parameters of the waveguides are given, particularly it is shown that for ensuring maximum vibration amplification factor it is necessary to choose central angles of the waveguide segments with account for calculated dependence between amplification factor and angle, characterized by presence of several local maxima of the amplification factor. It is noted that the high accuracy of the existing semi-analytical methods for calculating and designing ring-shaped waveguides is achieved using methods based on the application of Timoshenko-type equations of vibration.

Modelling a mechanical antenna for a calibrator for interferometric gravitational wave detector using finite elements method

Interferometric gravitational wave detectors (IGWD) are a very complex detector, the need to lock the detector in a dark fringe condition besides the vibrations that affect the mirrors, creates the necessity of using active suspension systems. These active systems make the system reach the desired sensitivity but make the calibration of such detectors much more difficult. To solve this problem a calibrator is proposed, a resonant mass gravitational wave detector could be used to detect the same signal in a narrower band and use the measured amplitude to calibrate the IGWD, as resonant mass gravitational wave detectors are easily calibrated. This work aims to design the mechanical antenna of such a calibrator. The main difficulty is to design the calibrator is the frequencies required to make the detection. These massive detectors usually were made in frequencies close to 1 kHz and the frequency range to operate for better sensitivity is around 100 Hz. The antenna is modelled in finite elements method and a design of such an antenna is presented.

Компактная многодиапазонная антенна с CPW питанием для систем связи 5G

В статье предложена многодиапазонная антенна с копланарным волноводным питанием для Wi-Fi и 5G приложений. Для получения требуемых частот в работе использовался инновационный метод, включающий в себя использование полос частотного сдвига FSS (frequency shifting strips) и U-образной щели. Для моделирования спроектированной антенны использовано программное обеспечение ANSYS HFSS, где моделирование электромагнитного поля выполнялось методом конечных элементов FEM (finite elements method). Разработанная антенна предназначена для работы в диапазонах частот 5G: 28, 35 и 37 ГГц с максимальным усилением 11,61 дБ и коэффициентом полезного действия 92%. Для проверки эффективности моделированного проекта результаты сравнивались с результатами измерений. В данной работе проведено сравнение характеристик предлагаемой антенны с характеристиками других существующих антенн. В работе представлена информация об усилении антенны, КСВН, распределениях поля, ширине полосы, распределениях поверхностного тока (поля E и H), и других характеристиках разработанной антенны.

Finite element modeling of multiple density materials of bone specimens for biomechanical behavior evaluation

The finite elements method allied with the computerized axial tomography (CT) is a mathematical modeling technique that allows constructing computational models for bone specimens from CT data. The objective of this work was to compare the experimental biomechanical behavior by three-point bending tests of porcine femur specimens with different types of computational models generated through the finite elements’ method and a multiple density materials assignation scheme. Using five femur specimens, 25 scenarios were created with differing quantities of materials. This latter was applied to computational models and in bone specimens subjected to failure. Among the three main highlights found, first, the results evidenced high precision in predicting experimental reaction force versus displacement in the models with larger number of assigned materials, with maximal results being an R2 of 0.99 and a minimum root-mean-square error of 3.29%. Secondly, measured and computed elastic stiffness values follow same trend with regard to specimen mass, and the latter underestimates stiffness values a 6% in average. Third and final highlight, this model can precisely and non-invasively assess bone tissue mechanical resistance based on subject-specific CT data, particularly if specimen deformation values at fracture are considered as part of the assessment procedure.