Vibration analysis of two-dimensional micromorphic structures using quadrilateral and triangular elements

PurposeThe paper aims to presents a numerical analysis of free vibration of micromorphic structures subjected to various boundary conditions.Design/methodology/approachTo accomplish this objective, first, a two-dimensional (2D) micromorphic formulation is presented and the matrix representation of this formulation is given. Then, two size-dependent quadrilateral and triangular elements are developed within the commercial finite element software ABAQUS. User element subroutine (UEL) is used to implement the micromorphic elements. These non-classical elements are capable of capturing the micro-structure effects by considering the micro-motion of materials. The effects of the side length-to-length scale parameter ratio and boundary conditions on the vibration behavior of 2D micro-structures are discussed in detail. The reliability of the present finite element method (FEM) is confirmed by the convergence studies and the obtained results are validated with the results available in the literature. Also, the results of micromorphic theory (MMT) are compared with those of micropolar and classical elasticity theories.FindingsThe study found that the size effect becomes very significant when the side length of micro-structures is close to the length scale parameter.Originality/value The study is to analyze the free vibrations of 2D micro-structures based on MMT; to develop a 2D formulation for micromorphic continua within ABAQUS; to propose quadrilateral and triangular micromorphic elements using UEL and to investigate size effects on the vibrational behavior of micro-structures with various geometries.

Semisolid Casting and Die Casting of Al-4.8%Mg-2%Si Alloy

An aluminum alloy, Al–4.8%Mg–2%Si, was cast by die casting and thixocasting, and the properties of the cast specimens were investigated. When the poured molten metal temperature was lower than 640 °C during die casting, it was lower than the liquidus temperature, and the metal became a semisolid slurry in the sleeve of the die casting machine; this fulfills the conditions for rheocasting. A tension test was conducted to investigate the effects of semisolid casting on the mechanical properties of Al–4.8%Mg–2%Si. The ultimate tensile strength and elongation of the ingots cast by die casting and rheocasting were affected by the size of ingot. When the ingot had a circular base of 4.5 mm diameter, the ultimate tensile strength and elongation were excellent; however, when the cross section of the ingot was a square with a side length of 20 mm, the tensile strength and elongation were inferior. The thixocasting was conducted using square ingots with a side length of 20 mm, and the tensile strength and elongation were poor in this case as well. The results of this study demonstrate that semisolid casting cannot improve the mechanical properties of Al–4.8%Mg–2%Si ingots with a high thickness. Semisolid casting cannot produce fine-grained Mg2Si, and the mechanical properties of the material could not be improved by this casting method.

Influence of active structure parameters on resonant frequency of acoustic transducer membranes

The paper presents the results of calculations of the resonant frequency of a multilayer square membrane for ultrasonic microelectromechanical sensors. Various combinations of active layer materials and metal electrodes were taken into account. The dependences of the resonant frequency on the side length of membrane, as well as on the thickness of active piezoelectric layer and metal electrode for SiO2/Ti/ZnO, SiO2/Al/ZnO, SiO2/Ti/PZT and SiO2/Al/PZT structures were ob-tained. According to the calculations, the values of the resonant frequencies are in the ranges of 46.1–498.3 kHz for SiO2/Ti/ZnO; 45.4–477.3 kHz for SiO2/Al/ZnO; 39.4–411.4 kHz for SiO2/Ti/PZT; 38.1–381 kHz for SiO2/Al/PZT. It is shown that the resonant frequency can be increased due to changes in the geometric parameters of the membrane; and the material and dimensions of the piezoelectric layer have the greatest influence. The results of analytical and numerical simulations for particular case of SiO2(1μm)/Ti(1μm)/ZnO(2μm)/Ti(1μm) membrane with a side length of 600 μm are also compared. The obtained results could be used to optimize the design and process technology of microelectrome-chanical ultrasonic sensors.

Magnetic field compensation coil design for magnetoencephalography

While optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately 5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.

A Survey on Function Spaces of John–Nirenberg Type

In this systematic review, the authors give a survey on the recent developments of both the John–Nirenberg space JNp and the space BMO as well as their vanishing subspaces such as VMO, XMO, CMO, VJNp, and CJNp on Rn or a given cube Q0⊂Rn with finite side length. In addition, some related open questions are also presented.

A Novel Miniaturized Four-Ridged Horn Antenna with Enhanced Gain

Miniaturization of wideband antennas has attracted much attention for its wide application in modern society. This article proposes a novel broadband miniaturized four-ridged horn antenna (FRHA) with high gain operating from 2.6 to 8.4 GHz. By filling the FRHA with the epoxy-laminated glass cloth board, the side length of the aperture realizes 48% reduction comparing to a traditional ridged horn antenna. The cuboid-shaped polyethylene lens provides good impedance matching between the antenna and the air at low frequencies and decreases the aperture phase error at high frequencies, which optimizes the radiating characteristics in the whole operating band.

Electromagnets for an endoscopic anastomosis tool in the colon

The goal of our research work is the development of a novel endoscopic anastomosis device for the colon. One of the main challenges in this context is the application of forces at the endoscope tip to rejoin the two bowel endings. Thus, we focus on a magnetic two-part compression implant approach. The implant halves are detached from the applicator units by means of electromagnets. In this contribution we present the results of our experiments to determine the implant design with special focus on tissue compression forces and the resultant electromagnet dimensioning to estimate size requirements of the application/detachment system. To achieve the targeted compression forces derived from literature, we used cubic N52 magnetized neodymium magnets1 with a side length of 5 mm and mild steel screws. For these magnets, we evaluated a required electromagnetic repulsion force of 4.1 N. For the electromagnetic detachment system this led to the need for 166 windings for the coils on oral side, and 146 windings for the coils at the aboral side. Based on these requirements, a colonoscope diameter (~14 mm) increase of 10.6 mm on the oral side and of 12 mm on the aboral side due to the application device must be assumed. Nevertheless, this diameter still remains within the size range of other colonoscopic tools, such as e.g., circular staplers.

Design of Low Cross-Polarization Tri-Reflector CATR with Standard Quadric Surfaces Working in Terahertz

In this paper, a tri-reflector compact antenna test range (CATR) consisting of a main parabolic reflector with a square aperture of 3 m in side length and two sub-reflectors of rotationally standard quadric surfaces working in terahertz is proposed. By using the equivalent paraboloid theory and cross-polarization elimination conditions and then combining with the appropriate shaped feed, the low cross-polarization and good quiet zone (QZ) performance of the system are achieved. The simulated results demonstrate that a cross-polarization isolation of >37 dB and a peak-to-peak amplitude (phase) ripple of <1.8 dB (13°) can be achieved on the principal cuts of the QZ at 100–500 GHz. At the same time, the QZ usage ratio of the CATR can reach 75%. The proposed tri-reflector CATR composed of standard quadric surfaces not only exhibits good quiet zone performance but also greatly reduces the manufacturing difficulty of the sub-reflectors and the construction cost of the system.

Magnetic Field Compensation Coil Design for Magnetoencephalography

While optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately ±5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved 10 times smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.

Development of Side Mold Control Equipment for Producing Free-Form Concrete Panels

Free-form concrete panel production requires an increasing amount of manpower because the molds cannot be reused. There are many limitations when it comes to reproducing accurate forms due to the many manual processes. Therefore, the current study developed side mold control equipment that can automatically fabricate molds for free-form concrete panels. The equipment is capable of molding various shapes and sustainable operation. However, there may be errors as it automatically produces various shapes. Therefore, it is necessary to check the errors between manufactured shapes and designed shapes. The shape created using the side mold control equipment showed less than 0.1° error in side angle and ±3 mm error in side length. Therefore, the equipment manufactured a precise shape. Based on the findings of the study, the side mold control equipment will be used to produce accurate shape of free-form concrete panels automatically.