Thin Sandwich Structures Research Articles

Electrically thin metasurface for broadband transmission enhancement by manipulating the amplitude and phase of the reflection coefficients

We present a broadband and electrically thin antireflective metasurface for enhanced electromagnetic transmission in the low gigahertz range. In this design, an electrically thin sandwich structure (∼λ/8) is proposed and studied numerically and experimentally. The destructive interference theory is used to elucidate the designing principle, and by simply tailoring the structural geometrical parameters, the interference conditions at two resonator-spacer interfaces can be tuned to satisfy over a broad frequency range. Measurement results show that transmittance is higher than 85% over a range with a relative bandwidth of 32%, reaching 95% at the maximum, comparing with the transmittance of 65% if no such metasurface is in place. A corresponding low reflectance can also be achieved over a wide range of incidence angles for transverse electric and transverse magnetic polarizations. More importantly, we find that this type of antireflective transmission enhancement is insensitive to the choice of resonators as long as the “spacer-substrate” interface is coated by split ring resonators. It thereby eases the design for a variety of transmission enhancement applications such as nondestructive testing applications and ultrathin detectors in the future.

Energy storage in structural composites by introducing CNT fiber/polymer electrolyte interleaves

This work presents a method to produce structural composites capable of energy storage. They are produced by integrating thin sandwich structures of CNT fiber veils and an ionic liquid-based polymer electrolyte between carbon fiber plies, followed by infusion and curing of an epoxy resin. The resulting structure behaves simultaneously as an electric double-layer capacitor and a structural composite, with flexural modulus of 60 GPa and flexural strength of 153 MPa, combined with 88 mF/g of specific capacitance and the highest power (30 W/kg) and energy (37.5 mWh/kg) densities reported so far for structural supercapacitors. In-situ electrochemical measurements during 4-point bending show that electrochemical performance is retained up to fracture, with minor changes in equivalent series resistance for interleaves under compressive stress. En route to improving interlaminar properties we produce grid-shaped interleaves that enable mechanical interconnection of plies by the stiff epoxy. Synchrotron 3D X-ray tomography analysis of the resulting hierarchical structure confirms the formation of interlaminar epoxy joints. The manuscript discusses encapsulation role of epoxy, demonstrated by charge-discharge measurements of composites immersed in water, a deleterious agent for ionic liquids. Finally, we show different architectures free of current collector and electrical insulators, in which both CNT fiber and CF act as active electrodes.

The effect of the viscoelastic film and metallic skin on the dynamic properties of thin sandwich structures

In this work, the influence of design parameters on the dynamic properties of thin sandwich structures composed of micron-size viscoelastic adhesive layers is analysed. Sandwiches composed of different types of viscoelastic film and metallic skins are characterised in the frequency bandwidth of 0–1kHz. The numerical modelling of thin sandwich structures is presented and validated with experimental results. A four-parameter fractional derivative model is used to describe the dynamic behaviour of the viscoelastic films, and a three-layer beam element is used to model the sandwich structures. The analysis of experimental and numerical results allows the establishment of design considerations to obtain thin sandwich structures with high stiffness and damping. The viscoelastic adhesive film should have a high shear modulus and loss factor, and the metallic skin should have a high storage modulus.

The influence of viscoelastic film thickness on the dynamic characteristics of thin sandwich structures

Passive damping techniques by means of viscoelastic materials are widely used for structural vibrations control. Sandwich structures composed of viscoelastic adhesive films and metallic constraining layers result in thin composite structures with improved dynamic capabilities. The nature and the small thickness of these sandwich structures enable them to be processed in conventional metal sheet transformation techniques to obtain components of complex geometries. In this work the influence of the viscoelastic film thickness on the dynamic properties, stiffness and damping, of thin sandwich structures is analysed from experimental and numerical results. Sandwich structures composed of same viscoelastic material but three different core thicknesses are tested and the dynamic properties of the viscoelastic film are obtained. From the experimental results a material model with fractional derivatives is proposed for the shear complex modulus of the viscoelastic adhesive film. The results show the viscoelastic film thickness has a greater influence in the loss factor than in the storage modulus, being this effect more pronounced at high frequencies. The bending stiffness of the sandwich structure is increased with core thickness even if the storage modulus is decreased. Therefore, the viscoelastic film thickness determines the vibrational response of thin sandwich structures.

Shielding calculation for the CSNS target station

In this paper we firstly calculate the one-dimension shielding models to give the basic data for the Chinese Spallation Neutron Source (CSNS) target station. Then the three-dimensional shielding calculations have been performed for the detailed design of the CSNS target station. The gaps and void spaces in the CSNS target station are considered for precise estimation. We find that 4.8-meter-radius steel adding 1.2-meter-thick magnetite concrete can satisfy the shielding requirement in the horizontal direction. The dose rate on the top of the ceiling is a little higher than 2.5μSv/h due to streaming effect, which originates from the moderator transfer lines. A thin sandwich structure will be adopted for decreasing residual radioactivity dose rate on the altitude directions after considering the engineering cost and maintenance. All these calculations lie on the Monte Carlo simulation code MCNPX2.5.0.

In situ optical observations of keyhole dynamics during laser drilling

To better understand the laser drilling process and especially to clarify keyhole dynamics in metal drilling, a quasi-two-dimensional drilling assembly was set up with a thin sandwich structure. Keyhole dynamics coupling multiple physical processes were recorded using high-speed photography, and clear images were obtained. The formation of keyholes was found not to be a single unified process, and the whole drilling process could be divided into five stages: an initial melt ejection, mild melting, rapid drilling, hole expansion, and backflow and recasting. As the keyhole evolved, the removal of material changed.

Radiation resistant bolometers with Al 2O 3 and AlN substrates, anodized aluminium support frames, and improved electrical contacts

Recent work has been devoted to develop a simplified bolometer type device which would enable in-reactor testing of more radiation resistant substrates, meander materials, and electrical contacts. The bolometer configurations based on a thin sandwich structure, make possible more reliable electrical connections, as well as facilitating PIE. Different materials for use as the insulating support frame for the delicate sensor substrate have been examined. Initially machineable glass ceramic (MACOR) was considered, and trial supports fabricated to test different configurations and electrical contact designs, however the high boron content makes this material unsuitable for a nuclear environment. Similar support frames were then made from alumina, this being the perfect choice for the application. But alumina was rejected due to cost of machining and fragility. Finally support frames of anodized aluminium were tested. These gave more than adequate electrical insulation for operating temperatures up to at least 400 °C. Ionizing radiation at high temperature and dose has no effect on the sensor resistance values. Several prototypes are now awaiting final in-reactor (BR2) characterization at SCK-CEN, Mol.

The Effects of Underlayers for SmCo$_5$Thin Films With Perpendicular Magnetic Anisotropy

In this paper, the magnetic properties of thin SmCo5 film has been studied. A thin sandwich structure, Ru/Cu/Ru, is proposed as a new structure of the underlayer for SmCo5 films with perpendicular magnetic anisotropy. The first Ru layer is deposited to improve the Cu(111) orientation, and the second Ru layer is to restrict the interlayer diffusion between Cu and SmCo5. The Sm-Co films as thin as 10 nm with excellent perpendicular anisotropy have been obtained with the total sandwich underlayer as thin as 15 nm.

Modelling and analysis of multilayered shells based on a timoshenko-type theory with six degrees of freedom

In this paper a theoretical approach to multilayered shell and plate analysis based on a kinematical model with six degrees of freedom is presented. The theory has been confirmed by some numerical examples. From these we draft the following conclusions: 1. The theory proposed for laminates can be used successfully also in the case of thin sandwich structures. It seems that the determination of stiffnesses is not so sensitive with regard to the ratios of the elastic moduli. 2. In the case of fibre reinforced laminates the results show a strong dependence not only on the fibre orientation angle, but also on the kind of lamination. These phenomena can be explained by the transformation rules of the local stiffness values. In many practical situations, simplified calculation formulae can be used for the local stiffness. 3. The results based on models with five or six degrees of freedom are very similar to standard situations with a simple geometry. In the cases of complicated geometries a model of six-degree-freedom provides a better agreement with results of there authors. 4. Further investigations should be continued on the effect of shear correction factors (see, e.g. [24]) and new classes of shell problems (stability, failure and inelastic material behavior).

Electrical conduction and observation of local defects in thin sandwich structures of Cu-SiO/CeO2-Cu

AC and DC conduction in MIM sandwich structures based on SiO/CeO2 as a dielectric prepared by the co-evaporation technique has been investigated before and after electroforming for different compositions. The electroformed samples show voltage-controlled negative resistance (VCNR), voltage-memory, thermal-voltage-memory and pressure-voltage-memory effects and the results are explained in terms of the filamentary model of electrical conduction. The positive electrode was investigated using a scanning electron microscope to observe the effects of electroforming and the liberation of gas as a result of the application of high electric fields

Observations of local defects caused by electrical conduction through thin sandwich structures of AgSiO/BaOAg

Studies of the electrodes of electroformed metal-SiO/BaO-metal thin film structures by means of optical and scanning electron microscopy provide evidence of the formation of conducting filaments in such structures. An explanation of the formation and subsequent operation of such structures as negative resistance and electron-emitting devices includes an electrolytic process along the filaments involving the liberation of oxygen gas at the anode.