Complex Multilayer Structures Research Articles

Ballistic resistance of spaced multi-layer plate structures: Experiments on Fibre Reinforced Plastic targets and an analytical framework for calculating the ballistic limit

As the use of complex multi-layer structures in defense, marine, aerospace and automotive applications becomes increasingly common, it is vital that the response of such structures to impact loading is better understood and that engineers have adequate analysis tools to design structures optimised for resistance to ballistic penetration. This paper presents the results of a series of ballistic impact experiments carried out on a range of spaced multi-layer fibre reinforced-plastic (FRP) composite targets, with a constant total number of plies per target, but varying numbers of plies per layer and varying layer arrangements. It is shown that varying the ratio of plies between layers can have a significant effect on resistance to ballistic penetration. In light of these experimental results, the validity of applying the Lambert–Jonas equation to spaced multi-layer structures is discussed and an extended framework developed to determine the ballistic limit of a projectile impacting such a structure. The extended Lambert–Jonas framework is then validated with data from the literature. It is hoped that this framework will allow engineers to quickly determine the optimum layer arrangement to maximise the ballistic resistance of complex spaced multi-layer structures.

Ultrafast element-specific magnetization dynamics of complex magnetic materials on a table-top

We review recent progress in femtosecond magnetization dynamics probed by extreme ultraviolet pulses from high-harmonic generation. In a transverse magneto-optical Kerr geometry, we established an ultrafast, element-specific experimental capability – on a table-top – for the measurement of magnetization dynamics in complex multi-sublattice magnets and multilayer magnetic structures. We show that this newly introduced technique is an artifact-free magnetic sensor, with only negligible non-magnetic (optical) contributions from the transient variation of the refractive index due to the presence of a non equilibrium hot-electron distribution. We then use these new experimental capabilities of ultrahigh time-resolution, combined with element-specific simultaneous probing, to disentangle important microscopic processes that drive magnetization dynamics on femtosecond timescales. We elucidate the role of exchange interaction on magnetization dynamics in strongly exchange-coupled alloys, and the role of photo-induced superdiffusive spin currents in magnetic multilayer stacks.

Laser induced fluorescence monitoring of the transport of small organic molecules in an organic vapor phase deposition system

Laser-induced fluorescence is employed for the accurate and real-time in-situ monitoring of the concentration of organic molecules in an organic vapor phase deposition (OVPD) chamber. We investigate the transport dynamics of organic species in a hot N2 carrier gas from the evaporation source to the substrate. Based on the time-dependent concentration of organic molecules obtained from their fluorescence intensity near the substrate, we find that carrier gas transport is accurately described by Poiseuille flow. The interplay between convective and diffusive forces gives rise to dispersion of organic molecules in the carrier gas, resulting in the development of plug flow as described by Taylor-Aris theory. Retention of molecules in chamber dead volumes delays transport and introduces tailing of the concentration transients. Our study indicates how OVPD system design and operating conditions can be optimized to limit the duration of transport transients, ultimately leading to precise control over the growth of complex multilayer thin film structures.

The Effect of Phase Composition on the Mechanical and Thermal Properties of LTCC Material

Low-temperature co-fired ceramic (LTCC) is an important material in the production of ceramic multilayer structures. Large and complex multilayer structures are usually fired at higher temperatures and/or longer firing times compared to the relatively thin LTCC tapes. The firing conditions of LTCC determine the phase composition and the microstructure, which both influence the physical characteristics, such as the mechanical and thermal properties. In this work the effect of the phase composition on the biaxial flexural strength and the temperature coefficient of expansion of the DuPont 951 LTCC is presented. The samples were fired at different temperatures and times to obtain different phase compositions. The phase composition, especially the mass fraction of anorthite, was correlated with the biaxial flexural strength and the thermal coefficient of expansion (TCE). A very long firing time, i.e., 100h at 800 °C, yields, apart from crystalline anorthite, the cristobalite phase. The anorthite that crystalizes from the glass phase in a dense LTCC material changes the crack-propagation mechanism and improves the biaxial flexural strength of the material. The major change in the biaxial flexural strength is observed when the anorthite phase appeared. The increasing mass fraction of anorthite does improve the biaxial flexural strength less drastically. With the increasing mass fraction of the anorthite, decreases of the TCE of the material and a small decrease of the density of the LTCC material occur.

Insight into the 3D Architecture and Quasicrystal Symmetry of Multilayer Nanorod Assemblies from Moiré Interference Patterns

Vertical nanorod assembly over three dimensions is shown to result in the formation of Moiré interference patterns arising from rotational offsets between respective monolayer sheets. Six distinct patterns are observed in HRTEM and angular dark-field STEM (DF-STEM) images, allowing the exact angle of rotation to be determined from their respective size and repeat order. At large rotation angles approaching 30°, the aperiodicity in the structure of the nanorod supercrystals becomes apparent, resulting in 12-fold ordering characteristics of a quasicrystal. The rotational offsets are further elucidated from Fourier transform and small angle electron diffraction, allowing interpretation of several multilayers when combined with DF-STEM and SEM. Pattern formation owing to angular rotation is differentiated from those occurring from a lateral shift, providing an important insight into the complex multilayered structures in assembled rods that may have an impact on their collective electronic or photonic properties. We also show how random tetrapods when present at low concentrations in colloidal nanorod solutions act as termination points for 2D sheet crystallization, impacting the size and shape of the resultant assemblies. The occurrence of Moiré patterns in rod assemblies demonstrates the extraordinary order achievable in their assembly and offers a nondestructive technique to precisely map the placement of each nanorod in this important nanoarchitecture.

ParAFEMCap: A Parallel Adaptive Finite-Element Method for 3-D VLSI Interconnect Capacitance Extraction

Parasitic extraction is one of the key techniques in very large scale integration design that has been widely used to build the equivalent-circuit model of interconnects. In this paper, a parallel adaptive finite-element method (AFEM) for capacitance extraction of large-scale interconnects (ParAFEMCap) is developed to provide extremely high parallel scalability and numerical accuracy. First, the proposed ParAFEMCap has the potential of high parallel scalability by taking advantages of several advanced parallel techniques, such as parallel adaptive mesh refinement and dynamic load balancing. To the best of the authors' knowledge, this is the first capacitance extraction field solver that is able to run in parallel on hundreds and even thousands of CPU cores. Second, the proposed ParAFEMCap is based on the AFEM, which is proven to converge to the exact solution of the electromagnetic problems in a theoretically quasi-optimal rate. The solution precision of ParAFEMCap can easily be controlled by varying the threshold for the a posteriori error estimator, while the computational time can easily be reduced by increasing the number of CPU cores. Moreover, ParAFEMCap is shown to have the same linear computation complexity as those integral-equation methods, which make it very promising for capacitance extraction of large-scale interconnect problems. Numerical experiments will demonstrate that ParAFEMCap has the advantages of high computational efficiency and accuracy for solving the capacitance extraction problem of large-scale interconnects with complex multilayer structures.

Mixed Convection of Non-Newtonian Fluids through Porous Medium Along a Heated Vertical Flat Plate with Magnetic Field

In This section we study of Mixed convective heat transfer of non-Newtonian fluids through porous medium with magnetic field on a flat plate has been investigated using a modified power - law viscosity model. This model does not contain physically unrealistic limits of zero or infinite viscosity as are encountered in the boundary - layer formulation with traditional models of viscosity for power - law fluids through porous medium with magnetic field. These unrealistic limits can introduce an irremovable singularity at the leading edge; the present modified model matches well with the measurement of viscosity, and does not introduce irremovable singularities. Therefore, the boundary layer equations can be solved by marching from the leading edge downstream as for Newtonian fluids. The numerical results are presented for a shear-thinning fluid in terms of the velocity and temperature distribution, and for important physical properties, namely the wall shear stress and heat transfer rates. valid at the leading edge of the boundary-layer. This similarity solution is the required upstream condition at the leading edge of the flat plate to integrate boundary-layer equations along the stream wise direction. Traditional power-law correlation, that in the limit of large or small shear rates, Traditional power-law correlations introduce non-removable singularities into boundary-layer formulations for infinite or zero viscosity. Without recognizing the cause of such unrealistic conditions, complex multi-layer structures have been introduced by many authors.

A programmable microfluidic cell array for combinatorial drug screening.

We describe the development of a fully automatic and programmable microfluidic cell culture array that integrates on-chip generation of drug concentrations and pair-wise combinations with parallel culture of cells for drug candidate screening applications. The device has 64 individually addressable cell culture chambers in which cells can be cultured and exposed either sequentially or simultaneously to 64 pair-wise concentration combinations of two drugs. For sequential exposure, a simple microfluidic diffusive mixer is used to generate different concentrations of drugs from two inputs. For generation of 64 pair-wise combinations from two drug inputs, a novel time dependent variable concentration scheme is used in conjunction with the simple diffusive mixer to generate the desired combinations without the need for complex multi-layer structures or continuous medium perfusion. The generation of drug combinations and exposure to specific cell culture chambers are controlled using a LabVIEW interface capable of automatically running a multi-day drug screening experiment. Our cell array does not require continuous perfusion for keeping cells exposed to concentration gradients, minimizing the amount of drug used per experiment, and cells cultured in the chamber are not exposed to significant shear stress continuously. The utility of this platform is demonstrated for inducing loss of viability of PC3 prostate cancer cells using combinations of either doxorubicin or mitoxantrone with TRAIL (TNF-alpha Related Apoptosis Inducing Ligand) either in a sequential or simultaneous format. Our results demonstrate that the device can capture the synergy between different sensitizer drugs and TRAIL and demonstrate the potential of the microfluidic cell array for screening and optimizing combinatorial drug treatments for cancer therapy.

Simulation of temperature field and melting depth of an Y 2O 3-stabilized ZrO 2 thermal barrier coating sealed by high-current pulsed electron beam

High-current pulsed electron beam is a promising technique for surface sealing of initially rough and porous Y 2O 3-stabilized ZrO 2 (YSZ) thermal barrier ceramic coatings. Due to the rapid remelting and solidification, the outer layer of the ceramic coating becomes smooth, dense and corrosion resistant such that the protective performance for turbine blades is enhanced. Because of the complex multi-layered structures, the high-current pulsed electron beam treatment requires specific parameter inputs which are related to the temperature fields induced by the electron energy deposition in the coatings. In the present work, a two-dimensional temperature field simulation is conducted to describe the temperature response and distribution in an Y 2O 3-stabilized ZrO 2 ceramic coating treated by high-current pulsed electron beam. The simulation reveals that the melting layer reaches a few micrometers in depth, and in particular at the pulse duration of 120 μs and the deposition energy density of 15 J/cm 2, the calculated melting depth of 4.4 μm is good agreement with the experimental results. The heating rate is up to 10 7–10 8 Ks − 1 and the temperature gradient is about 10 9 Km − 1 . It is pointed out that the ideal energy densities should be about 5–13 J/cm 2 at a pulse duration of 200 μs to seal the ceramic surface.

Evolution of tip shape during field evaporation of complex multilayer structures

Atom-probe tomography analysis of complex multilayer structures is a promising avenue for studying interfacial properties. However, significant artefacts in the three-dimensional reconstructed data arise due to the field evaporation process. To clarify the origin and impact of these artefacts for a FeCoB/FeCo/MgO/FeCo/IrMn multilayer, tip shapes were observed by transmission electron microscopy and compared to those obtained by finite difference modelling of electric fields and evaporation processes. It was found that the emitter shape is not spherical and its surface morphology evolves during successive evaporation of the different layers. This evolving morphology contributes to the artefacts generally observed in the reconstructed atom-probe data for multilayer structures because algorithms for three-dimensional reconstruction are based on the assumption that the shape of the emitter during field evaporation is spherical. Some proposed improvements to data reconstruction are proposed.

Measurement of layer-specific mechanical properties in multilayered biomaterials by micropipette aspiration

Many biomaterials and tissues are complex multilayered structures in which the individual layers have distinct mechanical properties that influence the mechanical behavior and define the local cellular microenvironment. Characterization of the mechanical properties of individual layers in intact tissues is technically challenging. Micropipette aspiration (MA) is a proven method for the analysis of local mechanical properties of soft single-layer biomaterials, but its applicability for multilayer structures has not been demonstrated. We sought to determine and validate MA experimental parameters that would permit measurement of the mechanical properties of only the top layer of an intact multilayer biomaterial or tissue. To do so, we performed parametric nonlinear finite-element (FE) analyses and validation experiments using a multilayer gelatin system. The parametric FE analyses demonstrated that measurement of the properties of only the top layer of a multilayer structure is sensitive to the ratio of the pipette inner diameter (D) to top layer thickness (ttop), and that accurate measurement of the top layer modulus requires D/ttop<1. These predictions were confirmed experimentally by MA of the gelatin system. Using this approach and an inverse FE method, the mean effective modulus of the fibrosa layer of intact porcine aortic valve leaflets was determined to be greater than that of the ventricularis layer (P<0.01), consistent with data obtained by tensile testing of dissected layers. This study provides practical guidelines for the use of MA to measure the mechanical properties of single layers in intact multilayer biomaterials and tissues.

Signal/Power Integrity Analysis for Multilayer Printed Circuit Boards Using Cascaded S-Parameters

A cascaded S-parameter method is proposed in this paper for signal/power integrity analysis of multiple vias in a multilayer printed circuit board (PCB). The proposed method enables efficient and accurate construction and simulation of physics-based via model for complex multilayer PCB structures involving vias. The physics-based via model describes the parasitic effects near each via region as well as mutual coupling among different vias. In this model, each via portion between two parallel plates is regarded as a three-port network with two coaxial ports and one radial port between the two plates. A procedure is first developed to obtain the S-parameters of a single plate pair, which combine the three-port via networks with the impedance matrix of the parallel-plate pair. Once the S-parameters of each plate pair are obtained, an assembling technique for cascading microwave networks is further developed. The method proposed in this paper has been validated by both simulations with a commercial circuit simulator and measurements.

Abstracts: Basic optics of effect materials

pp. 85–105 Effect materials derive their color and effect primarily from thin‐film interference. Effect materials have evolved over the decades from simple guanine crystals to the complex multilayer optical structures of today. The development of new complex effect materials requires an understanding of the optics of effect materials. Such an understanding would also benefit the cosmetic formulator as these new effect materials are introduced. The root of this understanding begins with basic optics. This paper covers the nature of light, interference of waves, thin‐film interference, color from interference, and color travel.

Analysis of Simultaneous Switching Noise Coupling in Multilayer Power/Ground Planes With Segmentation Method and Cavity Model

An accurate power bus model is essential for predicting noise coupling in high-speed printed circuit board (PCB) and package designs. With a complex multilayer structure, the power bus is often modeled using numerical simulation methods. However, full-wave approaches are computationally inefficient, or even infeasible for extremely complicated geometries. Fortunately, the segmentation method makes it possible to combine different types of models together, and both simulation accuracy and efficiency can be obtained through this “divide-and-conquer” strategy. After segmentation, one of the fundamental blocks is a parallel plane pair. For this block, analytical expressions for the impedance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> ) matrix are available for a rectangular plane pair and some special triangular plane pairs. The combination of the cavity model with the segmentation technique has been known to be an efficient way to analyze irregularly shaped multilayer structures. In this paper, this approach is further extended to the general multilayer structures with overlapping planes. Noise-coupling mechanisms are then studied, and the two main coupling mechanisms, the plane edge coupling and the via coupling, are further characterized. Engineering implications on reducing noise coupling in a practical multilayer PCB are discussed through a series of simulation examples.

Numerical Simulation for Surface Modification of Thermal Barrier Coatings by High-Current Pulse Electron Beam

High current pulsed electron beam is an effective technique for surface sealing of ceramic thermal barrier coatings prepared by electron beam physical vapor deposition. Due to the rapid remelting and solidification, the outer layers of ceramic coatings become smooth and dense, and the protective performance for turbine blades is effectively improved. Because of the complex multi-layered structures in the coatings, a high-current pulsed electron beam treatment requires specific parameter inputs which are related to the temperature field induced by electron energy deposition in the coatings. In this paper, a two-dimensional temperature simulation was performed to demonstrate the melting depth and temperature evolution in ceramic coatings treated by high-current pulsed electron beam. Different energy densities and pulses were studied and discussed for obtaining optimized parameters.

Mesostructured Assemblies of Ultrathin Superlong Tellurium Nanowires and Their Photoconductivity

Well-defined periodic mesostructures of hydrophilic ultrathin Te nanowires with aspect ratios of at least 10(4) can be produced by the Langmuir-Blodgett technique without any extra hydrophobic pretreatment or functionalization. Packing the arrayed nanowire monolayers will allow construction of nanomesh-like mesostructures or more complex multilayered structures composed of ultrathin nanowires on a planar substrate. The well-organized monolayer of Te nanowires with periodic mesostructures can be readily used as a stamp to transfer such mesostructured nanopatterns to other substrates or can be embedded within a polymer matrix. The mesostructures of ultrathin Te nanowire films show reversibly switched photoelectric properties between the lower- and higher-conductivity states when the light is off and on, and the photocurrent is influenced by the light intensity and the number of mesostructured nanowire monolayer films. This method can be extended for fabrication of other mesostructured assemblies of ultrathin nanowires or nanotubes.

A Novel Actuator for Simulation of Epidural Anesthesia and Other Needle Insertion Procedures

When navigating a needle from skin to epidural space, a skilled clinician maintains a mental model of the anatomy and uses the various forms of haptic and visual feedback to track the location of the needle tip. Simulating the procedure requires an actuator that can produce the feel of tissue layers even as the needle direction changes from the ideal path. A new actuator and algorithm architecture simulate forces associated with passing a needle through varying tissue layers. The actuator uses a set of cables to suspend a needle holder. The cables are wound onto spools controlled by brushless motors. An electromagnetic tracker is used to monitor the position of the needle tip. Novice and expert clinicians simulated epidural insertion with the simulator. Preliminary depth-time curves show that the user responds to changes in tissue properties as the needle is advanced. Some discrepancy in clinician response indicates that the feel of the simulator is sensitive to technique, thus perfect tissue property simulation has not been achieved. The new simulator is able to approximately reproduce properties of complex multilayer tissue structures, including fine-scale texture. Methods for improving fidelity of the simulation are identified.

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection.

Formation of Multilayer Ultrathin Assemblies Using Chemical Lithography

Ultrathin complex multilayer structures have many potential applications in molecular and organic electronics, sensing, biotechnology and other areas. Reported here is a method by which to construct multifunctional, multilayer, patterned structures, using alkanethiolate SAMs adsorbed on Au, UV photopatterning, and chemoselective covalent bond formation. We demonstrate that amide coupling is efficient for producing multilayer structures on -COOH-terminated SAMs, while oxime coupling is efficient for producing multilayer structures on -CHO-terminated SAMs. Reaction yields obtained are approximately 67% and approximately 84% for the coupling of the first layer (bilayer formation) for amide and oxime coupling, respectively. Subsequent adlayer formation occurs with approximately 100% yield in both cases. The resulting adlayers are chemically robust and are suitable for subsequent chemical processing. Finally, both chemistries are used to produce a complex multilayer structure atop a UV photopatterned SAM. The resulting construct is well-defined and has the same lateral resolution as the photopatterned SAM substrate. The method demonstrated here is synthetically flexible and allows for the assembly of functionally complex surfaces and, in principle, the incorporation of biomolecules and metals.

Hot-electron bolometer mixers for terahertz radiation

Hot-electron bolometer (HEB) mixers are used in many low noise heterodyne radio astronomical receivers. Their noise temperature is at the level of 10–15 times the quantum limit, and their gain bandwidth is from 2 GHz to slightly more than 5 GHz depending on the type of substrate material used for a device fabrication. The HEB mixers presented in this Letter are a complex multilayer thin-film structure containing an ultra-thin superconducting film of NbN as a detecting element, and a thick normal metal layer as an antenna structure. The overall performance of the device has been improved by optimisation of the HEB mixer fabrication steps starting with ultra-thin NbN films, followed by NbN/Au bi-layers for antenna structures. Patterning was achieved using electron-beam lithography and lift-off processes. The noise temperature of the HEB mixer fabricated with the improved technology is about 800 K, as measured in a cryogenic-free system with a quantum cascade laser as a local oscillator.