A Microporous Chitosan/Collagen Composite Encapsulated Small Tube of Nanoporous Anodic Aluminum Oxide for Long-Acting Drug Release

This study aims to develop a long-acting and implantable drug release device that can well control the release rate and concentration of the loaded drug. The proposed long-acting and implantable drug release device consists of a tubular nanoporous anodic aluminum oxide (AAO) and the microporous chitosan/collagen composite encapsulated inside it. The nanopore size of the AAO tube can be arranged by the anodization parameters to adjust the release rate and concentration, while the microporous chitosan/collagen composite can provide the device with a long-acting release property. Fabrication results indicated that the AAO tube has a uniform pore arrangement with pore size around 50 nm. And the synthesized microporous chitosan/collagen composites composites containing 90% of chitosan had the highest moisture content; therefore were used as the drug carriers. Release experiments demonstrate that the proposed long-acting drug release device had released only less than 60% of the loading drug at the 16th release day.

Fabrication of Plastic Micro-Channels for Microfluidics Solvent Extraction

In this work plastic micro channel systems were investigated as a potential device for micro solvent extraction of rare earth elements. The proposed microfluidic structures are made by laser welding of three layers of inexpensive thermoplastic films which form separate paths (top and bottom channels) for each of the immiscible fluids. The middle layer is perforated in order to provide contact between two fluids and to enable the extraction process. Experiments were performed to show that two different immiscible fluids (water and 1-octanol) can flow through the fabricated device and exit at separate outlets without mixing even when those fluids get into close contact within the main channel. Experimental results for single devices show that immiscible fluids can be brought into intimate contact and then separated with compliant polymeric microfluidic devices. The transfer of a compound from one immiscible fluid to the other was verified by dye exchange between the immiscible fluids. The same fabrication method is a promising technique for fabrication of massively parallel systems with larger throughput.

Anand Viscoplasticity Model for the Effect of Aging on Mechanical Behavior of SAC305 Operating at High Strain Rate and High Temperature

Portable products such as smartphones and tablets stay in the powered on condition for a majority of their operational life during which time the device internals are maintained at higher than ambient temperature. Thus, it would be expected for interconnects in portable products to be at a temperature high than room temperature when subjected to accidental drop or shock. Furthermore, electronics in missile-applications may be subjected to high strain rates after prolonged period of storage often at high temperature. Electronics systems including interconnects may experience high strain rates in the neighborhood of 1–100 per sec during operation at high temperature. However, the material properties of SAC305 leadfree solders at high strain rates and high operating temperatures are scarce after long-term storage. Furthermore, the solder interconnects in simulation of product drop are often modeled using elastic-plastic properties or linear elastic properties, neither of which accommodate the effect of operating temperature on the solder interconnect deformation at high operating temperature. SAC305 solders have been shown to demonstrate the significant degradation of mechanical properties including the tensile strength and the elastic modulus after exposure to high temperature storage for moderate periods of time. Previously, Anand’s viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components under thermo-mechanical deformation. Uniaxial stress-strain curves have been plotted over a wide range of strain rates (ε̇ = 10, 35, 50, 75 /sec) and temperatures (T = 25, 50, 75, 100, 125°C). Anand viscoplasticity constants have been calculated by non-linear fitting procedures. In addition, the accuracy of the extracted Anand constants has been evaluated by comparing the model prediction and experimental data.

Water Based Propellant for Cold Gas Thruster

Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) have produced ideas and techniques for creating new devices at the micro/nano scale. Nano/pico satellites have limited orientation capability partly due to the current state of microthruster devices. Development of a self-contained micro propulsion system would enable dynamic orbital maneuvering of pico- and nano-class satellites. The act of vaporizing a fluid via nanochannels to vacuum has not been studied and the limitations are unknown, but it could provide a novel method of propulsion for small satellites. However, solution properties are transient during vaporization which affects fluid flow. Thus, experiments have been designed to measure solution properties including density, evaporation rate, and vaporization pressure. A setup has been designed monitor the solution mass and volume inside a vacuum chamber. Evaporation of the solution is affected by the vacuum pressure, capillary tubing diameter, solution temperature, and solution concentration. When maintained at the solution vapor pressure, the vaporization rate has ranged from 0.003 to 0.025 grams per minute across the varying concentrations. Preliminary results have indicated some interesting trends regarding solution composition and vaporization rate. The results obtained from preliminary experiments will be used in conjunction with future experiments to determine the viability of nanochannels to be used in the small satellite propulsion system.

Multiphysics Model for Chlorine-Ion Related Corrosion in Cu-Al Wirebond Microelectronic Packages

The increasing price of gold has resulted in industry interest in use of copper as alternative wire bonds interconnect material. Copper wire has the advantages of the lower cost, lower thermal resistivity, lower electrical resistivity, higher mechanical strength and higher deformation stability over the gold wire. In spite of the upside above, the Cu-Al wire bond is susceptible to the electrolytic corrosion and the reliability of Cu-Al wire bond is of great concern. Typical electronic molding compounds are hydrophilic and absorb moisture when exposed to humid environmental conditions. EMC contain ionic contaminants including chloride ions as a result of the chemical synthesis of the subcomponents of the resin, etching of metallization and the decomposition of the die-attach glue. The presence of moisture in the operating environment of semiconductor package makes the ion more mobile in the EMC. The migration of chloride ions to the Cu-Al interface may induce electrolytic corrosion inside the package causing degradation of the bond interface resulting in eventual failure. The rate at which the corrosion happens in the microelectronic packages is dependent upon the rate at which the ions transport through the EMC in addition to the reaction rate at the interface. In this effort, a multiphysics model for galvanic corrosion in the presence of chloride has been presented. The contaminant diffusion along with the corrosion kinetics has been modeled. In addition, contaminated samples with known concentration of KCl contaminant have been subjected to the temperature humidity conditions of 130°C/100RH. The resistance of the Cu-Al interconnects in the PARR test have been monitored periodically using resistance spectroscopy. The diffusion coefficients of chloride ion has been measured in the electronic molding compound at various temperatures using two methods including diffusion cell and inductively coupled plasma (ICPMS). Moisture ingress into the EMC has been quantified through measurements of the weight gain in the EMC as a function of time. Tafel parameters including the open circuit potential and the slope of the polarization curve has been measured for both copper, aluminum under different concentrations of the ionic species and pH values in the EMC. The measurements have been incorporated into the COMSOL model to predict the corrosion current at the Cu-Al bond pad. The model predictions have been correlated with experimental data.

Convective Electronic Device Cooling Using Microencapsulated Phase Change Material Slurry in Planar Spiral Coil

The current trend in miniaturization of electronic devises requires more effective thermal management techniques to remove the heat to ensure the maximum performance of the devise. Among all available thermal management techniques for electronic cooling, convective heat transfer cooling has gained attentions due to low cost and maturity in the market. The single-phase convective heat removal technique suffers from the low heat carrying capacity since there is no phase change occurs during the process. On the other hand, Microencapsulated phase change materials (MPCMs) are gaining attention due to their high heat carrying capacity. MPCMs are composed of phase change material (PCM) as the core material that is encapsulated with micrometer size shell materials. The PCM inside the capsules may undergo a phase change as the temperature varies around the melting and freezing temperature points of the PCM. This leads to a significant heat gain/release due to the phase change of the PCM. In this paper, we are performing a numerical modeling on the performance of MPCMs mixed with single-phase base fluid when pumped through planar spiral coils. From electronic thermal management point of view, it is ideal to have an enhanced coolant that maintain the operating temperature under an allowable level uniformly. The behavior of MPCM slurry when pumped through planar spiral coils reveals unique patterns due to the centrifugal forces. The available data on MPCM slurry through spiral coil heat exchangers show the new patterns of velocity and heat transfer curves that require further investigation and scientific explanations. The current paper studies the steady conditions of flows under laminar regimes at different boundary conditions. A CAD model of a planar coil heat exchanger is developed in SolidWorks. The model is meshed and discretized in order to apply the governing equations into the model. ANSYS Fluent package is used to solve the fluid flow and heat transfer equations inside the geometry. The velocity and temperature profiles along the coil are studied and discussed to quantify the roles of different forces in such flows. The ultimate goal of this study to evaluate the efficacy of utilizing such formulated microencapsulated PCM slurry at different mass concentrations on electronic thermal management considering the cost associated to the added pressure drop when using MPCM slurry.

Design of Centrally Supported Biomimetic MEMS Microphone for Acoustic Source Localization

Biologically inspired unique perforated diaphragm architecture for acoustic source localization has been designed. The merely 500 μm separated structure of ears of fly Ormia ochracea which increases the interaural time and intensity differences of arriving sound has great ability to enhance the acoustic source localization. This remarkable capacity of fly to amplify direction cues for incoming sound along with squeeze film damping effects are the key inspirations for designing the diaphragm. In this design, we maintain a unique ratio between the number of holes and the diaphragm size and enhanced the acoustic directional sensitivity cues. A mechanical structure based on the ears of fly Ormia ochracea is modeled and the response is observed on different frequencies by considering the critical damping value and also on zero damping value. In one step further a perforated diaphragm is designed utilizing ANSYS software and is examined with fluid elements to estimate the damping value. A harmonic analysis is carried out in conjunction with estimated damping value 0.3325 and also on zero damping value. The figured results are very much similar to the modeled results and a range of 1 nm to 472 nm amplitude differences between two sides of the diaphragm is observed over the entire range of the frequency in damping case.

Enhanced Light Absorption in Thin Crystalline Silicon Solar Cells With Silica Nanoparticles

In this paper, numerical simulations are performed to investigate the effects of different configurations of dielectric SiO2 particles on the improvement of light absorption in 2-μm single crystal silicon photovoltaic solar cells. The numerical model is developed on the basis of the FDTD solution of the transient Maxwell equations and checked with analytical solutions for simple configurations and against experimental measurements of light absorption in bare Si films. The numerical model is also checked for mesh sensitivity such that the computed data are approximately mesh-insensitive. Computed results are analyzed and the short circuit current of the Si films is used as a measure of the efficiency for light trapping in Si films. Results show that with SiO2 nanoparticles closely packed atop the Si film, good improvement in light absorption efficiency is achieved if the particle is 700 nm in diameter. This is considered to be attributed to the anti-reflection effect of the particle layer and the whispering gallery mode of SiO2 particles excited by the incident light. If the closely arranged SiO2 nanoparticles are embedded half-way into a Si film through its top surface, the light absorption is enhanced by ∼120%, approaching to the Yablonovitch limit. The structured surface of the Si film can almost realize 100% anti-reflection of incident, because the use of the half embedded SiO2 particles in the top layer of the Si film creates a graded transition of the effective refractive index along the direction of incident; and as a result almost all the light with the wavelength below or near 500nm are absorbed due to the higher imaginary part of the refractive index. The improvement in light absorption with the wavelength greater than 500nm comes, however, from the resonance behavior of the SiO2 nanoparticles. Experiments are now planned and measurements of light absorption will be conducted with a photospectrometer to validate the above calculations.

Measurement of Leadframe Strain in Electrically Active Power Semiconductors

In this work, thermal-mechanical leadframe strain in an electrically active IGBT was measured using electronic speckle pattern interferometry (ESPI). ESPI is a non-contact optical technique capable of high resolution surface displacement measurements. The significant contribution of this paper is an experimental methodology by which strain can be measured in electrically active devices. A 3-D ESPI test stand was developed, combining two cameras to simultaneously capture the local (interconnect level) and global (device level) displacements. Through the combination of incremental sub-loads and mathematical recorrelation of speckle patterns, device power loads have been measured (which would have been otherwise impossible due to speckle decorrelation, which limits measurement of large deformations). A model-based tracking technique was developed from coupled experimental noise measurements and FE modeling — allowing for optimal strain solution to be extracted from noisy displacement results. The developed and experimentally-validated thermal-mechanical FE strain model agreed to within 7% of ESPI strain measurements.

Reduction of Nanowire Agglomeration via an Intermediate Membrane in Nanowires Preparation for Nanosensors Application

Nanowires are widely used as sensing components for lab-on-a-chip devices. One major problem in utilizing pre-grown nanowires in lab-on-a-chip applications is the agglomeration of nanowires during their preparation process. The common methods to reduce the agglomeration of nanowires include stirring, sonication and using of surfactants. However, these methods break the long nanowires and are not efficient to produce enough single nanowires. This paper shows a new method to improve the deposition process of individual nanowires. An intermediate membrane was used for the deposition of the nanowires after their preparation process. The membrane helps to filter the nanowire agglomerates and to deposit separated individual nanowires over a silicon surface underneath. The study also shows that the number of single nanowires is increased by increasing the tilt angle of the membrane. The method also helps achieving single long nanowires.