Search

Different types of surfactants; nonionic, anionic and cationic represented by Polyoxyethylene sorbitan monooleate (Tween 80), sodium dodecyl sulfate (SDS), and cetyltrimethylammonium bromide (CTAB) respectively were used to select a proper type of surfactant enhancing dispersion quality of multiwall carbon nanotubes (MWCNTs) in the epoxy resin. Hereinafter, the effect of one of the most severe space environment threats which are an electron beam on the candidate material used as a structural space material. The candidate material is characterized by furrier transformation infrared spectroscopy (FTIR), mechanical properties, surface tension, and electrical dispersion measurement. The mechanical results revealed that the strength increases by 10% while adding the CTAB surfactant, while decreases by 27% and 32% by adding tween-80 and SDS respectively. The anionic surfactant SDS, despite keeping the stiffness the reference sample it is the lower strength and elongation. The CTAB improves the mechanical properties by improving the strength and stiffness while elongation is significantly decreased by adding any of the surfactants. The surface tension of Tween 80 and anionic surfactant; SDS,  = 24.4 mN/m while the surface tension in case of the CTAB is  = 25.4 mN/m. Surface tension and electrical dispersion measurement results reveal that the nonionic surfactant Tween 80 led to a uniform dispersion of MWCNTs in the epoxy than other surfactants. The effect of 100-kGy irradiation via electron beam on the structure and its electrical properties of the epoxy composites was studied. Improving the dispersion quality of the MWCNTs in epoxy nanocomposites materials for spacecraft structure occurred.

Electrical cell-substrate impedance sensing (ECIS) is a powerful technique to monitor real-time cell behavior. In this study, an ECIS biosensor formed using two interdigitated electrode structures (IDEs) was used to monitor cell behavior and its response to toxicants. Three different sensors with varied electrode spacing were first modeled using COMSOL Multiphysics and then fabricated and tested. The silver/silver chloride IDEs were fabricated using a screen-printing technique and incorporated with polydimethylsiloxane (PDMS) cell culture wells. To study the effectiveness of the biosensor, A549 lung carcinoma cells were seeded in the culture wells together with collagen as an extracellular matrix (ECM) to promote cell attachment on electrodes. A549 cells were cultured in the chambers and impedance measurements were taken at 12-h intervals for 120 h. Cell index (CI) for both designs were calculated from the impedance measurement and plotted in comparison with the growth profile of the cells in T-flasks. To verify that the ECIS biosensor can also be used to study cell response to toxicants, the A549 cells were also treated with anti-cancer drug, paclitaxel, and its responses were monitored over 5 days. Both simulation and experimental results show better sensitivity for smaller spacing between electrodes. Graphical abstract The fabricated impedance biosensor used screen-printed silver/silver chloride IDEs. Simulation and experimental results show better sensitivity for smaller between electrodes.

Quartz Crystal Microbalance (QCM) is a mass detection sensor capable of measuring mass sensitivity at nanogram levels when based on a thickness shear mode piezoelectric crystal set at high frequencies. These sensors detect with high accuracy while benefiting from simple geometry, low costs, and ease of fabrication. Researchers prefer piezoelectric crystal sensors to the recent methods of gas chromatography/mass chromatography (GC/MC), high pressure liquid chromatography and nuclear magnetic resonance (NMR), which are time-consuming and not cost-effective. Unlike conventional QCM sensors that are limited to a single-electrode structure—which minimizes their scope of detection—the Multichannel QCM (MQCM) incorporates multiple sensors fabricated on a single crystal wafer. Each sensor is selectively coated with a sensing material that promotes the adsorption of target vapours. One of the widely used application of QCM sensors is in Volatile Organic Compounds (VOC) detection. This paper imparts a critical overview of recent publications on the application of MQCMs with various sensing materials.

The effect of gamma irradiation on the optical and electrical properties of the reinforced fiber polymeric based materials became an important issue. Fiberglass/epoxy and Kevlar fiber/epoxy were selected as investigated samples manufactured with hand lay-up without autoclave curing technique. The selected technique is simple and low cost while being rarely used in space materials production. The electric conductivity and dielectric constant for those samples were measured with increasing the gamma radiation dose. Moreover, the absorptivity, band gap and color change were determined. Fourier transform infrared (FTIR) was performed to each of the material's constituent to evaluate the change in the investigated materials due to radiation exposure dose. In this study, the change of electrical properties for both investigated materials showed a slight variation of the test parameters with respect to the gamma dose increase; this variation is placed in the insulators rang. The tested samples showed an insulator stable behavior during the test period. The change of optical properties for both composite specimens showed the maximum absorptivity at the gamma dose 750 kGy. These materials are suitable for structure materials and thermal control for orbital life less than 7 years. In addition, the transparency of epoxy matrix was degraded. However, there is no color change for either Kevlar fiber or fiberglass.

Quartz Crystal Microbalance (QCM) is a device that allows non-destructive measurements of r in situ reaction activities. In this article, an array comprising of six 3MHz QCM sensors in an array were characterized using a vector network analyzer and OpenQCM, a portable measuring instrument that measures change in resonance frequency. Measurements of S21 transmission characteristics using the vector network analyzer provides the resonance frequency and can also be used to derive the RLC equivalent electrical circuit values of a resonant two-port network based on the Butterworth-Van Dyke model. In this work, Rm, Lm, Cm and Co were obtained via curve-fitting of the measurement results to the simulated results. Measurements were done in triplicates to verify reproducibility for all 6 sensors. For comparison, measurements were also done using a portable, open-source instrument, OpenQCM. The OpenQCM instrument directly measures changes in resonance frequencies, making it ideal for biosensing experiments, which correlate changes in mass with changes in resonance frequencies. Comparison between resonance frequency measurements using VNA and OpenQCM exhibit low percentage difference 0.2%. This QCM sensor array has the potential of conducting real-time, point-of-care analyses for detection of biological molecules.

This paper reported a passive Q-switched erbium doped fiber laser (EDFL) using two-dimensional (2D) material of black phosphorus saturable absorber (BP-SA). The maximum output power reached is 3.54 mW, which is generated by pump power of 42.327 mW. The results show that, a stable pulse was generated with repetition rate starts at about 9.606 kHz and ends at about 44.72 kHz, and very narrow pulse width between 40.01 μs and 9.84 μs and pulse energy 80 nJ. Clearly, the stability of the Q-switched pulse train was achieved because the BP-SA film was inserted in the laser ring cavity.

In the vacuum deep space, outgassing has contributed to degraded mechanical performance of composite materials used in spacecraft. Three types of polymer based material we concerned on this study epoxy resin with carbon fiber, glass fiber, and Kevlar, which manufactured by hand lay-up method without autoclave curing which is a commercial method with low cost production. These materials have been widely used in satellite structures. The forth material is polyamide which is a commercial thin sheet layer used in multilayer insulation for spacecraft protection against space environment. The advantages of these materials considered as their high specific stiffness, near–zero coefficients of thermal expansion (CTE) and dimensional stabilities make them uniquely suited for applications in low specific weight environment.The materials screening and selection will be discussed according to the total mass loss, the dimensions stability, and collected volatile condensed materials resulted from outgassing test for the different materials types.

Rapid development in technology and society has generated diverse developments in many fields including biosensors in healthcare application. Here, the design of integrated biosensor comprises mass sensing (Quartz Crystal Microbalance) and electrochemistry sensing (Electrochemical Impedance Spectroscopy, EIS and Cyclic Voltammetry, CV) will be presented. The integrated sensor system is developed based on the innovative use of the top electrode of a quartz crystal microbalance (QCM) resonator as a working electrode for the electrochemistry technique. Integration of QCM with the electrochemistry technique is realized by fabricating a semicircular counter electrode near the upper electrode on the same side of the quartz crystal. CV and EIS measurement was conducted using finite element modeling, COMSOL™ 5.2 with the probe marker of 1 mmol L−1 of [Fe(CN) 6 ]3-/4- CV test was done to study the effect between increasing scan rate and peak current (anodic and cathodic) in observing the reversible electrochemical process. This observation is crucial in ensuring the electrochemical processes follow the Randles-Sevcik equation in characterizing the platform changes behavior. Later, EIS test was performed in order to measure the radius of the semicircle which reflects the charge transfer resistance (RCT) of the redox marker. To show the effectiveness of this sensor, gold immobilization surface was electrochemically simulated and reported. Thus, an ultra-sensitive biosensor that capable to produce multi-analysis in the detection of biological targets in terms of electrochemical change of electrode interfaces, which is the crucial step towards the engineering of advanced bioelectronics.

Modeling of Iron metal diffusion in liquid lead using molecular dynamics simulation has been done. Molecular dynamics simulations are used to predict the value of physical quantities that we want to know based on the designed material model and on the input simulation data. In this research, effect of different geometry of material models was observed to know the diffusion coefficient. The material system was iron (Fe) in liquid lead (Pb). The material models is designed using Packmol software to get the initial configuration of atom's arrangement by inputting the material's characteristics such as mass, density, volume, number of atoms. This work examines the diffusion coefficient of iron in molten lead metal with the geometric shape of the simulation system in the form of iron in molten metal for various simulation models of boxes in a box, balls in a box and balls in balls. To design simulated geometric shapes we use the Packmol program. To calculate the diffusion coefficient we use the molecular dynamics simulation method. To find out which geometry is suitable, we compare the diffusion coefficient of the simulation results with existing references. The diffusion coefficient value of the spherical iron (Fe) system in the spherical liquid lead (Pb) has the best value compared to the other two forms with an accuracy rate of 99.94% because it is influenced by the even distribution of atoms in each part.

The main objective of this article is to demonstrate by performing simulation measurements of biosensor that can detect the presence of pathogens through simultaneous mass and impedance techniques. This biosensor merges two biosensing techniques namely resonant frequency measurements and electrochemical impedance spectroscopy (EIS) on a single biosensor. Parallel measurements provide better sensitivities, have higher diagnostics accuracy and reduce the risk of false positives. Low cost, high resolution screen printing technology was used to fabricate the microelectromechanical array of μTAS on flexible piezoelectric substrates. The basic biosensor framework includes a substrate that highly sensitive sensor like thickness shear mode and immunosensor can be fabricated using quartz crystal lattice that integrated with electrochemical sensor [1]. The quartz crystal microbalance is a label free technique, which minimizes interference with the interaction being studied. A piezoelectric device is portable, simple and cost effective, and is suitable for real-time monitoring of biospecific interactions such as antigen-antibody, receptor ligand, and enzymes-substrate interactions with high sensitivity and specificity. For instance, the biological mixtures such as antibodies are capable of binding to terminal active functional groups (i.e., COOH, OH and NH2) of self-assembled monolayers (SAM) and immunocapture antigens such as glycoproptien or other targets[2]. The QCM can consequently detect mass changes due to these molecular interactions on the surface of the QCM. The top and bottom circular excitation electrodes with 150um diameter were modeled as gold (Au) films of 16 μm thickness. A sinusoidal voltage with amplitude of 5 mV was applied across the quartz crystal. Figure 1 shows the principle of integrated biosensors which gold electrodes were printed on both sides of a thin 500um quartz layer to form the quartz crystal microbalance (QCM)-impedance device. The silver (Ag) semicircular counter electrode was modeled around the top working electrode on the same area of the quartz crystal for performing the electrochemical impedance spectroscopy (EIS) experiments for detection of bacteria (E-Coli) and the results were compared to quartz crystal microbalance measurements. Furthermore, the use of gold surface can be incorporated into the transducer compatible with the biological samples such as use of highly specific monoclonal antibodies, and incorporation of amplification step to maximize the signal detection. In general, the quartz crystal is traditionally considered to be a mass sensitive sensor that produces response which it changes its resonance frequency to different thin film samples or liquids in contact with it surface. For a straight relationship between a thin film mass of the order of nanograms, the quartz crystal response will be of of the order of Hertz according to Eq. 1, Sauerbrey Equation [3]. ρq and μq are the specific density and the shear modulus in quartz, respectively. ϝ0 is the fundamental resonance frequency in quartz, related to its thickness, nq. Δm is the thin film mass deposited A, is the piezoelectrically active crystal area and n is the overtone number. Based on Eq. 1, it can be found that if the density of QCM changes, the resonant frequency of the device also changes, making the QCM suitable for monitoring changes in mass. In contact with liquids, the crystal is capable of giving information about the density-viscosity product (√ρn) of the fluid by changing its resonance frequency and quality Q-factor according with Eq.3, Kanazawa equation[3]: Where ρL and ηL are the density and viscosity in fluid respectively. Whilst, Eq. 4 indicates the decay characteristic length (δ) as linear relationship to the ratio viscosity to density of the liquid and inversely proportional the angular frequency (ω). Prior to device fabrication, 3D electric field analysis, resonant frequency simulations and thickness shear deformation were performed using automatic meshers by COMSOL Multiphysics. The resonator was modeled in three dimensions (3D), as an AT-cut quartz substrate of 500 μm thickness. The eigenfrequency analysis was performed to produce the quartz surface displacement and thickness shear deformation. The frequency domain analysis was conducted to obtain the resonant frequency of the resonator. Here we have tested the performance of the application of biosensors mainly in the detection of E-coli bacteria using QCM-impedance device using Escherichia coli cells as model of detection. Both frequency and impedance measurements were successfully obtained using cells both in media and in distilled water. We believe than this work offers a promising solution for the next generation of healthcare devices where high accuracy results are provided by low cost sensors.

Polymeric composites are widely used in manufacturing the space structures because of their superior light weight compared with either the metallic ferrous or non-ferrous materials. These materials should secure high strength to weight ratio and reasonable thermal and/or optical properties. In this work, the selected polymeric matrix composites reinforced with three different types of fibers, namely, carbon, fiberglass, and Kevlar were manufactured with the low-cost hand lay-up method. These samples were irradiated with different doses of γ-rays. These prescribed doses were chosen to simulate the charged particles space hazards in a well-defined orbit for 3.75, 5.625, and 7.5 years. Gases trapped during the manufacturing process were extracted and analyzed using the vacuum simulator facility at relatively high temperature to evaluate their effect on the optical surfaces. Mechanical properties variation of the irradiated composites was traced by tensile testing and correlated to the variation of their constituents’ molecular structure which was analyzed by the Fourier Transformation Infrared (FTIR) spectroscopy. Thermal stability of the irradiated composites constituents, with the previously prescribed doses, was monitored at a wide range of temperatures.

This paper reported a passive Q-switched erbium doped fiber laser (EDFL) using two-dimensional (2D) material of black phosphorus saturable absorber (BP-SA). The maximum output power reached is 3.54 mW, which is generated by pump power of 42.327 mW. The results show that a stable pulse was generated with repetition rate starts at about 9.606 kHz and ends at about 44.72 kHz and very narrow pulse width between 40.01 µs and 9.84 µs and pulse energy 80 nJ. Clearly, the stability of the Q-switched pulse train was achieved because the BP-SA film was inserted in the laser ring cavity.

This paper demonstrates the feasibility of a novel fabrication approach of MEMS resonators above standard CMOS circuitry and with zero-level vacuum package. As a proof of concept a monolithical CMOS-MEMS-closed loop oscillator showing dual-clock capabilities (11.9 MHz and 24.5 MHz) is presented. These two frequencies correspond to two different resonator modes, specifically the torsional and vertical out of plane, of a paddle shaped MEMS resonator.

This paper presents a newly developed flexible Polydimethylsiloxane (PDMS)-Copper (CU) patch antenna. The circular-shaped antenna consists of a 21.28mm radial size Cu patch embedded on a PDMS square substrate. PDMS has a low loss tangent of 0.004 and a relative permittivity of 2.74 that will enhance the RF parameters of the flexible antenna. There are three layers of material used to build the antenna. The first and the third layers are made from Cu tape and function as the ground and patch respectively. Meanwhile, the sandwiched layer is the PDMS substrate. However, several limitations of the antenna were observed, including low adhesiveness between layers, which made it impossible to perform metal and dielectric depositions. Thus, a thin layer of PDMS has been built on top of a patch layer to increase the adhesive strength between the copper patch and the PDMS substrate. The paper also discussed the return loss of the antenna with and without sandwich in planar, bending in x-axis and y-axis. The measurements using a vector network analyzer (VNA) demonstrated that the sandwich antenna can resonate at 2.33GHz with a low return loss of 42dB. The work is a proof of the principle that the PDMS substrate can be proposed as a good substrate for antenna in conformal applications.

The polyimide performance was monitored and evaluated after exposure to ionized and particulate radiation as a space hazard. The material was irradiated with three different doses 500, 750 and 1000kGy in CO60 source in the presence of air. Both non-irradiated and irradiated materials were characterized by tensile test, Thermo-Gravimetric Analysis (TGA) and Fourier Transform Infra-Red (FTIR). Quantum modeling was executed by using "Gaussian 5" software program for chemical structure verification. The non-irradiated material showed a super ductility but revealed a brittle behavior when irradiated with 500 and 1000 kGy gamma doses. Nevertheless, the material attained moderate ductility when exposed to 750kGy. Results by the stated characterization tools matched with the evaluated behavior and confirmed by the quantum modeling.

This paper presents use of the simple cantilever beam as RF CMOS-MEMS resonator, which can be scaled like transistor with improved performance. This resonator can be used in the oscillator and filter part of RF transceiver, which can actually be fabricated on chip without losing its Q-factor. The cantilever beam resonator was designed using COMSOL4.3b™ and produce resonance frequency at 10.2MHz, pull-in voltage at 1.5V and Q of 10000.

To date, there have been interests in designing the Micro-Electro-Mechanical System (MEMS) integrated with Complementary Metal-Oxide Semiconductor (CMOS) resonator for RF integrated circuits. This work presents the design of Clamped-Clamped (CC) and Clamped-Free (CF) beam resonators. These resonators provide on-chip low cost solutions for devices with much reduced chip area, besides having considerably reduced insertion losses due to nonexistent external bond wires. They can be integrated with amplifiers to form oscillators for generating clocks in the 2MHz and 20MHz range. The resonators require DC voltage maximally 10V for Clamped-Clamped and 7V for Clamped-free and 100mV AC voltage to electrostatically actuate the resonator's beams. The actuation is simulated and measured using Finite Element modeling software of COMSOL to obtain optimum design parameters. This paper makes a comparative review of different models for evaluating the designed resonator's performance in terms of resonance frequency under given pull-in voltage, and appropriate displacement.