Sameh Dardona

In situ spectroscopic ellipsometry studies of trivalent chromium coating on aluminum

In situ spectroscopic ellipsometry in the spectral region of 1.3–4.3 eV has been employed to monitor, in real-time, the formation of trivalent Cr process (TCP) conversion coatings on polished Al substrates. The measured ellipsometry parameters (Ψ and Δ), as a function of immersion time, reveal that the initial stages of film formation include the chemical thinning of the native oxide layer, formation of a very thin initiation layer and the subsequent rapid formation of the TCP film. The film optical constant is modeled using Cauchy dispersion relation and its thickness was determined as a function of immersion time during growth.

Polarization Controlled Kinetics and Composition of Trivalent Chromium Coatings on Aluminum

Combined in situ spectroscopic ellipsometry and electrochemistry have been employed to monitor, in real-time, the formation of trivalent Cr conversion coatings on polished Al substrates at applied sample potentials. It is found that the formation kinetics and chemical composition of the film can be controlled by adjusting the anodic and cathodic reactions. The growth kinetics are accelerated at more positive anodic potentials or more negative cathodic potentials. At more negative potentials, the percentage of chromium in the coating is found to increase, while the zirconium percentage decreases.

Modeling and characterization of partially inserted electrical connector faults

Faults within electrical connectors are prominent in avionics systems due to improper installation, corrosion, aging, and strained harnesses. These faults usually start off as undetectable with existing inspection techniques and increase in magnitude during the component lifetime. Detection and modeling of these faults are significantly more challenging than hard failures such as open and short circuits. Hence, enabling the capability to locate and characterize the precursors of these faults is critical for timely preventive maintenance and mitigation well before hard failures occur. In this paper, an electrical connector model based on a two-level nonlinear least squares approach is proposed. The connector is first characterized as a transmission line, broken into key components such as the pin, socket, and connector halves. Then, the fact that the resonance frequencies of the connector shift as insertion depth changes from a fully inserted to a barely touching contact is exploited. The model precisely c...

Direct write of copper-graphene composite using micro-cold spray

Direct write of a new class of composite materials containing copper and graphene in the powder phase is described. The composite was synthesized using batch electroless plating of copper for various times onto Nano Graphene Platelets (NGP) to control the amount of copper deposited within the loosely aggregated graphene powder. Copper deposition was confirmed by both Focused Ion Beam (FIB) and Auger electron spectroscopic analysis. A micro-cold spray technique was used to deposit traces that are ∼230 μm wide and ∼5 μm thick of the formulated copper/graphene powder onto a glass substrate. The deposited traces were found to have good adhesion to the substrate with ∼65x the copper bulk resistivity.

Physics based modeling of connectors faults

In this paper, a physics based connector model that consists of coaxial lines with different characteristic impedances and lengths is proposed. Method of Moments (MoM) analysis was performed using commercial electromagnetic simulation software, FEKO, for transverse electric and magnetic (TEM) wave propagation through the connector to optimize its physical parameters to fit its measured S parameters.

Modeling of partially inserted connector faults

A partially inserted electrical connector model based on a two-level nonlinear least squares (NLS) approach is proposed. The connector is characterized as a transmission line, broken into sections. The model precisely captures resonant frequency shifts as insertion depth changes from a fully inserted to a barely touching contact by varying only two length parameters.

Connector fault interrogation using UWB sources

A diagnostic method for detection and identification of precursors to partially inserted connector faults is presented. The proposed method shows that a miniaturized device including an UWB source and a mini spectrum analyzer can be employed as a small and low cost alternative to a large and expensive network analyzer to measure the response and resonant frequency shifts of a connector with a partially inserted pin-socket contact. The results are consistent with network analyzer measurements and demonstrate that a miniaturized device can be integrated into a connector harness for detection of fault precursors.