Hamidreza Alemohammad

Morphology and microstructure analysis of nano-silver thin films deposited by laser-assisted maskless microdeposition

In this paper, the morphology and microstructure of silver micro-lines fabricated by laser-assisted maskless microdeposition (LAMM) are investigated. In LAMM technology, suspensions of silver nano-particles are used for layer-by-layer deposition and laser post-sintering. One of the major issues in LAMM is the large number of parameters involved in the process, which in turn results in a challenging process optimization. To address this issue, a design of experiments (DOE) method is used. The topography of the sintered samples was investigated using scanning electron microscopy (SEM) and white light interferometry. The results of DOE show that the deposition flow rate and the deposition scanning speed can significantly affect the width of the fabricated patterns, while the deposition thickness is mostly affected by the laser power and the number of deposited layers. In the microstructural analysis, it is observed that high laser effective energies can increase the densification of the sintered layers, in which the particles are closely packed. This is also evident from the level of electrical conductivity of the sintered samples. It is shown that the conductivity of the sintered samples is increased up to 2 × 105 S m−1 by raising the laser effective energy density to 2.5 × 106 J m−3. In addition, the results of mechanical tests, performed by a nanoindentation instrument, give a hardness of 0.8 GPa and Youngs modulus of 50 GPa for the samples.

Metal Embedded Optical Fiber Sensors: Laser-Based Layered Manufacturing Procedures

This paper describes laser-based layered manufacturing processes for embedding optical fiber Bragg gratings (FBGs) in metal structures to develop cutting tools with embedded sensors. FBG is a type of optical fiber that is used for the measurement of parameters manifesting as the changes of strain or temperature. The unique features of FBGs have encouraged their widespread use in structural measurements, failure diagnostics, thermal measurements, pressure monitoring, etc. Considering the unique features of FBGs, embedding of the sensors in metal parts for in-situ load monitoring is a cutting-edge research topic with a variety of applications in machining tools, aerospace, and automotive industries. The metal embedding process is a challenging task, as the thermal decay of UV-written gratings can start at a temperature of � 200 � C and accelerates at higher temperatures. The embedding process described in this paper consists of low temperature laser microdeposition of on-fiber silver thin films followed by nickel electroplating in a steel part. A microscale laser-based direct write (DW) method, called laser-assisted maskless microdeposition (LAMM), is employed to deposit silver thin films on optical fibers. To attain thin films with optimum quality, a characterization scheme is designed to study the geometrical, mechanical, and microstructural properties of the thin films in terms of the LAMM process parameters. To realize the application of embedded FBG sensors in machining tools, the electroplating process is followed by the deposition of a layer of tungsten carbide-cobalt (WC-Co) by using laser solid freeform fabrication (LSFF). An optomechanical model is also developed to predict the optical response of the embedded FBGs. The performance of the embedded sensor is evaluated in a thermal cycle. The results show that the sensor attains its linear behavior after embedding. Microscopic analysis of the tool with the embedded sensor clearly exhibits the integrity of the deposited layers without cracks, porosity, and delamination. [DOI: 10.1115/1.4004203]

Simultaneous measurement of temperature and tensile loading using superstructure FBGs developed by laser direct writing of periodic on-fiber metallic films

This paper addresses the development of superstructure fiber Bragg gratings (FBGs) by laser-assisted direct writing of on-fiber metallic films. A novel laser direct write method is characterized to fabricate periodic films of silver nanoparticles on the non-planar surface of as-fabricated FBGs. Silver films with a thickness of 9 μm are fabricated around a Bragg grating optical fiber. The performance of the superstructure FBG is studied by applying temperature and tensile stress on the fiber. An opto-mechanical model is also developed to predict the optical response of the synthesized superstructure FBG under thermal and structural loadings. The results show that the reflectivity of sidebands in the reflection spectrum can be tuned up to 20% and 37% under thermal and structural loadings, respectively. In addition, the developed superstructure FBG is used for simultaneous measurement of force and temperature to eliminate the inherent limitation of regular FBGs in multi-parameter sensing. (Some figures in this article are in colour only in the electronic version)

Femtosecond laser micromachining of fibre Bragg gratings for simultaneous measurement of temperature and concentration of liquids

This paper is concerned with micromachining of optical fibre Bragg gratings (FBGs) using a femtosecond pulsed laser. The purpose of this work is to increase the sensitivity of FBGs for simultaneous monitoring of the concentration of chemicals and biological liquids and their temperature. A Ti : sapphire regenerative amplifier was utilized to inscribe micro-grooves with widths of 16 and 22 mu m in the cladding of the optical fibres. Due to the core-confined light propagation characteristics of FBGs, their sensitivity to the changes in the index of refraction of the surrounding medium is minimal. However, by creating micro-grooves in the cladding layer, the index of refraction of the surrounding medium becomes effective in the coupling of the propagating core modes. As the index of refraction of liquids depends on the composition and concentration, the FBG with micromachined cladding can provide enough sensitivity to be used in chemical sensing. The performance of the micromachined FBGs was investigated by immersing them in different liquid solutions of polyvinyl butyral (PVB) in ethanol and obtaining their thermal responses. Results showed that the optical response of the micromachined FBGs (i.e. red shift in Bragg wavelength) is different by up to 10% in PVB solutions in ethanol than in ethanol alone. The micromachined FBGs can be used to monitor the concentration as well as the temperature of a solution.

Laser-assisted surface patterning of magnesium with silver nanoparticles: synthesis, characterization and modelling

Surface patterning of biocompatible materials may improve cell adhesion, infiltration and proliferation. Magnesium is a biocompatible metal which has bioresorption capability, as well as a low elastic modulus. This unique combination of properties has attracted researchers to develop biodegradable magnesium devices. In this work, the patterning of magnesium with silver nanoparticles printed by the laser-assisted maskless microdeposition (LAMM) process was studied. The geometry and microstructure of the printed silver patterns and the diffusion zone at the Mg/Ag interface were studied using profilometry, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The TEM analysis suggested that some intermetallic particles may form at the interface during laser sintering. The penetration curve of the Ag–Mg diffusion couple was obtained using EDS analysis. A finite element model is developed to simulate the LAMM process of silver nanoparticles on magnesium substrates. The model included a thermal analysis for determining the temperature history throughout the process, coupled with a diffusion model for evaluating compositional profiles across the interface. A comparison of the predicted profiles with the EDS results showed that the modelling and the experimental results qualitatively match. The analysis of SEM micrographs of the sintered nanoparticles, in light of the thermal modelling results, suggested that a minimum laser heat input was required for effective sintering of the nanoparticles.

Modeling and Analysis of Fiber Optic Bragg Grating Shape Sensors

The present work aims at modeling of fiber Bragg gratings (FBG) used as shape sensors. FBGs, which are commonly used for sensing physical parameters (e.g., strain, temperature, pressure), can be effectively used for shape detection in flexible bodies. They can be embedded in flexible structures for in-situ measurement of curvature. In order to design the embedded sensors and identify the spectral response of FBG, the effects of different geometrical and structural parameters on the optical response of the fiber should be investigated. In this paper, an opto-mechanical model is developed to assess the shape detection with FBGs. In the proposed model, non-symmetric coating of optical fibers with metallic materials is investigated. The model is a combination of structural and optical analyses; the structural analysis is used to find the change in optical properties of the sensor due to photo-elastic effect and the optical analysis is conducted to find the spectral response of FBG. It is shown that the non-symmetric coating can increase the sensitivity of the sensor. While the bare sensor shows little sensitivity to the curvature, the sensitivity increases with non-symmetric coating.© 2007 ASME

Sintering Characterizations of Ag-Nano Film on Silicon Substrate

Nowadays, thin films have many applications in every field. So, in order to improve the performance of thin film devices, it is necessary to characterize their mechanical as well as electrical properties. In this research work we focus on the development of a model for the analysis of the mechanical and electrical properties of silver nanoparticles deposited on silicon substrates. The model consists of inter-particle diffusion modeling and finite element analysis. In this study, through the simulation of the sintering process, it is shown that how the geometry, density, and electrical resistance of the thin film layer are changed with sintering conditions. The model is also used to approximate the values of the film Youngs modulus. Comparing results with experimental results shows the high accuracy of this approach.

Dual-parameter optical fiber sensors for structural health monitoring

The development of dual-parameter, i.e., strain and temperature, optical fiber sensors based on fiber Bragg gratings (FBG) for structural health monitoring applications is presented. The sensors are based on our patented technology on multi-parameter superstructure FBGs with on-fiber patterned metal thin films. The design and fabrication of the sensors, senor packaging, and sensor calibration using our developed calibration setup are elaborated in this paper.

Superstructure fiber Bragg grating sensors with enhanced sensitivity using laser assisted direct writing of on-fiber thin films

The present paper is concerned with improving the sensing performance of optical fiber Bragg gratings (FBG) by the deposition of periodic metallic thin films around optical fibers to make superstructure FBGs (SFBG). Laser-Assisted Maskless Microdeposition (LAMM), which is an additive laser microdeposition method, is used to selectively deposit on-fiber thin films from silver nanoparticles. The LAMM process characterization, including the microstructure and mechanical properties of on-fiber thin films, are also presented. In addition, as the laser radiation is a major part of the process, the effects of parameters related to the laser treatment of samples are studied. To design the thin films, an optomechanical model of SFBG sensors with on-fiber thin films is developed. The sensitivity analysis and the capabilities of the sensor for multi-parameter sensing are also investigated.The present paper is concerned with improving the sensing performance of optical fiber Bragg gratings (FBG) by the deposition of periodic metallic thin films around optical fibers to make superstructure FBGs (SFBG). Laser-Assisted Maskless Microdeposition (LAMM), which is an additive laser microdeposition method, is used to selectively deposit on-fiber thin films from silver nanoparticles. The LAMM process characterization, including the microstructure and mechanical properties of on-fiber thin films, are also presented. In addition, as the laser radiation is a major part of the process, the effects of parameters related to the laser treatment of samples are studied. To design the thin films, an optomechanical model of SFBG sensors with on-fiber thin films is developed. The sensitivity analysis and the capabilities of the sensor for multi-parameter sensing are also investigated.

Numerical study of on-fiber metal film geometry on behavior of dual parameter SFBG sensors

In this paper, a numerical model for simulating a dual parameter super-structure FBG (SFBG) with on-fiber deposited thin films is developed. A periodic on-fiber thin coating of silver on FBG sensors provides the ability of measuring two parameters of strain and temperature simultaneously. The model consists of a mechanical model to determine the strain of the sensor caused by different loading conditions, coupled with an optical model to calculate the reflected spectrum of the SFBG sensor. A guideline is introduced for designing a SFBG by studying the effect of coating period, coating duty cycle, and coating thickness. The results show that the sideband spacing in such SFBGs is only affected by the coating period while the Bragg peak sensitivity does not depend on coating period. Also the coating duty cycle and the coating thickness can affect both sensitivity of the Bragg peak and the measuring range of a sensor. The validity of the results was studied by comparing with previously reported data.