A comparison of the machining performance of micro-EDM milling and sinking is proposed considering the fabrication of micro-channels with controlled sloped walls realized in a hardened steel workpiece. Adopting the fine-finishing machining regime for both micro-EDM techniques, the experimental results show that micro-EDM sinking is about 10 times faster than milling in the worst case, though a lack of accuracy in the final micro-features in the former case is detected due to not compensated tool wear. On the contrary, micro-EDM milling provides a better control of the micro-channel dimensions. Finally, a micro-filter mold for medical applications is machined in order to show the potential of the combination of both technologies.

An active optical switch based on the InGaAsP/InP photonic bandgap (PBG) buried waveguide is proposed. The device, which is made of a periodic grating patterned on a buried waveguide, exploits the localization of states in the PBG induced by the presence of an active defect. The wavelength of the localized state can be shifted by properly choosing the defect length and the injected current density in order to achieve a wavelength-selective switching behavior. Proprietary codes based on the bidirectional beam propagation method and the method of lines (BBPM-MoL) were used for the simulations of the optical device taking into account the rate equations to model the interaction between the optical signal and the active medium. Design curves are provided and parameterized to give general design rules. From the numerical analysis, the proposed device exhibits good theoretical performances in terms of crosstalk (CT < -20 dB), modulation depth (MD >0.9), response time (in the subnanosecond range), and maximum size (<170 mu m).

Aluminum alloys offer many machining advantages, such as excellent machinability and finish degree, outstanding tool life, and good corrosion resistance. They also display an elevated thermal exchange and weight reduction, which lead to easier handling compared to steels and make them good candidates for applications in the automotive and aerospace industry and in the field of mould production. Despite these recognized features, the machining accuracy, in particular in the micro-electro discharge machining (micro-EDM) process, needs further improvement. Revealing the nature of the Al alloys in EDM machining, some papers report of resolidifying layers in Al alloys appearing after the EDM process and grain compositions hugely affecting surface roughness. In particular, it has been observed that a thin and strong insulating layer due to the oxidation of the aluminum workpiece after machining leads to frequent tool breakage. In practice, this makes the micro-EDM process harder when micro-tools are meant to be used. However, to the best of our knowledge, the investigation of micro-EDM process performances of Al-Mg has not yet been fully explored. In this work, micro-EDM Al-Mg machining is presented: different energy levels were tested to find the proper parameter combination feasible to process micro-features. The machining geometrical limits are also investigated, putting in relation the energy levels to different electrode tool diameters. The experimental results are discussed on the basis of the evaluation of material removal rate (MRR), tool wear ratio (TWR), surface roughness and sparking gap. The machining of a micro-shaft housing component featuring high aspect ratio (HAR) is also shown as demonstrator to prove the effectiveness of the micro-EDM parameters selected from the previous trials.

In this paper we investigate on the spectral behaviour of slit array realized in a thick gold film surrounded by a homogeneous environment. The study has been performed by means of 3D-FDTD based codes, including the modelling of the metal dispersion through Drude-Lorentz fitting. The numerical results show that when the period p of the slit array is comparable to a multiple of the source wavelength, impinging at normal incidence, and the slit size is small enough to consider the input-output interfaces virtually smooth, transmission diagrams exhibit a minimum around lambda(min), where a matching condition occurs. Moreover when random variations of the slit spacing (elementary cell of the periodic structure composed by different periodicities) are considered, the matching condition for the N-th resonant order is asymptotically equal to that obtained when an array of slits having constant spacing equal to the averaged value of all periodicities is considered.

In this paper the performance of an optical organic sensor based on a plasmonic grating immersed in an asymmetric dielectric environment is investigated. Metal gratings offer the possibility to tailor the spectral response, in dependence of the geometrical parameter settings and variation of the refractive index of the surrounding media. It is then possible to obtain a reflection spectrum displaying a sharp dip that can be efficiently exploited to improve the detection of small quantities of organic materials. In particular, using a finite difference time domain (FDTD) based method, we demonstrate that the designed plasmonic grating, made of gold strips placed on a silicon substrate and covered by a generic organic material (analyte), exhibits an improved sensitivity for the detection of the overlayer thickness (analyte quantity). Nevertheless, this plasmonic sensor can also be used to determine the typology of the generic organic layer in dependence of the refractive index change. © 2011 Elsevier B.V. All rights reserved.

Recent scientific publications have highlighted the possibility of enhancing solar conversion efficiency in thin film solar cells using surface plasmon (SP) waves and resonances. One main strategy is to deposit layers of metal nanoparticles on the top of a thin film silicon solar cell which can increase light absorption and consequently the energy conversion in the frequency range where the silicon intrinsic absorptance is low. In this paper, we investigate the effects produced on the light absorption and scattering by silver nanoparticles, arranged in a periodic pattern, placed on the top of amorphous silicon (alpha-Si) thin layer. We propose different geometry of metal objects, quantifying the scattering (back and forward) determined by the nanoparticles in dependence of their shapes and Si thickness. The analysis reveals that the thickness of the substrate has huge influence on the scattering, in particular on the back one, when the nanoparticles have corners, whereas it seems less dramatic when rounded profiles are considered (nanospheres).

In this work, the implementation of an energetic model capable of predicting the energy consumption of a micro-electro discharge (micro-EDM) machine is presented. The developed model requires two main inputs: the estimate of the power absorbed by each subsystem composing the machine tool and the operation times, which includes the machining times. The power contributions can be determined via machine data sheets and via measurements. The energy consumption of a machine tool is due to two main contributions, ascribed to auxiliary units and to the manufacturing process itself. The developed model has been validated considering the micro-EDM milling of a circular pocket. The comparison between the estimated and measured energy consumption shows that the model is not only very accurate, but also very sensitive to the correct estimate of the machining times. Indeed, when the correction of the erosion time is operated by considering the actual value obtained by experiments instead of the one estimated by the CAD/CAM, the error referring to each energy contribution estimated by the model is greatly reduced. Furthermore, it can be noticed that most of the energy consumed by the micro-EDM manufacturing is actually inferable to the chiller unit.

The energetic model of a micro-EDM machine is presented. The model considers the energy required by the axis drivers, the micro-EDM generator, the air compressor and the chiller of the dielectric fluid. The model parameters have been experimentally identified during the micro-EDM machining of a blind hole. The resulting model is quite accurate and presents very small errors with respect to the actual energy used. However, the model is quite sensitive to the estimation of the machining time, which is provided by the CAD/CAM

In this paper, a novel plasmonic bandgap cavity inducing the enhancement of extraordinary optical transmission is presented. Numerical simulations have been performed to model a free-standing structure made of a one-dimensional periodic arrangement of gold strips. Two different values of the lattice constant have been properly chosen to realize a double heterostructure-like cavity to accomplish extraordinary optical transmission assisted by the formation of a plasmonic bandgap in the adjacent regions. Numerical results prove the capability of this optical device to efficiently transmit input light beams with far-field transmission values close to 100% due to the excitation of surface plasmon polariton resonant modes.

The power spectral density (PSD) of the voltage and current waveforms acquired during micro-EDM millingexperiments are calculated and analyzed. The estimate of the PSD in the frequency domain allows to identify thepulse energy contribution in relation to the dynamics of the erosion process. The first results show that most of theenergy released by the micro-EDM generator in the sparking gap during the erosion process is concentrated at thefundamental frequency set by the end-user, which in turns means that the process is stable. However, thecontribution to the fundamental frequency is not provided by normal pulses only, but also by arcs. Nonetheless, arelevant number of unpredictable events (arcs and delayed occurrence) leads to several non-negligible subharmoniccontribution, which witnesses the presence of inductive currents generated during the erosion process.

In this paper, the pulse discrimination of gap voltage and discharge current waveforms occurring during micro-EDM milling of micro-channels is analyzed in relation to process parameters variation and machining performance. The pulse classification algorithm discriminates voltage and current waveforms into four defined pulse types: short, arc, delayed and normal. The micro-channels are manufactured in hardened steel using an energy level corresponding to the finishing regime and varying pulse width, frequency, gain and gap. The analysis shows that when the erosion process is stable, normal discharges are predominant. Delayed and short pulses are very sporadic. A major number of arcs can be detected when the gap is decreased and gain increased, i.e. erosion speed and feed rate are increased and affect in particular tool wear. Also the increase of the pulse width has an effect on tool wear, though the percentage of the arcs remains small. On the contrary, material removal rate does not seem to be apparently related to the percentage of arcs as the process parameters are varied, since these values are spread in a constant range for all parameter combinations. The evaluation of the depth errors does not provide any significant insights about the erosion process in relation to the considered process parameters.

In this Letter, the study of a periodic structure composed of gold strips arranged in double-period unit cells, in a symmetric and asymmetric environment, is reported. The spectral maps show that the formation of the plasmonic bandgap and the extraordinary optical transmission are subjected to the proportion between the strip widths. Moreover, when the asymmetric environment is considered, high-transmittance and high-absorbance states arise. Hence, by controlling the geometrical parameters of the binary-periodic structure, it is possible to tailor the spectral response of the grating enhancing the desired features and exploiting them for different applications. (C) 2013 Optical Society of America

In this paper, the influence of tool path variation on micro-EDM milling performance of square micro-cavities havingthree different fill factors (FF, ratio between electrode toolsection area and feature section area) is presented. Threecavities for each considered FF have been machined and theexperimental results have been evaluated in terms of materialremoval rate (MRR) and tool wear ratio (TWR). The analysisshow that the machining of the cavity with medium FF displaysa MRR which is unexpectedly smaller than the onemeasured for the smallest cavity. The reason of such resultshas been investigated by analyzing the influence of tool pathon working conditions. Hence, a new set of micro-cavities hasbeen machined varying the path lengths. The new resultsconfirmed that, in dependence on the FF and cavity depth(expressed in terms of aspect ratio, AR), the proper setting ofthe tool path lengths can significantly improve the machiningperformance, in particular, in terms of MRR.

Advanced engineering ceramics display excellent mechanical properties such as high hardness, highcompressive strength, chemical stability, wear and thermal shock resistance. Due to their superior performance overother materials, the use of ceramics in a range of different applications is increasing year by year. Bio-ceramics, such asalumina, zirconia, titania, Si3N4-TiN, just to mention a few, have been of interest for many years for orthopaedic anddental applications. However, a number of challenges in their application still remain, including improvements in thematerial properties (mechanical and 'bio-compatible' feasibilities) and in the manufacturing process chain toward thefinal product. Electrical Discharge Machining (EDM) can be successfully employed to machine complex 3D geometriesalso on hard materials exhibiting a brittle behaviour, such as ceramics, on the condition that the limit of their lowelectrical resistivity is overcome. To this aim, some ceramic composites are synthesized using second electroconductivephases comprising Titanium, resulting in ZrO2-TiN, Si3N4-TiN, B4C-TiB2. Moreover, when ceramic-basedscaffolds and prostheses are fabricated, this additional phase seems to have a good physiological impact on cell growthand proliferation. In this paper, micro-EDM manufacturing of different micro-textures for scaffold realization made onSi3N4-TiN is presented and discussed. Different experiments have been performed in order to define optimal micro-EDM electrical parameters in terms of material removal rate (MRR) and tool wear ratio (TWR). Micro-electrodes withdifferent diameters are used for different machining regimes, roughing, semi-finishing and finishing, with the goal ofidentifying minimum geometrical limits on micro-pins textures machining and also taking into account that highaveraged surface roughness is required for this application.

Micro Electrical Discharge Machining (liEDM) technology is widely used to process conductive materials, regardless to their hardness and strength, and realize micro-sized feature components for industrial application. liEDM proves to be a very competitive fabrication technology since micro-sized features within 1 Lim of accuracy and with high surface quality (<0.1 Lim Ra) can be attained. When High Aspect Ratio (HAR) micro-features are machined via liEDM milling, the main problem is to identify the technological parameters and settings mainly affecting the process performance. In the present study the influence of the adjustment factor and flushing conditions are investigated and discussed for the machining of HAR cavities with different Fill Factor (FF). Material Removal Rate (MRR) and Tool Wear Ratio (TWR) are evaluated when deep cavities having variable square sections are machined on Ni-Cr-Mo steel workpiece. All tests are performed using a state of the art micro-EDM milling machine, with a Tungsten Carbide electrode tool and a dielectric oil for flushing. The experimental results presented here highlight different trends in the machining performance in dependence of AR and FF. In particular, MRR exhibits a decreasing trend where the curve slopes are strictly related to the FF and the initial adjustment factor. On the contrary,TWR, for higher FF, displays two distinct trends characterized by opposite slopes in each curve. Finally a nozzle for micro-injection with varying Aspect Ratio and Fill Factor is machined and presented as demonstrator.

The fabrication of personalized implants, tailored on patient needs, is a key issue for the future of several surgical fields. The presence of a prototyping service inside the hospital would be an added value for improving clinical activity. In this context, micro-Electro Discharge Machining is exploited to customize fixation devices in orthopedic surgery. An overview of the main devices is carried out in order to identify the main characteristics and to define the common fixation system specifications. The experimentation includes a technological evaluation of the proper micro-EDM technology, chosen according to the final design of the components. Two materials are investigated for the device fabrication: titanium and Si3N4-TiN ceramic composite. An optimization of the main technological parameters is performed in order to maximize the material removal rate ensuring the accuracy of the micro-features required. Finally, a test case is selected in order to evaluate the entire fabrication process chain.

This presentation reports the comparison of the machining performance of micro-EDM milling and sinking for the fabrication of micro-channels with controlled sloped walls realized in a hardened steel workpiece. The machining regime used for both micro-EDM sinking and milling is the fine-finishing. The results show that micro-EDM sinking is about 9 times faster than milling, though the effects of tool wear become relevant inducing a lack of accuracy in the final micro-features. Despite the slower machining time, micro-EDM milling provides a better control of the micro-channel dimensions and draft angles of the walls. No difference related to surface roughness is detected, since the energy level used in both approaches is the same. A micro-filter for hearing aid, dialysis media and inhaler, having a diameter of 2.3 mm characterized by a grid of 76 micro-pins, is machined in order to show the potential of the combination of both technologies

This paper reports the comparison of the machining performance of micro-EDM milling and sinking for the fabrication of micro-channels with controlled sloped walls realized in a hardened steel workpiece. The machining regime used for both micro-EDM sinking and milling is the fine-finishing. The results show that micro-EDM sinking is about 9 times faster than milling, though the effects of tool wear become relevant inducing a lack of accuracy in the final micro-features. Despite the slower machining time, micro-EDM milling provides a better control of the micro-channel dimensions and draft angles of the walls. No difference related to surface roughness is detected, since the energy level used in both approaches is the same. A micro-filter for hearing aid, dialysis media and inhaler, having a diameter of 2.3 mm characterized by a grid of 76 micro-pins, is machined in order to show the potential of the combination of both technologies.

We propose a novel bio-sensing platform based on the observation of the shift of theleaky surface plasmon mode that occurs at the edge of the plasmonic band gap of metal gratingsbased on two-dimensional gold nano-patch arrays when an analyte is deposited on the top of themetallic structure. We detail the numerical analysis, the fabrication and the characterization of thesetwo-dimensional arrangements of gold patches in linear regime showing that sensitivity of ourdevice approaches a value of 1000 nm/RIU with a corresponding Figure of Merit (FOM) of 222RIU-1. We provide experimental proof of the sensing capabilities of the device by observing colourvariations in the diffracted field when the air overlayer is replaced with a small quantity of IsopropylAlcohol (IPA). Effects of technological tolerance such as rounded corners and surface imperfectionsare also discussed. We also report proof of changes in colour intensities as a function of theair/filling ratio ad periodicity and discuss how they can be obtained by diffracted spectra. Finally wereport the numerical and experimental investigation of the non-linear behaviour of the devicehighlighting the Surface Enhanced Raman Scattering (SERS) performance.

We report on the formation of plasmonic bandgaps in two-dimensional periodic arrangements of gold patches. Orthogonal arrays of subwavelength slits with different periodicities have been studied by means of a three-dimensional finite-difference time-domain (FDTD) code, changing incident polarization and geometrical parameters. Spectral response of gold patches having different a form factor and surrounded by different media have been also investigated and compared in order to give a full description of bandgap shifts paving the way for the design of polarization-sensitive devices. (C) 2011 Optical Society of America

In this work, we investigate the effects produced on the light absorption and scattering by silver nanoparticles, arranged in a periodic pattern, placed on the top of amorphous thin silicon (?-Si) layer. Solar conversion efficiency in thin film solar cells can be enhanced exploiting surface plasmon (SP) waves and resonances. The deposition of metal nanoparticles layers on the top of a thin film silicon solar cell can increase light absorption and consequently the energy conversion in the frequency range where the silicon intrinsic absorptance is low. Our analysis reveals that the performance of each structure depends on shape, size and thickness of the substrate, which seems to hugely affect light scattering, and in particular the back one. © 2010 IEEE.

In this paper, the study of the micro-EDM milling of 3D sloped pockets realized in Si3N4-TiN ceramic composite is reported. The goal of the analysis is the investigation of geometrical errors affecting the surface accuracy of inclined walls, characterized by different draft angles. Preliminary experiments have been performed using two different levels of energy and varying the layer thickness used to implement the layer-by-layer strategy. Also the number of electrical touches done to monitor tool wear rate and depth error during each erosion process has been changed. The experimental results obtained by the measurements performed directly on the micro-EDM milling machine show that most of the errors on the manufacturing of inclined surfaces are found in the first part of the erosion process. These errors are mainly due to: the number of touches (control number) and the proper initial setting of the parameter assigned to compensate tool wear, the adjustment factor. Morphological measurements performed using a 3D high precision conoscopic holography scanner have confirmed that the surfaces of the inclined walls suffer of some defects on the top of the pockets. However the surface profiles of the inclined walls are quite good and no step-like trends have been detected, suggesting that the layer thicknesses for all trials have been properly set. Moreover, the draft angles values are very close to the ideal ones

In this paper, gap voltage and discharge current waveforms occurring during micro-EDM milling of micro-channels realized in a Si3N4-TiN workpiece are monitored and discriminated. The analysis is performed by implementing a design of experiment for the identification of the relationship existing among process parameters, machining performance and pulse type distribution. A pulse classification algorithm gathers gap voltage and current waveforms into four defined pulse types: short, arc, delayed and normal. The micro-channels are manufactured using an energy level corresponding to the finishing regime and varying pulse width, frequency and gap. The results show that material removal rate (MRR) benefits from the increase of normal and delayed pulses as expected. However, also arcs seems to increase MRR. Tool wear ratio (TWR) grows when normal pulses increases, whilst no particular influence is observed by delayed pulses. The peculiarity in TWR is found when arcs are considered: the values slightly decreases when arcs are more frequent, according to MRR behavior, but on the contrary with previous analysis done on different workpiece materials. This issue is currently under investigation

This paper discusses the performance of micro-electro-discharge machining (micro-EDM) process using different flushing media. Several tests have been performed considering a hardened steel thin workpiece machined via micro-EDM drilling and through-trench and different flushing fluids: deionized water, tap water, deionized water with Garnet, tap water with Garnet. Garnet is the abrasive material exploited in the micro-AWJ and the concentration per liter of water considered in micro-EDM experiments is the same as required in micro-abrasive water jet (micro-AWJ) machining. A customized system has been built on micro-EDM Sarix SX 200 HP machine to allow the water-based fluid refill and liquid level monitoring during the experiments. The micro-EDM trials have been carried out considering two machining regimes, roughing and semi finishing. The different water-based fluids have different electrical conductivities, which lead to different machining performance. Material removal rate (MRR) and tool wear ratio (TWR) have been estimated in terms of average and standard deviation. The results show that the presence of Garnet does not affect MRR consistently, since the particles do not play an active role in the erosion process but affect surface quality, as proved by the inspection of crater morphology and dimensions estimation performed via confocal microscope. For the considered experiments, MRR is generally increased as the conductivity decreases, in particular when semi-finishing regime is used. Also TWR decreases dramatically with the use of water-based fluids, since a protective recast layer is also deposited on the tool tip preventing wearing. Our analysis shows that micro-EDM can be successfully performed using the same liquid (water and abrasive) used in micro-AWJ, and so paves the way towards the implementation of a hybrid process based on micro-AWJ and micro-EDM technologies.

Micro-manufacturing emerged in the last years as a new engineering area with the potential of increasing peoples' quality of life through the production of innovative micro-devices to be used, for example, in the biomedical, micro-electronics or telecommunication sectors. The possibility to decrease the energy consumption makes the micro-manufacturing extremely appealing in terms of environmental protection. However, despite this common belief that the micro-scale implies a higher sustainability compared to traditional manufacturing processes, recent research shows that some factors can make micro-manufacturing processes not as sustainable as expected. In particular, the use of rare raw materials and the need of higher purity of processes, to preserve product quality and manufacturing equipment, can be a source for additional environmental burden and process costs. Consequently, research is needed to optimize micro-manufacturing processes in order to guarantee the minimum consumption of raw materials, consumables and energy. In this paper, the experimental results obtained by the micro-electrical discharge machining (micro-EDM) of micro-channels made on Ni-Cr-Mo steel is reported. The aim of such investigation is to shed a light on the relation and dependence between the material removal process, identified in the evaluation of material removal rate (MRR) and tool wear ratio (TWR), and some of the most important technological parameters (i.e., open voltage, discharge current, pulse width and frequency), in order to experimentally quantify the material waste produced and optimize the technological process in order to decrease it.