Browsing by Issue Date, starting with "2022-03-07"
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- Joining of fibre-reinforced thermoplastic polymer composites by friction stir welding—A reviewPublication . Pereira, Miguel A.R.; Galvão, Ivan; Costa, José D.; Amaro, A. M.; Leal, RuiThe objective of the current work is to show the potential of the friction stir welding (FSW) and its variants to join fibre-reinforced thermoplastic polymer (FRTP) composites. To accomplish that, the FSW technique and two other important variants, the friction stir spot welding (FSSW) and the refill friction stir spot welding (RFSSW), are presented and explained in a brief but complete way. Since the joining of FRTP composites by FSSW has not yet been demonstrated, the literature review will be focused on the FSW and RFSSW techniques. In each review, the welding conditions and parameters studied by the different authors are presented and discussed, as well as the most important conclusions taken from them. About FSW, it can be concluded that the rotational speed and the welding speed have great influence on heat generation, mixture quality, and fibre fragmentation degree, while the tilt angle only has residual influence on the process. The reduction of internal and external defects can be achieved by adjusting axial force and plunge depth. Threaded or grooved conical pins achieved better results than other geometries. Stationary shoulder tools showed better performance than conventional tools. Regarding the RFSSW, it has not yet been possible to deepen conclusions about most of the welding parameters, but its feasibility is demonstrated.
- Multichannel detector system for surface plasmon resonance biosensorsPublication . Fernandes, Miguel; Fantoni, Alessandro; Soares, Paulo; Lourenço, Paulo; Vieira, ManuelaPhotonic systems are gaining an important role in the field of medical diagnosis due to the achievable high sensitivity and selectivity and low cost, enabling the fabrication of disposable point of care diagnosis systems for multiple pathologies. In this work we present the detector subsystem developed for a multi-channel surface plasmon resonance (SPR) based sensor. The core of the system is a multimode interferometer splitter, fabricated in amorphous silicon, followed by multiple sensitive SPR structures with a functionalized gold layer that modulate the transmitted light waves, in the presence of the biomarker, which are then detected by infrared detectors. For this purpose a highly adaptable detection system based on a InGaAs line CCD device was developed. The IR sensor used in the prototype has 128 (50 x 250 μm) pixels but other formats are supported. To adapt to different light guiding structures, the CCD pixels can be combined forming multiple detection channels. Optical sensor configuration and readout operations are performed trough a USB connection using the SCPI standard. The system includes an analog front end with a programmable gain amplifier and offset adjustment followed by a fast analog to digital converter feeding the data to a STM32 family processor. A computer application was also developed for system configuration and signal readout and storage. The testing results from the complete system are presented. Documentation of the developed system is provided for third party use, all the material generated within this work is available online in a repository.
- Metamaterials in waveguide to fiber couplersPublication . Lourenço, Paulo; Fantoni, Alessandro; Costa, João; Fernandes, Miguel; Vieira, ManuelaCoupling light into or out of a photonic integrated circuit is often accomplished by establishing a vertical link between a single mode optical fibre and a resonant waveguide grating, which is then followed by a tapered and a single mode waveguides. For a chip to fibre coupler, the period of the diffraction grating is often apodized to achieve an optimal beam profile at the input of the optical fibre. The tapered waveguide operates as a spot-size converter, expanding laterally the light beam in the single mode waveguide, to match the profile of the fundamental mode of the resonant waveguide grating. In this work, we propose using subwavelength structures to modulate the refractive index of the tapered waveguide for the lateral expansion of the light beam, when operating at the 1550 nm wavelength. The engineered graded index structure is simulated through adequate numerical methods and its performance is analysed in terms of efficiency and mode profile matching. With our proposed inverted taper waveguide, we were able to obtain an adiabatic power transfer and coupling efficiency with the TE fundamental mode of -0.26 dB and -0.92 dB, respectively. This performance has been achieved in a structure 11.1 µm long and 14.27 µm wide. Furthermore, the obtained fields were fed into a resonant waveguide grating to evaluate the coupling efficiency into the fundamental mode of an optical fibre, resulting in an expected performance decrease of 0.1 dB and ~0.6 dB by comparing respectively with the power transfer and coupling efficiency of the resonant waveguide grating when propagating the calculated TE0 mode.
- Colour and image processing for output extraction of a LSPR sensorPublication . Mansour, Rima; Stojkovic, Vladan; Vygranenko, Yuri; Lourenço, Paulo; Jesus, Rui; Fantoni, AlessandroSensors based on the Local Surface plasmon Resonance (LSPR) are attractive due to their simple structure and good sensitivity, but the expensive optoelectronic part of the device is limiting the practical applications. There is a need for new strategies to bring the excellent detection properties of LSPR sensors to the playground of low-cost devices and materials. In this work, it is proposed a novel approach to the output extraction of from LSPR sensor whose sensing element is composed by metal nanoparticles (MNPs). Illuminated with an incident broad light source, the sensor produces a spectral transmission output where the MNPs act like a band-stop optical filter for a specific wavelength. An alteration of the refractive index in the surrounding medium corresponds directly to a shift of the filtering rejection band, which corresponds to a slight change in the colour of the light transmitted by the sensor elements. This colour change can be captured by a CMOS photo-camera, used as an image sensor. It is proposed in this paper an approach based on an automatized image processing algorithm for colour change detection, yielding to a system capable of detecting refractive index variations, avoiding the use of expensive spectrometers. The algorithm comprises three stages: (1) Region of interest detection: images are first cropped using the Otsu threshold binary image to remove the uninteresting areas in the image. (2) Image segmentation: using the watershed algorithm, the sensor elements (sample) area is detected automatically in the cropped image. The segmentation is done using the gradient image, where the watershed markers are the regions of low gradient and barriers are the areas of high values inside the image. (3) The resulted sample region is then processed to find its average or dominant LAB colour and then compare it to its corresponding sample image immersed in different mediums using the colour difference measurement CIEDE2000.
- Multi-micron dimensioning of amorphous silicon rib waveguidesPublication . Almeida, Daniel; Costa, João; Fantoni, Alessandro; Vieira, ManuelaWhile silicon photonics is considered as the key technology for future applications in optical transceivers, ASICs and sensing devices, there are still challenges to achieve generalized mass production of Photonic Integrated Circuits (PICs). One obstacle is the required extreme miniaturization of the photonic devices. Nevertheless, there is space for applications with equal interest and impact in the society that do not require the extreme performance associated with PICs built on a tenth of nanometer scale. Low-cost PICs can be obtained by increasing the size of the waveguides and devices to a multi-micron scale and in this case the machinery necessary for the device fabrication can be greatly simplified. The transfer of the amorphous silicon (a-Si:H) production technology developed in the past for the photovoltaic and flat panel displays can be adapted to the production of multi-micron size PICs targeting low-cost devices working with low frequency signals. To enable the use of such devices it is important to show that light and be coupled in and out of the waveguides efficiently without the need for diffraction gratings or other components that require sub-micron fabrication resolutions. In this article we perform simulation of the power transfer between a lensed 19.4 µm multimode optical fiber and a multi-micron a-Si:H rib waveguide, designed to support single-mode propagation. Light coupling efficiency is analyzed as a function of alignment and distance variations using the FDTD and the Beam Propagation methods. Results show a fundamental TM mode overlap over 80 % under optimal alignment conditions.