Composite structures widely used in advanced sectors as in the automotive and aeronautical fields, during their useful life are usually subject to dynamic events responsible for apparently invisible failures which, over time, severely compromise their performance. In this regard, a huge amount of experimental results, also validated by theoretical considerations, is available on the behaviour to damage caused by low velocity impacts (LVI) on laminate systems in polymeric composite and on their residual strength. However, until now the research interest has been mainly focused on thin composite laminates (less than 4 mm) and only very few experimental works are available concerning thick laminates (thickness higher than 4 mm) generally used in the skin of airplane wings, stringers, highly loaded components. This study aims to investigate simulated defects in carbon fiber reinforced polymers (CFRP) and of the damage deriving from LVI events, particularly peculiar to structures with higher bending stiffness such as thick ones and, therefore, to fill the current knowledge gap for a more appropriate use of the latter. To this end, thick carbon epoxy resin composite laminates, kindly supplied by Leonardo SpA and impacted at the Department of Industrial Engineering of the University of Naples Federico II, will be systematically investigated with well-established skills on infrared thermography, air coupled ultrasonic tests and shearography at the Institute of Applied Science and Intelligent Systems of the National Research Council. The combined results for both panels with simulated defects and impacted panels provided an accurate description of the different defects present in the thick panels involved in their damage process.
Composite honeycomb sandwich samples are commonly used because they offer a high strength-to-weight ratio, making them ideal for lightweight and durable structures. However, ensuring their structural integrity is essential for safety and performance. Multimodal NDT (Non-Destructive Testing) inspection and characterization of composite honeycomb sandwich samples is a critical process in various industries, including aerospace, automotive, and civil engineering. The use of NDT techniques makes it possible to verify the quality of the composite material and identify any defects. In this context, we provide a comparison of several techniques as nondestructive methods on a sample of interest to the aerospace industry and evaluates the parameters of their use: shearography, infrared thermography and laser ultrasonic. Using non-destructive testing techniques, it is possible to check the quality of composite materials and identify any programmed flaws. These techniques allow for frequent inspections without compromising the integrity of the material. This helps ensure the safety and reliability of products using composite materials. From the preliminary results it is evident that the combined use of the described non-destructive testing (NDT) techniques can significantly improve the reliability and accuracy of the quality control process for a wide variety of materials and defects.
Infrared imaging is a well-known non-invasive technology that in recent years has gained great interest in precision agriculture field. Plants are subjected to a wide range of biotic stresses caused by pathogenic bacteria, fungi, nematodes, and viruses that reduces productivity. In this work wild rocket (Diplotaxis tenuifolia) plants inoculated with the soil-borne pathogens Rhizoctonia solani Kühn, Sclerotinia sclerotiorum (Lib.) and Fusarium oxysporum f. sp. raphani were monitored daily in laboratory by means of the infrared imaging. Plant monitoring was performed with both active and passive approaches. The results obtained showed that the infrared imaging methods tested are promising for early diagnosis of soil-borne diseases by allowing their detection a few days before they are detectable through a visual analysis. These findings open up the possibility of developing new imaging systems for both proximal and remote sensing.
Photodetectors are of great interest in several technological applications thanks to their capability to convert an optical signal into an electrical one through light-matter interactions. In particular, broadband photodetectors are used in multiple applications such as environmental monitoring, imaging, fire detection, and astronomical observations. We present a two-dimensional photodiode heterojunction based on reduced graphene oxide (rGO) deposited on an n-type Silicon substrate. We report on the electro-optical properties of the device that have been measured in dark and light conditions into a spectral range from UV to IR. The room temperature current–voltage (I–V) measurements of rGO/n-Si photodetector exhibits a reverse saturation current linearly dependent on the light power. The main figures of merit of the photodetector such as linearity and responsivity have been evaluated and compared with the recent progress obtained substituting the rGO with a graphene single layer (Gr) on the similar n-Si substrate. The photoconductive properties and analysis of the two devices are presented and discussed. Finally, the experimental results demonstrate the feasibility of the rGO/n-Si and Gr/n-Si device to detect light from UV to IR light, nominating graphene-based heterojunction as a novel candidate for the realization of new broadband photodetectors.
In this paper we report the results related to an integrated approach for the working test of a titanium (Ti) panel as a component for a multi-mission modular satellite platform. The multifunctional panel here characterized has been made by additive manufacturing. The panel has been conceived integrating its mechanical properties for the structural support, electronic cabling, and for loading all the components and payloads of the satellite platform, with the innovative property of heat dissipation. In fact, this prototype module comprises internal heat pipes; The management of the heating in excess is still a demanding for the implementation of advanced modular and multi-mission satellite platform, in 50-kg microsatellite class, with possible housing of multiple interoperable payloads. In this framework, here we focus on the study and development of technologies and characterization of advanced smart structures through the use of innovative materials. The profile and section of the micro-channels have been designed to favor the liquid evaporation under heating in microgravity condition and thus for different space applications. In the following the characterization and test on the earth is illustrated and discussed for the prototype. We believe that functional panels with these novel characteristics would find application for energy waste recovery also in case of electronic dissipation for module dedicated to space exploration.
The analysis of innovative materials and processes stands at the frontier of a series of wide-ranging scientific problems and poses stimulating challenges from a scientific as well as technological point of view, by virtue of its connection with various industrial sectors, such as aerospace and aeronautics. In recent years, composite materials have found numerous applications due to their mechanical characteristics and properties, representing the evolution of materials science and technologies by fusing within them the best characteristics of multiple materials. The present work is focused on the characterization of composite materials, using non-destructive techniques (NDT), to check different kinds of defects eventually present for a quality control of the object under observation. Shearography and thermography are used as nondestructive methods. The former, is an optical interferometric method for the detection of surface or sub-surface defects, the latter is a diagnostic technique that, by measuring the infrared radiation emitted by a body, allows to determine its surface temperature and to understand the health status of the investigated object. The results of the shearography technique, including, are complementary to thermographic techniques and allow us to have a complete characterization of the object. Their use offers advantages related to visualization and testing of end products, as well as the noncontact nature, nondestructive and areal working principle, rapid response, high sensitivity, resolution, and accuracy.
In the last decade, smart materials have been developed in the fields of optical machines, sensors, motors, robots, and energy harvesting. This is due to their capability to respond to external stimuli or environmental changes. Among smart materials, photo-mobile polymers (PMPs) based on liquid crystals are the most promising in the field of photo-responsive actuators. These polymers are made with a mixture of liquid crystals containing azobenzene moieties that can undergo photoisomerization from trans to cis under UV light. This process leads to a macroscopic bending of the PMPs, which transforms light into mechanical energy. To enhance the PMPs' actuation, a novel liquid crystal nanocomposite is proposed. In our work, the nanocomposites are prepared with different concentrations of ZnO nanoparticles (NPs) embedded in the cross-linked polymer matrix. We have demonstrated that ZnO NPs improve the actuation and mechanical properties of the PMP, and the main aim of this assay is to optimize such effect as a function of the nanoparticles concentration. We also show the lowest and highest amounts of ZnO needed to enhance the bending behavior of the PMP. Optical, mechanical, and thermal analyses were performed to characterize the PMPs. Spectral characterization in UV/vis range of the bare and doped films, optical and atomic force microscopy, were used to comprehend the role of ZnO nanoparticles and their distribution among the liquid crystals. To study the dynamic response of the PMPs and their mechanical properties, lasers at different wavelengths were used.
Development of novel plasmonic nanopatterns is of great interest for various applications, including chemical and biological analysis. Systems based on gold nanoelements have been designed and tested in several research works for the study and detection of various kinds of biological analytes, giving appreciable results. Plasmonic properties associated to the nanostructure can be tuned by changing the size and the shape of the nanoparticles or the periodicity or, more in general, the geometry of the nanopattern. These features are key to many applications aiming at signal enhancement and low threshold sensing. In this work we present a study of periodic arrangements of novel plasmonic metamolecular unit cells made of triangular nanoelements. Nanostructures analyzed were fabricated using electron beam lithography technique (EBL) that allows to create patterns with high accuracy and repeatability. Morphological analysis was realized by Scanning Electron Microscopy (SEM) and their plasmonic properties were studied and compared using experimental set-up for Surface Plasmon Resonance (SPR) and Surface Enhanced Raman Spectroscopy (SERS) measurements. We tested the sensing performance of our nanostructures by analyzing the SARS-CoV-2 (COVID-19) Spike Antibody (3525) getting its molecular fingerprint. Our results suggest that these plasmonic patterns are promising to develop highly sensitive nanosensors for the detection of biological analytes.
Active Thermography (AT) is a well-known non-contact and non-invasive imaging technique that has gained great interests in agriculture in recent years. It has been used to evaluate physical and physiological characteristics of plants such as: transpiration rates, heat capacity of the leaves, local water content, response to UV interaction and it fits well with emerging demands of the precision agriculture management strategy. According to this technique, the surface of the sample under investigation is stimulated using an external heat source and its thermal response is detected and recorded using infrared camera. Different strategies can be used for both the measurement protocol and for data analysis. Copper has been widely used in agriculture as a fungicide and bactericide for many decades. Applied on leaf, copper based fungicide (CBF) remains deposited and it is not absorbed into plant tissues, causing accumulation problems that needs to be monitored and controlled, also by using modern technologies. In this work, we test and compare different AT methods to detect and to monitor the presence of CBF on leaves. Our experimental results demonstrate that methodological approaches based on AT can be used to engineer effective remote tools to evaluate in real-time the presence of copper on plants, allowing a tentative of quantification and, therefore, to optimize its use in the agricultural practices.
Plants are subjected to a wide range of stresses which reduces the productivity of agricultural crops. In the case of cereal cultivations, climate change impacts on their production mainly through abiotic and biotic stress due for example to heat and water stress but also to pathogens such as bacteria, fungi, nematodes and others. The area under cereal cultivation is increasing worldwide, but, due to these problems, the current rates of yield growth and overall production are not enough to satisfy future demand. For this motivation, there is the needs to monitor and to control the cultivations, also developing new technological solutions useful to better optimize the management strategies, increasing both the quality of products and the quantity of the annual cereal harvest. Infrared imaging is a well-known non-invasive and non-contact technique that represents an outstanding approach of analysis applied in many fields: engineering, medicine, veterinary, cultural heritage and others. In recent years it has been gaining great interest in agriculture as it is well suited to the emerging needs of the precision agriculture management strategies. In this work, we performed an in-field multispectral infrared monitoring of different cereal crops (durum wheat and common wheat) through the use of both LWIR and MWIR cameras. The monitoring carried out made it possible to identify, among the crops analyzed, those subject to higher stress levels and their response to the different spectral ranges used. The results obtained open to the possibility of identifying new figures of merit useful for an effective monitoring of cereal crops and measurable through remote instrumentation.
Composites represent the evolution of the material science and technologies. They are obtained by combining two or more materials of different nature with the aim of exploiting any synergies between the characteristic performances of the raw materials. Their properties, in fact, are influenced by those of the starting components but also by the quality of the interface generated between the combined phases as well as by their mutual distribution. The interphase, even if of minimal extension with respect to the main phases constituting the composite, plays a significant role in the control of the damage mechanisms, determines the breaking strength and the stress / deformation behavior of composite materials. In this work we study the effect of low pressure plasma treatment on intrinsically hydrophilic flax fiber fabrics to improve their adhesion to a hydrophobic polypropylene matrix. The fibers are treated using nitrogen (N2) plasma with four different exposure times. The interfacial adhesion actually achieved was indirectly quantified by interlaminar shear strength measurements. After this, the damaged areas were measured with non-destructive techniques, i.e. Electron Speckle Pattern Interferometry and Lock-in thermography.
The diagnostic of artworks represents a topic of high interest and at the same time a critical task. The development of effective tools based on advanced technologies for investigating and monitoring health-state of item of interest for cultural heritage is essential to assuring their preservation and restoration. In fact, detecting and preventing the formation of damages or assessing them for an accurate pre-restoration analysis are the main objectives of non-destructive investigation. In this study the combined use of Electronic Speckle Pattern Interferometry and Pulse Thermography Analysis, as complementary tools for cultural heritage artifacts diagnostics have been employed on poplar panels painted reproducing original painting methods adopted during the 16th and 17th centuries. Both techniques are full field, contactless, non-invasive and can provide relevant information about state of conservation. The concurrent investigations, allow to expand understanding the results of each individual technique, from which, in many cases, no exclusive assumption is possible. The applications include detection of detachments, micro-cracks, inclusions, and hidden damages. It is also possible the real time monitoring of the behaviour of the object according to the environment thermo-hygrometric changes. The porpoise of this work is to optimize the parameters of such NDT methods on the samples that were specially made by reproducing in high fidelity the structural properties and materials of the artwork. Results show that the employed diagnostic protocols, by speckle interferometry and pulse thermography, are a powerful tool in assessing the pre-restoration health-state and suitable for in situ analysis of wood artworks. Examples of analysis on different artworks are shown.
Plasmonic devices are of great interest for different applications including chemical sensing for food and water contaminants. Their properties to confine high electromagnetic fields strictly depend on the size, shape and, more in general, on the geometry of their basic constituents. In this work we fabricate and characterize two-dimensional periodic arrangements of novel plasmonic supra-molecular cells with different minimum intercell distance and in both nanopillars and nanocavities geometries. For patterns based on nanopillars we evaluate the bulk sensitivity associated to their localized surface plasmon resonance which results to have a value up to 408 nm/RIU while for the patterns based on nanocavities we found a SERS enhancement factor up to 2.1x106. We tested the sensing performance of these nanostructures analyzing different concentrations in water of fipronil pesticide using both LSPR and SERS tools. Our results suggest that these plasmonic patterns are promising to develop nanosensors for a dual-sensing detection of water contaminants with high sensitivity.
We utilize Digital Speckle Pattern Interferometry and Square Pulse Thermography Analysis, as complementary tools for
cultural heritage artifacts diagnostics. The concurrent utilization of two methods provide the possibility to complement
and validate the effective understanding of each individual technique results, that are not always easy to interpret. Both
techniques are non-invasive and can be applied on almost any type of archaeological finds, providing relevant
information about their state of conservation. The applications include the whole structure analysis, as well as the
detection of detachments, micro-cracks, hidden damages. The diagnostic investigation can be carried out before, during
and after a restoration. It is also possible the real time monitoring of the behavior of the object according to the
environment thermo-hygrometric changes. Examples of analysis on different artworks are illustrated.
By exploiting Metamaterials (MTMs) and Photonic Quasi-Crystals (PQCs), it is possible to realize man-made structures characterized by a selective EM response, which can be also controlled by combining the distinctive properties of reconfigurable soft-matter. By finely controlling lattice parameters of a given photonic structure, it is possible to optimize its extraction characteristics at a precise wavelength, or minimize the extraction of undesired modes. In general, however, once a structure is realized, its extraction properties cannot be varied. To cross this problem, it is possible to combine capabilities offered by both MTMs and PQCs with the reconfigurable properties of smart materials, such as Liquid Crystals (LCs); in this way, a completely new class of “reconfigurable metamaterials” (R-MTM) can be realized. We report here on the realization and characterization of a switchable photonic device, working in the visible range, based on nanostructured photonic quasi-crystals, layered with an azodye-doped nematic LC (NLC). The experimental characterization shows that its filtering effect is remarkable with its extraction spectra which can be controlled by applying an external voltage or by means of a laser light. The vertical extraction of the light, by the coupling of the modes guided by the PQC slab to the free radiation via Bragg scattering, consists of an extremely narrow orange emission band at 621 nm with a full width at half-maximum (FWHM) of 8 nm. In our opinion, these results represent a breakthrough in the realization of innovative MTMs based active photonic devices such as tunable MTMs or reconfigurable lasers and active filters.
The last decade has been characterized by artificial electromagnetic (EM) materials, including photonic crystals (PCs)
and photonic quasi-crystals (PQCs), making these very attractive given that there are new possibilities to control the EM
field in innovative way. Quasiperiodic crystals (QCs) are a new class of materials that have fascinating optical properties
lying somewhere between those of disordered and period structures. With the use of PCs and PQCs, it is possible to
synthesize novel artificial structures characterized by selective EM responses, which, in turn, undergo significant
frequency shifts, in presence of biological material.
In the present work we studied artificial EM nanomaterials to develop innovative plasmonic nanobiosensors based on
Surface Enhanced Raman Scattering (SERS) substrates and working in the visible and NIR frequency bands. A
fabricated gold PQC in a Thue Morse arrangement is proposed for the engineering of reproducible SERS substrates.
Structural characterization of this surface is performed by SEM and AFM. Optical properties of this plasmonic
nanostructure are evaluated via UV/ Vis absorption spectroscopy and surface–enhanced Raman spectroscopy (SERS).
Using a molecular monolayer of pMA (p-mercaptoaniline) as a Raman reporter, we show that a high value of SERS
enhancement factor (measured up to 1.4 x 107) can be achieved in a properly optimized photonic structure, in good
agreement with FDTD calculations. SERS enhancement factor is dependent on the plasmon absorption wavelength and
laser wavelength used in these experiments.
Light beam propagation at a prism-magnetic fluid film interface is experimentally studied. The magnetic fluid is made
through dispersion of synthesized cigar-shaped sub-micron particles of Fe2O3 in an oil solution. This was injected into a
glass cell with an active area of 10mm2 and a depth ranging from 10 microns to 30 microns whose base is a glass
microscope slide and on the top it was covered with a glass prism. The set up was developed by one of the authors to
measure light switching at a prism-liquid crystal interface in a previous publication.1 Polarized Light (TE or TM) from a
He-Ne laser impinges at the prism-magnetic film interface. The external reflected light is detected by a photodiode
connected to a data acquisition system. Since the properties of the magnetic fluid can be modulated by external magnetic
fields, we investigated the effects of the magnetic field on the refractive index of the magnetic fluid.
For our magnetic fluid, the reflection of light has been investigated as a function of particles concentration and thickness
of the films with a wavelength of 633nm and both TE and TM polarization, and applied magnetic fields up to 25 Oe. It
was found that the intensity of reflected light increases with increasing magnetic field up to 4 times the initial value, and
saturates at 20 Oe for TE light, while decreases with increasing magnetic field up to 4 times less for TM light with the
same saturation value. Moreover, under a given magnetic field, the output light increases with the increasing film
thickness in TE polarization, and decreases with the increasing film thickness in TM case. The refractive index of the
magnetic fluid depends on the concentration of the dilute oil-based magnetic fluid under zero field.
These behaviors are explained in terms of the organization of the submicron particles when the magnetic field is
applied.2 The cigar-shaped sub-micron particles are oriented along their long axis to form an organized mesostructure.
The different aggregation ability of the magnetic fluid particle is responsible for the variation of the optical properties
under different magnetic fields and for different polarization of the incident light.
It is noteworthly that the magnetically modulated refractive index of the magnetic fluid film could have great potential in
electro-optical applications. In particular, according to the experimental results, we believe that the fluid films that we
are proposing, thanks to the optical responses and the relative times, is a very good candidate to design Fiber Optical
Sensors (FOS) for magnetic fields.
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