The estimation of caloric content of vegetation is relevant in areas such as biofuels and forest fire prevention. In this work we explore the transmission mechanism of infrared radiation through a leaf by finite element analysis to determine the energy transmission and reflection. We quantify the absorption inside the leaf using a wavelength at 1064 nm. The results obtained are determined experimentally at incidence normal to the leaf surface. We use an infrared laser source, controlling its power settings and a neutral density filter for step-wise power increments. We assumed a non-porous, uniform material, a constant refractive index. We select a specific absorption coefficient according to the senescent state of the leaf. The results describe the relationship between the absorption measured experimentally and computed by finite element analysis (FEA).
3D printing technologies have allowed the development of prototypes in several fields, such as clinical, aerospace, and infrastructure, to name a few. Another use is to adapt the laboratory instruments to customized applications to improve experiments and measurements in the data acquisition process. Some equipment is modified to include low-cost cameras, optical components, sensors, and mechanical artifacts using printed accessories employing PLA or PETG filaments, such as telescopes, microscopes, and spectrometers. These accessories allow us to maximize the features of the instruments and reduce the research cost. We describe a semi-automatic method for microalgae counting based on a digital microscope adapted to a 3D printing mechanical support and image processing in Matlab. Calibration will be carried out using a Neubauer chamber but will not be required for measurements, which makes a difference compared to similar methods. The results obtained for micro-algae counting show an average error of less than 5% compared to visual counting conducted by a biochemical specialist. We are describe a simple and low-cost method of counting microalgae using 3D printing technologies.
A laser shock wave is a pressure wave that travels through a material at supersonic speed induced by a high-power laser pulse. Shock waves suddenly change direction as reflected at the physical limits of the medium, producing interference between the wave remnants. The reflected wave reaches the front surface transiting a distance as a function of the thickness and the reflection angle. The time it takes for the shock wave from being induced to reflect toward the front surface of the material can be used to determine the thickness of the propagation medium. A finite element method estimate the propagation of a laser shock wave in four basic geometric shapes of 6061-T6 aluminum alloy. The time it takes to reach the front surface of the geometric shapes is measured. Its controlled the material thickness and spatial coordinate of the induction. The effects of the porosity, absorption and transmission of the medium are ignored. The results demonstrate the feasibility of use the time-of flight as a thickness measurement and a distribution of compression and pressure zones inside the medium generated by the wave interference. Some applications of this method are to determine the thickness of solid materials, the estimation of caverns or aquifers on geophysics, and the determination of the density of a material.
Remote sensing used in vegetation monitoring has been a significant study area for decades. With the advent of multispectral and hyperspectral cameras, detecting healthy vegetation in forests and crops were more accessible through the ratio of different spectral bands that resulted in other vegetation indices. However, even with the usefulness and practicality of these methods, they need to be more accurate since they are relative values that depend on several factors of the internal composition of the vegetation. This work proposes the analysis of a spectral bandwidth of a central wavelength of 1 μm, using a conventional CCD camera as a detector with a bandpass filter with a linewidth of 10 nm. This range presents characteristics of water absorption but also reflectance due to the cellulose of the cell walls of the leaves. In this way, using the electro-optical array, the radiation reflected changes by several leaves will be analyzed considering the hydration and deterioration of the leaf.
A microlens array is a junction of small-sized lenses distributed one-with-other for decreasing the sizes in some sensors or CCD for applications where portability is mandatory. However, working with circular apertures reduces the arrangement efficiency due to the distance between each element. Using several parameters, as spatial distributions, optical apertures, and materials for the microlenses, prevents the light incidence on non- photosensitive areas due to diffraction. The study of these parameters employing the finite element method (FEM) is a complementary tool to arrangement optimization. We present an investigation based on FEM for microlens arrays optimization in two dimensions, where the arrangement, geometry, and materials for the array are changed. The analysis can be useful to estimate the incidence on a non-photosensitive surface due to diffraction of any aperture geometry, or lens material, knowing the focal length and the wavefront transmitted, as the previous step to the final elaboration.
A laser shock wave (LSW) is a pressure wave in the range of gigapascals, duration in the order of nanoseconds, propagates at rates higher than Mach 1, and is induced by high power laser pulses. As an LSW propagates inside a solid, some physical material characteristics in the area of incidence are improved due to a residual compression stress field. However, since the LSW pressure reaches some tens of GPa, tensile stress damages the solid due to a spallation process if the material is fewer than 1 mm thick. A shock wave mitigation structure coupled to a solid reduces the LSW pressure due structure walls reflections, avoiding the spallation. In this work, a FEM simulation of LSW propagation in a 1 mm thick aluminum slab with a matrix of mitigating structures attached to the back is performed. The relationship among the induction area of the LSW, and the relative location of each mitigation structure in the matrix, has a direct influence on the pressure field distribution.
A shock wave is a pressure wave in the order of giga-pascal, and duration of nanoseconds, which propagates above the speed of sound in a solid medium. The shock wave can be induced in a small area on the solid sample surface by a highpower density laser pulse. As a result, the propagation of the shock wave, inside the solid, is considerate spherical. Waveguides can be used to drive a shock wave to a different point of interest. However, semi-spherical wave propagation involves some problems inside the waveguide, such as multiple reflections, phase shifts, and pressure decays due to wall reflections, among others. In this work, is proposed a finite element simulation of a spherical shock wave propagation inside a solid. We describe a method to correct a semi-spherical wave to plane wave propagation. We assume a point source semi-spherical distribution inside the material. The shock wave dispersion to the confining media is disregarded. The flat reflector location and shock trap geometry restrict the radius of curvature of the spherical reflector. This method can be useful to analyze the impulse response of solids to an incoming plane wave.
A laser shock wave is a pressure wave in a gigapascal range propagating at speeds above the speed of sound in a medium, induced by a high-power density laser pulse. Its duration is of the order of magnitude of nanoseconds. When the shock wave propagates in a solid, some materials characteristics in the area where laser beam is incident, change due to the application of compressive residual stress. These may be hardness, corrosion resistance, stress-fatigue resistance, to name a few. The shock wave has been found useful for working materials in diverse application fields such as aeronautics, defense, material science, and micro-components. The shock wave pressure decreases drastically as it propagates inside the solid, making it difficult to obtain experimental data when the shock wave propagates in solids with a thickness greater than one millimeter. We employ finite element method for the solution of shock wave propagation problems. Its primary benefit is that wave pressure and velocity may be determined upon modeling for thicknesses greater than one millimeter. We demonstrate a non-linear relationship between the material thickness and the shock wave that decreases with increasing slab thickness. In addition, the relationship between thickness and shock wave velocity is found. We estimate the material thickness by obtaining the attenuation ratio of the shock wave pressure.
A laser shock wave is a mechanical high-pressure impulse with a duration of a few nanoseconds induced by a high power laser pulse. We performed wave pressure measurements in order to build and check mathematical models. They are used for wave applications in material science, health, and defense, to list a few. Piezoresistive methods have been shown to be highly sensitive, linear, and highly appropriate for practical implementation, compared with piezoelectric methods employed in shock wave pressure measurements. In this work, we develop a novel method to obtain the sensitivity of a piezoresistive measurement system. The results shows that it is possible to use a mechanical method to measure pressure of a laser induced shock wave in nanosecond range. Experimental pressure measurements are presented.
Strengthening techniques allows enhance metal physical properties. Laser shock peening (LSP) technique consist in a surface treatment which a high power laser pulse induces a compressive residual stress field through mechanical shock waves, increasing hardness, corrosion resistance, fatigue resistance. In comparison with the shot peening technique, LSP is a method that allows precision controlling the laser incidence on the surface under treatment increasing the surface quality in the surface under treatment. In this work, mechanical shock waves are induced in aluminum and measure using two different experimental approaches. First, using a PVDZ sensors and secondly, strain gauges are used. Experimental results are presented.
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