Paola Sansoni

Spectrally selective ultra-high temperature ceramic absorbers for high-temperature solar plants

Ultra-high temperature ceramics are the ideal materials for extreme conditions owing to their very high melting points and good thermo-mechanical properties at high temperatures. For these reasons, they are widely known as materials for aerospace applications. This paper presents a comparative spectral characterization of zirconium, hafnium, and tantalum carbides ultra-high temperature ceramics for concentrating solar power applications. Room-temperature reflectance spectra have been measured from the ultraviolet wavelength region to the mid-infrared band. Using these spectral properties, the ceramics were evaluated as sunlight absorbers in receivers for high-temperature thermodynamic solar plants.

On-line textile quality control using optical Fourier transforms

Fourier transformation and spatial filtering offer the possibility of detecting structural defects in a fabric. In this paper a method based on an optical Fourier transform technique during the weaving process is described. Significant variations in the Fourier pattern occurring in the presence of defective fabric are recognised with a CCD sensor joined to an electronic hardware system performing a simple algorithm.

Defect detection in textured materials by optical filtering with structured detectors and self‐adaptable masks

An optical method using Fourier transformation and spatial filtering is used to reveal defects in textured materials in real time. New optical structured filter types were developed including a self-adaptable mask made of photochromic polymers. The characteristics of these materials make possible very promising applications in pattern recognition such as that represented by a fabric.

Laboratory simulations of lidar returns from clouds: experimental and numerical results

The experimental results of laboratory simulations of lidar returns from clouds are presented. Measurements were carried out on laboratory-scaled cloud models by using a picosecond laser and a streak-camera system. The turbid structures simulating clouds were suspensions of polystyrene spheres in water. The geometrical situation was similar to that of an actual lidar sounding a cloud 1000 m distant and with a thickness of 300 m. Measurements were repeated for different concentrations and different sizes of spheres. The results show how the effect of multiple scattering depends on the scattering coefficient and on the phase function of the diffusers. The depolarization introduced by multiple scattering was also investigated. The results were also compared with numerical results obtained by Monte Carlo simulations. Substantially good agreement between numerical and experimental results was found. The measurements showed the adequacy of modern electro-optical systems to study the features of multiple-scattering effects on lidar echoes from atmosphere or ocean by means of experiments on well-controlled laboratory-scaled models. This adequacy provides the possibility of studying the influence of different effects in the laboratory in well-controlled situations.

Evaluation of Surface Slope Irregularity in Linear Parabolic Solar Collectors

The paper describes a methodology, very simple in its application, for measuring surface irregularities of linear parabolic collectors. This technique was principally developed to be applied in cases where it is difficult to use cumbersome instruments and to facilitate logistic management. The instruments to be employed are a digital camera and a grating. If the reflector surface is defective, the image of the grating, reflected on the solar collector, appears distorted. Analyzing the reflected image, we can obtain the local slope of the defective surface. These profilometric tests are useful to identify and monitor the mirror portions under mechanical stress and to estimate the losses caused by the light rays deflected outside the absorber.

Pointing Sensors and Sun Tracking Techniques

Every optical system for sunlight concentration requires following the sun in its movement. The sun tracking method is essentially chosen on the base of collection geometry and optical system configuration. A simple, useful, and original technique to realise sun tracking is proposed. It is based on a double guiding system using two complementary procedures. A passive tracking device performs a preliminary collector orientation. Then an active tracking system realises its fine positioning and adjustments exploiting an optical pointing sensor. The core of this active tracking device is the sun finder. Pointing sensors for fibre-coupled, CPV (Concentrating Photo voltaic), and linear collectors are presented, illustrating in detail the working principle and practical use. All sensors were optically characterised in laboratory, under controlled and reproducible conditions. Some field tests completed the experimentation evaluating the sensors performance in outdoor working conditions.

Weaving defect detection by Fourier imaging

An optical configuration for the detection of faults was developed and tested. The optical fourier transformation is the basic working principle of the system. When good fabric passes in front of the optical system the Fourier image, captured by the camera, shows well defined spots corresponding to the spatial frequencies of the tissue. If a defect occurs during production on the loom, the pattern changes significantly and a defect is easily detected in real time. A very simple electronic image processing based on thresholding and binary histograms allows to obtain very encouraging performance for its applicability to the looms. A compact device has been realized and tested in real working conditions on the loom.

Control of crankshaft finish by scattering technique

The paper describes a new sensor dedicated to measure and check the surface quality of mechanical products. The results were obtained comparing the light scattered from two different ranges of angles by means of 16 photodiodes. The device is designed for obtaining valid data from curved surfaces as that of a crankshaft. Experimental measurements show that the ratio between scattered and reflected light intensity increases with the surface roughness. This device was developed for the off-tolerance detection of mechanical pieces in industrial production. Results of surface quality on crankshaft supplied by Renault were carried out.

Optical control of surface finish

Abstract Measurement of surface roughness on mechanical components, which may incorporate also critical profiles, using diffused light techniques is a very complex problem. This paper describes a new optoelectronic device employing a diode laser and an array of discrete photodetectors placed on an arc of circle and interfaced with a data acquisition board. The device allows an extended range of roughness measurements; it is compact, easy to be used and almost insensitive to external noise and vibrations. It provides an estimation of the surface quality parameters comparing the scattered light at two different ranges of angles thereby overcoming many of the earlier limitations. The experiment has evidenced that there is a good agreement between measurement results and theoretical model usually applicable to normally distributed surfaces.

Solar Divergence Collimators for Optical Characterisation of Solar Components

Experimentation and laboratory optical tests on solar components are central aspects of the research on renewable energies. The key element of the proposed testing systems is a solar divergence collimator, which exactly reproduces in laboratory the sunlight divergence, while commercial solar simulators are mainly aimed to replicate intensity and spectrum of the sun. Precise solar divergence reproduction is essential to correctly assess the optical properties and to simulate the operative conditions of a solar collecting device. Optical characterisation and experimentation can give information about production quality and homogeneity; moreover, specific tests can address the serial production of solar components detecting defects type and location. For Concentrating Photovoltaic systems, appropriate tests can analyze solar concentrators of various shapes, dimensions, and collection features. Typically, to characterise a solar component the most important and commonly examined quantities are collection efficiency, image plane analysis, and angle dependence.